Buck Boost converter - Driver

Discussion in 'The Projects Forum' started by thedinuka, May 13, 2009.

  1. thedinuka

    Thread Starter New Member

    Mar 21, 2009
    HI, I'm developing a buck boost converter which should have the capability to take an input of 12 V and the produce an output of 5 - 30V

    I'm using an IR MOSFET for this and also IR2118 highside driver for this.
    My switching frequency is 16KHz.

    The converter tropology that I'm using is the general buck boost topology. It produces a negative output.
    V_out = - V_in*D / (1-D) , where D is the duty cycle of the PWM

    Everything works fine until I increase the output to about 12V (which actually is -12V). afterwards the output goes haywire. So I started debugging and realized that the MOSFET driver Vs pin has a negative voltage limit. When my output is 12V, the voltage on the 2118 Vs pin w.r.t ground is about -12V when the MOSFET is switched off.

    (in this topology, the voltage of the MOSFET source pin at MOSFET switch of is V_out, which in this case is -12V)

    So I think I' hitting the negative limit of the Vs pin of the FET driver. Any suggestions as to what I should do to get out of this problem ? I've looked around at the other highside driver ICs and all that have a very low negative limit.

    Hoping you all can figure out things here, I'm a bit desparate now.....
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  2. Darren Holdstock

    Active Member

    Feb 10, 2009
    You might try a similar sneaky technique to the one employed in this article from EDN: Buck Converter Uses Low-Side PWM IC. The author is switching a P-channel MOSFET, so you'd have to work out a way of powering the high-side N-channel driver by hanging it upside down from the MOSFET drain supply. The essential idea is to split the supplies and AC couple the signal interface between the different sections - there will be other ways of implementing this other than capacitive coupling, e.g. optocouplers, pulse transformers etc.
  3. Kernelspoke

    New Member

    Apr 7, 2011
    Did you solve your problem? Am really curious coz am working on one with an input voltage of 12 and an output of 3.3v to 19v with a current of 5A. I managed to have my source grounded with a 50N06. Am thinking of using a FOD3180 since it doesnt need to be high side driven
    Last edited: Apr 7, 2011
  4. shripad123

    New Member

    May 3, 2011
    hi guys,
    I am new to power Electronics , Can any help me in Boost converter I/P is 325Vdc(from bridge rectifier ) and to have output 350Vdc , 2A
  5. russpatterson

    Senior Member

    Feb 1, 2010
    Hey Shrip. You should start your own thread.