Hello.
I'm now designing the I/O Control Board by using ESP32 MCU.
24Vdc Relay will be used for Contact Output.
During Turning ON the relay for the AC 220V load by using 24V relay, 5V, 3.3V, 24V DC Power is ringing fastly (tens of nano seconds).
There's a freewheeling diode for coil. so, it's not a switching noise.
So, I thought it's due to capacitive coupling between relay contact(AC220V) and relay coil.
(Kind of common mode noise)
But, I was not true.
When just I connect the one 24V SMPS(for Protective Relay[EMC Passed]) and connect the external ac cord (without or with small load).
and I just directly check DC 24V line without load using oscilloscope.
But, 24Vdc was ringing (tens of nano seconds, almost down to 0~5V).
I used each long AC line to seperate phigically.
MCU was not malfunctioned for a long time.
(there hasn't been no problem)
But. I'm not sure what it is and what could be happend by this ringing wave form.
Did you have this kind of experience?