switching high voltage supply

Discussion in 'The Projects Forum' started by ingram010, May 4, 2007.

  1. ingram010

    Thread Starter New Member

    May 2, 2007
    6
    0
    I work in the R&D department for an electrolytic capacitor company. I have been asked to develop a completely automated data logging system using an Agilent aquasition unit.
    I have to measure 8 high voltage capacitors simultaneously, these capacitors will be measured for internal pressure via a pressure transducer, internal temperature vie a thermocouple and leakage current, they will be kept in an oven a 95 degrees for the duration of the test. The capacitors are supplied 500vdc using a GENH750w power supply, they will be under test conditions for weeks even months. The capacitors may reach 70psi at different rates therefore I need to turn off the supply to those particular capacitors individually.


    So, I have 8 outputs from a labjack U3 that go high when then the capacitors reach 70 psi, the labjack is powered by a USB. The idea in my head is to use the output to some how switch a Transistor,MOSFET,N Channel,SPP02N60S5 to turn on and off the supply to each individual capacitor, possibly using an opt isolator. I am thinking that I need to lower the 500vdc to something that can safely supply the gate of the mosfet.

    Please, please can someone offer some suggestions?

    Thanks

    John
     
  2. thingmaker3

    Retired Moderator

    May 16, 2005
    5,072
    6
    Sounds like you're using the N-channel on the high side. If that's so, try this:

    highside.jpg

    When signal from driver goes low, Q1 stops conducting. D1 is a 12V Zener to keep the gate-to-source voltage of Q2 from getting out of hand. Note you'll need to float a second power supply on top of your 500Vdc.

    I've had success with this trick in a 170Vdc H-bridge, as long as switching frequency stays relatively low.
     
  3. John Luciani

    Active Member

    Apr 3, 2007
    477
    0
    You could use a single isolated 10V and eight optos to drive the gates of
    eight 500V P-channel FET.

    Another idea is the photovoltaic gate drive ICs from IR -- PVI1050, PVI5050, etc.
    Be careful of these devices since they provide small gate drive currents. Your
    power MOSFET will take longer to turn-on. You could use an N-channel device
    with these drivers.

    (* jcl *)
     
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