Glass body (DO-35) · Ø 1.85 × 3.8 mmDumet lead (copper-clad)Cathode bandPins

Black DO-41 body or orange glass body, cathode stripe, “4733A” text
DO-41 body ≈ 5 × 2.7 mm · Example shown: 5.1 V zener, DO-35 glass case

Diodes

Zener diode

In simple terms

What is this?

In reverse, a bucket that overflows at a certain voltage; it drains the excess and keeps the level constant.

What is it for?

Keeps the voltage at a fixed value; works as a simple reference or protection.

Where do you see it?

Inside power supplies and small regulator circuits.

How do you spot it?

A black or glass cylinder with a strip at one end; it looks like a rectifier diode and is told apart by the code on it.

Caution:

Do not connect it without a series resistor, or too much current will burn it out; remember that it works in the reverse direction.

Technical definition

A diode that starts conducting at a certain reverse voltage (the zener voltage) and tries to hold that voltage constant. Together with a series resistor it forms a simple regulator or reference source. In the forward direction it behaves like a normal diode.

Zener voltage5.1 V

Power1 W

Example1N4733A

Schematic symbol Same in IEC and ANSI

IEC 60617: the drawing style used in Türkiye and Europe.

Pins 2

1Anode (A)Unstriped side; on a regulator it goes to groundA

2Cathode (K)Striped side; on a regulator it goes to plus after the series resistorK

Features typical

Zener voltage: 5.1 V (±5%, at 49 mA)
Power: 1 W
Test current: 49 mA
Max. zener current: ≈178 mA
Dynamic resistance: ≤ 7 Ω
Streak: 1N4728A–1N4764A: 3.3–100 V
Example part: 1N4733A (5.1 V, 1 W)

Common mistakes

Not adding a series resistorA zener doesn't limit current by itself. Without a series resistor it draws excess current and burns out.

Fitting it in the forward directionA zener works in reverse: the cathode (stripe) goes to plus. Fit it the normal way round and you only see ≈0.7 V.

Not calculating the powerZener power is P = Vz × Iz. Try not to exceed half of the 1 W limit.

Test with a multimeter

Test whether this part is good with the multimeter on the measurement screen.

Take a measurement

Where it is used

Simple 5.1 V referenceInput overvoltage clampingFixed threshold for a comparatorMOSFET gate protection

Try it in the Lab