AN2359 Datasheet, PDF (1/18 Pages) STMicroelectronics – Double output Buck-Boost converter with VIPerX2A

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
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