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Registered Member #15
Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068
Tantalum capacitor is fine for this application. Ideally, bipolar chip capacitor would be chosen, but its not really necessary for this particular design. Anyways, i doubt thats the issue.
Thanks for the photo. I was under impression this was one of our boards, but it is a homemade board so i really cannot comment on the construction etc...
One area of concern i have is the trace routing on the bridge circuit. It appears you have the wires all routes underneath the board. What you want to have is a very tightly coupled layout with the return layer directly underneath the gate drive circuitry (i.e. planes, or tightly twisted wires. This will reduce the parasitic inductance. You may be getting very high spikes and ringing with this layout and that may be causing the diodes to clamp excessively which is creating a "short" as seen by the UCC driver ICs.
Registered Member #6038
Joined: Mon Aug 06 2012, 11:31AM
Location: Salado, TX
Posts: 248
Thanks again for the comments on the circuit layout. I enjoy making my own boards but sometimes adds challenges. Really appreciate the offer too - will PM you.
Registered Member #7267
Joined: Tue Oct 16 2012, 12:16AM
Location: Detroit, Michigan
Posts: 407
EasternVoltageResearch wrote ...
One area of concern i have is the trace routing on the bridge circuit. It appears you have the wires all routes underneath the board. What you want to have is a very tightly coupled layout with the return layer directly underneath the gate drive circuitry (i.e. planes, or tightly twisted wires. This will reduce the parasitic inductance. You may be getting very high spikes and ringing with this layout and that may be causing the diodes to clamp excessively which is creating a "short" as seen by the UCC driver ICs.
What you are referring to is labeled as GATE_RTN on the schem, correct? What you're saying is put this directly underneath the gate drive to reduce parasitic inductance. Re. The voltage spikes, if this is the problem, wouldnt we be experiencing this even when the GDT's secondaries are disconnected from the bridge, or not necessarily?
I am etching two half bridge boards from the artwork on your site, thanks for making it available! (Wish you had 2nd gen artwork too ).
Registered Member #195
Joined: Fri Feb 17 2006, 08:27PM
Location: Berkeley, ca.
Posts: 1111
Bushman, eastern has lots of good ideas. personally it is your cap or your transformer sucking current from the IC. if the secondary side has any shorts or bad design that will draw to much current as well. the reason that I mentioned it is that tantalum will be a short in one polerty and be a capacitor in another. try replacing it with a poly cap that is 1 to 10uf just ti see if you can reduce the current. I would start with 1uf. make shore that the type of cap you pick has a low ESR and low ESL . do you have a scope?
Registered Member #6038
Joined: Mon Aug 06 2012, 11:31AM
Location: Salado, TX
Posts: 248
It definitely sounds like something on the secondary is causing heavy load. interesting thought on the circuit layout causing stray inductance and high spikes causing excessive clamping. Also did not realize the tantalum cap has an effect like that.
Why would only the inverting UCC37321 (not connected to the cap) be the one that is cooking? Is it because only when it is driving that the problem on the H-bridge is being induced? If so, does that tell us anything about what's going on? meaning is current in one direction causing an issue that the reverse is not? Just a thought...
Registered Member #15
Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068
Bushman wrote ...
It definitely sounds like something on the secondary is causing heavy load. interesting thought on the circuit layout causing stray inductance and high spikes causing excessive clamping. Also did not realize the tantalum cap has an effect like that.
Why would only the inverting UCC37321 (not connected to the cap) be the one that is cooking? Is it because only when it is driving that the problem on the H-bridge is being induced? If so, does that tell us anything about what's going on? meaning is current in one direction causing an issue that the reverse is not? Just a thought...
Maybe the particular capacitor you are using is acting funny in the reverse polarity. We don't have issues with the particular capacitors we use. You can try a bipolar as mentioned - they should be readily available from digikey etc...
We found 10uF to be the optimum value here. When you reflect the gate capacitance over to the primary side, it actually forms a capacitive voltage divider and will limit the voltage if the value is not correct.
Registered Member #195
Joined: Fri Feb 17 2006, 08:27PM
Location: Berkeley, ca.
Posts: 1111
I apoligise I looked closer at the circuit a little and the primary and secondary is 0 to vcc and a tantalum should be fine.
In your opening thread you state that your getting a signal out of the transformer secondaries that look fine. the problem started after connecting up the bridge board. I have to believe that this circuit works. There must be a problem with the components or your design so verifie that the components are good and in the proper order. Are the secondaries phased properly. It is all about eliminating the pausibilties and playing Sherlock Holms. Do you have a picture of the bottom of your h-bridge board
Registered Member #7267
Joined: Tue Oct 16 2012, 12:16AM
Location: Detroit, Michigan
Posts: 407
Well i do have somewhat good news. I rewound my GDT's but did not yet solder the molex connectors to the primaries or anything to the secondaries yet, so i could run a few tests. I decided to just attach the primaries to the driver outputs with alligator clips and scope the secondaries left disconnected from the bridge of course. This time I can finally hear my interrupter 100hz pitch from the GDT which before I could not. I must have had something wired wrong with the darn transformer, either that or the 1N5819 and gate resistors must have been bad or somehow screwing things up. Tmoro I will attach fresh diodes and resistors to the secondaries and see whatt happens when I connect to the bridge this time. Bushman, if you rewind your GDT too, try what I did. Temporarily attach the primaries to the drive outputs (nothing attached to secondary), with your modulator on, pump your signal generator into your feedback circuit as you normally would for testing, and let me know what happens.. can you hear the GDT singing to you..
Registered Member #195
Joined: Fri Feb 17 2006, 08:27PM
Location: Berkeley, ca.
Posts: 1111
Bushman, if you temporaraly replace the tantalum cap with a 100 or 200 ohm resistor you may be able to test with out blowing it out the IC. Watch out for spikes or negitive signals from the transformer. Maby some of your setup is working and camping the signal from the GDT
Also duble check if there are no solder jumps or beeds around the ic or under the sockets. Check it with a ohm meter to see if there are any shorts with the transformer out
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Gate Driver Problem
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