Omicron Gama 131, welding inverter, reverse engineering and repair

main power bus stabilizer: BDW93C on heatsink, with zener diode BDW blown, zener interupted

CATHODE BAND [ref] Mini MELF Device Type Black General purpose Yellow Switching Green Schottky Blue Zener

LM324 SG3525AP (== UC3525, first by On Semi, second by Texas Instruments)

SG3525 gate drive: starts at about 12V Vcc then the drive FET and transformer overheat significantly

gate drive waveforms: http://www.richieburnett.co.uk/temp/gdt/gdt2.html

• excess low-freq ringing: excessive leakage inductance; redesign transformer
• excess ringing on top of waves: lack of damping resistance, excessive leakage inductance; add resistor
• flat tops and bottoms with overshoots: increase damping resistance
• leading edges curved: overdamped; lower damping resistance
• curved to triangle-like: massively overdamped; lower damping resistance, or use stronger primary drive
• sloping tops/bottoms: low primary inductance; add turns
• excessively sloping tops/bottoms: way too low primary inductance; add many turns or use core with higher specific inductance (AL)

SMPS design calculators: http://schmidt-walter-schaltnetzteile.de/smps_e/smps_e.html

voltage conttrol:

TL431 2.5v reference, 4 µA pin current, max. 10mA pin current

100v output (say) 2.5v at 100v = 100k/2k5

divider: \ 100k 2k4 Vout o--------/\/\/\------/\/\/\--*--o GND \ 100k ZD >5v? -------/\/\/\--*--o Vref