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US ECCN: 3E991 and EU ECCN: EAR99
Application Report
SLUA735–February 2015
Rapid Transient Response With UCC28633
Primary-Side-Regulation (PSR) Flyback and
UCC24650 Wake-Up Monitor
Bernard Keogh ............................................................................. Systems Solutions & Marketing, HVPS
ABSTRACT
PSR flyback controllers make use of primary-side information to indirectly sense the output voltage for
regulation. This capability allows elimination of the conventional secondary-side error amplifier (typically
TL431) and feedback opto-coupler – saving cost and standby power. However, because the output
voltage can only be sampled during a switching cycle, there is always a trade-off with PSR between very-
low switching frequency to achieve low standby power and the need to keep switching frequency high to
maintain a fast transient response. This application note demonstrates how the UCC28633 PSR controller
can be combined with the UCC24650 secondary-side fast wake-up monitor to achieve low standby power
and fast transient response.
Topic ........................................................................................................................... Page
1 Introduction ........................................................................................................ 2
2 Transient Response versus Standby Power............................................................ 3
3 UCC28633 External Wake Input at VSENSE Pin ....................................................... 4
4 Practical Demonstration Using UCC28630-EVM572.................................................. 6
5 Test Results ........................................................................................................ 8
6 Summary and Conclusions ................................................................................. 12
7 References........................................................................................................ 12
8 Export Control Notice ......................................................................................... 12
1
SLUA735–February 2015 Rapid Transient Response With UCC28633 PSR-Flyback and UCC24650
Wake-Up Monitor
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