In 1955, American GH. Roger invented the self-oscillating push-pull transistor single-transformer dc converter, which was the beginning of realizing the high-frequency conversion control circuit. In 1957, American JenSen invented the self-excited push-pull double-transformer. In 1964, American scientists proposed to cancel the idea of series switching power supply for power frequency transformers, which obtained a fundamental way to reduce the volume and weight of power supply. By 1969, due to the high-power silicon transistor voltage resistance improvement, diode reverse recovery time and other improvements, finally made 25 KHZ switching power supply.
At present, with the characteristics of small, light and high efficiency, switching power supply is widely used in all kinds of electronic equipment, such as electronic computer dominated terminal equipment, communication equipment, and almost all electronic equipment, is an indispensable way for the rapid development of electronic information industry. At present, 100kHz power supply made of bipolar transistor and 500kHz power supply made of mos-fet have been applied in the market, but their frequency needs to be further improved. To increase switching frequency, it is necessary to reduce switching losses, and to reduce switching losses, it is necessary to have high-speed switching components. However, when the switching speed is increased, the surge or noise will be caused by the influence of the inductance distributed in the circuit and the charge stored in the capacitance or diode. This will not only affect the surrounding electronic equipment, but also greatly reduce the reliability of the power supply itself. Among them, r-c or l-c buffers can be used to prevent the voltage surge when the switch is opened and closed, and amorphous magnetic cores can be used for the stray surge caused by diode storage charge. However, for high-frequency above 1MHz, a resonant circuit should be used to make the voltage on the switch or the current through the switch sinusoidal, which can not only reduce switching losses, but also control the occurrence of the surge.
This switching mode is called resonant switching. At present, the research on this switching power supply is very active, because it can reduce the switching loss to zero in theory without greatly increasing the switching speed, and the noise is also small, it is expected to become a major way of switching power supply high-frequency. At present, many countries in the world are working on the practical research of multimegabyte Hz converter.