Part # AN1616 datasheet

Part Manufacturer: ST Microelectronics

ST Microelectronics


Part Details:

AN1616 APPLICATION NOTE THD-OPTIMIZER CIRCUITS FOR PFC PRE-REGULATORS by Claudio Adragna Although THD (Total Harmonic Distortion) is not explicitly considered in IEC 61000-3-2 standards, nei-ther it needs to be very low in order for a piece of equipment to get the presumption of conformity, how-ever it has become established to require an ultra-low THD in some applications such as electroniclamp ballast. This application note, after reviewing some basic theory regarding the main causes of distortion of thecurrent drawn from the mains by PFC pre-regulators, suggests a couple of simple and inexpensive cir-cuits that offer significant benefits in terms of THD reduction. The study has been carried out on a TM(Transition Mode) PFC stage using the L6561 IC and the experimental results are presented. Introduction: a little theoryTHD (Total Harmonic Distortion) is a convenient way of specifying how much a periodic waveform straysfrom a sinusoid with just a number. Mathematically: 2 A n 2 2 ARMS ­ A1 T HD n = 2 = ------------ = ---------------- , A A 1 1 where An is the RMS amplitude of the nth (n=1,2,...) harmonic component of the waveform, according toFourier s analysis, and ARMS is the overall effective amplitude. In other words, it is the ratio of the energyassociated to higher order harmonics (n>1) to the energy of the fundamental component (n=1), which hasthe same frequency as the waveform under consideration. THD is often expressed in %. Figure 1. Vector diagram and fundamental relationships between quantities involved in PFC P = Active (Real) Power 1 F 2 2 = Fun = + dam F P Q ent Q = Reactive Power al App. Power 2 2 A = F + D A = T D ota THD = = tan l Appare F n wer P

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