Transistor switch sandbox for 1S LiPo

I have interest in simple transistor switch which will enable the active buzzer (3V/20mA) when positive voltage is applied to input and vice versa - when input voltage drops to zero. Power source is a 1S LiPo battery, therefore I wanted to see the behavior of circuit in both cases when battery is full (4.2V) and empty (3.6V). The overall circuit contains 2 switching circuits: 1) High side switch at left. NPN transistor with load in collector circuit. Buzzer will sound when input voltage is raised. 2) Low side switch at left. PNP transistor with load in emiter circuit. Buzzer will sound when input voltage drops. I had an interest in exploring them both, so I put them in one box :) Currently I'm more interested in second one. I didn't found any element from EC stock library matching with active buzzer. So I did use a 3V/30mW lamp instead.

published 9 years ago