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

5.3 Transformer Construction

When the UCC25800-Q1 based bias supply is used in the inverter applications, especially for the high-side switches, the high dv/dt on the inverter switch node can couple through the bias supply transformer and causes extra EMI noise, as demonstrated in Table 5-1.

Table 5-1 Noise Coupling Through Bias Supply
(a) UCC25800-Q1 based gate driver bias supply in inverter application
(b) Noise coupling path from inverter power stage to bias supply

To minimize this noise coupling, it is desired to minimize the transformer primary-side to secondary-side capacitance. By physically distancing the primary-side winding and secondary-side winding, a transformer with split chamber bobbin can be used to achieve a minimum parasitic capacitance and simple manufacturing. The split chamber bobbin transformer is illustrated in Figure 5-2.

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(a) Transformer Structure (b) Transformer split chamber bobbin

Figure 5-2 Transformer Construction for Minimum Parasitic Capacitance