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To Find the Polarity of a Diode Overview

HolyDumphy
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Introduction

A Diode is an electronic device made of semiconductor materials and has unidirectional conductivity. So how to distinguish the positive and negative poles of the diode? Ordinary diodes (plug-in) can be judged by the length of the pins or the area of the inner piece of the straw hat. Ordinary SMD diodes can be judged according to the negative electrode at the end with the bar on it and so on. Next, here explains how to distinguish polarity of several commonly used diodes in detail.

semiconductor diodes

Zener Diode

Zener Diode

1. From the appearance point of view, the positive electrode of the metal-encapsulated Zener diode body is flat, and the negative electrode is semicircular.

2. One end with a color mark printed on the body of the plastic Zener diode is the negative electrode, and the other end is the positive electrode.

3. For zener diodes with unclear signs, you can also use a multimeter to determine its polarity. Set the multimeter to the position of the diode to be measured. Then adjust leads and measure, the buzzer sounds, the end of the red test lead is positive, and the end of the black test lead is negative.

Schottky Diode

Schottky Diode

1. Check the symbol mark.

The surface of the Schottky diode is generally marked with the symbols, the anode is represented by a triangular arrow symbol, and the other end is the cathode.

2. Check the diode color point.

On the case of point-contact Schottky diodes, there are generally polar colored dots (white or red). The end marked with a colored dot is the positive electrode. Other diodes are marked with a color ring, and the end with the color ring is the negative electrode. Based on the first measurement with a relatively small resistance value, the end connected to the black test lead is the positive pole, and the end connected to the red test pen is the negative pole.

Photodiode

Photodiode

1. Appearance Judgment

For a photodiode packaged in a metal case, there is a bump under the metal, the pin closest to the bump is positive, and the other pin is negative. In some photodiodes, one pin marked with a colored dot is the positive pole, and the other pin is the negative pole. In addition, the two pins of the photodiode are different, the long pin is the positive pole, and the short pin is the negative pole. For rectangular photodiodes, marks are often made to indicate that the direction of the light-receiving surface is positive, and the other direction is negative.

2. Multimeter Detection

For the unclear appearance of the photodiode, a multimeter can be used for detection. The method is as follows: put the multimeter in the “R×1” block, cover the transparent window of the photodiode with a piece of black paper, and separate the red and black test leads of the multimeter. Connected to the two pins of the photodiode, if the pointer of the multimeter deflects to the right, the electrode connected to the black test lead is positive, and the electrode connected to the red test lead is negative. If the pointer does not move during the test, the electrode connected to the red test lead is the positive electrode, and the electrode connected to the black test lead is the negative electrode.

Light-emitting Diode

Light-emitting Diodes

Light-emitting diodes are more commonly used, and the positive and negative poles are easy to distinguish. The long pin is the positive pole, and the short pin is the negative pole. If the pins are the same length, the extremely small metal inside the LED tube body is the positive electrode, and the large piece is the negative electrode.

TVS Diode

TVS Diode

1.TVS diodes are divided into unidirectional and bidirectional, and bidirectional TVS diodes have no polarity. The positive and negative poles of the unidirectional TVS tube are marked, a white bar or a white circle is the negative pole, and the unmarked end is the positive pole.

2.Look at the model number. From the surface of the model, we can judge the polarity. Although different brands have different naming methods, they all have rules.

3.Measure with a multimeter

<1>Measure the gear position of the diode, one side is open in one direction, and both sides have voltage in both directions.

<2> DC measurement, bidirectional symmetry, and only reverse has the avalanche breakdown characteristic.

Varactor Diode

Varactor Diode

Some varactor diodes are painted with a black mark on one end, this end is the negative electrode, and the other end is the positive electrode. There are also varactor diodes with a yellow ring and a red ring coated on both ends of the tube case. One end of the red ring is the positive electrode, and one end of the yellow ring is the negative electrode. You can also use the diode block of a digital multimeter to determine the positive and negative polarity of the diode by measuring the forward and reverse voltage drops.

Step-Recovary Diode

Step-Recovary Diode

The forward characteristic of the step recovery diode is the same as that of the ordinary diode, but the reverse characteristic is different. When the applied voltage is reversed, a large reverse current still flows through the step diode, and it switches to the cut-off state at a very fast speed until a certain moment. Its reverse characteristic is step-like.

Crystal Diode

crystal diode

The crystal diode is composed of a PN junction, two electrode leads and a tube case. Use wire leads to seal on both sides of the PN junction. The conduction direction of the PN junction is from the P-type semiconductor to the N-type semiconductor (P is the positive electrode and N is the negative electrode). The PN junction conducts forward and ends reversely.

Further Reading

11 Types of Diode Testing Overview

I'm a electronic editor interested in semiconductor as my work. Hope to share and get new ideas from here, if you have any interset of my electronic works, you can visit https://www.kynix.com/Blog/.

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