# Controller gate resistors



## DawidvC (Feb 14, 2010)

The gate of a mosfet is basically just a capacitance. To get faster switching speed for a particular mosfet, you need more gate drive current. This need still to be seen within the design parameters of the particular mosfets you are using. What it comes down to in your case is not the resistor value that was used originally, but the value best suited to the mosfets that you are using to do the upgrade with. If the 120 ohm resistors are giving you fast enough switching speed then I would not worry too much. Going for a higher value would slow down the switching speed, which could lead to heat dissipation problems, so I would not recommend that.

Hope that helped a bit

Regards
Dawid


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## JRP3 (Mar 7, 2008)

You ever look into modifying one of the Curtis 3 phase AC controllers? You'd be a hero if you could do that.


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## DawidvC (Feb 14, 2010)

I am more into IGBT's than mosfets. The (small) difference between the driver circuits can create big problems in changing from mosfets to igbt's, and I don't think I can do a mosfet replacement and feel good about the job - igbt or nothing .

If somebody can lay their hands on a blown controller and is willing to send it halfway to the back-end of the world, I would be more than willing to play around with it. If some of the new igbt modules can be hooked to the controller instead of the current mosfets, we are looking in the direction of some serious power.

Regards
Dawid


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## JRP3 (Mar 7, 2008)

I've never heard of a blown Curtis AC, probably because the software cuts it back on over temp and over voltage. I'm not sure how you'd kill one, though it's probably possible.


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## jehan12413 (Feb 4, 2010)

Thanks for the help. I guess once I try the latest one at full power I will find out. I have looked at the waveform but not under a heavy load.


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## DawidvC (Feb 14, 2010)

Let us know how it goes, then we can wrangle it around here some more.


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## jehan12413 (Feb 4, 2010)

So far I have only load tested with a single MOSFET to 15A cont and 20A surge at 200V. (Usually I install just one for testing to save all the work of soldering and then desoldering).It seemed to do ok at 15A which was past it's continuous rating so I guess my resistor values are ok.


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