Texas Instruments UCC28740EVM-525, Руководство пользователя

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SLUUAL8
1 Introduction
The UCC28740EVM-525 evaluation module is a 10 Watt off-line discontinuous mode (DCM) flyback
converter that provides constant-voltage (CV) and constant-current (CC) output regulation by using
an optical coupler for tight voltage regulation and improved the transient response to large load
steps and primary side control for accurate constant current regulation. The target application for this
converter design is USB adapters for consumer electronics. The UCC28740 uses frequency
modulation, peak primary current modulation, valley switching and valley skipping in its control
algorithm in order to maximize efficiency over the entire operating range.
2 Description
This evaluation module uses the
UCC28740 Constant-Voltage, Constant-Current Flyback Controller
Using Opto-Coupled Feed-Back
in a 10 W converter to provide 2 A of constant charge current. The
input accepts a voltge range of 85 VAC to 265 VAC. The output is designed for 5 V when in
constant voltage mode and will deliver 2.1 A of constant charge down to an output voltage of less
than 2 V. Depending upon the operating conditions, the control law algorithm will modulate the
switching frequency or the peak primary current to satisfy the power transfer requirements. As the
load is increased from zero, the converter will transition through a frequency modulation mode
where the peak primary current is held constant at one-quarter of its full-load peak value as the
switching frequency increases from a minimum value to maintain energy transfer up to 32 kHz.
When the load is increased to the level at which the switching frequency reaches 32 kHz, the
controller will keep the switching frequency fixed and modulate the peak primary current, increasing
it from one-quarter its peak value up to its maximum full load peak current value; this area of
operation is refered to as the amplitude modulation range. Further increase in load demand will
transition the controller into another frequency modulation mode where the peak primary current is
constant at its maximum designed value and the switching frequency is increased as needed, up to
the controller’s maximum 100 kHz switching frequency. Opto-coupled feed-back maintains a tightly
regulated output with fast dynamic response to load transients. The controller will further enhance
its efficient operation with valley switching. The UCC28740 also uses dithering of the gate drive
helps to ease EMI compliance.
This user’s guide provides the schematic, component list, assembly drawing, art work, and test set
up necessary to evaluate the UCC28740 in a typical off-line converter application.
2.1 Typical Applications
The UCC28740 is suited for use in isolated off-line systems requiring high efficiency and fault
protection features including:

USB-Compliant Adapters and Chargers for Consumer Electronics such as smart phones, tablet
computers, and cameras

Stand-by Supply for TV and Desktop

White Goods