Multimeter Testing Methods for General-Purpose Light-Emitting Diodes
Light emitting diode (LED) is a type of light emitting device that directly injects current. It is the result of the emission of photons when stimulated electrons inside a semiconductor crystal return from a high energy level to a low energy level, which is commonly known as spontaneous emission transition.
When a forward bias is applied to the PN junction of an LED, the injected minority carriers and majority carriers (electrons and holes) recombine and emit light It is worth noting that for a large number of particles at high energy levels, each spontaneously emits a column of light waves with an angular frequency of ν=Eg/h, but there is no fixed phase relationship between the light waves in each column, and they can have different polarization directions; And the light emitted by each particle propagates in all possible directions, this process is called spontaneous emission, and its emission wavelength can be expressed by the following equation:
λ(μm)=1.2396/Eg(eV)
Light emitting diodes (LEDs) are generally made of materials such as gallium arsenide and gallium phosphide. It has a PN junction inside and also has unidirectional conductivity, but the light-emitting diode emits light when conducting in the forward direction, and the brightness of the light increases with the increase of the conduction current. The color of the light is related to the wavelength.
Measure with a multimeter in the R × 10K range
Using a pointer multimeter with a 10k Ω range can roughly determine the quality of the light-emitting diode. Normally, the forward resistance of a diode ranges from tens to 200k Ω, and the reverse resistance is ∞. If the forward resistance is 0 or ∞, and the reverse resistance 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.
Use two multimeters to measure together
If there are two pointer multimeters (recommended for 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.
Measurement of external auxiliary 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.
