How to suppress DO spikes in I/O modules

Suppressing voltage spikes at the digital outputs of I/O modules requires a multi-pronged approach. For switching inductive loads, the freewheeling diode must be of fast recovery or ultra-fast recovery type, such as FR107 or ES1D, with its anode close to the negative terminal of the load and its cathode close to the positive terminal of the power supply to minimize loop area. An RC snubber circuit, typically 47Ω in series with 100pF, should be connected in parallel across the switching transistor to absorb voltage overshoot during turn-off. For MOSFET outputs, a resistor can be added to the gate drive circuit to slow down the switching speed, thereby reducing dv/dt.

Twisted-pair cables should be used for output cables, and if possible, common-mode chokes, such as the CML series, should be added at the ports. On the PCB, the power supply of the output drive circuit should be isolated with ferrite beads and fitted with large-capacity energy storage capacitors. For high-frequency spikes, ferrite beads can be connected in series on the output lines. Using an oscilloscope with a high-voltage differential probe to measure the voltage waveform at the output can accurately assess the spike amplitude and adjust the snubber circuit parameters accordingly. At the system level, ensure a stable ground return path for the inductive load.