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Testing of a drsstc driver

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Ben Solon

Tue Feb 07 2012, 04:29PM

Registered Member #3900 Joined: Thu May 19 2011, 08:28PM
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Posts: 600

Hey, can anyone tell me a way to test a driver un attached from the bridge? I understand that I must load the gate drive ic's otherwise the will burn. But how do I simulate the feedback signals? Function generator? 'cause I don't have one. I just want to see how my gate drive signals look without a bridge or coil. Just the logic board. Btw, I am using Steve wards drsstc 3 driver(not the universal one).
Thanks, Ben

Dr. ISOTOP

Tue Feb 07 2012, 04:50PM

Registered Member #2919 Joined: Fri Jun 11 2010, 06:30PM
Location: Cambridge, MA
Posts: 652

You don't need to load the driver to test it.
You can feed it a square wave from your favorite circuit that makes square waves to test it.

Gregory

Tue Feb 07 2012, 04:52PM

Registered Member #2922 Joined: Sun Jun 13 2010, 12:08AM
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Well, for test my drivers I aways use a function generator to introduce a square wave at the feedback input. And you can load the gate drivers with a 10ohm resistor only to see if it is managing the current. If you don't have a function generator, you can make one simple 555 astable to generate a square wave. For better gate driver test you can put the GDT in place with the secondaries loadeds with a resistor in sÃ©ries with a capacitor to *simulate* the gate capacitance.

ajacks504

Tue Feb 07 2012, 05:22PM

Registered Member #4396 Joined: Mon Feb 06 2012, 11:58PM
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Its a good idea to have a RC on the output for test, with a large value'd R to limit the current, that way you can see both sides of the bridge working.

You should see square wave that matches the feedback freq/duty cycle, but at the amplitude of the rectified mains.

A half bridge will alternate at +/- half mains. ex, 120VAC = ~170VDC. Bridge will put +85V, then -85, giving you a 170VDC swing on the primary.

I full bridge will alternate at +/- mains. ex, 120VAC = ~170VDC. Bridge will put +170V, then -170, giving you a 340VDC swing on the primary.

Use a variac when testing to be safe. Also remember that your scope's ground is mains earth, and hooking up a scope ground to the output provides a mains return. If in question, make your scope measurements differentially with 2 probes and look at the difference math trace, no danger there.

Ben Solon

Tue Feb 07 2012, 06:30PM

Registered Member #3900 Joined: Thu May 19 2011, 08:28PM
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Posts: 600

Ok, so I think i will rig up a 555 timer at about the estimated res frequency. I have a handheld scope however, so it is isolated from mains. Any other considerations I should keep in mind before testing this?

ajacks504

Tue Feb 07 2012, 07:37PM

Registered Member #4396 Joined: Mon Feb 06 2012, 11:58PM
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Posts: 30

If you are using the standard UCC gate drive, you don't have to make a 555 function generator to test it. Just disconnect the "interrupter" signal that goes to the ENABLES on the UCCs, and connect it to the input of the schmitt-triggered inverters where your feedback is to be connected.

The UCC parts have internal pull ups on the ENABLES, so you can just leave them floating. With it setup like this, your bridge will match your interrupter signal, and you won't have to build anything to test with, just a slight temporary reconfigure.

I know you may be more interested in seeing it perform at your resonance frequency, but chances are, if it works at the interrupter rate, its going to work at F-res. The only real thing to worry about is that your GDT isn't going to work quite as well at a higher frequency I believe. As long as you have used a reasonable torrid material, and enough of it, its probably not a worry.

Ben Solon

Tue Feb 07 2012, 11:33PM

Registered Member #3900 Joined: Thu May 19 2011, 08:28PM
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I think you misunderstand me. Probably my fault. I am testing my whole driver board- no bridge, no interupter all I want to do is make sure it functions properly before I fire it up on my bridge. The only way to do this(that I know of) is to trick it into thinking its getting feedback- hence the 555. I will be loading the ucc's with the gdt, so it has to be at my res freq or higher so the timing calculation of my gdt are correct.

teravolt

Wed Feb 08 2012, 04:37AM

Registered Member #195 Joined: Fri Feb 17 2006, 08:27PM
Location: Berkeley, ca.
Posts: 1111

if you want a perfict square wave feed the output of your 555 into a 7474 d-flipflop. Connect the 555 to the clock and conect the Q not to the D input. As you test it wach out for over heating in your driver IC. If so you may need a driver with a to-220-5 package. you may want to have your interupter handy to see if your gating proerly.

ajacks504

Wed Feb 08 2012, 02:07PM

Registered Member #4396 Joined: Mon Feb 06 2012, 11:58PM
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I see, yes, its probably best to use a function generator, or make your own generator with a 555. Sorry for the confusion.

Mads Barnkob

Wed Feb 08 2012, 10:27PM

Registered Member #1403 Joined: Tue Mar 18 2008, 06:05PM
Location: Denmark, Odense C
Posts: 1968

ben123324 wrote ...

I think you misunderstand me. Probably my fault. I am testing my whole driver board- no bridge, no interupter all I want to do is make sure it functions properly before I fire it up on my bridge. The only way to do this(that I know of) is to trick it into thinking its getting feedback- hence the 555. I will be loading the ucc's with the gdt, so it has to be at my res freq or higher so the timing calculation of my gdt are correct.

You still need a interrupter, else there is no way your driver would actually have a output, unless you made a terrible mistake in the design.

As others have suggested, use a interrupter and a 555 timer simulating the feedback. I used a 555 to simulate the feedback and my signal generator connected to overcurrent detection, feeding it a sinewave 0-5V to test my driver that was made for up to 500A peak.

Be sure to scope the output from the GDT, depending on the fiber optic receivers used, the signal can get inverted in regard to the orginal design of the circuits you use. You might end up with 200uS deadtime and rest ontime if its inverted. IGBTs do not like this for very long.

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