“This time, we talked about the circuit principle of a 220V LED lamp used at home. Broadly speaking, it is to reduce the input voltage through the resistance and capacitance step-down, and then through the rectifier bridge, filter capacitor, voltage regulator and additional components to drive multiple LED lights to glow. The specific circuit diagram is the one shown below, and the whole circuit has few components. Some inexpensive LED lights are essentially using this resistance capacitance step-down circuit. Here’s a wateproof led strip light.
Let’s talk about the principle. R is the discharge resistance, and typically 330 ~ 680KΩ resistance can be selected. Capacitor C1 is the capacitor that plays the role of depressor. There is a saying on the Internet that “”220V after resistance and capacitance step-down (with 1uF capacitor), about 70mA””. How is this? We understand that the DC current cannot pass through the capacitor, and the capacitive reactance generated by the capacitor in the case of AC is 1/(2*πfc), where π is a constant (commonly 3.14), f is the frequency of alternating current and the mains power is 50, and c is the capacitance value of the capacitor. According to this formula, when the capacitor is 1uF, the capacitive reactance can be calculated as about 3184.7Ω. Connected to the 220V power supply, the maximum output current is about 70mA (220/3184.7).
However, the most afraid of the resistance and capacitance step-down circuit is the open circuit. If there is no rectifier bridge and the circuit behind, then the output end of the capacitor C1 is directly connected with the 220V power supply, if people accidentally touch it will have the risk of electric shock. In a word, the principle of resistive capacitance step-down is to reduce the voltage through the way of impedance voltage division.
The rectifier bridge in the back is really the black block in the figure below. It can change alternating alternating alternating alternating current into direct current in the same direction, but the voltage ripple of this direct current is relatively large. The filter capacitor C2 in the back can make the ripple more gentle, but the ripple is too large compared with the DC in the dry battery.
The possible consequence is to feel that the bulb is flashing. In order to solve this problem, a voltage regulator is connected to the back, and the voltage output of the regulator tube is relatively constant. In this way, the output voltage is relatively constant, which can provide a constant voltage for the LED lamp behind.
However, the power provided by this circuit is not extremely large, one is limited to the step-down capacitor, and another is also limited to the voltage regulator, the current provided by the regulator itself is not extremely large.”