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Any logic-level FETs with breakdown 300V+?

Discussion in 'Electronic Components' started by Joerg, Oct 31, 2008.

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  1. Joerg

    Joerg Guest


    Just curious, although I am not holding my breath that any exist:

    Are there FETs with a Vds rating of 300V or higher, preferably DPAK
    (TO-252), that have a guaranteed Rdson of around 1ohm or less at Vgs of
    6V or less? 1A current or higher.

    With guaranteed I mean not in some graph but with an entry under "max"
    in the tables. The usual ones are only rated at 10V although the figures
    indicate that they could have rated them for lower gate drive voltages
    at lesser current. But the manufacturers chose not to and trying to get
    any endorsement to that effect is like kicking a big oak tree.

    The motivation is the usual. Logic drive, the typical MIC4422 or similar
    is too much money plus it would need its personal supply voltage which
    would have to be made.
  2. Jamie

    Jamie Guest

    how about that ?"
  3. JSprocket

    JSprocket Guest

    I've no idea, but seeing what will happen to the rest of the system if
    one fails d-g, I'd be tempted to opto isolate it. I've seen PCBs with a
    big, brown- edged hole where the electronics used to be.
  4. TheM

    TheM Guest

  5. Have not noticed any (though there are a few 200V small MOSFETs rated
    for logic-level drive, but higher Rds(on) and lower current rating
    than you want.

    OTOH, you'll have thousands of inexpensive jellybean choices if you
    make it 10V drive.

    Best regards,
    Spehro Pefhany
  6. Joerg

    Joerg Guest

    Way too slow. Most have turn-off times in the usec range. Sure, you can
    hold them a wee bit above saturation but then circuit complexity begins
    to eat real estate and pennies.
  7. Joerg

    Joerg Guest

  8. Joerg

    Joerg Guest

    We are fuse-protected :)
  9. Joerg

    Joerg Guest

    Yeah, which is what we'll do. I was just hoping. 10V drive will add a
    lot of stuff and we are really cramped for space on this one.

    I wish there were fast BJT under 15c with hold-off Schottky built in. Is
    there still time to write to Santa ...?
  10. Joerg

    Joerg Guest

    Sorry, should have mentioned that.
  11. Joerg

    Joerg Guest

    I could but then the transformed-up Cgs would hit us from behind. Looks
    like we might have to provide a clean and staunch 10V.
  12. Nico Coesel

    Nico Coesel Guest

    A two-stage solution (N channel pulling a P channel to ground) is out
    of the question?
  13. Joerg

    Joerg Guest

    Requires dead-time control (+8 parts) or we'll run a chance of sitting
    there at the EMC lab with egg in our faces.
  14. Jamie

    Jamie Guest

  15. Jamie

    Jamie Guest

    And why can't you use a charge pump inverter source on the driving side
    for the gate?
    I've done that before using simple things like a PNP for high side to
    drive the gate via a charge pump inverter and common on the low side via
    a open collector NPN drive.

    It works perfectly, since the charge pump reservoir cap has more than
    enough to over come the Cgs on the gate for the initial transition. You
    may also consider a low value R in series with gate to avoid parasitic
    noise, like ringing for example. Many times board design can over come
    this how ever, it does not hurt to through in a 1..10 R.

    Or, just use a ready made gate driver chip with the same characteristics."
  16. Eeyore

    Eeyore Guest

  17. Jamie

    Jamie Guest

    Jesus christ..
    You got to be kidding me.

    That fits every spec he was looking for with the exception of
    the gate voltage for which, is the simplest thing to work around. Which
    is why they make charge pump drivers in cases like this..

    Yes, it adds a little extra to the component count how ever, this has
    been answered many times with various types of gate drivers.

    This is 101 design techniques around FETS. Gate voltage in most
    cases is the smallest issues."
  18. Eeyore

    Eeyore Guest

    He specifically asked for LOGIC LEVEL !

  19. Joerg

    Joerg Guest

    Well, there ain't so much space left as for a carpenter ant to squish in
    there ;-)

    Needs a separate supply and thus even more space. But if all else fails
    that's what we'll have to do. On another design a month ago I did that
    but there I had over 200 square inches of free land. So I just stuck a
    claim somewhere ...
  20. Jamie

    Jamie Guest

    Making a low yield supply on board to drive a fet should be a trivial
    task, one that requires very little real-estate.
    The size of gate driver chips are very small these days. One could even
    plant a mini daughter board just in front/over the top of the FET if
    space is tight.

    Did that the other day btw, to modify a circuit that was already in
    use.! Needed to enhance a analog PID board, so I etched out a mini .5"
    square DS board and elevated it over the main board with the
    connection legs...

    In your case, I guess if you wanted to design this into your board you
    could use a header and simply make the danghter board removable."
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