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Close the switch to start. Use the two way switch to toggle between the two loads.
Typically, a linear regulator would require two error amplifiers and one subtractor in order to realise the Constant Current (CC) and Constant Voltage (CV) modes. In such a system, CV error amplifier is dominant under normal operating conditions; in the event of an overcurrent, the CC error amplifier assumes control and manipulates the CV error amplifier into thinking that it's outputting a voltage higher that what is required, thereby making it reduce the output voltage and hence limiting the output current. An example of such a system can be found here: https://everycircuit.com/circuit/5992318428250112
In this example, a single error amplifier takes care of both CC and CV. How? It's achieved simply by "multiplexing" the output current and voltage signals to the same error amplifier. By multiplexing, I mean using diode to connect the two signal to the same error amplifier, so that the higher voltage signal reaches the error amp.
Let us see how this works. Under normal operating conditions, voltage feedback is higher than the current feedback, so the diode "multiplexer" allows the voltage feedback signal to be seen by the error amp. Thus, the output voltage is kept at the set voltage.
But when the output current exceeds a certain value, the current feedback signal becomes greater than the voltage feedback signal (just slightly higher, enough to make it through the diode "multiplexer") and is now operated on by the error amp. The error amp reduces the output voltage to prevent any further increase in output current, thus limiting it. This further reduces the voltage feedback signal, due to which it definitely cannot have an influence on what the op amp does.
A diode is connected in series with the reference voltage in order to compensate for the diodes connected to the feedback networks. The exact, same diode must be used. Placing them in thermal contact with each other also helps.
PS: I have not tested this circuit on a breadboard.
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