I am an student and I have made a power supply which can provide either 18v AC or 28v DC(i use a switch to change the output between ac and dc)
Now I want to add something to allow me to vary the voltage but the only way that I found to be working is to connect it to a potentiometer and use it as a potential divider.so I bought 3 potentiometers (1k,5k,10k) to allow me to change the voltage with different accuracies.It is as if you change the voltage in 2 branches which are connected in parallel and when its providing max output voltage one of the branches is almost shorted out(very low resistance)(assuming no load is connected) so I'm worried if it is going to damage/burn the potentiometers.
The capacitor is an electrolyte 4.7 micro farad and the diodes are rated for 6 amps but I'm only drawing less than 1 amp (lets just assume maximum is 1 amp in this case) and I use 1 single pole double throw switch and 1 double pole double throw switch to safely discharge the cap and change between AC and DC.And this is what I designed as my potential divider.
My question is do I need a fixed resistor connected in series (between R3 and ground ) or not? And is there a better way to have something to provide variable voltage for both ac and dc or not?