dumb question about diode equivalency (4002 and 4004)

Discussion in 'General Electronics Chat' started by Steve C, Dec 7, 2008.

  1. Steve C

    Thread Starter Active Member

    Nov 29, 2008
    86
    0
    Hi all,

    I need to replace a pair of 4004 series diodes and I don't have any. Got a ton of 4002's though.

    I have no idea what purpose these diodes serve (they are on relay contactors) so I have no idea why they spec'd 4004's.

    I skimmed the datasheets looking for current and voltage specs and it looed like they were rated for the same current, and the 4004 to double the voltage.

    I figured I'd just put two 4002's in series and call it a day, but it can't be that simple, can it? Do I have to go out and buy some 4004's? Can I get by with a pair of 4002's?

    Thanks guys,

    -Steve

    edit: application is an automotive power window controller. the relays contactors supply power to the motor.
     
    Last edited: Dec 7, 2008
  2. bertus

    Administrator

    Apr 5, 2008
    15,648
    2,347
    Hello,

    It depends on the reverse voltage.
    When you take 2 X 4002 diodes, put a resistor of 470 K parallel to each diode to level the voltage accros them in reverse mode.

    Greetings,
    Bertus
     
  3. Steve C

    Thread Starter Active Member

    Nov 29, 2008
    86
    0
    I think the diode is there to prevent current flow in that particular direction. I'm not sure I can add 940k worth of resistance permitting current flow in that direction.
     
  4. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    1N4002's are rated for 100 PIV, where 1N4004's are rated for 400 PIV.

    You really should be OK with 1N4002's in an automotive environment. They're there to take care of the reverse EMF pulse that occurs when the coil is de-energized.

    If you have some small caps around (220pF to 470pF) you might wire them in parallel with the diodes. This will give these rather slow rectifiers time to switch on when they're forward biased by effectively increasing the EMF pulse rise time. It should also lower the peak current through the diode.
     
  5. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    The 1N4004 diodes were used instead of 1N4002s because maybe they were less expensive but either diode will work the same.
    If the 1N4004 diodes failed then maybe a diode with a higher current rating should be used.
     
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