Central issue: This article refers to the address: http:// Boost PFC circuit principle and advantages and disadvantages Step-down PFC circuit principle and advantages and disadvantages The principle and advantages and disadvantages of the buck-boost PFC circuit Forward PFC circuit principle and advantages and disadvantages Flyback PFC principle and its advantages and disadvantages Commonly used active power factor correction circuits are classified into continuous current mode control type and discontinuous current mode control type. Among them, the continuous current mode control type mainly includes a boost type (Boost), a buck type (Buck), and a buck-boost type (Buck-Boost); the discontinuous current mode control type has a forward type (Forward) and a reverse type. The focus of the fly back, the following describes the working principle of these circuits. 1. Step-up PFC circuit The main circuit of the step-up PFC is shown in Figure 1. The working process is as follows: When the switch Q is turned on, the current IL flows through the inductor L. Before the inductor is not saturated, the current increases linearly, and the electric energy is stored in the form of magnetic energy. In the inductor coil, at this time, the capacitor C discharge supplies energy to the load; when Q is turned off, the self-induced electromotive force VL is generated at both ends of L to keep the current direction unchanged. Thus, VL is in series with the power supply VIN to supply power to the capacitor and load. Figure 1. Step-up PFC main circuit. The advantages of this circuit are: (1) The input current is completely continuous and can be modulated during the sinusoidal period of the entire input voltage, so that a high power factor can be obtained; (2) The inductor current is the input current and is easy to adjust; (3) The gate drive signal of the switch tube is grounded with the output, and the driving is simple; (4) The input current is continuous, the current peak of the switch tube is small, and it has strong adaptability to the input voltage change, and is suitable for occasions where the grid voltage changes greatly. The main disadvantage is that the output voltage is relatively high, and the output short circuit protection cannot be realized by the switch tube. 2. Step-down PFC circuit The step-down PFC circuit is shown in Figure 2. The working process is as follows: When the switch Q is turned on, the current IL flows through the inductor, and the current IL increases linearly before the inductor is saturated; when the switch Q is turned off , L generates self-induced electromotive force at both ends, and supplies power to the capacitor and the load. Since the converter output voltage is lower than the power supply voltage, it is called a buck converter. Figure 2 Step-down PFC main circuit The main advantage of this circuit is that the maximum voltage of the switch tube is the maximum value of the input voltage, so the voltage stress of the switch tube is small; when the rear stage is short-circuited, the switch tube can be used. Achieve output short circuit protection. The main disadvantage of this circuit is that the circuit can only work when the input voltage is higher than the output voltage. Therefore, in each sinusoidal period, the circuit has a low input voltage and cannot work normally, and the output voltage is low. At the same power level, the current stress of the DC/DC converter of the latter stage is large; the signal of the gate of the switch tube is different from the output ground, the drive is more complicated, and the input current is interrupted, the power factor cannot be improved much, so Rarely adopted. Cnc Machining Parts,Cnc Machined Fitting Parts,Cnc Machining Accessories,Cnc Machining Aluminum Accessories Dongguan Formal Precision Metal Parts Co,. Ltd , https://www.formalmetal.com
