Zener Diode Calculator | StrokeForge Electronics

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Inputs

Common zener voltages:

Supply voltage (Vin)

Must be greater than Vz

Zener voltage (Vz)

Regulated output voltage

Load current (I_L)

Max current drawn by load

Min zener current (I_{Z min})

Keep >1 mA for stable regulation

Zener max power (P_{Z max})

From zener datasheet

Resistor series

Nearest standard resistor value

Results

Calculated R (exact)

—

R = (Vin − Vz) / (IZ_min + IL)

Nearest standard value

—

E24

Power rating needed: —

Current through R (full load)

—

Zener current (full load)

—

Zener current (no load)

—

Power in R

—

Zener power (worst case)

—

Efficiency (full load)

—

Vin must be greater than Vz.

Zener power exceeds rated maximum — use a higher wattage zener or reduce load current.

Zener power is close to the rated maximum (>70%) — consider a higher wattage device or add a heatsink.

Zener current at full load is very low. Regulation may be unstable — reduce IL or increase IZ_min.

Low efficiency (<50%) — zener regulators are inefficient by design. Consider a linear regulator (LM78xx) or switching regulator for better efficiency.

Circuit Diagram

Common Zener Diodes (E24 Vz series)

Vz	Package	Pmax (typical)	Iz test (mA)	Typical parts
2.4 V	DO-35 / DO-41	500 mW	5	BZX55C2V4, 1N4614
2.7 V	DO-35 / DO-41	500 mW	5	BZX55C2V7, 1N4615
3.3 V	DO-35 / DO-41	500 mW	20	BZX55C3V3, 1N5225B
3.6 V	DO-35 / DO-41	500 mW	20	BZX55C3V6, 1N5226B
3.9 V	DO-35 / DO-41	500 mW	20	BZX55C3V9, 1N5227B
4.3 V	DO-35 / DO-41	500 mW	20	BZX55C4V3, 1N5228B
4.7 V	DO-35 / DO-41	500 mW	20	BZX55C4V7, 1N4732A
5.1 V	DO-35 / DO-41	500 mW	20	BZX55C5V1, 1N4733A
5.6 V	DO-35 / DO-41	500 mW	20	BZX55C5V6, 1N4734A
6.2 V	DO-35 / DO-41	500 mW	20	BZX55C6V2, 1N4735A
6.8 V	DO-35 / DO-41	500 mW	20	BZX55C6V8, 1N4736A
7.5 V	DO-35 / DO-41	500 mW	20	BZX55C7V5, 1N4737A
8.2 V	DO-35 / DO-41	500 mW	20	BZX55C8V2, 1N4738A
9.1 V	DO-35 / DO-41	500 mW	20	BZX55C9V1, 1N4739A
10 V	DO-35 / DO-41	500 mW	20	BZX55C10, 1N4740A
12 V	DO-41	1 W	20	1N4742A, BZX79C12
15 V	DO-41	1 W	17	1N4744A, BZX79C15
18 V	DO-41	1 W	14	1N4746A, BZX79C18
24 V	DO-41	1 W	10.5	1N4749A, BZX79C24
30 V	DO-41	1 W	8.5	1N4752A, BZX79C30

How a zener regulator works

Operating principle

A zener diode conducts in reverse when voltage reaches its zener voltage (Vz), clamping the output. The series resistor R limits current and drops the excess voltage (Vin − Vz). The zener absorbs the difference between the current through R and the load current.

Limitations

Low efficiency — excess power wasted as heat in R and zener
Output voltage varies slightly with load (zener impedance)
Not suitable for high-current loads
Use LM78xx / LM317 for better regulation; switching regulator for efficiency