A section on the principle of a high-frequency switching power supply circuit. A high-frequency switching power supply consists of the following parts: 1. The main circuit is the entire process of inputting from the AC power grid and outputting DC power, including: (1) Input filter: Its function is to filter out the noise present in the power grid, and also to prevent the noise generated by the machine from being fed back to the public power grid. (2) Rectification and filtering: The AC power from the power grid is directly rectified into a smoother DC power for the next stage of conversion. (3) Inverter: The rectified DC power is converted into high-frequency AC power. This is the core part of the high-frequency switching power supply. The higher the frequency, the smaller the ratio of volume, weight and output power. (4) Output rectification and filtering: Provides a stable and reliable DC power supply according to the load requirements. 2. The control circuit samples from the output terminal, compares it with the set standard, and then controls the inverter to change its frequency or pulse width to achieve output stability. On the other hand, based on the data provided by the test circuit, the protection circuit identifies and provides the control circuit to carry out various protection measures for the whole machine. 3. In addition to providing various parameters of the protection circuit in operation, the detection circuit also provides various display instrument data. 4. Auxiliary power supply provides power to meet the different requirements of all individual circuits. Section Two: Switch-Controlled Voltage Regulator Principle Switch K repeatedly turns on and off at regular time intervals. When switch K is on, the input power supply E is supplied to the load RL through switch K and the filter circuit. During the entire on-time, power supply E provides energy to the load; when switch K is off, the input power supply E interrupts its energy supply. It is evident that the energy supply from the input power supply to the load is intermittent. To ensure a continuous energy supply to the load, the switching power supply must have an energy storage device. This device stores a portion of the energy when the switch is on and releases it to the load when the switch is off. The circuit in the diagram, consisting of inductor L, capacitor C2, and diode D, performs this function. Inductor L stores energy; when the switch is off, the energy stored in inductor L is released to the load through diode D, providing the load with continuous and stable energy. Because diode D ensures a continuous load current, it is called a freewheeling diode. The average voltage EAB between A and B can be expressed by the following formula: EAB = TON/T * E, where TON is the switching time each time the switch is turned on, and T is the switching cycle (i.e., the sum of the switching on time TON and the off time TOFF). As can be seen from the formula, changing the ratio of the switching on time to the cycle changes the average voltage between A and B. Therefore, automatically adjusting the ratio of TON and T with changes in load and input power supply voltage can keep the output voltage V0 constant. Changing the ratio of the on time TON to the cycle is equivalent to changing the duty cycle of the pulse; this method is called "Time Ratio Control" (TRC). According to the TRC control principle, there are three methods: 1. Pulse Width Modulation (PWM): The switching cycle is constant; the duty cycle is changed by changing the pulse width. 2. Pulse Frequency Modulation (PFM): The conduction pulse width is constant; the duty cycle is changed by changing the switching frequency. 3. Hybrid modulation: Both the conduction pulse width and the switching operating frequency are not fixed and can be changed. It is a hybrid of the above two methods. [b]Development and Trends of Switching Power Supplies[/b] In 1955, G.H. Roger invented the self-excited push-pull transistor single-transformer DC-DC converter, marking the beginning of high-frequency conversion control circuits. In 1957, Jen Sen invented the self-excited push-pull double transformer. In 1964, American scientists proposed the idea of ​​eliminating the power frequency transformer in a series switching power supply, which provided a fundamental way to reduce the size and weight of power supplies. By 1969, due to improvements in components such as the increased voltage withstand capability of high-power silicon transistors and the shortened reverse recovery time of diodes, a 25 kHz switching power supply was finally achieved. Currently, switching power supplies, characterized by their small size, light weight, and high efficiency, are widely used in almost all electronic devices, including various terminal devices and communication equipment, primarily computers. They are an indispensable power supply method for the rapid development of today's electronic information industry. Currently, commercially available switching power supplies using bipolar transistors (100kHz) and MOSFETs (500kHz) are already in practical use, but their frequencies need further improvement. Increasing the switching frequency requires reducing switching losses, which necessitates high-speed switching components. However, increased switching speed can lead to surges or noise due to distributed inductance and capacitance in the circuit or the charge stored in diodes. This not only affects surrounding electronic equipment but also significantly reduces the reliability of the power supply itself. To prevent voltage surges during switching, RC or LC buffers can be used, while magnetic buffers made with amorphous cores can be used to address current surges caused by diode charge storage. However, for frequencies above 1MHz, resonant circuits are required to make the voltage on the switch or the current through the switch sinusoidal, thus reducing switching losses and controlling surges. This switching method is called resonant switching. Research on this type of switching power supply is currently very active because it theoretically reduces switching losses to zero without significantly increasing switching speed, and also produces low noise. It is expected to become a major method for increasing the frequency of switching power supplies. Currently, many countries around the world are dedicated to the practical application of converters operating at several megaHz.