Solar PWM Charging Mosfet Selection

Discussion in 'General Electronics Chat' started by sonar_abhi, Apr 15, 2016.

  1. sonar_abhi

    Thread Starter New Member

    Mar 19, 2016
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    Hello Guys.

    I am making a Solar Charge Controller with PWM. For PWM, I need to connect the MOSFET to the high side so as to control the current going into the battery from the panel.

    If I connect an N channel MOSFET, that would need a charge pump to increase the gate voltage above the Vdd.
    But if I use a P channel MOSFET, that would not be necessity, since I only need to turn off the gate supply for the MOSFET to conduct and vice versa.

    Some of the examples on the net have used N channel with a charge pump and I really dont understand why they have not used a P channel MOSFET instead.

    What would be a better selection in terms of efficiency and power dissipation.

    Thanks
    AS
     
  2. DickCappels

    Moderator

    Aug 21, 2008
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    Your observation are valid. I would go with a P-channel MOSFET.

    [​IMG]

    The N-Channel MOSFET in the circuit above can be replaced with a diode, but at slightly lower efficiency.
     
    sonar_abhi likes this.
  3. sonar_abhi

    Thread Starter New Member

    Mar 19, 2016
    16
    0
    Hi DC,

    Thanks for the reply. Ideally, I would want the drop to be "0", but putting a N Mosfet instead of the diode, will again require a gate drive circuitry, won't it?

    Also can you please share the buck converter calculations?

    Regards,
    AS
     
  4. DickCappels

    Moderator

    Aug 21, 2008
    2,653
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    Yes, the N-channel would best be driven with a separate driver and a waveform that assures that the conduction of the two MOSFETs don't overlap.

    Here is an excellent explanation of a buck converter along with the formulas (link below).
    www.ti.com/lit/an/slva477b/slva477b.pdf
     
  5. Lestraveled

    Well-Known Member

    May 19, 2014
    1,957
    1,215
    @DickCappels @sonar_abhi

    Dick, I think Sonar is talking about a non-inductor based simple PWM charge controller, not a power converter.

    Sonar, "Charge Controllers" may be cheap and easy to build but they are not efficient. Dick is talking about a power converter, which is very efficient compared to a charge controller.

    What is your application?
     
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  6. ScottWang

    Moderator

    Aug 23, 2012
    4,855
    767
    What is the V/I of Solar panel?
    What are the V/I/R of Load?
    What kind of the battery and V/I?
     
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