Based on p.30 ARRL vol1&2
Current in Q2 mirrors current in Q1.
Uses:
A) to isolate reference current from the load current.
B) when more than one load current is needed.
While its true that the current is mirrored by Q2 it only applies up to a certain Rref/Rload ratio. In this particular circuit it is Rload<=2k. Try increasing Rload to see what happens to the current mirror.
Modified the circuit to use an AC signal as input to observe how the current is closely mirrored by the Q2, Q3 and Q4 transistors.
The Q3 and Q4 were added to show that loading has minimal effect on the source. Watch how closing sw1 and sw2 has minimal effect on reference current. MS 2023\10.
