SNVA559C September   2012  – February 2019 LM2574 , LM2575-N , LM2575HV , LM2576 , LM2576HV , LM2577

 

  1.   Switching regulator fundamentals
    1.     Trademarks
    2. 1 Switching Fundamentals
      1. 1.1 The Law of Inductance
      2. 1.2 Transformer Operation
      3. 1.3 Pulse Width Modulation (PWM)
    3. 2 Switching Converter Topologies
      1. 2.1  Buck Regulator
      2. 2.2  Continuous vs Discontinuous Operation
      3. 2.3  Boost Regulator
      4. 2.4  Output Current and Load Power
      5. 2.5  Buck-Boost (Inverting) Regulator
      6. 2.6  Flyback Regulator
      7. 2.7  Generating Multiple Outputs
      8. 2.8  Push-Pull Converter
      9. 2.9  Half-Bridge Converter
      10. 2.10 Full-Bridge Converter
    4. 3 Application Hints for Switching Regulators
      1. 3.1 Capacitor Parasitics Affecting Switching Regulator Performance
        1. 3.1.1 Input Capacitors
        2. 3.1.2 Output Capacitor ESR Effects
        3. 3.1.3 Bypass Capacitors
      2. 3.2 Proper Grounding
      3. 3.3 Transformer/Inductor Cores and Radiated Noise
      4. 3.4 Measuring Output Ripple Voltage
      5. 3.5 Measuring Regulator Efficiency of DC/DC Converters
      6. 3.6 Measuring Regulator Efficiency of Offline Converters
    5. 4 Application Circuits
      1. 4.1 LM2577: A Complete Flyback/Boost Regulator IC
        1. 4.1.1 Increasing Available Load Power in an LM2577 Boost Regulator
      2. 4.2 LM2577 Negative Buck Regulator
      3. 4.3 LM2577 Three-Output, Isolated Flyback Regulator
      4. 4.4 LM2575 and LM2576 Buck Regulators
      5. 4.5 Low Dropout, High Efficiency 5-V/3-A Buck Regulator
    6. 5 References and Related Products
  2.   Revision History

4.1 LM2577: A Complete Flyback/Boost Regulator IC

The LM2577 is an IC developed as part of the SIMPLE SWITCHER® product family. It is a current-mode control switching regulator, with a built-in NPN switch rated for 3-A switch current and 65-V breakdown voltage.

The most commonly used applications are for Flyback or Boost regulators (see Figure 25). In the Boost regulator, the output is always greater than the input. In the Flyback, the output may be greater than, less than, or equal to the input voltage.

basic_application_circuits_for_the_lm2577_snva559.gifFigure 25. Basic Application Circuits for the LM2577

The theory of operation of the flyback and boost converters has been previously covered, and will not be repeated here.

The LM2577 is targeted for applications with load power requirements up to a maximum of about 25 Watts, and can be used to implement boost or flyback regulators (with multiple output voltages available if flyback is selected).

The next sections will show the LM2577 being used in circuits which are more advanced than the typical applications (these circuits were generated as solutions for specific customer requirements).