LED Temperature Adaptive Control Circuit Using PTC and NTC Thermistors
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Solution Overview
Problem
Existing LED control circuits are costly and limited in functionality, failing to effectively manage current variations due to temperature changes, which can lead to instability and overheating issues in light emitting diodes.
Innovation Solution
A temperature adaptive control circuit using a combination of positive and negative temperature coefficient thermistors, connected in series or parallel with the LED load circuit, adjusts current flow based on the sum of their resistances to compensate for temperature-induced luminescent intensity variations and prevent overheating.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a complex feedback control loop circuit is used to control LED current, then LED stability is improved, but circuit cost and complexity increase
Solution Approach 1:
The patent combines temperature compensation and current control functions into a single circuit structure. The PTC and NTC thermistors are integrated with the LED drive circuit to form a unified temperature adaptive control system, eliminating the need for separate complex feedback control loops while maintaining LED stability across temperature variations.
Solution Approach 2:
The patent utilizes the temperature coefficient parameter changes of thermistors to automatically adjust circuit resistance and current. By selecting thermistors with specific beta values and arranging them in series/parallel configurations, the circuit dynamically adapts to temperature changes through parameter variation, achieving stable LED operation without complex control algorithms.
2Adaptability or versatility
If thermistors are used for temperature compensation, then temperature adaptability is improved, but circuit cost increases
Solution Approach 1:
The patent uses thermistor models with standardized beta values (e.g., beta=3000K, beta=4000K) that can be mass-produced and replaced. These standardized components allow for easy manufacturing and inventory management, reducing the cost impact of adding temperature compensation functionality while maintaining adaptability across different operating conditions.
Solution Approach 2:
The thermistor-based circuit serves multiple functions: temperature compensation, overheat protection, and current regulation. By making the circuit multi-functional, the patent reduces the need for additional separate components, thereby controlling overall circuit cost while achieving broad temperature adaptability from -40°C to 125°C operating range.
3Device complexity
If single-function current control is implemented, then circuit simplicity is maintained, but functional versatility is reduced
Solution Approach 1:
The patent designs a circuit where the same basic structure with PTC and NTC thermistors performs multiple functions: (1) temperature compensation for LED brightness, (2) overheat protection by limiting current at high temperatures, and (3) cold temperature compensation to maintain drive voltage. This multi-functionality is achieved without adding separate control circuits, maintaining simplicity while enhancing versatility.
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
The circuit maintains stable luminescent intensity within a desired range while providing overheating protection by automatically adjusting current flow, reducing the risk of LED damage and improving system reliability and cost-effectiveness.
Implementation Method 1
a positive temperature coefficient thermistor and a negative temperature coefficient thermistor connected in series
Implementation Method 2
a positive temperature coefficient thermistor and a negative temperature coefficient thermistor connected in series
Data Source
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AI summary
The present application provides a temperature adaptive control circuit for a light emitting diode and a lighting and/or signaling apparatus. The control circuit includes: a light emitting diode load circuit unit in which one or more light emitting diodes are connected; and a temperature adaptive circuit unit comprising a positive temperature coefficient thermistor and a negative temperature coefficient thermistor connected in series, wherein the temperature adaptive circuit unit is configured such that current flowing through the one or more light emitting diodes in the light emitting diode load circuit unit is a function of sum of resistance of the positive temperature coefficient thermistor and resistance of the negative temperature coefficient thermistor. It not only can compensate the variation of the luminescent intensity with the temperature in a desired working temperature for the LEDs, but also can achieve overheating protection for the LEDs to avoid damage thereof.