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Design PWM to cope with supercapacitor and battery(help)

  1. Feb 16, 2012 #1
    I need to design an electric circuit which require PWM to let the battery and supercapacitor take turn to supply current to the loads.

    stage1: battery charge up supercap and supply current to the load

    stage2: supercap voltage increase to a certain level, battery current is cut, supercap supply current to the loads

    stage3: voltage of supercap decrease to certain level, again, battery supply current to load and supercap.
    http://www.freeimagehosting.net/3eguo

    image http://www.freeimagehosting.net/3eguo

    my pwm and switch is not functioning well,
    the positive input signal undergoes damping oscillation
    and the switch (nmos) does not switch off as Vs>Vg

    can anyone help me in this project? I will provide any information if require to..
     
    Last edited: Feb 16, 2012
  2. jcsd
  3. Feb 17, 2012 #2
    http://img43.imageshack.us/img43/8094/projecto.png [Broken]

    here is the problem circuits
     
    Last edited by a moderator: May 5, 2017
  4. Feb 17, 2012 #3

    berkeman

    User Avatar

    Staff: Mentor

    You mention using an nmos FET, but your schematic shows a pmos FET...
     
    Last edited by a moderator: May 5, 2017
  5. Feb 17, 2012 #4
    thank for correcting , should be nmos as in schematic,
    it would be fine for pmos/nmos as long as 1 of them are functioning
     
  6. Feb 17, 2012 #5
    I'm thinking of replacing pwm to comparators.. any suggestion?
     
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