Application of Multimeter in Crystal Diode Detection
A crystal diode is a device composed of a PN structure with unidirectional conductivity. It exhibits low resistance when conducting in the forward direction, which is called the forward resistance of a transistor. When reverse biased, it exhibits high resistance, which is called the reverse resistance of a transistor. In short, the performance of crystal diodes can be simply judged based on the measurement of unidirectional conductivity.
1. Detection of ordinary diodes
Set the multimeter to the resistance mode of R * 100 or R * 1K, connect the red and black probes of the multimeter to the two ends of the diode respectively. If the measured resistance is relatively small (below several thousand ohms), then swap the red and black probes and connect them to the two ends of the diode. If the measured resistance is relatively large (several hundred thousand ohms), it indicates that the diode has unidirectional conductivity and good quality.
If the forward and reverse resistance of the diode are measured to be very small, even zero, it indicates that there is a short circuit inside the tube; If both the forward and reverse resistance of the diode are measured to be high, it indicates that there is an open circuit inside the tube.
2. Detection of voltage regulator diode
Place the multimeter in the R * 1K range and measure its forward resistance. Connect the black probe of the multimeter to the positive terminal of the voltage regulator diode and the red probe to the negative terminal of the voltage regulator diode; When measuring reverse resistance, the connection of the two probes is exactly opposite. Generally, the forward resistance is several thousand ohms to tens of thousands of ohms, and the reverse resistance is several hundred kiloohms or more.
3. Detection of Light Emitting Diodes
Place the multimeter in the R * 10k range. If the measured forward resistance is within 30K Ω and there is a bright spot on the LED chip with a reverse resistance value greater than several hundred kiloohms, it indicates that the tested LED is performing normally.
