PWM LED Driver Circuit With Periodic DAC Shutdown

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

Conventional Pulse Width Modulated (PWM) LED drivers suffer from high quiescent current, leading to energy inefficiency as they continue to draw power even when the LED is in an OFF state, resulting in wasted energy.

Innovation Solution

The introduction of a DAC_zero signal that disables the digital-to-analog converter (DAC) when the LED is in an OFF state, reducing power consumption by ensuring the driver is shut down during periods of inactivity.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If the DAC remains active to maintain accurate driving current, then output LED current accuracy is improved, but quiescent current increases leading to energy waste

Engineering Contradiction:

Improveoutput LED current accuracyVSAvoidquiescent current

Core Design Contradiction:

Measurement precisionVSUse of energy by moving object

Solution Approach 1:

The patent implements periodic action by enabling the DAC only during PWM high periods when accurate current control is needed, and disabling it during PWM low periods. This periodic enable/disable operation synchronized with the PWM signal achieves both energy savings and maintained current accuracy during active periods.

Inventive Principle:

Principle #19Periodic action

Solution Approach 2:

The patent applies preliminary action by enabling the DAC slightly before the PWM rising edge (using a delayed version of the PWM signal) to ensure the DAC is ready and stable before the PWM pulse begins, while still disabling it during the low period to save energy.

Inventive Principle:

Principle #10Preliminary action

2Use of energy by moving object

If the DAC is disabled to reduce power consumption, then energy efficiency is improved, but output LED current accuracy deteriorates

Engineering Contradiction:

Improvepower consumptionVSAvoidoutput LED current accuracy

Core Design Contradiction:

Use of energy by moving objectVSMeasurement precision

Solution Approach 1:

The DAC is periodically enabled during PWM high periods when current accuracy is needed and disabled during low periods to save power. This timing-based periodic operation resolves the contradiction by ensuring the DAC is active only when necessary for accurate current control.

Inventive Principle:

Principle #19Periodic action

Solution Approach 2:

The DAC is enabled in advance of the PWM pulse (using a delayed PWM signal) to ensure it is fully operational and accurate before the LED driving begins, while still allowing power savings during the off period.

Inventive Principle:

Principle #10Preliminary action

Data Source

PatentUS8148914B2Dynamic power saving pulse width modulated LED driver circuit

Publication Date: 2012.04.03 TEXAS INSTRUMENTS INC

AI summary

In accordance with an aspect of the present invention, an LED driving circuit includes a digital-to-analog converter and a driving portion. The circuit is operable to turn off the digital-to-analog converter at times when the driving portion is not providing a high signal. As such the digital-to-analog converter will waste less energy.