Hi. I need to select the highest of two reference voltages. The current needed is very low, less than 20 μA, but the voltage needs to be as precise as possible, and the references are very near the positive supply, which is 35v. There's also a negative supply there of the same value that can be used, as well as +6v and -6v.
I had thinked about a comparator driving a p-channel to connect one channel, and the other connected with just a 1k resistor, but it has it's own share of problems, like that annoying built-in mosfet diode (is there any mosfet without that?), and the max possible Vgs. Something like this (the schematic is incomplete, U1 is only there to show that the current needed is very low, and i didn't shown the comparator that drives the mosfet):
Maybe someone already did something like this? I accept suggestions, doesn't need to follow the schematic up there at all.
Thanks.
I had thinked about a comparator driving a p-channel to connect one channel, and the other connected with just a 1k resistor, but it has it's own share of problems, like that annoying built-in mosfet diode (is there any mosfet without that?), and the max possible Vgs. Something like this (the schematic is incomplete, U1 is only there to show that the current needed is very low, and i didn't shown the comparator that drives the mosfet):
Maybe someone already did something like this? I accept suggestions, doesn't need to follow the schematic up there at all.
Thanks.
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