Switching power supply is known as high-efficiency energy-saving power supply. It represents the development 

direction of regulated power supply and has become the mainstream product of regulated power supply. For more 

than 20 years, integrated switching power supplies have evolved in two directions. The first direction is the integration 

of the control circuit of the core unit of the switching power supply. In 1997, foreign countries first developed pulse-

width modulation (PWM) controller integrated circuits. Motorola, Silicon General, and Unitrode introduced a number 

of PWM chips. The typical products are MC3520. SG3524, UC3842. Since the 1990s, high-speed PWM and PFM 

(Pulse Frequency Modulation) chips with switching frequency up to 1MHz have been developed abroad. Typical 

products such as UC1825 and UC1864. The second direction is the centering, small power switching power supply 

to achieve monolithic integration. This is roughly divided into two phases: In the early 1980s, SGS-Thomson was the 

first to introduce the L4960 series of single-chip switching regulators. The company introduced the L4970A series in 

the 1990s. The utility model is characterized in that a pulse width modulator, a power output stage and a protection 

circuit are integrated in one chip, and the power frequency transformer is required to be isolated from the power grid 

when used, and is suitable for low voltage output (5.1~40V) and medium and medium power (400W or less). ), high 

current (1.5A ~ 10A), high efficiency (can exceed 90%) switching power supply. But in essence, it is still a DC/DC 

power converter.

        In 1994, Power Company first developed a three-terminal isolated pulse width modulation single-chip switching 

power supply in the world, which was hailed as “top-level switching power supply”. Its first generation is the TOPSwitch 

series, and the second generation is the TOPSwitch-II series that was introduced in 1997. In 1998, the company 

introduced the high-performance, low-power, low-cost four-terminal single-chip switching power supply TinySwitch series. 

After that, Motorola introduced the MC33370 series five-terminal single-chip switching power supply in 1999, also known 

as the HighVoltage Power Switching Regulator. At present, single-chip switching power 

supplies have formed four series and nearly 70 models.

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