Datasheet

SLUU087B
13
10-Watt Flyback Converter Using the UCC3809
16 Slope Compensation
All peak current-mode converters benefit from slope compensation, which is added to the current-sense signal,
to cancel the error introduced by sensing peak current instead of average current. The amount of inductor down
slope added to the FB pin was designed to be approximately 0.5 and the emitter follower configuration was used.
The step-by-step calculations are beyond the scope of this design note. Application Note U–111 (TI Literature
Number SLUA111) is an excellent reference for slope compensation design techniques.
17 Silkscreen
C10
C11
C12
J3
J4
+OUT
OUT
C7
C6
D2
R10
R11
C18
R7
J5
J2
48 IN
J1
+48 IN
SHUTDOWN
Q3
R24
C13
D4
C5
C14
D3
NOTE: High–temperature component. See EVM Warnings and Restrictions at the back of this document.
18 Conclusion
This design procedure addresses the major considerations and calculations used in the design of a 10-W
discontinuous-mode flyback converter. These include maximum duty cycle, inductor turns ratio, core selection,
primary inductance, gate drive, and current sensing. Major component selections such as switching element,
output diode, and output capacitors were also discussed as well as control loop compensation. This converter
is available as an evaluation module from Texas Instruments.
19 References
Bill Andreycak, Practical Considerations in High Performance MOSFET, IGBT and MCT Gate Drive Circuits,
Unitrode Application Note U–137, (TI Literature Number SLUA156), Unitrode Applications Handbook IC#1051,
1997.
Bill Andreycak, Practical Considerations in Current Mode Power Supplies, Unitrode Application Note U–111, (TI
Literature Number SLUA111), Unitrode Applications Handbook IC#1051, 1997.
Keith Billings, Switchmode Power Supply Handbook, McGraw–Hill, Inc.,1989.
Lloyd Dixon, Jr., Closing the Feedback Loop, Unitrode Power Supply Design Seminar Manual SEM–1100, 1996.