AN3089
Application note
19 V - 65 W quasi-resonant flyback adapter using L6566B and
TSM1014
Federico Levati
Introduction
This application note describes the characteristics and features of a 65 W demonstration
board (EVL6566B-65W-QR), tailored to the specifications of a typical hi-end portable
computer power supply. The peculiarities of this design are the very high average efficiency
of about 90%, without synchronous rectification, and very low no load consumption of
100 mW at 230 Vac. The result is that this converter is more than compliant with Energy
Star
®
eligibility criteria (EPA rev. 2.0 EPS).
Figure 1. EVL6566B-65W-QR: 65 W adapter demonstration board
October 2014
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Contents
AN3089
Contents
1
Main characteristics and circuit description . . . . . . . . . . . . . . . . . . . . . 5
1.1
1.2
1.3
1.4
1.5
1.6
1.7
1.8
1.9
Power stage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Startup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Brownout protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Output regulation feedback loop . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
L6566B current mode control and voltage feed forward function . . . . . . . . 7
L6566B short-circuit protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Overvoltage protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Overtemperature protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Burst mode operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
2
3
Efficiency measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Functional check . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
3.1
3.2
3.3
Standby and no load operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Overcurrent and short-circuit protection . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Overvoltage and open loop protection . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
4
5
6
7
8
Thermal map . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Conducted emission pre-compliance test . . . . . . . . . . . . . . . . . . . . . . 17
Bill of material . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Transformer specification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
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AN3089
List of tables
List of tables
Table 1.
Table 2.
Table 3.
Table 4.
Table 5.
Overall efficiency and no load consumption . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Thermal map reference points . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
EVL6566B-65W-QR demonstration board: bill of material . . . . . . . . . . . . . . . . . . . . . . . . . 18
Transformer winding data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Document revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
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List of figures
AN3089
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.
EVL6566B-65W-QR: 65 W adapter demonstration board . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Electrical diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Light-load efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Flyback stage waveforms at 115 V – 60 Hz – full load . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Flyback stage waveforms at 230 V – 50 Hz – full load . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Flyback stage waveforms at 115 V – 60 Hz – light-load . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Flyback stage waveforms at 230 V – 50 Hz – light-load . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
No load operation at 90 V – 50 Hz . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
No load operation at 265 V – 50 Hz . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Transition full load to no load at 265 Vac – 50 Hz . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Transition no load to full load at 265 Vac – 50 Hz . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Short-circuit at full load and 230 Vac – 50 Hz. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Short-circuit detail at full load and 230 Vac – 50 Hz . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Flyback open loop – detail at 230 V – 50 Hz – half load. . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Flyback open loop at 230 V – 50 Hz –half load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Thermal map at 115 Vac – 60 Hz – full load. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Thermal map at 230 Vac – 50 Hz – full load. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
CE average measurement at 115 Vac and full load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
CE average measurement at 230 Vac and full load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Transformer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Transformer winding diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
Transformer mechanical diagrams . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
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AN3089
Main characteristics and circuit description
1
Main characteristics and circuit description
The main features of the SMPS are listed below:
Universal input mains range: 90
264 Vac - frequency 45
65 Hz
Output voltage: 19 V at 3.42 A continuous operation
Mains harmonics: acc. to EN61000-3-2 Class-D or JEITA-MITI Class-D
Standby mains consumption: < 100 mW at 230 Vac
Average efficiency: better than 89% without synchronous rectification
EMI: according to EN55022-Class-B
Safety: according to EN60950
Dimensions: 58 x 121 mm, 25 mm maximum component height
PCB: single side, 35 µm, CEM-1, mixed PTH/SMT.
1.1
Power stage
The flyback converter implements the new ST dedicated current mode L6566B (U2)
controller operating in quasi-resonant mode and detecting the transformer demagnetization
through the ZCD (#11) pin.
R23 on the OSC (#13) pin sets the maximum switching frequency at about 165 kHz.
Because the maximum switching frequency is imposed, the converter operates in
discontinuous conduction mode during light-load operation. The L6566B valley skipping
function is capable of turning-on the MOSFET in valley switching even in DCM, therefore
reducing switching losses.
The MOSFET is a standard 800 V, STF7NM80, housed in a TO-220FP package, needing
just a small heatsink. The transformer is a layer type, using a standard ferrite size EER28L,
designed according to EN60950 and manufactured by MAGNETICA.
The flyback reflected voltage is ~150 V, providing enough room for the leakage inductance
voltage spike with a still margin for reliability of the MOSFET. The D5 rectifier and the D4
Transil™ clamp the peak of the leakage inductance voltage spike at MOSFET turn-off.
A small capacitance in parallel with D4 smooth leakage inductance spikes, reducing EMI
and Transil dissipation.
The output rectifiers are two STPS20H100CFP dual center tap Schottky diodes (D2 and D3)
in parallel, housed in the TO-220FP. They have been selected according to the maximum
reverse voltage, forward voltage drop, and power dissipation. The snubber, made up of R5,
R7 and C12, dampens the oscillation produced by the diode capacitance and the leakage
inductance.
A small LC filter has been added on the output, filtering the high frequency ripple and
spikes.
D6, R4, R5, R8, R9, Q2 and Q3 implement an output voltage “fast discharge” circuit, quickly
discharging the output capacitors when the converter is turned off. It has been implemented
to quickly decrease the residual output voltage after the converter is turned off at no load.
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