SLUU077C – September 2000 – Revised November 2002
3
UCC3817 BiCMOS Power Factor Preregulator
1
Introduction
This user’s guide details the Texas Instruments (TI) UCC3817–EVM BiCMOS Power Factor Preregulator
Evaluation Module (EVM) SLUU077. It includes a list of EVM features, a brief description of the module
illustrated with pictorial and schematic diagrams and EVM specifications.
The UCC3817 evaluation board is designed to illustrate the performance of the controller in a 250 W boost
converter with power factor correction. The board is designed to handle a universal input operating voltage
range (i.e. 85–265 V ac) with a regulated 385 V dc output.
CAUTION:
Proper precautions must be taken
when working with the board
D
High voltage levels are present on the evaluation board whenever it is energized.
D
The output capacitor has high levels of energy storage and it must be discharged before the load is removed.
Improper handling of the evaluation board could cause serious injury.
D
It is important to maintain the ambient temperature around the evaluation board to below 40
°
C during
operation
1.1
Evaluation Module Features
D
Designed for Compliance with IEC 1000-3-2 (Low Total Harmonic Distortion)
D
Worldwide Line Operation 85 V
RMS
to 265 V
RMS
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Regulated 385-V, 250-W(max), dc Output
D
Accurate Power Limiting
D
Accurate Overvoltage Protection
1.2
Description
The UCCx817 provides all the functions necessary for active power-factor-corrected preregulators. The
controller achieves near-unity power factor by shaping the ac input-line current waveform to correspond to that
of the ac input-line voltage. Average current-mode control maintains stable, low-distortion, sinusoidal line
current.
The controller’s operation is similar to previously designed Unitrode preregulators with an added feature to
reduce the RMS-current in the boost capacitor. The controller uses leading-edge modulation that, when
synchronized properly with a downstream dc-to-dc converter, reduces the RMS current in the boost capacitor.