1. Diode identification
Crystal diodes are commonly represented by VD and numbers in circuits, such as VD5 for diodes numbered 5. In national standard circuits, the commonly used symbols for diodes are simple to identify: the negative pole of a low-power diode is usually marked with a color ring on the surface; Some diodes also use the "P" and "N" symbols to determine the polarity of the diode, where "P" represents the positive pole and "N" represents the negative pole; Metal encapsulated diodes usually have diode symbols printed on their surfaces that match their polarity; LED usually uses pin length to identify positive and negative electrodes, with the long pin being positive and the short pin being negative The surface of the rectifier bridge is usually marked with the internal circuit structure or the names of the AC input and DC output terminals. The AC input terminal is commonly represented by "AC" or "~"; The DC output terminal is usually represented by the "~" symbol Due to the diverse shapes of SMD diodes, there are also various ways to label their polarity: in SMD diodes with leads, the end of the tube with a white color ring is the negative electrode; In SMD diodes with leads and colorless rings, the longer end of the lead is the positive electrode; In lead-free SMD diodes, the end with a ribbon or notch on the surface is the negative electrode
2. Diode detection
When using a pointer type multimeter to detect a diode, the black probe with a smaller value is connected to the positive end and the red probe is connected to the negative end.
. If the forward and reverse resistances are both infinite, it indicates that the diode has been opened and damaged; If both the forward and reverse resistances are 0, it indicates that the diode has been short circuited and damaged. Under normal circumstances, the forward resistance of germanium diodes is approximately 1.6k When using a digital multimeter to measure a diode, the red lead is connected to the positive pole of the diode, and the black lead is connected to the negative pole of the diode. At this point, the measured resistance value is the forward conduction resistance of the diode, which is exactly the opposite of the probe connection method of a pointer type multimeter If using the diode block of a digital multimeter to detect diodes is more convenient: place the digital multimeter in the diode block, and then connect the negative pole of the diode to the black lead of the digital multimeter, and the positive pole to the red lead. At this time, the display screen will displayFunction of testing report:
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