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How come there are components in TO220 packages that supposedly take 100A given their small legs? (programming.dev)

submitted 1 week ago* (last edited 1 week ago) by [email protected] to c/[email protected]

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Not sure if this is a dumb question but this has me quite puzzled.

The legs on TO220 packages are very small. How is it that there are e.g MOSFETS rated as being able to continuously conduct ~100A? e.g IRF1404Z

From what I understand such large currents need busbars on PCBs and these appear a lot larger than the legs on these components.

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[–] [email protected] 5 points 1 week ago

From the IRF1404Z data sheet:

Calculated continuous current based on maximum allowable junction temperature. Bond wire current limit is 120A. Note that current limitations arising from heating of the device leads may occur with some lead mounting arrangements.

You need to design the PCB so that the heat from the legs can be properly dissipated, or they won't live up to the rated current.

Also, traces on a PCB are much thinner than those legs. A trace with the same cross-sectional area would be impractically wide.