PTC Resistor LED Current Regulation

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Solution Overview

Problem

Conventional lighting devices using LEDs face inefficiencies due to varying battery discharge voltage, leading to fluctuations in LED current and power dissipation, especially when using fixed resistors or bulky switching regulators.

Innovation Solution

A temperature-based controller with a positive temperature coefficient (PTC) resistor is used in series with the LED, varying resistance based on the LED's temperature to maintain a constant light output and reduce current fluctuations, employing a thermally conductive substrate and optional insulator to manage thermal communication.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Device complexity

If a fixed current-limiting resistor is used to drive LED, then the circuit is simple, but the LED current varies significantly as battery voltage changes during discharge

Engineering Contradiction:

Improvecircuit complexityVSAvoidLED current stability

Core Design Contradiction:

Device complexityVSStability of the object's composition

Solution Approach 1:

The patent changes the resistance parameter dynamically by using a PTC resistor whose resistance increases with temperature. As LED current increases and heats the PTC resistor, its resistance increases automatically, reducing the current to maintain stability without complex control circuits.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The PTC resistor provides thermal feedback to the LED current. The resistor senses the temperature rise caused by increased current through the LED and automatically adjusts its resistance to counteract the current increase, creating a self-regulating system.

Inventive Principle:

Principle #23Feedback

2Use of energy by moving object

If the resistor value is optimized for fully charged batteries, then LED current is optimal at full charge, but current becomes too low as batteries discharge

Engineering Contradiction:

Improveenergy utilization efficiencyVSAvoidLED current consistency

Core Design Contradiction:

Use of energy by moving objectVSStability of the object's composition

Solution Approach 1:

The PTC resistor's temperature-dependent resistance parameter compensates for battery voltage changes. At full charge, the PTC operates at a baseline resistance for optimal current. As batteries discharge and voltage drops, the LED generates more heat to maintain current, heating the PTC and increasing its resistance to prevent excessive current draw.

Inventive Principle:

Principle #35Parameter changes

3Stability of the object's composition

If a switching regulator circuit is used to maintain constant LED current, then current regulation is improved, but the device becomes bulky and expensive

Engineering Contradiction:

ImproveLED current regulationVSAvoidcircuit size and cost

Core Design Contradiction:

Stability of the object's compositionVSDevice complexity

Solution Approach 1:

The PTC resistor creates a self-regulating system where the LED's own heat generation is used to control its current. The system serves itself by using the thermal effect of the LED operation to automatically regulate current without external control circuits, eliminating the need for bulky switching regulators.

Inventive Principle:

Principle #25Self-service

Solution Approach 2:

The patent replaces the mechanical/electronic switching regulator system with a thermal-based passive component. Instead of using active electronic control with switches and control circuits, the system uses the thermal properties of the PTC resistor to achieve current regulation.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

4Loss of energy

If a fixed resistor is used, then power dissipation in the resistor can be minimized at certain battery states, but LED current becomes unacceptably high at other states

Engineering Contradiction:

Improveresistor power dissipationVSAvoidexcessive LED current

Core Design Contradiction:

Loss of energyVSObject-affected harmful factors

Solution Approach 1:

The PTC resistor dynamically changes its resistance parameter based on temperature to balance power dissipation and current control. As temperature rises from increased LED current, the PTC resistance increases, automatically reducing current and power dissipation to safe levels without sacrificing LED performance.

Inventive Principle:

Principle #35Parameter changes

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 solution provides a relatively constant LED current and light output across varying battery discharge states, improving efficiency and reducing power dissipation, while being cost-effective and compact compared to traditional solutions.

Implementation Method 1

a positive temperature coefficient resistor in operative thermal communication and electrically in series with the LED. A resistance of the PTC resistor varies as a function of a temperature of the LED.

Methodology Applied

Scientific EffectPositive temperature coefficient (PTC) effect: Thermistor

Implementation Method 2

employing a thermally conductive substrate and optional insulator to manage thermal communication

Methodology Applied

Scientific EffectThermal conduction: Conduction (thermal)

Data Source

PatentUS8124918B2Positive temperature coefficient light emitting diode light

Publication Date: 2012.02.28 ENERGIZER BRANDS LLC

AI summary

An apparatus includes a light source, a substrate, a temperature-based controller and an insulator. The light source is mounted to the substrate. The temperature-based controller is electrically coupled to the light source and causes the light source to provide a relatively constant light output. The insulator is positioned proximate the temperature based controller.