PSU voltage spikes when turning mains on or off

[Mike Fikes]

I have a Korad KA3005D, which has an "Off/On" button for controlling whether the output is delivering power. This works fine in terms of regulating the voltage during these transitions.

But, I've noticed that when pressing the mains power button, the voltages can involve significant spikes. (Attached is a capture of the voltages when turning off the unit, where the oscilloscope probes are connected directly to the PSU output leads.)

Is this normal in PSUs? I'm still learning, but am presuming that, given this, it is prudent to not have the PSU connected to the DUT when turning mains on or off.

[Mike Fikes]

I think I was too quick to post / blame the Korad for the spikes, as I see them (or similar ones) on the oscilloscope trace when the scope probe is connected to the DUT rails (otherwise floating, unpowered), and the Korad's power is simply turned on or off. Perhaps this is jut the Korad's transformer causing ground reference to waver?

I have the Korad and Rigol both plugged into a Tripp-Lite Isobar power outlet strip (in separate "isolated filter banks", but perhaps this is insufficient to prevent the observed phenomenon).

[mcinque]

Did you check it with a proper bnc cable connected to a banana adapter like this to avoid picking up any interference with the ground clip of the dso probe? The ground cable of the probe can act like an antenna and pick up noise in the surroundings.



My rebranded KA3005D has some spikes at startup (not bad like that you posted, maybe you're picking some EMI coming from the power switch) but the worst feature is that it has 700mV overshoot for some mS when you enable the output  . It's considered somewhat "normal" for a cheap programmable psu.

[Mike Fikes]

No. Thanks. I'll look into getting proper BNC connectors.

When enabling the power for 5 V, I can confirm that I see a 440 mV overshoot on the KA3005D.

[mcinque]

Mine is worse than yours