PFC power factor correction circuit - Home Appliances

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Hello everyone, this is my first time sharing some technical content here. If you're an experienced engineer or expert, feel free to drop by and give me some feedback! I'm always looking to learn and improve. PFC stands for Power Factor Correction, which is a method used to improve the efficiency of electrical systems. According to national regulations, LCD TVs with a total power exceeding 75W must include a PFC circuit. The main goal of PFC is to make better use of the grid power and reduce interference in switching power supplies. A PFC circuit is also known as a boost post-regulation circuit. It's a parallel switching power supply that's placed between the rectifier and the filter capacitor. This helps stabilize the output voltage and improves overall performance. When VT1 is turned on, the voltage from the bridge rectifier BD1 is grounded through the energy storage inductor L1 and VT1. During this time, the inductor stores energy in the form of magnetic field. At the same time, the induced electromotive force has a positive polarity on the left and negative on the right. When VT1 is turned off, the induced electromotive force in the inductor reverses, converting the stored magnetic energy into electrical energy. Now, the polarity becomes positive on both ends. This voltage is then added to the output of the bridge rectifier, resulting in a voltage of approximately +380V, which charges the capacitor C1. When VT1 turns on again, the process repeats. However, at this point, the voltage stored in C1 is higher than the voltage at the positive terminal of diode D1, so D1 remains off. As a result, D1 operates intermittently. Since both the bridge rectifier and the inductor are supplying power to the load, the output voltage can reach as high as +375V to +400V. When the input voltage is 220V, the typical output of the PFC circuit is around +380V, which is why it's commonly referred to as the +380V rail.