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General Enginnering Problem Dealing with Voltage Supply

  1. Dec 6, 2012 #1
    Hello,

    So I'm facing some difficulties. I'm using a DC voltage supply and connecting it to a PIC Board. The AC adapter that comes with the board outputs 9V DC. To be safe I'm just using 5V from the DC voltage supply. When I connect it to the board the reading from the voltage supply drops to 4.3 volts and the current cutoffs too. Does this means that there is a short circuit with the board?

    Thanks
     
  2. jcsd
  3. Dec 6, 2012 #2
    First, why don't you want to use the AC adapter provided? If the adapter works, why lower the voltage?

    It could well be there are regulator inside the board to get 5V and it needs 9V to do that. Current drops off might means that you don't have enough voltage to even turn on the circuit and not drawing current. You don't have enough info for people to judge. But the most important question is why do you want to change something that is designed to work with and work?
     
  4. Dec 6, 2012 #3

    jim hardy

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    well you'd need to have an idea what is capacity of the supply, and what is demanded by the board. Capacity of supply will be written on it.

    Be aware that some power supplies, especially those meant for charging batteries, provide unfiltered DC and will drop their voltage when loaded. Also they'd be not good for the electronice on your board.
    To see if you have one of those, connect it(without the board) to your voltmater and select AC. If you read more than a couple tenths of a volt it is poorly filtered(if at all) so you probably need a different supply.
    To verify, select meter to DC and note reading, then unplug supply. If voltage drops immediately it is unfiltered, if it takes a second or two to bleed down then it IS filtered.
    So study both your supply and the manual that came with yuor board.
     
  5. Dec 6, 2012 #4
    Ok Thanks guys. I'm going to try this in the lab room tomorrow and will reply with my results. Once again, Thanks.
     
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