Voltage rating of p-channel MOSFET

Discussion in 'The Projects Forum' started by Tahmid, Jul 2, 2008.

  1. Tahmid

    Thread Starter Active Member

    Jul 2, 2008
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    Hi,
    I am new to this forum.
    I had a confusion on the voltage rating of p-channel enhancement MOSFETs. I have collected p-channel MOSFET :IXTH11P50 with -500v Vds from IXYS semiconductors. In the datasheet it is mentioned that it has a Vgs of +/- 20v.
    Since it is p-channel, current will go in through the source and out through the drain once the gate is pulled low. Here, both drain and gate are at ground level, so doesn't the MOSFET have to have a Vgs of -500v to be used at 500v?
    I tested with 12v and 20v and the p-channels worked fine, but with 200v/300v they were not working properly, rather, shorted, with no gate control.
    Why is this? If so, why is it mentioned -500v Vds in datasheet?

    All help would be appreciated in this regard.
    Thanks.
     
  2. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    The rating for Vgs is correct and means that with the source at 500V, you cannot pull the gate to ground. You will not find a Vgs much more than that value either. Check Application Note 18 from Zetex, which has a section: Level shifted PMOS Gate Drive. Sorry, I did not save the actual link. John

    Edit: Here's another link to follow. Discussion begins p. 18.

    http://focus.ti.com/lit/ml/slup169/slup169.pdf
     
    Last edited: Jul 2, 2008
  3. Tahmid

    Thread Starter Active Member

    Jul 2, 2008
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    Hi,
    Thanks for the quick reply.
    But does that mean that I cannot use the p channel mosfet at 500v?
    So, could you please tell me how to use the p channel as high side mosfet?
    Thanks in advance.
     
  4. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    You can use the P-channel at up to its rating (500V in this case; although, I tend not to go the maximum ratings). The point is that the gate cannot be pulled more than 20 V below the source. Thus, you need some way to level shift its drive, as described in the links given previously.

    Here is a previous thread discussing simple level shifters:

    http://forum.allaboutcircuits.com/showthread.php?t=9959

    Look particularly at post #8 by n9352527.

    John
     
  5. Tahmid

    Thread Starter Active Member

    Jul 2, 2008
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    John,
    Thank you very much. Now I am crystal clear.
    My heartiest thanks goes to you for your excellent co-operative approach.

    Thanks,
    Tahmid.
     
  6. Tahmid

    Thread Starter Active Member

    Jul 2, 2008
    344
    25
    Hi,
    Thanks again for help.
    I just had 1 last question. Say, if I were to use this circuit (I choose option C), at approximately, 220v and 300v, what would be the values of the resistors?
    Should I use 400v transistor here?
    Thanks again.
     
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