Diode is one of the earliest semiconductor devices, and its application is very wide. Especially in various electronic circuits, the use of diodes and resistors, capacitors, inductors and other components are reasonably connected to form circuits with different functions, which can achieve a variety of functions such as AC rectification, modulation signal detection, limiting and clamping, and voltage regulation of the power supply voltage.
Whether it is in the common radio circuit or in other household electrical products or industrial control circuits, traces of diodes can be found.
Characteristics and applications of diodes
Almost in all electronic circuits, semiconductor diodes are used, it plays an important role in many circuits, it is one of the earliest semiconductor devices, and its application is also very wide.
Diode application
1. Rectifier diode
By using a diode unidirectional conductivity, alternating current can be converted into pulsating direct current in a single direction.
2. Switch components
Under the action of forward voltage, the resistance of the diode is very small and it is in the on-state, which is equivalent to a switched-on switch. Under the action of reverse voltage, the resistance is very large and is in a cut-off state, like a disconnected switch. Using the switching characteristics of diodes, various logic circuits can be formed.
3. Limiting element
After the diode is switched on, its forward voltage drop remains basically unchanged (0.7V for the silicon tube and 0.3V for the germanium tube). By using this characteristic, the signal amplitude can be limited to a certain range as a limiting element in the circuit.
4. Relay diode
It plays a relay role in inductive loads such as inductance and relay of switching power supply.
5. Detection diode
It acts as a detector on the radio.
6. Varactor diode
Used in the high-frequency head of television.
How diodes work?
The crystal diode is a p-n junction formed by P-type semiconductor and N-type semiconductor, which forms a space charge layer on both sides of its interface and has a self-built electric field. When there is no applied voltage, the diffusion current caused by the difference of carrier concentration on both sides of the p-n junction and the drift current caused by the self-built electric field are equal and in electric equilibrium. When there is a forward voltage bias, the mutual suppression of the external electric field and the self-built electric field increases the carrier diffusion current and causes the forward current. When there is reverse voltage bias outside, the external electric field and the self-built electric field are further strengthened, forming a reverse saturation current I0 which is independent of the reverse bias voltage in a certain reverse voltage range. When the applied reverse voltage is high to a certain extent, the electric field strength in the p-n junction space charge layer reaches a critical value, resulting in a carrier doubling process, a large number of electron hole pairs, resulting in a large value of reverse breakdown current, called the breakdown phenomenon of diodes.
Type of diode
There are many types of diodes, according to the semiconductor material used, can be divided into germanium diodes (Ge tubes) and silicon diodes (Si tubes). According to its different uses, it can be divided into detection diode, rectifier diode, voltage regulator diode, switching diode, isolation diode, Schottky diode, light emitting diode and so on. According to the core structure, it can be divided into point contact diode, surface contact diode and plane diode. Point-contact diode is a very thin metal wire pressed on the surface of a smooth semiconductor chip, through a pulse current, so that one end of the wire and the chip firmly sintered together to form a "PN junction". Because it is a point contact, only a small current is allowed to pass through (not more than a few tens of MA), which is suitable for high-frequency small current circuits, such as radio detection. The "PN junction" area of the face-contact diode is large, allowing the passage of a large current (several amps to tens of amps), which is mainly used in the "rectification" circuit that converts alternating current into direct current. Planar diode is a special silicon diode, which can not only pass large current, but also has stable and reliable performance, and is mostly used in switching, pulse and high-frequency circuits.
Diode application circuit
1.Diode simple DC voltage regulator circuit
Diode simple voltage regulator circuit is mainly used in some local DC voltage supply circuit, because the circuit is simple, low cost, so it is widely used.
In the diode simple voltage regulator circuit, the main use of the diode tube pressure drop is basically unchanged.
The tube pressure drop characteristics of the diode: the tube pressure drop is basically unchanged after the diode is switched on, and the tube pressure drop is about 0.6V for the silicon diode and about 0.2V for the germanium diode.
2.Diode temperature compensation circuit
It is well known that the PN junction has a pressure drop of about 0.6V (referring to the silicon PN junction) after conduction, and the PN junction also has a temperature-dependent property: The pressure drop at both ends of the PN junction decreases slightly with the increase of temperature, and the higher the temperature is, the more the decrease is. Of course, the absolute value of the voltage drop at both ends of the PN junction is quite small for 0.6V, which can be used to form a temperature compensation circuit.
Diode, also known as crystal diode, diode for short, there is a PN junction inside the semiconductor diode with two lead terminals, this electronic device in accordance with the direction of the applied voltage, with one-way current conductivity. Generally speaking, a crystal diode is a p-n junction interface formed by the sintering of a P-type semiconductor and an N-type semiconductor.
I. Classification according to structure
Semiconductor diodes mainly rely on PN junctions to work. The point contact type and Schottky type, which are inseparable from the PN junction, are also included in the range of general diodes. Including these two models, according to the characteristics of the PN structure, the crystal diode is classified as follows:
1. Point contact diode
Point-contact diodes are formed by pressing a metal needle on a single chip of germanium or silicon and then passing the current method. Therefore, the electrostatic capacity of the PN junction is small, and it is suitable for high-frequency circuits. However, compared with the junction type, the point-contact type diode has poor forward and reverse characteristics, so it can not be used for high currents and rectification. Because of its simple construction, it is cheap. For the detection, rectification, modulation, mixing, and limiting of small signals and other general purposes, it is a wide range of applications.
2. Bond diode
Bonded diodes are formed by fusing a filament of germanium or silicon onto a single wafer or silver. Its characteristics are between point-contact diodes and alloy diodes. Compared with the point-contact type, although the PN junction capacity of the bond-type diode is slightly increased, the forward characteristics are particularly good. It is used as a switch and is sometimes used for detection and power supply rectification (not more than 50mA). In the bond type diode, the diode that is fused with gold wire is sometimes called the gold bond type, and the diode that is fused with silver wire is sometimes called the silver bond type.
3. Alloy diode
PN junction is formed by alloying indium, aluminum, and other metals on a single crystal of N-type germanium or silicon. Small forward voltage drop, suitable for high current rectification. Because of its large electrostatic capacity when the PN junction is reversed, it is not suitable for high-frequency detection and high-frequency rectification.
4. Diffusion diode
In a high-temperature P-type impurity gas, a single crystal of N-type germanium or silicon is heated so that one part of the surface of the single crystal becomes P-type. Due to the small forward voltage drop of the PN junction, it is suitable for high-current rectification. Recently, the mainstream use of high-current rectifiers has shifted from the silicon alloy type to the silicon diffusion type.
5. Mesa diode
Although the production method of the PN junction is the same as that of the diffusion type, only the PN junction and its necessary parts are retained, and the unnecessary parts are corroded with drugs. The rest of it takes on a surface shape, hence the name. In the initial production, the mesa type is made of semiconductor materials using the diffusion method. Therefore, this mesa type is also called the diffusion mesa type. For this type, it seems that there are very few product models for high current rectification and many product models for small current switches.
6. Planar diode
On a semiconductor single wafer (mainly N-type silicon single wafer), the P-type impurity is diffused, and the PN junction is formed by selectively diffusing only a part of the oxide film on the surface of the silicon wafer. Therefore, there is no need for drug corrosion to adjust the PN junction area. The semiconductor gets its name because the surface is made flat. Moreover, the PN-bound surface, because it is covered by an oxide film, is recognized as a type of good stability and long life. Initially, the semiconductor material used is formed by the epitaxial method, so the planar type is also called the epitaxial planar type. For planar diodes, it seems that there are few models used for high-current rectification, and many models for small-current switching.
7. Alloy diffusion diode
It is a kind of alloy type. Alloy materials are easily diffused materials. The material that is difficult to make can be over diffused with the alloy by cleverly mixing impurities, so as to obtain the proper concentration distribution of impurities in the formed PN junction. This method is suitable for manufacturing high-sensitivity varactor diodes.
8. Epitaxial diode
Diode formed by making PN junction by the process of epitaxial surface length. It takes a lot of skill to make it. Because the distribution of different concentrations of impurities can be controlled freely, it is suitable for the manufacture of high-sensitivity varactor diodes.
9. Schottky diode
The basic principle is: at the contact surface of a metal (such as lead) and a semiconductor (N-type silicon wafer), the Schottky is formed to block the reverse voltage. There are fundamental differences in the principle of rectification between the Schottky and PN junctions. Its voltage resistance is only about 40V. Its advantages are: the switching speed is very fast: the reverse recovery time is particularly short. Therefore, switching diodes and low-voltage high-current rectifier diodes can be made.
There are many types of diodes, according to the semiconductor material used, which can be divided into germanium diodes (Ge tubes) and silicon diodes (Si tubes). According to its different uses, it can be divided into detection diode, rectifier diode, voltage regulator diode, switching diode, isolation diode, Schottky diode, light emitting diode, silicon power switching diode, rotating diode, and so on. According to the core structure, it can be divided into a point contact diode, a surface contact diode, and a plane diode. Point-contact diode is a very thin metal wire pressed on the surface of a smooth semiconductor chip, through a pulse current, so that one end of the wire and the chip firmly sintered together to form a "PN junction". Because it is a point contact, only a small current is allowed to pass through (not more than a few tens of MA), which is suitable for high-frequency small current circuits, such as radio detection.
II. Classification according to use
1. Diode for detection
In terms of principle, taking out the modulation signal from the input signal is detection, and taking the size of the rectification current (100mA) as the boundary is usually called detection if the output current is less than 100mA. Germanium material point contact type, operating frequency up to 400MHz, small forward voltage drop, small junction capacitance, high detection efficiency, good frequency characteristics, 2AP type. Diodes similar to point-contact detection can be used in addition to detection, but also for limiting, clipping, modulation, mixing, switching, and other circuits. There are also two diode assemblies for frequency modulation detection with good characteristic consistency.
2. Rectifier diode
In principle, the DC that derives the output from the input AC is rectified. With the size of the rectification current (100mA) as the boundary, the output current greater than 100mA is usually called rectification. In junction type, the operating frequency is less than KHz, and the maximum reverse voltage is from 25 volts to 3000 volts A to X A total of 22 stops. The classification is as follows: ① silicon semiconductor rectifier diode type 2CZ, ② silicon bridge rectifier type QL, ③ 2CLG type for TV high voltage silicon stack operating frequency of nearly 100KHz.
3. Diode for limiting amplitude
Most diodes can be used as limiters. There are also specialized limiting diodes such as those used for protective meters and high-frequency Zener tubes. In order to make these diodes have a particularly strong effect of limiting sharp amplitudes, diodes made of silicon materials are usually used. There are also components for sale that combine a number of necessary rectifier diodes in series to form a whole, depending on the need to limit the voltage.
4. Modulation diode
It usually refers to a diode dedicated to ring modulation. It is a combination of four diodes with good forward characteristic consistency. Even though other varactor diodes have modulation uses, they are usually used directly for frequency modulation.
5. Mixing diode
When using diode mixing mode, Schottky type, and point-contact type diodes are mostly used in the frequency range of 500 ~ 10,000 Hz.
6. Diode for amplification
With diode amplification, there is rough amplification relying on negative resistance devices such as tunnel diodes and bulk effect diodes, and parametric amplification using varactor diodes. Therefore, amplification diodes usually refer to tunnel diodes, bulk effect diodes, and varactor diodes.
7. Switching diode
There are logic operations for use at small currents (10mA degree) and switching diodes for magnetic core excitation for use at hundreds of mA. Small current switching diodes are usually a bit of contact type and bond type diodes, but also at high temperatures may also work as silicon diffusion type, mesa type, and plane type diodes. The advantage of switching diodes is that the switching speed is fast. The Schottky diode has a very short switching time, so it is an ideal switching diode. 2AK type point contact for medium-speed switching circuit; 2CK planar contact for high-speed switching circuit; For switching, limiting, clamping, or detection circuits; Schottky (SBD) silicon high current switch, small forward voltage drop, fast speed, high efficiency.
8. Varactor diode
Small power diodes for automatic frequency control (AFC) and tuning are called varactor diodes. Japanese manufacturers also have many other names. The electrostatic capacity of the PN junction is changed by applying reverse voltage. Therefore, it is used for automatic frequency control, scanning oscillation, frequency modulation, and tuning. Usually, although the silicon diffusion type diode is used, special diodes such as alloy diffusion type, epitaxial combination type, and double diffusion type can also be used, because these diodes have a particularly large rate of change of electrostatic capacity for voltage. The junction capacitor changes with the reverse voltage VR, replacing the variable capacitor, and is used as a tuning circuit, oscillation circuit, and phase-locked loop, which is often used in the channel conversion and tuning circuit of the TV high-frequency head, mostly made of silicon material.
9. Frequency multiplier diode
For the frequency multiplication of the diode, the frequency multiplication depends on the varactor diode, and the frequency multiplication depends on the step (that is, the sharp change) diode. The frequency multiplier varactor diode is called a variable reactor, variable reactor, and automatic frequency control varactor diode working principle is the same, but the reactor structure can withstand high power. Step diodes are also known as step recovery diodes, and the reverse recovery time is short when switching from on-off to off, so its advantage is that the transfer time becomes significantly short quickly. If a sinusoidal wave is applied to a step diode, then the output waveform is suddenly clipped due to the short tt (transfer time), so many high-frequency harmonics can be generated.
10. Voltage regulator diode
It is a product that replaces the voltage regulator electronic diode. Made into a diffused or alloyed form of silicon. It is a diode whose reverse breakdown characteristic curve changes rapidly. Made for use as control voltage and standard voltage. The terminal voltage (also known as Zener voltage) when the diode works from about 3V to 150V, according to every 10%, can be divided into many levels. In terms of power, there are also products from 200mW to more than 100W. Working in the reverse breakdown state, silicon material, dynamic resistance RZ is very small, generally 2CW type; When two complementary diodes are connected in series in reverse to reduce the temperature coefficient, it is type 2DW.
Crystal diodes, also known as semiconductor diodes, were invented by Americans in 1947. Inside the semiconductor diode there is a PN junction and two outlet ends. This electronic device has a unidirectional current conductivity in the direction of applied voltage. Most of today's most common diodes use semiconductor materials such as silicon or germanium.
Then let's look at the classification of diodes.
11. PIN Diode
This is a crystal diode constructed by sandwiching a layer of intrinsic semiconductors (or semiconductors with low concentrations of impurities) between the P and N regions. The I in PIN is the English abbreviation of the meaning of "eigenvalue". When the operating frequency exceeds 100MHz, due to the storage effect of a few carriers and the transit time effect in the "intrinsic" layer, the diode loses the rectification effect and becomes an impedance element, and the impedance value changes with the bias voltage. At zero bias or DC reverse bias, the impedance in the "eigen" region is very high; In DC forward bias, the "eigen" region presents a low impedance state due to carrier injection. Therefore, the PIN diode can be used as a variable impedance element. It is often used in high-frequency switching (i.e. microwave switching), phase shifting, modulation, limiting and other circuits.
12. Avalanche Diode
It is a transistor that can produce high-frequency oscillations under the application of an applied voltage. The working principle of high frequency oscillation is a Luoan: the use of avalanche breakdown to inject carriers into the crystal, because the carrier needs a certain time to cross the chip, so its current lags behind the voltage, there is a delay time, if the transit time is properly controlled, then there will be a negative resistance effect on the current and voltage relationship, resulting in high frequency oscillation. It is often used in oscillating circuits in the microwave field.
13. Esaki (Tunnel Diode)
It is a crystal diode with tunnel effect current as the main current component. Its base materials are gallium arsenide and germanium. The N-type region of the P-type region is highly doped (that is, high concentration of impurities). The tunnel current is generated by the quantum mechanical effects of these degenerate semiconductors. There are three conditions for the tunnel effect to occur: (1) Fermi level is located in conduction band and full band; (2) The space charge layer width must be very narrow (less than 0.01 micron); The holes and electrons in the P-type and N-type regions of degenerate semiconductors have the possibility of overlapping at the same energy level. Esaki diode is a double-terminal active device. Its main parameters are peak-to-valley current ratio (IP/PV), where the subscript "P" represents "peak"; The subscript "V" stands for "valley". Esaki diodes can be used in low noise high frequency amplifiers and high frequency oscillators (operating frequencies up to the millimeter band), and can also be used in high-speed switching circuits.
14. fast turn-off (Step Recovary Diode)
It is also a diode with a PN junction. Its structural feature is that there is a steep impurity distribution area at the PN junction boundary, thus forming a "self-service electric field". Because PN junction conducts electricity with a few carriers at forward bias voltage, and has charge storage effect near PN junction, its reverse current needs to undergo a "storage time" before it can be reduced to the minimum value (reverse saturation current value). The "self-electric field" of the step recovery diode shortens the storage time, makes the reverse current cut off quickly, and produces rich harmonic components. The comb spectrum generation circuit can be designed by using these harmonic components. Fast turn-off (step recovery) diodes are used in pulse and higher harmonic circuits.
15. Schottky Barrier Diode
It is a diode with a "metal semiconductor junction" with Schottky characteristics. The forward starting voltage is low. In addition to the material, the metal layer can also be made of gold, molybdenum, nickel, titanium and other materials. Its semiconductor materials are silicon or gallium arsenide, mostly N-type semiconductors. The device is conducted by a large number of carriers, so its reverse saturation current is much larger than that of a PN junction with a small number of carriers. Because the few carriers in Schottky diodes have little storage effect, their frequency response is limited only by the RC time constant, so it is an ideal device for high frequency and fast switching. It operates at frequencies up to 100GHz. In addition, MIS (metal-insulator-semiconductor) Schottky diodes can be used to make solar cells or light-emitting diodes.
16. Damping diode
With high reverse working voltage and peak current, small forward voltage drop, high frequency high voltage rectifier diode, used in TV line scan circuit for damping and boost rectifier.
17. Transient voltage suppression diode
TVP tube for rapid overvoltage protection of the circuit, divided into bipolar and unipolar two, according to the peak power (500W-5000W) and voltage (8.2V ~ 200V) classification.
18. Double base diode (single junction transistor)
It is a three-terminal negative resistance device with two bases and one emitter. It is used in tension oscillation circuit and timing voltage readout circuit. It has the advantages of easy frequency adjustment and good temperature stability.
19. Light emitting diodes
Made of gallium phosphide, gallium phosphide arsenide material, small size, positive drive light. Low working current, low working current, uniform light, long life, red, yellow, green monochromatic light.
III. Classification according to characteristics
Point-contact diodes are classified as follows by forward and reverse characteristics.
1. Generally use point contact diode
This diode, as the title says, is usually used in detection and rectification circuits, and is an intermediate product whose forward and reverse characteristics are neither particularly good nor particularly bad. Such as: SD34, SD46, 1N34A and so on belong to this category.
2. High reverse voltage point contact diode
It is a product with high maximum peak reverse voltage and maximum DC reverse voltage. Used in detection and rectification of high voltage circuits. Diodes of this type generally have poor or average forward characteristics. In point-contact germanium diodes, there are SD38, 1N38A, OA81 and so on. This type of germanium diode has a limited voltage resistance. For higher requirements, there are silicon alloys and diffusion types.
3. Gigh reverse resistance point contact diode
The forward voltage characteristics are the same as those of ordinary diodes. Although its reverse voltage resistance is also particularly high, the reverse current is small, so its special feature is high reverse resistance. Used in high input resistance circuit and high resistance load resistance circuit, in terms of germanium material high reverse resistance diode, SD54, 1N54A and so on belong to this type of diode.
4. Gigh conduction point contact diode
It is the opposite of the high reverse resistance type. Its reverse characteristics, though poor, make the forward resistance sufficiently small. For high conduction point contact diodes, there are SD56, 1N56A and so on. For the diode with high conduction bond, better characteristics can be obtained. This type of diode, in the case of particularly low load resistance, the rectification efficiency is higher.
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