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Powered By Infinite Improbabilty Drive
Stone Mountain, GA
·Atlantic Nexus
reply to Stiv2k

Re: Trying to repair laptop charging circuit

Switch-mode supplies do not handle fast changes in the input voltage well. That is one reason they are often paired with a LDO regulator. They can also overshoot with sudden changes in load.

As the part is only 30V, the supply probably had a spike that exceeded the voltage causing the transistor to break down.

Used to live in Florida, lots of surges and power transitions. Had many switching power supplies fail or burn out downstream devices. Worst is when power cuts in/out several times over a few seconds. The supplier are running at a high PWM duty cycle to maintain the output voltage with a low input voltage. Then the input jumps and the output spikes. How much depends on the design of the supply (current or voltage mode design.)
Scott Henion

Embedded Systems Consultant,
SHDesigns home - DIY Welder