90- to 600-Vac Input Buck Topology Auxiliary Power Supply Reference Design

October 04, 2019 by Paul Shepard

The STEVAL-VP26K01B reference design from STMicroelectronics implements a 15 V-1.5 W buck converter for ultra-wide input voltage range auxiliary power supplies from 60- to 870-Vdc or 90- to 600-Vac. The highly compact design offers tight line and load regulation over the entire input and output range.

The board represents a very low-cost buck solution based on the new VIPER265KDTR offline high-voltage converter from the VIPerPlus family with 1050V Power MOSFET and pwm current-mode control. It allows direct connection to ultrawide range main without the need for input voltage limiter and/or stacked MOSFETs, therefore ensuring a minimal BOM.

The VIPER265KDTR operates at 60kHz fixed frequency with frequency jittering to meet the EMC standard requirements.


  • Ultra-wide input range: 90- to 600-Vac (50- to 60-HZ) or 60- to 870-Vdc
  • Output voltage: 15V
  • Output current: 100mA
  • Very compact size
  • Tight line and load regulation over the entire input and output range
  • Meets IEC55022 Class B conducted EMI even with a reduced EMI filter, thanks to the frequency jittering feature
  • RoHS compliant

STEVAL-VP26K01B reference design schematic. (click on schematic to enlarge)

VIPER265KDTR offline high-voltage converter

The device is a high voltage converter smartly integrating a 1050 V avalanche-rugged power section, with a pwm current mode control. The 1050 V-BV power MOSFET allows to extend input voltage range, and reduce the size of the DRAIN snubber circuit. This IC meets the most stringent energy-saving standards as it has very low consumption and operates in burst mode under light load.

The integrated HV startup, sense-FET, error amplifier and oscillator with jitter allow a complete application to be designed with the minimum number of components.

The VIPer26K supports the most common SMPS topologies such as: isolated flyback with optocoupler, primary-side regulation, non-isolated flyback with resistive feedback, buck, and buck boost.