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Registered Member #3885
Joined: Sun May 15 2011, 12:47AM
Location: Newton, Massachusetts, United States
Posts: 94
bwang wrote ...
Scope the output of the GDT and check its frequency. If it is too high, it overloads the UCC's and burns them up.
I'm not really sure there even will be an output - all I'm getting on the input is noise! If, however, the GDT is the problem, then what will I need about it to change to fix it? I have another GDT with more windings made of thinner wire that is wound tighter around the core; is it worth trying that one to see if it will work?
Registered Member #2919
Joined: Fri Jun 11 2010, 06:30PM
Location: Cambridge, MA
Posts: 652
Daniel Kramnik wrote ...
bwang wrote ...
Scope the output of the GDT and check its frequency. If it is too high, it overloads the UCC's and burns them up.
I'm not really sure there even will be an output - all I'm getting on the input is noise! If, however, the GDT is the problem, then what will I need about it to change to fix it? I have another GDT with more windings made of thinner wire that is wound tighter around the core; is it worth trying that one to see if it will work?
Thanks for the quick response!
Ah, there lies the problem. If you are getting garbage on the input, this garbage is very possibly very high-frequency garbage, which then causes your UCC's to drive your gates at some MHz -> liquid UCC's.
Registered Member #3885
Joined: Sun May 15 2011, 12:47AM
Location: Newton, Massachusetts, United States
Posts: 94
Inducktion wrote ...
Well, see if maybe the UCC's work with the GDT with a standard signal generator (555?) to narrow down the problem!
That seems like a good idea; I'll try seeing if adding a resistor on each side of the GDT input will help the heating go away (can't afford to blow my last pair of UCCs!) and then I'll try feeding the startup oscillator right to the UCCs' inputs. If the GDT gives me trouble, then I'll switch in the other one I have and see if it's any better.
bwang wrote ...
Ah, there lies the problem. If you are getting garbage on the input, this garbage is very possibly very high-frequency garbage, which then causes your UCC's to drive your gates at some MHz -> liquid UCC's.
There's very little noise on the UCCs' inputs, its only on the outputs and it's low in amplitude compared to the signal the UCCs should be giving (less than half a volt as compared to 12 volts). If there is high frequency noise appearing somewhere in the circuit, then what can I do about it?
Polonium210 wrote ...
May I ask where you got your GDT ferrite core from? What's the permeability?
I got my GDT (and CT) cores from Digikey. They are made by EPCOS and come with a variety of parameters. I purchased a few cores with AL = 4.3k and a few more with AL = 10k; I've read that anything 4k or above should work, so I don't think they're part of the problem.
If you're asking because you're searching for ferrite cores for your own coil, the Digikey part number I have (I only saved one of the bags) is 495-3862-ND and the manufacturer's part number is B64290L0618X830. The datasheet should be available on the Digikey product page and it contains the product numbers for cores with other AL values too. The cores run for around a few dollars a piece.
Registered Member #3637
Joined: Fri Jan 21 2011, 11:07PM
Location: Buffalo, NY
Posts: 1068
Oh, I had another idea; what are you using to feed to the UCC's inputs? If it's just an antenna, you could try squaring it up with a comparator or a schmitt trigger of sorts, to prevent it from having that high frequency noise. You could also try ferrite beads to get rid of the noise.
Registered Member #2919
Joined: Fri Jun 11 2010, 06:30PM
Location: Cambridge, MA
Posts: 652
Daniel Kramnik wrote ...
Inducktion wrote ...
Well, see if maybe the UCC's work with the GDT with a standard signal generator (555?) to narrow down the problem!
That seems like a good idea; I'll try seeing if adding a resistor on each side of the GDT input will help the heating go away (can't afford to blow my last pair of UCCs!) and then I'll try feeding the startup oscillator right to the UCCs' inputs. If the GDT gives me trouble, then I'll switch in the other one I have and see if it's any better.
bwang wrote ...
Ah, there lies the problem. If you are getting garbage on the input, this garbage is very possibly very high-frequency garbage, which then causes your UCC's to drive your gates at some MHz -> liquid UCC's.
There's very little noise on the UCCs' inputs, its only on the outputs and it's low in amplitude compared to the signal the UCCs should be giving (less than half a volt as compared to 12 volts). If there is high frequency noise appearing somewhere in the circuit, then what can I do about it?
Polonium210 wrote ...
May I ask where you got your GDT ferrite core from? What's the permeability?
I got my GDT (and CT) cores from Digikey. They are made by EPCOS and come with a variety of parameters. I purchased a few cores with AL = 4.3k and a few more with AL = 10k; I've read that anything 4k or above should work, so I don't think they're part of the problem.
If you're asking because you're searching for ferrite cores for your own coil, the Digikey part number I have (I only saved one of the bags) is 495-3862-ND and the manufacturer's part number is B64290L0618X830. The datasheet should be available on the Digikey product page and it contains the product numbers for cores with other AL values too. The cores run for around a few dollars a piece.
Registered Member #3885
Joined: Sun May 15 2011, 12:47AM
Location: Newton, Massachusetts, United States
Posts: 94
Inducktion wrote ...
Oh, I had another idea; what are you using to feed to the UCC's inputs? If it's just an antenna, you could try squaring it up with a comparator or a schmitt trigger of sorts, to prevent it from having that high frequency noise. You could also try ferrite beads to get rid of the noise.
I'm not using an antenna, I'm using secondary feedback with a CT and a 74HC14. As you can see from the scope shots, there is no high frequency noise on the UCCs' inputs.
bwang wrote ...
Post scope shots of the inputs to the UCCs.
Without any modifications to my setup (still only one 6.8R resistor, not feeding the startup signal directly to the UCCs), this is what the signals look like:
Picture 1: Voltage at pin 3 of the 555 timer startup oscillator [Y = 5V/div, X = 5uS/div]
100kHz square wave - exactly what it should be.
Picture 2: Voltage at pin 1 of the 74HC14 [Y = 5V/div, X = 5uS/div]
I have no idea what this signal is supposed to be - I couldn't get a good picture of it because it's extremely unstable and the frequency jumps around all over the place. I can only resolve it for a few tenths of a second before I need to readjust the time settings on the scope. When I do manage to resolve it, however, it appears to be a sine wave.
Picture 3: Voltage at pin 2 of the UCCs (input from the 74HC14) [Y = 5V/div, X = 5uS/div]
I don't know how how, but it looks like the 74HC14 managed to sort out the mess on pin 1 and make it into another 100kHz square wave, exactly what should happen if the startup oscillator is connected, but not what should happen if a feedback signal from the CT was present.
Picture 4: Voltage at pin 3 of the UCCs (signal from the external interrupter with PW and BPS set to max.) [Y = 5V/div, X = 0.5S/div]
This is exactly what it should look like, I get the same thing when I just connect the scope to the interrupter's output.
Edit: I just tried scoping the outputs of my UCCs again and found that my UCC37321 was giving a nice 12V square wave at 100kHz while my UCC37322 was giving an ugly 2V version of the interrupter signal and heating up. I'm going to need to replace the UCC37322 and use 2 resistors on the GDT to prevent any more chips from dying. This still, however, does not explain why my driver isn't working.
Registered Member #3637
Joined: Fri Jan 21 2011, 11:07PM
Location: Buffalo, NY
Posts: 1068
If you're getting a sine wave out of anything, that usually means that you've hit a resonant frequency of the tracings or something. Try a different frequency, maybe higher up, and that problem should disappear.
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UCC37322/1 DRSSTC Gate Driver Problems
