12v DC to 220v AC Converter Converter Circuit Using Astable Multivibrator Inverter circuits can either use thyristors as switching switching devices or transistors. Normally for low and medium power applications, applications, power transistors are used. The reason for using power transistor is they have very low output impedance, allowing maximum maximum current to flow at the output. One of the important applications of a transistor transistor is in switching. For this application, the transistor transistor is biased in saturation and cut-off region. hen the transistor is biased in saturation region, both the collector emitter and collector base !unctions are forward biased. "ere the collector emitter voltage is minimum and collector current is maximum. #nother important aspect aspect of this circuit circuit is the oscillator. oscillator. #n important use of $$$ Timer Timer I% is in in its use as an an astable multivibrator. multivibrator. #n astable multivibrator multivibrator produces an output signal which switches switches between the two states and hence can be used used as an oscillator. The The fre&uency of oscillation is determined by the values of capacitor and resistors. [Also Read: How Read: How To Make an Adu stable stab le Ti!er " Circuit Diagra!
Circuit Diagra! o# 12v DC to 220v AC Converter $ %lectronicsHub&'rg
Circuit Co!(onents •
'( ) (*'
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+( ) (
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+* ) ($
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+ ) (Ohms
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+/ ) (Ohms
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0( ) TI1/(
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0* ) TI1/*
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2( ) 2* ) (N/3
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% ) **uF
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T( ) (*'4**' step up transformer
Circuit Design %)(lanation 'scillator Design: #n astable multivibrator can be used as an oscillator. oscillator. "ere an astable multivibrator using $$$ timer timer is designed. e 5now, fre&uency fre&uency of oscillations for a $$$ timer in astable mode is given by6
# * 1&++,-R1.2/R2/C where +( is the resistance between discharge pin and 'cc, +* is the resistance between discharge pin and threshold pin and % is capacitance between threshold pin and ground. #lso the duty cycle of the output signal is given by6 D * -R1.R2,-R1.2/R2 7ince our re&uirement is f )$"8 and 2 ) $9 and assuming % to be .(uF, we can calculate the values of +( and +* to be ( and (/ Ohms respectively. "ere we prefer using a ($ potentiometer to fine tune the output signal. #lso a ceramic capacitor of .(uF is used between the control pin and ground. witcing Circuit Design:Our main aim is to develop an #% signal of **'. This re&uires use of high power transistors to allow the flow of maximum amount of current to the load. For this reason we use a power transistor TI1/( with a maximum collector current of :#, where the base current is given by the collector current divided by the 2% current gain. This gives a bias current of about ./# ;(, i.e./#. "owever since this current is more than the maximum base current of the transistor, we prefer a value less than the maximum base current. ?ON@ is about *'. Thus + b for each is calculated to be ( Ohms. 7ince the diodes are used for biasing, the forward voltage drop across the diodes should be e&ual to the forward voltage drops across the transistors. For this reason, diodes (N/3 are used. The design considerations for both the 1N1 and N1N transistors are same. e are using a 1N1 power transistor TI1/*. 'ut(ut 7oad Design: 7ince the output from the switching circuit is a pulse width modulated output, it might contain harmonic fre&uencies other than the fundamental #% fre&uency. For this reason, an electrolyte capacitor needs to be used to allow only the fundamental fre&uency to pass through it. "ere we use an electrolyte capacitor of **uF, large enough to filter out the harmonics. 7ince it is re&uired to get **' output, it is preferred to use a step up transformer. "ere a (*'4**' step up transformer is used.
12v DC to 220v AC Converter Circuit '(eration •
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hen this device is powered using the (*' battery, the $$$ timer connected in astable mode produces s&uare wave signal of $"8 fre&uency. hen the output is at logic high level, diode 2* will conduct and the current will pass through diode 2(, + to the base of transistor 0(. Thus transistor 0( will be switched on. hen the output is at logic low level, diode 2( will conduct and current will flow via and 2( and +/ to the base of 0*, causing it to be switched on. This allows the 2% voltage to be produced across the primary of the transformer at alternate intervals. The capacitor ensures that the fre&uency of the signal is at the re&uired fundamental fre&uency. This (*' #% signal across the primary of the transformer is then stepped up to **' #% signal across the transformer secondary.
A((lications o# 12v DC to 220v AC Converter Circuit (.
This circuit can be used in cars and other vehicles to charge small batteries.
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This circuit can be used to drive low power #% motors
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It can be used in solar power system.
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7ince $$$ Timer is used, the output may slightly vary around the re&uired duty cycle of $9, i.e. exact $9 duty cycle signal is hard to achieve. Ase of transistors reduces the efficiency of the circuit. Ase of switching transistors has the possibility of causing cross over distortion in the output signal. "owever this limitation has been reduced to some extent by the use of biasing diodes.
Instead of $$$ timer one can use any astable multivibrator. For example this circuits can also be build using //3 astable multivibrator,whose output current is amplified and applied to the transformer.
