AN2359
Application note
Double output Buck-Boost converter with VIPerX2A
Introduction
This paper introduces two off-line non-insulated SMPS double outputs in Buck–Boost
configuration based on VIPerX2A family The power supplies are operated in wide input
voltage range, i.e. 88 to 265VAC. They can supply small loads, such as a microcontroller,
triacs, display and peripherals in the industrial segment and home appliance. In the
applications where a double output is required, two different solutions can be used. The first
one regards an insulated converter topology, with second output generated by means of
one winding on the magnetic core of the inductor with a proper turns ratio. Nevertheless,
this solution is expensive in terms of transformer and can be used for medium and high
current or insulated applications. For low power and low cost applications, a non-insulated
converter topology can be used. The proposed topology, based on Buck-Boost converter, is
used to supply negative output voltage referred to neutral in all those applications where the
galvanic insulation is not required. The principle schematic is shown in figure below.
Proposed double output Buck-Boost topology
V
OUT1
is provided using the classic Buck-Boost configurations, while V
OUT2
is obtained
thanks to an intermediate tap on the inductor.
Compared to other already proposed solutions, the second output is obtained thanks to an
intermediate tap on a low cost inductor. This configuration limits the parasitic capacitive
effect between the two winding and improves the regulation at open load.
Further advantage is related to the regulation feedback connected on V
OUT2
. Thanks to this
regulation, it is possible to cover those applications where a low tolerance and low voltage is
required (i.e. a microcontroller) and a high tolerance and high voltage is required for the
auxiliary circuit (drivers, relays…).
December 2006
Rev 1
1/18
www.st.com
Contents
AN2359
Contents
1
2
3
VIPerX2 description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Output voltage selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Application example nº 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
3.1
3.2
Experimental results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Thermal measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
4
Application example nº 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
4.1
Experimental results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
5
6
7
Layout considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
2/18
AN2359
List of figures
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.
Converter schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Typical waveforms at 88V
AC
: open load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Typical waveforms at 88V
AC
: full load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Typical waveforms at 265V
AC
: open load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Typical waveforms at 265V
AC
: full load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Commutation at full load: 88V
AC
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Commutation at full load: 265V
AC
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Output ripple voltage at full load: 88V
AC
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Output ripple voltage at full load: 265V
AC
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Turn on losses measurement at full load: 88V
AC
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Turn on losses measurement at full load: 265V
AC
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
VIPer22A Thermal profile: at V
IN
= 88V
AC
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
VIPer22A Thermal profile: at V
IN
= 265V
AC
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
VIPer22A temperature at maximum load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Converter schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Typical waveforms at 300V
DC
and full load: commutation . . . . . . . . . . . . . . . . . . . . . . . . . 15
Typical waveforms at 300V
DC
and full load: detail . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
PCB Layout (not in scale). Option nº 1: -12V output voltage . . . . . . . . . . . . . . . . . . . . . . . 16
PCB Layout (not in scale). Option nº 2: -24V output voltage . . . . . . . . . . . . . . . . . . . . . . . 16
3/18
List of tables
AN2359
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.
Proposed converters. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
SMPS specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Component list . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Circuit characterization - V
IN
= 120V
DC
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Circuit characterization - V
IN
= 320V
DC
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Circuit characterization - V
IN
= 374V
DC
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
SMPS specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Component list . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Experimental results - V
IN
=120V
DC
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Experimental results - V
IN
=320V
DC
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Experimental results - V
IN
=374V
DC
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
4/18
AN2359
VIPerX2 description
1
VIPerX2 description
The proposed converters are based on The VIPerX2A family, which is a range of smart
power devices with current mode PWM controller, start-up circuit and protections integrated
in a monolithic chip using VIPower M0 Technology.
The VIPerX2A family includes:
–
–
VIPer12, with a 0.4A peak drain current limitation and 730V breakdown voltage;
VIPer22, with a 0.7A peak drain current limitation and 730V breakdown voltage.
The switching frequency is internally fixed at 60kHz by the integrated oscillator of the
VIPerX2.
The internal control circuit offers the following benefits:
–
–
–
Large input voltage range on the V DD pin accommodates changes in supply
voltage;
Automatic burst mode in low load condition;
Overload protection in hiccup mode.
The feedback pin FB is sensitive to current and controls the operation of the device.
2
Output voltage selection
Two converters with different output voltage are introduced in this paper. The main
specifications are listed in
Table 1.
Table 1.
Proposed converters
Output 1
-12V/150mA
-24V/100mA
Output 2
-5V/300mA
-5V/300mA
P
OUT(MAX)
3.3W
3.9W
As already discussed, V
OUT2
is obtained by means of an intermediate tap on the inductor.
This imposes, for the two solutions, a different design of the output inductor in terms of turns
ratio, i.e. n=1.4 for the –12V solution, against n=3.8 for the –24V solution (even if it could be
necessary to tune the turn ratio for proper output voltage).
Some disadvantage are related to the –12V solution:
–
The parasitic capacitance effect between the two windings is increased, compared
to the second one. This will bring about higher switching losses in turn-on (see
Figure 10.
and
Figure 11.)
and, consequently, a worsening in terms of efficiency;
A higher voltage diode is needed to supply the VIPer;
The peak current is twice higher, giving less output power margin for a given I
DLIM
.
–
–
Therefore, a –24V/-5V solution can be suitably used for all those applications where
efficiency and cost are important and, in general, in all the designs where a –24V output
voltage does not impact on the cost of the relays and drivers.
5/18
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