Würth Electronik Introduces Toroidal Power Factor Correction Inductors

Würth Electronik has announced the release of new variants of the company’s WE-TORPFC power factor correction (PFC) inductor series. The series, comprising 17 parts, is designed for use in continuous-conduction mode (CCM) boost converters and can handle power levels up to several kW and voltages up to 1000 VDC.

 

WE-TORPFC inductor family from Würth Electronik. Image used courtesy of Würth Electronik

 

Different from traditional PFC inductors that are bobbin wound, Würth’s new toroidal magnetics use flat wire windings that result in reduced winding losses and better thermal management.

The new series is available in several surface mount package sizes with inductance specifications ranging from 118-720 µH. The series is suitable for a wide range of power factor correction applications that include industrial AC/DC power supplies and solar inverters. 

 

Inductor Design Considerations

An inductor is constructed by winding a wire around a plastic (air core) or ferrite core. When the core is cylindrical, the inductor is referred to as a bobbin wound, and when the core is toroidal, or shaped like a donut, it is referred to as a toroidal wound.  

 

Inductor, transformer, and choke construction. Image used courtesy of Electronics and You

 

When choosing between a bobbin or toroidal construction, one must consider factors such as the electrical characteristics, package configuration, and manufacturing complexity.   

Compared with Würth’s current family of bobbin wound PFC chokes, the new toroidal inductors accommodate higher current levels (above 20 A) and inductance values below 150 µH. 

The new toroidal series is also available in surface mount (SMD) packaging that supports high-volume, solder-reflow manufacturing processes.   

 

Flat Wire Windings

The windings for the new toroidal chokes have lower series DC resistances than Würth’s bobbin wound devices. This is likely explained by the flat wire windings that result in fewer I2R losses, less dissipated heat, and better efficiency.  

 

WE-TORPFC SMD toroidal choke with electrical circuit. Image used courtesy of Würth Electronik

 

Unlike the bobbin wound chokes, the toroidal inductors are constructed as traditional single winding inductors. The WE-PFC series uses a configuration similar to a transformer, with two windings around a common core. 

The matched inductances of the dual winding construction can be useful for electromagnetic compatibility (EMC) and the suppression of common mode interfering signals (EMI).   

 

WE-PFC through hole bobbin choke with electrical circuit. Image used courtesy of Würth Electronik

 

Active PFC for AC Powered Equipment

For AC-powered equipment like power tools, line power is first rectified to a regulated DC voltage before being inverted back to AC through a switching bridge inverter that powers the motor. 

 

Power supply architecture for an AC power tool. Image used courtesy of Würth Electronik

 

In this power supply configuration, the PFC inductor performs a similar function to that of a boost converter, working in tandem with the switching FET to capture DC energy at the output of the rectifier and step it up to a well-regulated DC voltage that is applied across the output storage capacitors (input of the DC/AC inverter).   

The PFC stage, formed by the PFC inductor and switching FET, serves to regulate the DC link voltage (output capacitors) and input current to ensure phase alignment with the line voltage for more efficient power transfer.