Voltage regulator tube
1 job characteristics and application of voltage stabilizing tube called zener diode, physical appearance see below. Usually use the word "V", it is a special manufacturing process of silicon diodes, as long as the reverse current does not exceed the current limit, the pipe work will not be damaged in the breakdown region and reversible breakdown, and the common diode destructive breakdown is different. When the regulator operates in the reverse breakdown region, it uses the steep reverse breakdown characteristics to stabilize the voltage in the circuit.

Integral circuit symbol of voltage regulator tube
The positive characteristic of the volt ampere characteristic curve of the regulator is the same as that of the common diode. Reverse curve in the breakdown region than ordinary diode more steep, which indicates that the breakdown voltage regulator tube, through the current change tube (Iz), and the voltage across the tube changes (Vz) is very small, or keep a fixed value of voltage at both ends of the pipe. Voltage regulator circuit in the main function is to play a stabilizing role.
Volt ampere characteristic curve
2 main parameters of voltage regulator
Stable voltage VZ means the reverse breakdown voltage of the regulator.
The stable current IZ refers to the reference current value of the tube when it is working normally, the value of which is between the maximum current IZmax and the minimum current IZmin in the voltage regulation area. When the current flowing through the tube is less than IZmin, the pipe can not play the role of voltage regulation.
The maximum stable current IZmax refers to the maximum operating current of the regulator, more than Izmax
Dissipation power PZM means the maximum power dissipation of a tube from thermal breakdown. It is approximately equal to the product of the stable voltage and the maximum stable current, i.e., PZM=VZ = IZmax.
Dynamic resistance rZ reflects the performance of the voltage regulator, the smaller the dynamic resistance, the better the performance of voltage regulator.
Temperature coefficient K temperature coefficient reflects the change of stable voltage caused by temperature change.
Two, LED
A light emitting diode is a semiconductor device that converts electrical energy into light energy. The light emitting diode gap and GaAs semiconductor materials, circuit symbols and photos below.

Light emitting diode circuit symbol

Led physical map
As to the light emitting diode with bias current flows through the diode can emit light, this is because the electron and hole junction direct composite release energy results. Many kinds of light emitting diode, according to the color of light can be divided into: red, blue, yellow, green, and blue color light emitting diode and infrared diode eyes cannot see; according to the shape can be divided into: circular, square and so on.
Three, photodiode
Photodiode, also known as photodiode. The photodiode is composed of a PN structure, but its larger PN junction area, through a glass window on the tube shell to receive incoming light. When there is no light, the reverse resistance is very large and the reverse current is very small. When the light is irradiated, the reverse resistance decreases and the reverse current increases.

Photodiode circuit symbol

Photodiode element shape
LED application circuit as shown below.

6V DC voltage indication 220V AC indication
Four, leadless chip diode
Leadless chip diode at both ends of the solder joint element, widely used in electronic products at present, which is characterized by small size, light weight, good performance of high frequency, simple shape, size standard, convenient for automatic assembly.
1 Schottky diode
There are two common types of Schottky diode packaging: one is a chip in the two pin package, see figure (a); the other is a chip SOT-23 package (MMBD), see figure (B).
2 zener diode
Chip zener diode voltage regulator value of 2 ~ 30V, the rated power of 0.5W of the regulator tube in the form of SOT-23, SOT-89 (1W) package, 1W (C).
3 Switching Diode
This kind of tube is used in the digital pulse circuit and the electronic switch circuit. The chip switch tube is divided into two types: single switch diode and compound switch diode
4 composite diode
"Composite diode" refers to a package, contains more than 2 diodes, to meet the different requirements of the circuit, can reduce the number and volume of components at the same time, the combination form of composite diode: common cathode, anode pole, tandem and independent type and other types, as shown below.
Composite diode combination