Switching power has such outstanding advantages as high efficiency, light weight, small volume and wide range of voltage. Since its advent in the mid twentieth Century, it has developed extremely rapidly. It has been widely used in the fields of computer, communications, space, office and household appliances, and greatly replaced the potential of linear voltage regulator. Improving the integration of circuit is one of the pursuit of switching power supply, and it is monolithic integrated for small and medium power switching power supply. The switch integrated regulator is to integrate the control circuit, the power switch tube and the protection circuit into one chip, and the switch power, which is composed of the switch integrated regulator, is called the single chip switching power supply. The monolithic switching power supply series of PI is its notable representative.
The 250W switching power supply circuit designed by TOPSwitch GX is shown in Figure 1. The DC voltage is added to the TOPSwitch - GX drain D by the original side of the transformer; the frequency selector F and the limit current set end X are connected to the source S, then the functions of the two ends are all useless, that is, it does not set the limit current from the outside, automatically sets the self protected current ILIMIT, the switching frequency is 132K, and the control pole is connected to the optocoupler LTV817. The feedback signal is accepted to control the duty ratio of the internal integrated high voltage MOS tube; the line detection terminal L is connected by a 2M Omega resistance and the positive end of the DC high voltage input to realize the line voltage detection of overvoltage and under voltage feedforward. The capacitance C1 is a high frequency filter capacitor; the transient voltage suppressor P6KE200 and the super fast recovery diode BYV26C constitute a clamping circuit, and in which the RC absorption circuit (composed of R2, R3 and C6) is made, so that the voltage can be clamped to the 200V so that the switching power can be started or overloaded in addition to the energy in the partial leakage. The leakage voltage of the TOPSwitch - GX internal integrated MOS tube is not more than 700V; the secondary output of the high frequency transformer T1 is output after MURl640CT rectification and C9, C10 and C11 filtering, then the output voltage is obtained after the magnetic bead L1 and C12 filter off the switch noise.
Single chip switching power supply has the remarkable advantages of monolithic integrated, simpler peripheral circuit, better performance index, complete isolation with no power frequency transformer and so on. It is an ideal choice for us to design the switching power supply below 290W.