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

4.1 One Resonant Capacitor, Voltage Doubler

Figure 4-1 One Resonant Capacitor, Voltage Doubler

In this configuration, only one capacitor Cr is needed for the resonant capacitor. There is a DC voltage offset on the resonant capacitor and the voltage doubling is achieved through the transformer voltage in series with the DC offset of the resonant capacitor. When the transformer secondary-side voltage is positive, it adds together with the resonant capacitor offset voltage, diode D1 is conducting, and the transformer delivers energy to the output. When the transformer voltage is negative, D1 is off and D2 is conducting. In this way, the output capacitor Cout is refreshed in one half of the switching cycle. In the other half switching cycle, the output capacitor gets no energy from the transformer and supplies the load using its stored energy. The output capacitor Cout should be much larger (> 10 times) than the resonant capacitor Cr. Or in other words, the output capacitor Cout can be considered as a high-frequency short at the switching frequency.