A p-n junction is called a semiconductor diode. Since it only leads in one direction, it is used for correction purposes. Since it consists of crystalline silicon or germanium. It is also known as crystal diode. The diode symbol is: Although all diodes straighten in the same direction, the term rectifier is generally used for diodes intended for power supply applications to distinguish them from diodes intended for small signal circuits. Diodes are often used to divert harmful high voltages from sensitive electronic devices. Under normal circumstances, they are usually inversely biased (non-conductive). When the voltage rises above the normal range, the diodes are polarized forward (conductive). For example, diodes in motor controllers (stepper motor and H-bridge) and relay circuits are used to quickly shut down coils without the harmful voltage spikes that would otherwise occur. (A diode used in such an application is called a flyback diode.) Many ICs also include diodes on connector pins to prevent external voltages from damaging their sensitive transistors. Special diodes are used to protect against higher power surges (see diode types above). Thermoionic diodes (vacuum tubes) and semiconductor diodes (semiconductor diodes) were developed separately around the same time, in the early 1900s, as radio receiver detectors. [7] Until the 1950s, vacuum diodes were more commonly used in radios because early point contact semiconductor diodes were less stable.

In addition, most receiver sets had vacuum tubes for amplification, which thermoionic diodes could easily hold in the tube (e.g., 12SQ7 dual diode triodes), and vacuum tube rectifiers and gas-filled rectifiers were able to handle some high-voltage/high-current rectifier tasks better than semiconductor diodes (such as selenium rectifiers) available at the time. Perfectly efficient diodes appear to be open circuits with negative voltage and look like short circuits. However, as diodes admit some inefficiency, their current-voltage relationship is non-linear. Therefore, you should consult the data sheet of a diode to visualize a diagram of the forward voltage curve of a particular diode relative to its forward current so that you can choose the right diode for your particular project. A diode consists of two words, meaning «Di» means two and «Ode» means electrodes, meaning that a device or component has two electrodes. (i.e. cathode and anode). A diode is an electronic device with a unidirectional power supply with two terminals.

A semiconductor diode is the first diode to form in semiconductor electronic devices, after which there were many new innovations. However, the most commonly used diode is a semiconductor diode. When a negative charge is applied on the n side and a positive charge on the p side, the electrons «jump» on this compound and the current flows only in one direction. This is the main property of the diode; Conventional electricity flows only in this direction, from the positive side to the negative side. At the same time, electrons flow only from the negative side to the positive side in only one direction. This is because electrons are negatively charged and attracted to the positive end of a battery. The I-V characteristic of a diode can be approached by four operating ranges: Light-emitting diodes (LEDs) are p-n junctions that emit light when a current passes through them. Multiple p-n junction diodes can be connected in series to create a rectifier (an electrical component that converts alternating current into direct current). Zener diodes have a well-defined breakdown voltage, so that at this voltage the current flows in the opposite direction and a constant voltage can be maintained despite voltage or current fluctuations.

In varactor diodes (or varicap), the variation of the bias causes a variation in the capacitance of the diode; These diodes have many applications for signal transmission and are used throughout the radio and television industry. (For more information about these and other types of diodes, see Semiconductor device.) Although LEDs may be the most well-known application for the average person, by far the most common application is the use of diodes for rectification from alternating current to direct current. Using diodes, different types of rectifier circuits can be created, the most basic of which are half-wave, full-wave center and full bridge rectifiers. These are extremely important in electronic power supplies — for example, the charger of a laptop — where alternating current from the power supply must be converted into direct current which can then be stored. At the time of their invention, asymmetrically conductive devices were known as rectifiers. In 1919, the year tetrodes were invented, William Henry Eccles coined the term diode from the Greek roots di (from δί), meaning «two», and ode (from οδός), meaning «path». However, the word diode as well as triode, tetrode, pentode, hexodus were already used as terms of multiplex telegraphy. [22] The tubular diode uses two active elements (cathode and plate) and one passive element (the filament or heater). In typical operation, the cathode is heated by the filament and AC voltage is applied to the cathode. The heated cathode releases excited electrons, which flow to the plate (anode) and become the rectified current. The diode allows current to flow in only one direction.

For example, if current were applied to the plate, no electron flow could occur because the electrons in the plate are not heated by the filament. Another type of junction diode, the Schottky diode, is formed from a metal-semiconductor junction instead of a p-n junction, which reduces capacitance and increases switching speed. [29] [30] The first use of the diode was the demodulation of amplitude modulated (AM) radio emissions. The history of this discovery is discussed in detail in the article Crystal detector. In summary, an AM signal consists of alternating the positive and negative peaks of a radio carrier wave whose amplitude or envelope is proportional to the original audio signal. The diode is similar to the AM radio frequency signal and leaves only the positive peaks of the carrier wave. The audio is then extracted from the rectified carrier wave using a simple filter and fed into an audio amplifier or transducer that generates sound waves through audio speakers. A diode is a semiconductor device that allows electric current to flow in only one direction. A common example is LED (Light Emitting Diode), which is used to backlight various flat screens. Diodes have many applications, including signal limiters, voltage regulators, rectifiers, switches, modulators, etc. The effect can be significant when large currents are switched very quickly.

[32] Some reverse recovery time tr (on the order of tens of nanoseconds to microseconds) may be required to eliminate the inverse recovery load Qr from the diode. During this recovery time, the diode can effectively drive in the opposite direction. This can result in a large current in the opposite direction for a short time while the diode is polarized backwards. The amplitude of such an inverse current is determined by the operating circuit (i.e. the series resistor) and the diode is in the memory phase. [33] In some real-world cases, it is important to consider the losses caused by this less than ideal diode effect. [34] However, if the rate of current increase is not as strong (e.g., line frequency), the effect can be safely ignored. For most applications, the effect is negligible even with Schottky diodes. The most common function of a diode is to circulate an electric current in one direction (called the front direction of the diode) while blocking it in the opposite direction (the opposite direction). As such, the diode can be thought of as an electronic version of a check valve. This unidirectional behavior is called rectification and is used to convert alternating current (AC) to direct current (DC).

As rectifiers, diodes can be used for tasks such as extracting modulation from radio signals in radio receivers. The diodes can be combined with other components to build AND and OR logic gates. This is called diode logic. The behavior of a semiconductor diode in a circuit is indicated by its current-voltage characteristic or I-V graph (see graph below). The shape of the curve is determined by the transport of charge carriers through the so-called depletion layer or exhaustion region, which exists at the p-n junction between different semiconductors. When a p-n junction is generated for the first time, the electrons in the conduction band (mobile) diffuse from the n-doped region to the p-doped region, where there is a large population of holes (free points for electrons) with which the electrons «recombine». When a moving electron recombines with a hole, the hole and electron disappear, leaving a positively charged (doping) stationary donor on the N side and a negatively charged acceptor (doping) on the P side. The area around the p-n junction is depleted by charge carriers and therefore behaves as an insulator. An important application of diodes is the conversion of alternating current to direct current.