24V regulated DC power supply output 47V

Discussion in 'General Electronics Chat' started by eman, Aug 6, 2006.

  1. eman

    Thread Starter New Member

    Aug 5, 2006
    3
    0
    Hi everybody!

    I've got a 24V regulated DC power supply (current 10A). But now its output is 47V. Does anybody tell me what is the problem and what I can do to troubleshoot this power supply ?
    Thank you.
     
  2. hgmjr

    Moderator

    Jan 28, 2005
    9,030
    214
    eman, (name spelled backwards, clever)

    Does your power supply have externally available output sense terminals? There would be two of them. One is labeled sense(+) and the other is labeled sense(-). When not being used these two sense terminals should be connected to their corresponding output voltage terminals. Sense(+) should connect to 24V and sense(-) should connect to the 24V return terminal. This would be explained in the datasheet for the power supply. Although 47 volts is way beyond the range that is usually available in a sensing supply it is worth a check just to rule this out.

    Was the power supply subjected to some sort of stressful event that might have caused it to fail?

    Is the power supply a linear AC-to-DC type or is it a switching power supply?

    Do you have access to the schematics for the power supply?

    hgmjr
     
  3. eman

    Thread Starter New Member

    Aug 5, 2006
    3
    0
    Hi Hgmjr,
    Thanks for your reply.
    It's a switching power supply. It's a VS3 Astec PS.
    I don't know much about this. I don't have the schema,either.
    It does have a control connector. There are the (+) Remote Sense terminal & (-) Remote Sense terminal. Is that what you mentioned above?
    If you have any ideas, pls let me know.
    Thank you very much.
     
  4. hgmjr

    Moderator

    Jan 28, 2005
    9,030
    214
    Yep. those are the terminals that I was referring to. I gather you have checked them and they are connected properly.

    With a switching power supply, there are a number of things that can cause the symptom you are seeing. Without a schematic you are in for a lengthy exercise in troubleshooting 101. If time is critical, then you may want to consider ordering a new one. However, if you have the time and the equipment needed (a good DSO) to troubleshoot the supply then I am sure you will find a number of members here in the forum that can suggest some things to look for myself included.

    hgmjr
     
  5. Gadget

    Distinguished Member

    Jan 10, 2006
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    0
    In a switching PSU there is normally a Voltage sense input on the control chip which comes from a voltage divider from the output. The voltage divider values are chosen so that at the correct output voltage, the voltage going to the sense input of the chip is the same as the chips internal reference. The Chip trys to maintain this state by altering the PWM output to the switching devices, so regulates the output. Changing the divider will alter the output volts... and you can often find a trimmer Pot in this divider for fine output voltage adjustment.
    The first thing I would be checking is the integrity of this divider.
     
  6. eman

    Thread Starter New Member

    Aug 5, 2006
    3
    0
    You're right,Hgmjr and Gadget. The problem is the wrong value resistor in the divider. I've replaced this resistor and the PSU works well.
    Again,thanks a lot !!!
     
  7. hgmjr

    Moderator

    Jan 28, 2005
    9,030
    214
    Thanks for the credit eman but I can claim none of it for it was gadget and he alone who was responsible for producing the "deus ex machina".

    Well done, gadget.

    hgmjr
     
  8. Gadget

    Distinguished Member

    Jan 10, 2006
    613
    0
    If only all my bench work was as rapidly dispatched.
    No Probs eman, glad to have helped.
     
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