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

8.2 EMI performance with an inverter power stage

The LLC converter and flyback converter EMI performances are also measured when they are used to bias an inverter gate drivers. A half-bridge inverter design based on Recom Power inverter EVM R-REF01-HB was biased with an LLC converter and the flyback converter, respectively. The EMI noise is measured from the 24-V input side, and the inverter is powered through a high-voltage power supply with 400-V DC output. The inverter is switched at 20 kHz with 50% duty cycle with no load. The inverter creates high dv/dt through its switch node and coupled through the transformer parasitic capacitance. This coupled noise can be measured through the LISN connected at the 24-V input. The measurement setup is shown in Figure 8-4. Similar to the stand alone board setup, no EMI filter is used to measure the raw noise coming from the setup.

Figure 8-4 Inverter Setup For Measuring EMI Performance

The measured EMI performances is summarized in Figure 8-5 and Figure 8-6. The noise floor is raised due to the noise generated by the inverter power stage. However, it can be observed that the LLC converter still provides much lower EMI noise performance comparing with flyback converter, especially at the higher frequency range.

Figure 8-5 EMI Performance Measured Using LLC Converter Biasing Inverter
Figure 8-6 EMI Performance Measured Using flyback Converter Biasing Inverter