The MOSFET has a gate capacitance (Input capacitance) of around 1 nF. If I drive the MOSFET by using a pull up resistor at 5V, say 1kohm, and pull it down using an npn transistor, then I could drive the MOSFET w/a higher gate voltage. However, this will limit my switching speed...
To have a 5V drop over a 1kohm resistor, the npn transistor must sink at least 5mA.
With the resistor/capacitor, I'd have an RC constant of 1e3Ohms*1e-9F = 1uS. If I want to switch at 20khz, this has a period of 50uS, which means that my switching time (fall/rise time) would be about 2-4% of the entire period. If I switched even slower, this would work better.
Does this sound reasonable?
Matt