Detailed explanation of the detection method of ordinary diodes

In electronic components, diodes are not unfamiliar to everyone. Diodes are common and commonly used components in semiconductor electronic circuits. Although the diode is small, it plays a pivotal role in the semiconductor industry. According to the purpose of the diode, it is divided into ordinary diodes and special diodes. Ordinary diodes are divided into rectifier diodes, detector diodes and switching diodes, which are also commonly used. In semiconductor circuits, ordinary diodes often have various problems. Let's introduce two detection methods for ordinary diodes.
1. Measure with an analog multimeter
The detection of ordinary diodes is based on the unidirectional conductivity of the diode. By measuring the forward and reverse resistance of the diode, the quality of the diode can be easily judged. Generally, set the multimeter to the RX1k position, connect the black test lead to the anode of the diode and the red test lead to the cathode of the diode, which is called forward measurement. The resistance value obtained by the forward measurement is called forward resistance, as shown in Figure 1. The measured forward resistance is 5.2kΩ. Generally, the forward resistance value of a diode is several thousand ohms, and the smaller the value, the better. Connect the black test lead of the multimeter to the cathode of the diode and the red test lead to the anode of the diode, which is called reverse measurement. The resistance value obtained by reverse measurement is called reverse resistance. As shown in Figure 2, the measured reverse resistance is infinite. .


Figure 1 Use a pointer multimeter to measure the diode forward


Figure 2 Reverse measurement of diode with pointer multimeter


For a diode, when measuring in the forward direction, if the diode is turned on (the pointer deflects greatly), and when measuring in the reverse direction, the diode does not work (the pointer does not deflect), it means the diode is good. If the resistance value of the diode is 0 during forward or reverse measurement, it indicates that the diode has broken down. If the resistance of the diode is infinite during forward or reverse measurement, it means that the diode is open. If the forward resistance or the reverse resistance are relatively close, the diode has failed.
For detection diodes or low-power rectifier tubes, the multimeter should be set to Rx100, and its forward resistance is about several hundred ohms (silicon tube is several thousand ohms): for rectifier diodes, especially high-power rectifier diodes, the multimeter should be dialed To Rx1k gear, its forward resistance is about ten or a few ohms. When detecting the reverse resistance, in addition to the high-power silicon rectifier diodes, the multimeter should generally be set to the Rx1k gear, and its resistance should be more than several hundred kiloohms.
By the way, it is not advisable to use Rx1k and Rx10k files to detect the positive and negative resistance values of general low-power diodes. This is because the former has a large forward current through the diode, which may burn the tube; the latter has too high a reverse voltage across the diode, which will easily break the tube. In addition, the forward and reverse resistance of the diode varies with the measuring range of the meter (Rx100 or Rx1k), and even the difference is quite large. This is a normal phenomenon.
2. Measure with a digital multimeter
Digital multimeters, like analog multimeters, also have ohm gears. However, due to the different measurement principles of the two, the ohm gears of digital multimeters cannot determine the positive and negative poles of diodes. However, digital multimeters have a dedicated measurement file for diodes that can be used to judge The polarity of the diode. Use a digital multimeter to determine the diode polarity as shown in Figure 3.




Figure 3 Use a digital multimeter to determine the polarity of the diode
(a) No conduction; (b) conduction


When testing and judging, dial the digital multimeter to the special file marked with the symbol of the diode, and then use the red and black test pens to test the two poles of the diode respectively, and the positive and negative measurements will show "1" during the measurement, as shown in Figure 3 (a ), and the number from 100 to 800 is displayed. As shown in Figure 3(b), the measurement that displays the number from 100 to 800 shall prevail. The red test lead is connected to the anode of the diode, and the black test lead is connected to the diode’s negative electrode. In Figure 3, the display "1" indicates that the diode is not turned on, and the display 566 indicates that the diode is turned on, and the current turn-on voltage of the diode is 566mv (that is, 0.566V).
The above two methods are the basic methods for detecting ordinary diodes. When ordinary diodes have malfunctions, I hope to provide you with corresponding methods for reference. In the follow-up, we will continue to introduce other basic knowledge about diodes for everyone to learn and use.