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How to vary current at constant voltage?

  1. Jan 5, 2015 #1
    if you have a power source, how do you keep the voltage constant while varying the current?
  2. jcsd
  3. Jan 5, 2015 #2


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    Gold Member

    Vary the load.

    Actually, I'm not sure I understand your question. If your voltage is constant, there will be a maximum current you can provide from that source (not because of the fixed voltage but because that's how power sources work ... they are not infinite) and it will provide any value in that range depending on the load.
  4. Jan 5, 2015 #3
    this is a pretty ghetto solution but, after the load, could i reverse bias a few zener diodes to get the V back up?
  5. Jan 5, 2015 #4


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    Gold Member

    Huh ??? I have no idea what you mean. Draw a circuit diagram. I'm sure the answer is no, but I'd still like to see a diagram.

    What do you mean "get the V back up" ? What would have made the V go down?

    Do you have any understanding of electronics at all?
  6. Jan 5, 2015 #5
    are you saying if you apply a load across something, there is no potential drop?...

    i need a power source with a certain voltage and current output. the power source i have at hand has the correct voltage i need, but it has 10 times the current output i need (at that particular voltage). you suggested a load to lower the current. fine, but i need to put the this load in series with the actual load that i'm trying to power which will mess with the potential across the actual load i need to power. so to get this potential back up to the original V_out by the power source, i was asking if reverse biasing a few zener diodes in series would raise the potential without affcting the current output of the power source.
  7. Jan 5, 2015 #6


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    You misunderstand power sources. The fact that your source CAN put out 10 times the current you need does not mean it WILL put out that current. It will put out whatever current is drawn by your load. That is, if you have a 10volt power source that can produce one million amps of current and you hook it to a 10 ohm load, it will put out 1 amp of current. The fact that it CAN put out one million amps is irrelevant.

    If your understanding of electronics is this minimal, you should consult someone in your area about what it is that you are doing. OR ... provide an exact circuit diagram here so that we can give you better advice.
  8. Jan 5, 2015 #7


    Staff: Mentor

    A power plant delivers 0-100% of rated power to the grid keeping voltage nearly constant.

    A wall plug delivers 0-100% of the breaker rated current to your devices while keeping voltage nearly constant.

    Are you asking how that works?
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