Will a 5V power supply enable a 3V circuit of a bell?
I've designed my Power supply using a 12V step-down transformer and 7805 chip which gives an output voltage of 5V whereas the circuit requires 3V to get operated.
Depending upon how you derive your 12v supply you have enough voltage to arrange an asymmetric ± supply or even a second small negative one. You can use this to return the reference pin of the 7805 to the negative rail instead of zero. With suitable choice of rails you can arrange the output of the regulator to be 3 volts above zero, but 5 volts above the negative rail.
I would prefer to use an LM117 although it is 1.5a it will drop as low as 1.2v -36v. My ST databook says L200 min voltage is 2.85v , thats a bit too close for comfort to 3v.