TIDUFC8 July   2025

 

  1.   1
  2.   Description
  3.   Resources
  4.   Features
  5.   Applications
  6.   6
  7. 1System Description
  8. 2System Overview
    1. 2.1 Block Diagram
    2. 2.2 Design Considerations
      1. 2.2.1 Introduction
      2. 2.2.2 Basic Operation Principles and ZVS Requirements
    3. 2.3 Highlighted Products
      1. 2.3.1 UCC27288
      2. 2.3.2 UCC23513
      3. 2.3.3 TMS320F2800137
      4. 2.3.4 TLV9062
      5. 2.3.5 INA181
      6. 2.3.6 TPSM861252
      7. 2.3.7 AMC0311R
  9. 3System Design Theory
    1. 3.1 Design Theory
      1. 3.1.1 Resonant Tank Design
      2. 3.1.2 Full-Range ZVS Realization
      3. 3.1.3 Total Control Algorithm
      4. 3.1.4 Resonant Tank RMS Current Analysis
    2. 3.2 Hardware Design Theory
      1. 3.2.1 Resonant Capacitors
      2. 3.2.2 Power Stage
      3. 3.2.3 Voltage Sensing
      4. 3.2.4 Current Sensing
  10. 4Hardware, Software, Testing Requirements, and Test Results
    1. 4.1 Hardware Requirements
    2. 4.2 Software Requirements
      1. 4.2.1 Simulation
    3. 4.3 Test Setup
    4. 4.4 Test Results
  11. 5Design and Documentation Support
    1. 5.1 Design Files
      1. 5.1.1 Schematics
      2. 5.1.2 BOM
      3. 5.1.3 PCB Layout Recommendations
        1. 5.1.3.1 Layout Prints
    2. 5.2 Tools
    3. 5.3 Documentation Support
    4. 5.4 Support Resources
    5. 5.5 Trademarks
  12. 6About the Author

3.1.4 Resonant Tank RMS Current Analysis

As Section 3.1.3 describes, the design of the resonator does not affect the RMS value of the resonator current. The resonator current is carefully analyzed in this section.

The normalized expression of the resonant current, ires_pu(t), is obtained in Equation 4, so the expression of the effective value of the resonant current ires_rms_pu(t) can be calculated based on Equation 10.

Equation 10. ires_rms_pu(t)=12π∫02π[ires_pu(t)]2dωt=22πXresM2-2MCosθ+1

This expression shows that the current RMS value of the resonant tank is related to resonant impedance Xres, phase shift angle θ, and voltage gain M, and the resonant impedance Xres is related to the switching frequency and resonant design. At this time, this can be seen that the effective current value of the resonant tank is related to a variety of factors, and this seems that this is inconsistent with the previously provided analysis.

The average output power Po_pu and output current Io_pu of the converter can be calculated using the primary-side or secondary-side bridge voltage (that is, vA_pu(t) or vB_pu(t)) and tank current ires_pu(t).

Equation 11. Po_pu(t)=12π∫02πVA_pu(t)ires_pu(t)dt=8Mπ2Xressinθ
Equation 12. Io_pu(t)=8π2Xressinθ

The resonant tank impedance Xres can be obtained from the output current Io_pu expression Equation 13.

Equation 13. Xres=8π2Io_pu(t)sinθ

Bring this into the expression of the effective value of the resonant current ires_rms_pu(t), and can get Equation 14.

Equation 14. ires_rms_pu(t)=22πXresM2-2MCosθ+1=πIo_pu(t)22sinθM2-2MCosθ+1

The latest expression shows that the effective current value of the resonant tank ires_rms_pu(t) is only related to the output current Io_pu, voltage gain M, and phase shift angle θ at this time. Because the phase shift angle θ = 2arctan(1/M), the RMS current value at this time is only related to the input and output voltage and the output current at this time. This can be understood that under a certain input and output, the power level is determined, and the current RMS value is also determined.