BJT current source

NPN BJT current source 2N3904 set by zener diode for 5mA schematic and pictorial diagram by electronzap
NPN BJT current source 2N3904 set by zener diode for 5mA schematic and pictorial diagram by electronzap

As long as the load doesn’t consume too much power…

  • 5.6V zener diode sets base voltage to 5.6V, which sets the voltage across the emitter resistor to 5V due to the 0.6 base to emitter voltage drop.
  • 1,000Ω with 5V across it, passes 5V/1000Ω = 0.005A , which is usually referred to as 5mA, through it.
  • All series components with the emitter resistor will pass that same amount of current (because they are in series).

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