Classification and application of switching power supply

　　Classification and application of switching power supply

　　1.1 Classified by connection mode before load

　　The series connection of the switch tube and the load in the switching power supply is called a series switching power supply, and the parallel connection of the switching tube and the load is called a parallel switching power supply. The output end of the series switching power supply is directly connected to the power grid through a switching regulator and a rectifier diode. Due to the poor isolation of the power grid, the entire equipment bottom board is electrified, which is usually called a hot plate. This inconvenient external interface, such as audio and video interfaces, headphones Interface, etc. Parallel self-excited switching power supply has a high-frequency transformer for electrical isolation between its output terminal and the power grid.

　　1.2 Classified by voltage regulation operation mode

　　The regulation and voltage stabilization of the switching power supply is completed by adjusting the duty cycle of the power switch tube. Suppose the switching period of the switch tube is T, and in a period, the on-time is ton, then the duty cycle is defined as D=tonT. In a switching power supply, there are two ways to manipulate the duty cycle: pulse width modulation (PWM) and pulse frequency modulation (PWF). In the pulse width manipulation, the switching frequency (switching period T) is kept unchanged, and the duty cycle D is transformed through the transformation ton, thereby achieving the purpose of transforming the output voltage. That is, the larger the D, the larger the output voltage after filtering; the smaller the D, the smaller the output voltage after filtering. In the frequency control mode, the on-time ton is kept unchanged, and the duty cycle is changed after the switching frequency (that is, the switching period T). Because the operating frequency of the frequency control mode is changed, the design of the subsequent circuit filter is very inconvenient. Therefore, most of the switching power supplies at this stage use PWM control.

　　1.3 Classification by incentive method

　　The excitation signal required for the operation of the switching regulator comes from outside the switching power supply and is called the other excitation type. If the excitation is generated by the self-excited oscillation, it is called the self-excitation type. Normally, it uses the line-reverse pulse as the excitation signal for the switching regulator to turn on. In order to synchronize the oscillation frequency with the line frequency, part of the self-excited switching power supply also uses the line-reverse pulse as the trigger level. At this stage, the most widely used is the self-excited parallel switching power supply controlled by PWM.

　　Application of switching power supply

　　Due to the development and growth of power electronic technology, especially the rapid development and growth of high-power MOS tube technology, the operating frequency of the switching power supply is increased to 150-200kHz, which leads to smaller power loss and the efficiency of the power supply reaches 90% to 95%. Replacing the power frequency transformer with a high-frequency transformer can greatly reduce the volume and weight; in addition, the output voltage ripple is reduced to within 0.05%, and the stability reaches 0.5% to 1%. The anti-interference ability is strong and the degree of intelligence is high. With excellent characteristics, high-power switching power supplies are mainly used in industry and military. In pulse power technology applications such as particle accelerators, electromagnetic emission, electromagnetic propulsion, and microwave weapons, the average power of power supply equipment is usually hundreds of kilowatts or even more than a few megawatts, and the volume and weight are only a few tenths of linear power supplies. The low-power switching power supply is mainly used in small household appliances, IT and other fields, such as computers, color TVs, smart homes, cameras, set-top boxes, VCDs, electronic game consoles and other electronic products.

　　2.1 Communication power

　　The rapid development of the communication industry has greatly promoted the development of communication power supplies. High-frequency miniaturized switching power supplies and technologies have become the mainstream of modern communication power supply systems. In the communication field, the rectifier is generally called the primary power supply, and the DC-DC (DC/DC) converter is called the secondary power supply. The primary power supply is to transform a single-phase or three-phase AC power grid into a DC power supply with a nominal value of 48V. For example, in the primary power supply for program-controlled switches, the traditional phase-controlled regulated power supply has long been replaced by a high-frequency switching power supply. It uses the high-frequency operation of MOSFET or IGBT, and the switching frequency is usually controlled in the range of 50-100kHz to achieve high Efficiency and miniaturization. In recent years, the power storage capacity of the primary power supply has continued to expand, and the storage capacity of a single unit has been expanded from 48V/12.5A to 48V/200A, 48V/400A.

　　The continuous improvement of the processing speed of communication equipment has promoted the continuous improvement of the operating frequency. There are many types of integrated circuits used, and the power supply voltage requirements are also different, generally more than 10 types. In the communication power supply system, select high-power-density high-frequency DC -DC isolation power module, which converts the intermediate bus voltage (usually 48V DC) into various DC voltages required, which can greatly reduce loss, facilitate maintenance, and is very convenient to assemble and increase. Usually it can be directly installed on the standard control board, and the requirement for the secondary power supply is high power density. As the amount of communication storage continues to increase, the amount of communication power storage will also continue to increase.

　　2.2 High frequency inverter rectifier welding machine power supply

　　The high-frequency inverter rectifier welding machine power supply is a high-performance, efficient, and material-saving new welding machine power supply, which symbolizes the development direction of today's welding machine power supply. Because of the commercialization of IGBT high-capacity modules, this kind of power supply has broader application prospects.

　　Inverter welding machine power supplies mostly use AC-DC-AC-DC (AC-DC-AC-DC) conversion methods. The 50Hz alternating current is converted into direct current by full bridge rectification, and the PWM high-frequency conversion part composed of IGBTs inverts the direct current into a high-frequency rectangular wave of 20kHz, coupled with a high-frequency transformer, rectified and filtered into a stable direct current, and used as a power supply arc.

　　Because the working conditions of the welding machine power supply are bad, and it is often in short-circuit, arcing, and open-circuit alternate changes, the working reliability of the high-frequency inverter rectifier welding machine power supply has become the most core issue, and it is also the most concerned by customers. problem. The microprocessor is selected as the relevant controller of pulse width modulation (PWM), and with the acquisition and analysis of multiple parameters and multiple information, the purpose of predicting the various working conditions of the system is achieved, so that the system can be adjusted and processed in advance to solve the problem. Reliability of high-power IGBT inverter power supply at this stage. Foreign inverter welding machines can achieve a rated welding current of 300A, a load duration of 60%, a full load voltage of 60 to 75V, a current adjustment range of 5 to 300A, and a net weight of 29kg.

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