Fixed and switching hybrid regulated power supply electronic circuit diagram

　　The circuit is shown in the figure. Its core device IC1 is TOP221 , a three-terminal high-voltage switch integrated circuit, which integrates a voltage-type pulse width modulation oscillator, a reference voltage source, an error amplifier, a high-voltage startup current limiting resistor, and overheating protection circuits. In addition, a 700V N-channel power field effect transistor is integrated on the chip, and its operating frequency can reach 100kHz, the driving power consumption is small, the maximum duty cycle is 70%, and the efficiency can reach 90%. Therefore, the switching power supply has few peripheral components and high reliability. The drain D of IC1 is connected to high voltage, the source S is connected to zero potential, and the startup capacitor C3 is connected between the control electrode C and the zero potential. Usually the capacitance value is 47μF. The input current of the control electrode C will change the duty cycle of the pulse width modulation. When the input current increases, the duty cycle will decrease.

　　The control current comes from a secondary winding 3, 4 of the high-frequency switching transformer T. The volume of the ferrite core of T is only 19mm×17mm×5mm. VD5 suppresses the reverse peak spike pulse. The working process of the peripheral circuit of IC1 is very simple: when the output voltage increases, the input current of the C pole of IC1 will also increase, and the output pulse duty cycle will decrease, thereby reducing the output voltage.