Varactor diode is a special diode made based on the principle of P-N junction space charge having capacitance characteristics. The capacitance between the two poles of the diode is 3-50 pF, which is actually a voltage controlled fine-tuning capacitor mainly used for tuning circuits.

(5) Photodiode

Photodiode, also known as photodiode, has the circuit symbol of LED-13.jpg

The characteristic of a photodiode is that when it is exposed to light, the reverse impedance of the diode will change accordingly (with the increase of light exposure, the reverse impedance will decrease from large to small). Using this characteristic, photodiodes are commonly used as photoelectric sensor devices.

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Switching diodes are generally packaged in glass or ceramic shells to reduce the capacitance of the tube shell.

The time from cutoff (high impedance) to conduction (low impedance) of a general switching diode is called the turn-on time; The time from conduction to cutoff is called the reverse recovery time, and the sum of the two times is collectively referred to as the switching time.

The switching time of a switching diode is very short, making it an ideal electronic switch with fast switching speed, small size, long lifespan, and high reliability.

Light emitting diodes are devices that convert electrical energy into light energy. LEDs made of different materials can emit light of different colors, including red, yellow, green, orange, and others.

Usually, semiconductor diodes are named using the direct labeling method, but the specific naming specifications vary depending on the country, region, and manufacturer.

(1) Naming and labeling of domestic diodes

The naming specifications of domestic diodes are to label the category, material, specifications, and other main parameters of crystal diodes on the surface of the diode. According to national labeling regulations, the naming of crystal diodes consists of five parts.

① Product Name: Use the number "2" to represent the diode and the effective polarity pin.

④ Serial number: represented by a number, indicating different varieties of similar products to distinguish their external dimensions and performance indicators, sometimes omitted.

⑤ Specification number: Use letters to indicate the specifications, models, and grades of diode production, sometimes omitted.

Example:

According to regulations, the annotation text for "3DU28" on the diode indicates that there are 3 PN junctions on the diode, "D" indicates that the diode is a P-type silicon material diode, "U" indicates that the diode belongs to a photoelectric tube, and "28" is the product number of the diode.

(2) Naming and labeling of American made diodes

The naming of diodes produced in the United States is quite confusing. According to the regulations of the American Electronics Industry Association,

The naming of diode models consists of five parts.

③ Registration Mark: Electronic Industries Association (EIA) registration mark. N indicates that the device has been registered with the Electronic Industries Association (EIA) in the United States.

④ Serial number: Represented by multiple digits, the registration sequence number of the American Electronics Industry Association.

⑤ Specification number: Use letters to represent the improved product logo of the same model. A. B, C, D... The different grades of the same model of device are represented by letters=

② Registration Mark: The JEIA registration mark of the Japan Electronics Industry Association, represented by a letter S, indicates a semiconductor device that has been registered with JEIA.

③ Material/Polarity: Represented by letters, indicating the polarity and type of material used for the diode.

④ Serial number: Use numbers to represent the sequence number registered with the Japan Electronics Industry Association (JEIA), with integers starting from "11" indicating the sequence number registered with JEIA; Devices with the same performance from different companies can use the same serial number; The larger the number, the more recent the product.

⑤ Specification number: Use letters to represent the improved product logo of the same model. A. B, C, D, E, and F indicate that this device is an improved version of the prototype product.

Note: Common diode parameters:

On the diode, the annotation text "1N4004" can be seen. According to regulations, "1" refers to the diode, "N" indicates that the diode is an N-type diode, and "4004" is the number of the diode.

3、 Understand the main parameters of diodes

1. Common parameters

(1) Maximum overall current

The maximum rectified current refers to the maximum forward average current allowed to pass through a diode during long-term continuous operation, which is related to the PN junction area and external heat dissipation conditions. The larger the PN junction area, the greater the maximum rectified current. When the current exceeds the allowable value, the PN junction will burn out due to overheating. In a rectifier circuit, the forward current of the diode must be less than this value.

(2) Maximum reverse voltage

The maximum reverse voltage refers to the highest reverse operating voltage provided to ensure that the diode is not broken down. The maximum reverse voltage in the relevant information is about half of the breakdown voltage to ensure the safe operation of the diode. The maximum reverse voltage of point contact diodes is about tens of volts, while surface contact diodes can reach hundreds of volts. If the diode is subjected to excessive reverse voltage in the circuit, it will be damaged.

(3) Maximum reverse current

The maximum reverse current refers to the reverse current of a diode when the maximum reverse voltage is applied at a specified temperature during operation. The larger the reverse current, the worse the unidirectional conductivity of the diode, and the greater the influence of temperature; The smaller the reverse current, the better the unidirectional conductivity of the diode. The reverse current of silicon tubes is relatively small, usually below a few microamperes; The reverse current of germanium tubes is relatively large, generally ranging from tens of microamperes to hundreds of microamperes.

It is worth noting that there is a close relationship between reverse current and temperature, with the reverse current doubling for every 10 ℃ increase in temperature.

(4) Maximum operating frequency

The maximum operating frequency refers to the highest frequency at which a diode can operate normally. When selecting a diode, its operating frequency must be lower than the maximum operating frequency. When the maximum operating frequency is exceeded, the diode will not be able to exhibit good unidirectional conductivity due to the effect of junction capacitance.