Classification of crystal diodes

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Classification of crystal diodes

Classification by use 1. Detection diode 　　In principle, extracting the modulated signal from the input signal is detection. Taking the size of the rectified current (100mA) as the boundary, the output current less than 100mA is usually called detection. Germanium material point contact type, operating frequency can reach 400MHz, small forward voltage drop, small junction capacitance, high detection efficiency, good frequency characteristics, is 2AP type. Similar to the point contact type, the detection diode can be used for limiting, clipping, modulation, mixing, switching and other circuits in addition to detection. There are also two diode assemblies with good characteristic consistency for FM detection . 2. Rectification diode 　　In principle, getting the output DC from the input AC is rectification. Taking the size of the rectified current (100mA) as the boundary, the output current greater than 100mA is usually called rectification. Surface junction type, operating frequency less than KHz, the maximum reverse voltage is from 25V to 3000V, divided into 22 levels from A to X. The classification is as follows: ① Silicon semiconductor rectifier diode 2CZ type, ② Silicon bridge rectifier QL type, ③ 2CLG type used for TV high voltage silicon stack with working frequency of nearly 100KHz. 3. Limiting diode 　　Most diodes can be used as limiters. There are also special limiting diodes such as those used for protecting instruments and high-frequency Zener diodes . In order to make these diodes have a particularly strong function of limiting sharp amplitudes, diodes made of silicon materials are usually used. There are also such components for sale: according to the need to limit the voltage, several necessary rectifier diodes are connected in series to form a whole . 4. Modulation diodes 　　Usually refers to diodes dedicated to ring modulation. It is a combination of four diodes with good forward characteristic consistency. Even if other variable capacitance diodes have modulation purposes, they are usually used directly for frequency modulation. 5. Mixing diodes When using the diode mixing method, Schottky type and point contact type diodes 　　are mostly used in the frequency range of 500 to 10,000Hz . 6. Diodes for Amplification 　　Diode amplification generally includes amplification by negative resistance devices such as tunnel diodes and body effect diodes, and parametric amplification by varactor diodes. Therefore, diodes for amplification usually refer to tunnel diodes, body effect diodes, and varactor diodes. 7. Diodes for Switching 　　There are switching diodes for logic operations used at low currents (about 10mA) and magnetic core excitation used at hundreds of milliamperes . Low-current switching diodes usually include point contact type and key type diodes, as well as silicon diffusion type, table type, and planar type diodes that can work at high temperatures . The specialty of switching diodes is fast switching speed. The switching time of Schottky diodes is very short, so they are ideal switching diodes. 2AK type point contact is used for medium-speed switching circuits; 2CK type planar contact is used for high-speed switching circuits; used for switching, limiting, clamping or detection circuits; Schottky (SBD) silicon large current switch, small forward voltage drop, fast speed, high efficiency. 8. Varactor diodes Small power diodes used for automatic frequency control (AFC) and tuning are called varactor diodes. Japanese manufacturers also have many other names. By applying reverse voltage, the electrostatic capacitance of its PN junction changes. Therefore, it is used for automatic frequency control, scanning oscillation, frequency modulation and tuning. Usually, although silicon diffusion diodes are used, special diodes such as alloy diffusion type, epitaxial bonding type, double diffusion type, etc. can also be used, because the change rate of the electrostatic capacitance of these diodes is particularly large for voltage . The junction capacitance changes with the reverse voltage VR, replacing the variable capacitor, and is used as a tuning circuit, oscillation circuit, and phase-locked loop. It is often used in the channel switching and tuning circuit of the high-frequency head of a TV set, and is mostly made of silicon material. 9. Frequency multiplication diodes 　　As for the frequency multiplication effect of diodes, there are frequency multiplication relying on varactor diodes and frequency multiplication relying on step (i.e., rapid change) diodes . The variable capacitance diode used for frequency multiplication is called a variable reactor. Although the working principle of the variable reactor is the same as that of the variable capacitance diode used for automatic frequency control, the structure of the reactor can withstand high power. The step diode is also called the step recovery diode. The reverse recovery time trr when switching from on to off is short. Therefore, its feature is that the transition time to rapidly turn off is significantly short. If a sine wave is applied to the step diode, then because tt (transition time) is short, the output waveform is abruptly cut off, so many high-frequency harmonics can be generated. 10. Zener diode 　　It is a product that replaces the voltage-stabilizing electronic diode. It is made into a diffusion type or alloy type of silicon. It is a diode with a sharp change in the reverse breakdown characteristic curve . It is made for use as a control voltage and standard voltage. The terminal voltage (also called Zener voltage) of the diode when it is working ranges from about 3V to 150V, and can be divided into many levels at intervals of 10%. In terms of power, there are also products ranging from 200mW to more than 100W. Working in the reverse breakdown state, made of silicon material, the dynamic resistance RZ is very small, generally 2CW type; two complementary diodes are connected in series in reverse to reduce the temperature coefficient, which is 2DW type. 11. PIN diode (PIN Diode) 　　This is a crystal diode constructed by sandwiching a layer of intrinsic semiconductor (or semiconductor with low concentration of impurities) between the P region and the N region. The I in PIN is the English abbreviation of "intrinsic". When its operating frequency exceeds 100MHz, due to the storage effect of minority carriers and the transit time effect in the "intrinsic" layer, the diode loses its rectification effect and becomes an impedance element, and its impedance value changes with the bias voltage. In zero bias or DC reverse bias, the impedance of the "intrinsic" region is very high; in DC forward bias, due to the injection of carriers into the "intrinsic" region, the "intrinsic" region presents a low impedance state. Therefore, the PIN diode can be used as a variable impedance element. It is often used in high-frequency switches (i.e. microwave switches), phase shifting, modulation, limiting and other circuits. 12. Avalanche Diode: 　　It is a transistor that can generate high-frequency oscillation under the action of external voltage. The working principle of generating high-frequency oscillation is as follows: using avalanche breakdown to inject carriers into the crystal, because it takes a certain amount of time for the carriers to cross the chip, the current lags behind the voltage , resulting in a delay time. If the crossing time is properly controlled, then a negative resistance effect will appear in the relationship between current and voltage. 13. Tunnel Diode 　　It is a crystal diode with tunnel effect current as the main current component. Its base material is gallium arsenide and germanium. Its P-type region and N-type region are highly doped (i.e. , high concentration of impurities). Tunnel current is generated by the quantum mechanical effect of these degenerate semiconductors. The tunnel effect has the following three conditions: ① The Fermi level is located in the conduction band and the full band; ② The width of the space charge layer must be very narrow (less than 0.01 micron); the holes and electrons in the P-type region and N-type region of the degenerate semiconductor have the possibility of overlapping . Tunnel diode is a two-terminal active device. Its main parameters are the peak-to-valley current ratio (IP/PV), where the subscript "P" represents "peak" and the subscript "V" represents "valley". Tunnel diode can be used in low-noise high-frequency amplifiers and high-frequency oscillators (its operating frequency can reach the millimeter wave band), and can also be used in high-speed switching circuits. 14. Fast turn-off (step recovery) diode (Step Recovary Diode) 　　It is also a diode with PN junction. Its structural characteristics are: there is a steep impurity distribution area at the boundary of the PN junction, thus forming a "self-help electric field". Because the PN junction conducts electricity with minority carriers under forward bias and has a charge storage effect near the PN junction, its reverse current needs to experience a "storage time" before it can drop to the minimum value (reverse saturation current value). The "self-help electric field" of the step recovery diode shortens the storage time, makes the reverse current cut off quickly, and generates rich harmonic components. These harmonic components can be used to design a comb spectrum generation circuit. Fast turn-off (step recovery) diodes are used in pulse and high-order harmonic circuits. 15. Schottky diode (Schottky Barrier Diode) 　　It is a diode with a "metal semiconductor junction" with Schottky characteristics. Its forward starting voltage is low. In addition to materials, its metal layer can also use gold, molybdenum, nickel, titanium and other materials. Its semiconductor material is silicon or gallium arsenide, mostly N-type semiconductor . This device is conducted by majority carriers, so its reverse saturation current is much larger . Since the storage effect of minority carriers in Schottky diodes is very small, its frequency response is only limited by the RC time constant , so it is an ideal device for high frequency and fast switching. Its operating frequency can reach 100GHz. In addition, MIS (metal- insulator-semiconductor) Schottky diodes can be used to make solar cells or light-emitting diodes. 16. Damping diodes It 　　has a high reverse working voltage and peak current, a small forward voltage drop, and a high-frequency and high-voltage rectifier diode. It is used in TV line scanning circuits for damping and boost rectification. 17. Transient voltage suppression diode 　　TVP tube, which provides rapid overvoltage protection for the circuit, is divided into bipolar and unipolar types, and is classified according to peak power (500W-5000W) and voltage (8.2V~200V). 18. Double-base diode (unijunction transistor) 　　A three-terminal negative resistance device with two bases and one emitter. It is used in relaxation oscillation circuits and timing voltage readout circuits. It has the advantages of easy frequency adjustment and good temperature stability. 19. Light-emitting diode 　　Made of gallium phosphide and gallium arsenide phosphide materials, it is small in size and emits light in the forward direction. It has low operating voltage, low operating current, uniform light emission, long life, and can emit red, yellow, and green monochromatic light. 3. Classification by characteristics Point contact diodes are classified according to forward and reverse characteristics as follows. 1. General point contact diodes This type of diode is usually used in detection and rectification circuits as the title says. It is an intermediate product with neither particularly good nor particularly bad forward and reverse characteristics. For example: SD34, SD46, 1N34A, etc. belong to this category. 2. High reverse withstand voltage point contact diodes 　　It is a product with very high maximum peak reverse voltage and maximum DC reverse voltage. It is used for detection and rectification of high-voltage circuits. This type of diode generally has poor or average forward characteristics. Among the point contact type germanium diodes, there are SD38, 1N38A, OA81, etc. The withstand voltage of this type of germanium material diode is limited. When the requirements are higher, there are silicon alloy and diffusion types. 3. High reverse resistance point contact type diode 　　The forward voltage characteristics are the same as those of general diodes. Although its reverse withstand voltage is also particularly high, the reverse current is small, so its specialty is high reverse resistance. Used in circuits with high input resistance and circuits with high resistance load resistance, as for germanium material high reverse resistance type diodes, SD54, 1N54A, etc. belong to this type of diode. 4. High conduction point contact type diode 　　It is the opposite of the high reverse resistance type. Although its reverse characteristics are very poor, it makes the forward resistance small enough. For high conduction point contact type diodes, there are SD56, 1N56A, etc. For high conduction key type diodes, better characteristics can be obtained . This type of diode has a high rectification efficiency when the load resistance is particularly low.

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