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UC2854BMDWREP Fiches technique(PDF) 10 Page - Texas Instruments |
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UC2854BMDWREP Fiches technique(HTML) 10 Page - Texas Instruments |
10 / 38 page ± K V § · ¨ ¸ © ¹ UDG−03110 10 11 6 8 15 1 16 ENA VSENSE IAC VRMS VCC GND GTDRV 2.65 V / 2.15 V 3 V 7 VAO 13 SS X2 A B C (A) 16 V / 10 V (B) 10.5 V / 10 V 5 MOUT 4 ISENSE 3 CAO 14 CT OSC 12 RSET S Q R R 2 PKLMT 20 V IC POWER 7.5 V REF 9 REF RUN 7.1 V RUN VCC 14 µA I MOUT A B C UC2854B-EP SGLS318A – NOVEMBER 2005 – REVISED NOVEMBER 2015 www.ti.com 8 Detailed Description 8.1 Overview The objective of active power factor correction is to make the input to a power supply look like a simple resistor. An active power factor corrector does this by programming the input current in response to the input voltage. As long as the ratio between the voltage and current is a constant the input will be resistive and the power factor will be 1.0. When the ratio deviates from a constant the input will contain phase displacement, harmonic distortion or both and either one will degrade the power factor. UC3854 configured as a boost converter can be used to meet the system needs. A boost regulator is an excellent choice for the power stage of an active power factor corrector because the input current is continuous and this produces the lowest level of conducted noise and the best input current waveform. The disadvantage of the boost regulator is the high output voltage required. The output voltage must be greater than the highest expected peak input voltage. The boost regulator input current must be forced or programmed to be proportional to the input voltage waveform for power factor correction. Feedback is necessary to control the input current and either peak current mode control or average current mode control may be used. Both techniques may be implemented with the UC3854. 8.2 Functional Block Diagram 8.3 Feature Description The UC2854B is designed as a pin compatible upgrade to the industry standard UC2854 active power factor correction circuits. The circuit enhancements allow the user to eliminate in most cases several external components currently required to successfully apply the UC2854. In addition, linearity improvements to the multiply, square and divide circuitry optimizes overall system performance. Detailed descriptions of the circuit enhancements are provided below. For in-depth design applications reference data see the application notes, UC2854 Controlled Power Factor Correction Circuit Design (SLUA144) and UC2854A and UC2854B Advanced Power Factor Correction Control ICs (SLUA177). 8.3.1 Multiply/Square and Divide The UC2854B multiplier design maintains the same gain constant as the UC2854. The relationship between the inputs and output current is given as: 10 Submit Documentation Feedback Copyright © 2005–2015, Texas Instruments Incorporated Product Folder Links: UC2854B-EP |
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