15V/3.5A 52W switching power supply circuit

The circuit of 15V/3.5A 52W switching power supply composed of MC33374T/TV is shown in the figure. The allowable variation range of its AC input voltage u is 92~276V. The rectifier bridges VD1~VD4 use four 1N5406 3A/600V silicon rectifier tubes. The primary protection circuit consists of an RC absorption circuit (R2, C2) and a clamping circuit (VDz, VD5), which can effectively suppress the peak voltage caused by the leakage inductance of the high-frequency transformer and protect the power switch tube inside the MC33374 from damage. . VDz uses a P6KE200A transient voltage suppression diode (TVS) with a reverse breakdown voltage UB=200V. VD5 uses MURl60 ultra-fast recovery diode (SRD). Note that the serial numbers of the resistor-capacitor components R1 and C3 in the figure are vacant. If necessary, the series circuit of R2 and C2 can be changed to R1 (20kΩ, 2W) and C3 (0.1μF, 400V) in parallel and then in series with super After fast recovery diodes, an R, C, and VD type protection circuit is formed. 　　C5 is the bypass capacitor at the Vcc end. S is the button that controls the on and off status of the switch regulated power supply. After R7 is connected in series to S, the reliability of mode conversion can be improved. VD6 and C6 form the high-frequency rectification filter at the output end of the feedback coil. The secondary high-frequency rectifier uses a high-current, low-voltage drop Schottky diode, model MBR20100CT (20A/100V). This tube is a common cathode pair tube. The two negative poles (cathode) are short-circuited internally. When used, the two positive poles (anode) need to be connected externally and connected in parallel. The output filter circuit is composed of C8, C11, L, C12 and C13. In view of the fact that the inductance of the filter inductor L is very small, only 5.0μH, and the equivalent inductance Lo present on the large-capacity filter capacitors C8 and Cl1 will directly affect the actual inductance from L to L+Lo, so the feeder needs to be Circle N3 is wound with 7 turns of φ0.55mm enameled wire, and should be wound in the middle of the frame to reduce leakage inductance; then also wind two layers of polyester film. The ferrite core model is E25. To prevent magnetic saturation, an air gap of 0.43mm should be left between the two E-shaped cores. The main technical indicators of this power supply are shown in the table below