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Adaptive Pre-Loading for Narrow Range Power Supplies

IP.com Disclosure Number: IPCOM000120476D
Original Publication Date: 1991-Apr-01
Included in the Prior Art Database: 2005-Apr-02
Document File: 1 page(s) / 58K

Publishing Venue

IBM

Related People

Claassen, CH: AUTHOR

Abstract

A circuit is described which ensures a minimum output load for a power supply without impacting its maximum output capability. External load currents reduce the preload until the preload reaches zero after the load currents exceed the set preload value.

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This is the abbreviated version, containing approximately 64% of the total text.

Adaptive Pre-Loading for Narrow Range Power Supplies

      A circuit is described which ensures a minimum output load for
a power supply without impacting its maximum output capability.
External load currents reduce the preload until the preload reaches
zero after the load currents exceed the set preload value.

      Very often the specifications for a power supply call for tight
regulation from zero load current to its total capability.
Especially multi-output switchers exhibit cross-regulation problems
when one output is subjected to extremes, not to mention the classic
ferro-resonant transformer supplies with their narrow operating
ranges.

      The first remedy which comes to mind is a fixed resistive
pre-load which takes care of the minimum load needs of the supply and
is transparent to the user.  In order to meet the full load
requirement, however, the supply may have to be re-sized since the
preload is now added to the full load requirement.  The simple
resistive preload now exerts a cost penalty on the whole design.

      This is a case for the adaptive preload circuit.  It ensures
that minimum load conditions are always met, but relinquishes its
load current by the time the supply reaches full required output.
The overcurrent sense resistor present in many regulator circuits
finds double use as a current sense resistor (Rs).  Otherwise, it is
simply added as part of the adaptive preload circuit.

      The figure shows the schematic of su...