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R&S HMP4040 voltage spike at PSU turn-off
electr_peter:
R&S support was contacted on voltage spike issue (PSU ON + channels OFF -> mains off), still waiting for a response.
--- Quote from: rf-messkopf on October 07, 2023, 10:43:38 pm ---My HMP4040 does not do that. See the attachment: 3V directly into the scope input, and then mains power off.
--- End quote ---
Initial observation was on voltage spike with channels turned off (PSU ON + channels OFF -> mains off). Can you check what happens in that case?
(PSU ON + channels ON -> mains off) spike could be a different issue (but not conclusive at this point).
rf-messkopf:
--- Quote from: electr_peter on October 08, 2023, 11:27:34 am ---
--- Quote from: rf-messkopf on October 07, 2023, 10:43:38 pm ---My HMP4040 does not do that. See the attachment: 3V directly into the scope input, and then mains power off.
--- End quote ---
Initial observation was on voltage spike with channels turned off (PSU ON + channels OFF -> mains off). Can you check what happens in that case?
(PSU ON + channels ON -> mains off) spike could be a different issue (but not conclusive at this point).
--- End quote ---
See the attachment: PSU switched on and output directly into scope, channel off; then PSU mains power off. The output ramps up to 1V and hangs there for about 6 seconds.
Not pretty, but not much of a problem for most circuits.
rf-messkopf:
--- Quote from: rf-messkopf on October 08, 2023, 01:17:46 pm ---See the attachment: PSU switched on and output directly into scope, channel off; then PSU mains power off. The output ramps up to 1V and hangs there for about 6 seconds.
--- End quote ---
Same test but with 47 ohms load. Then the voltage only ramps up to a bit over 50 mV.
tooki:
--- Quote from: EEVblog on October 05, 2023, 04:57:55 am ---
--- Quote from: mawyatt on October 05, 2023, 03:03:51 am ---Is that the correct image with the 4 ohm load? It has the same time code and looks the same.
--- End quote ---
There was an error in the upload. But it displays ok for me now, time in the images is different.
--- End quote ---
FYI, despite showing different file names, sizes, and thumbnails, it’s actually loading the same image for both, at least for me.
electr_peter:
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).
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