AN3105
Application note
48 V - 130 W high efficiency converter with PFC for LED street
lighting applications - European version
By Claudio Spini
Introduction
Nowadays, LEDs are becoming ever more popular, thanks to their particular characteristics,
such as high efficiency and long life, and therefore they are pushing the innovation of current
lamp types and strongly contributing to reducing the energy consumption for internal or
external lighting. This is also the case in street lighting applications, where higher efficiency
and long life are vital for reducing costs.
For these reasons a street lighting power supply designed to power an LED lamp must have
high efficiency and at least a similar lifetime, in order to guarantee the maintenance free
operation required by these kinds of applications.
This application note describes the characteristics and features of a 130 W demonstration
board (EVL130W-SL-EU), tailored on an LED power supply specification for street lighting.
The circuit is composed of two stages; a front-end PFC using the L6562AT and an LLC
resonant converter based on the L6599AT.
The peculiarities of this design are; very high efficiency, extended European input mains
range (177-277 V
AC
) operation, and long term reliability.
Because reliability (MTBF - “Mean Time Between Failures”) in power supplies is typically
affected by electrolytic capacitors and their typical high failure rate, unless using very
expensive types, this board offers a very innovative design approach as the board doesn't
implement any electrolytic capacitors, which are replaced by film capacitors from EPCOS.
Component de-rating has also been carefully applied during the design phase, decreasing
the component stress as recommended by MIL-HDBK-217D. The number of components,
thanks to the use of the new L6562AT and L6599AT devices, has also been minimized,
therefore increasing the MTBF and optimizing the total component cost. Thanks to the high
efficiency achieved no heatsinks are required. The resonant stage power components are
SMT, like most of the passive components, therefore decreasing production costs.
The board also has protections in case of overload or short-circuit, open-loop by each stage,
or input overvoltage. Because of the particular application, all protections, in the case of
intervention, are auto-restart.
Figure 1.
EVL130W-SL-EU: 130 W SMPS for LED street lighting applications
September 2012
Doc ID 16774 Rev 2
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www.st.com
Contents
AN3105
Contents
1
Main characteristics and circuit description . . . . . . . . . . . . . . . . . . . . . 4
1.1
1.2
1.3
1.4
1.5
1.6
Power Factor corrector . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Resonant power stage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Startup sequence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Output voltage feedback loop . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
L6599AT overload and short-circuit protection . . . . . . . . . . . . . . . . . . . . . . 6
Overvoltage and open-loop protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2
3
4
Efficiency measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Input current harmonics measurement . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Functional check . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
4.1
4.2
4.3
4.4
4.5
4.6
PFC circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Half-bridge resonant LLC circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Dynamic load operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Overcurrent and overvoltage protection . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Converter startup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Thermal map . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
5
6
7
8
9
Conducted emission pre-compliance test: peak measurement . . . . . 19
Bill of material . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
PFC coil specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
Transformer specification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
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AN3105
List of figures
List of figures
Figure 1.
Figure 2.
Figure 3.
Figure 4.
Figure 5.
Figure 6.
Figure 7.
Figure 8.
Figure 9.
Figure 10.
Figure 11.
Figure 12.
Figure 13.
Figure 14.
Figure 15.
Figure 16.
Figure 17.
Figure 18.
Figure 19.
Figure 20.
EVL130W-SL-EU: 130 W SMPS for LED street lighting applications. . . . . . . . . . . . . . . . . . 1
EVL130W-SL-EU demonstration board: electrical diagram . . . . . . . . . . . . . . . . . . . . . . . . . 7
EVL130W-SL-EU demonstration board efficiency diagrams . . . . . . . . . . . . . . . . . . . . . . . . 8
EVL130W-SL-EU demonstration board: compliance to EN61000-3-2 Class-C standard . . 9
EVL130W-SL-EU demonstration board: input current waveform at 230 V - 50 Hz - 130 W
load and 65 W load. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
EVL130W-SL-EU demonstration board: Power Factor and Total Harmonic Distortion vs.
load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
EVL130W-SL-EU demonstration board: PFC stage and L6562AT waveforms at 230 V -
50 Hz - full load – detail . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
EVL130W-SL-EU demonstration board: primary and secondary side resonant stage
waveforms at 230 V - 50 Hz - full load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
EVL130W-SL-EU demonstration board: high and low frequency ripple on output voltage at
230 V - 50 Hz - full load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
EVL130W-SL-EU demonstration board: output voltage variation driving a CC LED converter
- PWM = 90% and PWM = 15% . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
EVL130W-SL-EU demonstration board: short-circuit at 230 V
AC
- 50 Hz - full load and open
loop protection intervention at 20 W load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
EVL130W-SL-EU demonstration board: startup at 230 V
AC
- 50 Hz - full load . . . . . . . . . 16
Thermal map at 230 V
AC
- 50 Hz - full load - PCB top side . . . . . . . . . . . . . . . . . . . . . . . . 17
Thermal map at 230 V
AC
- 50 Hz - full load - PCB bottom side . . . . . . . . . . . . . . . . . . . . . 18
CE peak measure at 230 V
AC
and full load - phase wire . . . . . . . . . . . . . . . . . . . . . . . . . . 19
CE peak measure at 230 V
AC
and full load - neutral wire . . . . . . . . . . . . . . . . . . . . . . . . . 19
PFC coil electrical diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
PFC coil mechanical aspect(1) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
Transformer electrical diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
Transformer overall drawing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
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Main characteristics and circuit description
AN3105
1
Main characteristics and circuit description
The main features of the SMPS are:
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Extended European input mains range: 177 to 277 V
AC
- frequency 45 to 55 Hz
Output voltage: 48 V at 2.7 A
Long-life electrolytic capacitors are not used
Mains harmonics: acc. to EN61000-3-2 Class-C
Efficiency at full load: better than 90%
EMI: according to EN55022-Class-B
Safety: double insulation, according to EN60950, SELV
Dimensions: 75 x 135 mm, 30 mm components maximum height
No heatsinks needed
PCB: single side, 35 µm, FR-4, mixed PTH/SMT
1.1
Power Factor corrector
The PFC stage, working in transition mode, acts as a pre-regulator and powers the resonant
stage with the output voltage of 450 V. The PFC power topology is a conventional boost
converter, connected to the output of the rectifier bridge D3. It is completed by the coil L1,
manufactured by MAGNETICA, the diode D2 and the capacitors C5, C6, and C7 in parallel.
The PFC output capacitors are film type, 5 µF - 800 V, manufactured by EPCOS. Using film
capacitors to replace the typical electrolytic capacitors considerably increases the MTBF of
the board.
The boost switch is represented by the Power MOSFET Q2. The board is equipped with an
input EMI filter necessary to filter the commutation noise coming from the boost stage. The
PFC implements the L6562AT controller, a small and inexpensive controller which is
guaranteed for operation over a wide temperature range.
At startup, the L6562AT is supplied by the startup resistors R5, R8, and R13 charging the
capacitor C13; once the PFC begins switching, a charge pump connected to the auxiliary
winding of the PFC inductor L1 supplies both PFC and resonant controllers via a small
linear regulator realized by Q1. Once both stages have been activated, the controllers are
also supplied by the auxiliary winding of the resonant transformer, assuring correct supply
voltage during all load condition operations. The L1 auxiliary winding is also connected to
the L6562AT pin #5 (ZCD) through the resistor R18. Its purpose is to provide the information
that L1 has demagnetized, needed by the internal logic to trigger a new switching cycle. The
PFC boost peak current is sensed by resistor R34 in series to the MOSFET source; the
signal is fed into pin #4 (CS) of the L6562AT, via the filter R27 and C16.
The dividers R7, R12, R14, and R22 provide the information on the instantaneous mains
voltage to the L6562AT multiplier which is used to modulate the peak current of the boost.
The resistors R2, R6, R9 with R15 and R16 are dedicated to sensing the output voltage and
feed, to the L6562AT, the feedback information necessary to keep the output voltage
regulated. The components C11 and R20 (C12 is shorted) make up the error amplifier
compensation network necessary to keep the required loop stability.
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Main characteristics and circuit description
1.2
Resonant power stage
The down-stream converter is a resonant LLC half-bridge stage working with 50 percent
fixed duty cycle and variable frequency. It implements the ST L6599AT, integrating all
functions necessary to properly control the resonant topology.
The resonant transformer, manufactured by MAGNETICA, uses the integrated magnetic
approach, so the leakage inductance is used for resonant operation of the circuit. Therefore,
no external, additional coil is needed for the resonance. The transformer secondary winding
configuration is the typical centre tap, using a couple of type STPS10150CG power Schottky
rectifiers. The output capacitors are film type, 4.7 µF - 63 V from EPCOS. Like for the PFC
stage, using film capacitors allows to increase considerably the MTBF of the board.
A small LC filter has been added on the output, in order to filter the high frequency ripple.
D21, D22, and R55 implement a voltage controlled bleeder; in the case of no-load operation
of the SMPS, this circuit provides a bleeder limiting the increase of output voltage, but not
affecting efficiency during normal operation. Please note that the converter has not been
designed to work in this condition and therefore its mains consumption is not optimized
(~3 W).
1.3
Startup sequence
The PFC acts as master and therefore starts first; the resonant stage operates only if the
PFC is delivering the nominal output voltage to prevent the resonant converter from working
with a too low input voltage which can cause incorrect capacitive mode operation. Therefore
both stages are designed to work according to this sequence.
For correct sequencing, the L6599AT makes use of the LINE pin (#7) to sense the PFC
output voltage via a resistor divider. The L6599AT LINE pin (#7) has an internal comparator
which has a hysteresis allowing the turn-on and turn-off voltage to be set independently. At
startup, the LLC stage starts once the PFC output voltage reaches ~ 430 V, while the turn-
off threshold has been set to ~ 330 V.
1.4
Output voltage feedback loop
The output voltage is kept stable by means of a feedback loop implementing a typical circuit
using a TS2431 to modulate the current in the optocoupler diode.
On the primary side, R43 - connecting pin RF
MIN
(#4) to the optocoupler's phototransistor -
allows the L6599AT oscillator frequency to be modulated, therefore keeping the output
voltage regulated. It also sets the maximum switching frequency at about 130 kHz. R42,
which connects the same pin to ground, sets the minimum switching frequency. The R-C
series R37 and C24 sets both soft-start maximum frequency and duration.
All demonstration boards implement the voltage loop circuitry described above but in case
a current loop is also required it can be achieved by implementing the following modifications:
●
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Replace R30 and R31 0R0
Ω
resistors with sensing resistors, 0R033 and 0R039
respectively, both 0805
Populate on PCB U4 and the relevant components reported on the schematic as N.M.:
C36 = 1N0-0805; C37 = 100NF-0805; R51 = 15R-0805; R56 = 1K0-0805; R61 =22K-
1206; C41 = 2N2-0805; U5 = SEA05TR
Remove the TS2431AILT
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