Introduction
A diode is a two-terminal electronic component that conducts current primarily in one direction (asymmetric conductance); it has low (ideally zero) resistance in one direction, and high (ideally infinite) resistance in the other. A diode vacuum tube or thermionic diode is a vacuum tube with two electrodes, a heated cathode and a plate, in which electrons can flow in only one direction, from cathode to plate. A semiconductor diode, the most common type today, is a crystalline piece of semiconductor material with a p–n junction connected to two electrical terminals.[5] Semiconductor diodes were the first semiconductor electronic devices. The discovery of asymmetric electrical conduction across the contact between a crystalline mineral and a metal was made by German physicist Ferdinand Braun in 1874. Today, most diodes are made of silicon, but other materials such as gallium arsenide and germanium are used.
Article Core
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Purpose
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Introduce what the diode is.
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Application
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Semiconductor industry.
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Keywords
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Diode.
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Catalog
Introduction
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1. Definition of Diode
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2. Volt-ampere Characteristics of Diode
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3. Forward Characteristics of Diode
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4. Reverse Characteristics of Diode
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5. Rectifier Circuit
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5.1 One-way Half-wave Rectifier Circuit
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5.2 Full Wave Rectifier Circuit
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Types of Diode
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Rectifier Diode
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Detection Diode
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Switch Diode
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Zener Diode
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Fast Recovery Diode
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Schottky Barrier Diode
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Transient Voltage Suppression Diode
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Light Emitting Diode
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Avalanche Diode
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DIAC
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Varactor Diode
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Operating Principle of Diode
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Diode Function
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Identification and Detection of Diode
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Diode Identification
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Diode Detection
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Main Parameters of Diode
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1. Maximum Rectifier Current (IF)
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2. Highest Reverse Working Voltage (Udrm)
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3. Reverse Current (Idrm)
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4. Dynamic Resistance (Rd)
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5. Highest Working Frequency (Fm)
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6. Voltage Temperature Coefficient (αuz)
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Parameter Symbols
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Basic Concepts of Diode
1, Definition of Diode
The diode consists of a die, a package and two electrodes. The die is a PN junction. A lead is drawn at each end of the PN junction, and a plastic diode, glass or metal material is used as the package to form a crystal diode, as shown in the following figure. The electrode drawn in the P region is referred to as a positive electrode or an anode, and the electrode extracted in the N region is referred to as a negative electrode or a cathode.
2. Volt-ampere Characteristics of Diode
The volt-ampere characteristic of a diode is the relationship between the voltage applied across the diode and the current flowing through the diode. The curve used to qualitatively describe the relationship between the two is called the volt-ampere characteristic curve. The volt-ampere characteristics of the silicon diode observed by the transistor plotter are shown in the figure below.
3. Forward Characteristics of Diode
1) When the applied forward voltage is small, the diode exhibits a large resistance, the forward current is almost zero, and the curve OA segment is called a non-conducting region or a dead region. Generally, the dead zone voltage of the silicon tube is about 0.5 volt, and the dead zone voltage of germanium is about 0.2 volt. This voltage value is also called the threshold voltage or the threshold voltage.
2) When the applied forward voltage exceeds the deadband voltage, the electric field in the PN junction is almost cancelled, the resistance of the diode is small, the forward current begins to increase, and enters the forward conduction region, but the voltage is not proportional to the current, for example, AB. segment. The forward current increases rapidly with the increase of the applied voltage. For example, the characteristic curve of the BC section is steep, and the volt-ampere relationship is approximately linear, and is in a fully conducting state.
3) The forward voltage at both ends after the diode is turned on is called the forward voltage drop (or tube voltage drop) and is almost constant. The tube pressure drop of the silicon tube is about 0.7V, and the tube pressure drop of the germanium tube is about 0.3V.
4. Reverse Characteristics of Diode
1) When the diode is subjected to a reverse voltage, the internal electric field of the PN junction is strengthened, and the diode exhibits a large resistance, and there is only a small reverse current. In practical applications, the smaller the reverse current, the larger the reverse resistance of the diode and the better the reverse cutoff performance. Generally, the reverse saturation current of a silicon diode is below several tens of microamps, the germanium diode is several hundred microamperes, and the high power diode is slightly larger.
2) When the reverse voltage increases to a certain value, the reverse current sharply increases and enters the reverse breakdown region, and its corresponding voltage is called the reverse breakdown voltage. If the current is too large after the diode is broken down, the tube will be damaged. Therefore, the reverse voltage of the diode must not exceed the breakdown voltage except for the Zener diode.
5. Rectifier Circuit
5.1 One-way Half-wave Rectifier Circuit
The diode is like an automatic switch. When u2 is positive half cycle, the power supply is automatically connected to the load. When u2 is negative half cycle, the power supply and load are automatically cut off. Therefore, as shown in the figure below, the pulsating DC voltage uo with the same direction and size change on the load is shown in the figure below. Since this circuit has an output only in the positive half cycle of u2, it is called a half-wave rectification circuit. If the polarity of the rectifier diode is reversed, a negative DC ripple voltage can be obtained.
5.2 Full Wave Rectifier Circuit
Rectification principle:
Set the voltage on the secondary side of the transformer to:
1) When u2 is positive half cycle, the potential at point A is the highest, the potential at point V is the lowest, diodes V1 and V3 are turned on, V2 and V4 are turned off, and the current path is A→V1→RL→V3→B.
2) When u2 is negative half cycle, the potential at point B is the highest, the potential at point A is the lowest, diodes V2 and V4 are on, V1 and V3 are off, and the current path is B→V2→RL→V4→A.
It can be seen that in a period of change of u2, the current from top to bottom always flows through the load RL, and the waveform of the voltage and current is a full-wave pulsating DC voltage and current, as shown in the following figure.
Types of Diode
There are many types of diodes: according to materials, there are germanium diodes, silicon diodes, gallium arsenide diodes, etc.; according to the manufacturing process can be divided into surface contact diodes and point contact diodes; according to different uses can be divided into rectifier diodes, detection diodes, Zener diodes, varactors, photodiodes, light-emitting diodes, switching diodes, fast recovery diodes, etc.; the type of connection can be divided into semiconductor junction diodes, metal semiconductor contact diodes, etc.; Conventional packaged diodes, special packaged diodes, etc. The following uses the application as an example to introduce the characteristics of different types of diodes.
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