1、 The common diode has a cathode line mark, and one pole is the negative pole;

2、 The long leg of LED is positive, and the short leg is negative. If the feet are the same length, the big point on the inside of the LED is the negative pole, and the small point is the positive pole. Some light-emitting diodes have a small plane, and a lead near the small plane is the negative pole. SMD light-emitting diodes generally have a small bump to distinguish the positive and negative poles. Those with special marks are negative poles, and those without special marks are positive poles.

In the multimeter, the red pen is followed by "+" and the black pen is followed by "-"; When measuring the light-emitting diode, the low barrier cannot be measured. The RX10K gear can be used to measure. Two probes contact the two stages of the diode. If the resistance is low, the black lead is connected to the positive electrode, and the resistance is high, the black lead is connected to the negative electrode. If the light-emitting diode is connected to the TTL module for use, it is generally necessary to connect a 470R step-down resistor in series to prevent damage to the device.

1. The LED with larger identification size has some markings near the pole pins, such as cutting corners, coloring, or different pin sizes. Generally, the marked, small, and short side of the pin is the cathode (i.e. negative electrode), while the smaller size 0805 and 0603 packages have a "T" shape or inverted triangular symbol at the bottom, and the horizontal side of the symbol "T" is the positive electrode; The "edge" of the triangle symbol is positive in polarity, while the "angle" is negative in polarity.

2. When using a multimeter to measure the positive and negative poles of the chip LED, the gear of "R * 10k" must be used for detection. Connect the two probes with the two leads of the LED during detection. If the needle deflects more than half and there is a bright spot in the LED, it means that the chip LED is connected in the positive direction. At this point, the black lead is connected to the positive electrode, and the red lead is connected to the negative electrode. Then connect the two probes to the LED (reverse access type), and the probe will not move. Whether it is forward or reverse access, the meter needle does not move or deflects to the end, indicating that the chip LED is damaged. But for beginners, they don't know how to use a multimeter at all. In fact, we all know that light-emitting diodes with higher power are divided into positive and negative poles. Each pole represents one end, with an extra pin at one end. Upon closer inspection, it can be observed that there is a small hole on this pin. The end with a small hole is the positive electrode, and the other end is the negative electrode.

3. Observe the electrode inside the tube. The smaller one is the positive electrode, while the larger one resembling a bowl is the negative electrode.

4. Look at the missing corner. In the LED energy-saving lamp lighting industry, 5050 chip LED is often used. This kind of chip LED is square. One of the four right angles has a small missing corner. The end with the small missing corner is the negative pole, and the other end is the positive pole. 5. Look at the pin The LED pin is generally long at the positive end and short at the negative end.

3、 Crystal diode

The crystal diode is composed of a PN junction, two electrode leads and a tube shell. On both sides of the PN junction, lead out wires and package them, which is called crystal diode. The letter symbol of crystal diode is V. The conduction direction of PN junction is from P-type semiconductor to N-type semiconductor, that is, P to N conduction (P is positive, N is negative). The PN junction has the characteristics of forward conduction, reverse cutoff, and single-phase conductivity.

Diode package and its direction are shown as follows:

The method of judging diode direction through screen printing on PCB in PCB is summarized as follows:

Normally:

1. The end with a gap is the negative electrode;

2. The end with a horizontal bar is the negative electrode;

3. The end with a white parallel bar is the negative pole;

4. One end of the triangle arrow direction is the negative electrode;

5. One end of the small circle of the plug-in diode screen printing is the negative pole, and the big circle is the positive pole.

In the case of vertical welding, the original body is located in the positive coil

6. The square hole of the plug-in LED is the first pin of the positive pole.