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FFPF10H60S Datasheet(PDF) 9 Page - Fairchild Semiconductor |
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FFPF10H60S Datasheet(HTML) 9 Page - Fairchild Semiconductor |
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9 / 15 page  AN-6982 APPLICATION NOTE © 2010 Fairchild Semiconductor Corporation www.fairchildsemi.com Rev. 1.0.0 • 6/8/10 9 , (1 cos(4 )) D AVG BOUT LINE I If t π =− ⋅ ⋅ BOUT I , 2 BOUT BOUT RIPPLE LINE BOUT I V fC π = BOUT V , DAVG I D I Figure 16. PFC Output Voltage Ripple (Design Example) With the ripple specification of 12VPP, the capacitor should be: , 0.9 239 22 50 12 BOUT BOUT LINE BOUT RIPPLE I CF fV μ ππ >= = ⋅⋅ ⋅ ⋅ Since minimum allowable output voltage during one cycle line (20ms) drop-outs is 310V, the capacitor should be: 3 22 2 2 , 2 2 349 20 10 260 387 310 BOUT HOLD BOUT OUT OUT MIN Pt CF VV μ − ⋅ ⋅⋅ × >= = −− Thus, 270 μF capacitor is selected for the PFC output capacitor. [STEP-5] PFC Output Sensing Circuit To improve system efficiency at low-line and light-load condition, FAN6982 provides two-level PFC output voltage. As shown in Figure 17, the range function can be enabled or disabled through a resistor connected to ground or VREF. FAN6982 monitors VEA and VRMS voltages to adjust the PFC output voltage and enables a 20µA current source. The PFC output voltage when 20µA is enabled is given as: 2 2 20 (1 ) 2.5 FB BOUT BOUT μAR VV - × =× (23) It is typical to set the second boost output voltage as 340V~300V. It should be checked if the output voltage is higher than the peak of the line voltage 12 3 2 3 2.45 2 RMS RMS RMS BOUT RMS RR R V R π ++ ⋅⋅ < (24) Figure 17. Block of Range Function The voltage divider network for the PFC output voltage sensing should be designed such that FBPFC voltage is 2.5V at nominal PFC output voltage: 2 12 2.5 FB BOUT FB FB R VV RR ×= + (25) (Design Example) Assuming the second level of PFC output voltage is 347V: 2 2 6 6 2.5 (1 ) 20 10 347 2.5 (1 ) 12.9 387 20 10 BOUT FB BOUT V R V k − − =− ⋅ × = −⋅ = Ω × 13k Ω is selected for RFB2. It is checked if the output voltage is higher than the peak of the line voltage: 12 3 3 63 3 3 2.45 2 2 10 200 10 36 10 2.45 2 36 10 239 347 RMS RMS RMS RMS RR R R VV π π ++ ⋅⋅ ×+ × + × =⋅ ⋅ × =< Then, to obtain 387V for nominal PFC output, 12 3 (1) 2.5 387 (1) 13 10 1999 2.5 BOUT FB FB V RR k =− ⋅ = −⋅ × = Ω 2M Ω is selected for RFB1. 2.5V + - VDD RFB1 RFB2 FBPFC 20µA 1.95/2.45 VEA VRMS + - 1.95/2.45 VREF EN + - 3.75 SGND VBOUT |
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