Thyristors for PFC Inrush Current Limiting

Thyristor-based Inrush Current Limiting for Power Factor Correction Topologies

Watch Replay

Watch the presentation for an introduction into how ST's silicon-controlled rectifiers (SCR) optimize inrush current limiting in the latest PFC front-ends for power designs

During this one-hour recording, we will discuss the use of thyristors, also knows as SCRs, as active elements in limiting inrush current into the inputs of AC/DC converters with power factor correction (PFC).

With voltage ratings at both 600 V to 1200 V, ST’s 150 °C rated SCR portfolio enables precise control of AC line inputs to a wide variety of power levels and topologies. In particular, the ability to control the inrush current into AC powered supplies at > 1 kW is a key application of these niche devices. We will review why and how this is such a beneficial technique for the power supply engineer, especially for the latest in bridgeless PFC topologies.

You will learn:

  • Why inrush current limiting is needed
  • Popular passive techniques for inrush current limiting and their drawbacks
  • About ST’s thyristor technology
  • How to implement inrush current limiting in popular PFC topologies
  • Application examples specific to new bridgeless PFCs
  • Resources available to aid in the design of SCR-controlled inrush current limiters


Jeff Halbig holds both B.S. and M.Eng degrees in Electrical Engineering and Computer Science from Massachusetts Institute of Technology. After 8 years of power supply design, Jeff joined STMicroelectronics as a product marketing engineer for power discrete in 2012. He has been marketing manager for power transistors since 2014 and leads a team promoting power solutions focusing on the Industrial market.    

About Thyristors from STMicroelectronics

Featuring immunity to surges and transients in static states and commutations, our silicon-controlled rectifiers (SCR), also known as thyristors, are ideal for single- and three-phase power line networks, even in harsh environments up to 150 °C.

In addition to AC, DC and capacitive ignitor circuits, these unidirectional switches are found in high-voltage industrial circuits as well as automotive equipment and all other segments where electromechanical relays are not operative or unreliable.

Whenever a bidirectional switch function is needed at 20 A and more, a back-to-back SCR configuration will work with no compromise on the function/immunity.