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How to Connect NPN to PNP

Transistors are semiconductors that can amplify signals. Bipolar transistors, which come in NPN and PNP types, have three leads known as the base, collector and emitter. You can connect the two types to form useful circuits. For example, a complementary Darlington pair increases the amplification of the current. It uses a PNP collector attached to an NPN̵7;s base. A push-pull emitter follower, made with an NPN emitter connected to a PNP emitter, has a current that does not flow for an entire AC cycle. Practice with a metronome circuit built with a Darlington pair.

Things You'll Need

3N904 NPN transistor
3N906 PNP transistor
Breadboard
Jumper wires
50-kilohm potentiometer
10-kilohm resistor
33-microfarad capacitor
Mini speaker
9-volt battery
Battery holder

Instructions

- 1
  Attach the PNP transistor into the upper section of the breadboard, and add the NPN to the lower section. You must orient the components parallel to the breadboard, with each of their leads in separate columns.
- 2
  Attach the base of the PNP to the NPN̵7;s collector. Use a jumper wire to connect the PNP̵7;s emitter to a row or column on the breadboard serving as the voltage source. Attach the NPN̵7;s emitter to a row or column chosen as ground.
- 3
  Add the middle lead of the potentiometer to the NPN̵7;s base, and place its right lead to ground. Attach a 50-kilohm potentiometer's left lead to an empty column on the breadboard, and add one side of a 10-kilohm resistor. Connect the other end of the resistor to the voltage source row or column.
- 4
  Connect one end of a 33-microfarad capacitor to the NPN base. If the capacitor is electrolytic, this end must be its positive side. Attach the capacitor̵7;s other end to the PNP̵7;s collector. Connect one speaker lead to this collector column, and connect the speaker̵7;s other lead to ground.
- 5
  Attach a 9-volt battery to a battery holder, and connect it to the circuit. When you turn the potentiometer̵7;s knob, the number of speaker clicks will increase or decrease.

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