h bridge for high voltage

Discussion in 'General Electronics Chat' started by ariemeir, Jun 27, 2013.

  1. ariemeir

    Thread Starter Member

    Jun 24, 2011
    Hi guys,

    I have a high voltage source (~400v, generated from a disposable camera)
    and i would like to use it to generate roughly 100us pulses into a purely resistive load (say once a second). (Assume i have enough capacitance next to the camera so drops are not a problem).

    The thing is that i want these pulses to be bipolar, somewhat alike a motor which i want to spin in alternate directions.So naturally i started looking at h-bridge topologies.

    I have 4 high voltage n-channels in my disposal so i thought - wouldn't it be neat if i could come up with an h-bridge running on 4 n-channels ? (23nm60nd)
    I found this circuit with 4 n-channels:

    But the problem (as the author indeed mentions) is that the source of A1 is floating, so if i simply crank the gate to 5v, it wouldn't set the source to 5v, indeed when measured it is roughly 3v or so. The author suggests using a hbridge driver circuit, or i guess i could use a p-channel, but then - how do i avoid using the 400v switching signals i need to keep this h-bridge turned off (or even on, i cannot take it all the way to ground - only 20v or so below the source voltage)

    My question is :
    What would be a quick and dirty way for me to implement this dual polarity switching capability. Please note that i am switching the voltage basically into a resistor, so the inductive considerations relevant to motors shouldn't pose constraint in my case.

    Thanks for all advice !
  2. BobTPH

    Senior Member

    Jun 5, 2013
    You need a high and low side driver IC. You can find these that are designed to drive N channel MOSFETS one the high side. Make sure it allows more than 400V.

    ariemeir likes this.
  3. ariemeir

    Thread Starter Member

    Jun 24, 2011
    Dear BobTPH, thanks for your reply,

    I found this module http://www.fairchildsemi.com/ds/FA/FAN7390.pdf
    which seems to fit my voltage levels and the price tag.

    Inside digikey this component's location is
    PMIC - MOSFET, Bridge Drivers - External Switch

    I tried to find an explanation for the difference external vs. internal switch, but with no success - could you share a few words on this ?

    Also , in a typical application circuit of the above driver
    I found this module http://www.fairchildsemi.com/ds/FA/FAN7390.pdf
    (page 2)
    i see some components such as Rboot, Cboot, Dboot , but the datasheet doesn't mention how these should be chosen. Since this is my first time using a mosfet driver, would you provide a few words of guidance how to go about this ?

    Thanks a lot.
  4. shortbus

    AAC Fanatic!

    Sep 30, 2009
    ariemeir likes this.