Hi
in this thread:
https://www.eevblog.com/forum/beginners/transformer-tap-switching-between-serial-and-parallel/I'm asking about help regarding the switching of transformer taps to reduce power dissipation on the series pass transistor of my lab power supply design.
With this being dealt, new issues arise: I'm feeding the op-amps from the transformer which is now being switched between 9V and 18V. Until now, I had a 7818 VREG which made a stable 18V for the opamps.
Now, when the transformer is being switched to 9V, that VREG will go wild, I guess, but while being at 9V on the transformer side, I won't need 18V at the opamps either.
So I thought I could maybe high-side switch the voltage supply rail of the opamp and put in another VREG (let's say 7809) and switch between the 7818 and the 7809, based on whether the transformer currently is outputting 9V or 18V AC.
Would this work or is it a bad idea?
Obviously I could use a separate transformer for the opamp supply voltage but I'm already planning to use a separate lower voltage transformer for the micro controller and stuff and I'd prefer not to have three transformers in the design, if possible.
Also, I don't want any switching regulator action in this design, that's what doesn't make things easier.
Thanks!