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Mosfets and pulsed current

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chris414

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I'm trying to protect my h-bridge mosfets from short circuits while testing. I am using SFP30N06 mosfets which are rated to 30amps continuous drain and 120amps pulsed. I am using 2 12V lead acid batteries (ie. 24V), so to limit the current to 120amps I would just need to add in a 0.2ohm resistor (make it a bit more for safety). For my application this resistor would not have a significant effect on performance, but my question is this: would the mosfets tolerate a 120amp pulse for long enough in order for the fuse (a standard 15amp fuse) to blow so that the mosfets are not damaged?
 
No.The 120 amp pulse is for a very short period of time and if you try to entend this to a time-length that will explode the fuse, you take the rise of exceeding the time-duration for the MOSFET.
The allowable pulse duration is 300uS or about 2% of the duration of the signal. A fuse will take much longer than this to explode.
 
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What is the normal maximum operating current of your bridge? Do you really need to go to 120A?
 
According to the SOA on the datasheet, at 24V you can get about 100A for about 100us.

Remember, the 120A figure is the ABSOLUTE MAXIMUM. That means there is no tolerance at all. If you go 120.1A then you've killed it. Maximum Electrical Characteristics are NOT operating points. Use the SOA graph to determine how much actual current you can handle.
 
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