I have an iVac Switch Box, and I would like to increase the current threshold that it uses to turn
on the second device (usually a shop vac).
Attached are photos and my hand-drawn reverse engineered schematic.
It looks like in "auto" mode, a current transformer senses the current going to the tool. The circuit
uses half-wave rectification, and then clamps the maximum voltage to 10V with a zener (1N4740A). There
is a capcitor for smoothing and, I think, for a small delay after current is sensed and then a bit
longer delay when current goes away. The voltage feeds the gate of a power mosfet, an STP3NK60ZFP
with typical Vgs(th) of 3.75V, and a range of 3V-4.5V.
Are there any suggestions for easy ways to adjust the device's turn on current threshold higher? Just
changing resistor values to scale down the voltage at the mosfet gate would seem to also significantly
throw off the turn-on and turn-off times, which is not desireable.