Following the design concept outlined in Section 3.2, the overall circuit for relay weld detection based on ISOM8118-Q1 is recommended as follows. In this circuit, the AMC0330S-Q1 is an isolated sampling operational amplifier that samples the AC port voltage. Its single-ended output simplifies the design of conditioning circuits, providing a reference for monitoring the actual voltage on the relay contact side. In the event of a relay weld, the current flows through the current-limiting resistor R1 and into the ISOM8118-Q1 chip input, and the ISOM8118-Q1 generates output current I_C with reference to I_F, creating a voltage drop across the pull-up resistor R2 connected to the MCU’s input. The MCU’s GPIO port determines a possible weld with edge signals and finally confirms the relay contact status in conjunction with the ADC sample result from the AMC0330S-Q1 and the MCU’s command sent to the relay.

In weld detection circuit designs, many variables affect how to properly use an opto-emulator, including grid voltage, MCU’s supply voltage, and so forth. Specific parameters and selections are analyzed in the following sections, assuming the grid voltage is 220VRMS sinusoidal AC voltage and the MCU’s supply voltage is 3.3V.