I want to switch a negative voltage with a microcontroller, the controller runs from 0 and 5v, and I need to switch -12v 100ma.
I got the thing to work with a opto isolator, but it doesnt seem very 'elegant', what would be a good way to do this with a transistor or 2.
Here's the LTspice simulation of a two transistor circuit to switch a negative supply voltage from a positive signal (which I think is what you wanted).
The N-MOSFET can be just about any device with a low enough ON resistance.
Great thanks all.
I'd had the idea of common a base tranny as a switch but couldnt remember the circuit.
I want to switch the low side rather than the high side, looking at mikes post #6, all I need to do is mirror the circuit around Q2 and use n Npn tranny with its emmitter tied to v-, and have R1 inline with its base.
What does D1 do?
The msofet is a good idea too, I'd not thought about fets, that Aon device is pretty good at 18mohm on resistance.
Here's the LTspice simulation of a two transistor circuit to switch a negative supply voltage from a positive signal (which I think is what you wanted).
The N-MOSFET can be just about any device with a low enough ON resistance.
I'm Wally.
Most MOSFETs have a 20V rating and I didn't check that one in particular.
But certainly you would need to add a base resistor for that MOSFET to reduce the maximum Vgs.
I'm Wally.
Most MOSFETs have a 20V rating and I didn't check that one in particular.
But certainly you would need to add a base resistor for that MOSFET to reduce the maximum Vgs.