PWM Fault Module for LED Driver Idle Mode

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Solution Overview

Problem

Existing microcontroller-based systems for driving LEDs require significant analogue resources for voltage and current regulation, leading to high silicon area consumption and power dissipation, especially due to the need for ADC resources and current limiting resistors.

Innovation Solution

A PWM architecture with a fault mode module that regulates LED voltage and current without using ADC resources, allowing the CPU to be in idle mode and detecting faults such as open LEDs, weak batteries, and voltage issues, using a hardware regulation loop with a PWM generator and comparator.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If ADC resources and current sensing circuitry are used for LED voltage and current regulation, then measurement precision is improved, but device complexity and silicon area consumption increase

Engineering Contradiction:

ImproveLED voltage and current measurement precisionVSAvoidmicrocontroller hardware complexity

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent replaces the ADC-based measurement system with a PWM-based indirect measurement system. Instead of directly measuring LED voltage and current using ADC resources, the system uses PWM duty cycle control and timing measurements to infer LED operating parameters, thereby eliminating the need for complex ADC circuitry and current sensing hardware.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent introduces a PWM signal as an intermediary between the microcontroller and the LED driver circuit. The PWM signal serves as a mediator that allows the microcontroller to control LED current indirectly through duty cycle modulation, avoiding direct electrical connection and measurement that would require ADC resources.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Reliability

If ADC resources are used for real-time LED regulation, then reliability is improved, but power consumption increases

Engineering Contradiction:

ImproveLED regulation reliabilityVSAvoidmicrocontroller power consumption

Core Design Contradiction:

ReliabilityVSUse of energy by moving object

Solution Approach 1:

The patent employs periodic PWM signals for LED control instead of continuous ADC sampling. The PWM timer generates periodic pulses at a fixed frequency, and the microcontroller only needs to process timing events at these periodic intervals, significantly reducing CPU activity and power consumption compared to continuous real-time ADC monitoring.

Inventive Principle:

Principle #19Periodic action

Solution Approach 2:

The PWM timer module autonomously generates control signals and performs timing measurements without requiring continuous CPU intervention. The hardware regulation loop using PWM operates independently, allowing the microcontroller to enter low-power idle mode while maintaining reliable LED regulation, thus reducing overall system power consumption.

Inventive Principle:

Principle #25Self-service

3Measurement precision

If the CPU actively regulates LED parameters, then control precision is improved, but the CPU cannot be placed in idle mode, increasing power consumption

Engineering Contradiction:

ImproveLED parameter control precisionVSAvoidCPU power consumption

Core Design Contradiction:

Measurement precisionVSUse of energy by moving object

Solution Approach 1:

The patent transitions from static CPU-based regulation to dynamic hardware-based PWM regulation. The PWM timer and comparator circuits dynamically adjust LED control parameters in real-time without CPU intervention, enabling the CPU to switch between active and idle states based on system requirements while maintaining precise LED control through hardware automation.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The patent implements a hardware feedback loop using PWM timing measurements and comparator circuits that automatically regulate LED parameters. The feedback mechanism operates independently of the CPU, continuously monitoring LED status through PWM signal characteristics and adjusting control parameters accordingly, allowing the CPU to remain in idle mode while maintaining precise control.

Inventive Principle:

Principle #23Feedback

Data Source

PatentUS9167646B2Pulse width modulation fault mode for illuminating device drivers

Publication Date: 2015.10.20 ATMEL CORP

AI summary

A PWM architecture of a microcontroller is disclosed that includes a fault module for regulating and detecting faults in current sensing or illuminating devices (e.g., LED strings). The fault module is part of a hardware regulation loop of LED voltage and LED current that allows the CPU to be placed in idle mode (“IDLE”) while an LED string is regulated in illumination. The microcontroller includes a PWM generator having a double channels PWM timer with a specific fault mode and an amplified comparator with a voltage reference. The architecture allows tuning of various parameters, including LED peak current, LED voltage supply, LED voltage regulation step and LED dimming value. In IDLE mode, the hardware regulation loop can regulate LED peak current and LED voltage supply without any CPU resource (microcontroller in IDLE mode). The fault module part of the hardware regulation loop can also detect and inform the CPU of: 1) an open LED; 2) a weak battery; and 3) an LED voltage that is under a target value.