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Will this circuit work for a 3A load?

Discussion in 'General Electronics Discussion' started by hrishib, Sep 4, 2013.

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  1. hrishib


    Aug 30, 2013
    Hi, I found this over-voltage protection circuit on the web and I was wondering if this would be able to drive a 3A load? I'm building a LM1085 based regulator which inherently has some current limiting protection and I was hoping to use this for over-voltage protection. Any help would be appreciated. Thanks.

    Attached Files:

  2. duke37


    Jan 9, 2011
    I will try to post for the third time, I hope they all do not show.

    The circuit will work but not for long, the 1N4007 is a 1A diode. The IRFZ44 55V 49A 17.5mohm FET and will be adequate.

    I would fit a fuse to protect against long term high voltage.
  3. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

    Nov 28, 2011
    As Duke points out, the 1N4007 input diode is only rated for 1A. A 1N5407 is rated for 3A maximum current. Schottky diodes are available with higher ratings and have lower forward voltage drops but can be damaged by reverse voltage spikes. Look on Digikey, Mouser etc.

    Another approach to reverse voltage protection which doesn't introduce a voltage drop and therefore waste voltage is a diode connected backwards across the input terminals; in this case a series fuse should also be used.

    That circuit interrupts the negative circuit so it won't work if there's a common ground rail shared by the input and output circuits. It's generally better to interrupt the positive rail but this makes the circuit more complicated.

    The MOSFET could be replaced by one with lower ON-resistance. Again, look on Digikey or Mouser. An IRFZ44 passing 3A will drop up to 0.084V depending on the manufacturer and will dissipate up to 0.25W. It will not require a heatsink but will get somewhat warm.
  4. hrishib


    Aug 30, 2013
    Thanks Duke and KrisBlue. Appreciate the help! :)
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