Diode classification, circuit symbol and multimeter to measure LED positive and negative

1. According to the semiconductor material used, it can be divided into a germanium diode (Ge tube) and a silicon diode (Si tube).

2, according to its different purposes, can be divided into detection diodes, rectifier diodes, Zener diodes, switching diodes, isolation diodes, Schottky diodes, light-emitting diodes, silicon power switching diodes, rotating diodes and so on.

3, according to the die structure, can be divided into point contact diodes, surface contact diodes and planar diodes.

1) Rectifier diode

A diode that rectifies an alternating current source into a direct current is called a rectifier diode.

2) Detector diode

The detector diode is a device for detecting a low frequency signal superimposed on a high frequency carrier, and has high detection efficiency and good frequency characteristics.

3) Switching diode

In pulse digital circuits , the diode used to turn the circuit on and off is called a switching diode. It features short reverse recovery time and can meet the needs of high frequency and ultra high frequency applications.

4) Zener diode

The Zener diode is a surface-bonded crystal diode made of silicon material, which is characterized by the fact that the voltage at the reverse breakdown of the PN junction does not change substantially with the change of current to achieve the purpose of voltage regulation because it can The circuit plays a role of voltage regulation, so it is called a Zener diode (referred to as a voltage regulator tube).

5) Varactor diode

The varactor diode is a nonlinear capacitive element made by utilizing the characteristic that the capacitance of the PN junction changes with an applied bias voltage, and is widely used in microwave circuits such as parametric amplifiers, electronic tuning, and frequency multipliers.

6) Transient voltage suppressor TVS

A solid state diode specifically designed for ESD protection. The TVS diode is connected in parallel with the protected circuit. When the transient voltage exceeds the normal operating voltage of the circuit, the diode avalanches, providing a path for the transient current to protect the internal circuit from excessive voltage breakdown.

7) Light-emitting diode

Made of gallium phosphide or phosphorous arsenide material, it is small in size and positively drives light. Low working voltage, small working current, uniform illumination, long life, red, yellow and green monochromatic light.

8) Schottky diode

The basic principle is to block the reverse voltage with the already formed Schottky on the contact surface of the metal (for example, lead) and the semiconductor (N-type silicon wafer). There is a fundamental difference between the Schottky and PN junction rectification principles. Its pressure resistance is only about 40V. Its speciality is: the switching speed is very fast: the reverse recovery time trr is particularly short. Therefore, a switching diode and a low-voltage high-current rectifier diode can be fabricated.

Two: the characteristics of the diode

The forward and reverse characteristics of the diode are illustrated by simple experiments.

1. Forward characteristics.

In the electronic circuit, the positive pole of the diode is connected to the high potential end, the negative pole is connected to the low potential end, and the diode is turned on. This connection method is called forward biasing. It must be stated that when the forward voltage applied across the diode is small, the diode is still not conducting, and the forward current flowing through the diode is very weak.

Only when the forward voltage reaches a certain value (this value is called "threshold voltage", the xenon tube is about 0.2V, and the silicon tube is about 0.6V), the diode can be turned on. The voltage across the diode remains essentially constant after conduction (the transistor is approximately 0.3V and the silicon tube is approximately 0.7V) and is referred to as the "forward voltage drop" of the diode.

2. Reverse characteristics.

In the electronic circuit, the positive pole of the diode is connected to the low potential end, and the negative pole is connected to the high potential end. At this time, almost no current flows in the diode, and the diode is in an off state. This connection method is called reverse bias. When the diode is reverse biased, there is still a weak reverse current flowing through the diode, called the leakage current. When the reverse voltage across the diode increases to a certain value, the reverse current will increase sharply and the diode will lose its unidirectional conduction characteristics. This state is called diode breakdown.

Three: circuit symbol of the diode

How to distinguish the positive and negative electrodes of self-flashing diodes with a multimeter

Test the positive and negative poles of the self-flashing LED, and use the multimeter R×1kΩ or R×10kΩ (for example, the MF47 multimeter). When using the RXlkQ file, the two red and black test leads are respectively connected to the two leads of the flash LED, and then the red and black test leads are reversed and then the two leads of the flash LED are measured, and the resistance is large once (the needle is also Slightly oscillating), the black pen is connected to the positive pole of the self-flashing diode, and the red pen is connected to the negative pole of the self-flashing diode, as shown in the following figure.

If the R × 10kΩ file is used to measure as described above, the amplitude of the primary hand swing with a large resistance is more than 1cm, and there will be a flash of light in the die. This phenomenon indicates that the polarity of the power supply connected to the self-flashing diode is correct (ie, the black meter is connected to the positive pole of the self-flashing LED), and the circuit begins to oscillate.