AN827 Datasheet, PDF (1/20 Pages) STMicroelectronics – A 500W HIGH POWER FACTOR WITH THE L4981A

AN827
APPLICATION NOTE
A 500W HIGH POWER FACTOR WITH THE L4981A
CONTINUOUS MODE IC
The widespread use of passive AC/DC off-line converters causes low power factor and high line current
harmonic distortion. To reduce these phenomena and to comply with relevant regulatory agency require-
ments , designers are employing active power factor correction in their off-line SMPS applications. This
paper describes a practical, low cost and easy to implement 500W power factor corrected application
that employs the L4981A Continuous Mode PFC IC.
INTRODUCTION
Reduction of line current harmonic distortion and improvement of power factor is of great concern to many de-
signers of off-line switched mode power supplies. This concern has been motivated by present and impending
regulatory requirements regarding line current harmonics. The reasons for improving power factor and reducing
line current harmonic distortion are well known and understood. Active power factor correction using the boost
topology and operating in the continuous inductor current control mode is an excellent method to comply with
these requirements and is well accepted in the industry.
This paper will present a practical power factor corrected design for a 500 Watt output and universal mains input
application. The detailed derivations of all power, IC biasing and control component values and types will be
shown. The evaluation results from an actual working demoboard will be presented as well as several relevant
oscillograms.
DESIGN SPECIFICATIONS
The design specifications given below are realized by the implementation of a functional demoboard.
The design target specifications are as follows:
– Universal mains input AC voltage V_irms = 88Vac to 264Vac, 60/50Hz
– DC regulated output voltage V_out = 400Vdc
– Full load output ripple voltage ∆V_ripple = ±8V
– Rated output power P_out = 500W
– Maximum output overvoltage V_omax = 450V
– Switching frequency f_sw = 80kHz
– Maximum inductor current ripple ∆I_L = 23%
– Input power factor PF > 0.99
– Input line current total harmonic distortion <5%
To meet these specifications, the selection of component values and material types is very important. The next
sections will describe the component selection criteria along with some critical derivations. For detailed expla-
nations on the controller operation and pin description, refer to Application
Note AN628 Designing A High Power Factor Switching Preregulator With The L4981 Continuous Mode [1] and
the corresponding Datasheet L4981A/B Power Factor Corrector [2].
November 2003
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