12V, 20W switching DC regulated power supply circuit composed of TOP224P
The 12V, 20W switching DC regulated power supply circuit composed of TOP224P is shown in the figure. Two integrated circuits are used in the circuit: TOP224P three-terminal monolithic switching power supply (IC1), PC817A linear optocoupler (IC2). The AC power supply is rectified and filtered by UR and Cl to generate DC high voltage Ui, which supplies power to the primary winding of the high-frequency transformer T. VDz1 and VD1 can clamp the peak voltage generated by the 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 Vla, C2, Ll and C3 to obtain 12V output voltage Uo. The value of Uo is set by the sum of the stable voltage Uz2 of VDz2, the forward voltage drop UF of the LED in the optocoupler, and the voltage drop on R1. Other output voltage values can also be obtained by changing the turns ratio of the high-frequency transformer and the stabilized voltage value of VDz2. R2 and VDz25 also provide a preload for 12V output to improve load regulation at light load. After the feedback winding voltage is rectified and filtered by VD3 and C4, it supplies the bias voltage required by TOP224P. The control terminal current is adjusted by R2 and VDz2, and the purpose of voltage regulation is achieved by changing the output duty cycle. The common-mode choke coil L2 can reduce the common-mode leakage current generated by the high-voltage switching waveform of the primary winding connected to the D terminal. C7 is a protection capacitor, which is used to filter out the interference caused by the coupling capacitance of the primary and secondary windings. C6 can reduce the differential mode leakage current generated by the fundamental and harmonics of the primary winding current. C5 can not only filter out the peak current added to the control terminal, but also determine the self-starting frequency. It also compensates the control loop together with R1 and R3.
The main technical indicators of the power supply are as follows:
AC input voltage range: u=85～265V;
Input grid frequency: fLl=47～440Hz;
Output voltage (Io=1.67A): Uo=12V;
Maximum output current: IOM=1.67A;
Continuous output power: Po=20W (TA=25°C, or 15W (TA=50°C);
Voltage adjustment rate: η=78%;
Maximum output ripple voltage: ±60mV;
Working temperature range: TA=0～50℃.
