H bridge Logic

Discussion in 'General Electronics Chat' started by clintonb, May 14, 2015.

  1. clintonb

    Thread Starter Active Member

    Mar 6, 2011
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    I was looking at an H bridge this weekend and ran a few simulations to run a simple Light source.

    It makes perfect sense that a controller can sink and source and each will control the direction of current flow. Obviously makes no difference to the filament globe but a motor would turn in different directions.

    What happens if the motors voltage exceeds the gate voltage supplied by the controller? No problem on the N channel mosfets because it Vgs that controls the gate. The P channel mosfets however work on Vgs which will always be open.

    Do they normally work on a 5V supply and then boost his voltage to what is required?
     
  2. Hypatia's Protege

    Distinguished Member

    Mar 1, 2015
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    I'm not sure I understand your question?:confused:

    In any event a 'charge pump' scheme will be required for proper biasing of the two signal-ground level estranged devices (Re: a bridge composed of four like polarity 'switches').

    Best regards
    HP
     
    Last edited: May 14, 2015
  3. ScottWang

    Moderator

    Aug 23, 2012
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    Attach the schematic and labeling enough infos then it will be help.
     
  4. RRITESH KAKKAR

    Senior Member

    Jun 29, 2010
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    Hello,
    I have worked on L298/L293/MOSFET H bridges....
     
  5. clintonb

    Thread Starter Active Member

    Mar 6, 2011
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    My understanding of the problem was perhaps a bit off. I ran a few more trials and every time the entire circuit burns out. The problem, and perhaps a bettr question, involves the gate drain voltage of the mosfet. If a 5v controller controlled a 30v supply for a motor it exceeds the gate drain voltage. How is this being achieved with a power mosfet?
     
  6. ronv

    AAC Fanatic!

    Nov 12, 2008
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    You need to post a schematic to be sure, but it sounds like you are trying to drive the PFETs with 5 volts and ground while the source is hooked to +30 volts.
    2 things wrong with that. When the gate is ground that is probably above the gate to source voltage spec and when the gate is at +5 it won't turn it off.
     
  7. ian field

    Distinguished Member

    Oct 27, 2012
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    If you were using all N-channel, you'd need some provision for driving the high side gates above Vcc - there are high side driver chips that take care of the messy bits for you.

    As you mention P-channel devices - you shouldn't need a high side driver as such, but you do need to ensure the top and bottom MOSFETs never conduct simultaneously.

    On an SMPSU control chip, this is the dead time control feature. Have a look at appnotes for chips like the SG/UC3524 etc, this should provide a reasonably good explanation that you can see how it applies to your application.
     
  8. RRITESH KAKKAR

    Senior Member

    Jun 29, 2010
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