Does anyone see an issue with this circuit? We just want to turn off the power to the circuit when the base is grounded (S? on the "1" setting).

 

In the 'off' position current flows through the 330R resistor. Hope this isn't battery powered!

 

Note that the output of transistor emitter is about 0.7V below VIN+.
Is that acceptable for you application?

 

I think you would be better off using an FET.

 

I think you would be better off using an FET.

I was wondering that. So instead of the "base" we have the gate, will this setup be acceptable for that?

 

In the 'off' position current flows through the 330R resistor. Hope this isn't battery powered!

It is and I was wondering that myself. Off the top you of your head (besides the fact that this is more of a FET application), do you have a recommendation of a circuit that would cut off the power the circuit when the slide switch is in the off position? I wish I could just make the different positions pull down to ground and have the signals be active high (switch 3 and 4 from gnd to 3V) and have a pchannel FET turn off the rest of the circuit when the gate is high but that would leave current still going to the FET.

 

Note that the output of transistor emitter is about 0.7V below VIN+.
Is that acceptable for you application?

Good call. It would work for fully charge batteries but could definitely do without the voltage drop.

 

How about this? it's late and I'm tired, couldn't find a 4 way switch for the sketch. Q1 will be in saturation when it's on, so will loose very little voltage to the load. You will need to select R1 value to supply enough base current to Q1. R6 is 1M0, enough to turn on Q3, and will take very little power in the off position. Q3 should be ok with 3 volts on the gate, but the threshold range on the datasheet ranges from 0.8 to 3 volt, hopefully you'll be lucky with a low threshold sample.
(yes, I apologise for the crappy switch wiring)

 

There are chips that'll do this job far better/cheaper than discrete parts eg SLG59M1709V or NCP45560IMNTWG.

 

I'm way to old to see smt devices!

 

a pchannel FET turn off the rest of the circuit when the gate is high but that would leave current still going to the FET.

And this is a problem because?

 

How about this then... Irf7317 is a dual n+p MOSFET.

+3v on the gate of the n-channel turns it and the p-channel on. 0v turns both off. No current flows in either MOSFET in the off state.

 

There are chips that'll do this job far better/cheaper than discrete parts eg SLG59M1709V or NCP45560IMNTWG.

Thanks Irving,
I'll take a look at those CMOS parts.