Other Parts Discussed in Thread: , TIDA-01505
Tool/software:
Dear TI Team,
I have selected the UCC28C56H controller for my flyback application and have been performing the design calculations using the UCC28C56H-Q1 datasheet, as the reference design there is very close to my requirements. I would appreciate your clarification on the following points.
Application specifications:
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Input Voltage: 85 – 1000 VDC
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Output Voltage: 25 V / 80 W
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Switching frequency: 40 kHz
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Calculated values: Lm = 600 µH, Turns ratio = 12.5:1 (Np:Ns::75:6) Aux winding = 5 turns, Rsense = 0.35 Ω, Secondary peak current ≈ 35 A
Questions:
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Can I directly use the HV startup circuit from the datasheet application note, since my input range is similar? Should I reduce R5 to adjust the startup current? Also, since D9 is shown as an 18 V zener (below UVLO_on), would it be better to select a 19 V or 20 V zener to avoid premature clamping?
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I am struggling with the calculation of slope compensation, current filtering, and leading-edge blanking. Section 9.2.2.13 of the datasheet provides general guidance, but not a clear derivation. Could you provide more detailed design equations or an example?
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The same uncertainty applies to the soft-start parameters — could you advise on how these should be calculated?
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My calculated secondary peak current is ~35 A. Since Schottky diodes with this rating become expensive, would it be acceptable to use a 10 A Schottky diode with Ifsm > 100 A, given the pulsed current profile?
I would greatly appreciate your guidance. Please let me know if further details are required from my side.
