High voltage PWM three-terminal switching power supply

The simplest actual circuit of 5V/5W switching power supply is as shown in the figure. TOP210 (IC1) in the picture is a three-terminal PWM switch. IC1 contains PWM controller, power MOSFET and various protection circuits. The cost of this 5V/5W switching power supply is lower than that of commonly used linear power supplies.

The AC input voltage range of this power supply is 85~265V. When the load changes from 10% to 100% of the rated load, the power supply voltage regulation rate and load current regulation rate can reach +-5%. The power supply also has overvoltage, overtemperature protection and current limiting functions.

The D pin of TOP210 is the drain of the internal output MOSFET, and the C pin is the internal error amplifier and feedback current input pin, which is used to adjust the duty cycle of the switching power supply. The S pin is the source of the internal MOSFET and the common terminal of the internal control circuit.

The DC high voltage after the AC input voltage is rectified by VD1-VD4 is added to one end of the primary coil of transformer T1, and the other end of the primary coil is added to the drain of the TOP210 internal output MOSFET. VD5 and VD6 form a clamping circuit to limit the peak voltage of the pulse front caused by the leakage inductance of the transformer to a safe value. The operating frequency of this power supply is l00kHz. After the secondary voltage of the transformer is rectified by VD7 and filtered by C2, C3 and L2, it outputs a stable voltage of 5V. L1, C7, C4, and C5 are used to reduce the conducted radiation current to reduce the radio frequency interference generated by the switching power supply. The voltage at both ends of the feedback coil is rectified by VD8, current-limited and filtered by R1 and C6, and then added to the control pin of TOP210. The voltage at both ends of C6 is adjusted by TOP201 to stabilize the output voltage.