Diode Code Identification
Diode Code Identification:
How to identify the Diode?
Engineering 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:
 Two letters and three figures
 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:
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.