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FET driver not working..why?

Discussion in 'Electronic Design' started by Robert Baer, Nov 4, 2012.

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  1. Robert Baer

    Robert Baer Guest

    For schematic,see the PDF at http://www.oil4lessllc.org/Misc/ .
    Basically, i amusing a 555 to drive the input of an IR2118, which is
    a high side inverting FET driver.
    have it all wired as per diagram in the datasheet.
    Using a 12V supply for the 555 and see a 12V positive gate pulse WRT
    FET source.
    I adjust supply on the drain to see what is (not) happening; a 100
    ohm load is from source to ground.
    All i see is a 12V pulse across the load; *not* that adjustable
    supply voltage; and _that_ is what i want: the supply to be switched to
    the load.
    So..pray tell what this idiot is doing wrong and indicate how to fix
    (pulse transformer for gate drive?).
     
  2. Guest

    you made a wrong connection, +12V should not be connected to pin8 on
    the ir2118

    gate drive voltage is on 0.47u charged via the diode when the fet is
    off

    -Lasse
     
  3. Also the bootstrap diode is recommended to be ultra-fast recovery-- a
    1N4007 is more like ultra-slow. You could change it for a UF4007 or
    UF4004.


    Best regards,
    Spehro Pefhany
     
  4. Guest

    You need to move the 12V connection from VB to VCC, and also connect a bootstrap capacitor between VB and VS, on the order of 10x Cin, and as mentioned use fast recovery diode between the VB-VCC.
     
  5. Guest

    and looking at again, the +12V need to be connected to Vcc, and the
    0.47u
    bootstrap cap goes between pin 8 and pin 6, not between pin8 and
    ground

    must have been going a little too fast ;)

    -Lasse
     
  6. Jamie

    Jamie Guest

    Nice, that link totally shut down my FF when I clicked in the PDF link..

    Shut it down with no notice and when I restarted it, all it did was
    restore my other tab and had the audacity to not even apologies for it!


    Oh well.

    Jamie
     
  7. John S

    John S Guest

    Wow! You're even more incompetent than I imagined.
     
  8. Jamie

    Jamie Guest

    No asshole, the link was block via my ISP when Acrobat tried to load
    it. You are a total imbecile, one that really does not know what ****
    they are talking about and likes shaving their own foot in their month

    I hope you like eating shit, because it appears that you walk in it
    all day, and after putting your foot in your mouth like you do, often,
    it must not be too tasty by now..

    what a winner of a child your mother had.. You must of been the
    drippings from the sheet on that one knight out she couldn't remember.

    Jamie
     
  9. Good point. It expects to be actively or passively pulled down within
    a couple volts of ground during the 'off' times.


    Best regards,
    Spehro Pefhany
     
  10. Robert Baer

    Robert Baer Guest

    You are probably incorrect, but the wiring is directly from the data
    sheet.
     
  11. Robert Baer

    Robert Baer Guest

    What i want is the FET to completely turn on and off - thereby giving
    the load a HV pulse.
     
  12. Robert Baer

    Robert Baer Guest

    AFAIK not stated in the data sheet.
    Excellent point..thanks.
     
  13. Robert Baer

    Robert Baer Guest

    Thanks.
    That connection was drawn wrong.
     
  14. Robert Baer

    Robert Baer Guest

    Check.
     
  15. Guest

    Try this. LTSpice format. Your drawing looks good , so you've obviously corrected it in the mean time. Never tried this with dropbox before , so hope it works.

    https://www.dropbox.com/sh/cqh7lzfr0otyy58/anDm0atzqa

    Cheers
    Ned
     
  16. John S

    John S Guest

    Unlike you, I have never shaved my own foot in my month.

    English must be your third language.
     
  17. John S

    John S Guest

    Well, he probably "designed" it. What would you expect from a pig (ham)
    who runs to the ARRL and claims "Daddy! Daddy! .. he picked on me"
     
  18. Robert Baer

    Robert Baer Guest

    Had a more serious problem that totally explained the why: the FET
    drain was open(!).
    Schematic has been updated and corrected.
    Works nice into a 100 ohm resistor as load.
    Next will be the acid test..
    The load will be the B+ (bottom) end of the flyback transformer in
    the TV set; a 33uF filter cap will be across that load for a
    closer-to-DC (adjustable) drive.
     
  19. Robert Baer

    Robert Baer Guest

    Only the cap was wrong..
     
  20. Robert Baer

    Robert Baer Guest

    "Time step too small; time = 6.47366e-06, timestep = 1.25e-19;
    trouble with u2:diode25-instance d:u2:_md4_d3 OK"
     
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