Top-left corner: Follower
Vc = Vb - 0.6V
Top-right corner: Current source - fixed (the emitter resistor was added)
Ie = (V b - V be) / R emitter
(Variable resistor can be changed to show that Ic / I e is fixed)
https://en.m.wikipedia.org/wiki/Current_source (in the "Zener diode current source" section.)
Bottom-left corner: Amplifier
Ice is controlled by Vb. A current source with a "current sensing" collector resistor.
Bottom-right: The switch
Ib = 10 * Ice_min (base current 10x overdriven)
