DP832 overvoltage protection issue

[Redeeman]

I have a DP832 with model hacked into DP832A (though i highly doubt this influences anything)

I notice that when setting the OVP to for example 12.1v, if i then go back and ramp the voltage up very quickly, the voltage shoots significantly above 12.1v before the output is turned off. I havent measured how much or how long, but I had a 12v fan connected, and it was enough that i was able to hear it spin up to a significantly higher RPM for a moment.

This is a bit surprising, wouldnt it be completely sensible to expect the OVP to not even allow the user interface to set a higher voltage to begin with? am I missing something?

[thm_w]

I believe it is software controlled, so it can be very slow to respond.
Code seems non-optimal if its letting you set it above the OVP level, but there may be reasons for that. The RD6006 I have behaves similarly, and apparently many other supplies.

https://www.eevblog.com/forum/testgear/rigol-dp832-ovp-overshooting-with-huge-delay/

[Redeeman]

would be interesting to know what (if any) reasons there are for the software to allow setting of higher output than OVP is set to. I really can not see a reason

[RoGeorge]

The software does not want to allow over voltage to happen, but this is the best it can do.

To detect over-voltage, it first need to measure the voltage.  Most probably it's not made at a single ADC measurement, but a few reads are averaged over a period of time for a better resolution (oversampling).  Then, there are many other things that need to be run by a single processor, not only the OVP subroutine, so the subroutine that compares the voltage needs to wait it's turn to be run.

All these takes time, and by the time the software decides to shut down the output, the output voltage might have already overshoot a lot.

[TurboTom]

would be interesting to know what (if any) reasons there are for the software to allow setting of higher output than OVP is set to. I really can not see a reason

Imagine you want to constant-current charge a battery (reverse current blocking diode required and threshold voltage considered) and you'ld like to use the voltage limit to terminate the charging process. This would required initially setting a higher output voltage, otherwise the limit voltage would never be reached since the PSU would switch over to constant voltage mode before.

There may be other application where being able to set a higher output voltage than the limit, and being permitted to enable the output, makes absolute sense.

... just my two cents...