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Design of a Common Core Output Inductor Around a Control Winding in a Push-Pull Multi-Output Converter

IP.com Disclosure Number: IPCOM000043137D
Original Publication Date: 1984-Jul-01
Included in the Prior Art Database: 2005-Feb-04
Document File: 3 page(s) / 36K

Publishing Venue

IBM

Related People

Azzis, D: AUTHOR [+3]

Abstract

A common core inductor (CCI) is used as the filter choke of a multi-output power supply. Previous designs of this kind required high control of coupling coefficients and turn ratios which is extremely difficult to achieve. In many cases, designers introduce little self-inductances in series with each winding of the CCI to obtain leakage inductance adjustment. In this design simplicity took over, so that stability could be easily met and so that device volume and cost savings could be real. The only consequence is a non-optimum transient response on a non-loop controlled output.

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Design of a Common Core Output Inductor Around a Control Winding in a Push-Pull Multi-Output Converter

A common core inductor (CCI) is used as the filter choke of a multi-output power supply. Previous designs of this kind required high control of coupling coefficients and turn ratios which is extremely difficult to achieve. In many cases, designers introduce little self-inductances in series with each winding of the CCI to obtain leakage inductance adjustment. In this design simplicity took over, so that stability could be easily met and so that device volume and cost savings could be real. The only consequence is a non-optimum transient response on a non-loop controlled output. The design justification is based on the following analysis: For each output of the converter and for the "on" time of the switches, we have,

(Image Omitted)

where w = duty cycle

By taking the difference between 1) and 2), we get the

inductor voltages:

(Image Omitted)

This relation shows that the inductor voltages are proportional to the transformer secondary voltages. It occurs that all inductor voltages can be generated within a common core transformer, what we call a common core inductor. It also occurs that all the windings of the CCI have to be in the same ratio as the transformer secondaries. To have a stable circuit, it is necessary to have a positive current ripple in the regulated output inductor[*]. This condition means that the output is gaining energy during the "on" time of t...