Pnp Transistor Switch Circuit. As a result the transistor is off and no current can flow through the bulb. Pnp transistor switching circuit the concept of pnp transistor as a switch is that the current stops flow from collector to emitter only when a minimum voltage of 0 7v is supplied to the base terminal.
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As a result the transistor is off and no current can flow through the bulb. The circuit in the above figure shows the pnp transistor as a switch. But this is well below the supply voltage so the transistor is still on.
For a simple circuit like this it s common to connect the emitter to the plus from your power source.
For the pnp transistor the base terminal is always negatively biased with respect to the emitter. The difference this time is that we are switching power with a pnp transistor sourcing current instead of switching ground with an npn transistor sinking current. At 54 volts the zener is conducting and the voltage at r2 and d1 is 6 volts. In the first transistor the base is grounded and no current can flow into it.
