AN4496 Datasheet, PDF (1/18 Pages) STMicroelectronics – How to get a high power factor with the HVLED815PF device

AN4496
Application note
How to get a high power factor with the HVLED815PF device
Stefano Signoria
Introduction
The standard application of the HVLED8xxPF (HVLED807PF, HVLED815PF) is a constant
current (CC) LED driver. The average output current I_OUT, as described in the HVLED815PF
datasheet (section 4.5 Constant current operation), does not depend on the value or the
waveform of the input voltage V_IN, then can be used in standard or high power factor
implementation.
Two methods of implementing the high power factor (HPF) based on the HVLED8xxPF
family are current in use: the current sense modulation and ILED modulation. In either case
the input voltage after rectification is not smoothed and the waveform on the bulk capacitor
is a semi-sinusoidal waveform. The voltage on the bulk capacitor, V_RECT, contains
information about the phase and waveform of V_IN.
With the first method, the additional circuitry in Figure 1 applies a DC offset and
a modulation, both proportional to the V_RECT, to the CS pin and permits to obtain an HPF.
This solution is described in detail in 1. of Section 3.
The second one, shown in Figure 2, applies a modulation of the ILED pin proportional to the
V_RECT and features HPF in a single range application (refer to the AN4129 for further
details). This application note describes how to modify the basic circuit to support wide input
range applications.
1
Figure 1. CS HPF; additional components
Figure 2. ILED HPF; additional component
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September 2014
DocID026370 Rev 1
1/18
www.st.com
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