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DC Power supply behaving weirdly:What reason could it be?

  1. May 14, 2014 #1
    I'm using a DC power supply connected to a TPIC 1021 chip(basically a serial transceiver).

    I need 12V to power the chip and my DC power supply is equipped with 2 knobs,one changes the voltage and the other changes the current. For some reason,when I get to 5V and turn the volt knob further,the power supply switches automatically to current mode i.e the LED on current indicator turns on. I can't go further than 5V unless I turn the current knob a little and only after that do I can get to turn to 12V.

    Step a. I turn the voltage knob to 5V. The voltage LED switches off and the current LED turns ON.

    Step b. After my current LED turns ON,I turn the current knob just a little ->Now my voltage LED turns back ON and only now do I get to change the voltage to 12V.

    Why does this happen?
    1.Is it because there's a possible short-circuit?
    2.Has it got something to do with Power=Voltage*Current ? [Its weird that the power supply could supply 5V at 0 ampere and not 12V at 0 amps].

    Your views please.
  2. jcsd
  3. May 14, 2014 #2
    Unless there's a good reason to limit the current going to your device turn the current limit knob fully clockwise then set your voltage. Your current knob isn't a current controller but a current limiter. Think of a resistive circuit as you raise the voltage on your power supply the current increases until it reaches the limit set, if you carry on turning the voltage knob the current can't go up so the voltage stays steady, if you now increase the current limit that will also let the voltage increase till you reach the voltage you set.
  4. May 14, 2014 #3


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    What are you seeing as a current when you get to the 12 volts? From the chip's datasheet, in normal mode operation it's typically only 1.2 mA (assuming a typical 14 volt supply).
  5. May 15, 2014 #4
    A problem existing with my Dc Power supply when there is too much load(i.e chip TPIC1021) on it. As you can see in the video below,there are 2 knobs-one for changing the voltage and the other for changing the current. Normally,I would just change the volt knob but after my bluetooth module got fried,I have this problem.
    The problem:
    The voltage needle won't go above 5V unless I tinker with the current knob,as in the first instance of the video.
    In second instance in the video,all I have to do is unplug one of the loads and I can go all the way to 12V without tinkering with the current knob.
    What phenomenon explains this? Checked 10 times for short-circuits,none found. My fear is that the chip(load) got fried and there is an internal short circuit. Still doesn't explain why the DC Power Supply acts like this.

    Video link of what exactly is happening:
  6. May 15, 2014 #5
    Jobrag:Before some of the components got fried,I could just rotate the voltage knob and it would go all the way to 12V. After I took away some of the burnt-up modules,I am faced with this problem. If what you say about current limiter is true,I could actually not rotate the current knob AT-ALL when everything was new,spic and span.
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