SNVA994A February   2022  – March 2023 LM5157 , LM5157-Q1 , LM51571-Q1 , LM5158 , LM5158-Q1 , LM51581 , LM51581-Q1

 

  1.   1
  2.   Trademarks
  3. 1Introduction
  4. 2Example Application
  5. 3Calculations and Component Selection
    1. 3.1 Switching Frequency
    2. 3.2 Transformer Selection
      1. 3.2.1 Maximum Duty Cycle and Turns Ratio Selection
      2. 3.2.2 Primary Winding Inductance Selection
    3. 3.3 Slope Compensation Check
    4. 3.4 Diode Selection
    5. 3.5 Output Capacitor Selection
    6. 3.6 Input Capacitor Selection
    7. 3.7 UVLO Resistor Selection
    8. 3.8 Control Loop Compensation
      1. 3.8.1 Crossover Frequency (fcross) Selection
      2. 3.8.2 RCOMP Selection
      3. 3.8.3 CCOMP Selection
      4. 3.8.4 CHF Selection
  6. 4Component Selection Summary
    1. 4.1 Application Circuit
    2. 4.2 Bill of Materials
  7. 5Small Signal Frequency Analysis
    1. 5.1 Flyback Regulator Modulator Modeling
    2. 5.2 Compensation Modeling
  8. 6Revision History

1

The LM5157x/LM5158x device is a wide-input range, non-synchronous converter with an integrated power MOSFET. The commonly supported configurations include Boost, Flyback and SEPIC topologies. This report focuses on designing the LM5157x/LM5158x as a primary side regulated (PSR) flyback converter. The design procedure is generic on selecting suitable components of the PSR flyback converter for the given application specification. The LM5175EVM-FLY evaluation module is used as the example to illustrate the design procedure, and the circuit performance results are also presented in the LM5157EVM-FLY User's Guide. For typical applications the LM5157/58 Flyback Controller Quick Start Calculator can also be used to efficiently complete the calculations described in this report.