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Author Topic: Dumb down MOSFET Selection?  (Read 1614 times)
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A few weeks ago I read (it could be on this forum) that the TO-220 could not have 100A through the pins, even though the mosfet was specified for that amount of current.


I wondered about that myself... having worked a fair bit on big-ass electrical installation jobs and seeing the size of conductors needed to handle 100A, I thought seeing TO-220 packaged parts being rated for hundreds of amps seemed a bit ridiculous!
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Even with PWM you will still see the initial current draw, that is why you over spec parts so that they can deal with it. the initial start up current is nothing to do with the speed, as far as the fan is concerned as soon as it gets power it is coming on it knows nothing about the fact it is about to go off again and how long it will be on for initially.

Remember that there is a specification for vehicle stuff and that includes load dumps and spikes of up to 150 V are seen as normal should they occur and it is your problem to deal with that. 55V on 12V on but make sure you put protection in, for 24V I'd be tempted to try higher. It is also expected that the vehicle could see 24V for some seconds (jump starting from a recovery vehicle) so deal with that too.
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A few weeks ago I read (it could be on this forum) that the TO-220 could not have 100A through the pins, even though the mosfet was specified for that amount of current.


I wondered about that myself... having worked a fair bit on big-ass electrical installation jobs and seeing the size of conductors needed to handle 100A, I thought seeing TO-220 packaged parts being rated for hundreds of amps seemed a bit ridiculous!

Actually TO220 package can take 100A, just not for very long!  Its the gold bonding wires to the chip itself that
will fail first, and at very high currents the magnetic force may break them before they vaporize for all I know!
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Spec on the linked mosfet
 Continuous Drain Current Id: 120A

The more important aspect of the spec (and the reason I pickled that one) is the low Rds(on), because you need a very low Rds(on) to keep the power dissipation manageable.

In view of the high current, I suggest you use at least 2 mosfets in parallel, driven by a mosfet driver IC.
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