Zener and BJT series-pass regulator
Single transistor or Darlington follower with Zener loading and power accounting.
Development preview. Check the assumptions below before relying on a result. Calculations run in your browser.
How it calculates
Assumptions
- Constant effective beta and junction drop; Darlington beta must be entered as a composite gain.
- Output resistance is a small-signal estimate using the final emitter-junction thermal voltage at 25 °C. Check pass-device safe operating area separately.
Worked example
These are the calculator's default inputs. Change any input above to recalculate.
Inputs
- Pass device
- single
- Input voltage
- 12 V
- Zener voltage at reference current
- 5.6 V
- Zener dynamic resistance
- 5 Ω
- Zener reference current
- 0.01 A
- Minimum Zener current
- 0.003 A
- Zener feed resistor
- 330 Ω
- Load current
- 0.1 A
- Effective composite beta
- 100
- VBE per junction
- 0.7 V
Results
- Output voltage
- 4.94139 V
- Zener current
- 0.0182784 A
- Base current
- 0.000990099 A
- Pass-device power
- 0.699565 W
- Zener power
- 0.103116 W
- Feed-resistor power
- 0.122521 W
- Incremental output resistance
- 0.305692 Ω