Mosfet gate related problem

Discussion in 'General Electronics Chat' started by ashkarmalik, Nov 17, 2012.

  1. ashkarmalik

    Thread Starter Member

    Jul 1, 2012
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    Q1.What does a gate charge of 28nC @ 10v of Mosfet related to as,i.E if the gate is been driven by 14v VGS then does the gate charge gets decreases or remains constant.

    Q2. If i am driving a 2Hp 48v PMDC motor using a N-channel Mosfet then what is the minimum VDS should i opt for my Mosfet.:rolleyes:
     
  2. SPQR

    Member

    Nov 4, 2011
    379
    48
    On a good day, I'm lucky to be able to spell "MOSFET":D,
    but I found THIS datasheet.
    HERE is another very nice datasheet that discusses gate charge.

    It seems that gate charge is fixed for any given device, though it can be different between manufacturers.
    And apparently gate charge is more important with rapid cycling of the device.
    Are you using PWM to drive the motor, or just using the MOSFET to turn it off and on?

    Based on both your questions, it seems that you are trying to select a good MOSFET for driving a 48 volt 2 HP DC magnet motor, is that right?

    If that is the case, HERE is a great article on MOSFET selection for driving DC motors.

    At least my answer will bounce you back to the top of the stack, where experts can see it again.
     
    ashkarmalik likes this.
  3. ashkarmalik

    Thread Starter Member

    Jul 1, 2012
    55
    1
    Thank you for your reply....and sorry for that mistake [M.O.S.F.E.T] :p
    Could u please answer another question.
    Q.I have connected the MOSFET gate drive with a series 22ohm resistance and gate Drive kinda blown up because the output got loose connection from the wiper motor and there were 2-3 sparks created during the loose connection.
    So why did my drive Blown up?
    And now I placed up a new Drive IC But the change in PWM Duty dosn't effect the motor speed whats is happening.I am totally confused.
     
    Last edited: Nov 18, 2012
  4. SPQR

    Member

    Nov 4, 2011
    379
    48
    In terms of your first question, the MOSFET "blew up" because some voltage or current parameter was exceeded
    (a general, boring answer that applies to all ICs).

    In terms of your second question, I think it would be better if you gave us more information.
    Schematics of your control circuitry.
    Type of MOSFET.
    Exact type of motor.
    Perhaps some pictures of your setup.

    Then perhaps more help would be available.


    NB: My comment on "spelling" of MOSFET is actually a joke. In American English if you see a phrase "I'm lucky to be able to spell 'XXXX' " - it means that the person writing it, or saying it, doesn't know very much about the 'XXXX'.:)

    I'm not a sports fan, so when people try to talk to me about the LA Lakers I say
    "I'm lucky to be able to spell "basketball" - which means I know very little about it.:D
     
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  5. ashkarmalik

    Thread Starter Member

    Jul 1, 2012
    55
    1
    MOSFET-CSD18533KCS
    Vdss-60v
    Drives 70A @100deg C
    Vgss (min)(MAX)-1.9v;20V
    To220 Package



    GATE DRIVER-UCC37322
    PDIP TYPE
    9A Peak Current @ 14V DC

    Motor Car wiper Windshield Motor Rated @ 12v , 32 Amp Ideal
     
  6. bertus

    Administrator

    Apr 5, 2008
    15,648
    2,346
    Hello,

    Is the circuit for automotive use?
    You might know that we do not support ANY automotive subjects.
    (see the Terms of Service )

    Bertus
     
  7. ashkarmalik

    Thread Starter Member

    Jul 1, 2012
    55
    1
    No,Its not for Automotive use
    I am planning it to run for my Heavy duty Conveyer
     
  8. ashkarmalik

    Thread Starter Member

    Jul 1, 2012
    55
    1
    Check out the Schematic
     
  9. crutschow

    Expert

    Mar 14, 2008
    13,009
    3,233
    One obvious problem is that you don't have an inductive spike suppression diode across the motor. Without that, switching off the motor can generate large transient voltages which can blow the MOSFET. Place a 10A or larger diode from the MOSFET drain to the plus side of the motor power source (anode to drain).
     
  10. ashkarmalik

    Thread Starter Member

    Jul 1, 2012
    55
    1
    Ok I would Place a 10a Diode in parallel to the motor,But Can U please tell me why my MOSFET are not responding to the change in PWM Duty cycle?
     
  11. ashkarmalik

    Thread Starter Member

    Jul 1, 2012
    55
    1
    And One more thing that some time my 22R resistance was also heating Vigorously before the MOSFET Gate drive blow up,Is it that there is ringing problem in the gate connection.
     
  12. crutschow

    Expert

    Mar 14, 2008
    13,009
    3,233
    Perhaps the MOSFET was already blown.
     
  13. crutschow

    Expert

    Mar 14, 2008
    13,009
    3,233
    No, ringing would not cause heating in a 22Ω resistor. If you have heating, it likely means the MOSFET gate was shorted.
     
  14. ashkarmalik

    Thread Starter Member

    Jul 1, 2012
    55
    1
    And one more thing I want to ask,
    Would 4 IRFP260 Mosfets would be sufficient to drive the 2Hp 48v Motor,and how would I calculate the optimal Mosfet for a 48v motor,
    and how to mound capacitors for that much load?
    What about the freewheeling diodes ...How much power does the freewheeling diodes would be there(voltage and current)
     
  15. ashkarmalik

    Thread Starter Member

    Jul 1, 2012
    55
    1
    Someone please reply to my post
     
  16. SPQR

    Member

    Nov 4, 2011
    379
    48
  17. ashkarmalik

    Thread Starter Member

    Jul 1, 2012
    55
    1
    And what about the freewheeling diodes
     
  18. SPQR

    Member

    Nov 4, 2011
    379
    48
    HERE is a nice little something on the freewheeling diode from Wiki.
    I had seen those before, and didn't realize that had so many names -

    Inductive spike suppression diode (Thanks crutschow!)
    Freewheeling diode
    Flyback diode
    Snubber diode
    Catch diode
    Suppressor diode

    In that text they recommend a Schottky diode because of its speed and low forward resistance.

    So the question is, what is the maximum reverse voltage that the diode can handle. The Wiki says that you might need as much as 10x the forward voltage. That would be 480 volts in your situation.

    So I went to Jameco and searched for all Schottky diodes, and sorted them from most expensive to least expensive (I assume a large reverse voltage diode would be expensive) and found these:

    40CPQ100 max rev voltage = 100
    43CTQ100PBF 100
    12CWQ10FN 100
    MBRF20200CTG 200 (now we're getting somewhere!)

    So we're still not up to 480 reverse volts.
    BUT! I wonder if you could put two of them in parallel?

    Again, you need to take everything I say with a grain of salt - I'm not an expert.

    Let's hope one of the experts chimes in in a minute.
     
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  19. crutschow

    Expert

    Mar 14, 2008
    13,009
    3,233
    The snubber diode across the motor only needs to handle the power supply voltage since it is forward biased when the reverse transient occurs. So a diode with a voltage rating about twice the power supply voltage should be fine.

    Note: You put diodes in series, not parallel to increase the voltage rating.
     
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  20. ashkarmalik

    Thread Starter Member

    Jul 1, 2012
    55
    1
    That was a lot of detailed explanation on the snubber aka freewheeling diode SPQR,
    and crutschow as you stated that a Schottky diode with a ratting of double the power supply voltage would be sufficient.and what about the current rating for them to suppress the load of motor's current (2Hp 48v PMDC)
     
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