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2020-12-16 16:07
Design of monolithic switching power supply
Switching power supply has the outstanding advantages of high efficiency, light weight, small volume and wide voltage stabilizing range. Since its advent in the mid-20th century, it has developed extremely rapidly. It has been widely used in computers, communications, aerospace, office and household appliances, and has the potential to replace linear voltage stabilizing power supply. Improving the integration of circuit is one of the pursuit of switching power supply. For medium and small power switching power supply, it is to realize single chip integration. Switching integrated voltage regulator refers to the integration of control circuit, power switch tube and protection circuit into one chip, and the switching power supply composed of switching integrated voltage regulator is called monolithic switching power supply. The single chip switching power supply series of American PI company is its remarkable representative. The 250W switching power supply circuit designed by
TOPSwitch GX is shown in Figure 1. The DC voltage is added to the drain D of TOPSwitch GX through the primary side of the transformer; If the frequency selection terminal F and limit current setting terminal X are connected with the source s, the functions of both ends are useless, that is, the limit current is not set from the outside, the self-protection current ilimit is automatically set internally, and the switching working frequency is 132k; The control pole is connected with the optocoupler ltv817 and receives the feedback signal to control the duty cycle of the internally integrated high-voltage power MOS tube; Line detection end l passes through a 2mω The resistance is connected with the positive end of the DC high voltage input to realize the line voltage detection of the feedforward of the overvoltage and undervoltage line voltage. Capacitor C1 is a high-frequency filter capacitor; The transient voltage suppressor p6ke200 and the ultrafast recovery diode byv26c form a clamping circuit, in which the RC absorption circuit (composed of R2, R3 and C6) is connected in series. In this way, in addition to absorbing part of the energy in the leakage inductance, the voltage can also be clamped at 200V, so that the drain voltage of the integrated MOS transistor in TOPSwitch GX does not exceed 700V when the switching power supply is started or overloaded; The secondary output of high-frequency transformer T1 is rectified by murl640ct and filtered by C9, C10 and C11, and then the output voltage is obtained after the switching noise is filtered by magnetic beads L1 and C12; VD4 and C14 constitute a soft start circuit.
single chip switching power supply has the remarkable advantages of single chip integration, simpler peripheral circuit, better performance index and complete isolation without power frequency transformer. It is an ideal choice for us to design switching power supply below 290w.
TOPSwitch GX is shown in Figure 1. The DC voltage is added to the drain D of TOPSwitch GX through the primary side of the transformer; If the frequency selection terminal F and limit current setting terminal X are connected with the source s, the functions of both ends are useless, that is, the limit current is not set from the outside, the self-protection current ilimit is automatically set internally, and the switching working frequency is 132k; The control pole is connected with the optocoupler ltv817 and receives the feedback signal to control the duty cycle of the internally integrated high-voltage power MOS tube; Line detection end l passes through a 2mω The resistance is connected with the positive end of the DC high voltage input to realize the line voltage detection of the feedforward of the overvoltage and undervoltage line voltage. Capacitor C1 is a high-frequency filter capacitor; The transient voltage suppressor p6ke200 and the ultrafast recovery diode byv26c form a clamping circuit, in which the RC absorption circuit (composed of R2, R3 and C6) is connected in series. In this way, in addition to absorbing part of the energy in the leakage inductance, the voltage can also be clamped at 200V, so that the drain voltage of the integrated MOS transistor in TOPSwitch GX does not exceed 700V when the switching power supply is started or overloaded; The secondary output of high-frequency transformer T1 is rectified by murl640ct and filtered by C9, C10 and C11, and then the output voltage is obtained after the switching noise is filtered by magnetic beads L1 and C12; VD4 and C14 constitute a soft start circuit.
single chip switching power supply has the remarkable advantages of single chip integration, simpler peripheral circuit, better performance index and complete isolation without power frequency transformer. It is an ideal choice for us to design switching power supply below 290w.
