SLUAAB9A March   2021  – December 2021 UCC25800-Q1

 

  1.   Trademarks
  2. 1 Introduction
  3. 2 Open-Loop LLC Converter Operation Principle
  4. 3 Primary-side and Secondary-side Resonant Configurations
  5. 4 Rectification Methods
    1. 4.1 One Resonant Capacitor, Voltage Doubler
    2. 4.2 Two Resonant Capacitors, Voltage Doubler
    3. 4.3 One Resonant Capacitor, Full-wave Rectifier
  6. 5  LLC Transformer Design Steps
    1. 5.1 Transformer Turns Ratio Selection
    2. 5.2 Transformer Volt-second Rating Calculation
    3. 5.3 Transformer Construction
    4. 5.4 Transformer Winding Selection
    5. 5.5 Transformer Inductance
      1. 5.5.1 Leakage inductance
      2. 5.5.2 Magnetizing inductance
    6. 5.6 Transformer Selections
  7. 6 Negative Voltage Generation
    1. 6.1 Using a Zener Diode
    2. 6.2 Using a Shunt Regulator
    3. 6.3 Using a Shunt Regulator and Linear Regulator
  8. 7 Multiple-output Design
    1. 7.1 One UCC25800-Q1 Drives Each Output
    2. 7.2 Transformer With Multiple Secondary-side Windings
    3. 7.3 Multiple Transformers
  9. 8 EMI Performance
    1. 8.1 EMI Performance With Standalone Converter
    2. 8.2 EMI performance with an inverter power stage
  10. 9 Common-Mode Transient Immunity (CMTI)
  11. 10Summary
  12. 11Revision History

5.5.1 Leakage inductance

When the split chamber bobbin is used, the primary-side winding and secondary-side winding are physically separated. The coupling between two windings is poor and large leakage inductance is created. When using the secondary-side resonant, the method described in Figure 5-3 can be used to measure the leakage inductance (Lk) from the transformer secondary side. The leakage inductance is measured on the secondary side when the primary side is shorted. Following the same principle, when the primary-side resonant is used, measure the leakage inductance from the transformer primary side with the secondary side shorted. Once the leakage inductance is measured, the resonant capacitor Cr can be selected according to Equation 11. In this equation, Lk is the leakage inductance measured and f0 is the resonant frequency. The resonant frequency can be chosen as 10% above the switching frequency to allow component tolerances. If the one resonant capacitor configuration is used, the resonant capacitor should be the calculated total resonant capacitor Cr.

Equation 11. C r 1 = C r 2 = 1 2 C r = 1 2 × 1 4 π 2 L k f 0 2