AN2941
Application note
19 V - 75 W SMPS compliant with latest ENERGY STAR
®
criteria
using the L6563S and the L6566A
Introduction
This application note describes the characteristics and the features of a 75 W reference
board (p/n EVL6566A-75WES4), tailored on specifications of a typical high-end portable
computer power supply. The peculiarities of this design are the very high efficiency at light
load and the excellent global efficiency for a two-stage architecture. The high efficiency at
high load is achieved by not using synchronized rectification at the secondary side and
therefore offering a very cost-effective solution.
Efficiency during active-load and light-load operation are compliant with ENERGY STAR
®
eligibility criteria for both external (EPA rev. 2.0 EPS) and computer integrated (EPA rev. 4.0
computers) power supply. In addition this design is even compliant with the latest computer
document (EPA rev. 5.0 computers) whose effective date is July 2009.
Figure 1.
L6566A and L6563S-75W ENERGY STAR
®
compliant adapter
demonstration board (p/n EVL6566A-75WES4)
November 2010
Doc ID 15447 Rev 4
1/37
www.st.com
Contents
AN2941
Contents
1
2
3
4
5
6
7
8
9
10
Main characteristics and circuit description . . . . . . . . . . . . . . . . . . . . . 5
Efficiency measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Harmonic content measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Functional check . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Thermal map . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Conducted emission pre-compliance test . . . . . . . . . . . . . . . . . . . . . . 24
Bill of material . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
PFC coil specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
Transformer specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
2/37
Doc ID 15447 Rev 4
AN2941
List of tables
List of tables
Table 1.
Table 2.
Table 3.
Table 4.
Table 5.
Table 6.
Table 7.
Table 8.
Table 9.
Overall efficiency compared to “EPA rev. 2.0 EPS” . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Overall efficiency compared to “EPA rev. 4.0 computers” . . . . . . . . . . . . . . . . . . . . . . . . . 13
Overall efficiency compared to “EPA rev. 5.0 computers” . . . . . . . . . . . . . . . . . . . . . . . . . 14
Output voltage at OVP intervention vs. input voltage and output power . . . . . . . . . . . . . . 22
Thermal maps reference points . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Bill of material . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
PFC coil winding data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
Transformer winding data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
Document revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
Doc ID 15447 Rev 4
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List of figures
AN2941
List of figures
Figure 1.
L6566A and L6563S-75W ENERGY STAR® compliant adapter demonstration board (p/n
EVL6566A-75WES4) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Figure 2.
Typical transition mode PFC electrical diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Figure 3.
Sensorless PFC electrical diagram. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Figure 4.
Sensorless PFC operation theory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Figure 5.
Electrical diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Figure 6.
Light-load efficiency measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Figure 7.
EVL6566A-75WES4 compliance to EN61000-3-2 standard at 230 Vac-50 Hz, full load . . 15
Figure 8.
EVL6566A-75WES4 compliance to JEITA-MITI standard at 100 Vac-50 Hz, full load. . . . 15
Figure 9.
Flyback stage waveforms at 115 V-60 Hz - full load. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Figure 10. Flyback stage waveforms at 230 V -50 Hz - full load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Figure 11. Flyback stage waveforms at 115 V-60 Hz - 20 W load . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Figure 12. Flyback stage waveforms at 230 V -50 Hz - 20 W load . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Figure 13. No-load operation at 90 V-60 Hz . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Figure 14. No-load operation at 265 V-50 Hz . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Figure 15. Transition full load to no load at 265 Vac-50 Hz . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Figure 16. Transition no load to full load at 265 Vac-50 Hz . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Figure 17. Short-circuit at full load and 230 Vac - 50 Hz . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Figure 18. Short-circuit details at full load and 230 Vac - 50 Hz . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Figure 19. EVL6566-75WES4 PFC open loop at 115 Vac-60 Hz - full load . . . . . . . . . . . . . . . . . . . . 20
Figure 20. Flyback open loop at 230 V-50 Hz half load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Figure 21. Flyback open loop at 230 V-50 Hz half load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Figure 22. Flyback open loop - restart option 230 Vac 50 Hz - half load . . . . . . . . . . . . . . . . . . . . . . . 21
Figure 23. Thermal map at 115 Vac-60 Hz - full load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Figure 24. Thermal map at 230 Vac-50 Hz - full load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Figure 25. CE average measure at 115 Vac and full load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
Figure 26. CE average measure at 230 Vac and full load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
Figure 27. PFC coil electrical diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
Figure 28. PFC coil mechanical aspect . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
Figure 29. Transformer electrical diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
Figure 30. Transformer winding cross view . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
Figure 31. Transformer mechanical aspect . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
4/37
Doc ID 15447 Rev 4
AN2941
Main characteristics and circuit description
1
Main characteristics and circuit description
The main features of the SMPS are listed as follows:
●
●
●
●
●
●
●
●
●
Universal input mains range: 90÷264 Vac - frequency 45
÷
65 Hz
Output voltage: 19 V at 4 A continuous operation
Mains harmonics: according to EN61000-3-2 Class-D or JEITA-MITI Class-D
Standby mains consumption: < 0.14 W at 230 Vac
Active load average efficiency: better than 87% without synchronous rectification
EMI: according to EN55022-Class-B
Safety: according to EN60950
Dimensions: 78 x 170 mm, 25 mm maximum height of components
PCB: Single-side, 70 µm, CEM-1, mixed PTH/SMT
The circuit is composed of two stages: a front-end PFC using the L6563S and a flyback
converter based on the L6566A. The CV/CC controller TSM1014 allows the correct current
limitation on the secondary side. The flyback stage works as master and it is dedicated to
control the circuit operation including the standby and protections. Additionally, it switches
on and off the PFC stage by means of a dedicated pin (VCC_PFC), thus helping to achieve
an excellent efficiency even at light load, with low complexity.
PFC stage
The main function of the PFC is to keep the current absorbed from the power line tracking
the line voltage to comply with the EN61000-3-2 or other similar regulations and to regulate
the output voltage of the boost stage powering the downstream converter. Therefore, it is
necessary to sense the PFC output voltage as well as the input coming from the mains and
feed these two signals to the controller. The simplest way to implement these functions is to
sense both input and output voltage through two resistor dividers as shown in
Figure 2.
These resistors are in the MΩ range (6.6 MΩ for the input divider and 2 MΩ for the output
divider of the example in the figure), however their power dissipation, which is negligible at
full load, becomes significant at light load. Even if the PFC is turned off at light load, the
power dissipation of the two dividers is always there. Additionally, at light load both the input
and the output voltages become very close to the peak value of the rectified mains because
the input and output capacitors act as peak detectors of the rectified mains voltage.
Considering the worst case for power consumption, once the SMPS is working at european
mains range, the power dissipation of these two dividers can be easily calculated as follows:
P
MULT
V
230 V
⋅
2
=
IN
=
R
MULT
6.6M
Ω
2
2
(
)
2
=
16mW
P
FB
V
230 V
⋅
2
=
OUT
=
R
MULT
2M
Ω
(
)
2
=
53mW
For example, if we calculate the impact of these losses with a 1 W output load, these two
circuits affect the overall efficiency by about 7%.
Doc ID 15447 Rev 4
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