Isolated Buck Converter Primary-Side Current Feedback

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Solution Overview

Problem

Traditional flyback converters and isolated buck converters face challenges in accurately regulating secondary-side output voltage due to leakage inductance and forward voltage drop, leading to voltage droop and degradation in regulation at lower input voltages and higher output currents, resulting in a cumbersome design process and higher component count.

Innovation Solution

The method involves measuring a parameter on the primary side of an isolated buck converter that is dependent on the secondary-side output voltage or current, and adjusting the duty cycle of the converter in proportion to this measurement to improve voltage regulation on the secondary side.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of manufacture

If traditional feedback regulation using primary-side output voltage is used in isolated buck converters, then the design process is simpler, but secondary-side voltage regulation degrades at lower input voltages and higher output currents due to leakage inductance and forward voltage drop

Engineering Contradiction:

Improvedesign process simplicityVSAvoidsecondary-side voltage regulation accuracy

Core Design Contradiction:

Ease of manufactureVSManufacturing precision

Solution Approach 1:

The patent introduces a feedback mechanism that measures the current through the high-side transistor and uses this information to dynamically adjust the duty cycle. This feedback loop compensates for voltage drops caused by leakage inductance and diode forward voltage, maintaining accurate secondary-side voltage regulation without requiring complex compensation design or additional components on the secondary side

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The patent replaces the traditional mechanical/electrical feedback approach (using physical voltage sensing and regulation circuits) with a control algorithm that processes current measurements and computes duty cycle adjustments. This substitution of measurement and control methods enables precise regulation while keeping the hardware design simple

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Manufacturing precision

If elaborate compensation design is used in flyback converters to achieve stability, then secondary-side voltage regulation accuracy improves, but device complexity and component count increase

Engineering Contradiction:

Improvevoltage regulation accuracyVSAvoidcomponent count

Core Design Contradiction:

Manufacturing precisionVSDevice complexity

Solution Approach 1:

The patent enables the isolated buck converter to self-regulate by using its own internal current measurements to automatically adjust its duty cycle. The high-side transistor current measurement provides inherent information about secondary-side loading conditions, eliminating the need for external compensation components or complex regulation circuits

Inventive Principle:

Principle #25Self-service

Solution Approach 2:

The patent makes the current measurement serve multiple functions: it provides information for secondary-side voltage regulation, indicates loading conditions, and enables dynamic duty cycle adjustment. This multi-functional use of a single measurement simplifies the overall design while achieving accurate regulation

Inventive Principle:

Principle #6Universality (Multi-functionality)

3Device complexity

If primary-side output voltage regulation is used, then the control circuit is simpler, but voltage droop on the secondary side is not detected and regulation degrades

Engineering Contradiction:

Improvecontrol circuit complexityVSAvoidsecondary-side voltage detection accuracy

Core Design Contradiction:

Device complexityVSMeasurement precision

Solution Approach 1:

The patent uses the high-side transistor current measurement as an intermediary parameter that indirectly reflects secondary-side voltage conditions. By measuring this current and using it to adjust the duty cycle, the system achieves secondary-side voltage regulation without directly sensing secondary-side voltage, thus maintaining simple control circuitry while improving regulation accuracy

Inventive Principle:

Principle #24Intermediary (Mediator)

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

This approach effectively reduces voltage variation on the secondary side by directly accounting for secondary-side changes in the primary-side control, enhancing regulation accuracy and reducing the complexity and cost of the design.

Implementation Method 1

a transformer having a primary side and a secondary side

Methodology Applied

Scientific EffectElectromagnetic induction: Electromagnetic Induction

Implementation Method 2

rectifying the secondary winding voltage using a diode and a capacitor

Methodology Applied

Scientific EffectRectification: Diode

Data Source

PatentUS10367420B2Load regulation for the isolated output in an isolated buck converter

Publication Date: 2019.07.30 TEXAS INSTRUMENTS INC

AI summary

Methods and circuits for regulating the voltage of the isolated output of an isolated buck converter. Pursuant to a representative method, a parameter of the primary side of an isolated buck transformer is measured, wherein the parameter is dependent in part upon the output voltage on the secondary side of the transformer. The duty cycle of the isolated buck converter is set based at least in part on the value of the measured parameter.