Electronic Communication Projects

Posted on Feb 7, 2014

When the output of our multivibrator is low, Q1 (because it is NPN transistor) will be OFF and Q2(because it is PNP transistor) will be ON. So the negative terminal of capacitor C3 will be connected to ground. It will charge from the power supply and through the D1 diode. Second Half: When the o/p of multivibrator is High, Q1 will be ON and Q2 will be OFF.

Electronic Communication Projects
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The C4 capacitor will be charged by the voltage of C3 capacitor. But its discharge through transistor Q1 is blocked by D1 diode. Discharge of C4 through Q1 during next half (that is low voltage of the multivibrator) is blocked by D2 diode. The basic difference between last post of 12v DC to 240v AC and this circuit is that there is a Bridger Rectifier added at the o/p of the transformer. And there are some p-n diodes added so that the reverse current is not allowed and the circuit is safe from accidental reverse currents. This circuit contains the 555 as an astable multivibrator. Diode D1 is added to ensure the 50% duty cycle of the multivibrator. For half of the time Q1 is OFF which is driven by direct voltage coming from the multivibrator. To be specific Q1 will be OFF for the time when o/p of multivibrator is low. Now, Q2 is connected to the collector of Q1. So, Q2 will be ON for the period when o/p multivibrator is low and Q1 is OFF. For next period Q1 will be ON and Q2 will be OFF. So this design ensures constant voltage supply for Transistor. The circuit contains an astable multivibrator using 555. For low voltage o/p of multivibrator, Q1 will be OFF and Q2 will be ON, and for high voltage o/p of multivibrator, Q1 will be ON and Q2 will be OFF.

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