Diode detection methods and experience
- Aug 02, 2022
Detection of low power crystal diodes
A) Distinguish positive and negative electrodes
Observe the symbols on the housing. The diode symbol is usually marked on the housing of the diode, with the triangular arrow at one end being the positive electrode and the other end being the negative electrode.
Observe the color spots on the casing. On the housing of point-contact diodes, a polar color dot (white or red) is usually marked. Generally, the end marked with a colored dot is the positive electrode. Some diodes are marked with a color ring, and the end with the color ring is the negative electrode.
Subject to the measurement with the 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 operating frequency fM
The operating frequency of a crystal diode can be found in the relevant characteristic table. In practice, it is often used to observe the antenna inside the diode to distinguish it. For example, point-contact diodes belong to high-frequency tubes, while surface-contact diodes are mostly low-frequency tubes. In addition, you can also use the multimeter R×1k block for testing. Generally, those with a forward resistance less than 1K are mostly high-frequency tubes.
C) Detect the highest reverse breakdown voltage VRM
For alternating current, because it is constantly changing, the highest reverse working voltage is the peak alternating voltage that the diode can withstand. It should be pointed out that the highest reverse working voltage is not the breakdown voltage of the diode. In general, the breakdown voltage of a diode is much higher (about twice as high) than the highest reverse working voltage.
Testing glass-encapsulated silicon high-speed switching diodes
The method for testing silicon high-speed switching diodes is the same as for normal diodes. The difference is that the forward resistance of this tube is larger. Measured with R×1k electrical barrier, the general forward resistance value is 5K ~ 10K, and the reverse resistance value is infinite.
Detection of fast recovery, ultrafast recovery diodes
The method of detecting fast recovery and ultrafast recovery diodes with a multimeter is basically the same as that of detecting plastic-encapsulated silicon rectifier diodes. That is, first use the R×1k block to test its unidirectional conductivity. Generally, the forward resistance is about 45K, and the reverse resistance is infinite. Then use the R×1 block to test again. Generally, the forward resistance is several, and the reverse resistance is still the same. to infinity.
Detection of bidirectional trigger diodes
Put the multimeter in the R×1K block, 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 swings to the right, indicating that the tube under test has a leakage fault.
Put the multimeter in the corresponding DC voltage range. The test voltage is provided by a megohmmeter. During the test, shake the megohmmeter, the voltage value indicated by the multimeter is the VBO value of the tube under test. Then swap the two pins of the tube under test and measure the VBR value in the same way. Finally, compare VBO with VBR. The smaller the difference between the absolute values of the two, the better the symmetry of the tested bidirectional trigger diode.
Detection of Transient Voltage Suppression Diodes (TVS)
Use the multimeter R×1K to measure the quality of the tube. 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 bidirectional polar type TVS, the resistance value between the two pins should be infinite when the red and black test pens are exchanged arbitrarily, otherwise, the performance of the tube is poor or damaged.