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| Lab power supply over-voltage when turning on |
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| raresvintea:
Hello, we have some lab power supplies that have a strange and annoying issue. When you turn it on, the set voltage is 12v and it overshoots with 72V for a small time and kills boards or if you turn it on it remain on 65V and we need to turn it off again... How can i manage this? -limit somehow this peak -detect over voltage and disconnect the output -make a simple on off switch, first turn on the power supply and push a button that will turn on the output and it will compare the output voltage with a set limit and stays off. |
| pevonous:
Have you tired to open it up and check inside of it, sometimes, there has a problem of MOSFEET issue on it. I don't know if it can help you or not. |
| raresvintea:
This symtom is rare, but when it is present, blew the board |
| David Hess:
That sort of thing is not as rare as it should be. It indicates a poor design. |
| DaJMasta:
Could certainly be a design issue with the PSU, but make sure you're not adding too much inductance to the front end, it can magnify the issue if the switch on time is pretty quick. Otherwise, if you're manually switching the output, maybe just putting a DPDT switch between the output of the supply and the input of your device and leaving it disconnected while the supply is first switched on, then connecting it later. It's a stopgap, but it's a simple solution if you're not using the programmable switching features the supply may have. Another option would be trying to load the output and seeing if the response changes. Even a 10k load resistor in parallel with your load or something may be enough to change the way the supply responds initially to that output is more in line with what it should be, or perhaps an NTC thermistor in series with the power line to take the edge off the spike. There's also the option of a TVS diode in parallel rated a bit above your 12V requirement to take the edge off. How are you testing this, though? 72V is a LOT for a normal linear lab power supply who's normal transformer taps used for a 12V output level for a power supply... it likely cannot be connected to that voltage internally unless the maximum supply voltage exceeds 72V, so I suspect some sort of probing issue. Again inductance is a concern if the power on is a fast edge, but this isn't typically how lab supplies operate. Are you referencing your device to a ground different ground? Is the ground connected to the power supply floating ground before the power is switched on? While some of the earlier measures could alleviate the symptoms, I really wonder if that voltage is actually present and whether it should even be possible under normal operation. |
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