For the project I intend on using this in it would be beneficial to be able to switch output voltage from GND to 8V. Maximum expected current on this output will be ~20mA.
What I came up with is this:
(544UD1 is a dual supply not rail-to-rail op amp that I have available,2T3117a is an NPN bjt: UcbMax=60V;UceMax=60V;UebMax=4V, Vref is done with voltage divider instead of Zener as in source schematic, switching on/off is done with analog switch placed on reference voltage)
What I am worried about is that Qbase drops to -15V while QEmitter is in range from GND to 8V. This seems to violate UebMax rating.
This however does not fully address the problem (note time ~28ms) as Qbase can drop faster than Qemitter:
Simulation does not seem to mind this spec violation but I am not sure what happens in real life at this point.
Is there a simple way to address this issue?
- Should a different BJT be used? (Though many small BJTs have Ueb in range of 4V to 6V as far as I am aware)
- Should a different Op-Amp be used? Strictly single supply or dual supply can be used as well?
- Should an analog switch be placed elsewhere?