Diode Code Identification

Diode Code Identification:

How to identify the Diode?

Diode_PinoutsEngineering students coming out of college are well familiar with the Resistor code identification. But they are not familiar with the diode code identification. This post will solve that problem. Generally in diodes, some letter with some numbers are mentioned. What does it mean?  Before understanding about the identification of diode codes, let us quickly refresh the basics of diode.

What is Diode?
A diode is so-called because it has two terminals: the anode, which is the positive terminal, and the cathode, which is the negative terminal. In the case of a p-n junction diode the anode is the p-type and the cathode is the n-type. It is the simplest of semiconductor devices. It is having characteristics that closely match those of a simple switch. It is made up of various materials like Silicon, Germanium, Silicon Carbide(SiC).

In addition to the PN junction diode, other types of diodes are also manufactured for specific applications. These special diodes are two terminal devices with their doping levels carefully selected to give the desired characteristics. Some of the special diodes areZener diode, Schottky diode,Varactor Diode, Tunnel diode, Gunn Diode, Light Emitting Diode(LED) etc.

Apart from Schottky Diode, rest of the diodes are made by forming P-type semiconductor to N-type semiconductor. A schottky diode is formed between a semiconductor and a metal layer. The charge storage that limits the reverse recovery of junction diodes does not occur in schottky diodes and reverse recovery is very fast. These diodes are characterized by a lower forward voltage than silicon junction diodes and a larger reverse leakage current. With their low forward voltage and rapid reverse recovery they are widely used in low-voltage switching power supplies. The forward biased schottky diode’s V-I characteristics is of the same form as for a junction diode.

The European System(ES) Diode Code Identification consists of an alphanumeric code as per below:
[1] Two letters and three figures
[2] Three letters and two figures
The first naming method is for General purpose diodes and the second option is for special purpose diodes.
As shown in the above figure, mostly cathode terminal is identified with the help of marking of the stripe.

First letter = Semiconductor material
A – Germanium
B – Silicon
C – Gallium Arsenide
D – Photodiodes

Second Letter = Application
A – General Purpose diode
B – Variable capacitance diode
E – Tunnel diode
P – Photo diode
Q – Light Emitting Diode
T – Controlled Diode
X – Varactor Diode
Y – Power rectifier
Z – Zener Diode

Third letter – The third letter does not have any particular significance. The letter is used to mention the specialized application of the diode.

Zener Diode Code Identification:

Zener Diodes  have an additional letter which will appear after the numbers. This letter denotes the tolerance of the zener voltages. The following letters are used for this purpose:

A ±1%
B ±2%
C ±5%
D ±10%
Zener diodes have additional characters which will indicate the zener voltage.
Ex: 5V1 indicate 5.1V

Now try to identify the following diodes

A quick question?
How do you identify the cathode and anode terminals in the thru hole LED?
In LEDs, the cathode terminal lead is longer than anode terminal. By comparing the length of the terminals we can identify the terminals of the LED.

Read Further:
How Zener Diode works as a Voltage Regulator?
Power BJT: Introduction, Structure, Characteristics
Comparison of MOSFET with BJT

Thanks for reading…

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11 Responses

  1. mahesh says:

    I did not understand the diode code identification please explain clearly dont mind

  2. mykal says:

    Not sure if I am geting this BZY88C4V7 is B – Silicon Z – Zener Diode C ±5% 4.7v

  3. Himanshu says:

    i have 62Z schottky diode can u tell me with whom should i replace the same.

  4. Ace says:

    I have a diode with a marking of A4V5N, I cant find the datasheet of this. Is this the correct part number?

    Please help

  5. RONALD says:

    Pls,.help me to find a replacement for 3358r diode use for fire alarm switch series to the control panel with 24v supply thank you

  6. ah wie says:


  7. HyLite says:

    0 for 6. Seems the article fell short.

  8. vanlewen, d says:

    reads ‘the letter after the number means’……..hello . Never says what the numbers mean. practicly worthless info without that!

  9. Biju says:

    Please tell me about GM 54 (look like diode)
    SMD type i search in the internet.
    Please help me any knows

  10. Trevor Allen says:

    I have a Diode that has failed, it is simply a almost spherical in shape, colour is creamy white with a black line at one end, there are four blue dots evenly spaced around the circumference of the white body. the circuit board is from an old Japanese picture Monitor and is connected to the Fly back transformer.
    Can you help in identifying this

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