25w quasi-resonant flyback converter for set-top box ...skory. 25w quasi-resonant flyback converter

Download 25W quasi-resonant flyback converter for set-top box ...skory. 25W QUASI-RESONANT FLYBACK CONVERTER

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  • AN1376 APPLICATION NOTE

    25W QUASI-RESONANT FLYBACK CONVERTER FOR SET-TOP BOX APPLICATION USING THE L6565

    This document describes a reference design of a 25W Switch Mode Power Supply dedicated to Set-Top Box application. The board accepts full range input voltage (90 to 265Vrms) and delivers 5 outputs. It is based on the new controller L6565, working in variable frequency mode.

    1 INTRODUCTION Set-Top Boxes are growing very fast and they are becoming very popular in all Countries ei- ther for satellite or cable decoding. Hence the market is asking for solutions having high cost effectiveness, providing for good performances, low noise, small volumes at low cost. The Quasi-resonant operation and the high flexibility of the L6565 make it a very suitable device, able to satisfy all the requirements with only few external components.

    The board has been designed with mixed technology components, both PTH and SMT. For this reason some components are doubled, in accordance with their ratings.

    Rev. 2

    1/35AN1376/0904

  • AN1376 APPLICATION NOTE

    2 MAIN CHARACTERISTICS The main characteristics of the SMPS are listed here below:

    ■ INPUT VOLTAGE: Vin: 90 - 264 Vrms f: 45-66 Hz

    ■ OUTPUT VOLTAGES:

    NOTES: (A) Dedicated to 5V digital circuitry and to 3.3v local post regulators (B) Dedicated to SCART, LNBP21 for satellite STB. For other applications the current is 0.4A (C) Dedicated to 5V local post regulators (D) Dedicated to tuner

    ■ STAND-BY No stand-by mode is foreseen by equipment

    ■ OVERCURRENT PROTECTION On all outputs, with auto-restart at short protection

    ■ PCB TYPE & SIZE: Cu Single Side 35 um, FR-4, 122.5 x 75 mm

    ■ SAFETY: In acc. with EN60950, creepage and clearance minimum distance 6.4mm

    ■ EMI: In acc. with EN50022 Class B

    Vout (V): Iout (A): Pout (W): STABILITY NOTES

    3.3 2.00 6.6 +/- 2%

    5 1.1 5.5 +/- 2% (A)

    12 0.7 8.4 +/- 5% (B)

    7 0.5 3.5 +/- 8% (C)

    30 0.015 0.45 +/- 2% (D)

    POUT (W) = 24.45

    2/35

  • AN1376 APPLICATION NOTE

    3 ELECTRICAL DIAGRAM

    Figure 1. Electrical Diagram

    D 1

    S M

    B Y

    T 0

    1 -4

    0 0

    C 1

    2 2

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    -1 6

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    D 3

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    W P

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    3/35

  • AN1376 APPLICATION NOTE

    The switching frequency (minimum is ~30 kHz @Vin = 80 VDC) has been chosen to get a com- promise between the trans

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