On 2013-05-24 4:21 PM, RussellMc wrote:
> What they say, but ...
>=20
> 6V gate drive is getting low if you can tolerate 18V.

The datasheet for the MOSFETs I'm using shows that they fully turn on at
6V, and still more than enough at 5V. I also don't want to charge the
MOSFET gate to high voltages if I can avoid it since the gate charge
increases linearly without lowering the Rds any noticeable amount further.

> The "whole regulator" is worth tens of cents and you are supplying it
> not "just for the gate driver but "just for the MOSFETS and whatever
> they are doing". Is the take really so value-less?
> Even when required capacitors are added, cost is unlikely to be a good
> reason for doing this. Size may be.

You're right, I've decided to use a linear regulator.

> If you use an 18V zener (less whatever safety margin is required) then
> it needs to supply (just enough current at 16V so you'll be
> dissipating Imax x (2-16) =3D 8 x I_max Watts.
> A 10V zener in series will dissipate up to 10 x Imax Watts at any
> Voltage.  I'ts more complex than that but essentially you'll disispate
> about the same either way and have ~=3D 16V min gate drive using a
> conventional zener.

I don't think I could use a Zener in parallel for a gate driver IC
supply. The gate driver and the average current to switch the gate will
be below 100mA, but I'm relying on high pulse current when switching to
charge the MOSFET gate fast enough. I could use a big capacitor in
parallel with the Zener, but then again, I might as well use a 1.5A
linear regulator and be done with it. So that's what I'll do.

--=20
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