When the output is set to logic high, diode D2 will conduct, and current will flow through diode D1, R3, and into the base of transistor Q1.The 555 timer connected in astable mode creates a square wave signal with a frequency of 50Hz when supplied by a 12V battery.12v DC to 220v AC Converter Circuit Operation A 12V/220V step up transformer is utilised in this application. It is preferable to utilise a step up transformer because 220V output is required. We utilise a 2200uF electrolytic capacitor to filter out the harmonics in this case. As a result, an electrolyte capacitor must be utilised to ensure that only the fundamental frequency passes through. We are using a PNP power transistor TIP42.īecause the switching circuit’s output is a pulse width modulated output, it could contain harmonic frequencies other than the basic AC frequency. The design considerations for both the PNP and NPN transistors are same. Since the diodes are used for biasing, the forward voltage drop across the diodes should be equal to the forward voltage drops across the transistors. Thus R b for each is calculated to be 10 Ohms. The bias resistor is then calculated as follows:įor each transistor, the V BE(ON) is about 2V. However, because this current exceeds the transistor’s maximum base current, we prefer a value less than the maximum base current. This results in a bias current of approximately 0.4A *10, or 4A. As a result, we employ a TIP41 power transistor with a maximum collector current of 6A and a base current equal to the collector current divided by the DC current gain.
To allow the maximum amount of current to flow to the load, high-power transistors must be used.
Here we prefer using a 150K potentiometer to fine tune the output signal.Īlso a ceramic capacitor of 0.01uF is used between the control pin and ground.ĭesigning a Switching Circuit: Our major goal is to create a 220V AC signal. Since our requirement is f =50Hz and D = 50% and assuming C to be 0.1uF, we can calculate the values of R1 and R2 to be 10K and 140K Ohms respectively. Also the duty cycle of the output signal is given by: Where R1 is the resistance between discharge pin and Vcc, R2 is the resistance between discharge pin and threshold pin and C is capacitance between threshold pin and ground. We know, frequency of oscillations for a 555 timer in astable mode is given by: Here an astable multivibrator using 555 timer is designed. Oscillator Design:An astable multivibrator can be used as an oscillator. The frequency of oscillation is determined by the values of capacitor and resistors. An important use of 555 Timer IC is in its use as an astable multivibrator.Īn astable multivibrator produces an output signal which switches between the two states and hence can be used as an oscillator. The collector emitter voltage is lowest here, and the collector current is highest.Īnother important aspect of this circuit is the oscillator. The transistor is biassed in the saturation and cut-off regions for this application.īoth the collector emitter and collector base junctions are forward biassed when the transistor is driven in the saturation region. Switching is one of the most essential applications of a transistor. The use of power transistors is due to their extremely low output impedance, which allows maximum current to flow at the output. Power transistors are commonly utilised in low and medium power applications. Inverter circuits can use thyristors or transistors as switching devices. 12v DC to 220v AC Converter Circuit Using Astable Multivibrator In order to increase the capacity of the inverter, the number of MOSFETS must be increased. The transformer combines both the inverting signals to generate a 220V alternating square wave output.īy using a 24V battery, loads up to 85W can be powered, but the design is inefficient. turns ratio of the transformer must be 1:19 in order to convert 12V to 220V.
These amplified signals are given to the step-up transformer with its center tap connected to 12V DC.
The inverting signals from the oscillator are amplified by the Power MOSFETS T1 and T4. The frequency of the square wave generated by the astable multivibrator can be calculated using the formula below. The frequency will be determined by the values of R1, R2, and C1 (R4, R3, and C2 are all the same). Inverting square waves are generated by each transistor. The oscillator is made up of R1, R2, R3, R4, C1, C2, T2, and T3. This can be accomplished by building an Astable multivibrator that generates a 50Hz square wave. Because the frequency of the AC supply is 50Hz, a 50Hz oscillator is required. The circuit is made up of three components: an oscillator, an amplifier, and a transformer.
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