MOSFET Driver - Vcc=+5v

Discussion in 'General Electronics Chat' started by nztech, Feb 24, 2009.

  1. nztech

    Thread Starter Active Member

    Feb 24, 2009
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    Hi all,

    Can someone please assist as I am wanting to power on 3 power MOSFETs not simultaniously to a motor with 3 steps.
    what I am wanting to know is how these MOSFET high side drivers work.

    I have a source to motor +12V and regulated for the supply to all electronics at +5V 7805.

    If I run the MOSFET driver chip at +5V rails will the output voltage output to the MOSFET fed gate be pumped to +10V?
    Is this the design of the chip?

    If possible a recommendation would be much appreciated to drive these 3 MOSFETs.

    Kind Regards
     
  2. mik3

    Senior Member

    Feb 4, 2008
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    You can use the MOS as low side drivers as to eliminate the need of a MOS IC driver. If you need a high side drive then use a MOS IC driver to bootstrap the gate voltage and turn the MOS fully on.

    Also, note that most MOS need 10V Vgs to fully turn on expect some designs for logic levels and turn on with 5V.
     
  3. nztech

    Thread Starter Active Member

    Feb 24, 2009
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    Isn't the low-side used for P-Channel to set the gate low?
    I need to turn the N-channel on which will require 10V to turn on fully.

    Is this what a high-side MOSFET Driver do from a 5V rail supply?

    Cheers
     
  4. mik3

    Senior Member

    Feb 4, 2008
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    If you use a logic level MOS and connect its source to ground and the load on its drain and power supply then you will be able to turn it on with 5V.
     
  5. nztech

    Thread Starter Active Member

    Feb 24, 2009
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    The MOSFET's I have are not TTL based hence the driver required. This driver is the issue I am not too sure of.
    Would the driver do this with v5 rails?
     
  6. nztech

    Thread Starter Active Member

    Feb 24, 2009
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    Does anyone have the practically on how a MOSFET Driver chip can up the gate voltage?
    Is this possible?
     
  7. nztech

    Thread Starter Active Member

    Feb 24, 2009
    44
    0
    Hi all,

    Can someone please assist as I am wanting to power on MOSFETs to a motor with 3 step windings/3 speeds.
    what I am wanting to know is how these N-MOSFET high side drivers work.

    I have a source to motor +12V and regulated for the supply to all electronics at +5V 7805.

    Question:
    1. If I run the MOSFET driver chip at +5V rail will the output voltage output to the MOSFET fed gate be pumped to +10V?

    2. I need about 10V to turn the MOSFET on fully. MOSFET's supplied are not TTL driven, hence I require a driver circuit.
    Is this the design of the chip as I am not too familiar with these?

    If possible a recommendation would be much appreciated to drive these 3 MOSFETs.
     
  8. nztech

    Thread Starter Active Member

    Feb 24, 2009
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    as per this diagram attached?
    Thanks
     
  9. nztech

    Thread Starter Active Member

    Feb 24, 2009
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    Is a MZX620/MAX621 suitable?
     
  10. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    It is explained in the datasheet for the Max621 you suggested in your other post. Simply put, imagine a capacitor that is charged up by a source. It is then electronically flipped and put in series with the source to effectively double the voltage.

    John
     
  11. nztech

    Thread Starter Active Member

    Feb 24, 2009
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    A N-channel requires a high side 10V to switch on whereas a P-channel requires a negitive voltage to turn on.
    Hence the High-side Mosfet driver is set to drive the n-Channel connected to the GND and switching the Drain +ve.

    Cheers
     
  12. nztech

    Thread Starter Active Member

    Feb 24, 2009
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    Cheers, basically a non-inverting op-amp and a inverting op-amp creating a +5v and -5V input gate drive, but reference -5V thus giving a 10V drive.
    If this is undrestandable..
    Also as per schematic the N-channel from the MAX621 should be ok?
    This is to drive a motor.

    Regards
     
  13. nztech

    Thread Starter Active Member

    Feb 24, 2009
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    Any feedback on this?
     
  14. nztech

    Thread Starter Active Member

    Feb 24, 2009
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    Any feedback on this?
     
  15. jpanhalt

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    Jan 18, 2008
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    Your two threads on essentially the same subject are confusing.

    From what I gather, you are considering N-channel topside and P-channel on the bottom. That is opposite usual practice. Why do you want to do it that way?

    It seems that your PWM supply will be at 5V and you are planning to use the Max621 to generate Vcc+10V or so. For a topside , N-channel mosfet with a drain at 12V, that may not be enough to fully turn it on, unless it has a logic-level gate.

    Also, the Max621 puts out only 25 mA, which may cause relatively slow switching for large mosfets. The Max621 datasheet shows an example. You also seem to be considering using a couple of op-amps to generate the PWM, but have not made any mention of dead-time between turning on the top and bottom. Slow switching and no dead-time may lead to shoot-through (i.e., both top and bottom mosfets are on at the same time).

    In sum, I think it would help to: 1) Post your schematic; and 2) Stick to one thread on this subject.

    John
     
  16. mik3

    Senior Member

    Feb 4, 2008
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    Post a schematic of what are you thinking to do.
     
  17. nztech

    Thread Starter Active Member

    Feb 24, 2009
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    attached can you review
     
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  18. bertus

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    Apr 5, 2008
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  19. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    The block diagram looks OK to me based on the Max621 driver. The circuit posted by bertus makes sense too, of course. However, for motor control, I would be concerned about its switching speed. If the Max621 would be current-limited, the bertus circuit would be even more so. The later has the possible advantage of optical isolation.

    John
     
  20. nztech

    Thread Starter Active Member

    Feb 24, 2009
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    Thanks for that.
    Instead of 12V supply can I use +5V?
    This is the supply I am feeding all chips. Will this give me +10V MOSFET Drive.
     
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