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UCC3818A Datasheet(PDF) 8 Page - Texas Instruments |
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UCC3818A Datasheet(HTML) 8 Page - Texas Instruments |
8 / 33 page UCC2817A, UCC2818A UCC3817A, UCC3818A SLUS577B − SEPTEMBER, 2003 − REVISED FEBRUARY 2006 8 www.ti.com APPLICATION INFORMATION The UCC3817A is a BiCMOS average current mode boost controller for high power factor, high efficiency preregulator power supplies. Figure 1 shows the UCC3817A in a 250-W PFC preregulator circuit. Off-line switching power converters normally have an input current that is not sinusoidal. The input current waveform has a high harmonic content because current is drawn in pulses at the peaks of the input voltage waveform. An active power factor correction circuit programs the input current to follow the line voltage, forcing the converter to look like a resistive load to the line. A resistive load has 0 ° phase displacement between the current and voltage waveforms. Power factor can be defined in terms of the phase angle between two sinusoidal waveforms of the same frequency: PF + cos Q Therefore, a purely resistive load would have a power factor of 1. In practice, power factors of 0.999 with THD (total harmonic distortion) of less than 3% are possible with a well-designed circuit. Following guidelines are provided to design PFC boost converters using the UCC3817A. NOTE: Schottky diodes, D5 and D6, are required to protect the PFC controller from electrical over stress during system power up. UDG-98183 1 11 7 16 GND DRVOUT R17 20 Ω 15 C3 1 µF CER VCC C2 100 µ F AI EI 14 C1 560pF 13 C4 0.01 µF 12 R1 12k R3 20k R2 499k R4 249k R5 10k C5 1 µF 9 4 10 VREF VCC CT SS RT VSENSE OVP/EN VREF VAOUT 3 8 2 VFF C6 2.2 µF C7 150nF R7 100k 6 5 R9 4.02k C8 270pF R8 12k D6 R10 4.02k D5 R11 10k R12 2k R14 0.25 Ω 3W C13 0.47 µF 600V C14 1.5 µ F 400V R13 383k IAC R18 24k R15 24k R16 100 Ω VCC C10 1 µ F C11 1 µF D7 D8 L1 1mH D2 6A, 600V D1 8A, 600V C12 220 µF 450V VOUT 385V−DC + − PKLIMIT CAOUT CAI MOUT IAC VO UCC3817A VLINE 85−270 VAC VREF C9 1.2nF R6 30k 6A 600V D3 Q1 F1 VO D4 R19 499k R20 274k R21 383k AC2 AC1 C15 2.2 µ F IRFP450 Figure 1. Typical Application Circuit (1) |
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