Capacitor step-down power supply principle and calculation formula
The small transformerless switching power supply uses a transformer power supply with a large volume, which is difficult to use in some small-volume production. The small transformerless power supply described in this paper can provide 3~15V voltage and 150mA maximum current, which can meet the power supply requirements of small electronic equipment. As shown in the figure, 220V is filtered by D2 rectifier C1 as the conduction driving voltage of Q1. When the positive half cycle of 220V starts, but the voltage on the sliding end of W is not large enough, Q2 is in the off state, and the voltage on C1 is increased by R4. Q1 is turned on at the gate of Q1, and capacitor C2 is quickly charged by D1, R5, and Q1 in the positive half cycle of 220V. When the voltage at the wiper terminal of W rises enough to turn on D3 and Q2, the gate of Q1 loses its voltage and turns off. Adjust W to adjust the charging time of C2, which adjusts the output voltage. Since the on-time of Q1 is extremely short, C2 uses a large-capacity capacitor to ensure a smoother output voltage. R5 in the circuit is a current limiting resistor that reduces the peak value of the C2 charging current. The Zener diode D5 is designed to prevent Q1 from being damaged due to excessive gate voltage. D4 is used as output protection. When the voltage across C2 is too high, D4 and Q2 are turned on, and Q1 is turned off. Because the circuit does not work during the negative half cycle of the mains, in order to increase the output current, a rectifier bridge can be added to the input terminal to make the positive and negative half cycles of the mains available, which can increase the output current by 80mA. Can improve the smoothness of the output voltage. In practical applications, the potentiometers W and R3 can be replaced by a fixed resistor. When the output voltage stability is high, a three-terminal regulator IC can be added. This circuit is simple and works as long as the soldering is correct. There is no isolation measure for this circuit. Do not connect the L and N lines of the power supply when using. ![]()
1
1
Foshan Lanxun Trading Co., Ltd. , http://www.chpigmentpaste.com