UCC28610
www.ti.com ......................................................................................................................................... SLUS888C–JANUARY 2009–REVISED SEPTEMBER 2009
APPLICATION INFORMATION
General Operation
The flyback converter is attractive for low power AC/DC applications because it provides output isolation and
wide input operating abilities using a minimum number of components. Operation of the flyback converter in
Discontinuous Conduction Mode (DCM) is especially attractive because it eliminates reverse recovery losses in
the output rectifier and it simplifies control.
The UCC28610 is a flyback controller for 12-W to 65-W, peak AC/DC power supply applications that require both
low AC line power during no-load operation and high average efficiency. This controller limits the converter to
DCM operation. It does not allow Continuous Conduction Mode (CCM) operation. Forced DCM operation results
in a uniquely safe current limit characteristic that is insensitive to AC line variations. The peak current mode
modulator does not need slope compensation because the converter operates in DCM.
The operation of the UCC28610 is facilitated by driving the external high voltage MOSFET through the source.
This configuration is called a cascode driver. It features fast start-up and low input power under no-load
conditions without having high voltage connections to the control device. The cascode driver has no effect on the
general operation of the flyback converter.
The feedback pin uses current rather than voltage. This unique feature minimizes primary side power
consumption during no-load operation by avoiding external resistive conversion from opto-coupler current to
voltage.
Average efficiency is optimized by the UCC28610 between peak power and 22% peak power with constant peak
current, variable off-time modulation. This modulation tends to make the efficiency constant between 22% and
100% peak load, eliminating the need to over-design to meet average efficiency levels that are required by
EnergyStar™.
Copyright © 2009, Texas Instruments Incorporated
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