Buck LED Current Regulation with Segmented Feedback

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Solution Overview

Problem

Existing LED control techniques face challenges with poor transient response, excessive die space requirements, and limitations on operating frequencies, input voltages, and output voltages when regulating the average current through light emitting diodes.

Innovation Solution

A buck constant average current regulation system that includes a floating average current buck regulator with an error amplifier, active capacitance multiplier, comparator, and pulse width modulation logic, coupled with an averaging circuit to control the average current through LEDs, allowing for efficient regulation without phase lag and maintaining constant transconductance.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If average current regulation techniques are used for LEDs, then current control is achieved, but transient response deteriorates

Engineering Contradiction:

Improveaverage current controlVSAvoidtransient response

Core Design Contradiction:

Measurement precisionVSSpeed

Solution Approach 1:

The feedback signal is segmented into two components: an instantaneous component fed directly to the error amplifier for fast transient response, and an averaged component used for steady-state regulation. This segmentation allows the system to simultaneously achieve precise average current control and fast transient response without the phase lag problems of conventional averaged controllers.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

An intermediary circuit is introduced that selectively routes instantaneous feedback during transient conditions and averaged feedback during steady-state conditions. This intermediary mechanism enables the controller to adaptively switch between fast response mode and precise regulation mode, resolving the contradiction between transient response speed and average current control accuracy.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Measurement precision

If conventional LED control circuits are used, then current regulation is achieved, but die space increases

Engineering Contradiction:

Improvecurrent regulationVSAvoiddie space

Core Design Contradiction:

Measurement precisionVSArea of stationary object

Solution Approach 1:

The error amplifier and averaging function are merged into a single integrated circuit block. The instantaneous feedback path and averaged feedback path are combined within the same controller, eliminating the need for separate external low-pass filter circuits and reducing the overall die space required for implementation.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The controller is designed with multi-functionality, where the same error amplifier processes both instantaneous and averaged feedback signals depending on operating conditions. This universal approach eliminates the need for dedicated separate circuits for different control functions, thereby reducing die space while maintaining regulation precision.

Inventive Principle:

Principle #6Universality (Multi-functionality)

3Device complexity

If peak current regulation is used, then simple control is achieved, but LED lifespan and consistency deteriorate

Engineering Contradiction:

Improvecontrol simplicityVSAvoidLED lifespan

Core Design Contradiction:

Device complexityVSReliability

Solution Approach 1:

The system employs dual feedback mechanisms: instantaneous feedback for rapid transient correction and averaged feedback for maintaining precise average current levels. This comprehensive feedback approach ensures that LEDs are regulated by their actual average current consumption rather than peak current, preventing thermal stress and extending LED lifespan while maintaining simple buck converter architecture.

Inventive Principle:

Principle #23Feedback

4Measurement precision

If low-pass filters are added for averaging, then average current control improves, but frequency response and die space worsen

Engineering Contradiction:

Improveaverage current controlVSAvoidcircuit components

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The external low-pass filter component is extracted and replaced by an integrated averaging function implemented within the controller's digital or analog circuitry. This extraction eliminates the need for separate passive filter components (resistors, capacitors, inductors) while maintaining the average current control function, thereby reducing die space and improving frequency response.

Inventive Principle:

Principle #2Taking out (Extraction)

Data Source

PatentUS8288953B1Buck constant average current regulation of light emitting diodes

Publication Date: 2012.10.16 NAT SEMICON CORP

AI summary

An apparatus includes pulse width modulation (PWM) circuitry configured to generate a PWM signal based on a feedback voltage associated with current flowing through a load, such as one or more light emitting diodes (LEDs). The apparatus also includes a power switch configured to control the current flowing through the load on the PWM signal. The apparatus further includes averaging circuitry configured to provide an average of the feedback voltage to the PWM circuitry. The averaging circuitry is may be configured to provide the feedback voltage to the PWM circuitry during a first phase of operation and to provide the average of the feedback voltage to the PWM circuitry during a second phase of operation. The average of the feedback voltage may be referenced to a reference voltage received by an error amplifier in the PWM circuitry during both the first and second phases of operation.