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Ground voltage??

Discussion in 'General Electronics Discussion' started by gsg, Jul 8, 2010.

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  1. gsg


    Jul 8, 2010

    I'm trying to debug a micro-controller circuit (with dsPIC33) and I'm getting some voltage problems.

    I have a 7805 regulator and another 3.3v regulator (LE33).When connected in the circuit, the 7805 gives an output of around 2v and it keeps decreasing steadily. The voltage measured at input pins of 7805 is around 3v.

    When I tried building the 7805 circuit on a separate breadboard it gives correct output but when I join these terminals to the PCB supply pins the voltages drop as before.

    Is it possible that the ground plane of the PCB is somehow getting a voltage and is not at 0v. If so how can i debug this circuit?
    Please help!
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    Jan 21, 2010
    Show us the circuit diagram -- that will help a lot.

    Measure the total current drawn by the circuit, and the input voltage while under load.

    Also measure the voltage across the 3 terminal regulator. Ensure that the ground pin of the 7805 is actually connected.
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