ST AN1514 Application note
AN1514
Application note
VIPower: double output buck or
buck-boost converter using VIPer12A-E/22A-E
Introduction
This paper introduces two double output off-line non isolated SMPS based on the
VIPerX2A-E family. The first SMPS is a Buck converter with two positive outputs and the
second one is a Buck-Boost converter with two negative outputs. The use of VIPer12A-E or
VIPer22A-E in both converters depends on the output power specifications. The power
supplies are operated in off-line mode with an extended wide range of the input voltage,
from 80 to 285 Vac. The target applications are small loads, such as microcontrollers,
motors, displays and peripherals in several industrial and home appliances.
Two converter topologies are introduced in this paper. The considered double output
converters are based on the VIPerX2A-E device family and are suitable for non isolated offline applications. VIPerX2A-E is a low cost monolithic smart power with a PWM controller,
start-up circuit and protection integrated on the same chip. The power stage consists of a
vertical Power MOSFET with 730 V breakdown voltage and 0.32 A for VIPer12A-E or 0.56 A
for VIPer22A-E maximum drain current with internal limitation.
The use of a VIPower device makes the design very simple and easy, since several features
are integrated in the smart power IC. The first SMPS is a Buck converter with two positive
outputs and the second one is a Buck-Boost converter with two negative outputs. The use of
VIPer12A-E or VIPer22A-E in both converters depends on the output power specifications.
The power supplies are operated in off-line mode with an extended wide range of the input
voltage, from 80 to 285 Vac.
The target applications are small loads, such as microcontrollers, motors, displays and
peripherals in several industrial and home appliances with power level up to 6-8 W.
September 2007 Rev 2 1/17
www.st.com
Contents AN1514
Contents
1 Off-line double output converters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2 VIPer application examples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.1 Double output buck converter using VIPer12A-E . . . . . . . . . . . . . . . . . . . . 6
2.1.1 Experimental results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
2.2 Double output buck-boost converter using VIPer22A-E . . . . . . . . . . . . . . . 9
2.2.1 Experimental results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
2.2.2 Thermal measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
3 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
4 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
2/17
AN1514 List of tables
List of tables
Table 1. Buck converter specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Table 2. Component list . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Table 3. Load regulation at V
Table 4. Load regulation at V
Table 5. Buck-boost converter specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Table 6. Component list . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Table 7. Load regulation at V
Table 8. Load regulation at V
Table 9. Thermal characterization (package: DIP8; R
T
=25°C). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
amb
Table 10. Document revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
=80V
in
=285V
in
=80V
in
=285V
in
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
acrms
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
acrms
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
acrms
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
acrms
=45°C/W mounted by socket;
thj-lead
3/17
List of figures AN1514
List of figures
Figure 1. Double output buck topology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Figure 2. Double output buck-boost topology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Figure 3. Converter schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Figure 4. Board layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Figure 5. Board prototype . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Figure 6. Efficiency vs. output power . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Figure 7. Converter schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Figure 8. Efficiency vs. output power . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Figure 9. V
Figure 10. V
Figure 11. VIPer22A-E temperature at maximum load with parasitic capacitance . . . . . . . . . . . . . . . 13
Figure 12. V
Figure 13. Conducted emissions at full load with EN55014 limits: line emissions. . . . . . . . . . . . . . . . 15
Figure 14. Conducted emissions at full load with EN55014 limits: neutral emissions . . . . . . . . . . . . . 15
=80V
in
=285V
in
and ID at Vin=230V
DS
acrms
acrms
, I
out2
, I
out2
=75 mA, CH1=V
=75 mA, CH1=V
, I
acrms
=250 mA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
out
out1
out1
, CH2=I
, CH2=I
, CH3=ILp, CH4=V
out1
, CH3=ILp, CH4=V
out1
. . . . . . . . . . . . . 13
out2
. . . . . . . . . . . . 13
out2
4/17
AN1514 Off-line double output converters
1 Off-line double output converters
In these circuits the first output is obtained using the standard buck or buck-boost topology,
while the second output is obtained by means of a second winding on the main inductor.
This output is directly coupled with the first one in flyback mode and its value is given by the
turns ratio n. The inductor is still low cost since a drum core can be used and the coupling
between the two windings is not as critical as in a flyback converter. The electrical
schematics of both configurations are shown in Figure 1 and Figure 2.
2 VIPer application examples
In this section two VIPerX2A-E application examples are introduced:
1. Double output buck converter 24 V at 30 mA, 5 V at 50 mA
2. Double output buck-boost converter (-24 V) at 250 mA, (-5 V) at 70 mA.
Figure 1. Double output buck topology
Figure 2. Double output buck-boost topology
5/17
VIPer application examples AN1514
2.1 Double output buck converter using VIPer12A-E
The proposed power supply, shown in Figure 3, is based on VIPer12A-E. The specifications
of the converter are listed in Ta b le 1 . The input section consists of a resistor as a fuse, a
single diode rectifier, and an input LC filter. Such a filter provides both DC voltage
stabilization and improved EMI performance (compliant with EN55022 Class B standard).
The capacitor Cin1 could be connected to provide further reduction of conducted EMI, if
required.
The switching frequency is 60 kHz, given by the integrated oscillator of the VIPer12A-E.
Figure 3. Converter schematic
D
3
D
z
C
3
D
2
V
FB
dd
D
R
f
r
L
f
VIPer12A-E
D
C
4
S
n
C
D
2
L
V
AC
C
in1
C
in
D
1
C
1
D
z1
+5V
z2
V
out2
+24V
V
out1
R
burden
GND
Table 1. Buck converter specifications
Parameter Value
AC input voltage V
Output current I
Output current I
Output voltage V
Output voltage V
inac
out
out2
out1
out2
80 - 285 Vac
30 mA
50 mA
+24±10%V
+5 V±5%
Switching frequency 60 kHz
Output power ~ 1 W
The two outputs are provided using a buck converter for the 24 V output, named "V
a coupled inductor in flyback mode for the 5 V output, named "V
feedback is connected to "V
" as well as the supply circuit of the VIPer12A-E. Doing so,
out1
". The regulation
out2
out1
", and
only one high voltage diode and one capacitor are needed, i.e. D3 and C3 in Figure 3,
reducing the complexity and the cost of the circuit.
The output inductor, L, has two coupled windings on the same ferrite core, with a proper turn
ratio and coupling factor in order to get the correct output voltage. In particular, 1.5 mH
inductor is used, with N1=200t - wound on the ferrite core of "PANASONIC ELC10D152E"
inductor - and N2=60t. Zener diodes, Dz1 and Dz2 protect both outputs against overvoltage.
6/17
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