Transistor PNP – BD140G

Transistors amplify current. For example, they can be used to amplify the small output current from a logic IC so that it can operate a lamp, relay, motor or other high current device. In many circuits a resistor is used to convert the changing current to a changing voltage, so the transistor is being used to amplify voltage.

The difference between NPN and PNP transistors:

  • NPN. If the base is at a higher voltage than the emitter, current flows from collector to emitter.
  • NPN. Small amount of current also flows from base to emitter.
  • NPN. Voltage at base controls amount of current flow through transistor (collector to emitter).

  • PNP. If the base is at a lower voltage than the emitter, current flows from emitter to collector.
  • PNP. Small amount of current also flows from emitter to base.
  • PNP. Voltage at base controls amount of current flow through transistor (emitter to collector).

BD140G