TIDUBE1D January   2016  – August 2024

 

  1.   1
  2.   Description
  3.   Resources
  4.   Features
  5.   Applications
  6.   6
  7. 1System Description
    1. 1.1 Key System Specifications
  8. 2System Overview
    1. 2.1 Block Diagram
    2. 2.2 Highlighted Products and Key Advantages
      1. 2.2.1 UCC28180 – PFC Controller
      2. 2.2.2 UCC27524 – Dual Low-Side Gate Driver
      3. 2.2.3 UCC28881 – 700-V Off-Line Converter
    3. 2.3 System Design Theory
      1. 2.3.1 Selecting Switching Frequency
      2. 2.3.2 Calculating Output Capacitance
      3. 2.3.3 Calculating PFC Choke Inductor
      4. 2.3.4 Selecting Switching Element
      5. 2.3.5 Boost Follower Control Circuit
      6. 2.3.6 Bias Power
      7. 2.3.7 On-Off Switch
      8. 2.3.8 Thermal Design
  9. 3Hardware, Testing Requirements, and Test Results
    1. 3.1 Required Hardware
      1. 3.1.1 Test Conditions
      2. 3.1.2 Recommended Equipment
      3. 3.1.3 Procedure
    2. 3.2 Test Results
      1. 3.2.1 Performance Data
        1. 3.2.1.1 Efficiency and iTHD
        2. 3.2.1.2 Standby Power and Output Voltage
      2. 3.2.2 Performance Curves
        1. 3.2.2.1 Efficiency Curve
        2. 3.2.2.2 Voltage Follower Performance
      3. 3.2.3 Functional Waveforms
        1. 3.2.3.1 Power On Sequence
        2. 3.2.3.2 Inrush Current Protection
        3. 3.2.3.3 Switching Node
        4. 3.2.3.4 Waveform Under 3.5kW, 230VAC
      4. 3.2.4 Thermal Measurements
  10. 4Design Files
    1. 4.1 Schematics
    2. 4.2 Bill of Materials
  11. 5Documentation Support
  12. 6Trademarks
  13. 7About the Author
  14. 8Revision History

2.3.3 Calculating PFC Choke Inductor

The UCC28180 is a CCM controller; however, if the chosen inductor allows a relatively high ripple current, the converter becomes forced to operate in discontinuous mode (DCM) at light loads and at the higher input voltage range. High-inductor ripple current affects the CCM/DCM boundary and results in a higher light-load THD. This type of current also affects the choices for the input capacitor, RSENSE, and CICOMP values. Allowing an inductor ripple current, ΔIRIPPLE, of 20% or less enables the converter to operate in CCM over the majority of the operating range. However, this low-inductor ripple current requires a boost inductor that has a higher inductance value, and the inductor itself is physically large. This design takes certain measures to optimize performance with size and cost. The inductor is sized to have a 40% peak-to-peak ripple current with a focus on minimizing space and the knowledge that the converter operates in DCM at the higher input voltages and at light loads; however, the converter is well optimized for a nominal input voltage of 230-V AC at the full load.

Calculate the minimum value of the duty cycle, DMIN, as Equation 5 shows:

Equation 5. TIDA-00779

Based upon the allowable inductor ripple current of 40%, the PFC choke inductor, LBST, is selected after determining the maximum inductor peak current, IPK, as Equation 6 shows:

Equation 6. TIDA-00779

Calculate the minimum value of the c, LMIN, based upon the acceptable ripple current, IRIPPLE, as Equation 7 shows:

Equation 7. TIDA-00779

The actual value of the PFC choke inductor used is LMIN = 180 μH