Basic knowledge and detection methods of crystal diodes 5

2. Detection of ordinary light-emitting diodes

(1) Use a multimeter to test. Using a pointer multimeter with a 10k Ω range can roughly determine the quality of the light-emitting diode. Under normal circumstances, the forward resistance of a diode ranges from tens to 200k Ω, while the reverse resistance has a value of ∝. If the forward resistance value is 0 or ∞, and the reverse resistance value is very small or 0, it is prone to damage. This detection method cannot physically observe the light emission of the light-emitting tube, as the 10k Ω range cannot provide a large forward current to the LED.

If there are two pointer multimeters (preferably of the same model), it can better check the light emission of the LED. Connect the "+" terminal of one multimeter to the "-" terminal of the other multimeter using a wire. The remaining "-" pens are connected to the positive pole (P area) of the tested LED, and the remaining "+" pens are connected to the negative pole (N area) of the tested LED. Both multimeters are set to the X 10 Ω range. Under normal circumstances, it can light up normally after being connected. If the brightness is very low or even does not emit light, both multimeters can be set to * 1 Ω. If it is still very dark or even does not emit light, it indicates that the LED has poor performance or is damaged. It should be noted that the two multimeters should not be placed at x 1 Ω at the beginning of the measurement to avoid excessive current and damage to the light-emitting diode.

(2) Measurement of external power supply. The photoelectric and electrical characteristics of light-emitting diodes can be accurately measured using a 3V voltage regulator or two series connected dry batteries and a multimeter (either pointer or digital). To achieve this, the circuit can be connected as shown in Figure 10. If the measured VF is between 1.4 and 3V and the luminous brightness is normal, it can indicate that the luminescence is normal. If VF=0 or VF ≈ 3V is measured and no light is emitted, it indicates that the light-emitting tube is broken.