Re: High side high voltage MOSFET switching with 3V logic drive?
Yes your right, im thinking of Vbe.
The photodiode in the PC817 states Vf of 1.2-1.4v, at a test If of 5mA, max 20mA, which does indeed come out at 330R for 3v 5mA, and as im only activating one out of the 18 at a time, i'll be able to get away with just the one resistor.
My remaining worry then for this part of the project (apart from whether I can physically fit the whole lot into the radio) is whether the 80v maximum will be exceeded or approached too closely on any of the higher ranges. I'll need to actually measure the voltages out of each step of the divider chain to establish that, but if so it will just mean I have to choose a higher rated device for those lines
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