Electrical

Flyback Diode for Relay Protection

Electrical Diagrams · made in Skemio

Ladder circuit showing a 12V switched source across parallel rungs: a 12V relay coil, a 1N4007 flyback diode, and an LED status indicator.
Ladder circuit showing a 12V switched source across parallel rungs: a 12V relay coil, a 1N4007 flyback diode, and an LED status indicator.
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What it shows

  • Coil inductance opposes sudden current interruption: V = -L (di/dt).
  • Parallel flyback diode recirculates collapsing magnetic coil energy safely.
  • Clamps peak collector spike to supply voltage plus 0.7 V forward drop.

The takeaway

Always clamp relay coils with a parallel reverse-biased diode to save driver transistors from back-EMF.

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