LED Driver Cycle-by-Cycle Feedback Control

Solution Overview

Problem

Switch-mode converters face inaccuracies in maintaining a consistent mean LED current level when increasing switching frequency, due to circuit delays and parasitic capacitance effects, which hampers the ability to reduce circuit size and improve response time.

Innovation Solution

A method and circuit arrangement that introduce a cycle-by-cycle feedback control to adjust the valley and peak current levels based on an integral correction, ensuring accurate mean LED current delivery by determining current level errors and applying corrections in successive oscillation cycles.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Speed

If switching frequency is increased to reduce circuit size and improve response time, then circuit size decreases and response time improves, but current control accuracy deteriorates due to circuit delays and parasitic capacitance effects

Engineering Contradiction:

Improveresponse timeVSAvoidcurrent control accuracy

Core Design Contradiction:

SpeedVSMeasurement precision

Solution Approach 1:

The patent implements cycle-by-cycle feedback control where the actual LED current is measured and compared with the reference current in each oscillation cycle. The feedback signal is used to adjust the peak current level dynamically, compensating for inaccuracies caused by high switching frequency, circuit delays, and parasitic capacitance effects.

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The patent dynamically adjusts the peak current level parameter based on the feedback from the actual current measurement. By changing the peak current level in response to detected errors, the system maintains accurate current control even at high switching frequencies where fixed parameter control would fail.

Inventive Principle:

Principle #35Parameter changes

2Volume of moving object

If switching frequency is increased to reduce circuit size, then circuit size decreases, but current control accuracy deteriorates due to circuit delays and parasitic capacitance effects

Engineering Contradiction:

Improvecircuit sizeVSAvoidcurrent control accuracy

Core Design Contradiction:

Volume of moving objectVSMeasurement precision

Solution Approach 1:

The patent implements cycle-by-cycle feedback control where the actual LED current is measured and compared with the reference current in each oscillation cycle. The feedback signal is used to adjust the peak current level dynamically, compensating for inaccuracies caused by high switching frequency, circuit delays, and parasitic capacitance effects.

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The patent dynamically adjusts the peak current level parameter based on the feedback from the actual current measurement. By changing the peak current level in response to detected errors, the system maintains accurate current control even at high switching frequencies where fixed parameter control would fail.

Inventive Principle:

Principle #35Parameter changes

3Measurement precision

If cycle-by-cycle feedback control is implemented to improve current control accuracy, then current control accuracy improves, but device complexity increases

Engineering Contradiction:

Improvecurrent control accuracyVSAvoidcontrol circuit complexity

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The control circuit uses the existing oscillation components and current path to provide self-measurement and self-correction. The actual LED current serves as the feedback signal, and the peak current level adjustment automatically compensates for errors without requiring external intervention or complex additional circuitry.

Inventive Principle:

Principle #25Self-service

Solution Approach 2:

The feedback control mechanism is integrated into the existing LED driver circuit architecture. The same oscillation circuit that generates the LED current drive also provides the basis for current measurement and correction, making the control circuit serve multiple functions simultaneously and reducing overall system complexity.

Inventive Principle:

Principle #6Universality (Multi-functionality)

Data Source

PatentUS8723446B2Method and circuit arrangement for cycle-by-cycle control of a LED current flowing through a LED circuit arrangement, and associated circuit composition and lighting system

Publication Date: 2014.05.13 NXP BV

AI summary

The invention provides a method for cycle-by-cycle control of a LED current (ILED) flowing through a LED circuit arrangement (LEDCIRC) at a mean LED current level. The method comprises a) establishing a converter current (IL), b) establishing an oscillation of the converter current (IL) between substantially a valley current level and substantially a peak current level, c) feeding the LED circuit arrangement (LEDCIRC) with the converter current (IL) as the LED current during a part of an oscillation cycle of the oscillation of the converter current, d) determining a current level correction for compensating a current level error between an integral over an oscillation cycle of the LED current and a reference, the reference being representative of the mean LED current level, and e) adjusting at least one of the valley current level and the peak current level with the current level correction for use in a successive cycle of the oscillation of the converter current. The invention also provides a circuit arrangement operable for using the method, a LED driver IC using the circuit arrangement, a circuit composition with at least one LED and the circuit arrangement, and a lighting system with the circuit composition.