Switching power supply has outstanding advantages such as high efficiency, light weight, small size, and wide voltage regulation range. Since its appearance in the mid-20th century, it has developed extremely rapidly and has been widely used in computers, communications, aerospace, office, and household appliances. It has the potential to replace the linear regulated power supply. Improving the integration of circuits is one of the pursuits of switching power supplies, and for small and medium power switching power supplies, it is to achieve monolithic integration. Switching integrated voltage stabilizer refers to the integration of control circuit, power switch tube and protection circuit etc. in a chip, and the switching power supply composed of the integrated switching voltage stabilizer is called monolithic switching power supply. The single-chip switching power supply series of American PI Company is its notable representative.

    The 250W switching power supply circuit designed by TOPSwitch-GX is shown in Figure 1. The DC voltage is applied to the drain D of TOPSwitch—GX through the primary side of the transformer; the frequency selection terminal F and the limit current setting terminal X are connected to the source S, and the functions of the two terminals are useless, that is, the limit is not set from the outside Current, the internal self-protection current ILIMIT is automatically set, and the switching frequency is 132K; the control pole is connected to the optocoupler LTV817, and receives feedback signals to control the duty cycle of the internal integrated high-voltage power MOS tube; the line detection terminal L passes a 2MΩ The resistor is connected to the positive terminal of the DC high voltage input to realize the line voltage detection of overvoltage and undervoltage line voltage feedforward. Capacitor C1 is a high-frequency filter capacitor; transient voltage suppressor P6KE200 and ultra-fast recovery diode BYV26C form a clamping circuit, and an RC absorption circuit (consisting of R2, R3 and C6) is connected in series, so as to absorb part of the leakage inductance. In addition to the energy in the medium, the voltage can also be clamped at 200V, so that the drain voltage of the TOPSwitch-GX internal integrated MOS tube does not exceed 700V when the switching power supply is started or overloaded; the secondary side output of the high-frequency transformer T1 passes MURl640CT After rectifying and filtering with C9, C10 and C11, and then filtering out the switching noise through magnetic beads L1 and C12, the output voltage is obtained; VD4 and C14 form a soft-start circuit.

    The single-chip switching power supply has obvious advantages such as monolithic integration, simpler peripheral circuits, better performance indicators, and complete isolation with no power frequency transformer electrical appliances. It is our ideal choice for designing switching power supplies below 290W.