Forrest Christian wrote:
> http://bit.ly/MOSFET_Driver_250nS
>=20
> Amazingly simple driver circuit is attached.
>=20
> Short version: Treat the level-shift transistor as an inverting
> amplifier, not a switch.

Albeit one with a rather high output impedance (5K ohms). If we assume that
the current through that transistor is on the order of 3 mA when "on", then
this is also the peak current available to the emitter followers at the
beginning of each transition, and it tapers down from there as the transiti=
on
proceeds. This value, multiplied by the beta of the emitter followers, beco=
mes
a limiting current for the drive of the MOSFET gate.

Another way of looking at this is that the 5K impedance of the level shifte=
r,
divided by the beta of the emitter followers, is already an effective serie=
s
resistance for the MOSFET gate.

-- Dave Tweed
--=20
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist
.