SNVAA33 December   2021 LM61460 , LM61460-Q1 , LM61495 , LM61495-Q1

 

  1.   Trademarks
  2. 1USB Type-C Specifications
  3. 2Popular AC Adapter Design
  4. 3Dynamic Output Voltage Control Methods
    1. 3.1 Method 1: Feedback Resistor Switch Network
    2. 3.2 Method 2: Feedback Current Injection Network
  5. 4Schematic
  6. 5Lab Measurements
    1. 5.1 Bench Measurement (VOUT = 5 V)
    2. 5.2 Bench Measurement (VOUT = 9 V)
    3. 5.3 Bench Measurement (VOUT = 15 V)
    4. 5.4 Bench Measurement (VOUT = 20 V)
  7. 6Summary
  8. 7References

2 Popular AC Adapter Design

Popular designs for source-only AC/DC adapter takes the input AC voltage through an EMI filter and bridge rectifier. The EMI filter is used to ensure noise is not introduced to the input and the bridge rectifier provides a DC voltage to the quasi-resonant flyback (QRF) power stage. The QRF converter then provides a large step down secondary output voltage of ~21V while meeting isolated safety requirement. Since the secondary output of the flyback is loosely regulated using an auxiliary winding to provide voltage information reflected back to the primary side, an intermediary and well-regulated buck converter takes the flyback output voltage and provides another step down voltage to power the downstream personal electronic devices. The system is well-isolated from the input AC source because of the bridge and diode rectification and the output voltage is well-regulated because of the step down buck converter. Typical output voltages in USB Type-C applications are: 3.3 V, 5 V, 9 V, 15 V, and 20 V. Figure 2-1 shows a typical system block diagram for a dual-port AC/DC adapter.

The buck converter is selected to meet the following design requirements for USB Type-C applications listed below:

  • Small form factor and thermally efficient solution
  • Dynamic output voltage scalability
  • High output current capability with good thermal performance to achieve up to 5A to meet USB PD 3.0 specifications
GUID-20211202-SS0I-FQPC-2C72-V8CHTTK37THB-low.gif Figure 2-1 Dual-Port USB Type-C Power Brick