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I think my ucc37322 is dead; it reads a resistance of about 8 ohms from pin 1 to 4 and 4 ohms from 1 to 5. I've already replaced my UCCs once (because they started smoking), am I right about the 322 being dead?
Yeah if 1:4 or 1:5 or 8:4 or 8:5 reads < several tens of kilo-ohms it is likely dead.
UCC chips are easy to kill if your GDT isn't properly made, sized, and constructed of suitable materials, as well as if you let them run without feedback. The problem is that parasitic reactances and noise will cause the UCC chips to oscillate at VERY high frequency (typically I've measures around 8MHz!), which causes a lot of thermal stress on the chips, leading to their death. Be sure you didn't forget the DC blocking capacitor between the outputs of the UCC chips otherwise one will present a dead short to the other. You should ideally have a low-esr low inductance capacitor for this job, I like WIMA PP-film/foil 0.1uF pulse rated caps for this. I once killed a set by forgetting to install this cap while breadboarding. D'oh!
Without knowing when they started smoking (during coil operation or when no DC bus power (and thus no feedback) was present) it is hard to diagnose further, but I've made tons of CW coils and never had any die from thermal death while running at only 300KHz. I've routinely pushed them as high as 1100KHz without them dying, but I did watch the temperatures, and that's when driving huge gate capacitances!
I once made a SSTC kit someone put out and they used tantalum capacitors for the dc-block and decoupling caps; nearly every capacitor failed as a short. It ruined the UCC chips, the Schmitt trigger, and the linear regulators. These days I only trust Nichicon, WIMA, and Epcos caps and I only use electrolytic, ceramic, and PP-film/foil
You should check your driver for shorts; remove the GDT, CT (if used), and input power connectors. Remove all the logic chips used. Measure the resistance between the 12V and ground rails. It should read a VERY high resistance, if not then you have a circuit fault. You can't do this test with those components I mentioned still attached though.
Registered Member #4074
Joined: Mon Aug 29 2011, 06:58AM
Location: Australia
Posts: 335
From the pictures it certainly looks like the GDT is connected between the Gate and Drain pins on your bridge MOSFETs, and thermal insulators are missing, as Sigurthr said. Perhaps double check the MOSFET pinout and see if there is any continuity between the drains of both transistors?
Yeah if 1:4 or 1:5 or 8:4 or 8:5 reads < several tens of kilo-ohms it is likely dead.
UCC chips are easy to kill if your GDT isn't properly made, sized, and constructed of suitable materials, as well as if you let them run without feedback. The problem is that parasitic reactances and noise will cause the UCC chips to oscillate at VERY high frequency (typically I've measures around 8MHz!), which causes a lot of thermal stress on the chips, leading to their death. Be sure you didn't forget the DC blocking capacitor between the outputs of the UCC chips otherwise one will present a dead short to the other. You should ideally have a low-esr low inductance capacitor for this job, I like WIMA PP-film/foil 0.1uF pulse rated caps for this. I once killed a set by forgetting to install this cap while breadboarding. D'oh!
Without knowing when they started smoking (during coil operation or when no DC bus power (and thus no feedback) was present) it is hard to diagnose further, but I've made tons of CW coils and never had any die from thermal death while running at only 300KHz. I've routinely pushed them as high as 1100KHz without them dying, but I did watch the temperatures, and that's when driving huge gate capacitances!
Yep, it was mentioned earlier in this thread and I should have paid attention. It was without the coil running (no sparks yet).
Sigurthr wrote ...
I once made a SSTC kit someone put out and they used tantalum capacitors for the dc-block and decoupling caps; nearly every capacitor failed as a short. It ruined the UCC chips, the Schmitt trigger, and the linear regulators. These days I only trust Nichicon, WIMA, and Epcos caps and I only use electrolytic, ceramic, and PP-film/foil
I'll replace that cap with a better one, I just used run of the mill .1uf caps. I keep forgetting this isn't a run of the mill project :P Edit: Like these?
Sigurthr wrote ...
You should check your driver for shorts; remove the GDT, CT (if used), and input power connectors. Remove all the logic chips used. Measure the resistance between the 12V and ground rails. It should read a VERY high resistance, if not then you have a circuit fault. You can't do this test with those components I mentioned still attached though.
I removed the chips, power and GDT and there's no continuity between the power and ground, even on the meter's highest setting.
GrantX wrote ...
From the pictures it certainly looks like the GDT is connected between the Gate and Drain pins on your bridge MOSFETs, and thermal insulators are missing, as Sigurthr said. Perhaps double check the MOSFET pinout and see if there is any continuity between the drains of both transistors?
Before I hooked everything up I tested this, there was no continuity. I checked the pinout. Isn't the GDT supposed to be between the gate and drain? Looks like it on the schematic.
Registered Member #4104
Joined: Fri Sept 23 2011, 06:54PM
Location: Uk .
Posts: 122
gate and drain = NO NO NO NO NO :P ,
That's a mosfet symbol , it dosent directly translate to the real mosfet , That connection on the circuit diagram is the mosfets gate pin and source pin , NOT its drain pin , Don't assume " drain " is the negative pin
On a mosfet The drain is the "in" and source is "out" , Read the Data sheet and it will show you this .
The GDT goes between the gate and source pin , All you are doing with the drain and gate pin connected is frying the high side mosfet every time power is applied and probably giving the gate drive IC's a unhappy death .
Yep, it was mentioned earlier in this thread and I should have paid attention. It was without the coil running (no sparks yet).
that'll do it!.
wrote ...
I'll replace that cap with a better one, I just used run of the mill .1uf caps. I keep forgetting this isn't a run of the mill project :P Edit: Like these?
Yup those are the ones I use. They work phenomenally well.
wrote ...
I removed the chips, power and GDT and there's no continuity between the power and ground, even on the meter's highest setting.
Good good!
Cheezey wrote ...
Before I hooked everything up I tested this, there was no continuity. I checked the pinout. Isn't the GDT supposed to be between the gate and drain? Looks like it on the schematic.
BINGO! I thought that is what it looked like. Do not feel bad, BJTs and their pinouts are my bane. I routinely blow them up because they don't have a standardized pinout like FETs do and they don't conform to the parallel equivalency FET pinout. Here's why it kept blowing UCCs, FETs, and popping the breaker. GDT secondary and tertiary get connected between Gate and Source pins, which are the outer-most two pins on a standard package FET. Twirly nailed it on the head; Drain is Current IN, Source is Current OUT. With a N-channel FET the Source nearly always goes to "ground", which means that the load is between the current supply and the Drain. The reason why you need a GDT for a half/full bridge is because you can't ground the Source of the high side FET as it is one of the output terminals so in order to have a return path for current from the high side Gate you need some kind of isolated signal source that won't short out the output of the bridge.
Registered Member #834
Joined: Tue Jun 12 2007, 10:57PM
Location: Brazil
Posts: 644
Checking the pinouts of the devices in the Internet is trivial and absolutely necessary. Mosfets can also be easily checked with a resistance meter (the gate looks open and there is a diode from source to drain. It is also easy to use the meter to turn the mosfet on and off). To avoid disasters, always connect an incandescent lamp (100W, if you still can find one) in series with the power line during initial tests.
BINGO! I thought that is what it looked like. Do not feel bad, BJTs and their pinouts are my bane. I routinely blow them up because they don't have a standardized pinout like FETs do and they don't conform to the parallel equivalency FET pinout. Here's why it kept blowing UCCs, FETs, and popping the breaker. GDT secondary and tertiary get connected between Gate and Source pins, which are the outer-most two pins on a standard package FET. Twirly nailed it on the head; Drain is Current IN, Gate is Current OUT. With a N-channel FET the Source nearly always goes to "ground", which means that the load is between the current supply and the Drain. The reason why you need a GDT for a half/full bridge is because you can't ground the Source of the high side FET as it is one of the output terminals so in order to have a return path for current from the high side Gate you need some kind of isolated signal source that won't short out the output of the bridge.
Oh :( That's annoying
But yay! Once I replace a couple of things, I just might have a working coil!
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Can I run Steve Ward's Mini SSTC without an interrupter?
