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Analysis of Current-Injected Controlled Multi-Output Switching Converters

IP.com Disclosure Number: IPCOM000101346D
Original Publication Date: 1990-Aug-01
Included in the Prior Art Database: 2005-Mar-16
Document File: 4 page(s) / 107K

Publishing Venue

IBM

Related People

Kelkar, SS: AUTHOR

Abstract

A popular technique used in switching converter power processors is current-injected control in which the transistor switch current is sensed and used by the loop to modulate the duty cycle. The technique is applicable to multi-output regulators also; disclosed is a model that facilitates the analysis of such circuits.

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This is the abbreviated version, containing approximately 52% of the total text.

Analysis of Current-Injected Controlled Multi-Output Switching Converters

       A popular technique used in switching converter power
processors is current-injected control in which the transistor switch
current is sensed and used by the loop to modulate the duty cycle.
The technique is applicable to multi-output regulators also;
disclosed is a model that facilitates the analysis of such circuits.

      Fig. 1 shows a three-output two-transistor forward converter
with coupled inductors used at the outputs to improve
cross-regulation. The output voltage Vo is sensed by the control loop
as is the current in the transistor switches.  The concept of using
analog models for the digital portions of switching converters has
been disclosed earlier.  Using this approach it is possible to find
the applicable analog model to represent the power stage switching
cell outlined in Fig. 1. The key contribution in this disclosure is
the development of an analog model for the control loop switching
cell shown in Fig. 1.

      Fig. 2 shows the basic action of current mode control where the
error voltage output of the error amplifier Ve is compared with the
sensed switch current ip to determine the duty cycle.  The on-time
Ton is determined when the error voltage is equal to the current

                            (Image Omitted)

 where
k is the gain in the current loop (includes current sense transformer
turns and sense resistor value), m is the slope of the external ramp
used for stability, and m1, m2 and m3 are the current slopes in the
three output inductors.
where k12, k23 and k13 are the coupling coefficients between L1, L2
and L3, and VL1, VL2 and VL3 are the voltages across the inductors
L1, L2 and L3 during the on-time Ton.

 ...