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Making switching NPN with PNP

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There is a small circuit schematic attached where I am using voltage regulator 7812. I input 24VDC and 12VDC comes out from OUT pin. I want to make switch off & on NPN transistor with 12VDC buy using PNP transistor before NPN. And I will use PC printer port to provide the 1 & 0 pulse of 5VDC then how I should wire the circuit I want to just get the idea. Or is there any other way to do the same?


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  • 2 weeks later...

Your new circuit is missing a resistor between the collector of the A733 PNP transistor and the base of the TIP142 darlington transistor. The 4.7k resistor is noy much of a load for the very powerful darlington transistor. Unless we know the load current then we cannot recommend the value of the missing resistor.

The 7812 needs an input capacitor and an output capacitor near it as shown on its datasheet.

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