The function of Schottky Diode in switching Power supply

The function of Schottky Diode in switching Power supply.
Switching power supply is a kind of power supply which uses modern power electronic technology to control the time ratio of switching on and off to maintain a stable output voltage. Switching power supply is generally composed of pulse width modulation (PWM) control IC and MOSFET. With the development and innovation of power electronics technology, the switching power supply technology is constantly innovating. At present, switching power supply is widely used in almost all electronic devices because of its small size, light weight and high efficiency, and it is an indispensable way of power supply for the rapid development of electronic information industry.
Switching power supply products are widely used in industrial automation control, military equipment, scientific research equipment, LED lighting, industrial control equipment, communication equipment, power equipment, instrumentation, medical equipment, semiconductor refrigeration heating, air purifier, electronic refrigerator, liquid crystal display, LED lamps, communication equipment, audio-visual products, security monitoring, LED light belt, computer chassis, digital products and instruments and other fields.
Schottky diode.
Schottky diodes are metal-semiconductor devices made of precious metals (gold, silver, aluminum, platinum, etc.) An as positive electrodes and N-type semiconductor B as negative electrodes. Because there are a large number of electrons in N-type semiconductors and only a very small amount of free electrons in precious metals, electrons are diffused from high concentration B to low concentration A. Obviously, there is no hole in metal A, so there is no diffusion movement of hole from A to B. With the continuous diffusion of electrons from B to Aline B, the electron concentration on the surface of B decreases gradually, and the surface electrical neutrality is destroyed, so a potential barrier is formed, and the direction of the electric field is Benza. However, under the action of the electric field, the electrons in A will also drift from A to B, thus weakening the electric field formed by the diffusion motion. When the space charge region of a certain width is established, the electron drift motion caused by the electric field and the electron diffusion motion caused by different concentrations reach a relative balance, and the Schottky barrier is formed.
The internal circuit structure of a typical Schottky rectifier is based on N-type semiconductors, on which an N-epitaxial layer is formed with arsenic as a dopant. The anode is made of materials such as molybdenum or aluminum. Silicon dioxide (SiO2) is used to eliminate the electric field in the edge area and improve the voltage withstand value of the diodee. The N-type substrate has a very small on-state resistance, and its doping concentration is 100% higher than that of the H-layer. An N + cathode layer is formed under the substrate, and its function is to reduce the contact resistance of the cathode. By adjusting the structural parameters, a Schottky barrier is formed between the N-type substrate and the anode metal, as shown in the figure. When a forward bias voltage is added at both ends of the Schottky barrier (the anode metal is connected to the positive pole of the power supply, and the N-type substrate is connected to the negative pole of the power supply), the Schottky barrier layer becomes narrower and its internal resistance becomes smaller; on the contrary, if a reverse bias voltage is added at both ends of the Schottky barrier, the Schottky barrier layer becomes wider and its internal resistance becomes larger.
To sum up, the structure principle of Schottky rectifier diodee is very different from that of PN junction rectifier diodee. Generally speaking, PN junction rectifier diodee is called junction rectifier diodee, while metal-semi-conduit rectifier diodee is called Schottky rectifier diodee. Aluminum-silicon Schottky diode manufactured by silicon plane process has also come out, which can not only save precious metals, greatly reduce the cost, but also improve the consistency of parameters.
Schottky diode is a kind of hot carrier diode. Schottky diode, also known as Schottky barrier diode, is a low-power, ultra-high-speed semiconductor device. Schottky diode is widely used in frequency converters, switching power supplies, drivers and other circuits. Schottky diodes are used as low-voltage, high-frequency, high-current rectifier diodes, protection diodes, continuous current diodes and so on. Schottky diodes are used as rectifier diodes and small signal detection diodes in microwave communication circuits. What does Schottky diodes do? The following is the editor's introduction to Schottky diodes.
Schottky Diode-principle.
Schottky diode is a kind of metal semiconductor device made of precious metals such as gold, aluminum, silver and platinum An as positive electrode and N-type semiconductor B as negative electrode, and then making use of the potential barrier formed between them. Schottky diodes because there are a large number of electrons in N-type semiconductors and only a few free electrons in precious metals, the electrons in Schottky diodes are diffused from high concentration B to low concentration A. There is no hole in Schottky diode metal A, and there is no hole diffusion from A to B. As the electron concentration on the surface of Schottky diodes diffuses from B to A _ (1) B decreases gradually, the surface is electrically neutral, and a potential barrier is formed.
Schottky diodes-advantages.
Schottky diodes have the advantages of high switching frequency and low forward voltage, but the reverse breakdown voltage of Schottky diodes is relatively low, generally no higher than 60V, and the highest is only about 100V, so that the application range of Schottky diodes is limited. Only fast recovery epitaxial diodes and ultra fast recovery diodes are used when high frequency rectifier diodes above 100V for transformer secondary use, power switching devices continuous current diodes in power factor correction circuits, high speed diodes between 600V~1.2kV in RCD buffer circuits, and 600V diodes for PFC boost are used. At present, Schottky diodes have made a breakthrough, 150V and 200V high voltage have been put on the market, and Schottky diodes made of new materials that exceed 1kV have also been successfully developed.
Schottky diode-action.
Schottky diode, also known as Schottky barrier diode (SBD), is a low-power, ultra-high-speed semiconductor device. The most remarkable feature of Schottky diode is that the reverse recovery time is very short, and the positive guide voltage drop is only about 0.4V. Schottky diodes are mostly used as rectifier diodes in high frequency, high current rectifier diodes, low voltage, continuous current diodes, protection diodes, small signal detection diodes, microwave communications and other circuits. Schottky diodes are common in communication power supply, frequency converter and so on. Schottky diodes are clamped by connecting diodes in the switching circuit of a bipolar transistor.
Schottky diodes-characteristics.
Because the base barrier height of Schottky diodes is lower than that of PN junction, the forward guide threshold voltage and forward voltage drop of Schottky diodes are lower than that of PN junction diodes. Because Schottky diode is a multi-carrier conductive device, there is no minority carrier lifetime and inverse.