This is a circuit to test zener diodes.


It should be noted that this circuit could be dangerous. It is tied directly to an AC line, and has an output of 300V. The output has resistors on each line, which limits the current making it a bit safer, but will still give you quite a shock.

It should be switched off while attaching diode


  • S1: SPDT switch
  • S2: Pushbutton switch
  • N1: Neon lamp
  • D1: 1N4004, 1A 400V Rectifier
  • D2: 1N4004, 1A 400V Rectifier
  • C1: Electrolytic Capacitor 100uF 200V
  • C2: Electrolytic Capacitor 100uF 200V
  • R1: 33kΩ Resistor 1/2W
  • R2: 2.7kΩ Resistor 1/4W
  • R3: 1MΩ Resistor 1/4W
  • R4: 24kΩ Resistor 1W, or 2x 48kΩ Resistor 1/2W in parallel.
  • R5: 48kΩ Resistor 1W, or 2x 100kΩ Resistor 1/2W in parallel.




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