85- to 480-Vac Input 15-Watt Low-Noise Flyback AC-DC Reference Design

The PMP22144 reference design from Texas Instruments uses a UCC28742 flyback controller and an ATL432LI shunt reference to produce an isolated 24-V output capable of 0.625A from an 85- to 480-Vac input. All components are placed on one side of the board to reduce complexity and cost. The design can achieve 80% efficiency across various input conditions.

This reference design is optimized for use in electricity meters and general industrial applications. Its compact size (2" x 3.31") minimizes solution size area.

Single-side assembly and the use of a 2-layer printed circuit board reduces manufacturing costs. And the PMP22144 provides a low noise output of less than 100-mV peak-to-peak voltage ripple for sensitive loads.

The UCC28742

The UCC28742 off-line flyback controller is a highly-integrated, 6-pin secondary-side regulated pwm controller for efficient ac-dc power supplies. It is an isolated-flyback power-supply controller that provides Constant-Voltage (CV) using an optical coupler to improve transient response to large-load steps. This device processes information from optocoupled feedback and an auxiliary flyback winding for high-performance control of output voltage and current.

The UCC28742 employs advanced control algorithms to achieve high operating efficiency and performance. The drive output interfaces to a MOSFET power switch. Discontinuous conduction mode (DCM) with valley-switching reduces switching losses. Modulation of switching frequency and primary current-peak amplitude (FM and AM) keeps the conversion efficiency high across the entire load and line ranges.

The controller has a maximum switching frequency of 80kHz and always maintains control of the peak-primary current in the transformer. A minimum switching frequency of 200Hz facilitates the achievement of low no-load input power.

Summary of Features

• Opto-Coupled Feedback Enables up to 1% Regulation
• Accurate Current Limit with Overload Timeout Protection and Delayed Hiccup Response
• Resonant-Ring Valley-Switching Operation for Highest Overall Efficiency
• 80-kHz Maximum Switching Frequency
• Frequency Dithering to Ease EMI Compliance
• Clamped Gate-Drive Output for MOSFET
• Ultra-Low Start-Up Current and Large VDD Hysteresis
  • High Value Start-Up Resistor
  • Low Bias Capacitance
• Fault Protections
  • Input Low Line
  • Output Over-Voltage
  • Over-Current
  • Short-Circuit
• SOT23-6 Package