I am trying to design and build a regulated power supply for my "lab" using transistors and op-amps. I have found many circuits on various websites that all appear similar. I thought I would try to build one piece of the power supply at a time, starting with the constant voltage supply (easier than the current portion, I think). The schematic is below [\$V_1\$ comes from a 4:1 transformer at 120V primary across a 3A diode bridge, giving approximately 28V]:
I know I am missing a filter capacitor on the output of the bridge.
If I was to set the pot to 1 volt at the non-inverting input, the op-amp will adjust its output to obtain 1 volt on the inverting input, which is the same as the emitter. Assuming a base-emitter drop of 0.6 volts, this will cause a current to flow through the collector of approximately 1.1A. But what happens if I put a 1kohm resistor in for the load? I can't push 1A through 1kohm at 1volt. My collector current would have to fall to 1 mA, so does that mean the collector voltage falls with it to get 1mA across the 25 ohm collector resistor? What happens when I short the emitter directly to the negative of the supply, with 1 volt on the non-inverting input? I can't have 1 volt and 0 volt at the same point. This is where I am most confused I think.
Assuming \$\beta = 200\$, a base current of 0.1 mA would flow, meaning I do not need a base resistor and the op-amp should source 0.1 mA okay.