I'm making a 0-±12V 20mA supply for breadboard. Circuit simulates fine with ltspice. How to implement tracking (or tracking ratio) WITHOUT opamp?
I found a schematic here https://groenholdt.net/projects/LAB-PSU/schematic-and-pcb.html but it is a bit difficult for me to understand and extract the relevant part.
I'm thinking of using a ganged dual potentiometer for the voltage control, and another potentiometer to adjust the tracking ratio... saves space.
Any help will be appreciated. (I know how to do it with opamp, just trying to see if it can be done with just one or two transistors... maybe smaller pcb without saving any money, since lm358 are already so cheap.)
PS: At 12V 20mA, the MMBT3904 and MMBT3906 seems to dissipate about 220mW. Will this be a problem? Any tips on if PCB layout (large collector pad) will help? Dissipation will likely be <150mW during normal use. Otherwise will have to put in BD139 / BD140 in darlington configuration (will also increase voltage drop).