Running AC Analyses on PFC Converters


Previously Held on Nov 17th, 2016

Running AC analyses on PFC converters has always been challenging because the circuit has no true steady-state when the input voltage is sinusoidal. The SIMPLIS POP and AC analyses assume the converter has a single operating frequency, namely the switching frequency. As soon as the sinusoidal input voltage is applied to the converter, running a POP analysis becomes difficult, but as you will see, not impossible. Tricks for running a POP and AC analysis on a PFC converter with an AC input voltage will be discussed and the loop gain results obtained with a DC input will be compared to the loop gain results when the converter is operating with an AC input.

Before a POP analysis can be run on a PFC converter, the non-linear block multiplier must be replaced with a multiplier which is compatible with the POP and AC analyses. A pulse-width modulated multiplier will be presented and it's operation discussed.

PFC converters with a continuously variable switching frequency cannot successfully complete a POP analysis with an AC input, and therefore the Multi-Tone AC analysis must be used. The Multi-Tone AC analysis injects a series of time-domain sinusoidal voltages into the control loop and extracts the frequency response using fourier techniques applied to the time-domain simulation data.

In this one hour webinar, strategies for measuring the loop gain, input impedance, and output impedance of a PFC front end converter will be discussed.

- You can join our session by using a Mac, PC or a mobile device.
- The Webinar will be recorded and the recording will be available after the webinar.
- Links to reference materials are available at our website:

- Welcome and introductions
- Presentation Content
- Questions and Answers

Link to Webinar Recording

The webinar recording can be viewed at this link: Running AC Analyses on PFC Converters (51:15)


Running a POP Analysis On PFC Converters

  • DC Input
  • AC Input
  • PWM Multpliers
  • Harmonic Relationship Between Line and Switching Frequency

AC Analysis

  • Is using a DC input "good enough?"
  • Using Multi-Tone AC Analysis on Converters Which Cannot Run POP

Reference Materials

Schematics and presentation slides for the webinar can be downloaded here:

[Note - this archive was updated after the webinar with two new circuits which show how to measure the current loop gain of a converter - see 6_ac_input_setup_current_loop.sxsch and 7_ac_input_current_loop.sxsch]