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MOSFET built in bypass diodes?

Discussion in 'Electronic Basics' started by example John Smith, Sep 16, 2005.

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  1. I have IRF1404 and IRF4905 hexfet/mosfets. Do these have built in drain-source reverse voltage protection diodes? Looking at the data sheets I see it shows internal zener diodes inside the device's
    symbol. If they are, there is no need to use external ones in my circuit right?

    Also the datasheets dont seem to show a pinout. ??!! Looking at the pins from the front it should be Gate Drain Source right?

  2. The structure of the MOSFET includes a diode across drain to source.
    Whether you need an external one in addition, depends on how you like
    the performance of that internal one.

    For example, in some H-bridge applications, the body diode can carry a
    significant current and add a significant amount of heat to the die,
    and the reverse recovery losses can also get pretty big. Paralleling
    the fet with a Schottky diode can help all these negatives.

    And don't confuse a drain to source diode with one across an inductive
    drain load. They are not equivalent in function.
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