Electronics > Projects, Designs, and Technical Stuff
Question about potentiometer wiper failure in bench power supplies
moffy:
I made this comment about a PSU design with the same issue:
"there might be a problem with the design. If you lose the connection between the pot and the 'adj' pin the output of the regulator is going to go high. If a pot develops a dead spot or fails you could get the full input voltage across your test circuit which you are powering. It would be better to fail safe or low output voltage. The 'adj' pin needs, say a resistor permanently connected, to make the output voltage low in the case of a failure of the pot or connection."
In this discussion: Projects, Designs, and Technical Stuff / Re: Building a simple compact dual rail linear bench supply
It takes a bit of thought and effort to make things fail safe. The other issue with pots is that they can be panel mounted and use wires and connectors to the board, which adds an extra failure point.
Conrad Hoffman:
This is the same problem many audio amplifiers have with the bias pot. Pot goes open, amplifier goes to full bias and the outputs overheat and fail. Good designs don't do that. BTW, wiper current should be kept to a minimum for most pots if you want reliability.
pardo-bsso:
Hi, check here: http://www.imajeenyus.com/electronics/20160517_potentiometer_feedback/index.shtml
Besides going over the open wiper problem that article also explores different configurations and the response they give (voltage output vs. pot position).
TheMG:
Maybe the manufacturers didn't really expect the equipment to be in service for so long that the pots start going bad?
Anyways, when I designed my own bench supply, the pot simply provides a reference voltage to a negative feedback loop comparator. If the wiper of the pot goes open the reference voltage goes to zero and consequently so does the output.
ArthurDent:
A lot of the better (read 'expensive') bench power supplies have OVP, OCP, and even OPP settings to protect equipment you're testing. Here are photos of a couple. The GW Instek power supply is a modern supply with an encoder and no pot for adjustments.
Navigation
[0] Message Index
[#] Next page
[*] Previous page
Go to full version