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Secondary Post-Regulation in Power Processors using a Synchronous Regulator

IP.com Disclosure Number: IPCOM000119694D
Original Publication Date: 1991-Feb-01
Included in the Prior Art Database: 2005-Apr-02
Document File: 3 page(s) / 94K

Publishing Venue

IBM

Related People

Kelkar, S: AUTHOR

Abstract

Secondary post-regulation is often desired in multi-output power processors, especially when tight regulation is needed on all outputs. Magnetic amplifiers have been proposed as suitable post-regulators. This article outlines a technique of using the well-known buck regulator to achieve good regulation on secondary outputs.

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Secondary Post-Regulation in Power Processors using a Synchronous
Regulator

      Secondary post-regulation is often desired in
multi-output power processors, especially when tight regulation is
needed on all outputs.  Magnetic amplifiers have been proposed as
suitable post-regulators.  This article outlines a technique of using
the well-known buck regulator to achieve good regulation on secondary
outputs.

      Fig. 1 shows a schematic of a two-output power processor with a
buck regulator providing closed-loop control for the second output.
The main control loop senses both the output voltage Vo1 and the
voltage across the inductor to produce the duty cycle.  The buck
regulator has its own control loop with the two control chips
synchronized using standard techniques.  A small value capacitor in
series with the power transformer ensures that it will not saturate.
Fig. 2 shows the relationship between the two voltages V1 and V2, as
well as the current in the switch pairs 1,3 and 2,4.  It can be seen
that one of the key design considerations is to ensure that the
maximum on time demanded by the buck post-regulator, Ton2, must
always be less than the minimum on time, Ton1, produced by the main
control loop.  This is because the voltage available at the input to
the buck regulator is a series of pulses with variable on time
controlled by the main control loop.

      Ensuring that the condition above is satisfied is made easier
because the duty cycle in both fullbridge and buck regulators is
directly influenced by the supply voltage but weakly dependent on the
load.  Thus, supply voltage changes will affect both regulators to
the same extent, but load changes will need much smaller duty cycle
adjustments.  The turns ratio of the power transformer winding
feeding the post-regulator is a variable that depends on the supply
vol...