Re: What Driver Voltage to Drive a Mosfet? (SMPS app)

On Mon, 30 Jul 2007 19:22:52 +0200, Andy F Z <andy@fzsmth> wrote:

D from BC wrote:
My power mosfet has an absolute gate spec of 30VDC.
Most of the Mosfet data*** gate behavior graphs only go to 10V.

Is there a drive voltage that'll provide low switching loss?
Looks like there's a 6V to 30V range to choose from.

Mosfet Specs
Gate charge 40nC
Input capacitance 1500pF
Absolute max gate voltage 30V
Id=10amps @Vgs=7V

Circuit Specs
f=600khz
Id=2amps
Mosfet driver can be powered up to 36V.
D from BC

Do you mean by loss the energy dissipation on the Drain-Source side of
the MOSFET, during the switching? It will largely depend on how fast the
MOSFET goes from the "open" to "closed" state. I would start by choosing
first the Vgs_1 high enough to get the Vds under load as low as you need
it for your "charge" part of the cycle, and then would go on optimizing
the circuit on the Mosfet drive side to get Vgs from 0 to Vgs_1 and back
as fast as possible. Then simulate and validate the energy dissipation.

-- Andy

Yup..it's the gate peak voltage for low drain source switching loss.
I'm letting the mosfet do whatever it can do in the way of rapid
current rise and fall times for reducing Pds switching loss.

Are you saying I should use the lowest gate voltage possible for
sufficient drain current?
That way there is less gate charging and discharging?
A gate charged to say 6V can be discharged faster than say a gate
charged to 20V.

D from BC
.