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how do i drop voltage of a power supply

Discussion in 'Power Electronics' started by daniel barter, Jun 6, 2016.

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  1. daniel barter

    daniel barter

    Jun 6, 2016
    Hi I am new to electronics so go easy on me. I am trying to drop to voltage of my power supply / battery charger from 29v 5a down to 25v 5a. Is there a easy way of doing this? can I just use a diode and resistor on output? any advice regards dan
  2. Colin Mitchell

    Colin Mitchell

    Aug 31, 2014
    Just use some 10 amp diodes.
    daniel barter likes this.
  3. shrtrnd


    Jan 15, 2010
    I'm going to stick my 2-cents worth in here.
    I don't know your battery charger circuit, but some of them indicate a higher voltage when unloaded, than they do with a load. Just suggesting you verify that your power supply output with it's load, is still higher than you want, if you haven't done that already.
    daniel barter and Arouse1973 like this.
  4. daniel barter

    daniel barter

    Jun 6, 2016
    Thanks for your reply, how many 10 amp diodes would I need?
  5. daniel barter

    daniel barter

    Jun 6, 2016
    I have already checked that and as the charger is designed for lion batteries it will not drop below 29v
  6. hevans1944

    hevans1944 Hop - AC8NS

    Jun 21, 2012
    The forward voltage drop across each diode will be approximately 0.6 V to 0.7 V at 5 A current. So to drop 29 V to 25 V you need to drop 4 V across the series-connected string of diodes. Do the math: 4 / 0.7 = 5.7 ==> six diodes, or maybe seven diodes if 4 / 0.6 = 6.6.

    This is a "quick and dirty" way to drop power supply voltage. If you need a precision reduction, use a three-terminal voltage regulator with an external transistor to carry the 5 A. Many circuits available to search for and try out on the Internet.
    (*steve*), davenn and daniel barter like this.
  7. BobK


    Jan 5, 2010
    And, no matter how you do it, you will need a heat sink since there is 20W to dissapate.

    hevans1944 likes this.
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