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Unformatted text preview:   To be instantaneously proportional to input voltage •  I = kV –  Makes circuit “look” like a resistor –  May change the constant k over time •  Often done in a separate input stage •  Trivially achieved with DCM boost input stage •  Can be accomplished with CCM boost input stage and current-mode control PFC Input Stage PFC Boost Forward Output Stage DCM of Flyback 1kHz Input Frequency Constant Pulse Width Two Other Strategies LT1248 TYPICAL APPLICATI UO 300W, 382V Preregulator T 90V TO 270V EMI FILTER 6A MURH860 750µH* + VOUT – 0.47µF 20k 20k 1% RS 0.2Ω 0.047µF RREF 4k 330k 4k 100pF 1nF 0.1µF VAOUT VCC – 8 EA 7.5V OVP 13 12µA SS + IA GND 15 VCC – + 7µA I 2I I=AB IB M 200µA2 + + 5V + IM – + CA R R – 32k – – 50k 1 M1 – 7.9V 4.7nF PKLIM 2 3 CAOUT 56µF 35V – VSENSE IAC ISENSE + Q GTDR 16 10Ω S RUN 0.7V – 6 4 + 11 1M 2.2V + EN/SYNC 5 + 20k RUN – 2.6V/2.2V 10 MOUT VCC = 18V** 7.5V VREF + 16V TO 10V VREF 9 7 + 1M 1% IRF840 OSC ONE SHOT 200ns 16V SYNC † 1N5819 0.01µF CSET * 1. COILTRONICS CTX02-12236-1 (TYPE 52 CORE) AIR MOVEMENT NEEDED AT POWER LEVEL GREATER THAN 250W. 2. COILTRONICS CTX02-12295 (MAGNETICS Kool Mµ® 77930 CORE) ** SEE START-UP AND SUPPLY VOLTAGE SECTION FOR VCC GENERATOR. † THIS SCHOTTKY DIODE IS TO CLAMP GTDR WHEN MOS SWITCH TURNS OFF. PARASITIC INDUCTANCE AND GATE CAPACITANCE MAY TURN ON CHIP SUBSTRATE DIODE AND CAUSE ERRATIC OPERATIONS IF GTDR IS NOT CLAMPED. 1000pF 14 12 RSET 15k Kool Mµ is a registered trademark of Magnetics, Inc. 1248 TA01 180µF Summary of PFC •  Input current must be proportional to input voltage –  Harmonics limited by regulation •  PFC input stage regulates input current –  DCM – constant pulse width –  CCM – multiply input voltage by voltage error signal and regulate current to this value –  CrCM – Constant on-time variable frequency Inverters Inverter •  PFC regulates an AC input current –  Converts AC power to DC power •  Inv...
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This document was uploaded on 04/07/2014.

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