15W Quasi-Resonant Flyback AC-DC Power Supply – Reference Design

March 19, 2020 by Paul Shepard

The STEVAl-ISA171V1 reference design from STMicroelectronics implements a 15 W ac-dc power supply designed in quasi-resonant flyback topology for a wide-range input voltage. Its key features are its small size and minimal bill of material, high efficiency and low standby consumption.

The core of the application is the VIPER35, the quasi-resonant offline high voltage converter from the VIPerPLUS product family.

The VIPER35 integrates an 800 V rugged power MOSFET with pwm current-mode control.

Extremely low consumption under no-load conditions is ensured thanks to burst mode operation that reduces the average switching frequency and minimizes all frequency-related losses.

The VIPER35 operates in quasi resonant mode, a feature that helps to meet the EMI standards.

STEVAL-ISA171V1 circuit schematic (click on schematic to enlarge)

Key Features:

  • Wide input voltage range: 90- to 264-Vac
  • Output voltage: 12V
  • Output current: 1.25A
  • Rated output power: 15W
  • Quasi resonant operation
  • Input power standby at 230Vac: < 30mW
  • Active mode efficiency: >82%
  • EMI: pre-compliance with EN55022-Class-B
  • RoHS compliant