Datasheet
UCC2897A
SLUS829D -- AUGUST 2008 -- REVISED JULY 2009
26
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ADDITIONAL APPLICATION INFORMATION
This solution uses the regulated output voltage across the output inductor during the freewheeling period to
generate a quasi-regulated bias for the control circuits.
Both of the illustrated solution provides reliable bias power during normal operation. Note that in both cases,
the bias voltages are proportional to the output voltage. This nature of the bootstrap bias supply c auses the
converter to operate in a hiccup mode under significant overload or under short-circuit conditions as the
bootstrap winding is not able to hold the bias rail above the undervoltage lockout threshold of the controller.
Another biasing solution, based on the active circuit shown on the previous page with components Q10, C18,
R19, D10 and D12. Such a circuit may be used in the applications where the allowed biasing capacitor size is
limited to optimize the board spaceutilization.
References and Additional Development Tools
1. Evaluation Module: UCC2891EVM, 48-V to 3.3-V, 30-A Forward Converter with Active Clamp Reset.
2. User’s Guide: Using the UCC2891EVM, 48-V to 3.3-V, 30-A Forward Converter with Active Clamp Reset,
(SLUU178)
3. Application Note: Designing for High Efficiency with the UCC2891 Active Clamp PWM Controller, Steve
Mappus (SLUA303)
4. Power Supply Design Seminar Topic: Design Considerations for Active C lamp and Reset Technique, D.
Dalal, SEM1100--Topic3 (SLUP112)
5. Power Supply Design Seminar Topic: Active Clamp and Reset Technique Enhances Forward Converter
Performance, B. Andreycak, SEM1000--Topic 3. (SLUP108)
6. Power Supply Design Seminar Topic: Design and Application Guide for High Speed MOSFET Gate Drive
Circuits, L. Balogh, SEM1400--Topic 2 (SLUP169)
7. Datasheet: UCC3580, Single Ended Active-Clamp/Reset PWM Controller, (SLUS292)
8. Evaluation Module: UCC3580EVM, Flyback Converters, Active Clamp vs. Hard--Switched.
9. Reference D esigns: Highly Efficient 100W Isolated Power Supply Reference Design Using UCC3580--1.
Texas Instruments Hardware Reference Design Number PMP206.
10. Reference Designs: Active Clamp Forward Reference Design using UCC3580--1. Texas Instruments
Hardware Reference D esign N umber PMP368