multiple rectifiers in parallel

Discussion in 'The Projects Forum' started by mckaype, May 31, 2006.

  1. mckaype

    Thread Starter New Member

    May 31, 2006
    Hi People,
    Newbie here with a question - I've got 6)ea 25A single phase (silicon) bridge rectifiers that are rated for 800V peak reverse voltage. They are model EGC5327.
    I have a three phase variable voltage & frequency AC imput that will exceed the current rating of each of the rectifiers. I intend to parallel two rectifiers per phase.
    Can somebody please help me out with a schematic that shows the connections?
    Thanks much
  2. n9352527

    AAC Fanatic!

    Oct 14, 2005
    Something to think of: The forward drop voltages of diodes, even the ones that are of the same type, are not matched. Therefore the current through them would not be equally distributed when they are in parallel. Furthermore, the forward drop voltage also depends on the temperature, and the diode that carries more current would have a higher temperature resulting in lower forward drop voltage and in turn causing more current to flow through that diode instead of the other one. This might result in thermal runaway for one of the diode and a small bang.

    It's like parallelling two BJTs without current sharing resistors. You could, of course, use current sharing resistors (one resistor each in series for each diode) if you want to spend some money to buy them and the small loss of power is not a problem for you. But I personally think buying a bigger rated diodes is the way to go.