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Pulse Transformer Feedback Interface for Pulse Width Modulation Control in Switching Regulators

IP.com Disclosure Number: IPCOM000050976D
Original Publication Date: 1982-Dec-01
Included in the Prior Art Database: 2005-Feb-10
Document File: 3 page(s) / 39K

Publishing Venue

IBM

Related People

Hanson, TW: AUTHOR [+2]

Abstract

This circuit provides an error feedback interface for pulse-width modulation control in switching regulators. It transmits a sample ration of sensed voltage across the secondary to primary interface to an error amplifier. The secondary to primary isolation is provided by a pulse transformer.

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Pulse Transformer Feedback Interface for Pulse Width Modulation Control in Switching Regulators

This circuit provides an error feedback interface for pulse-width modulation control in switching regulators. It transmits a sample ration of sensed voltage across the secondary to primary interface to an error amplifier. The secondary to primary isolation is provided by a pulse transformer.

The circuit, shown schematically in the figure, must control the power in the primary of the power transformer (T1) in order to maintain (regulate) outputs from that transformer. Switching regulators control the power through the power transformer by adjusting the power applied to the primary of the transformer. Primary power adjustment is accomplished by alternately turning the power through the primary on and off, and adjusting the amount of time the power is applied and removed (on/off). This technique is known as pulse-width modulation.

Pulse-width modulation control is obtained by sampling the output of the power transformer, comparing it to a known constant reference voltage, and adjusting the pulse width so as to maintain a constant output.

The quality of regulation is dependent on many factors, one of which is the integrity of the sample voltage. If attenuation occurs in the sample voltage before the comparison to the reference, then the result is a degradation of output regulation.

Switching regulators place the comparison of the reference close to the sensed voltage to minimize attenuation. Therefore, the comparison usually takes place in the output (secondary) circuit area. However, the switch (transistor Q1) that controls the power applied to the power transformer is located in the primary circuit.

Isolation between primary power and secondary power is a necessary safety precaution in power supplies.

The subject circuit permits the comparison of secondary voltage to take place in the primary circuit by transmitting a sample voltage across the secondary to primary interface with minimal attenuation.

The representative environment (see figure) is a flyback switching regulator with multiple output levels and one sensing level. However, the subject control circuit concepts are readily extended to other types of switching regulators.

Referring to the figure, the output voltage(s) are developed from the s...