Art of Electronics 3rd ed. Exercise 2.11
You have +5V and +15V regulated supplies available in a circuit. Design a 5mA npn current sink using the +5V to bias the base. What is the output compliance?
Ic=5mA
Ve≈Vb-0.6≈4.4V
Re=Ve/Ic=4.4/0.005=880Ω
Compliance voltage:
Vc≳ Ve + 0.1V for the transistor to be in the linear region
Vc≳4.4+0.1=4.5V
Vcompliance= 15-4.5≈10.5V
This means that when Vc drops below the compilance voltage the current sink cannot work as expected.
