Electronic – Sinking and sourcing current


I have been reading that NPN transistors are sinking and PNP are sourcing devices. I do not really understand this concept. It says current source device connects load to Vcc and current sinking device connects to ground (low voltage).

So does connecting a load at emitter of NPN transistor make it sourcing?

Best Answer

In a very simple form, relative to VCC, think of the transistor as either coming before or after the device.

If the transistor is connected between VCC and the device, it is sourcing current.

If the transistor is connected between the device and ground, it is sinking current.

Sink vs Source

(Image from CircuitsToday.com)

Some articles that describe things in more detail: