Switching DC regulated power supply circuit based on TOP224P

　　This article introduces a switching DC regulated power supply circuit based on TOP224P. As shown in the figure below, two integrated circuits are used in the circuit: TOP224P three-terminal monolithic switching power supply (IC1) and PC817A linear optocoupler (IC2). After the AC power is rectified and filtered by UR and Cl, a DC high voltage Ui is generated to supply power to the primary winding of the high-frequency transformer T.

　　VDz1 and VD1 can clamp the peak voltage generated by leakage inductance to a safe value and attenuate the ringing voltage. VDz1 uses a P6KE200 transient voltage suppressor with a reverse breakdown voltage of 200V, and VDl uses a 1A/600V UF4005 ultra-fast recovery diode. The secondary winding voltage is rectified and filtered by V砬, C2, L1 and C3 to obtain a 12V output voltage Uo. The Uo value is set by the sum of the VDz2 stable voltage Uz2, the forward voltage drop UF of the LED in the optocoupler , and the voltage drop on R1. Other output voltage values ​​can be obtained by changing the turns ratio of the high-frequency transformer and the voltage regulation value of VDz2. R2 and VDz25 also provide a dummy load for the 12V output to improve the load regulation rate under light load. The feedback winding voltage is rectified and filtered by VD3 and C4 to provide the required bias voltage for TOP224P. The control terminal current is adjusted by R2 and VDz2, and the voltage regulation is achieved by changing the output duty cycle. The common mode choke L2 can reduce the common mode leakage current generated by the high voltage switch waveform of the primary winding connected to the D terminal. C7 is a protection capacitor used to filter out the interference caused by the coupling capacitor of the primary and secondary windings. C6 can reduce the differential mode leakage current generated by the fundamental wave and harmonics of the primary winding current.