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Are logic level gate mosfet slower than regular mosfet?

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ZeroResistance:
1. Are logic level gate mosfet only used for static applications? Can they be used for medium frequency 10khz, switching?
2. Are they slow in turn on? Will they heat more that the typcal mosfet + gate driver combination?

I'm looking at switching 10's of amps at a frequency between 5 to 15khz. voltages would be around 10 to 20V.

T3sl4co1l:
1. No, they're used all the way up into the MHz.  Design accordingly though.
2. In reference to 10V drive, turn-on is faster, but turn-off is slower (can you reason out why?).

Also, low voltage (Vdss < 30V) parts have lower Vgs(max) and higher gain, allowing quite good performance at Vgs(on) = 5V), even Vgs(on) as low as 1.8V for some battery management transistors (which are available with Vdss ~ 6V and Rds(on) < 1mohm!).  If you have the choice between a higher or lower voltage part (say with a topology tradeoff, half bridge vs. push-pull?), it can be better to go with the lower voltage -- higher performance -- part.

Tim

ZeroResistance:

--- Quote from: T3sl4co1l on October 29, 2018, 06:06:01 am ---1. No, they're used all the way up into the MHz.  Design accordingly though.
2. In reference to 10V drive, turn-on is faster, but turn-off is slower (can you reason out why?).

Also, low voltage (Vdss < 30V) parts have lower Vgs(max) and higher gain, allowing quite good performance at Vgs(on) = 5V), even Vgs(on) as low as 1.8V for some battery management transistors (which are available with Vdss ~ 6V and Rds(on) < 1mohm!).  If you have the choice between a higher or lower voltage part (say with a topology tradeoff, half bridge vs. push-pull?), it can be better to go with the lower voltage -- higher performance -- part.

Tim

--- End quote ---



 :-+
Thanks, I will think about the slow turn off issue, cannot say why it turns of slowly currently  :-\
Will the gate present a significant load on the driving pin, lets say a microcontroller I/o pin |@ 10khz frequency.
what kind of drive requirements is one looking at?
I see that mouser as a Vgs(th) column in the selection table no Vgs(on) so I would have to click on each entry to find the Vgs(on)?

Ian.M:
As a rough rule of thumb, look for max Vgs(th) less than half your logic '1' level.

The gate looks like a *LARGE* capacitive load, so whether or not your MCU will be happy driving it direct depends on its output characteristics and tolerance for brief overloads.  At 10KHz you'll *probably* get away with it unless your MCU has really wimpy pin drivers.

T3sl4co1l:
For a transistor of that size, I would recommend a driver, not a bare MCU pin.  A 74HC3G04 (all sections wired in parallel) would be good enough, or a proper driver of any various sort (discrete or integrated, however you like).

If you go discrete, I'd kind of hesitate against using a complementary emitter follower output stage, because of the 0.7V offset.  It's usually okay for logic level gates still, but there may be better ways.  Unfortunately that rules out most simple methods (at least that I know of, and can think of), so I'd stick with the parallel logic gates or integrated driver.

Note that Rds(on) is always better at higher Vgs(on), with a lot of 5V "logic level" spec'd parts being headline spec'd at 10V.  If you have the higher voltage available, it's worth borrowing.

Tim

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