Hello all,

I'm trying to minimize the losses in an H bridge for a 12V brush motor
(>40A stall current). One thing I'm thinking of is replacing the p-channel
high-side MOSFET with an n-channel MOSFET and the associated, more complex
driver.

I looked into what is available in form of ICs (like National LM9061 or
Micrel MIC5021), and it seems to me they guarantee only gate-source
voltages of 7V (LM9061) or even only 4V (MIC5021). Since most low Rdson
MOSFETs require Vgs in the range of >10V for this to happen, and reducing
Rdson is probably the main reason for using an n-channel MOSFET as
high-side driver, I'm a bit stumped. I thought it was easier to find a
MOSFET high-side driver that outputs a guaranteed Vgs of 10V or 12V
floating over Vsource. 

Am I missing something here?

My current approach is to use a simple boost switcher to provide an
auxiliary voltage that is guaranteed to be >12V over the board supply and
then take it from there, with zeners and optos. It doesn't have to be
terribly fast; I'm doing the PWM with the low side drivers -- but I need
the lowest Rdson I can get, so I really need >12V Vgs. 

Any better ideas?

Thanks for hints, tips, pointers, (preferably constructive) criticism,
anything at all... :)

Gerhard

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