Transistor System Turn off Circuit

Thread Starter

phippstech

Joined Jan 27, 2020
14
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).

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Thread Starter

phippstech

Joined Jan 27, 2020
14
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.
 

Martin_R

Joined Aug 28, 2019
103
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)Screenshot 2021-07-09 225330.jpg
 

Irving

Joined Jan 30, 2016
2,308
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.

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