单芯片功率因素纠正离线式电源

离线式电源的功率因素校正(PFC)目的在于减少输入电流和满足未来稳压的需要。桥式整流器后接大电容的开关电源易产生谐波电流。这些谐波电流只是增加了电源输入电流的RMS，而对真正的功率没有任何贡献。典型的解决方案是对现有的设计增加一个PFC预稳压器和单独的控制器。LT1508和LT1509通过将PFC和脉宽调制器(PWM)集成到芯片内部，取消了独立控制器，PFC通过编程升压稳压器的输入电流来获得。
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Single IC, Power Factor Corrected, Off-Line Supply
Design Note 143
Kurk Mathews

An ever increasing number of off-line power supplies now lower part count and improved PC board layout. Start-up is
include power factor correction (PFC) in order to reduce controlled by separate PFC and PWM soft start pins. The
input current and meet future regulatory requirements. PWM Soft Start pin is held low, disabling the PWM output
Switching power supplies that incorporate a bridge recti- until the PFC stage is in regulation. The PWM will remain
fier followed by bulk capacitance create harmonic cur- enabled as long as the PFC output voltage stays above 73%
rents. These harmo