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R&S HMP4040 voltage spike at PSU turn-off
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mawyatt:

--- Quote from: electr_peter on October 09, 2023, 04:31:36 pm ---There is response from R&S, paraphrasing:

Firstly, R&S recommends to turn-off channels normally and only then switch off PSU - this way voltages spikes are not generated. In R&S HMP FAQ section this is mentioned Best way to switch off the HMP series power supply
Channels are controlled via relays and PSU even tries to be gentle on contacts Switch cycles of the HMP Series

Second, on the main issue about voltage spikes with channels turned off, there is no official fix for this behavior. As I understand, these spikes are very limited in power (2.3-2.6V, ~2-3mA max) and probably can be mitigated by capacitors and parasitic loads on PCBs anyway. From posts we see there are at least several revisions of PSU HW with different resistances on output. My PSU has ~10 kOhm across the output, but with external 2 kOhm load voltage spike is reduced to OP mentioned levels of 0.5-1.0V. I can deal with that.
But don't directly connect some sensitive laser diode to PSU and switch it on/off willy-nilly.

According to R&S, both points are related to complicated regulated PSU circuits which have limited control of outputs when turning off (there are at least 3 rails in each PSU channel).

--- End quote ---

Haven't some folks experienced/shown significant levels of overshoot and energy at turn off? It's hard to tell with this web site's ability to totally screw up images, arrangements and such (really needs to be fixed, even messed with Dave's own images)!!

WRT to R&S response, one should Not turn the power off before Disengaging the outputs, that's fine and certainly good practice but as mentioned by believe nctnico, what about a Power Outage??? Does one expect to lose valuable CMOS circuits with a random power outage??

Also, if we owned one of these R&S supplies (we don't), would be asking R&S how come other supplies do not exhibit this level of overshoot at turn off of main power? BTW we check for similar kind of behavior (just disengaging the output) since way back we lost some very expensive custom ICs to a similar issue with a rogue Power Designs power supply. We just checked our supplies for the condition with the outputs engaged and cycling the power off, all behaved nicely without any hint of overshoot!! So we know our various Siglent's (3), GW Instek, and Korad (2) don't do this!!!

Honestly quite surprised at apparently R&S more lackadaisical response to this issue.

Best,
rf-messkopf:

--- Quote from: mawyatt on October 09, 2023, 05:32:33 pm ---Haven't some folks experienced/shown significant levels of overshoot and energy at turn off? It's hard to tell with this web site's ability to totally screw up images, arrangements and such (really needs to be fixed, even messed with Dave's own images)!!

--- End quote ---

There must have been a circuit change down the line. My fairly recent HMP4040 does not overshoot at all (see my posting above). Also, other folks seem to be aware that units up to a certain (unknown) production date can overshoot at mains turnoff or power failure, see e.g. this posting in a German forum.

The issue with the outputs of disabled channels ramping up to about 1V open circuit (on my unit) at mains turnoff seems to be pretty benign as this voltage reduces to a few tens of millivolts with only a light load. Certainly this is not nice, but I don't think this is a big problem, at least not as far as I am concerned. Anyway, it is hard to understand why this is happening at all because the PSU seems to disconnect disabled outputs by relays. Anyone interested to do some reverse engineering?

As I'm not affected by the overshoot at mains turnoff I can say that I've been quite happy with the HMP4040 so far.

Edit: In this posting in a German electronics forum someone claims that he knows cases in which the overshoot issue at mains turnoff or power outage has been fixed under warranty on HMP2020 and HMP4040 PSUs, and that newer units already have a modified circuit (mine does, obviously).

Maybe pdenisowski can comment on this.
pdenisowski:

--- Quote from: rf-messkopf on October 09, 2023, 09:00:31 pm ---Maybe pdenisowski can comment on this.

--- End quote ---

We're looking into it.  As you say, it's not an issue with current production HMPs and I'm hoping to have an update shortly.

tautech:

--- Quote from: pdenisowski on October 09, 2023, 10:32:45 pm ---(Und danke für die Links - die hatte ich auch noch nicht gesehen)

--- End quote ---
:-//
Some R&S secret code ?
mawyatt:

--- Quote from: rf-messkopf on October 09, 2023, 09:00:31 pm ---
Edit: In this posting in a German electronics forum someone claims that he knows cases in which the overshoot issue at mains turnoff or power outage has been fixed under warranty on HMP2020 and HMP4040 PSUs, and that newer units already have a modified circuit (mine does, obviously).

Maybe pdenisowski can comment on this.

--- End quote ---

That's good to know for folks with these that do exhibit this behavior, R&S apparently is not leaving them hanging!!

Would be interesting to know what the culprit is and the cure/fix?

Best,
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