NPN Bipolar Junction Transistors (BJT) is technically used to make a current sink, but commonly anything that sets a specific current through series components or load is called a current source.
NPN BJT diagrams
- Voltage is applied to the base of the transistor.
- That voltage minus the base to emitter diode drop (approx. 0.6-0.7) is applied to the emitter resistor.
- Emitter resistor sets the current (voltage across it, divided by it’s resistance) through it, plus through the collector to emitter, and any series components on the collector side of the transistor.
- The supply voltage must be high enough to power all components for the amount of current.
- NPN BJT current source is on the more negative side of the load. So, it actually sinks current as far as accurate analysis is concerned.
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