AN2432
Application note
EVALSTSR30-60W: 60W AC-DC Adapter
with synchronous rectification using L6668 and STSR30
Introduction
This document describes a 60W adapter application using the L6668 fixed frequency
current mode PWM controller and the STSR30 smart driver for flyback synchronous
rectification.
This chipset guarantees low no-load consumption and high efficiency, making it easy to
comply with world-wide mandatory and voluntary energy saving requirements.
EVALSTSR30-60W demo board
October 2006
Rev 2
1/27
www.st.com
AN2432
Contents
Contents
1
Adapter features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.1
1.2
Main characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Circuit description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2
3
Electrical performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Functional check . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
3.1
3.2
3.3
3.4
3.5
Start-up behavior at full load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Wake-up time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Power-down . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Short-circuit tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Overvoltage protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
4
5
6
7
8
Conducted noise measurements (pre-compliance test) . . . . . . . . . . . 17
Thermal measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Bill of materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
PCB layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Transformer specification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
8.1
8.2
Electrical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
Mechanical aspect . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
9
Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
2/27
List of figures
AN2432
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.
Electrical diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
VIN = 115VRMS - 60Hz . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
VIN = 230VRMS - 50Hz . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
VIN = 115VRMS - 60Hz . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
VIN = 230VRMS - 50Hz . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
VIN = 115VAC - CCM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
CCM - Anticipation detail . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
VIN = 230VAC - DCM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
DCM - INHIBIT synchronization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Burst mode operation at 230VAC and no load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Start-up at 88VAC - 60Hz . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Start-up at 264VAC - 50Hz . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Wake-up at 115VAC - 60Hz . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Wake-up at 230VAC - 50Hz . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Power-down at 115VAC - 60Hz . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Power-down at 230VAC - 50Hz . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Short circuit at 88VAC - 60Hz . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Short circuit at 264VAC - 50Hz . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
OVP at 115VAC - full load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
OVP at 230VAC - full load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
OVP at 115VAC - no load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
OVP at 230VAC - no load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
CE peak measure at 115VAC and full load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
CE peak measure at 230VAC and full load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
VIN = 115VAC - full load. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
VIN = 230VAC - full load. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Silk screen - top side . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Silk screen - bottom side . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Copper tracks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Transformer electrical diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
Windings position . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
3/10
AN2432
List of tables
List of tables
Table 1.
Table 2.
Table 3.
Table 4.
Table 5.
Table 6.
Table 7.
Table 8.
Table 9.
Table 10.
Table 11.
Table 12.
Table 13.
Line and load regulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Efficiency at 115VRMS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Efficiency at 230VRMS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
No load consumption . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Power consumption with 0.5W output . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Mandatory energy saving requirements (from 1 January 2008) . . . . . . . . . . . . . . . . . . . . . 12
Voluntary energy saving requirements (from 1 January 2008) . . . . . . . . . . . . . . . . . . . . . . 12
Comparison between standard and SR flyback . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Key components temperature at 115VAC - full load. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Key components temperature at 230VAC - full load. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Part list . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Winding characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
4/10
Adapter features
AN2432
1
1.1
Adapter features
Main characteristics
The 60W AC-DC adapter board described in this application note has the following main
characteristics:
●
Input:
–
V
IN
: 88 ~ 264 V
RMS
–
f: 45 ~ 66 Hz
Output:
–
12V
DC
± 2% - 5A
No - Load:
–
Pin below 0.3W
Short circuit: protected with Auto-Restart feature
PCB type and size:
–
FR4
–
Single side: 70 µm
–
120 x 75 mm
Safety: according to EN60065
EMI: Compliance with EN55022 - Class B specifications
●
●
●
●
●
●
1.2
Circuit description
This circuit implements a flyback transformer which is a very popular topology for this kind of
application and power level, thanks to its simplicity and good trade-off between cost and
performance. To improve the converter's efficiency, the EVALSTSR30 demo board uses
synchronous rectification.
The converter works in both Continuous and Discontinuous conduction mode depending on
the input voltage (the circuit has a wide input voltage range) and the output load. The
68-kHz switching frequency provides a good compromise between the transformer size and
the harmonics of the switching frequency, optimizing input filter.
The input section includes protection elements (varistor, fuse and NTC for inrush current
limiting), a standard Pi-filter for EMC suppression, a bridge and an electrolytic bulk capacitor
as the front-end AC-DC converter. The transformer is a layer type, uses a standard ETD34
ferrite core and is designed to have a reflected voltage of 95V. The power MOS is a 700V -
1Ω and a transil clamp network is used for leakage inductance demagnetization.
On the primary side, the ST L6668 PWM controller integrates all the functions needed in a
SMPS (switch mode power supply) and enables building a complete system with a low
amount of external components. It includes a high voltage start-up generator, an
overvoltage protection input, frequency foldback for better efficiency at light loads,
programmable burst mode operation and soft start circuit.
5/27
工业自动化与控制
京公网安备 11010802033920号
Copyright © 2005-2026 EEWORLD.com.cn, Inc. All rights reserved
电子工程世界
