ESD Shunt diodes perform which function in a circuit?

• A. Short out the power supply during ESD events
• B. Filter noise
• C. Regulate voltage
• D. Store charge

Answer: (C)

ESD shunt diodes protect a circuit by handling voltage spikes. They sit off during normal operation, but when an ESD pulse drives the line above a safe threshold, these diodes turn on and conduct a large current, pulling the voltage back down to a safe level. In that moment they act like a voltage regulator for the transient, keeping the protected node from rising to damaging levels by shunting the excess energy away (often to ground or to Vcc).

They aren’t meant to filter general noise—that’s the job of filters and proper grounding. They don’t store charge like capacitors, and they don’t continuously short the power supply; their purpose is to clamp transient voltages to a safe level during an ESD event.