Brief single 2N3904 NPN bipolar junction transistor BJT LED flasher circuit

One NPN bipolar junction transistor can flash an LED if wired up the right way.

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Diagram:

Single 2N3904 NPN bipolar junction transistor BJT LED flasher circuit schematic diagram by electronzap
Single 2N3904 NPN bipolar junction transistor BJT LED flasher circuit schematic diagram by electronzap’

The emitter to base diode has a relatively low breakdown voltage. That is why you don’t normally want to connect the emitter to the positive side of the circuit, but that is what we are taking advantage of in this circuit. Once the E-B breakdowns in this circuit, the current rapidly surges from emitter to collector since the base is floating. Once the voltage drops too much to sustain that runaway current, it stops flowing.

Collector to base diode can handle a lot more reverse voltage. That is why the connector is usually connected to the positive side of the circuit.

Video:

Single 2N3904 NPN bipolar junction transistor BJT LED flasher electronics circuit how to DIY

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