FAQ03629 of Solid-state Relays FAQ

The current-limiting resistor built into the Solid-state Relays may have experienced an open circuit error caused by application of overvoltage to the Solid-state Relays output terminal due to noise surge (including high frequency noise).

Solid-state Relays Internal Circuit with Problematic Section

Note:Depending on the Solid-state Relays, the I/O insulation element may be a photocoupler, and the load switching (output) element may be a thyristor.

Possible Causes:

1.A surge voltage was caused by the load power supply, or other loads connected to the load power supply line.

2.An inverter-controlled power supply was used (including high-frequency noise).

Reference Information Relating to Protection against External Noise

As protection against external noise, it is recommended that an overvoltage protection element (e.g., a varistor) be externally connected to the power supply line.

Connection Example 1

Connection Example 2

Note:Check the manufacturer's information for how to connect the overvoltage protection element.