What is a diode?

A diode is a semiconductor that only allows current to flow in one direction, it is a one way valve for electricity.

Diodes come in all shapes and sizes, the most important difference in them is the current rating, i.e. how much you can push through without overheating and burning the diode up. Here I demonstrate different diodes.

Here I show how to test a diode. Testing is done with a multimeter, an analog multimeter is preffered.

Here is some information on the numbers you may find on a diode.

First Letter

Specifies semiconductor material

Second Letter

Specifies type of device

Subsequent Characters

A

Germanium

B

Silicon

C

Gallium Arsenide

R

Compound materials

A

Diode – low power or signal

B

Diode – variable capacitance

C

Transistor – audio frequency, low power

D

Transistor – audio frequency, power

E

Tunnel diode

F

Transistor – high frequency, low power

G

Miscellaneous devices

H

Diode – sensitive to magnetism

L

Transistor – high frequency, power

N

Photocoupler

P

Light detector

Q

Light emitter

R

Switching device, low power, e.g. thyristor, diac, unijunction

S

Transistor – switching low power

T

Switching device, low power, e.g. thyristor, triac

U

Transistor – switching, power

W

Surface acoustic wave device

X

Diode multiplier

Y

Diode rectifying

Z

Diode – voltage reference

The characters following the first two letters form the serial number of the device. Those intended for domestic use have three numbers, but those intended for commercial or industrial use have letter followed by two numbers, i.e. A10 – Z99.