The 4 N channel mosfet H Bridge trig voltage

Discussion in 'General Electronics Chat' started by LAOADAM, Feb 24, 2019.

  1. LAOADAM

    Thread Starter Member

    Nov 21, 2018
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    I made a all N channel Mosfet H Bridge, as picture attached, few questions:
    1. the H Bridge can be driven by the voltage of 6 - 24 V, not like said need a voltage of higher than output V, that is 24 V here?
    2. The gate voltage can't go to 0 V when the switch is off?
    3. Can I use this Bridge to drive a 400W motor manually or need few Mosfet in parallel?

    Thanks

    sorry about the picture does not show, I posted at https://imgur.com/gallery/XFwHX0z and I don't know why?
    [​IMG]
    [​IMG]
     
  2. bertus

    Administrator

    Apr 5, 2008
    19,424
    3,935
    Hello,

    The pictures don't show.
    Please upload the pictures using the "Upload a File" button, below the reply box.

    Bertus
     
  3. LAOADAM

    Thread Starter Member

    Nov 21, 2018
    116
    0
    @bertus
    thank you Bertus, I've edited it. Please help.
     
  4. crutschow

    Expert

    Mar 14, 2008
    21,757
    6,271
    I don't really understand what that means. :confused:

    The gate voltage for those top MOSFETs needs to be at least 10V higher then their source voltage to full turn-on with minimum ON-resistance.

    upload_2019-2-24_23-14-16.png

    This is usually done with a bootstrap, high-side MOSFET gate driver circuit.
     
  5. LAOADAM

    Thread Starter Member

    Nov 21, 2018
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    Because I got message that the N channel MOSFET can be driven by the voltage higher than the output voltage, say if the output V=12v, the drive V = ~20v, maybe I am wrong.
    Do you have idea about the questions 2 and 3?
    Thanks
     
  6. Alec_t

    AAC Fanatic!

    Sep 17, 2013
    9,513
    2,303
    If the high-side FETs (Q1,Q3) drain voltage is 12V then you need 24V gate voltage to turn those FETs on fully. But you are applying the same voltage to the gates of the low-side FETs (Q2,Q4). The absolute maximum gate-source voltage for the specified FETS is only ±20V (per the datasheet), so the lo-side FETs would die.
    2) Yes it can.
    3) 400W at assumed 12V implies a running current of ~33A. That is within the 80A continuous rating of the FETs. However, motor stall current could be well over 150A, which the FET can sustain for only a few mS to keep within the safe operating area, so you would probably need to parallel-connect FETs. That is not a trivial thing to do if the FETS are to share the load equally.
     
  7. LAOADAM

    Thread Starter Member

    Nov 21, 2018
    116
    0
    Thank you Alec_t,

    1. What can I do if I need turn on two MOSFETs one at high side and one at low side? say Q1 and Q4? do I need to put different voltage to different MOS ? if I employ a high side driver, just driver the high side MOS only?

    2. I measured the Vg_GND = ~0.4v, how to make it 0 when turn off the switch?

    3. I’ll parallel them 2 or 3. BTW, the SOA of MOSFET shown different time area, say 10ms / 100us? Is it mean I can use the 100us area ampere only by the PWM cycle less than 100us?
     
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