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FCP11N60 Datasheet(PDF) 2 Page - Fairchild Semiconductor |
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FCP11N60 Datasheet(HTML) 2 Page - Fairchild Semiconductor |
2 / 15 page AN-6982 APPLICATION NOTE © 2010 Fairchild Semiconductor Corporation www.fairchildsemi.com Rev. 1.0.0 • 6/8/10 2 Functional Description Widely used operation modes for the boost converter are continuous conduction mode (CCM) and boundary conduction mode (BCM). These two descriptive names refer to the current flowing through the energy storage inductor of the boost converter, as depicted in Figure 2. The inductor current in CCM is continuous; while in BCM, the new switching period is initiated when the inductor current returns to zero, which is at the boundary of continuous conduction and discontinuous conduction operations. CCM PFC is commonly used for high-power applications above 300W since the inductor current has a small ripple and higher power factor can be obtained than BCM operation. Due to the reverse-recovery current of the output diode, using a high-speed diode with a small reverse recovery current is crucial to achieve high efficiency and low EMI. Figure 2. CCM vs. BCM Control Current and Voltage Control of PFC As shown in Figure 3, the FAN6982 employs two control loops for power factor correction: a current-control loop and a voltage-control loop. The current-control loop shapes inductor current, as shown in Figure 4, such that voltage drop across the internal resistor RM should be same as the averaged voltage drop across the sensing resistor, RCS, during one switching cycle: 0 () S T LCS MO M S I Rdt I R T 1 ⋅= ⋅ ∫ (1) where the internal resistor RM is typically 5.7kΩ; the output current of gain modulator, IMO, is given as a function of input current of IAC pin; and voltages of the VRMS and VEA pins are calculated as: 2 10.5 ( - 0.7) (- 0.7) EA MO AC MAX RMS EA V II VV × =× (2) Figure 3. Current and Voltage Control Feedback Circuit M MO CS R I R =⋅ Figure 4. Operation Waveforms of CCM PFC The voltage-control loop regulates PFC output voltage using an internal error amplifier such that the FBPFC voltage is same as the internal reference of 2.5V. Note that, from Equation (2), the voltages of VEA should be almost constant to obtain pure sinusoidal reference for the input current shaping. Because there is always twice the line frequency ripple in the PFC output voltage, a narrow bandwidth should be used for the output voltage-control loop to minimize the line frequency ripple. Otherwise, the control loop tries to remove the output voltage ripple, changing the error amplifier output voltage as shown in Figure 5, which causes distortion of the input current. |
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Similar Description - FCP11N60 |
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