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Topic: MOSFET driver external circuit (Read 1 time) previous topic - next topic

FardinB

Hello and thanks for the replies,

So I looked at the graph in fig 8 and I understand what you are saying about the DC current capacity of the mosfet. However I have been safely switching 30A at 12V, and that is also outside the dotted line for DC. The thing is the mosfet does not even get warm (maybe because I have a heat sink on it). This leads me to believe that the graph is not very accurate (or is accurate without the heat sink). Increasing the number of mosfets is certainly an improvement but I am still not sure if that is really needed. This mosfet has impressive characteristics and putting 2 in parallel might be overkill for this application.
My question is about the driver. What value of gate resistor do I need for a period of 300ms (again I am NOT PWMing the Mosfet). Essentially the mosfet is acting as a switch that is only on for a period of 300ms.

Thanks

winner10920

You don't want any gate resistor, you want it to switch as fast as possible to limit losses

dhenry

Quote
the graph is not very accurate (or is accurate without the heat sink)


It is accurate. Just that no one in this thread has been able to read it accurately.

Quote
You don't want any gate resistor, you want it to switch as fast as possible to limit losses


Bingo!

You do, however, use gate resistors from time to time for dead time management.

oric_dan


I have been safely switching 30A at 12V, and that is also outside the dotted line for DC. The thing is the mosfet does not even get warm (maybe because I have a heat sink on it). This leads me to believe that the graph is not very accurate (or is accurate without the heat sink). Increasing the number of mosfets is certainly an improvement but I am still not sure if that is really needed. This mosfet has impressive characteristics and putting 2 in parallel might be overkill for this application.
My question is about the driver. What value of gate resistor do I need for a period of 300ms (again I am NOT PWMing the Mosfet). Essentially the mosfet is acting as a switch that is only on for a period of 300ms


Oops, I misread you last time, and looked it up for 300-usec. Duh, 300-msec is much different.

However, you were saying 60A, now you're saying 30A. That's a difference of 4X in dissipation, and
that's also much different. For Rds = 2-milliohms, Pd = 30A*30A*0.002ohms = 1.8W, which is not
much when using a heatsink. OTOH, with 60A*60A*0.002 = 7.2W, you'd probably see some heat-up.



FardinB

I tested the mosfet with 30A and I needed to know if it can handle 60A for 300 ms (and it can with a heat sink). From you power dissipation calculation, even with 60A passing through the dissipation is small. Also I have a heat sink attached, which make this work even better.

About the gate resistor, I tried a different driver with 220 Ohm resistor and it blew up. This driver had  +/- 9A peak current. So you would think it would work for this application, But NOOOOO!!! The part number was UCC37322P, if you are curious.
This was the reason that I choose the new beefier driver. +/- 14A and +/- 4A continuous at room temp! However I am afraid that if I dont put any gate resistor, this thing would blow up too. Share your thoughts.

Thanks

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