How to use a multimeter to detect light-emitting diode LED
Light-emitting diode (LED) is a direct current injection light-emitting device, is a semiconductor crystal within the excited electrons from the high-energy level back to the low-energy level, the result of the emission of photons, which is usually referred to as spontaneous emission jump. When the PN junction of the LED is forward biased, the injected minority carriers and the majority carriers (electrons and holes) compound and emit light. It is worth noting that, for a large number of particles in the high energy level of each of them are spontaneously emitted a column of a column of angular frequency of ν = Eg / h of light waves, but the columns of light waves do not have a fixed phase relationship between the different directions of polarisation, and each particle emitted by the propagation of the light along all possible directions, this process is called spontaneous emission. The emission wavelength can be expressed by the following formula.
λ(μm)=1.2396/Eg(eV)
Light emitting diodes (LEDs) are generally made of materials such as gallium arsenide and gallium phosphide. Its internal existence of a PN junction, also has a unidirectional conductivity, but the light-emitting diode will emit light in the forward conduction, the brightness of the light with the increase in the conduction current and enhancement of the colour of the light and wavelength.
Ordinary light-emitting diode multimeter detection method:
With the number of Fluke digital multimeter R × 10K file measurement
The use of × 10kΩ block pointer multimeter can be roughly determine the good and bad light-emitting diodes. When normal, the diode forward resistance resistance value of tens to 200kΩ, the value of the reverse resistance is ∝. If the forward resistance value of 0 or ∞, the reverse resistance value is very small or 0, it is easy to damage. Kind of detection methods, can not field to see the light-emitting situation of the light-emitting diode, because × 10kΩ block can not provide a large forward current to the LED.
With two multimeter with the measurement
If there are two pointer multimeter (preferably the same type) can better check the light-emitting diode light-emitting situation. Use a wire to connect the "+" terminal of one multimeter to the "-" terminal of the other. The remaining "-" pen connected to the positive pole of the measured light-emitting diode (P area), the remaining "+" pen connected to the negative pole of the measured light-emitting diode (N area). Two multimeter are set × 10Ω block. Under normal circumstances, the normal light can be connected. If the brightness is very low, or even do not emit light, the two multimeter are dialled to × 1Ω if, if still very dark, or even do not emit light, then the light-emitting diode performance ** or damage. It should be noted that you can not begin to measure the two multimeter placed in the × 1 Ω, so as not to overcurrent, damage to the light-emitting diode.
External auxiliary power supply measurement
With 3V regulated source or two series-connected dry cell and multimeter (pointer or digital can be) can be more accurate measurement of light-emitting diode light, electrical characteristics. To do this, connect the circuit as shown in Figure 10. If the measured VF between 1.4 ~ 3V, and the light-emitting brightness is normal, it can be said that the light-emitting normal. If the measured VF = 0 or VF ≈ 3V, and does not emit light, that the light-emitting tube is bad.
