# Voltage regulator circuit calculations (zener diodes, transistors)

The circuit given in the following Figure is a voltage regulator which is used to supply a constant voltage. It has the following properties: Vin = 20V, Rs = 1 kΩ, R1 = 200 Ω, R2 = 800 Ω, R3 = 2 KΩ, RL = 100 Ω, Vz = 5.6V, βdc = 100.

Vin = 20V Rs = 1kΩ R1 = 200Ω R2 = 800Ω R3 = 2kΩ Rl = 200Ω Vz = 5.6V βdc = 100

Vf = 0.7V (?) Vout = 5.6V (?) Ic2 = ? Ib2 = ? Ic1 = ? Iz = ? PQ2 = ? Pz = ? RL = ?

I am having immense trouble with this one. So far, Vz = Vout when using a Zener diode? So 5.6v? Vf = 0.7v? (Threshold voltage of a diode?)

Any help would be appreciated!

• Have you tried to simulate the circuit, poke around and see what values affects which parameters? Commented Dec 12, 2023 at 9:52
• I have replicated the circuit and placed current probes but I am getting 0 on all of them. I'm out of my depth. Commented Dec 14, 2023 at 19:44
• Please share a screenshot. This problem should be entirely solvable in SPICE. Commented Dec 14, 2023 at 20:08