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Gate resistro mosfet IRFP450

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sandms

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hi everyone!
First, sorry on my bad english....
How to limit drain-source current to 6A ( irfp450 max curent is 14A) by gate resistor?
My gate-source voltage is about 6 volts.
I need that beacose i have plasma cutter with 2sk2873 mosfet-s(that burned),and i want to swap that fet-s with irfp450.Is it possible?
Gate resistor on that 2sk2873 currently is 6,8 ohm!
Thanks for help!
 
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As long as you have fixed what burned the 2SK2873 you should be able to replace it with the IRFP450 without any changes. It is the load resistance that limits the drain to source current not the gate resistor. Usually with an NMOS FET the load will be in the drain so you need to check there for a short if you haven't found what made your first FET burn.
 
Its generally not too good of an idea to limit current in a circuit with a MOSFET. They will get too hot. A MOSFET is great as a switch, either fully on or fully off.
 
ok, what is then solution? When I took burned Fet-s of the board, plasma is again worked ok because that burned Fet-s were in the short-circuit and protection is working - not alowing to cut
 
I'm not sure how your machine works. Are there many FETS in parallel?
Does this failure happen often? Or just once?
Maybe it would be possible to protect the fets with a fuse if the high current is just to start the arc.
 
ronv - yes,there many FETS in parallel- 12 FETS (4 groups; in every group are 3 FETS in parallel).
I have remove 1 FET from every group (3 FETS were in the short-circuit), and plasma working now but with 8 FETS - (4 groups; in every group are 2 FETS).
And yes -this failure happened just once!
 
If you are going to change to the IRF450 you should change all the fets as they have different on resistance etc. than the
2SK2870. If it is OK now maybe just a bad part. The IRF450 is a stronger part so you may have more safety margin.
 
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