Voltage Regulator Circuit

Maybe you can find something here....

https://electronicspost.com/dc-voltage-regulator-circuit/

If you identify what the acronym ICVR (or ICUR) stands for I might be able to help. If this stands for Integrated Circuit Voltage Regulator then the question is between which two leads (1,2 or 2,3) will the integrated circuit maintain a fixed voltage of presumably 5V? [I suspect the voltage regulation is across 2,3.]

Hint: What's the voltage between pins 2 and 3 of the voltage regulator IC?

I know pins 2 &3 are 5 volts, but how does R3 affect the total output voltage, also what the heck is the leftmost ICVR doing in the cicuit?

If pins 2 and 3 have 5v between them and R3 is at it's mid position then you can work out the voltage across R3 (assuming no current flows into or out of pin2.
Ignore ICVR 'cos I dunno what its doing either!
Del

Now we are getting somewhere.

For the time being let's forget about the upstream ICVR and make the assumption that the voltage applied to the downstream ICVR is large enough for the downstream ICVR to regulate 5V at pins 2 & 3. We must also make the assumption that the input impedance of pin 2 of these ICVRs must be at least two orders of magnitude greater than the value of any of these resistors. In other words the current flowing into pin 2 is neglidgeable. (This tiny current can induce another problem but lets ignore that for now.) With the wiper of R3 set to exactly midpoint the voltage across half of R3 (aka ICVR V_2,3) will be 5V therefore the voltage across all of R3 will be ....

Now this analysis makes the critical assumption that the voltage applied to the downstream ICVR is large enough for regulation. Every ICVR has some voltage drop across their input to output terminals when they are regulating. This voltage will change depending on the IC design. When they are not regulating but still functioning this voltage drop approaches zero, depending on the amount of current drawn. The current flowing into the downstream regulator must flow through R2. The maximum voltage across R2 is set by the upstream ICVR to 5V. The upstream ICVR is therefore current limiting the downstream components to 5V/R2. A voltage regulator has been converted to a current regulator.

Now there are a few additional concerns one will have to investigate like power dissipation, temperature stability, frequency stability (if the load changes in value) an accomplished engineer will consider to make a real circuit but real circuits almost never appear in an exam.

OK, another hint: Pins 2 and 3 on the leftmost ICVR have 5 volts or less between them. Suppose R2 = 5 ohms and you short-circuit your load. How much current will flow?

Maybe it will help to understand how the ICVR works. If the voltage between pins 2 and 3 is less than 5 volts, it is turned on and conducts current between pins 1 and 3. When the 2-3 voltage reaches 5 volts, it starts to turn off. When the 2-3 voltage is greater than 5 volts it is turned off.

When it is used to regulate voltage, the voltage regulator is at the point where it is partially on, partially off. If the output voltage is too high, the regulator starts shutting down, lowering the output voltage. If the output voltage is too low, the regulator starts conducting more to raise the output voltage.

The leftmost regulator is a current limiter. It is normally turned on (pins 2-3 less than 5 volts). If the amount of current causes the drop across R2 to exceed 5 volts, the regulator starts shutting down, limiting the current. The current limit value is controlled by the value of R2.

Ok now it makes sense. The first icvr is like a fuse, the second one controls the output voltage, which i now think is going to be 10 vdc, if the second half of R3 also has 5 volts across it.

Thanks for all the helpful answers.

Assumes the load is small enough that the unknown R2 does not cause the upstream regulator to current limit.

10 volts, R2 sets the maximum current.