FSQ0565R(2007) 查看數據表（PDF） - Fairchild Semiconductor

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FSQ0565R
(Rev.:2007)

Green-Mode Fairchild Power Switch (FPS™) for Quasi-Resonant Operation - Low EMI and High Efficiency

Fairchild Semiconductor 

If no valley is found during tW, the internal SenseFET is

forced to turn on at the end of tW (Case D). Therefore,

the devices have a minimum switching frequency of

48kHz and a maximum switching frequency of 67kHz.

8. AVS (Alternating Valley Switching): Due to the

quasi-resonant operation with limited frequency, the

switching frequency varies depending on input voltage,

load transition, and so on. At high input voltage, the

switching on time is relatively small compared to low

input voltage. The input voltage variance is small and the

switching frequency modulation width becomes small. To

improve the EMI performance, AVS is enabled when

input voltage is high and the switching on time is small.

Internally, quasi-resonant operation is divided into two

categories; one is first valley switching and the other is

second-valley switching after blanking time. In AVS, two

successive occurrences of first-valley switching and the

other two successive occurrences of second-valley

switching is alternatively selected to maximize frequency

modulation. As depicted in Figure 35, the switching

frequency hops when the input voltage is high. The

internal timing diagram of AVS is described in Figure 36.

Figure 34. QRC Operation with Limited Frequency

Figure 35. Switching Frequency Range

Figure 36. Alternating Valley Switching (AVS)

© 2007 Fairchild Semiconductor Corporation

FSQ0565R, FSQ0765R Rev. 1.0.0

16

www.fairchildsemi.com

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