Transistor As A Switch

TRANSISTOR AS A SWITCH

Pauline Joyce A. Pasia College of Engineering, Architecture and Fine Arts, Batangas State University Barangay Alangilan, Batangas City, Philippines Laboratory No. 1 Group 5 I.

Introduction A transistor is a semiconductor device that exhibits all the properties of a switch, allowing or blocking the flow of electrons. It has three terminals, one for input, one for output and one for controlling switching. It is the fundamental building block of modern electronic devices and is commonly found in circuit boards as discrete parts or embedded into integrated circuits.

rapidly changes the material from an insulator to conductive state, thereby allowing the flow of electricity. Transistors are created through a chemical process known as doping, where the semiconductive material either gains an extra negative charge (N-type) or extra positive charge (P-type). There are two configurations for this, either PNP or NPN with the middle material acting as the base or flow control. A very small change in the current or voltage in the middle base layer results in a large amount of electricity flowing through the whole component. In this aspect, it can be used as an amplifier.

The transistor is composed of a semiconductive material, usually silicon, and at least three terminals for connecting to the external circuit. It was invented in 1947 by William Shockley, Walter Brattain and John Bardeen, who were jointly awarded the Nobel Prize in Physics for catapulting technological development. Their achievement is responsible for such modern appliances as wide screen TVs, smartphones, tablets and other electronic computing devices. The most basic function of a transistor is as an electronic switch, which allows electrons to flow from its collector side out through the emitter side. The base or middle of the transistor acts as the real switch control electrode through which electron stimulation

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Objectives 1. Understand the importance of cutoff and saturation to the operation of a transistor switch. 2. Define the purpose of a transistor switch. 3. Identify the function of a transistor switch. Materials 1. DC Power supply 2. DMM 3. Breadboard 4. Resistors (1kΩ & 10kΩ) 5. 2N3904 (npn) 6. 2N3906 (pnp)

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V.

6. Connect point A to -5V. Measure and record in Table 27-2.1 the voltage from point B to ground. 7. Construct a table of your results that will contrast the two circuits.

Procedures 1. Connect the circuit in Fig 272.3. Apply the correct polarity on the voltage to  .

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2. Connect point A to ground. Measure and record in Table 27-2.1 the voltage fro point B to ground.

Result and Findings

These are the result from the experiment that we conduct base on the instruction.

3. Connect point A to +5V. Measure and record in Table 27-2.1 the voltage from point B to ground.

Photo no. 1

4. Connect the circuit of Fig. 272.4. Apply the correct polarity of voltage to VCC.

5. Connect point A to ground. Measure and record in Table

This measurement result +4.943V is from the procedure step no. 2 where the base of the transistor is connected at the ground with the Vcc measures 5V.

Photo no. 2



measures 5V with the Vcc measures also 5V.

Point B to ground Point B to ground

5 6

+4.685 V -4.944 V

Questions:

Photo no. 3

This measurement result +4.685V is from the procedure step no. 5 where the base of the transistor is connected at the ground with the Vcc measures -5V.

Photo no. 4

This measurement result 4.944V is from the procedure step no. 2 where the base of the transistor is connected at the dc voltage source measures -5V with the Vcc measures also -5V. Table 27-2.1

Procedure Step

Function and Measurement

Value

1. In the prior circuits, what voltage level would a binary 1 represent? A binary 0? Ans: Binary Numbers are the flow of information in the form of zeros and ones used by digital computers and systems. enerally, a logic “1” represents a higher voltage, such as 5 volts, which is commonly referred to as a HIGH value, while a logic “0” represents a low voltage, such as 0 volts or ground, and is commonly referred to as a LOW value. These two discrete voltage levels representing the digital values of “1’s” (one’s) and “0’s” (zero’s) are commonly called: BInary digiTS, and in digital and computational circuits and applications they are normally referred to as binary BITS. 2. Are the answers the same for both the circuits circuits shown in Fig. 27-2.3 and 27-2.4? Ans: The answer from the Fig. 27-



Fig. 21-2.3 results to +4.943 V and the Fig. 27-2.4 is -4.815 V. 3. What is saturation? How is it demonstrated in this experiment? Ans: The transistor acts like a short circuit. Current freely flows from collector to emitter. Saturation is used whenever a quantity cannot increase or decrease above or below a certain value. In the experiment the saturation happens when we increases the supply from 5V to 10V the result value become constant. 4. What is cut-off? How is it demonstrated in this experiment? Ans: The transistor acts like an open circuit. No current flows from collector to emitter. In the experiment the cut-off happens when the base is connected to the ground. 5. Are the saturation and cut-off points the same for both the circuits shown in Figs. 27-2.3 and 27-2.4? Do the difference affect overall outcomes? Explain Ans: The saturation and cut-off

circuit is not connect to a voltage supply it is on the cutoff region and when the voltage source apply in the base of the transistor of the circuit it calls electrons that connect the base and collector and allow the current to flow and will conduct to the saturation region. VII.

Summary The experiment shows how the transistor works. The difference of pnp and npn transistor. It also elaborate how transistor become a switch. The experiment also shown the characteristic of the transistor when it is in either at the saturation or cut-off region. By constructing circuit Fig 27-2.3 we used the 2N3904 a npn transistor and for Fig 27-2.3 we used the 2N3906 a pnp transistor we also used the DC power supply for the Vcc. In Fig 27-2.3 circuit, the procedure step 2 where point A is connected to the ground the result value is + 4.943V and in the procedure step 3 where point A is connected to a supply +5V the result is -4.815V. While in Fig 27-2.4 where whe re in procedure step 5 the VCC is in negative value and point A is connected to the ground the result value is +4.685V and in procedure step 6 still the Vcc is at negative value and point A is connected to -5V the result value is -4.944V.



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Conclusion Doing this experiment I able to identify the basic function of the transistor with the help of the procedures above. It is important to perform the experiment to easily understand how transistor act as a switch and by the given instruction and the result value I able to determine while the transistor is at cut-off region where transistor is at open circuit there is no current flowing from the base to the emitter and the transistor is at saturation region when point A has a voltage supply where the current freely flowing from the collector to the emitter of a transistor.

Transistor As A Switch

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