TIDUF04A December   2022  – December 2025

 

  1.   1
  2.   Description
  3.   Resources
  4.   Features
  5.   Applications
  6.   6
  7. 1System Description
    1.     8
    2. 1.1 EV Charging Station Challenges
      1. 1.1.1 Efficient Relay and Contactor Drive
      2. 1.1.2 Contact Weld Detection
    3. 1.2 Key System Specifications
  8. 2System Overview
    1. 2.1 Block Diagram
    2. 2.2 Design Considerations
      1. 2.2.1 Isolated AC/DC Power Supply Design
        1. 2.2.1.1  Input Bulk Capacitance and Minimum Bulk Voltage
        2. 2.2.1.2  Transformer Turns-Ratio, Primary Inductance, and Primary Peak Current
        3. 2.2.1.3  Transformer Parameter Calculations: Primary and Secondary RMS Currents
        4. 2.2.1.4  Main Switching Power MOSFET Selection
        5. 2.2.1.5  Rectifying Diode Selection
        6. 2.2.1.6  Output Capacitor Selection
        7. 2.2.1.7  Capacitance on VDD Pin
        8. 2.2.1.8  Open-loop Voltage Regulation Versus Pin Resistor Divider, Line Compensation Resistor
        9. 2.2.1.9  Feedback Elements
        10. 2.2.1.10 Backup Power Supply
        11. 2.2.1.11 Supercapacitor Selection
        12. 2.2.1.12 Supercapacitor Charger Design
      2. 2.2.2 Relay Drive and Weld Detect
    3. 2.3 Highlighted Products
      1. 2.3.1 UCC28742
      2. 2.3.2 DRV8220
      3. 2.3.3 ATL431
      4. 2.3.4 TL431
      5. 2.3.5 TPS55330
      6. 2.3.6 TPS259470
      7. 2.3.7 TL7705A
  9. 3Hardware, Testing Requirements, and Test Results
    1. 3.1 Hardware Requirements
    2. 3.2 Test Requirements
      1. 3.2.1 Power Supply Test Setup
      2. 3.2.2 Weld Detect Test Setup
    3. 3.3 Test Results
      1. 3.3.1 Isolated AC/DC Power Supply Based on UCC28742
        1. 3.3.1.1 Efficiency and Output Voltage Cross Regulation
        2. 3.3.1.2 Output Voltage Ripple Waveforms
        3. 3.3.1.3 Start, Shutdown, Backup Power, and Transient Response Waveforms
        4. 3.3.1.4 Thermal Performance
      2. 3.3.2 DRV8220-Based Relay Drive
      3. 3.3.3 Isolated Line Voltage Sensing
  10. 4Design and Documentation Support
    1. 4.1 Design Files
      1. 4.1.1 Schematics
      2. 4.1.2 Bill of Materials
    2. 4.2 Documentation Support
    3. 4.3 Support Resources
    4. 4.4 Trademarks
  11. 5About the Author
  12. 6Revision History

3.3.1.3 Start, Shutdown, Backup Power, and Transient Response Waveforms

Figure 3-10 shows the behavior of the converter during start-up (AC source turned on) with –12 V, +12 V and +12 Vp at full load. C1 is –12-V output at 100 mA, C2 is +12-V output at 100 mA, C3 is +12 Vp at 2.2 A.

TIDA-010239 Behavior of the Converter During Start-Up Figure 3-10 Behavior of the Converter During Start-Up

Figure 3-11 shows the behavior of the converter during shutdown (AC source disconnected) with –12 V, +12 V and +12 Vp at full load. C1 is –12-V output at 100 mA, C2 is +12-V output at 100 mA, C3 is +12 Vp at 2.2 A.

TIDA-010239 Behavior of the Converter During Shutdown Figure 3-11 Behavior of the Converter During Shutdown

Figure 3-12 shows the behavior of the converter, loaded according to the specifications with 12 Vp at 0.44 A, and 5-V rail at 275 mA. Here the trace C2 is 12-Vp output (TP4_P), C1 is 5-V output and C4 is input VAC.

TIDA-010239 Backup Supply Behavior After AC Source is Disconnected Figure 3-12 Backup Supply Behavior After AC Source is Disconnected

Figure 3-13 shows the transient response of the 5 VOUT when switched between zero and 1 A load current.

TIDA-010239 Transient on 5 VOUT 0–1 A Load Figure 3-13 Transient on 5 VOUT 0–1 A Load

Figure 3-14 shows the transient response of the 3.3 VOUT when switched between zero and 1-A load current.

TIDA-010239 Transients on 3.3 VOUT 0 A to 1 A Figure 3-14 Transients on 3.3 VOUT 0 A to 1 A

Figure 3-15 shows the transient response of the converter with zero to 2-A transients on 12 VOUT, while 12 V and –12 V are loaded both at 100 mA. C1 is –12-V output at 100 mA, C2 is +12-V output at 100 mA, C3 is +12 Vp with switched load and C4 is the 12 Vp output current.

TIDA-010239 Transient Response of the Converter With Zero to 2-A Transients on 12 VOUT Figure 3-15 Transient Response of the Converter With Zero to 2-A Transients on 12 VOUT

Figure 3-16 shows the transient response of the converter with zero to 2-A transients on 12 VOUT, while 12 V and –12 V are both loaded at zero current. C1 is –12-V output at 0 mA, C2 is +12-V output at 0 mA, C3 is +12 Vp with switched load and C4 is the 12-Vp output current.

TIDA-010239 Transient Response of the Converter With Zero to 2-A Transients on 12 VOUT Figure 3-16 Transient Response of the Converter With Zero to 2-A Transients on 12 VOUT

Figure 3-17 shows the transient response of –12-V output with 12 Vp fully loaded. C1 is –12-V output switched from 100 mA to zero and C4 is the –12-V output current.

TIDA-010239 Transient Response of –12-V Output With 12 Vp Fully Loaded Figure 3-17 Transient Response of –12-V Output With 12 Vp Fully Loaded

Figure 3-18 shows the transient response of –12-V output with 12 Vp fully loaded. C1 is –12-V output switched from zero to 100 mA and C4 is the –12-V output current.

TIDA-010239 Transient Response of –12-V Output With 12 Vp Fully Loaded Figure 3-18 Transient Response of –12-V Output With 12 Vp Fully Loaded

Figure 3-19 shows the transient response of +12-V output with 12 Vp fully loaded. C2 is +12-V output switched from zero to 100 mA and C4 is the +12-V output current.

TIDA-010239 Transient Response of +12-V Output With 12 Vp Fully Loaded Figure 3-19 Transient Response of +12-V Output With 12 Vp Fully Loaded

Figure 3-20 shows the transient response of +12-V output with 12 Vp fully loaded. C2 is +12-V output switched from 100 mA to zero and C4 is the +12-V output current.

TIDA-010239 Transient Response of +12-V Output With 12 Vp Fully Loaded Figure 3-20 Transient Response of +12-V Output With 12 Vp Fully Loaded