Bus overvoltage clamp circuit

Linear and non linear

Bus overvoltage clamp circuit

Postby Jerry » Mon Feb 14, 2011 2:08 am

The servo motors on my machine regenerate back into the bus on my laser cutter. Under quick deceleration it can trip the overvoltage alarm on the drives. So I want to build a clamp circuit that would bleed off extra voltage past, say, 50v dc.

So I am thinking, 50v Zener diode triggers the gate on a small IGBT (Got a bunch) Which puts a power resistor in across the bus.

I have not found much info on this kind of circuit, but something like the basic circuit in this paper:

http://pubpages.unh.edu/~aperkins/pdf/M ... nction.pdf

-Jerry
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Re: Bus overvoltage clamp circuit

Postby johnf » Mon Feb 14, 2011 2:16 am

Jerry
have look at what I did on the turbo controller
bag ass fet with the zeners on the gate works a treat, Big IGBT would work well.

big for the FET is good it can handle huge transient current and this for a few seconds without heatsink.

emergency stop on the controller decelerates the motor to nearly nothing over two seconds.
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Re: Bus overvoltage clamp circuit

Postby Doug Coulter » Mon Feb 14, 2011 3:19 am

Just make sure whatever you use turns on the fet or igbt all the way (threshold of some sort that produces full gate drive) or you might have safe operating area issues. Let the cheap resistor take the heat! There are fancier ways of course, but that should do it well enough.
Posting as just me, not as the forum owner. Everything I say is "in my opinion" and YMMV -- which should go for everyone without saying.
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Re: Bus overvoltage clamp circuit

Postby Jerry » Mon Feb 14, 2011 4:19 am

I have a few of these guys that I scavenged out of plasm cutters:

http://www.dianyuan.com/bbs/u/24/1102661360.pdf
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Re: Bus overvoltage clamp circuit

Postby Jerry » Mon Feb 14, 2011 4:33 am

Wow, John. Thats almost exactly what I was thinking except using a resistor to take the load.

Any reason to use multiple zeners in series? Also couldnt find the specs on the ones you used there.
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Re: Bus overvoltage clamp circuit

Postby johnf » Mon Feb 14, 2011 5:12 am

Jerry
lower voltage zeners have steeper turn on curves and I did not want to get them dissipating any appreciable power changing their turn on characteristics.

a series resistor will work to save heat in the FET but will reduce the stiffness of the clamp.
all depends on the potential energy stored in the motor
ie modify accordingly
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