problem in h-bridge hardware

Discussion in 'The Projects Forum' started by syed hassan, Apr 15, 2015.

  1. syed hassan

    Thread Starter New Member

    Mar 11, 2015
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    hello everyone
    i am facing a problem due to which my project has been stuck around. i need your urgent help
    actually i am trying to implement the following circuit at bread board and testing it at low voltages
    my problem is the V(gs) is zero due to which no current is passing through mosfet and mosfets are unable to turn on
    what step do i need to take in order to make this circuit work efficiently
    at inputs i am applying a pwm signal of 50Hz with dead time of 100 usec
    can anyone plz help me out in troubleshoot my problem?
     
  2. crutschow

    Expert

    Mar 14, 2008
    13,009
    3,233
    To troubleshoot, you trace the signal, either from the source to the MOSFET, or from the MOSFET back to the source, to see where the signal is disappearing. It's sort of a detective "whodunit" game.
    It requires understanding everything about how the circuit is supposed to operate and then determining what part is not operating as planned.
    Troubleshooting is often the most difficult part of any electronic design.
     
  3. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Any reason you do not appear to be using the Pic PWM module?
    Max.
     
  4. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Also curious why the need for the 7408's?
    Max.
     
  5. syed hassan

    Thread Starter New Member

    Mar 11, 2015
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    i have done it many times but what i think is the function of bootstrap is not being performed as it should be.due to which gate voltage is exactly the same as that of source voltage.while it should be 10v more than the source voltage.
    now i want you to help me out how i cater this issue?
     
  6. syed hassan

    Thread Starter New Member

    Mar 11, 2015
    13
    0
    max forget about pwm signal and 7408.if i just apply 5v at HI and 0v at LI still i am facing the same problem
    plz tell me where the circuit is not performing its function properly?
     
  7. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    If those are constant voltages then the lower FET never turns on and the bootstrap can't work.
     
  8. syed hassan

    Thread Starter New Member

    Mar 11, 2015
    13
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    but if i apply the pwm signal of 50Hz then will the bootstrap will work?
     
  9. MaxHeadRoom

    Expert

    Jul 18, 2013
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    As Alec t says.

    I still am wondering why you would chose a Pic with a PWM module and not take advantage of it?
    This will turn on the relevant lower FET and PWM the top one, also with the hi-lo side switches the PWM signal can not be 100% pulse width.
    Max.
     
  10. syed hassan

    Thread Starter New Member

    Mar 11, 2015
    13
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    max i am unable to get what you are trying to say.can you please elaborate it ?
    and one more thing that i want you to tell me that i am using 33uf electrolytic capacitor along 100nf ceramic capacitor for bootstrap purpose.will it work for my circuit and provide necessary voltage to gate to turn on the mosfet?
     
  11. MaxHeadRoom

    Expert

    Jul 18, 2013
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    If you study the 18F4431 manual it will explain using the CCP module in PWM mode.
    This is the results obtainable for outputs.
    The IR PWM high side switch requires the bottom FET on and the upper switching a PWM signal <100%, IOW both upper and lower cannot be full on.
    Max.
     
  12. syed hassan

    Thread Starter New Member

    Mar 11, 2015
    13
    0
    max i appreciate your kind replies
    but my issue is not pwm but the gate to source voltage and bootstrapping mechanism
    can you please guide me in this respect
    i have already generated pwm signal using pic18f4431 and ccp module in pwm mode
     
  13. MaxHeadRoom

    Expert

    Jul 18, 2013
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