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How to Test Diode? Instruction to 11 Types of Diode Testing



Diode is no stranger to any electronic lovers, that’s why it is important to learn how to test a diode to know it’s still good-working or not. In this article today, we are going to introduce the testing method of 11 different kinds of diodes.




Catalog

I. Testing of Normal Diode

II. Testing of Other 11 Types of Diodes

2.1 Testing of Low-power Crystal Diodes

2.2 Testing of Glass-sealed Silicon High-speed Switching Diodes

2.3 Testing of Fast Recovery and Ultra-fast Recovery Diodes

2.4 Testing of Bidirectional Trigger Diode

2.5 Testing of Transient Voltage Suppression Diode (TVS)

2.6 Testing of High-frequency Varistor Diodes

2.7 Testing of Varactor Diode

2.8 Testing of Monochromatic Light-emitting Diodes

2.9 Testing of Infrared Light-emitting Diodes

2.10 Testing of Infrared Receiving Diode

2.11 Testing of Laser Diode

FAQ


I. Testing of Normal Diode

This video shows how to test a diode.


II. Testing of Other 11 Types of diodes


2.1 Testing of Low-power Crystal Diodes


A. Discrimination of positive and negative electrodes

(1) Observe the symbol mark on the housing. Usually, the diode is marked with the symbol of the diode on the housing of the diode, one end with a triangular arrow is the positive electrode, and the other end is the negative electrode.

(2) Observe the color dots on the shell. The case of point contact diodes is usually marked with polar color points (white or red).

Generally, 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.

(3) Based on measurement with a smaller resistance value, the end connected to the black test lead is the positive electrode, and the end connected to the red test lead is the negative electrode.

 

B. Detect the highest working frequency fM. The operating frequency of crystal diodes can be found in the related characteristic table. In practice, the contact wires inside the diodes are often used to distinguish them.

 

For example, point-contact diodes are high-frequency tubes, and surface-contact diodes are mostly low-frequency tubes. In addition, you can also use a multimeter R×1k block to test, generally, the forward resistance is less than 1k mostly in high-frequency tubes.

 

C. Detect the highest reverse breakdown voltage VRM. For alternating current, because of constant changes, the highest reverse working voltage is also the peak alternating current voltage that the diode barriers.

 

It should be pointed out that the highest reverse working voltage is not the breakdown voltage of the diode. Under normal circumstances, the breakdown voltage of the diode is much higher than the maximum reverse working voltage (about twice as high). 


2.2 Testing of Glass-sealed Silicon High-speed Switching Diodes

The method of detecting silicon high-speed switching diodes is the same as that of ordinary diodes. The difference is that the forward resistance of this tube is relatively large. Measured with R×1k electrical barrier, the general forward resistance value is 5k~10k, and the reverse resistance value is infinite.    


2.3 Testing of Fast Recovery and Ultra-fast Recovery Diodes

The method of using a multi-meter to detect fast recovery and ultra-fast recovery diodes is basically the same as that of plastic-encapsulated silicon rectifier diodes. That is, first use the R×1k block to test its unidirectional conductivity. Generally, the forward resistance is about 4.5k, and the reverse resistance is infinite; then use the R×1 block to repeat the test. The general forward resistance is a few k, and the reverse The resistance is still infinite.


2.4 Testing of Bidirectional Trigger Diode

 First, put the multimeter in the R×1k gear, and measure the forward and reverse resistance values of the bidirectional trigger diode should be infinite. If the test leads are exchanged for measurement, the pointer of the multimeter will swing to the right, indicating that the tube under test has a leakage fault.

 

Place the multimeter in the corresponding DC voltage block. The test voltage is provided by a megohmmeter. During the test, shake the megohmmeter, and the voltage value indicated by the multimeter is the VBO value of the tube under test. Then change the two pins of the tested tube, and measure the VBR value in the same way.

 

Finally, compare VBO and VBR. The smaller the difference between the absolute values of the two, the better the symmetry of the tested bidirectional trigger diode.


2.5 Testing of Transient Voltage Suppression Diode (TVS)

First, measure the quality of the tube with a multimeter R×1k block.

 

For unipolar TVS, according to the method of measuring ordinary diodes, the forward and reverse resistance can be measured. Generally, the forward resistance is about 4kΩ, and the reverse resistance is infinite.

 

For the two-way polar TVS, the resistance value between the two pins should be infinite when the red and black test leads are exchanged arbitrarily, otherwise, it means that the tube has poor performance or has been damaged.


2.6 Testing of High-frequency Varistor Diodes

A. Identify the positive and negative poles

The difference in appearance between high-frequency varistor diodes and ordinary diodes is that their color code is different. The color code of ordinary diodes is generally black, while the color code of high-frequency varistor diodes is light. Its polarity law is similar to that of ordinary diodes, that is, the end with the green ring is the cathode, and the end without the green ring is the anode.

 

B. Measure the forward and reverse resistance to judge whether it is good or bad

The specific method is the same as the method of measuring the forward and reverse resistance of ordinary diodes. When measuring with the R×1k block of a 500-type multimeter, the forward resistance of a normal high-frequency varistor diode is 5k~5.5k, and the reverse resistance is infinite.


2.7 Testing of Varactor Diode

Put the multimeter in the R×10k block, no matter how the red and black test leads are interchanged for measurement, the resistance between the two pins of the varactor diode should be infinite. If during the measurement, it is found that the pointer of the multimeter swings slightly to the right or the resistance value is zero, it indicates that the varactor diode under test has a leakage fault or has been broken down.


For the loss of varactor diode capacity or internal open-circuit fault, it is impossible to detect and distinguish with a multimeter. When necessary, the replacement method can be used for inspection and judgment.


2.8 Testing of Monochromatic Light-emitting Diodes

Attach a 1.5V dry battery to the outside of the multimeter, and set the multimeter to R×10 or R×100 gear. This connection is equivalent to connecting a 1.5V voltage to the multimeter in series to increase the detection voltage to 3V (the turn-on voltage of the light-emitting diode is 2V).


When testing, use the two test pens of the multimeter to alternate the two pins contacting the light-emitting diode. If the performance of the tube is good, it must be able to emit light normally once. At this time, the black test lead is connected to the positive electrode, and the red test lead is connected to the negative electrode.


2.9 Testing of Infrared Light-emitting Diodes

A. Distinguish the positive and negative electrodes of infrared light-emitting diodes. Infrared LEDs have two pins, usually the long pin is the anode and the short pin is the cathode. Because the infrared light-emitting diode is transparent, the electrodes in the shell are clearly visible, the wider and larger internal electrode is the negative electrode, and the narrower and smaller one is the positive electrode.


B. Place the multimeter in the R×1k block and measure the forward and reverse resistance of the infrared light-emitting diode. Generally, the forward resistance should be about 30k, and the reverse resistance should be above 500k, so that the tube can be used normally. The larger the reverse resistance, the better.


2.10 Testing of Infrared Receiving Diode


A. Identify pin polarity


(1) Recognize from the appearance. The appearance color of common infrared receiving diodes is black. When identifying the pins, face the light-receiving window, and from left to right, they are positive and negative respectively. In addition, there is a small oblique plane at the top of the tube body of the infrared receiving diode. Usually, the pin with the oblique plane at one end is the negative electrode, and the other end is the positive electrode.


(2) Put the multimeter in the R×1k block to check the method of judging the positive and negative electrodes of ordinary diodes, that is, exchange the red and black test leads to measure the resistance between the two pins of the tube. When it is normal, the resistance value obtained It should be one big and one small. Based on the one with the smaller resistance value, the pin connected to the red test lead is the negative pole, and the pin connected to the black test pen is the positive pole.


B. The detection performance is good or bad. Use a multimeter to electrically block and measure the forward and reverse resistance of the infrared receiving diode. According to the value of the forward and reverse resistance, the quality of the infrared receiving diode can be preliminarily judged.


2.11 Testing of Laser Diode

Place the multimeter in the R×1k block, and determine the order of the pins of the laser diode according to the method of detecting the forward and reverse resistance of ordinary diodes.


But pay attention to the detection, because the forward voltage drop of the laser diode is larger than that of the ordinary diode, so when detecting the forward resistance, the pointer of the multimeter is only slightly deflected to the right, and the reverse resistance is infinite.


FAQ


1. What is diode and its symbol?

Diode, an electrical component that allows the flow of current in only one direction. In circuit diagrams, a diode is represented by a triangle with a line across one vertex.


2. What is special about a diode?

Some semiconductor junctions, composed of special chemical combinations, emit radiant energy within the spectrum of visible light as the electrons change energy levels. Simply put, these junctions glow when forward biased. A diode intentionally designed to glow like a lamp is called a light-emitting diode, or LED.


3. Are diodes AC or DC?

It allows current to flow easily in one direction, but severely restricts current from flowing in the opposite direction. Diodes are also known as rectifiers because they change alternating current (ac) into pulsating direct current (dc). Diodes are rated according to their type, voltage, and current capacity.


4. Why do we use zener diode?

Zener diodes are used for voltage regulation, as reference elements, surge suppressors, and in switching applications and clipper circuits. The load voltage equals breakdown voltage VZ of the diode. The series resistor limits the current through the diode and drops the excess voltage when the diode is conducting.


5. What is unit of diode?

A diode is not a measurable quantity. Hence,it does not have a unit. Generally,for a diode,we measure characteristics like forward voltage drop,reverse voltage drop and reverse breakdown voltage which are usually measured in Volts.


6. Do diodes have resistance?

Just like a resistor or any other load in a circuit, a diode offers resistance in a circuit. Unlike resistors, though, diodes are not linear devices. This means that the resistance of diodes does not vary directly and proportional to the amount of voltage and current applied to them.


7. Does diode reduce current?

Ideally, diodes will block any and all current flowing the reverse direction, or just act like a short-circuit if current flow is forward. Unfortunately, actual diode behavior isn't quite ideal. Diodes do consume some amount of power when conducting forward current, and they won't block out all reverse current.


8. How are diodes classified?

Diodes are classified according to their characteristics and are offered in a number of different types, including rectifiers, switching diodes, Schottky barrier diodes, Zener (constant voltage) diodes, and diodes designed for high-frequency applications.


9. What is the most common diode?

The most commonly used signal diode is the 1N4148. This diode has a close brother called 1N914 that can be used in its place if you can't find a 1N4148. This diode has a forward-voltage drop of 0.7 and a peak inverse voltage of 100 V, and can carry a maximum of 200 mA of current.


10. What is the difference between a Zener diode and a Schottky diode?

As their switching speed is very high, Schottky diodes recover very fast when the current reverses, resulting in only a very small reverse current overshoot. ... A special type of diode, called the Zener diode, blocks the current through it up to a certain voltage when reverse biased.


11. What is difference between Schottky diode and normal diode?

In the normal rectifier grade PN junction diode, the junction is formed between P type semiconductor to N type semiconductor. Whereas in Schottky diode the junction is in between N type semiconductor to Metal plate. The schottky barrier diode has electrons as majority carriers on both sides of the junction.


12. Why it is called diode?

A diode is called a diode because it has two distinct electrodes (i.e. terminals), called the anode and the cathode. A diode is electrically asymmetric because current can flow freely from the anode to the cathode, but not in the other direction. In this way, it functions as a one-way valve for current.


13. Is a diode the same as a resistor?

Key Difference: A diode is a type of electrical device that allows the current to move through it in only one direction. ... A resistor is an electric component that is used to provide resistance to current in the circuit. They are mostly used to produce heat or light.


14. How much voltage can a diode take?

Silicon diodes have a forward voltage of approximately 0.7 volts. Germanium diodes have a forward voltage of approximately 0.3 volts. The maximum reverse-bias voltage that a diode can withstand without “breaking down” is called the Peak Inverse Voltage, or PIV rating.


15. Can a resistor replace a diode?

Diodes only conduct in one direction whereas resistors conduct in both directions. Without analyzing the actual circuit the results would be unpredictable but, generally speaking, being that diodes & resistors are designed to do different things, substituting one for the other is something you wouldn't want to do.