Gate driver options for N-channel MOSFET H-bridge

Discussion in 'General Electronics Chat' started by us202000, Oct 14, 2011.

  1. us202000

    Thread Starter New Member

    Jul 5, 2011
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    Hi,
    As a newbie to h-bridge I am a little confused about the options for choosing a MOSFET H-bridge gate drivers for a 24v DC motor(about 10A). It appears that a simple way to drive the H-bridge is to turn on the high side which then can trigger the low side as in Eugene Blanchard's design here H-bridge using P and N channel FETs - The Using MOSFETS Website (note that the label there probably should have been "N channel MOSFET" instead of P and N). Also, there are probably other ways to provide the high voltage needed for the high side, as well as using opto switches. In any case, the point is that all is needed in his design is to turn on the high side and trigger the low side. I like the simplicity in this design and it sounds great. But somehow, the figure is labeled as "Obsolete". Does anyone know why?

    I understand that there are special chips such as IR2110, or HIP48xx series but can someone comment on what additional benefits these chips offer compared to Eugene's design? Does his design have a high probability of shoot through (don't know how deadtime is handled here)? Also, any comments on the choice between IR2110 and HIP48xx series would be appreciated. Thanks.
     
  2. SgtWookie

    Expert

    Jul 17, 2007
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  3. us202000

    Thread Starter New Member

    Jul 5, 2011
    13
    0
    SgtWookie,

    Thank you for providing the reference. I read those and somehow I got an impresssion that the problem Eugene had in that design was due to the mixed use of P&N channel MOSFETs. Nevertheless, he did conclude that the ideal design should have separate controls for each MOSFET. That's good to know.

    Now, the IR2110 appears to be a good choice but I wasn't sure whether it has optoisolation? If not, do I need optocouplers between the microcontroller and the IR2110? If yes, then why not use the optocouplers to drive the MOSFET directly (I haven't seen many designs like this). This is still not clear to me. Pleas advice. Thanks.
     
  4. SgtWookie

    Expert

    Jul 17, 2007
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    No, the IR2110 does not have built-in optoisolators.
    It does not provide for "dead time", either. Just in case you were not aware of the requirement for dead time ... MOSFETs turn OFF more slowly than they turn ON. If you attempt to turn on a high side MOSFET at the same time you're turning OFF a low-side MOSFET (or vice versa), you will wind up having both of them turned on at the same time, causing the dreaded "shoot-through" condition, which will lead to loud "bangs", flashes of light, and smoke.

    The IR2110 is also a bit tough to understand in the beginning, particularly the boost cap. The low-side MOSFET needs to be turned ON in order for it to charge; at that point, it is the only ground path for the low side of the capacitor. If the capacitor doesn't get charged, you won't be able to turn on the high-side MOSFET.

    The boost cap also needs to be charged back up periodically. You can't just leave the high-side MOSFET turned on indefinitely, as that boost cap will lose it's charge, and the MOSFET will fall into the linear conduction region (not fully turned on), and it will burn up.

    Optoisolators also have a problem in that they are generally quite slow. There is a newer technology called "digital isolators" that really is sort of a new face on an old idea; using capacitors to block the DC levels, but pass the effects of AC signals. However, in this case it's passing on logic level signals while providing isolation. Google is your friend here.
     
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