High side switch

Discussion in 'General Electronics Chat' started by SVS, May 6, 2014.

  1. SVS

    Thread Starter Member

    Aug 16, 2012
    89
    4
    Hi Everyone,

    I would like to implement a high side ON-OFF switch .
    The high side has a voltage of 200 V DC. This 200 V DC is fed to the half bridge circuit which has an inductive load and I would like to control the high side 200 V DC using an additional circuit.

    So, I have simulated a circuit which theoretically looks pretty solid( from simulation).

    Do you guys think it is a good solution ?
    Can I find an opto coupler in such ratings and also an isolated DC12 V power supply?
    I have attached the image below.

    Or some other better topology?

    Thank you !!
     
    Last edited: May 6, 2014
  2. wayneh

    Expert

    Sep 9, 2010
    12,090
    3,027
    Do you know that the driving transistors are necessary? In other words, could you simplify the circuit by just using the optocoupler to drive the MOSFET?

    You might be able to just use a resistor and a 12V zener to get enough current to drive the gate. For higher frequency, you may need something else to get more current. DC-DC converter.
     
  3. crutschow

    Expert

    Mar 14, 2008
    12,984
    3,223
    That circuit is incorrect so I don't see how the sim could work. The P-MOSFET source and drain must be reversed for a high-side switch. And a high-side switch would require 200V (220V in your sim) on the gate to turn off the MOSFET (Vgs=0v). For that you could use a bootstrap driver.

    Note that you should select a model number for the MOSFET. The generic (default) model can give unreal results.
     
  4. AnalogKid

    Distinguished Member

    Aug 1, 2013
    4,515
    1,246
    What he has drawn is an N-channel MOSFET, and that part of the circuit will work correctly as shown if he truly has a floating battery source for Vgs.

    However, the lower PNP drive transistor is upside down.

    The drive signal is a 50/50 squareware at 0.1 Hz. At that speed you can use an opto gate driver that has a photovoltaic cell inside instead of a transistor. It will drive the gate without the battery, signal transistors, etc. Opto, pulldown resistor, FET.

    ak
     
  5. SVS

    Thread Starter Member

    Aug 16, 2012
    89
    4
    Sorry!! The PNP transistor was upside down. That was my mistake.
    The circuit works fine.

    The drive signal is just an example. The purpose of this circuit is just to switch ON and let the circuit in ON state for a long time and then switch OFF . That s the reason why Bootstrap capacitor is not an option and 12 V isolated supply is the best.

    Can you please just post a rough schematic or an example circuit using opto gate driver as I am new with this terminology.??
     
  6. SVS

    Thread Starter Member

    Aug 16, 2012
    89
    4
    At that speed you can use an opto gate driver that has a photovoltaic cell inside instead of a transistor. It will drive the gate without the battery, signal transistors, etc. Opto, pulldown resistor, FET.


    Some IC suggestions please??
    Rail voltage 220 V DC
     
  7. AnalogKid

    Distinguished Member

    Aug 1, 2013
    4,515
    1,246
    SVS likes this.
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