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Registered Member #3294
Joined: Sat Oct 09 2010, 04:52AM
Location:
Posts: 6
Got a small half bridge sstc working , Just got a few question regrading Gdt waveforms, Do I need a 2 channel oscilloscope to measure the wave form, And what is the proper way to do it, I would rather not break my scope.This site richieburnett should fine as a guide line for what I should be getting. Tried to read from the gates on my igbt's but the wave form looked scary.
It seems to run alright thou,my sstc Using a arduino micro controller hooked up with fiber optics. the driver board is one of Steve wards miniSSTC, just modified for optics, and got rid of the antenna after it got hit and fried the 74hc14
Registered Member #2288
Joined: Wed Aug 12 2009, 10:42PM
Location: Cambridge, MA
Posts: 179
You would of course need a two channel scope to look at the primary and secondary simultaneously, but you can easily look at the secondary waveform with a single channel scope. Just clip ground of the scope probe onto the emitter and the signal to the gate. You just have to be careful of what is powering the bridge when doing this. You can't run off of rectified mains without an isolation transformer when doing this, you will need a floating power supply. Otherwise damage may occur to the scope, bridge, or both.
Or even safer, put a test signal into the feedback and don't even power the bridge. Then there is no concern over grounds and you can connect your scope basically anywhere in the circuit.
Registered Member #4396
Joined: Mon Feb 06 2012, 11:58PM
Location:
Posts: 30
Remember that the ground probe on the scope is earth, unless you have a battery powered scope. The easiest way to look at those waveforms without having to worry about grounding is to use 2 probes and make a differential measurement.
Tie both probe grounds together, put one probe on either side of the GDT, then setup a math trace to view C1-C2, where C1 is the channel at higher potential. This shows you exactly the waveform that you desire at the IGBT gate input.
Px32 wrote ...
Put a probe on the onto the igbt checked them both same wave on both Scope That doesn't seem right. no power was applied on the bridge.
you cant see the GDT waveforms without the bridge running, or at least having a function generator driving the feedback. Are you using UCC 321/322's? I'll bet that you were looking at the enable signal for the UCCs that is driven by the interrupter 555 oscillator, those waveforms WILL be the same.
If you are driving the feedback circuit with a function generator, and have 321/322, you should see 2 approx square waves 180deg out of phase with each other.
Keep in mind that the UCC's outputs glitch when you enable them (this is what kicks off the initial feedback cycle).
Registered Member #3294
Joined: Sat Oct 09 2010, 04:52AM
Location:
Posts: 6
Don't have a 555 driving my UCC's their being driven trough a pin on the 74hc14 which is hooked up to a fiber optic receiver, I would have connected the fiber optic receiver directly to the UCC's pin 2 but then when i generated a signal using a micro controller, it was inverted.
Tried it again with power on the bridge just a little bit. Ended up getting this Wave both grounds were tied together, channels were added and channel 2 was inverted.
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Gdt Waveform Question, Scope, Waveform shape
