Multimeter to measure the causes of LED lamp beads do not light up
LED, also known as light-emitting diode is a type of diode, so the diode has the same characteristics of light-emitting diodes.
Diode Characteristics
Diode has forward conduction reverse up to the characteristics, that is, it only allows the current from one end of the diode to flow to the other end; if the direction of the opposite, then the current will be blocked can not pass. For a diode to achieve forward conduction and reverse cut-off, one condition must be met - the voltage applied in the forward direction is greater than the conduction voltage.
We can think of the diode as an iron door, the iron door is only allowed to push open from the outside to the inside, and in turn from the inside to the outside can not be pushed. This is analogous to the unidirectional conduction characteristic of a diode.
Similarly, because this iron gate is heavy, although it can be pushed open from the outside in, but it needs to apply a certain force to do so. This is analogous to the conduction voltage of a diode.
Measuring light-emitting diodes with a multimeter
The multimeter has a diode mode, which is usually combined with the beep mode. The no-load voltage (i.e., the voltage between the two pens when the multimeter is not connected to a resistor) of the diode file of a digital multimeter is very low, generally about 3V, which may vary slightly from one multimeter to another.
Different colours and models of light-emitting diodes have different conduction voltages, generally the voltage drop of red, yellow and orange light-emitting diodes is about 1.8-2.2V; white, green, blue and pink light-emitting diodes have a voltage drop of about 2.7-3.3V; and LED light beads for home use are generally about 3V.
Summary
Because different light-emitting diode conduction voltage is not the same, this parameter range is very large, so the multimeter to measure the LED light beads do not light this is very normal. Even if the same multimeter to measure the different colours of the LED lamp beads, their brightness is not the same, generally the brightest red, blue darkest, purple can not even light up.
It can be seen that the multimeter measurement LED lamp beads do not light, may be the cause of the pen and the diode positive and negative poles are reversed.
For the pointer multimeter, the black pen connected to the diode positive, red pen connected to the diode negative; for the digital multimeter, the red pen connected to the diode positive, black pen connected to the diode negative.
If the multimeter is connected to the correct case, the multimeter LED lamp beads do not light up, the main reason is that the multimeter output voltage is not enough, the diode conduction voltage is high, it is recommended to change to × 100 gear or × 1K gear measurement.
