Something went BANG

Just a reminder: ~3milliFarads at 800V is a lot of stored energy!

This is the story of how Yotacoil destroyed one of my cm300 (1400V, 300A continuous, Yotacoil uses them soft-switched at up to 1200A in bursts) half bridges. In this case, the controller that chooses when to switch the transistors on and off malfunctioned. This caused the transistors to be switched when they were carrying maximum current, which is called hard switching. This instantly destroyed the top transistor of this half-bridge brick. Unfortunately, this left the top transistor short (closed, conducting), so when the controller turned on the bottom switch, the entire capacitance on the bridge shot through the destroyed top transistor and the conducting bottom transistor. This dead short instantly giga-detonated the bond-wires through sheer excessive current. The newly-plasma wires pressurized the plastic case so much that the lid exploded off. That’s right, this transistor was opened due to an electrical fault. After the wires were broken, the transistors no longer conducted. I guess you could say it failed open.