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Looking for PWM controller to toggle external high power NFETS (or IGBTs) for plasma arc circuit

JS777
Prodigy 70 points
Other Parts Discussed in Thread: UCC27531

I'm trying to select a PWM controller to control external fets for a simple plasma arc eval circuit.

 

Application:

Very simple plasma arc eval circuit. PWM controller to controll 2 or more external low RSon NFETS or IGBTs. These switches will switch Vin on/off chopping current to the load (which is a plasma arc). I would think I don't need any fancy PWM controllers; I just need a reasonably robust and fast controller that is meant to drive external fets.


Requirements:

- Vin = 100V (only the fets will be exposed to this voltage)

- load current = 30A

- PWM controller that can toggle external high power fets at 500-800kHz and drive them on/off very quickly

My hope is to have a very simple PWM circuit with basic LC filtering + big smoothing inductors and use 500V+ rated fets to handle the large voltage ripples that will ensue. If there's a TI pwm eval board that I can hook up my external fets to, that would be nice.

Thanks in advance!

  • 0
    TI__Mastermind 34465 points
    Hi,
    If I understand your application correctly the power supply for the plasma arc controls the current and you wish to test the response by switching its output on and off at 500-800 kHz
    If this is correct then you need a driver for the IGBT switches on the output of the plasma arc and not a PWM controller
    Or maybe you need a PWM controller that is running open loop that drives the IGBT's
    Take a look at the data sheet on the page showing an open loop test fixture
    www.ti.com/.../uc2842.pdf
    You can adjust the PWM output with a potentiometer and use this to drive the IGBT switch
    You will need to interface this low level signal with an IGBT driver before connecting to the IGBT.

    Regards
    John
  • 0 in reply to John Griffin1
    Prodigy 70 points

    Thanks for the reply, John! Yes you understand my application perfectly. Are there PWM controllers that have IGBT or power fet drivers built in? An all-in-one would be nice, but I can go with PWM -> driver -> fet if need be.

    Attaching a rough schematic of the setup as well.

  • 0 in reply to JS777
    TI__Mastermind 34465 points
    Hi JS777,
    There is no controller with an integrated driver output although the driver section of the controller is optimised for a high speed, high current output.
    For your application I suggest you use the UCC27531 IGBT driver.

    One thing about your circuit is that you will need some overvoltage protection for the IGBT.
    The plasma cutter you are testing has a constant current output of 30A during the arc and the arc voltage is limited to 100V by the power supply.
    But when you turn off the IGBT the current that was flowing in the smoothing inductor has no path to flow and it will cause a large voltage across the IGBT equal to V=L*dI/dT. This voltage will be much greater than 100V.
    Therefore you need a transient suppressor across the IGBT that is capable of absorbing this stored inductive energy.
    Regards
    John
  • 0 in reply to John Griffin1
    Prodigy 70 points
    Thanks! I'll take a look at that driver.

    Yes, I will definitely need some overvoltage protection. I also found some IGBTs on digikey that are rated for 900+ volts. Do you think a higher max voltage IGBT would handle the inductive spikes better? I haven't yet calculated the theoretical voltage spikes.
  • 0 in reply to JS777
    TI__Mastermind 34465 points

    Yes try 900v or 1200v parts

    Test at a lo value of current and increase to 35A when everything looks ok.

    Good Luck 

    John