DC-DC Buck Converter not working with low output load

Discussion in 'General Electronics Chat' started by Joseph Trapnell, Feb 25, 2016.

  1. Joseph Trapnell

    Thread Starter New Member

    Feb 25, 2016
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    I have made a simple buck converter that gives me a clean output of 5v when I have a load of 391 ohms, however if I reduce the load to say 5 ohms it gives me no more than 380mV on the the output. Does anybody know why this may be?
     
  2. ronv

    AAC Fanatic!

    Nov 12, 2008
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    Maybe you could post a schematic of what you have.
     
  3. kubeek

    AAC Fanatic!

    Sep 20, 2005
    4,670
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    Post you schematic and what coil you use.
     
  4. Roderick Young

    Member

    Feb 22, 2015
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    A low-ohm resistor is actually called a "heavy" load, by the way.

    If you are using a commercial circuit, it could be that the circuit is going into shutdown and protecting itself from overcurrent.

    If the circuit is your own design, it could be that you are not able to maintain a high enough duty cycle to generate a 5-volt output at 1 amp. Or it could be that your method of sensing the output voltage is flawed. The output could have 5-volt spikes, but an average voltage of 0.38 volt, for example. If you have unintentionally built a peak detector for your feedback circuit, that could explain what is going on. Try increasing the output capacitance.

    Can you post a schematic? Even a hand drawn one helps tremendously in diagnosing your issue.

    Also, check your input source. For example, if the input to your circuit is a 9-volt battery, the battery is simply not capable of delivering that kind of current. When you put the 5 ohm resistor on the output of the converter, does the input drop to an abnormally low voltage, too?
     
    Evanguy likes this.
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