����� ���� ������ ��������� PROJECT REPORT Submitted in partial fulfillment of the requirements for the award of degree of Bachelor of Technology In Electrical and Electronics Engineering
By V DATTA VISWAS KUMAR
(08241A0206)
N KRISHNA MOHAN
(08241A0219)
M MANOJ
(08241A0222)
B VIKAS NAIK
(08241A0254)
P N V G RAJA NARAYANA RAO
(07241A0213)
Department of Electrical and Electronics Engineering Gokaraju Rangaraju institute of Engineering and Technology (Affiliated to Jawaharlal Nehru Technological University) Hyderabad 2012
Department of Electrical and Electronics Engineering GOKARAJU RANGARAJU RANGARAJU INSTITUTE OF ENGINEERING & TECH. (Affiliated to Jawaharlal Nehru Technological University)
Hyderabad. Hyderabad.
CERTIFICATE This is to certify that the project entitled “ DC-AC FULL BRIDGE CONVERTER ” has been submitted by V DATTA VISWAS KUMAR
(08241A0206)
N KRISHNA MOHAN
(08241A0219)
M MANOJ
(08241A0222)
B VIKAS NAIK
(08241A0254)
P N V G RAJA NARAYANA RAO
(07241A0213)
In partial fulfillment of the requirements for the award of degree of Bachelor of Technology in Electr Electrical ical and Electronics Engineering from from Jawaharlal Nehru Technological University, Hyderabad. The results embodied in this project have not been submitted to any other University or Institution for the award of any degree or diploma.
Guide S. Radhika A�����. ��������� ���� �� ���������� & ����������� ����
Head of Department P.M.Sarma ��������� & ��� ���� �� ���������� &����������� ����
Department of Electrical and Electronics Engineering GOKARAJU RANGARAJU RANGARAJU INSTITUTE OF ENGINEERING & TECH. (Affiliated to Jawaharlal Nehru Technological University)
Hyderabad. Hyderabad.
CERTIFICATE This is to certify that the project entitled “ DC-AC FULL BRIDGE CONVERTER ” has been submitted by V DATTA VISWAS KUMAR
(08241A0206)
N KRISHNA MOHAN
(08241A0219)
M MANOJ
(08241A0222)
B VIKAS NAIK
(08241A0254)
P N V G RAJA NARAYANA RAO
(07241A0213)
In partial fulfillment of the requirements for the award of degree of Bachelor of Technology in Electr Electrical ical and Electronics Engineering from from Jawaharlal Nehru Technological University, Hyderabad. The results embodied in this project have not been submitted to any other University or Institution for the award of any degree or diploma.
Guide S. Radhika A�����. ��������� ���� �� ���������� & ����������� ����
Head of Department P.M.Sarma ��������� & ��� ���� �� ���������� &����������� ����
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(08241�0206)
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(08241�0222)
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�������� Mobility and versatility have become a must for the fast-paced society today. People can no longer afford to be tied down to a fixed power source
location when using their equipments. Overcoming the obstacle of fixed power has led to the invention of DC/AC power inverters. While the position of power inverter in the market is relatively well established, there are several features that can be improved upon. A comparison analysis of the different power inverter has been compiled. Aside from the differences in power wattage, cost per wattage, efficiency and harmonic contend, power inverters can be categorized into three groups: square wave, modified sine wave, and pure sine wave. A cost analysis of the different types of inverter shows that sine wave power inverter, though has the best power quality performance, has a big spike in cost per unit power. Another feature which can be improved is the efficiency of the inverter. The standard sine wave in the market has an average efficiency of 85-90%. Power dissipated due to efficiency flaws will be dissipated as heat and the 10-15% power lost in the will shorten operational lifespan of inverters. The quality of the output power could also be improved. It is imperative that the output signal be as clean as possible. Distortion in the output signal leads to less efficient output and in the case of a square wave , which has a lot of unwanted harmonics, it will damage some sensitive equipment. In designing any type of power supply, it is important to examine the intended market and place the product in a particular niche market. Our market niche will be to design a 300watts power inverter that will provide optimum pure sine wave performance with minimal cost. In meeting the design requirements, there are several technical challenges that must be overcome. Our single, most difficult constraint will be to produce power at a lower power per unit cost than exists in the market. Our efficiency will be greater than 90 percent. This insures that, with a maximum load, less than 10% of power will be dissipated as heat. The total harmonic distortion will be less than 5 percent. With a total harmonic distortion this low and a pure sine wave output, we will be able to power even the most sensitive loads. The fundamental step in approaching the challenges was to examine the methods used by existing companies for building power inverters. In examining their methods, many areas were open for potential improvement. These areas include the DC/DC step up converter, the DC/AC inverter, and the feedback control system. The DC/DC step up converter in our design will use a high frequency transformer, enabling us to reduce the size of the converter considerably. The use of a high frequency transformer will also enable us to meet our efficiency constraint. A high switching frequency will improve the efficiency of the inverter. In theory, a 100 percent efficient converter could be created. However, due to the limitations of actual device material, our efficiency will be between 90 and 100 percent. The DC/AC inverter circuit will use a microprocessor to digitally pulse the transistors. This will allow us to produce a pure sine wave output. This feature will also allow us to enter other markets more easily. For instance, in Europe the fundamental frequency is 50 Hz. The frequency can be changed from 60 Hz to 50 Hz by simply editing the source code.
The feedback control system will be used to regulate the output voltage of the DC/DC converter. This is necessary since the current will vary will the load. The feedback control system will be accomplished using by sampling the output with an integrated circuit. Most of the design constraints set for the inverter were met. However, the one important constraint which the power inverter didn’t meet was the 300W continuous power, which was probably because of the transformer and the traces on the PCB. The inverter produces a clean sine wave with 7% of harmonic distortion and has efficiency greater than 90%. Overall, it is a well designed project and a lot has been accomplished over the two semesters. This design if well marketed, will offer the power inverter market a premium product at a lower cost than before. Future work could be done to further improve efficiency, total harmonic distortion, and size. With these additional improvements, the standard could be raised for future DC/AC power supplies.
CONTENTS Page numbers ACKNOWLEDGMENTS ABSRACT LIST OF TABLES LIST OF FIGURES
������� 1 1. INTRODUCTION
������� 2 2 DESIGN REQUIREMENTS 2.1 Technical design constraints 2.2 Practical design constraints
������� 3 3 APPROACH 3.1 DC power supplies 3.1.1 power inverters 3.2 Hardware design 3.2.1 PWM control circuit 3.2.2 Sinusoidal PWM control circuit 3.2.3 Full bridge inverters 3.3.4 Low pass filter 3.3 Software design
������� 4 4 EVALUATION 4.1 Test specification 4.2 Test certificate - Simulation 4.3 Test certificate – Hardware 4.4 Test certificate- Software
i ii - iii iv v – vi 1 1
������� 5 5 SUMMARY
CHAPTER 6 6 PROBLEMS CHAPTER 7 7 SOFTWARE USED
CHAPTER 8 8 IC DETAILS 8.1 DESCRIPTION OF IC 8.2 OPERATION 8.3 OP-AMP CHARACTERISTICS 8.3.1 ideal op-amps 8.3.2 Real op-amps 8.4 DC IMPERFECTIOS 8.4.1 finite gain 8.4.2 finite input impedance 8.4.3 non-zero output impedance 8.4.4 input current 8.4.5 input off-set voltage 8.4.6 common mode gain 8.4.7 output sink current 8.4.8 temperature effects 8.4.9 power supply rejections 8.4.10 drifts
8.4.11 noise
8.5 AC IMPERFECTIONS 8.5.1 finite bandwidth 8.5.2 input capacitance 8.5.3 common mode gain
8.6 POWER CONSIDERATION 8.6.1 limited output current 8.6.2 limited dissipated power 8.7 LM 339 8.7.1 input voltage range 8.7.2 op-amp voltage comparator 8.7.3 dedicated voltage comparator chip 8.7.4 speed and power 8.7.5 features of LM339 8.7.6 applications of LM339 CHAPTER 9 9 HARDWARE 9.1 DC-AC converter 9.2 Triangular pulse generator 9.3 Complete circuit diagram
CHAPTER 9 9 HARDWARE CHAPTER 10 10 RESULT
CHAPTER 11 11 APPENDIX 11.1 DATA SHEETS OF COMPONENTS
CHAPTER 12 12 REFERENCES
List of figures Figure 3.1 Block diagram of power inverter. Figure 3.2 Triangular wave generator and its wave form Figure 3.3 Theory of PWM components Figure 3.4 Full bridge converter Figure 3.5 unfiltered output Figure 3.6 Frequency spectrum of unfiltered full Bridge inverter. Figure 3.7 Schematic diagram of low pass filter Figure 3.8 Hand made inductor Figure 3.9 Circuit diagram Figure 4.1 Test setup for full bridge inverter Figure 4.2 Test setup for low pass filter Figure 4.3 DC/AC inverter Figure 4.4 simulation certificate for DC/AC inverter Figure 4.5 Simulation certification of filtered DC/AC inverter Figure 8.1:An op-amp without negative feedback Figure 8.2: An op-amp with negative feedback (a non-inverting Amp) Figure 8.3 ideal op-amps Figure 8.4 comparator Figure 8.5 various comparators Figure 8.6 pin diagram of lm 339 Figure 9.1 DC-AC converter Figure 9.2 Triangular pulse generator Figure 9.3 Complete circuit diagram Figure 9.4 Final output
List of tables Table 2.1 :Design constraints Table 2.2: practical constraints Table 10.1 output result
������� 1 ������������ DC-AC inverters are electronic devices used to produce mains voltage. AC power from low voltage DC energy mains voltage. AC power from low voltage DC energy(from a battery or solar panel). This makes them very suitable for when you need to use AC power tools or appliances but the usual AC mains power is not available. Examples include operating appliances in caravans and mobile homes, and also running audio, video and computing equipment in remote areas. Most inverters do their job by performing two main functions: first they convert the incoming DC into AC, and then they step up the resulting AC to mains voltage level using a transformer. And the goal of the designer is to have the inverter perform these functions as efficiently as possible .so that as much as possible of the energy drawn from the battery or solar panel is converted into mains voltage AC, and as little as possible is wasted as heat. By switching the two MOSFETs on alternately, the current is made to flow first in one half of the primary and then in the other, producing an alternating magnetic flux in the transformer’s core. As a result a corresponding AC voltage is induced in the transformer’s secondary winding, and as the secondary has about 10 times the number of turns in the primary, the induced AC voltage is much higher: around 170V peak to peak. Note that because the switching MOSFETs are simply being turned on and off, this type of inverter does not produce AC of the same pure sinewave. type as the AC power mains. The output waveform is essentially alternating rectangular pulses. However the width of the pulses and the spacing between them is chosen so that the ratio between the RMS value of the output waveform and its peak-to-peak value is actually quite similar to that of a pure sine wave. The resulting wave form is usually called a .modified sine wave., and as the RMS voltage is close to 230V many AC tools and appliances are able to operate from such a waveform without problems.
������� 2 ������ ������������ There are several factors involving power that can be easily overlooked by the average person. These issues deal primarily with efficiency but are not limited to it. First, the amount of power consumed by the load must be looked at. Different devices call for different power wattages. Because of this fact, our inverter would not be able to power larger devices that require a lot of power. This does not affect the efficiency of our device; it is just one of its limitations. Next, the sensitivity of the load being driven should be considered. This means the output signal of the inverter must provide a cleaner signal without distortion for more sensitive devices. The amount of undesired harmonics present in our output signal would need to be limited.
2.1 ��������� ������ �����������: Our five technical design constraints are shown in Table 1. These design constraints will rely heavily on the pure sine wave output. A pure sine wave output will be obtained through the use of a microprocessor and high frequency switching. The DC/AC power inverter being built will be driven using 12 VDC. It will then convert this DC voltage in to a functional 120 VAC power source. This power source will be capable of supplying 300 watts of continuous power and 600 watts of peak power. The output obtained will be as close as possible to a pure sine wave signal. As mentioned before, the major factor in power is efficiency. This is directly related to the output signal of the power supply. Due to this fact, it is extremely critical that the output be as close to a pure sine wave as possible. Most power inverters do not produce a pure sine wave output, and their performance is a reflection of that fact. This power inverter will operate using high frequency switching technology. The harmonics that are produced using high frequency switching will include those near the range of the switching frequency, and those that are of a relatively higher order than the 60 Hz frequency. Most of the harmonics will be the ones that are higher in order than the 60 Hz frequency. These harmonics can be isolated using a small low-pass filter. This translates into a much cleaner output signal. The power inverter will produce an output signal that contains no more than 5 % of total harmonic distortion. Also, the use of high frequency switching will minimize the size of parts used for the construction of the inverter.
NAME Voltage Power Efficiency Output Total Harmonic Distortion
DESCRIPTION We will convert 12 (V DC) to 12(V AC). We will provide 300 (W) indefinitely. We will provide 600 (W) during a power surge. The inverter will operate at no less than 90 %. This inverter will produce a pure sine wave output The amount of undesirable harmonics present in our output will be less than 5%.
Table 2.1: DESIGN CONSTRAINTS
2.2 ��������� ������ �����������: Our five practical design constraints are shown in Table 2.2. These design constraints will shield the user from unnecessary harm and give the user
a functional device. The basic economics of a project like this has to do with the price of parts. The price of parts dictates the price of the inverter. The most costly part will be the microprocessor. By minimizing the parts cost, the price of the inverter should be comparable to other sine wave inverters on the market. For practical use,an adapter which will be used to connect the inverter to the 12 VDC system of an automobile. Appropriate gauge wire will connect the cigarette lighter adapter to the inverter. A blade style fuse will protect the inverter form over-current conditions. The output will be provided using a single output receptacle to deliver the 12VAC. For mobility sake the whole inverter will be no larger than 8” long, 4.75” wide, and 2.5” high.
TYPE
NAME
The expected retail value of this product is expected to be 2000 rupess SHIELD The inverter will shut down when an input PROTECTION voltage which is greater than 20 volts is applied. heavy duty wiring harness will be used to FUNCTIONALITY USER INTERFACE access a vehicles electrical system, and a single output receptacle will deliver the output power. The physical dimensions will be 8” long, MANUFACTURABILITY SIZE 4.75” wide, and 2.5” high. Safety will be given high priority to avoid HEALTH AND SAFETY SAFETY electrical fires and shock. This will be implemented using thermal and short circuit protection Table 2.2- Practical constraints of DC-AC inverter.
ECONOMIC
COST
DESCRIPTION
������� 3 �������� This section explains the theory that must be considered along with the approach that has allowed for the successful implementation of the power inverter. It is worth mentioning that power inverter design requires knowledge of various areas in electrical and computer engineering including circuit analysis, power electronics, microprocessors, electromagnetic, signals and systems, and feedback controls. A general knowledge of these areas is critical in order to fully understand the physical behavior of each circuit component, as well as the interaction with other components. This section begins with a general overview of the technology considered in this project and then elaborates on the key design issues pertaining to both the hardware and software.
3.1.1 ����� ���������: Though the methods involved in constructing a power inverter are practically unlimited, they all En compass the common goal of altering an incoming DC voltage to form a sinusoidal output signal. Regardless of the specific design implementation, a quality power inverter should provide the end-user with desirable voltage, current, and frequency output characteristics that meet or exceed the standards for specific appliances. Often, consumers are satisfied with the least expensive inverter that will provide an adequate power level to allow constant operation of particular devices. Regardless of price, a close examination of the output waveform can distinguish the quality between particular power inverters. For example, many inexpensive power inverters create what is called a “modified sine wave”. Figure 3.1 shows an actual power inverter sold inexpensively. The problem with this type of inverter is the harshness with which it switches. Harsh switching causes a high harmonic distortion in the output signal. Harmonic distortion is simply the amount of power that is contained in other frequencies other than the fundamental frequency. The harsh switching actually causes voltage and current spikes in the output signal. This often reduces the useful life of electronic devices. In many case, the connected device may fail to operate. This is why a sinusoidal waveform is the preferred and more expensive output waveform.
3.2 ���� ���� ������: One of the most important considerations in building a pure sine-wave inverter is the output signal. As the name implies, a pure sine-wave inverter should produce an output signal with few fluctuations in DC/AC Power Inverter voltage and current. These signal fluctuations, or harmonics, are generated by rapidly switching the transistors that are used in creating the final output. In order to meet the 5% total harmonic distortion design requirement, a pulse width modulated (PWM) switch-mode power supply was chosen over the square-wave or modified square wave topologies. The PWM method allows for filtering many unwanted harmonics in the output signal, which is not possible in square-wave and modified square wave inverters. Choosing parts for the power inverter involved extensive research of the advantages and disadvantages of particular circuit topologies. Some of the major factors that determined the topology of choice for this project include power capabilities,
efficiency, size, and cost. This project has been broken down into one major circuit topology. The circuit topology DC/AC inverter.
BLOCK DIAGRAM OF DC TO AC CONVERTER:
DC INPUT
Figure 3.1: Block diagram of DC-AC converter
3.2.1: ��� ������� �������: It is designed to operate under 5 Volts, but different voltages can be applied as well, taking in account the maximum operation voltage of the OP-AMPS. The two op-amps currently used are the known 741 chips. Different OP-Amps can be used as well, and also dual chips for simplicity. The right OP-Amp will operate as an integrator and the left as a comparator. When power is given to the circuit, the comparator drives it's output HIGH. This signal is driven to the integrator through the resistor R. The capacitor C then starts to charge gradually with RC time constant. While the capacitor is charging, the output of the integrator is also taken to it's low state with the same rate. When the positive input of the comparator, through the voltage divider that the 47K and 100K resistors perform, is driven low enough, then it changes state, and the integrator starts operating vice-versa. It is easily understood that the frequency of oscillation will only have to do with the RC standard. That is true. A half cycle period is exactly the result of the R x C. A full cycle is twice this amount. Therefore, the frequency is:
FOSC =
1 2xRxC
In our test circuit, the R resistor is 22K and the C capacitor is 100nF. The oscillation frequency would be:
FOSC =
1 -
2 x 22x10 x 100x10
And that would make 227,27Hz approximately. In real life, the frequency measured was about 218Hz. This is a rather small (tiny) difference between the theoretical and the practical value, considering that the resistors have 5% accuracy and so does the capacitor as well.
Elimination the DC voltage from the output
If you watch the output signal in a oscilloscope, then you will notice that the triangle waveform is above of the zero voltage. The offset is caused by DC voltage. In order to eliminate this voltage shift, you should add a capacitor in series to the circuit. The value of the capacitor should be chosen accordint tot he oscillation frequency of the circuit. For low frequencies, 1-100 Hz, a 4.7uF to 10uF would work just fine. Above you should consider using smaller capacitors. A wrong capacitor selection would cause signal distortion and sometimes will add significant resistance to the output. The following circuit demonstrates the previous circuit with a series capacitor.
Figure 3.2:Triangular wave generator and its waveforms
As you can see, the waveform right after the capacitor is slightly above the zero voltage, where the waveform before the capacitor is several voltages above, due to the DC voltage shift. Now the output is easier to be used.
3.2.2 ���������� ��� ����������: These circuits compared a small voltage sinusoidal wave (reference signal) to a small voltage saw-tooth wave (control frequency signal). At each point where the sinusoidal and saw-tooth signals intersect, the output of the comparator toggles from a high state to a low state. To illustrate the theory behind sinusoidal PWM, Figure 3.5 shows the expected output of a sine wave compared to a saw-tooth wave. The duty cycle Actually varies according to the time between sampling the reference sine wave. REFERENCE FREQUENCY
CONTROL FREQUENCY
PWM OUTPUT
Figure 3.5: Theory PWM components
3.2.3 ���� ������ ��������: The full-bridge inverter circuit, as shown in Figure 3.6, is very simple to construct because it only consists of four switches. The function of the full-bridge inverter is to convert the 170 VDC link voltage supplied by the DC-DC converter into a 340 VAC (120 V RMS), 60 Hz sine wave. The transistors chosen for the full-bridge inverter circuit were the IRF740A’s. The IRFZ44A transistors were chosen because they have the appropriate voltage and current ratings (Vdss = 400V, Id = 10A). The two complimentary PWM pulses produced by the sinusoidal PWM controller circuit are fed into the full-bridge inverter. One signal is sent in parallel to mosfets T1 and T4. The other signal is sent in parallel to transistors T2 and T3. Programming the signals into the microcontroller as compliments of one another allows for transistors T1 and T4 to be on while transistors T2 and T3 are off, and vice versa. The basic principle with sinusoidal PWM is to divide the period of the desired sine wave output into a large number of evenly spaced intervals. In each interval, the control signal remains on for part of the time and off for the other part of the time. The ratio of the “on time” to “off time” at any given instant determines the amplitude of the desired output signal.
Figure 3.6 Full bridge converter
Figure 3.7 unfiltered output
3.2.4 ��� ���� ������: In order to eliminate the switching frequency and all multiples of the switching frequency, a low-pass filter had to be inserted after the output of the full-bridge inverter. A low-pass filter only allows frequencies below the cutoff-frequency to pass. The filter
will reject any frequency above the cutoff frequency. The cutoff frequency can be set by the following formula: F cutoff 2π = 1 /2√ LC Figure 3.8 shows the switching harmonics that resulted from an 18 kHz switching frequency. It should be noted that the harmonics are located at the switching frequency and multiples of the switching frequency. The switching frequency was intentionally set at 18 kHz so it would be rather distant from the 60 Hz fundamental frequency. This would allow for a high cutoff frequency, which by equation ??, allows for small LC components. The large distance between the unwanted harmonics and the fundamental frequency is also beneficial because it allows for a large margin of error in the filter values .
Figure 3.8
Frequency spectrum of unfiltered full bridge output
An L-C low-pass filter was chosen for the power inverter. This topology, as shown in Figure 13, is simple to build, contains few components, and can handle high currents.
Figure 3.9 Low pass filter schematic
Figure 3.10
Hand made inductor
3.3 �������� ������:
Figure 3.11 circuit diagram
������� 4 ���������� 4.1 ���� �������������: The test specifications explain the methods used to show that design constraints have been met. The power inverter is composed of many components that require testing separately and as a complete system. Testing each component individually helps to locate unique problems that are specific to each component. Complete system testing will ensure that each hardware and software component is fully functional at a mutual level.
4.1.1 ����������: PSIM is a vital circuit simulation environment that allows rapid testing of parameters such as voltage, current, power, frequency, and total harmonic distortion. PSIM only generates theoretical circuit output values which would only be observed under ideal conditions. Therefore, PSIM will only be used as a guide for the comparison of hand calculated measurements or laboratory experimentations. The PSIM circuit simulation environment will be used to verify the design of the DC-DC converter and the DC-AC inverter. Both circuits and corresponding subcircuits will be simulated in a similar manner, with the proper parts selected from existing PSIM libraries. Most of the analog parts that comprise the power inverter are standard parts and will pose no problems in simulation; however, the integrated circuits for both the DC-DC converter and the DC-AC inverter will be simulated with the use of ideal sources that will be modified to duplicate each controller’s desired output waveform. The DC-DC circuit contains a half-bridge converter and a transformer that were simulated in PSIM to compare simulated results with experimental results. For correct operation of the DC-DC converter, two complementary square wave pulses must constantly pulse the two MOSFET transistors of the half-bridge circuit. Specifically, these two square-wave pulses were created by selecting “vpulse” from the PSIM library. Simulated in PSIM and was used to verify the experimental results. Four N-channel MOSFET transistors were used to construct the full-bridge inverter. To obtain the necessary sinusoidal PWM signal to switch the four MOSFETs, two comparators with part number uA741 were used. Both comparators were set up to compare a 60 Hz sine wave with an 18 kHz saw tooth wave. The PWM output of the comparators was used to switch the transistors to “chop” the 170 VDC link voltage supplied by the DCDC converter to an 18 kHz PWM waveform. An LC low-pass filter was added to the full-bridge inverter to filter frequencies higher than the 60 Hz fundamental frequency. The complete DC-AC inverter simulation yielded a voltage of 120 VAC, a frequency of 60 Hz, and a total harmonic distortion of less than 5%.
4.1.2 ��������: All individual hardware design is tested using an oscilloscope and a digital multi-meter. The key components of the overall power inverter are a PWM control circuit, a half-bridge inverter, a
transformer, a sinusoidal PWM controller, a full-bridge inverter, and a low-pass filter. Each component was tested for the desired voltages, currents, efficiencies, and frequencies. The following sub-sections demonstrate the tests that were performed on the power inverter hardware.
���� ������ ��������: The test setup for the full bridge inverter is illustrated in Figure 4.3. The procedure for testing the full bridge inverter is located below the test setup.
Figure 4.1 Test setup for full bridge inverter 1. Connect the circuit shown in Figure 4.1. 2. Feed the outputs from the sinusoidal PWM controller to the four MOSFET transistors. 3. Using the oscilloscope, perform a differential measurement across the 50 Ω load. Note: the 10X probes must be used when measuring voltages over 100 VAC. 4. Verify that the voltage across the 50 Ω load is a PWM pulse that is 340 V peak-to-peak with a frequency of 18 kHz. 5. Verify that the ammeter reads 2.5 A.
��� ���� ������: The test setup for the low-pass filter is illustrated in Figure 4.4. The procedure for testing the low-pass filter is located below the test setup.
Figure 4.2 Low pass filter test setup 1. Connect the circuit as shown in Figure 4.2. 2. Feed the 340 V peak-to-peak PWM pulse from the full-bridge inverter to the LC filter. 3. Perform a differential measurement on the oscilloscope across the 50 Ω load. 4. Verify that the voltage is 340 V peak-to-peak with a frequency of 60 Hz. Note: the 10X probes must be used when measuring voltages over 100 VAC.
4.2 ���� �������������� ����������: The DC/AC power inverter was simulated in the PSIM environment. The entire project, except for the half-bridge PWM control circuit and the full-bridge sinusoidal PWM control circuit, was simulated using ideal parts in PSIM. The complexity of the two PWM circuits was such that they could not be simulated effectively or exactly implemented using the available parts in PSIM. The test procedures written in the test specification section of this document were followed step by step in order to ensure that the power inverter worked according to theory. The two major circuits tested in PSIM were the DC/DC converter and the DC/AC inverter, which are discussed below.
��/�� ��������: Figure 4.3 shows the PSIM schematic that was used to simulate the output of the DC/AC inverter. The expected output of the DC/AC inverter is a 12 VAC RMS, 50 Hz sine wave.
Figure 4.3 DC/AC inverter
Figure 4.4 simulation certificate for DC/AC inverter
Figure 4.5 is an 4added simulation test result showing that only the 50 Hz fundamental frequency remains after filtering with a low-pass filter.
Figure 4.5 Simulation certification of filtered DC/AC inverter frequency spectrum
4.3 ���� ����������� � ��������: ���� ������ ��� ������� ������� : Figure 4.10 illustrates the prototype output from a breadboard. The results were found using the test procedure located in section 4.1.2 of this document. This control circuit is used to pulse the MOSFETs of the half-bridge converter. The expected output is two complimentary pulses that are 180º out of phase with amplitude of approximately 12 VAC at a frequency of 100 kHz. The results were close enough to verify that the prototype works correctly.
Figure 4.6 Half-bridge control circuit pulses
������� 5 ������� 5.1 �������: Mobility and versatility have become a must for the fast-paced society today. People can no longer afford to be tied down to a fixed power source location when using their equipments. Overcoming the obstacle of fixed power has led to the invention of DC/AC power inverters. While the position of power inverter in the market is relatively well established, there are several features that can be improved upon. A comparison analysis of the different power inverter has been compiled. Aside from the differences in power wattage, cost per wattage, efficiency and harmonic contend, power inverters can be categorized into three groups: square wave, modified sine wave, and pure sine wave. A cost analysis of the different types of inverter shows that sine wave power inverter, though has the best power quality performance, has a big spike in cost per unit power. Another feature which can be improved is the efficiency of the inverter. The standard sine wave in the market has an average efficiency of 85-90%. Power dissipated due to efficiency flaws will be dissipated as heat and the 10-15% power lost in the will shorten operational life span of inverters. The quality of the output power could also be improved. It is imperative that the output signal be as clean as possible. Distortion in the output signal leads to a less efficient output and in the case of a square wave, which has a lot of unwanted harmonics, it will damage some sensitive equipment. In designing any type of power supply, it is important to examine the intended market and place the product in a particular niche market. Our market niche will be to design a 300watts power inverter that will provide optimum pure sine wave performance with minimal cost. In meeting the design requirements, there are several technical challenges that must be overcome. Our single, most difficult constraint will be to produce power at a lower power per unit cost than exists in the market. Our efficiency will be greater than 90 percent. This insures that, with a maximum load, less than 10% of power will be dissipated as heat. The total harmonic distortion will be less than 5 percent. With a total harmonic distortion this low and a pure sine wave output, we will be able to power even the most sensitive loads. The fundamental step in approaching the challenges was to examine the methods used by existing companies for building power inverters. In examining their methods, many areas were open for potential improvement. These areas include the DC/DC step up converter, the DC/AC inverter, and the feedback control system. The DC/DC step up converter in our design will use a high frequency transformer, enabling us to reduce the size of the converter considerably. The use of a high frequency transformer will also enable us to meet our efficiency constraint. A high switching frequency will improve the efficiency of the inverter. In theory, a 100 percent efficient converter could be created. However, due to the limitations of actual device material, our efficiency will be between 90 and 100 percent. The DC/AC inverter circuit will use a microprocessor to digitally pulse the transistors. This will allow us to produce a pure sine wave output. This feature will also allow us to enter other markets more easily. For instance, in Europe the fundamental frequency is 50 Hz. The frequency can be changed from 60 Hz to 50 Hz by simply editing the source code. The feedback control system will be used to regulate the output voltage of the DC/DC converter. This is necessary since the current will vary will the load. The feedback control system will be accomplished using by sampling the output with an integrated circuit.
Most of the design constraints set for the inverter were met. However, the one important constraint which the power inverter didn’t meet was the 300W continuous power, which was probably because of the transformer and the traces on the PCB. The inverter produces a clean sine wave with 7% of harmonic distortion and has efficiency greater than 90%. Overall, it is a well designed project and a lot has been accomplished over the two semesters. This design if well marketed, will offer the power inverter market a premium product at a lower cost than before. Future work could be done to further improve efficiency, total harmonic distortion, and size. With these additional improvements, the standard could be raised for future DC/AC power supplies.
������� 6 �������� Power inverters, regardless of size, are typically constructed of a DC-DC converter and a DC-AC inverter. These are the two major circuit components that work together to convert the input voltage from a vehicle battery into a desirable AC output waveform. In the INDIA, the standard AC output waveform consists of a voltage of 230 VAC and a frequency of 50 HZ. Due to this standard, Electronic mobility has always been an issue when it comes to our mobile environment. Therefore, a mobile means of providing AC voltage is needed. The majority of portable electronic devices are more easily powered using 230 VAC. When these devices need to be used in a remote or mobile setting there is a problem. Most people have access to 12 VDC generated by the standard power supply system of a mobile vehicle, such as an automobile, ATV, or agriculture equipment. A power inverter of DC to AC type will be needed to convert 12 VDC to 230 VAC with acceptable power output. Power inverters were first invented using a square wave as the output form. This led to many different problems involving the functionality of devices that were being powered because they were designed to work with a sine wave instead of a square wave. There were some changes made to the hardware to eliminate the harsh corners from the square wave to transform it to a “modified sine wave”. It was mainly marketers who coined the term “modified sine wave” which in all reality is nothing more than a modified square wave. Power inverters that used a “modified sine wave” did not eliminate the problems associated with square wave inverters. They did however, minimize these problems. Although most people without a background in electronics do not know the difference, a “modified square wave” can have detrimental effects on electrical loads. First of all, abnormal heat will be produced, causing a reduction in product reliability, efficiency, and useful life. Another disadvantage of a “modified sine wave” is that its choppy waveform can confuse the operation of some digital timing devices. This can cause a device to perform undesirable or abnormal functions. Also, nearly 5 % of household electronics will not even work with a modified sine wave. The advantages of a true sine wave inverter are usually reflected in the final market price. Power inverters are usually described as having either a high or low switching frequency. Switching frequency refers to the rate at which the input DC voltage is oscillated to create an AC output. Low frequency inverters oscillate a DC voltage at 50 Hz. Then they step that voltage up to the desired amplitude using a bulky and a heavy transformer. High frequency inverters, on the other hand, use a small and lightweight transformer. A high frequency inverter will produce many harmonics near the range of the switching frequency. However, most of the harmonics are relatively higher in order than the 50 Hz fundamental frequency. These harmonics can be isolated using a small low-pass filter. In turn, isolation of harmonics will result in less buzzing in audio equipment and less interference in other electronic equipment such as radios and televisions. When you think mobility, a unit that’s the size of a laptop doesn’t seem awfully large. But consider the trend in electronics these days, a laptop seems gigantic as compared to some of the microscopic devices and apertures that are being massed produced. Therefore a trend in electronics, as is has been in the past decades, is miniaturization.
Size and bulk determines mobility. And for a unit as useful as a power inverter, smallness should be one of the top priorities in designing this unit. In order to create a more compact unit, it requires the use of as many devices of negligible size as possible. These devices, or integrated circuits, must also be able to accomplish as many feats as possible within there small stature. Multiple functions in these integrated circuits are a property that should be examined first. The increase in demand for mobile AC power sources has led to an increase in market supply. However, these inverters that use the “modified sine wave” technology tend to produce a lot of heat do to power loss. Their efficiency is also less than proficient. The price of an inverter like this is considerably less than one with a pure sine wave output, but it is also reflected in their operational efficiency. The design that we will implement will solve the problem associated with “modified sine wave” inverters by using a microprocessor to obtain a more efficient and smooth means of switching the inverter’s transistors. This will reflect, in the overall design, a greater efficiency, less power loss to heat, the ability to power even the most sensitive digital devices, minimize the size of the final product, and make it a more versatile product in the global economy.
������� 7 �������� ���� 7.1 ����� ���: PSIM is a vital circuit simulation environment that allows rapid testing of parameters such as voltage, current, power, frequency, and total harmonic distortion. PSIM only generates theoretical circuit output values which would only be observed under ideal conditions. Therefore, PSIM will only be used as a guide for the comparison of hand calculated measurements or laboratory experimentations. The PSIM circuit simulation environment will be used to verify the design of the DC-DC converter and the DC-AC inverter. Both circuits and corresponding subcircuits will be simulated in a similar manner, with the proper parts selected from existing PSIM libraries. Most of the analog parts that comprise the power inverter are standard parts and will pose no problems in simulation; however, the integrated circuits for both the DC-DC converter and the DC-AC inverter will be simulated with the use of ideal sources that will be modified to duplicate each controller’s desired output waveform. The DC-DC circuit contains a half-bridge converter and a transformer that were simulated in PSIM to compare simulated results with experimental results. For correct operation of the DC-DC converter, two complementary square wave pulses must constantly pulse the two MOSFET transistors of the half-bridge circuit. Specifically, these two square-wave pulses were created by selecting “vpulse” from the PSIM library. simulated in PSIM and was used to verify the experimental results. Four N-channel MOSFET transistors were used to construct the full-bridge inverter. To obtain the necessary sinusoidal PWM signal to switch the four MOSFETs, two comparators with part number uA741 were used. Both comparators were set up to compare a 50 Hz sine wave with an 18 kHz saw tooth wave. The PWM output of the comparators was used to switch the transistors to “chop” the 15 VDC link voltage supplied by the DC-DC converter to an 18 kHz PWM waveform. An LC low-pass filter was added to the full-bridge inverter to filter frequencies higher than the 50 Hz fundamental frequency. The complete DC-AC inverter simulation yielded a voltage of 120 VAC, a frequency of 50 Hz, and a total harmonic distortion of less than 5%.
������� 8 �� ������� 8.1����������� �� ��: 8.1.1 ��741: An operational amplifier ("op-amp") is a DC-coupled high-gain electronic voltage a mplifier with a differential input and, usually, a single-ended output.[1] An op-amp produces an output voltage that is typically hundreds of thousands times larger than the voltage difference between its input terminals. Operational amplifiers had their origins in analog co mputers where they were used in many linear, non-linear and frequency-dependent c ircuits. Characteristics of a circuit using an op-amp are set by external components with little dependence on temperature changes or manufacturing variations in the op-amp itself, which makes op-amps popular building blocks for circuit design. Op-amps are among the most widely used electronic devices today, being used in a vast array of consumer, industrial, and scientific devices. Many standard IC op-amps cost only a few cents in moderate production volume; however so me integrated or hybrid operational amplifiers with special performance specifications may cost over $100 US in small quantities.[citation needed ] Opamps may be packaged as components, or used as elements of more complex integrated circuits. The op-amp is one type of differential amplifier. Other types of differential amplifier include the fully differential amplifier (similar to the op-amp, but with two outputs), the instrumentation amplifier (usually built from three op-amps), the isolation amplifier (similar to the instrumentation amplifier, but with tolerance to common-mode vo ltages that would destroy an ordinary op-amp), and negative feedback amplifier (usually built from one or more op-amps and a resistive feedback network).
8.2 Operation
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The amplifier's differential inputs consist of a V + input and a V − input, and ideally the op-amp amplifies only the difference in voltage between the two, which is called the differential input voltage. The output voltage of the op-amp is given by the equation:
where V + is the voltage at the non-inverting terminal, V − is the voltage at the inverting terminal and AOL is the open-loop gain of the amplifier (the term "open-loop" refers to the absence of a feedback loop from the output to the input). The magnitude of AOL is typically very large—10,000 o r more for integrated circuit op-amps— and therefore even a quite small difference between V + and V − drives the amplifier output nearly to the supply voltage. This is called saturation of the amplifier. The magnitude of AOL is not well controlled by the manufacturing process, and so it is impractical to use an operational amplifier as a stand-alone differential amplifier. Without negative feedback, and perhaps with positive feedback for regeneration, an op-amp acts as a comparator. If the inverting input is held at ground (0 V) directly or by a resistor, and the input voltage Vin applied to the non-inverting input is positive, the output will be maximum positive; if Vin is negative, the output will be maximum negative. Since there is no feedback from the output to either input, this is an open loop circuit acting as a comparator. The circuit's gain is just the AOL< of the op-amp.
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If predictable operation is desired, negative feedback is used, by applying a portion of the output voltage to the inverting input. The closed loop feedback greatly reduces the gain of the amplifier. If negative feedback is used, the circuit's overall gain and other parameters become determined more by the feedback network than by the op-amp itself. If the feedback network is made of components with relatively constant, stable values, the unpredictability and inconstancy of the op-amp's parameters do not seriously affect the circuit's performance. Typically the o p-amp's very large gain is controlled by negative feedback, which largely determines the magnitude of its output ("closed-loop") voltage gain in amplifier applications, or the transfer function required (in
analog computers). High input impedance at the input terminals and low output impedance at the output terminal(s) are important typical characteristics. For example, in a non-inverting amplifier (see the figure on the right) adding a negative feedback via the voltage divider Rf ,R g reduces the gain. Equilibrium will be established when Vout is just sufficient to reach around and "pull" the inverting input to the same voltage as Vin. The voltage gain of the entire circuit is determined by 1 + R /R f g. As a simple example, if Vin = 1 V and Rf = Rg, Vout will be 2 V, the amount required to keep V– at 1 V. Because of the feedback provided by Rf ,Rg this is a closed loop circuit. Its overall gain V out / Vin is called the closed-loop gain ACL. Because the feedback is negative, in this case ACL is less than the AOL of the op-amp. Another way of looking at it is to make two relatively valid assumptions: One, that when an opamp is being operated in linear mode, the difference in voltage between the non-inverting (+) pin and the inverting (-) pin is so small as to be considered negligible.[3] The second assumption is that the input impedance at both + and - pins is extremely high (at least several megohms with modern op-amps). Thus, when the circuit to the right is operated as a non-inverting linear amplifier, Vin will appear at the + and - pins and create a current i through Rg equal to Vin/Rg. Since Kirchoff's current law states that the same current must leave a node as enter it, and since the impedance into the - pin is near infinity, we can assume the overwhelming majority of the same current i travels through Rf, creating an output voltage equal to Vin + i*Rf. By combining terms, we can easily determine the gain of this particular type of circuit.
8.3 Op-amp characteristics 8.3.1 ����� �������
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An ideal op-amp is usually considered to have the following properties, and they are considered to hold for all input voltages: •
•
•
•
•
•
•
•
• • •
Infinite open-loop gain (when doing theoretical analysis, a limit may be taken as open loop gain AOL goes to infinity). Infinite voltage range available at the output ( ) (in practice the voltages available from the output are limited by the supply voltages and ). The power supply sources are called rails. Infinite bandwidth (i.e., the frequency magnitude response is considered to be flat everywhere with zero phase shift). Infinite input impedance (��, �� ��� �������, , ��� ���� ������� ����� ���� �� ). ���� ����� ������� (�.�., ����� �� ������� �� �� �� ������� �� ���� ������� ���� ��� ������). ���� ����� ������ ������� (�.�., ���� ��� ����� ��������� ��� ������� �� ���� ��� ������ �� � ������� ������ �� ). �������� ���� ���� (�.�., ��� ���� �� ������ �� ��� ������ ������� �� ���������) ��� ����� ��������� (���� ������ ������� ��� ������� ��������� �� ��� �����������). ���� ������ ��������� (�.�., , �� ���� ������ ������� ���� ��� ���� ���� ������ �������). ���� �����. �������� ����������� ��������� ����� (����). �������� ����� ������ ��������� ����� ��� ���� ����� ������ �����.
These ideals can be summarized by the two "golden rules":
,
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The first rule only applies in the usual case where the op-amp is used in a closed-loop design (negative feedback, where there is a signal path of some sort feeding back from the output to the inverting input). These rules are commonly used as a good first approximation for analyzing or designing op-amp circuits. In practice, none of these ideals can be perfectly realized, and various shortcomings and compromises have to be accepted. Depending on the parameters of interest, a real op-amp may be modeled to take account of some of the non-infinite or non-zero parameters using equivalent resistors and capacitors in the op-amp model. The designer can then include the effects of these undesirable, but real, effects into the overall performance of the final circuit. Some parameters may turn out to have negligible effect on the final design while others represent actual limitations of the final performance,that must be evaluated.
8.3.2 ���� ������� Real op-amps differ from the ideal model in various respects.
8.4 DC imperfections Real operational amplifiers suffer from several non-ideal effects:
8.4.1 ������ ���� Open-loop gain is infinite in the ideal operational amplifier but finite in real operational amplifiers. Typical devices exhibit open-loop DC gain ranging from 100,000 to over 1 million. So long as the loop gain (i.e., the product of open-loop and feedback gains) is very large, the circuit gain will be determined entirely by the amount of negative feedback (i.e., it will be independent of open-loop gain). In cases where closed-loop gain must be very high, the feedback gain will be very low, and the low feedback gain causes low loop gain; in these cases, the operational amplifier will cease to behave ideally.
8.4.2������ ����� ���������� The differential input impedance of the operational amplifier is defined as the impedance between its two inputs; the common-mode input impedance is the impedance from each input to ground. MOSFET-input operational amplifiers often have protection circuits that effectively short circuit any input differences greater than a small threshold, so the input impedance can appear to be very low in some tests. However, as long as these operational
amplifiers are used in a typical high-gain negative feedback application, these protection circuits will be inactive. The input bias and leakage currents described below are a more important design parameter for typical operational amplifier applications.
8.4.3 �������� ������ ��������� Low output impedance is important for low-impedance loads; for these loads, the voltage drop across the output impedance of the amplifier will be significant. Hence, the output impedance of the amplifier limits the maximum power that can be provided. In configurations with a voltage-sensing negative feedback, the output impedance of the amplifier is effectively lowered; thus, in linear applications, op-amps usually exhibit a very low output impedance indeed. Negative feedback can not, however, reduce the limitations that R load in conjunction with R out place on the maximum and minimum possible output voltages; it can only reduce output errors within that range. Low-impedance outputs typically require high quiescent (i.e., idle) current in the output stage and will dissipate more power, so low-power designs may purposely sacrifice low output impedance.
8.4.4 ����� ������� Due to biasing requirements or leakage, a small amount of current (typically ~10 nanoamperes for bipolar op-amps, tens of picoamperes for JFET input stages, and only a few pA for MOSFET input stages) flows into the inputs. When large resistors or sources with high output impedances are used in the circuit, these small currents can produce large unmodeled voltage drops. If the input currents are matched, and the impedance looking out of both inputs are matched, then the voltages produced at each input will be equal. Because the operational amplifier operates on the difference between its inputs, these matched voltages will have no effect (unless the operational amplifier has poor CMRR, which is described below). It is more common for the input currents (or the impedances looking out of each input) to be slightly mismatched, and so a small offset voltage (different from the input offset voltage below) can be produced. This offset voltage can create offsets or drifting in the operational amplifier. It can often be nulled externally; however, many operational amplifiers include offset null or balance pins and some procedure for using them to remove this offset. Some operational amplifiers attempt to nullify this offset automatically.
8.4.5 ����� ������ ������� This voltage, which is what is required across the op-amp's input terminals to drive the output voltage to zero, is related to the mismatches in input bias current. In the perfect amplifier, there would be no input offset voltage. However, it exists in actual op-amps
because of imperfections in the differential amplifier that constitutes the input stage of the vast majority of these devices. Input offset voltage creates two problems: First, due to the amplifier's high voltage gain, it virtually assures that the amplifier output will go into saturation if it is operated without negative feedback, even when the input terminals are wired together. Second, in a closed loop, negative feedback configuration, the input offset voltage is amplified along with the signal and this may pose a problem if high precision DC amplification is required or if the input signal is very small.
8.4.6 ����������� ���� A perfect operational amplifier amplifies only the voltage difference between its two inputs, completely rejecting all voltages that are common to both. However, the differential input stage of an operational amplifier is never perfect, leading to the amplification of these identical voltages to some degree. The standard measure of this defect is called the common-mode rejection ratio (denoted CMRR). Minimization of common mode gain is usually important in non-inverting amplifiers (described below) that operate at high amplification.
8.4.7 ������ ���� ������� The output sink current is maximum current allowed to sink into the output stage. Some manufacturers show the output voltage vs. the output sink current plot, which gives an idea of the output voltage when it is sinking current from another source into the output pin.
8.4.8 ����������� ������� A�� ���������� ������ ���� �����������. ����������� ����� �� ��� ����� ������ ������� �� ���������� ���������.
8.4.9 ������������ ��������� The output of a perfect operational amplifier will be completely independent from ripples that arrive on its power supply inputs. Every real operational amplifier has a specified power supply rejection ratio (PSRR) that reflects how well the op-amp can reject changes in its supply voltage. Copious use of bypass capacitors can improve the PSRR of many devices, including the operational amplifier.
8.4.10 ����� Real op-amp parameters are subject to slow change over time and with changes in temperature, input conditions, etc.
8.4.11 ����� A��������� �������� ������ ������� �� ��� ������ ���� ���� ����� �� �� ������ �������. ���� ��� �� ��� �� ������� ����� ��� ������� ����� �� ��� �������. ��� ������������ ���� ���� ���� �� ���� ���������, ����� ������� � ���� ��������� �������������.
8.5 AC imperfections The op-amp gain calculated at DC does not apply at higher frequencies. Thus, for high-speed operation, more sophisticated considerations must be used in an op-amp circuit design.
8.5.1 ������ ��������� A�� ���������� ���� ������ ���������. �� � ����� �������������, ��� ������ ��� ��� ��������� �������� �� �� ���������� ���� ����. ���� ��, ��� ���� �� � ������� ������ �� ��������� ������������ �� ��������� ��� �� ������������� �� ��� �������������� ������� (�B��). ��� �������, �� ������ ���� � �B�� �� 1 ��� ����� ���� � ���� �� 5 �� 200 ���, ��� � ���� �� 1 �� 1 ���. ���� ������� �������� ������� ���� ��� ���� ���� �� ���� �� ��� ������ ����� �� ��� ��������������� �� � ����������� �������� ������ ���� ���� ���� �� ���� ��� ��� ������ ��������� ����� �� ��� �B�� ������� �� ��� �� ����. ��� ������ ��������� �� �� ������ ��� �� ��� ������ � � ������� ��������, ���������: •
���������. A��������� ���� ��� ��������� ���������� �� � ����� ���������� ������� ��� ����� ������ ��� ��� ��������� ������ ���� ��� ���� �� ����������� �� ���� �������� ��������. ��� �������, � ���������� ������ ������ ����� �� ��������� ������������� ���� ��
����� ������ �� ��� ���� ��������� ���� ��������� �������������� �� ������� �� 180 �������. �� ����� �����, ��� �������� ������� ��� �� ���������� �� ����� �� ��������� ������������, ����� ��������� ��� ���� �� ����� ������ �� ��� ����� ���� �������. ��� ������� �������� ��� ��������� ���� ������������ ���������� ���� � �������� ������� ���������. A������������, ��� ������������ ��� �� ����������� ������ ��� ����������� ��������� ���� ��� �������� �� � �������� ���� ���� ������������ ���������� ��� �������������� ���� �� ��� ����������� ���������. ��� �������� �� ���� ���� ��� �� ����� ���������� �� ��� ������������ �� ���������� �� ��� ������� �������� ����� ������� �������� �� ��� ������. �� �������, ������������� ��������� ������������ ������� ��� ��������� �� ��� ������ ���� �������. ���� ��� ������� ����������� � ��� �� ����, ������ ��������� ������������ �� ����� ��� ������ ������� ��� ��������� ��������� ���� �� ������������ ���; ������������, ������������ ���� ���� ����������� ���� ��� ���� ��� �� ������� ���� ������ ����������. •
�����, ����������, ��� ����� �������. Reduced bandwidth also results in lower amounts of feedback at higher frequencies, producing higher distortion,
noise, and output impedance and also reduced output phase linearity as the frequency increases. Typical low-cost, general-purpose op-amps exhibit a GBWP of a few megahertz. Specialty and high-speed op-amps exist that can achieve a GBWP of hundreds of megahertz. For very high-frequency circuits, a current-feedback operational amplifier is often used.
8.5.2 Input capacitance Most important for high frequency operation because it further reduces the open-loop bandwidth of the amplifier.
8.5.3 ����������� ���� ��� �� �������������, �����. ������ ������� �� ������� �� � ������� ��� ������� ����� ����� �� ��� ����� ������ ������� ���������� ������ ���� ��� ������ �� ��� ��������� ������� ���� ����� ��� �� ������� ��� ��: •
•
�� ��� ���� �� �� ������ ����� � ������� ����� ������, � ������� ���� ���� �������� �� ������ ���� �� ���� �������� �� ���� ��� ����� ���� ���� ������� �� �������; �� �� ��� ���� �� �� ������ ����� � ������ ������ �������, ������ � ������� ���� ���� �������� �� ������ ���� �� ���� �������� ���� ���� �������, �� � ������ �� ����� �� ������ ���� ��� ���������'� ���� �� ��� ���������� �� ����� � � ����� ��� ����� ���������
8.5.4 ������� ��� ���������'� ������ ������� ������� ��� ������� ���� �� ������. �������� �� ��� ���� ����, �� �� ������� ��������� �� ����� ��� �����������. ���� ������� ������, ������� ��������� �� ��� ����� ������ ���� �� ������ �� ��� ���� �� ������ �� ��� ������. ������� �� ������� ������ �� �������� ������������ �� ��� ���������, ���������� ����� ���� �� ��������� ��� ��������� ������������.
8.5.5 ���������� ������������ ������������ ��� ������ ������� ��� ��� �� ���������� ������������ �� ��� ���������� ������� ��� ����� ��������. �� �� �������� ������ ���������� ���� ��� ����� ������ �� � ��������. ���� ������ ���� �� ���� ����� �� � ��������� ������� �� ����������� �������� �������� �� ����.
8.6 Power considerations 8.6.1 ������� ������ ������� The output current must be finite. In practice, most op-amps are designed to limit the output current so as not to exceed a specified level – around 25 mA for a type 741 IC op-
amp – thus protecting the op-amp and associated circuitry from damage. Modern designs are electronically more rugged than earlier implementations and some can sustain direct short circuits on their outputs without damage.
8.6.2 ������� ���������� ����� ��� ������ ������� ����� ������� ��� ������'� �������� ������ ���������, ����������� ����. �� ��� ������ ���������� ��� ���� �����, ���� ��� ����������� ���� �������� ����� ���� ���� �����. ��� ������ ��� ����� ������� ��������, �� �� ��� �� ���������.
Modern integrated FET or MOSFET op-amps approximate more closely the ideal op-amp than bipolar ICs when it comes to input impedance and input bias and offset currents. Bipolars are generally better when it comes to input voltage offset, and often have lower noise. Generally, at room temperature, with a fairly large signal, and limited bandwidth, FET and MOSFET op-amps now offer better performance.
8.7 ��339: In electronics, a comparator is a device that compares two voltages or currents and switches its output to indicate which is larger. They are commonly used in devices such as Analog-to-digital converters (ADCs).
8.7.1 ����� ������� �����: •
The input voltages must stay within the limits specified by the manufacturer. Early integrated comparators, like the LM111 family, and certain high-speed comparators like the LM119 family, require input voltage ranges substantially lower than the power supply voltages (±15 V vs. 36V). Rail-torail comparators allow any input voltages within the power supply range. When powered from a bipolar (dual rail) supply,
or, when powered from a uni polar TTL/CMOS power supply:
Specific rail-to-rail comparators with p-n-p input transistors, like the LM139 family, allow input potential to drop 0.3 Volts below the negative supply rail, but do not allow it to rise above the positive rail. Specific ultra-fast comparators, like the LMH7322, allow input signal to swing below the negative rail and above the positive rail, although by a narrow margin of only 0.2V.
Differential input voltage (the voltage between two inputs) o f a modern rail-to-rail comparator is usually limited only by the full swing of power supply.
8.7.2 ������ ������� ����������: An operational amplifier (op-amp) has a well balanced d ifference input and a very high gain. This parallels the characteristics of comparators and can be substituted in applications with low-performance requirements. In theory, a standard op-amp operating in open-loop configuration (without negative feedback) may be used as a low-performance comparator. When the non-inverting input (V+) is at a higher voltage than the inverting input (V-), the high gain of the op-amp causes the output to saturate at the highest positive voltage it can output. When the non-inverting input (V+) drops below the inverting input (V-), the output saturates at the most negative voltage it can output. The op-amp's output voltage is limited by the supply voltage. An op-amp operating in a linear mode with negative feedback, using a balanced, split-voltage power supply, (powered by ± VS) its transfer function is typically written as: . However, this equation may not be applicable to a comparator circuit which is non-linear and operates open-loop (no negative feedback). In practice, using an operational amplifier as a comparator presents several disadvantages as compared to using a dedicated comparator: 1. Op-amps are designed to operate in the linear mode with negative feedback. Hence, an op-amp typically has a lengthy recovery time from saturation. Almost all op-a mps have an internal compensation capacitor which imposes slew rate limitations for high frequency signals. Consequently an op-amp makes a sloppy comparator with propagation delays that can be as slow as tens of microseconds. 2. Since op-amps do not have any internal hysteresis an external hysteresis network is always necessary for slow moving input signals. 3. The quiescent current specification of an op-amp is valid only when the feedback is active. Some op-amps show an increased quiescent current when the inputs are not equal. 4. A comparator is designed to produce well limited output voltages that easily interface with digital logic. Compatibility with digital logic must be ver ified while using an opamp as a comparator. 5. Some multiple-section opamps may exhibit extreme channel-channel interaction when used as comparators. 6. Many opamps have back to back diodes between their inputs. Opamp inputs usually follow each other so this is fine. But comparator inputs are not usually the same. The diodes can cause unexpected current through inputs.
Figure 8.4 comparator
8.7.3 ��������� ������� ���������� ����: A dedicated voltage comparator will generally be faster than a general-purpose operational amplifier pressed into service as a comparator. A dedicated voltage comparator may also contain additional features such as an accurate, internal voltage reference, an adjustable hysteresis and a clock gated input. A dedicated voltage comparator chip such as LM339 is designed to interface with a digital logic interface (to a TTL or a CMOS). The output is a binary state often used to interface real world signals to digital circuitry (see analog to digital converter). If there is a fixed voltage source from, for example, a DC adjustable device in the signal path, a comparator is just the equivalent of a cascade of amplifiers. When the voltages are nearly equal, the output voltage will not fall into one of the logic levels, thus analog signals will enter the digital domain with unpredictable results. To make this range as small as possible, the amplifier cascade is high gain. The circuit consists of mainly Bipolar transistors except perhaps in the beginning stage which will likely be field effect transistors. For very high frequencies, the input impedance of the stages is low. This reduces the saturation of the slow, large P-N junction bipolar transistors that would otherwise lead to long recovery times. Fast small Schottky diodes, like those found in binary logic designs, improve the performance significantly though the performance still lags that of circuits with amplifiers using analog signals. Slew rate has no meaning for these devices. For applications in flash ADCs the distributed signal across 8 ports matches the voltage and current gain after each amplifier, and resistors then behave as level-shifters. The LM339 accomplishes this with an open collector output. When the inverting input is at a higher voltage than the non inverting input, the output of the comparator connects to the negative power supply. When the non inverting input is higher than the inverting input, the output is 'floating' (has a very high impedance to ground).
INPUT ->+ +>-
OUTPUT Grounded Floating
With a pull-up resistor and a 0 to +5V power supply, the output takes on the voltages 0 or +5 and can interface with TTL logic:
����
����
.
Figure 8.5 various comparators
8.7.4 ����� ��� �����: While in general comparators are "fast," their circuits are not immune to the classic speed-power tradeoff. High speed comparators use transistors with larger aspect ratios and hence also consume more power. Depending on the application, select either a comparator with high speed or one that saves power. For example, nano-powered comparators in space-saving chip-scale packages (UCSP), DFN or SC70 packages such as MAX9027, LTC1540, LPV7215, MAX9060 and MCP6541 are ideal for ultra-low-power, portable applications. Likewise if a comparator is needed to implement a relaxation oscillator circuit to create a high speed clock signal then comparators having few nano seconds of propagation delay may be suitable. ADCMP572 (CML o utput), LMH7220 (LVDS Output), MAX999 (CMOS output / TTL output), LT1719 (CMOS output / TTL output), MAX9010 (TTL o utput), and MAX9601 (PECL output) are examples of some good high speed comparators.
Figure 8.7 LM339 pin diagram
8.7.5 �������� �� ��339: •
Wide single supply voltage range = 2V
•
Very low supply current draw (0.8mA) independent of supply.
•
Low input biasing current 25nA
•
Low input offset current +(-) 5 nA
•
Input common-node voltage range includes ground.
•
Different input voltage range equals to power supply voltage
•
Low output 250mV at 4mA saturation voltage.
•
Output voltage compatible with TTL, DTL, ECL, MOS, CMOS logic systems.
8.7.6 ������������ �� ��339: 1. 2. 3. 4. 5.
Analog to digital converters Wide range VCD MOS clock generator HV logic gates Multivibrators.
CHAPTER 9 HARDWARE 9.1 CIRCUIT OF DC-AC CONVERTER
Figure 9.1 dc-ac converter
9.2 TRIANGULAR PULSE GENERATOR:
Figure 9.2 triangular pulse generator
9.3 COMPLETE CIRCUIT DIGRAM:
Figure 9.3 complete circuit diagram
9.4 TOTAL OUTPUT OF DC-AC CONVERTER:
Figure 9.4 output of DC-AC converter
������� 10 ������ 10.1 ������:
������ ������ 1 2 3
�����
12 15 20 ����� 10.1 ������ ������
������ 12 17 23
10.2 ������ �����: For our future purpose by using micro controller we can swich off and on the dc-ac converter. Like when the power is switched off the microcontroller automatically triggers the mosfet and ac voltage is produced. when power is on the micro controller switches off the triggering of mosfet and normal power supply is used. This DC-AC converter is further used to switch on led’s and tube lights for internal use by using dc supply.
CHAPTER 11 APPENDIX 11.1���� ����� �� ���������� ����: 11.1.1 ����� (��4007): In electronics, a diode is a type of two-terminal electronic component with nonlinear resistance and conductance (i.e., a nonlinear current–voltage characteristic), distinguishing it from components such as two-terminal linear resistors which obey Ohm's law. A semiconductor diode, the most common type today, is a crystalline piece of [ semiconductor material connected to two electrical terminals. A vacuum tube diode (now rarely used except in some high-power technologies) is a vacuum tube with two electrodes: a plate and a cathode.
11.1.2 ��������: •
Diffused Junction
•
High Current Capability and Low Forward
•
Surge Overload Rating to 30A Peak
•
Low Reverse Leakage Current
•
Case: DO-41
•
Case Material: Molded Plastic. UL Flammability Classification
•
Rating 94V-0
•
Moisture Sensitivity: Level 1 per J-STD-020D
•
Terminals: Finish - Bright Tin. Plated Leads Solderable per
•
MIL-STD-202
•
Polarity: Cathode Band
•
Mounting Position: Any
•
Ordering Information:
•
Marking: Type Number
•
Weight: 0.30 grams (approximate)
Voltage Drop
11.1.3 ��������������: •
Peak Repetitive Reverse Voltage(V rrm)
=50V
•
Working Peak Reverse Voltage(V rwm)
=50V
•
DC Blocking Voltage(Vr)
=40V
•
RMS Reverse Voltage VR(RMS)
=35V
•
Average Rectified Output Current (Note 1) @ TA = 75°C IO 1.0 A
•
Non-Repetitive Peak Forward Surge Current 8.3ms
•
single half sine-wave superimposed on rated load IFSM
•
Forward Voltage @ IF = 1.0A VFM 1.0 V
=30 A
•
Peak Reverse Current @TA = 25°C
50 µA
at Rated DC Blocking Voltage @ TA = 100°C IRM
5.0
•
Typical Junction Capacitance (Note 2) Cj 15 8 pF
•
Typical Thermal Resistance Junction to Ambient 100 K/W
•
Maximum DC Blocking Voltage Temperature TA +150 °C
•
Operating and Storage Temperature Range TJ, TSTG -65 to +150 °C
11.2 ������: The metal–oxide–semiconductor field-effect transistor (MOSFET, MOS-FET, or MOS FET) is a transistor used for amplifying or switching electronic signals.
11.2.1 ��������: •
Very Low RDS(on) at 4.5V VGS
•
Ultra-Low Gate Impedance
•
Fully Characterized Avalanche Voltage and Current.
11.2.2 ��������������: •
Drain-to-Source Voltage
=30V
•
Gate-to-Source Voltage
=20V
•
Continuous Drain Current, VGS @ 10V
=56A
•
Continuous Drain Current, VGS @ 10V
=39A
•
Pulsed Drain Current
=20A
•
PD @TC = 25°C Maximum Power Dissipation =50W
•
PD @TC = 100°C Maximum Power Dissipation=25W
•
Linear Derating Factor
=0.33W/c
•
TJ Operating Junction and
•
TSTG Storage Temperature Range
=-55 to 75c
11.3 �������������� �� ��339: ����
Input Bias Current Input Offset Current Input Common Mode Voltage Range Supply Current ICC mA RL = 8 (For All Comparators RL = 8, VCC = 30 Vdc Voltage Gain Large Signal Response Time Response Time Output Sink Current ISink Saturation Voltage Output Leakage Current
��� � � 0
��� 2 5 �
��� 5 5 ����1.5
�
0.8
2
�
1
2.5
50 �
200 300
� �
� 6
1.3 16
� �
� �
130 0.1
400 �