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Homemade IGBT MIG welder with ATX PSU parts. [blown yet again][blown count: 5]

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strawberry:
you should set dead time for IGBT. TL494/KA7500 is determined by DT pin voltage

xavier60:

--- Quote from: strawberry on July 01, 2019, 06:23:55 am ---you should set dead time for IGBT. TL494/KA7500 is determined by DT pin voltage

--- End quote ---
The maximum duty cycle would be something less than 50% with only one output used.
What bothers me about the TL494 is not being certain that double pulse suppression  has been added.

xavier60:
Gate drive for a one or two switch forward inverter is complicated by  the changing symmetry of the drive waveform with change of duty cycle.
I remember with one welder that I repaid, the drive transformer had a large inductance and was driven by a single MOSFET in flyback mode. The flyback voltage was clamped by Zener diode across the primary.
I wonder if the same drive that's normally used for half-bridge forward inverters can be used. The negative pulse will just be ignored by the IGBTs.

Refrigerator:

--- Quote from: xavier60 on July 01, 2019, 10:44:31 am ---
--- Quote from: strawberry on July 01, 2019, 06:23:55 am ---you should set dead time for IGBT. TL494/KA7500 is determined by DT pin voltage

--- End quote ---
The maximum duty cycle would be something less than 50% with only one output used.
What bothers me about the TL494 is not being certain that double pulse suppression  has been added.

--- End quote ---

One thing i noticed when testing the circuit out is that the voltage on the open collectors of the TL494 does not go down to 0V but rather to something like 0.7V, which explains why there are almost always one or two diodes between the base drive transistor emitters and ground in the ATX PSU schematics.

Refrigerator:
Well i seem to have run out of solder for today but i finished the bridge rectifier and while i was at it i added a simple relay circuit to bypass the PTC resistor after two seconds, this way i won't cook the PTC.
Pretty much the same thing done as in big old CRT TVs.

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