An LED (light emitting diode) is a semiconductor diode,specifically a p-n junction, that emits light when a positive current flows from the anode (labelled ‘+’, i.e., positive) to the cathode (labelled ‘-’, i.e., negative).
The symbol of the diode is usually represented by an arrow that meets the vertical line at the front end,and the direction of the arrow indicates the direction of current flow that can make the light emitting diode.Sometimes additional arrows are included in the symbol to clearly indicate the direction in which the LED emits light.
Most packages for LEDs include wires and a plastic lens,not the LED itself.The long lead on the package represents the anode or positive terminal of the light emitting diode.When viewing the LED from the bottom,the wire near the bottom plane of the package is the cathode side.
Light emitting diode failure characteristics:
- Open circuit: diode positive and negative poles are disconnected, forward and reverse resistance is infinite, resulting in an open circuit.
- Breakdown: diode positive and negative path, positive and negative resistance is the same or close to the resistance is not infinity. The performance of the breakdown varies from circuit to circuit.
- Increased forward resistance: diode forward resistance is too large, resulting in an increase in the signal voltage drop, the output signal voltage is reduced, and easy to heat damage. This failure affects the unidirectional conductivity of the diode.
- Decrease in reverse resistance: diode reverse resistance becomes smaller, the same damage to its unidirectional conductivity.
- Performance degradation: although the diode is not obvious open-circuit or breakdown phenomenon, but performance degradation, affecting circuit stability and output signal voltage.
How to check led with multimeter:
Multimeters are divided into digital and pointer multimeters.When testing the quality of a lamp,a pointer multimeter is usually more appropriate than a digital multimeter because a digital multimeter outputs a lower voltage and a smaller current,which is not enough to light the beads on an light emitting diode,while a pointer multimeter outputs a higher voltage and a larger current,which is enough to make the beads on an LED lamp glow.The following are specific steps for testing the lamp:
The lamp is usually composed of two parts:one is the driving power supply,which is used to provide stable voltage and current for the light emitting diode;the other part is the lamp strip,which mainly plays the role of light emission.When encountering a damaged lamp,first check the driving power supply. Set the pointer multimeter to DC voltage or current,according to the nameplate information on the drive power supply,measure its output voltage and current is within the normal range.If it is not within the normal range,it means that the drive power supply has been damaged,and it needs to be disassembled and overhauled in accordance with the method of repairing the switching power supply,until the voltage and current return to normal.
Drive power supply repair,the next test the quality of the strip.Specific method is: the pointer multimeter adjusted to the resistance X1k gear to light up the lamp on the light emitting diode.When measuring the LED lamp beads,you need to pay attention to its positive and negative poles.Usually,the black pen connects the positive pole of the lamp bead,the red pen connects the negative pole, at this time the lamp bead should be normal light.If the lamp bead is not bright, dim or bright, it should be replaced so as not to affect the service life of the light emitting diode.
When replacing the led light emitting diode,pay attention to the power and polarity of the lamp beads,it is best to choose the same type of lamp beads,because different models of lamp beads can withstand different currents,long time use is easy to damage.When replacing the lamp beads,it will be more convenient to use a hot air gun (blowing chrome iron) for dismantling and installing,because the heat dissipation area of the light strip is large,and it may be inconvenient to dismantle it by using ordinary electric chrome iron and easy to damage the circuit board.
