What is the function of a suppression diode in a relay?

• A. To regulate coil current
• B. To reduce high voltage spikes
• C. To indicate relay status
• D. To switch AC to DC

Answer: (B)

When a relay coil is energized, current builds up in an inductor. If the power is removed, the collapsing magnetic field tries to keep the current flowing and can generate a large voltage spike that can damage driving circuitry. A suppression diode is placed across the coil in reverse bias during normal operation. When power is cut, the coil current flows through the diode instead of creating a huge spike, clamping the voltage to about the supply level plus a diode drop and letting the coil energy dissipate safely. It protects switching devices from damage and reduces electrical noise. This doesn’t regulate coil current, indicate relay status, or convert AC to DC.