Browse Prior Art Database

PFC output voltage modulation used to provide SMPS regulation Disclosure Number: IPCOM000204505D
Publication Date: 2011-Feb-28
Document File: 3 page(s) / 21K

Publishing Venue

The Prior Art Database

This text was extracted from a PDF file.
This is the abbreviated version, containing approximately 52% of the total text.

Page 01 of 3

PFC output voltage modulation used to provide SMPS regulation


Power supplies producing several hundreds watts of regulated output voltage generally use frequency modulation and /or duty cycle variations to adapt the power transfer to the input voltage and output power variations.

Such power supplies are generally made of a PFC (Power Factor Controller) stage followed by a SMPS (Switch Mode Power Supply) stage.

In some applications it is advantageous to have the SMPS functioning at a fixed frequency, or with low frequency variations and / or low duty cycle variations.

The idea presented here is to modulate the input voltage of the SMPS (PFC output) according to the SMPS regulation needs to reduce the frequency and / or conduction time variations of the SMPS.

Description of the invention

The principle of this invention is presented in the figure 1 here below:



Figure 1: Block diagram of the invention

The input voltage of the SMPS (PFC output, at the Bulk capacitor) is modulated by the SMPS regulation to reduce frequency or conduction time variations.

The two regulation loops (PFC + SMPS) are combined in the PFC Feedback network block, which receives signals from the output of the PFC stage and from the SMPS Feedback network to elaborate the new PFC feedback signal.

The SMPS regulation maintains a fast transient response to the quick load variations.

The low bandwidth PFC regulation maintains the proper line current shaping.

The output voltage of the PFC is well adapted to the needs of the SMPS.

ONS01105_DefensivePublication_Final.docx Page 1 of 3

Ac line

PFC stage

Bulk capacitor


Downstream converter (w/ or w/o isolation)



   Feedback network
(w/ or w/o isolation)


Feedback network

Circuit for bulk voltage modulation

Page 02 of 3

A way to realize the new PFC feedback signal is describe in the figure 2 here below:

(This page contains 00 pictures or other non-text object)

Figure 2: New PFC feedback

An opto-coupler provides a voltage ("FB") that is scaled down by the resistors divider (R9, R8) to form the signal "HB LLC Feedback"

The signal "HB LLC Feedback" is fed to the feedback pin to accurately regulate the SMPS output voltage
The (R8, R9) divider increases the FB swing compared to that of the "HB LLC Feedback" signal as required by the SMPS controller.

The bottom resistor of the PFC feedback network is spited into two or more series resistors (R4, R6//R5, R12 here).

The anode of a TLV431 is connected to the one that is connected to ground.