INDUSTRIAL ELECTRONICS

SMPS Back-EMF Protection Circuit for PLC Relay Coil

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UPDATED 2026-09-22
EXAMPLESMPS Back-EMF Protection Circuit for PLC Relay Coil
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CASE ANALYSIS

Scenario

An industrial PLC output module drives a relay coil from a 60V SMPS. The design shows a flyback diode and RC snubber across the coil to clamp turn-off transients before they damage the switching MOSFET.

Key decisions

  • Flyback diode D1 placed anti-parallel across relay coil
  • Series RC snubber (R1 + C1) across coil to damp ringing
  • Low-side N-MOSFET M1 switches coil to V− rail
  • V+ / V− rails labeled from 60V SMPS

When to reuse this

Use when designing or documenting DC relay coil suppression in PLC outputs, industrial controls, or any low-side switched inductive load.

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