二极管

USB

三极管

可控硅(晶闸管)

场效应管(MOSFET)

集成电路

连接器

LED系列产品

电感器

继电器

传感器

电容器

电阻器

保护器件

光电器件

压电晶体

开关原件

功率模块

1. Introduction
The FAN7528 is an active power factor correction (PFC) controller for the boost PFC application which operates in the critical conduction mode (CRM). The critical conduction mode boost power factor converter operates at the boundary of continuous conduction mode and discontinuous conduction mode. The CRM PFC controllers are of two kinds: the current mode CRM PFC controller and the voltage mode CRM PFC controller. For the current mode, a boost switch is turned on when the inductor current reaches zero and turned off when the inductor current meets the desired current reference. In this case, the rectified AC line voltage should be sensed to generate the current reference as in the FAN7527B, however the sensing network can cause additional power

loss. In the voltage mode, the switch turn-on is the same as that of the current mode, but the switch turn-off is determined by an internal ramp signal. The ramp signal is compared with an error amplifier output and the switch turn-on time is controlled to be constant as shown in Fig. 1. If the turn-on time is constant, the peak inductor current is proportional to the rectified AC line voltage as shown in Fig. 2. In this way, the input current waveform follows the waveform of the input voltage, thereby obtaining a good power factor. The FAN7528 is a voltage mode CRM PFC controller. Because the voltage mode CRM PFC controller does not need the rectified AC line voltage information, it can save the power loss of the sensing network.