11 common tricks: MURF1660AC diode test method

1. Detection of low power crystal diodes

A Identify positive and negative electrodes.

(a) Observe the symbol on the shell. Usually the diode shell is marked with the diode symbol, the end with a triangular arrow is the positive pole, and the other end is the negative pole.

(b) Observe the color dot on the shell. The shell of the point contact diode is usually marked with a polarity color dot (white or red). Generally, the end marked with the color dot is the positive pole. Some diodes are marked with a color ring, and the end with the color ring is the negative pole.

(c) Taking the measurement with smaller resistance as the reference, 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 maximum operating frequency fM.

The operating frequency of crystal diodes can be found in the relevant characteristic table. In practice, it is often distinguished by observing the contacts inside the diode. For example, point contact diodes are high-frequency tubes, and surface contact diodes are mostly low-frequency tubes. In addition, it can also be tested with the multimeter R×1k block. Generally, those with forward resistance less than 1k are mostly high-frequency tubes.

C detects the highest reverse breakdown voltage VRM.

For AC, because it is constantly changing, the maximum reverse working voltage is the AC peak voltage that the diode can withstand. It should be pointed out that the maximum reverse working voltage is not the breakdown voltage of the diode. Generally speaking, the breakdown voltage of the diode is much higher than the maximum reverse working voltage (about twice as high).

2. Detection of glass-sealed silicon high-speed switching diodes

The method of testing silicon high-speed switching diodes is the same as that of testing ordinary diodes. The difference is that the forward resistance of this type of diode is larger. Using an R×1k resistor to measure, the forward resistance value is generally 5k~10k, and the reverse resistance value is infinite.

3. Detection of fast recovery and ultrafast recovery diodes

The method of using a multimeter to test fast recovery and ultra-fast recovery diodes is basically the same as the method of testing 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 a few and the reverse resistance is still infinite.

4. Detection of bidirectional trigger diode

Set the multimeter to the R×1k position, and the forward and reverse resistance values ​​of the bidirectional trigger diode should be infinite. If the multimeter pointer swings to the right when the test leads are swapped, it means that the tube under test has a leakage fault. Set the multimeter to the corresponding DC voltage position. The test voltage is provided by the 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 swap the two pins of the tube under test, and use the same method to measure the VBR value. Finally, compare VBO with VBR. The smaller the difference between the absolute values ​​of the two, the better the symmetry of the bidirectional trigger diode under test.

5. Transient Voltage Suppression Diode (TVS) Detection

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

For a bidirectional TVS, the resistance value between the two pins measured by arbitrarily swapping the red and black test leads should be infinite. Otherwise, it means that the tube has poor performance or is damaged.

6. Detection of high frequency varistor diode

A Identify the positive and negative poles

The difference between the high-frequency varistor diode and the ordinary diode in appearance is the color code. The color code of the ordinary diode is generally black, while the color code of the high-frequency varistor diode is light. Its polarity rule is similar to that of the ordinary diode, that is, the end with the green ring is the negative pole, and the end without the green ring is the positive pole.

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

The specific method is the same as the method of measuring the forward and reverse resistance of an ordinary diode. When using a 500-type multimeter with the R×1k block for measurement, the forward resistance of a normal high-frequency varistor diode is 5k~55k, and the reverse resistance is infinite.

7 Detection of varactor diode

Set the multimeter to the R×10k position. No matter how the red and black test leads are swapped, the resistance between the two pins of the varactor diode should be infinite. If the multimeter pointer swings slightly to the right or the resistance is zero during the measurement, it means that the varactor diode under test has a leakage fault or has been broken down. The multimeter cannot detect and judge the loss of capacity of the varactor diode or the internal open circuit fault. If necessary, the replacement method can be used for inspection and judgment.

8 Detection of Monochrome LEDs

Attach a 15V dry battery to the outside of the multimeter and set the multimeter to R×10 or R×100. This connection is equivalent to connecting a 15V voltage in series to the multimeter, increasing the detection voltage to 3V (the turn-on voltage of the light-emitting diode is 2V). When testing, use the two probes of the multimeter to alternately touch the two pins of the light-emitting diode. If the tube performs well, it must be able to emit light normally once. At this time, the black probe is connected to the positive pole and the red probe is connected to the negative pole.

9 Detection of infrared light emitting diodes

A. Identify the positive and negative electrodes of infrared light-emitting diodes. Infrared light-emitting diodes have two pins, usually the longer pin is the positive electrode and the shorter pin is the negative electrode. Because infrared light-emitting diodes are transparent, the electrodes inside the tube shell are clearly visible. The wider and larger internal electrode is the negative electrode, while the narrower and smaller one is the positive electrode.

B. Set the multimeter to R×1k and measure the forward and reverse resistance of the infrared light-emitting diode. Usually, the forward resistance should be around 30k and the reverse resistance should be above 500k. Only then can the tube be used normally. The larger the reverse resistance, the better.

10 Detection of infrared receiving diode

A. Identify pin polarity

(a) Identify from the appearance. Common infrared receiving diodes are black in color. When identifying the pins, facing the light receiving window, from left to right, they are positive and negative. In addition, there is a small chamfered plane on the top of the infrared receiving diode. Usually, the pin with this chamfered plane is the negative pole, and the other end is the positive pole.

(b) Set the multimeter to the R×1k position and use the method used to identify the positive and negative electrodes of ordinary diodes to check, that is, swap the red and black test leads twice to measure the resistance between the two pins of the diode. Under normal circumstances, the resistance value should be one large and one small. The one with the smaller resistance value shall prevail. The pin connected to the red test lead is the negative pole, and the pin connected to the black test lead is the positive pole.

B. Good or bad detection performance.

Use the resistance block of a multimeter to measure the forward and reverse resistance of the infrared receiving diode. Based on the values ​​of the forward and reverse resistance, you can preliminarily determine whether the infrared receiving diode is good or bad.

11 Laser diode detection

Set the multimeter to R×1k and determine the pin arrangement order of the laser diode by following the method of testing the forward and reverse resistance of an ordinary diode. However, it should be noted that since the forward voltage drop of a laser diode is larger than that of an ordinary diode, when testing the forward resistance, the multimeter pointer will only slightly deflect to the right, while the reverse resistance will be infinite.