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Alasdair
Regular Member

Joined: 12/01/2011
Location: Australia
Posts: 62

Posted: 02:46pm 04 May 2011

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While I'm still logged on, another device in
IGBT range is HGTG12N60A4 which can
run in parralel pair using gate decoupling
resistors (4R7) it will deliver 96 amps pulsed
per device at up to 600 volts, has about 18ns
switching speed for very low dissipation, a pair
will pass nearly 200 amps up to 600v, and
they're under $4 each. You'd need a driver
transistor like a BC327 to give good low
impedance drive into the gates to ensure
maximum slew rate, but you could throw
just about any voltage in and get nice
clean grunt out. Similarly to the pswgt-300
trick, use plenty of filter caps between source
and ground to keep the source impedance
down, just ensure the voltage can stand up.
Computer supply hv filter caps would be a
good resource for these.
Regards Alasdair.

Amc-elec

VK4AYQ
Guru

Joined: 02/12/2009
Location: Australia
Posts: 2539

Posted: 03:19pm 04 May 2011

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Hi Alasdair

Thanks for the tip on these, I have tried to use fets but run into voltage and current issues with the ones I have tried.

I have a circuit for a PWM HHO driver that I have used as a driver but it has issues with the drive side and I had to put a small transformer in the drive to isolate the circuits. The voltage regulation isn't much of an issue on the output side as it ties to battery voltage but I am trying to alter the pulse width on the input to maintain voltage there as the mill goes up in speed. It runs at at 20K by the way so may be suitable for the IGBT.

The output goes to the battery bank and that dumps into the grid so that side isn't a problem, just tracking the input voltage to maintain a maximum of 250 volts DC input is the issue.
I will try and find a circuit to use the IGBT instead of the FETS as it sounds like they are ideal. Back to ebay to track some down, thanks for the help. I have a welder that the controller board died in and I cant find out what is wrong, so I could use the output stage from that at a pinch, it runs at full amps all the time and I haven't managed to cook it yet so it must be good.

All the best

Bob

Foolin Around

Alasdair
Regular Member

Joined: 12/01/2011
Location: Australia
Posts: 62

Posted: 04:39am 05 May 2011

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Hi Bob,
I think mosfets would be a bit frail for what
your doing. I'd use a TL494 Pwm chip, and
drive igbt's. Using v-ref pin this chip will regulate
by varying pulse width according to ref voltage.
It's a universal regulator for that application, very
easy to use, cheap and regular size dil package.
You do need to deliver a regulated supply voltage
to it, about 12volts from memory. Your welder
fault is probably the logic regulator, probably a
VIC240, a 5 pin 220 style package which fails
catastrophically and takes out zeners caps and
resistors by passing 380v down a 12v rail. I've
fixed a few of those, and modified the circuit
to prevent repeat blow ups. Google should give
you some application circuits for the TL494.
Best of luck
Regards Alasdair.

Amc-elec

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