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Registered Member #4992
Joined: Wed May 23 2012, 03:57PM
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Posts: 108
I dont know what else to do, i even added a resistor between the gate and the source to increase the reverse bias but it stil does the same thing. Its as if the gate is in a constant short with drain.
Registered Member #190
Joined: Fri Feb 17 2006, 12:00AM
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Posts: 1567
Shrad wrote ...
in the schematic T2 and R15 are shorted to ground (in the bridge)
I need to fix that typo. That is just the current-sense coil and both connections go to a meter of some kind to measure the current. This is not the source of his problem.
Here is a similar schematic from the website tutorial with a correct rendering of the current-sense resistor:
Registered Member #190
Joined: Fri Feb 17 2006, 12:00AM
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Posts: 1567
furnace wrote ...
I dont know what else to do, i even added a resistor between the gate and the source to increase the reverse bias but it stil does the same thing. Its as if the gate is in a constant short with drain.
Don't just add resistors. What type of capacitance do you have for your +15vdc supply going to the inverting/non-inverting chips supplying the gate-drive transformer? I had about 2000uf. I don't know if this is part of your problem. You might want to check the voltage supply going to the chps and make sure it isn't sagging.
Registered Member #3215
Joined: Sun Sept 19 2010, 08:42PM
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Posts: 780
if you use scavenged parts you should measure all your electrolytics, as some could heat inside or have some faults which appear only when they are self heated to some extent
Registered Member #4992
Joined: Wed May 23 2012, 03:57PM
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Posts: 108
I have 2500uf caps on my 15voilt supply and i have checked the caps already over and over. This is the signal of the gate drive on the 2 mosfets with power turned on from the variac.
Registered Member #190
Joined: Fri Feb 17 2006, 12:00AM
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Posts: 1567
The voltages are different. This looks like 10v on one; 15v on the other. I would disconnect your load. If this is what you have with no load you need to figure out why the voltages are not the same. What is the signal like without the mosfets? In other words, what is the signal like coming right off of the GDT?
Registered Member #4992
Joined: Wed May 23 2012, 03:57PM
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Posts: 108
The signal coming from the gdt is perfect with no Load and the voltage output is the same, it's only when I Turn the variac on than the one signal stars to increase like it shows on the picture.
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Induction heater
