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Registered Member #3781
Joined: Sat Mar 26 2011, 02:25AM
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Posts: 701
Website: Schematic:
Well I built it, but before I test it out, I don't think my driver is working as it should... Steve says there's supposed to be a 24v (12 and -12) potential between the outputs of the gate drivers but I'm only getting a potential of 6 volts. I'm powering just the driver board (no GDT) with a computer PSU and I've triple checked my wiring.
The output from the hex inverter and 555 timer are both high which causes the ucc37321 to output low and the ucc37322 to output high. I measured the output from both gate drivers and I'm getting ~6v from the ucc37322 and 0v from the ucc37321.
Registered Member #15
Joined: Thu Feb 02 2006, 01:11PM
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Posts: 3068
Okay. First off, disconnect the gate transformer from the UCC chips and then retake your measurements.
1. Ensure you indeed have 12V on each UCC chip.
2. Check each UCC output. Each output should be 12V to GND.
3. There is NOT 12 to -12V between outputs of the gate drivers. On the primary side it is just 0V to +12V of each driver. They are just driven alternatively so on the secondary of the gate transformer you will have a +/- swing.
If you measure the outputs differentially, then you will see a +24V swing, but single-endedly, you will not.
Ripples from the capacitance must never be below 14V for the LM7812 otherwise you won't have a solid 12V... Can you describe your input circuitry? I'm surprised he has a 20V 1A and not a 25V 2A transformer... I've seen this circuit on instructables...
yup yup found it: He gives good pictures of how it should look.. HAHA! He has a 25V 2A transformer like how I figured it could seriously help.. yeah honestly that could be a problem. I noticed Steve for his micro sstc lowered in his second schematic the amount of capacitance to handle the ripple current... He likes to dance on the lines between functioning and minimal parts count.
Registered Member #3781
Joined: Sat Mar 26 2011, 02:25AM
Location:
Posts: 701
EasternVoltageResearch wrote ...
Okay. First off, disconnect the gate transformer from the UCC chips and then retake your measurements.
1. Ensure you indeed have 12V on each UCC chip.
2. Check each UCC output. Each output should be 12V to GND.
3. There is NOT 12 to -12V between outputs of the gate drivers. On the primary side it is just 0V to +12V of each driver. They are just driven alternatively so on the secondary of the gate transformer you will have a +/- swing.
If you measure the outputs differentially, then you will see a +24V swing, but single-endedly, you will not.
Yeah I did all this and one is still outputting 0v and other is outputting 6v. I think I'm just going to rebuild my driver board. I need to make the connections shorter and I want to use a TL494 anyway.
twist2b wrote ...
Ripples from the capacitance must never be below 14V for the LM7812 otherwise you won't have a solid 12V... Can you describe your input circuitry?
I'm using a computer power supply to power this thing:
Yeah EasterVoltageResearch is asking a valuable question. Since you are driving it with a power supply that I know nothing about... it somehow could be that you are not feeding enough volts. You have to make sure you ground BOTH gnd pins and 12V to BOTH vcc pins.. otherwise you are going to get odd results... Also, I say go with the TL494 cause than you can use an AUDIO source! :D
Also, I don't doubt your intelligence... just saying this has gotten me before... BUT: 1) if you are measuring with a multi-meter than 6V makes sense because the resultant voltage shown for a 50% duty cycle will be HALF 2) if you are using an oscilloscope than you could have it set to 2V per deviation.
I'm just saying be weary of that fact. Also, the least amount of wiring you can do is better but I think yours looks fine man.. It's clean and easy to follow just from looking at the picture :D
Registered Member #3781
Joined: Sat Mar 26 2011, 02:25AM
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Posts: 701
Thanks for the advice guys. I ended up just rebuilding the whole thing and I checked each part with a scope. Everything looked great so I hooked it to the mains and it works great! Here's a video:
It's running at a frequency of about 350khz
I have a few questions though. The GDT I used is a found GDT and I have no idea if it's rated for high frequencies, is there a way to figure out if one of my other found GDT's would work better haha? Also, the heat sink barely gets warm to the touch so does that mean I can reduce the number of turns on the primary? It's currently at 4 turns and I was afraid of reducing it anymore. My UCC drivers are hot to the touch, is this normal? Should I go back and send a 350khz wave through the GDT since this is the operating frequency of the coil? (It is actually adjustable between 300 and 500khz)
Thanks again.
EDIT: Scope images: Here's the outputs from the GDT: ,Ix2GTGY#1
Registered Member #15
Joined: Thu Feb 02 2006, 01:11PM
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Posts: 3068
If you are running a high duty (i.e. CW) then yes, your UCC should be hot. Remember, that in DRSSTCs, we run at very low duty cycles, so our gate drivers do not get hot. But if you have a SSTC that is running high duties, the UCCs can get VERY hot.
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