New Industry Products

STMicroelectronics Unveils High Voltage Offline AC/DC Converter IC

December 21, 2020 by Gary Elinoff

The new units are optimized for isolated and non-isolated buck, flyback, and buck-boost converters

The VIPer31 is ST’s first converter to offer an 18 watt flyback topology with an input mains range of 85 to 265 VAC. It is the latest addition to its popular VIPerPlus family of highly integrated power converters. The 18 watt capability and its RDS(ON) of 3.5Ω both represent considerable improvements over earlier members of the VIPer family.


The VIPer31.
The VIPer31. Image courtesy of ST


The VIPer31 Series

There are currently eight members of the series, the VIPER317, VIPER318 and VIPER319 have drain current limit protections (IDLIM) of 710, 850 and 990 mA, respectively. There are also X, L and H variants featuring jittered switching frequencies (Fosc) of 30, 60 and 132 kHz, respectively. The option to choose the Fosc affords the designer more flexibility in EMI filter design.

The power section is built around an 800 volt avalanche-rugged MOSFET, allowing for an extended input voltage range. This also serves to reduce the size of the DRAIN snubber circuit. This highly integrated IC requires few ancillary components. This enables a smaller BOM, saving cost, board space and streamlining both the design and manufacturing processes.

The VIPer31 operates from a supply voltage range of 4.5 to 30 volts. With an input voltage of 230 VAC it features a no-load power consumption below 20 mW. 


Image courtesy of VIPer31 Data Sheet
Image courtesy of VIPer31 Data Sheet


Undervoltage and Overvoltage Protection


This kicks in when the mains voltage goes below a UVP point the designer can choose. The rectified mains voltage can be connected to the UVP pin through a voltage divider, and the data sheet details how to choose the proper resistance values of the divider to specify the UVP.

When the mains voltage rises above the UVP point, after a typical 30 ms, the VIPer31 reawakens.

Alternately, the UVP pin can be used to shut the unit down; no output power will be delivered. This will achieve the lowest input power power possible while the VIPer31 is still connected to the power mains.



There is also an overvoltage pin, and its control, too is realized through a connection to the rectified mains through a voltage divider.

If both undervoltage and overvoltage protection is desired, it is actually possible to specify both, each point independent of the other, through a three resistor divider network. 



The ViPer31 is aimed at switched-mode power supplies (SMPS) used in:

  • Smart home devices
  • Air conditioning
  • Home appliances
  • Power adaptors
  • Motor control
  • Building Automation
  • Metering
  • Lighting


Physical and Environmental Characteristics 

The VIPER317 is available in a 9.9 by 6 mm SO16N package. 

As different applications require different levels of environmental compliance, ST offers the device in different grades of its of ECOPACK packages


Getting to Market Faster 

The STEVAL-VP319X1B is an evaluation board based on the VIPER319X 


The STEVAL-VP319X1B. Image courtesy of ST


This evaluation board allows the designer to explore the behavior of a 5 volt, 3 watt buck converter with an input voltage ranging over 85 to 265 VAC that is based on a VIPER319X.