Transistor (PNP)

Meet the PNP bipolar transistor, the NPN gatekeeper’s partner. It also has a base (B), collector (C), and emitter (E), but its working voltages and current directions are reversed. In a suitable circuit, pulling the base below the emitter’s voltage lets a small current flow out of the base and controls a larger current from emitter to collector. Like NPN, it can switch a light or amplify a changing signal, using energy from the power supply.

The emitter arrow points inwards for PNP. To switch from the positive side of a supply, connect the emitter to positive and pull the base lower through a resistor to turn it on. Bringing the base back to the emitter’s voltage turns it off. Check the part’s pin order and limits: NPN and PNP cannot simply swap places.

At the lantern gate, a PNP transistor guards the battery’s positive side. A control circuit pulls its base lower through a resistor to light an LED lantern. A separate resistor limits the LED current; bringing the base back to the emitter’s voltage puts the lantern to sleep.