December 2006

Rev 1

1/18

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

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.

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…).

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