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Very simple high side mosfet driver



Jan 1, 1970
For some odd reason while trying to sleep this idea of a mosfet driver
popped into my head.

Curious to as it's effectiveness.

The idea is to use an op amp to provide a virtual ground between the source
of the high side mosfet and the gate but connected through a zener(and diode
to prevent reverse current).

The circuit is connected as follows to a high side zener:

1. + of op amp connected to source of mosfet

2. - connected to a zener in series and to the output of the op amp.

3. The zener's cathode is connected to the gate of the mosfet.

4. The gate is driven with some resistance.

The idea is that when you ground the gate the zener kicks in. The op amp
provides the zener with a virtual ground and essentially level shifts the
zener to keep the gate to source voltage lower than the zener voltage.

The circuit works fine in simulation and in theory seems like it would work.

One can remove the op amp and connect the zener's anode to the mosfet
source. The problem with this, and what the op amp fixes, is that when the
gate is grounded(through the resistor of course) V_GS will potentially be
out of spec.

I'm not sure I've ever seen such a simple solution for high side driving
probably for good reason. One needs at the very lest a gate vcc of probably
10V or larger than supply vcc shifting the problem of level shifting to
power supply issues.

In any case I thought it was a nifty little thing that just "appeared" to my
brain for no real reason and the fact that it actually works was quite
surprising(I guess there is something going on in this ol' noggin).

In the simulation, with several hundreds of pF of gate and zener the
response seems quite fast so possibly the only drawback is the higher Vcc?