25 W wide-range high power factor buck

AN4314
Application note
25 W wide-range high power factor buck-boost converter
demonstration board using the L6564H
Introduction
This application note describes a wide-range non-isolated 25 W regulated LED driver with
high power factor. The EVL6564H-25W-BB demonstration board is well-suited to the
Japanese market due to the broad use of standard 100 Vac lighting applications and also
200 Vac tubes in building automation systems.
The EVL6564H-25W-BB demonstration board has been designed in order to obtain the
highest possible power factor over the entire input mains voltage, remaining compliant to
EN55022 Class-B and keeping the average output current in a tight band with different LED
characteristics.
The board is based on ST's L6564H power factor controller and the SEA05L CC-CV
controller for LED current regulation in a non-isolated flyback configuration.
The form factor has been designed to fit into a standard LED driver case, facilitating the
replacement of the incandescent flood lamps up to 80-100 W power.
Figure 1. EVL6564H-25W-BB demonstration board using the L6564H
July 2013
DocID024821 Rev 2
1/31
www.st.com
Contents
AN4314
Contents
1
Main characteristics and circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2
LED current ripple definition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
3
Electrical diagram and bill of material . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
4
Performance and considerations with LED Loads . . . . . . . . . . . . . . . 12
5
PFC waveforms
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
5.1
Input and output current and voltage waveforms . . . . . . . . . . . . . . . . . . . 16
5.2
Transition mode operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
5.3
Start-up . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
5.4
Line sags and fast on-off . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
5.5
Load disconnection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
5.6
Short-circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
5.7
Feedback failure protection (open loop) . . . . . . . . . . . . . . . . . . . . . . . . . . 24
6
Harmonic content measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
7
Thermal measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
8
Conducted emission pre-compliance test . . . . . . . . . . . . . . . . . . . . . . 27
9
PCB Layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
10
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
11
Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
2/31
DocID024821 Rev 2
AN4314
List of tables
List of tables
Table 1.
Table 2.
Table 3.
Table 4.
Main characteristics and circuit. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Bill of material . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Measured temperature at 100 Vac/50 Hz and 230 Vac/50 Hz. . . . . . . . . . . . . . . . . . . . . . . 26
Document revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
DocID024821 Rev 2
3/31
31
List of figures
AN4314
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.
Figure 21.
Figure 22.
Figure 23.
Figure 24.
Figure 25.
Figure 26.
Figure 27.
Figure 28.
Figure 29.
Figure 30.
Figure 31.
Figure 32.
Figure 33.
Figure 34.
Figure 35.
Figure 36.
Figure 37.
Figure 38.
Figure 39.
4/31
EVL6564H-25W-BB demonstration board using the L6564H. . . . . . . . . . . . . . . . . . . . . . . . 1
EVL6564H-25W-BB demonstration board: electrical schematic. . . . . . . . . . . . . . . . . . . . . . 8
LED string voltage vs. line voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
LED current vs. line voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Power factor vs. line voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
THD vs. line voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Efficiency vs. line voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Input current waveform at 100 Vac -50 Hz . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
input current waveform at 230 Vac -50 Hz . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
TM operation at 100 Vac - 0.35 A - fsw =35 kHz. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
TM operation at 230 Vac - 0.35 A- fsw = 50 kHz. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Start-up at 100 Vac - 0.35 A . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Start-up at 230 Vac - 0.35 A . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
TOFF = 40 ms at 100 Vac / 50 Hz - 0.35 A . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
TOFF = 40 ms at 230 Vac / 50 Hz - 0.35 A . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
TOFF = 500 ms at 100 Vac/50 Hz - 0.35 A . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
TOFF = 500 ms at 230 Vac/50 Hz - 0.35 A . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Load disconnection transition at 100 Vac/50 Hz . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
No load at 100 Vac/50 Hz . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Load disconnection transition at 230 Vac/50 Hz . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
No load at 230 Vac/50 Hz . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Short circuit at 100 Vac . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
Short circuit at 230 Vac . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
Overload behavior after a short circuit at 100 Vac . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Overload behavior after a short circuit at 230 Vac . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Short circuit removal at 100 Vac . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Short circuit removal at 230 Vac . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Feedback failure protection at 100 Vac/50 Hz. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
Feedback failure protection at 230 Vac/50 Hz. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
EVL6564H-25W-BB at 100 Vac/50 Hz compliance
with JEIDA-MITI class-C limits at PF = 0.9801 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
EVL6564H-25W-BB at 230 Vac/50 Hz compliance
with EN61000-3-2 class-C limits at PF = 0.9180 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
Thermal map at 100 Vac/50 Hz . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
Thermal map at 230 Vac/50 Hz . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
100 Vac/50 Hz - phase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
100 Vac/50 Hz - neutral. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
230 Vac/50Hz - phase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
230 Vac/50Hz - neutral . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
Bottom layer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
Top layer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
DocID024821 Rev 2
AN4314
1
Main characteristics and circuit
Main characteristics and circuit
The main characteristics of this single-stage LED driver demonstration board are given in
the table below.
Table 1. Main characteristics and circuit
Parameter
Value
Line voltage range
85 to 265 VAC
Line frequency (fL)
47-63 Hz
LED string voltage drop
70 V ±10 % (23-LED p.n. X42182) [6]
LED nominal current
350 mA ±3 %
LED current ripple pk-pk
100 mA
Rated output power
25 W
Power factor
> 0.9
Efficiency
> 89 @ 230 V
Maximum ambient temperature 50 °C
Conducted EMI
In accordance with EN55022 Class-B
Protections
Preventing overvoltage, load disconnection and short-circuit
The main feature of the converter is that the input current is almost in phase with the mains
voltage; therefore the power factor is close to unity. This is achieved by the L6564H
controller, which shapes the input current as a sine wave in phase with the mains voltage.
An external high-voltage startup circuitry is not needed because it is already embedded in
the IC.
The power supply utilizes a typical non-isolated buck-boost converter topology with a simple
inductor to transfer energy to the LED load.
The converter is connected after the mains rectifier and the capacitor filter, which in this
case is quite small, to avoid damage to the shape of the input current. The buck-boost
switch is represented by the power MOSFET Q3 and driven by the L6564H.
At startup, a 0.85 mA internal current source of the L6564H charges the VCC capacitor (C8),
until the voltage on the Vcc pin reaches the startup threshold, then it is shut down.
The T1 auxiliary winding (pins 6-7), the charge pump (C14, R16, D4) and the BJT voltage
regulator (Q2, DZ2, R3) generate a constant VCC voltage that powers the L6564H during
normal TM operation.
R37 is also connected to the auxiliary winding to provide the transformer demagnetization
signal to the L6564H ZCD pin, turning on the MOSFET at any switching cycle. The
MOSFET used is the STI8N65M5, a new MDmesh™ V, low-cost, low on-resistance, 710 V
device housed in an I2PAK package [5], and without any heatsink.
The multilayer inductor, using a standard ferrite size EF-25, is manufactured by Magnetica.
DocID024821 Rev 2
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31
Main characteristics and circuit
AN4314
The resistors R27 and R26 sense the current flowing into the inductor primary side. Once
the signal at the current sense pin has reached the level programmed by the internal
multiplier of the L6564H, the MOSFET turns off.
The divider R13, R14, R15 and R30 provides the L6564H multiplier pin with instantaneous
voltage information which is used to modulate the current flowing into the inductor.
To maintain a constant (average) output current, some kind of regulation is required and for
this reason, on the output side, an error amplifier (inside the SEA05L) senses the LED
current on sense resistors R6, R7, and it drives the input of the internal error amplifier of the
L6564H. As a consequence, the PWM comparator is modulated too.
The inductor T1 is charged by Q3 when it is turned on, and it discharges into the output
capacitor C3 and into the LED load when Q3 turns off.
Due to the topology, the LED string load is connected to a floating output so the loop is
closed through a current mirror formed by two high-voltage BJTs (Q4, Q5). For the constant
current regulation an SEA05L CC-CV has been used. The current loop regulates the LED
current at a nominal level of 350 mA, the nominal voltage drop of the LED string is 70 Vdc
with a tolerance of 10 %. Normally the voltage loop does not operate in the range
63 V - 77 Vdc, but it works in case the LED string opens to protect the output bulk capacitor
C3 from overvoltage. The R8, R9 divider senses the output voltage and regulates the output
voltage to around 84 Vdc.
In case one of the loops fails and the output voltage is no longer regulated, a protection
preventing an open loop is performed using the PFC_OK pin, the L6564H sensing the
increase of the auxiliary winding voltage.
The board is equipped with an input EMI pi-filter stage (C2-L1-C6) connected after the input
connector. An input fuse and a varistor (VR1) are also provided at the input of the board,
protecting from short-circuits and improving immunity against input voltage fast transients.
In order to prevent a short-circuit of the output stage, an external, low-cost circuit
(composed of Q6, Q9, Q8, R23, R24, R32, R20, D3, D8, R40) disables the L6564H using
the PFC_OK pin. The circuit is composed of a buffer stage (Q6, R23) connected to the
feedback loop. When Q9 is off, a current through the R32 resistor connected to VCC_PROT
will charge the C7 capacitor up to a voltage level imposed by the sum of two diode voltage
drops (D7 + D3). At that voltage level, the transistor Q8 will switch on and it pulls the
PFC_OK pin to ground, disabling the L6564H controller. Removing the short, the C7
capacitor will discharge through R40 connected to the Gate Drive pin during the MOSFET
off-time (low state).
The time constant R32 with C7 is set in order to mask the transition time during startup. In
fact during this time phase, when the loop is still open, the feedback signal is still low and it
could activate the protection unnecessarily.
The board has been designed using the procedure described in AN1059 [1] used to design
a standard high-power factor flyback. This application note has been used as a reference for
calculating this demonstration board, since the buck-boost topology can be considered as a
simple flyback with a unity transformer turn ratio and with the output voltage corresponding
to the reflected voltage of the flyback.
A description of the dimensioning of the output capacitor and the LED current ripple
definition appears in Section 2 as it is not included in AN1059 [1].
6/31
DocID024821 Rev 2
AN4314
2
LED current ripple definition
LED current ripple definition
In a typical LED application the definition of ripple current must be carefully considered. We
have defined a current ripple lower than 100 mA pk-pk, corresponding to about 30 % of the
average LED current. This parameter depends only on two factors, one is linked to the load
and the other to the converter as follows:
–
the dynamic resistance of the LED string RDtot
–
the output capacitor value of the converter Co
The following formula describes the relation between the current ripple and the previous two
factors:
Equation 1
I ripple ∝
I OUT
1 + (4 ⋅ π ⋅ f l ⋅ RDtot ⋅ C O ) 2
First, note that the value of the output capacitor will depend on the load so it is important to
know the final application of the converter.
Second, the form factor of the converter will depend on the output capacitor size and, as a
consequence, on the output current ripple specification.
In this application a 680 μF capacitor has been selected in order to maintain the current
ripple below 100 mA.
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31
Electrical diagram and bill of material
3
AN4314
Electrical diagram and bill of material
Figure 2. EVL6564H-25W-BB demonstration board: electrical schematic
8/31
DocID024821 Rev 2
AN4314
Electrical diagram and bill of material
Table 2. Bill of material
Ref.
Part N.
Type
Supplier
BR1
2KBP08M
Bridge rect. 2 A 800 V
Conn.1
Line-input
Connector MKDS 1.5/3-5.08-PS.5.08
Phoenix contact
Conn.2
DC-OUT
Connector MKDS 1.5/2-5.08-PS.5.08
Phoenix contact
C1
2.2 nF
Ceramic capacitor X1/Y2+-20%-P.7,5 mm
Murata
C2
150 nF
Capacitor MKP+-20%-PS15-X2
Epcos
C6
150 nF
Capacitor MKP+-20%-PS15-X2
Epcos
C3
680 uF
Electrolytic capacitor V.105 °C-PW-8000h
C4
220 nF
Capacitor MKP+-5%-200 Vac-PS15
Epcos
C5
3.3 uF
Ceramic capacitor X7S 10% EIA1210-SMD
Kemet
C7
22 uF
Electrolytic capacitor V.105 °C-2000h-PW
Nichicon
C8
33 uF
Electrolytic capacitor V.105 °C-10000h-YXM
Rubycon
C9
10 nF N.M.
C10
Vishay
Nichicon
Capacitor X7R 10% EIA0805-SMD
Murata
100 nF
Ceramic capacitor X7R 10% EIA1206-SMD
Yageo
C11
100 nF
Ceramic capacitor X7R 10% EIA0805-SMD
Kemet
C23
100 nF
Ceramic capacitor X7R 10% EIA0805-SMD
Kemet
C12
2.2 nF
Capacitor X7R 10% EIA0805-SMD
Kemet
C17
2.2 nF
Capacitor X7R 10% EIA0805-SMD
Kemet
C18
2.2 nF
Capacitor X7R 10% EIA0805-SMD
Kemet
C21
2.2 nF
Capacitor X7R 10% EIA0805-SMD
Kemet
C13
220 nF
Ceramic capacitor Y5V -20+80% EIA0805-SMD
C14
22 nF
Ceramic capacitor X7R 5% EIA1206-SMD
Kemet
C15
1 μF
Ceramic capacitor X7R 10%-EIA0805-SMD
Murata
C16
1 μF
Ceramic capacitor X7R 10%-EIA0805-SMD
Murata
C19
1 μF
Ceramic capacitor X7R 5%-EIA0805-SMD
Kemet
C20
220 pF N.M. Capacitor HV-U2J-5% EIA1206-SMD
Ceramic capacitor C0G 5% EIA0805-SMD
AVX
Murata
C22
220 pF
DZ1
BZV55-C24
Zener-diode 5%-Sz 19.6 mV/K-SMD
NXP
DZ2
BZV55-C15
Zener-diode 5%-Sz 11.4 mV/K-SMD
NXP
D1
STTH2L06
Ultrafast-diode 85 ns
STMicroelectronics
D2
LL4148
Fast-diode 4 ns-SMD
Vishay
D3
LL4148
Fast-diode 4 ns-SMD
Vishay
D4
LL4148
Fast-diode 4 ns-SMD
Vishay
D5
LL4148
Fast-diode 4 ns-SMD
Vishay
D6
LL4148
Fast-diode 4 ns-SMD
Vishay
D7
LL4148
Fast-diode 4 ns-SMD
Vishay
DocID024821 Rev 2
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9/31
31
Electrical diagram and bill of material
AN4314
Table 2. Bill of material (continued)
Ref.
Part N.
Type
D8
BAT48J
Schottky-diode SMD-MK 48
STMicroelectronics
D9
STPS3150U
Schottky-diode Vf 0, 82 V @ 25 °C 3 A-SMDMKG315
STMicroelectronics
F1
2AT
Fuse 2 A 250 V 8.5 x 4-392/TE05-TIME-LAG
Littelfuse
J1
PS10 mm
Wire jumper 0 Ω
-
J2
PS30 mm
Wire jumper 0 Ω
-
J3
PS23 mm
Wire jumper 0 Ω
-
J4
PS20 mm
Wire jumper 0 Ω
-
J5
PS29 mm
Wire jumper 0 Ω
-
J6
PS12 mm
Wire jumper 0 Ω
-
J7
PS24 mm
Wire jumper 0 Ω
-
J8
PS5 mm
Wire jumper 0 Ω
-
L1
62 mH
Q1
10/31
Common mode chokes-270 Vac max
ZTX560-N.M. BJT.PNP-hfe 50 to 300
BJT.NPN-hfe 40 to 180
Supplier
Magnetica
Diode Inc.
Q2
MJE243G
Q3
STI8N65M5
Q4
FZT560
BJT.PNP-SMD-hfe 50 to 300
Diode Inc.
Q5
FZT560
BJT.PNP-SMD-hfe 50 to 300
Diode Inc.
Q6
BC847C
BJT.NPN-hfe 420 to 800-SMD-MK1G
NXP
Q8
BC847C
BJT.NPN-hfe 420 to 800-SMD-MK1G
NXP
Q9
BC847C
BJT.NPN-hfe 420 to 800-SMD-MK1G
NXP
Q7
STN715N.M.
BJT.NPN-SMD-hfe80-MK N715
R1
8.2 K
Resistor 1%
TE-LR1F8K2
R2
N.M.
Resistor 1%
TE-LR1F8K2
R3
20 K
Resistor 1%
TE-LR1F20K
R4
N.M.
Resistor 1%-150Vac/dc -EIA0805-SMD
Vishay
R5
1K
Resistor 1%-150 Vac/dc -EIA0805-SMD
Vishay
R6
0.15
Resistor 1%-200 Vac/dc -EIA1206-SMD
IRC-LRC
R7
3.3
Resistor 1%-200 Vac/dc -EIA1206-SMD
Vishay
R8
330 K
Resistor 1%-200 Vac/dc -EIA1206-SMD
Vishay
R9
10 K
Resistor 1%-150 Vac/dc -EIA0805-SMD
Vishay
R10
270 K
Resistor 1%-150 Vac/dc -EIA0805-SMD
Vishay
R11
62 K
Resistor 1%-150 Vac/dc -EIA0805-SMD
Vishay
R12
10 K
Resistor 1%-200 Vac/dc -EIA1206-SMD
Vishay
MOSFET-N-0.6 Ω-tr/tf 14/11 ns-trr 200 ns
DocID024821 Rev 2
ON
STMicroelectronics
STMicroelectronics
AN4314
Electrical diagram and bill of material
Table 2. Bill of material (continued)
Ref.
Part N.
R13
2.2 M
Resistor 1%-200 Vac/dc -EIA1206-SMD
Vishay
R14
2M
Resistor 1%-200 Vac/dc -EIA1206-SMD
Vishay
R15
2M
Resistor 1%-200 Vac/dc -EIA1206-SMD
Vishay
R16
12
Resistor 1%-200 Vac/dc -EIA1206-SMD
Vishay
R17
0
Resistor 1%-200 Vac/dc -EIA1206-SMD
Vishay
R18
0
Resistor 1%-200 Vac/dc -EIA1206-SMD
Vishay
R31
0
Resistor 1%-200 Vac/dc -EIA1206-SMD
Vishay
R19
750
Resistor 1%-200 Vac/dc -EIA1206-SMD
Vishay
R20
47 K
Resistor 1%-150 Vac/dc -EIA0805-SMD
Vishay
C//R20
10 nF
Ceramic capacitor X7R 10% EIA0805-SMD
Kemet
R21
5.6 K
Resistor 1%-150 Vac/dc -EIA0805-SMD
Vishay
R22
390 K
Resistor 1%-150 Vac/dc -EIA0805-SMD
Vishay
R23
12 K
Resistor 1%-150 Vac/dc -EIA0805-SMD
Vishay
R24
470
Resistor 1%-150 Vac/dc -EIA0805-SMD
Vishay
R25
20 K
Resistor 1%-150 Vac/dc -EIA0805-SMD
Vishay
R26
0.82
Resistor 1% EIA1210-SMD
Rohm
R27
0.82
Resistor 1% EIA1210-SMD
Rohm
R28
51 K
Resistor 1%-150 Vac/dc -EIA0805-SMD
Vishay
R29
1M
Resistor 1%-50 Vac/dc -EIA0805-SMD
Vishay
R30
51 K
Resistor 1%-50 Vac/dc -EIA0805-SMD
Vishay
R32
330 K
Resistor 1%-150 Vac/dc -EIA0805-SMD
Vishay
R33
680 K
Resistor 1%-200 Vac/dc -EIA1206-SMD
Vishay
R34
56 K
Resistor 5% -150 Vac/dc -EIA0805-SMD
Vishay
R35
0
Resistor 1%-150 Vac/dc -EIA0805-SMD
Vishay
R36
220
Resistor 5%-200 Vac/dc -EIA1206-SMD
Vishay
R37
36 K
Resistor 1%-150 Vac/dc -EIA0805-SMD
Vishay
R38
100 K
Resistor 5%-150 Vac/dc -EIA0805-SMD
Vishay
R39
27
Resistor 5%-200 Vac/dc -EIA1206-SMD
Vishay
R40
510 K
Resistor 1%-150 Vac/dc -EIA0805-SMD
Vishay
T1
680 uH
Lighting buck/boost inductor 40 kHz
U1
SEA05L
I.C.-CC/CV controller 3.5 to 36 V-Vac 0.5%Iacc 4%-MK S5L-SMD
STMicroelectronics
U2
L6564H
I.C.-PFC controller HVS-TM-SMD
STMicroelectronics
VR1
300 Vac
VDR-300 Vac-385 Vdc-47J-D12 mm
(1)
Type
Supplier
Magnetica
Epcos
1. Add a 10 nF capacitor in parallel to R20 (0805).
DocID024821 Rev 2
11/31
31
Performance and considerations with LED loads
4
AN4314
Performance and considerations with LED loads
The board has been designed to source 350 mA nominal value into a string of 23 LEDs of
about 1 W power and a forward drop of 3.2 V typical at ambient temperature. The LEDS
used to test the demonstration board have been furnished by Seoul Semiconductor (part
number X42182) [6].
In order to reproduce the possible LED string drop variation due to thermal heating of a
single LED, measurements have been done first by loading the SMPS with a string of 23
LEDs having a voltage drop of 71 Vdc, then loading 22 LEDs (68 Vdc) and finally 24 (75 Vdc).
The behavior of the board has been checked also at the limit of the LED tolerance of the
voltage drop, at -10 %, that is, 63 Vdc and +10 %, that is, 77 Vdc by using an active load.
Figure 3 represents the different load voltage drops of the LEDs, applied to the converter, at
each point of the wide-range mains. This figure is necessary to understand the following
Figure 4, 5, 6 and 7.
Figure 3. LED string voltage vs. line voltage
/('6WULQJYROWDJH>[email protected]
9GF
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Figure 4 shows the LED string current versus the mains input voltage according to the load.
The LED current has been set at 350 mA nominal, using Equation 2 and considering the
internal Vcsth of SEA05L (see datasheet):
Equation 2
RS _ SEA05 L =
50mV
= 0.14Ω
350mA
The SEA05L perfectly regulates the current loop over the entire mains voltage and load
range [-10 %, +10 %].
12/31
DocID024821 Rev 2
AN4314
Performance and considerations with LED loads
Figure 4. LED current vs. line voltage
/('FXUUHQW>[email protected]
9GF
/('
/('
/('
9GF
9LQ>[email protected]
$09
Unlike boost topology, the buck-boost topology does not permit unity power factor even in
an ideal case. From AN1059 [1], the ratio is defined as:
Equation 3
KV =
V PK
Vout
The power factor is a function of Kv where Vpk is the input peak mains voltage and Vout is
the nominal 70 Vdc LED voltage drop.
The current would normally be sinusoidal for Kv = 0 but will be distorted from an ideal
sinusoid in proportion to the increase of KV. Since Kv in this application varies according to
the mains [85-265] Vac in the range [1.7-5.3], a different PF versus input line voltage has
been measured.
The PF is then affected by the current phase shift caused by the CX capacitor of the input
EMI. A common-mode choke with high leakage value has been selected in order to increase
the power of the EMI filter but at the same time reducing the two CX capacitors.
The test results of the following Figure 5 and Figure 6 show the PF and THD versus line
voltage. The power factor remains above 0.9 up to the European range even considering
the minimum tolerance value of the LED voltage drop (-10 %).
Considering the LED voltage drop variation, the PF remains above 0.9 until 250 Vac.
DocID024821 Rev 2
13/31
31
Performance and considerations with LED loads
AN4314
Figure 5. Power factor vs. line voltage
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9GF
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Figure 6. THD vs. line voltage
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14/31
DocID024821 Rev 2
AN4314
Performance and considerations with LED loads
Finally the efficiency of the converter has been measured showing a curve varying between
89 % and 90 %.
Figure 7. Efficiency vs. line voltage
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The voltage drop between the emitter and collector of the Vcc voltage regulator Q2 of the
self-supply network increases with the input line voltage. The power losses on this BJT can
be calculated as:
Equation 4
Plosses = Vce ⋅ I pump
The current consumption of the L6564H and driving circuitry is 5 mA and the Q2 voltage
drop can reach 70 V at high mains, so the power losses are around 350 mW, that is, 1.5 %
of the total output power.
We can note that the losses at an input voltage above 200 Vac become significant, causing a
slight decrease of efficiency as visible in the diagram.
DocID024821 Rev 2
15/31
31
PFC waveforms
AN4314
5
PFC waveforms
5.1
Input and output current and voltage waveforms
The waveforms of the input current and drain voltage at the nominal input voltage mains
(100 Vac/50 Hz or 230 Vac/50 Hz) and 23-LED load condition are illustrated in Figure 8 and
Figure 9.
.
Figure 8. Input current waveform at 100 Vac 50 Hz
CH1: DRAIN
CH2: Input PFC Current
CH3: LED current
CH4: LED voltage drop
AM13768V1
Figure 9. input current waveform at 230 Vac 50 Hz
CH1: DRAIN
CH2: Input PFC Current
CH3: LED current
CH4: LED voltage drop
AM13769V1
Note that the regulated LED current remains constant over the entire input mains voltage
and with the variation of the LED voltage drop.
Drain voltage is modulated by the sinusoidal shape of the input rectified mains voltage. It
increases with the input line voltage.
As described in Section 4, the PFC input current has more distortion at high mains, but it
remains well below the harmonic limits of the international regulations. The LED current
ripple amplitude (CH3) is below 100 mA pk-pk according to the calculation and the LED
current is at the same level at both input voltages.
16/31
DocID024821 Rev 2
AN4314
5.2
PFC waveforms
Transition mode operation
The ZCD pin, GD and CS pin have also been checked in order to show transition mode
operation Figure 10 and Figure 11.
Figure 10. TM operation at 100 Vac - 0.35 A fsw = 35 kHz
CH1: DRAIN
CH2: GD
CH3: ZCD
CH4: CS
AM13770V1
Figure 11. TM operation at 230 Vac - 0.35 Afsw = 50 kHz
CH1: DRAIN
CH2: GD
CH3: ZCD
CH4: CS
AM13771V1
An inductor value of 680 μH has been selected in order to get the converter to operate at
very low frequency (35 kHz at 100 Vac), minimizing the EMI filter and optimizing the power
factor.
Turn-on of the MOSFET depends on the ZCD triggering signal during its falling edge, turnoff depends on the CS signal and its comparison with the internal feedback signal (MULT x
COMP).
5.3
Startup
With a 33 μF capacitor on the VCC pin, the L6564H turns on typically in less than 600 ms
and the LED light appears 100 ms later. The turn-on time of the device depends on the
value of the VCC capacitor and the charging current of the HVS, according to the following
equation (L6564H datasheet [3]):
Equation 5
Tstart −up = CVCC ⋅
DocID024821 Rev 2
Vturn−on
I ch arg e
17/31
31
PFC waveforms
AN4314
After turn-on the L6564H starts switching, absorbing energy from the VCC capacitor. During
normal operation the external charge pump provides energy to supply the IC. The power
delivered by the charge pump depends on the input mains voltage, the LED voltage drop
and on the primary-to-auxiliary turn ratio (n = 4.34):
Equation 6
V AUX _ TON = −
VAC IN
n
V AUX _ TOFF =
VOUT
n
The self-supplied circuitry has two worst-case conditions, one is when the circuit is
operating at minimum input mains voltage (85 Vac), and the second one is a lower voltage
drop tolerance (63 Vdc) of the LEDs. Design has to take into account both worst case
conditions contemporaneously.
The voltage regulator (Q2, DZ2, R3) regulates the VCC voltage at about 14 Vdc. After the
L6564H starts switching, the output capacitor voltage rises up until it reaches the nominal
voltage drop of the LEDs. Figure 12 and Figure 13 show the startup phase at the two
nominal conditions.
Figure 12. Startup at 100 Vac - 0.35 A
CH1: PFC_OK
CH2: FB (sensed on R17)
CH3: C7 voltage
CH4: Vcc
18/31
AM13772V1
Figure 13. Startup at 230 Vac - 0.35 A
CH1: PFC_OK
CH2: FB (sensed on R17)
CH3: C7 voltage
CH4: Vcc
DocID024821 Rev 2
AM13773V1
AN4314
PFC waveforms
Note that during startup, the loop is still open and the feedback signal (CH2-sensed on R17)
is still low. The time constant - R32 with C7 - (see CH3- voltage on C7 capacitor) is set in
order to mask this transition time, preventing the activation of the protection unnecessarily.
5.4
Line sags and fast on-off
The circuit behavior during a mains sags sequence has been tested, varying the OFF time
period of the line. Figure 14 and Figure 15 show the behavior during two missed cycles of
20 ms each (line is at 50 Hz).
Figure 14. TOFF = 40 ms at 100 Vac / 50 Hz 0.35 A
&+3)&B2.
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Figure 15. TOFF = 40 ms at 230 Vac / 50 Hz 0.35 A
&+3)&B2.
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&+&YROWDJH
&+9FF
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If VCC doesn't discharge until its turn-off level during the missed cycles, the converter
restarts immediately. During the missed cycles, the protection on the PFC_OK pin is
correctly inactivated.
DocID024821 Rev 2
19/31
31
PFC waveforms
AN4314
Figure 16. TOFF = 500 ms at 100 Vac/50 Hz 0.35 A
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Figure 17. TOFF = 500 ms at 230 Vac/50 Hz 0.35 A
&+9$&
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Figure 16 and Figure 17 show the circuit behavior during a mains interruption of 500 ms, as
in the case of a fast on-off-on cycle.
If the OFF time increases, VCC discharges until turn-off level, the HVS generator shuts down
and it is re-enabled only when the VCC voltage reaches the restart threshold. This is the
cause of the delay in the appearance of the LED light when the OFF time period of the line
is compared to a manual button switch ON and OFF (T > 500 ms).
5.5
Load disconnection
During load disconnection, the output voltage is controlled by the voltage loop and the
converter works in auto-restart. Figure 18 and Figure 20 represent the load disconnection
transition at 100 Vac/50 Hz and 230 Vac/50 Hz. Figure 19 and Figure 21 show the behavior
during the no-load condition.
20/31
DocID024821 Rev 2
AN4314
PFC waveforms
Figure 18. Load disconnection transition at
100 Vac/50 Hz
&+*'
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Figure 20. Load disconnection transition at
230 Vac/50 Hz
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Figure 19. No load at 100 Vac/50 Hz
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Figure 21. No load at 230 Vac/50 Hz
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When the load is disconnected, first the current loop tries to compensate the low current
sensed on R6 and R7 and increases the output of U1 (pin 5). As a consequence, the COMP
pin increases too, but as the output voltage reaches about 85 Vdc, the voltage loop
operates, and the output of U1 is forced to decrease. The overlap of these two effects can
be seen on the COMP pin (CH2). As this signal falls, it triggers the burst mode. During this
operation the output voltage of the converter decreases, VCC voltage reaches its turn-off
level and the L6564H shuts down. Only when VCC voltage reaches the VCC-restart
threshold does the HVS generator pump current into the VCC capacitor and the L6564H
restarts switching.
DocID024821 Rev 2
21/31
31
PFC waveforms
AN4314
The intervention of the voltage loop can be set using:
Equation 7
VOVP = 2.5V ⋅
R8 + R9
R8
considering that the internal reference of the SEA05L is 2.5 V typ. [4].
The speed of the voltage loop can be increased by fine-tuning the C11, R10 network. A high
value of C15 slows down the voltage loop reaction, but it filters the output capacitor voltage
ripple, affecting the power factor. In this design a compromise has been found.
5.6
Short-circuit
During a short of the output connector, all the energy stored in the output electrolytic
capacitor C3 is discharged into the output side loop, and no current will flow into the external
LEDs, preventing their failure. The SEA05L CC-CV controller is no longer supplied and it
cannot regulate the loop. A peak high current of 60 A has been measured during 100 ns
flowing from the output capacitor into the output side loop. In order to protect the sense
resistor of the cc-cv controller, a Schottky diode D9 of 80 A surge current (see STPS3150U
datasheet [7]) has been added in the demonstration board.
After this initial transient the short-circuit protection, described above, senses the feedback
signal and disables the L6564H from the PFC_OK pin (see disable function of the L6564H
[3]).
The behavior of the protection has been tested with positive results over the entire input
voltage range; only the two nominal conditions at 100 Vac and 230 Vac have been discussed
in this application note.
Figure 22. Short-circuit at 100 Vac
&+3)&B2.
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Figure 23. Short-circuit at 230 Vac
&+3)&B2.
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Figure 22 and Figure 23 show that PFC_OK is pulled to GND when the voltage on the C7
capacitor reaches the value of 3 x Vbe (2 x Vf (LL4148) + BC847C Vbe).
22/31
DocID024821 Rev 2
AN4314
PFC waveforms
Figure 24 and Figure 25 show the resulting hiccup mode of the converter during shorts,
when the protection is tripped.
Figure 24. Overload behavior after a shortcircuit at 100 Vac
&+3)&B2.
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Figure 26. Short-circuit removal at 100 Vac
&+3)&B2.
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Figure 25. Overload behavior after a shortcircuit at 230 Vac
&+3)&B2.
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Figure 27. Short-circuit removal at 230 Vac
&+3)&B2.
&+)%VHQVHGRQ5
&+&YROWDJH
&+9FF
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Figure 26 and Figure 27 show the behavior after the short removal. The startup sequence is
activated.
DocID024821 Rev 2
23/31
31
PFC waveforms
5.7
AN4314
Feedback failure protection (open loop)
A kind of protection that any power supply must have is one which prevents the failure of the
feedback circuitry. If a failure occurs, for example degradation of one BJT (Q4 or Q5), the
output voltage can increase, damaging the electrolytic capacitor and the LED load.
Figure 28 and Figure 29 show the board behavior opening the loop by removing the resistor
R17 (0 Ω).
Figure 28. Feedback failure protection
at 100 Vac/50 Hz
&+3)&B2.
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Figure 29. Feedback failure protection
at 230 Vac/50 Hz
&+3)&B2.
&+&203
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The feedback signal on C15 falls, activating the same external protection that pulls down the
PFC_OK (CH1) pin below its disable threshold. The delay in triggering is due to the
charging time of the capacitor C7 through R32. The output voltage (CH3) is limited.
24/31
DocID024821 Rev 2
AN4314
Harmonic content measurement
One of the main purposes of this converter is the correction of input current distortion,
decreasing the harmonic contents below the limits of the actual regulation. Therefore, the
board has been tested according to the Japanese standard JEIDA-MITI Class-C and
European standard EN61000-3-2 Class-C, at full load and both nominal input voltage
mains.
Figure 30. EVL6564H-25W-BB at 100 Vac/50 Hz compliance with JEIDA-MITI class-C
limits at PF = 0.9801
0HDVXUHGYDOXH
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$09
Figure 31. EVL6564H-25W-BB at 230 Vac/50 Hz compliance with EN61000-3-2 class-C
limits at PF = 0.9180
0HDVXUHGYDOXH
(1 &ODVV&OLP LWV
+DUPRQLF&XUUHQW>[email protected]
6
Harmonic content measurement
+DUPRQLF2UGHU>[email protected]
$09
As shown in the figures that follow, the circuit is capable of reducing the harmonics well
below the limits of both regulations.
DocID024821 Rev 2
25/31
31
Thermal measurements
7
AN4314
Thermal measurements
To check the reliability of the design, thermal mapping using an IR camera was carried out.
Figure 32 and Figure 33 show thermal measurements on the component side of the board
at nominal input voltages and full load. Pointers show the relevant temperature of key
components. Table 3 provides the correlation between the measured points and
components for both thermal maps. The ambient temperature during both measurements
was 25 °C. According to these measurement results, all components on the board function
within their temperature limits.
Figure 32. Thermal map at 100 Vac/50 Hz
Figure 33. Thermal map at 230 Vac/50 Hz
$09
$09
Table 3. Measured temperature at 100 Vac/50 Hz and 230 Vac/50 Hz
Point
26/31
Component
Temp. at 100 Vac (ºC)
Temp. at 230 Vac(ºC)
A
Common-mode choke
46.9
35.5
B
Diode bridge
46.9
35.5
C
Output diode D1
61.4
63.7
D
R1 (SEA05-FB bias)
70.1
71.8
E
Q3 inductor choke T1-L
51.4
54.4
F
Q3 inductor choke T1-R
48.6
52.7
G
BJT voltage regulator
44.4
64.0
H
MOSFET
46.3
50.3
DocID024821 Rev 2
AN4314
8
Conducted emission pre-compliance test
Conducted emission pre-compliance test
The following graphs show the average measurements of the conducted noise with a 23LED load and nominal mains voltages. The limits shown on the diagrams are those of
EN55022 class-B, which is the most popular standard for European equipment. As visible,
good margins with respect to the limits are present in all test conditions. Increasing the CX
capacitor value of the EMI filter will improve the safety margin but will affect the PF. A
compromise has been found in this design.
Figure 34. 100 Vac/50 Hz - phase
Figure 35. 100 Vac/50 Hz - neutral
$09
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Figure 36. 230 Vac/50 Hz - phase
Figure 37. 230 Vac/50 Hz - neutral
$09
$09
Note that a CY capacitor between the negative output pin of the converter and ground has
been placed to filter common-mode noise flowing into the demonstration board.
A small filter capacitor between the SEA05L output (pin 5) and SEA05L GND (pin 2) has
also been placed for the same reason.
The C20 capacitor between the drain and source of Q3 acts as a snubber and it has been
foreseen to increase the safety margin.
DocID024821 Rev 2
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31
PCB layout
9
AN4314
PCB layout
Figure 38 and Figure 39 show the layout of the PCB.
The demonstration board has been designed to fit in a typical LED driver case so the
maximum height is 20 mm, maximum length is 90 mm and the maximum width is less than
65 mm.
Of course the form factor could be further reduced depending on the capacitor value. Here a
very narrow current ripple has been defined as a specification, but accepting a higher value,
the capacitor size could be further reduced.
Figure 38. Bottom layer
28/31
Figure 39. Top layer
DocID024821 Rev 2
AN4314
10
References
References
1.
AN1059 - Design equations of high-power-factor flyback converters based on the
L6561
2.
AN1060 - Flyback converters with the L6561 PFC controller
3.
L6564H - datasheet
4.
SEA05L - datasheet
5.
STI8N65M5 - datasheet
6.
X42182 LED - datasheet (Seoul Semiconductor)
7.
STPS3150U - datasheet
8.
STTH2L06 - datasheet
DocID024821 Rev 2
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31
Revision history
11
AN4314
Revision history
Table 4. Document revision history
30/31
Date
Revision
Changes
18-Jul-2013
1
Initial release.
29-Jul-2013
2
Corrected rendition errors in Figures 14 to 29.
DocID024821 Rev 2
AN4314
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