LED Drive Circuit Temperature Compensation
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Solution Overview
Problem
LED driving circuits used in vehicle-mounted optical communications are inadequately affected by temperature fluctuations, leading to insufficient characteristics and performance issues due to heat and environmental factors.
Innovation Solution
An LED driving circuit is designed with a temperature compensated current generating circuit that includes a temperature detecting circuit, comparators, and current increasing circuits to gradually increase the driving current, compensating for temperature fluctuations and preventing pulse width distortion and jitter, using capacitors to control the transistor and generate a gradually increasing voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If temperature compensated current is applied to the first current source, then emission output is compensated for temperature fluctuation, but pulse width distortion and jitter may occur if the current increases too rapidly
Solution Approach 1:
The patent applies dynamics by making the current increase rate variable through capacitor discharge. The current increases gradually rather than instantly, with the rate controlled by the capacitor discharge characteristics. This dynamic adjustment allows the system to adapt the current change rate to prevent pulse width distortion while still compensating for temperature effects on emission output.
Solution Approach 2:
The patent changes the current parameter over time through capacitor discharge, transitioning from a fixed current to a time-varying current that increases gradually. This parameter change approach allows the system to compensate for temperature effects while controlling the rate of change to maintain pulse width accuracy and prevent jitter.
2Reliability
If the temperature compensated current is increased to compensate for emission output, then the lowering of emission output is suppressed, but the driving current and emission output may become excessive
Solution Approach 1:
The patent applies preliminary action by pre-charging capacitors before the temperature compensation takes effect. When temperature compensation is needed, the capacitors discharge to provide a controlled current increase, preventing the need for excessive current adjustments and avoiding over-compensation that would lead to excessive driving current and emission output.
3Speed
If a peaking current generating circuit is used to improve response characteristics, then high-speed performance is achieved, but the circuit is strongly affected by heat and temperature effects
Solution Approach 1:
The patent applies feedback by using a temperature detecting circuit to monitor the actual temperature of the LED and adjust the driving current accordingly. This closed-loop temperature compensation feedback mechanism allows the system to maintain stable emission output despite temperature changes, reducing the temperature sensitivity that plagues conventional high-speed LED driving circuits with peaking current generating circuits.
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 solution effectively compensates for temperature-induced fluctuations in LED emission output, improving the circuit's characteristics and preventing excessive current or pulse distortion, ensuring stable and efficient optical communication across varying temperatures.
Implementation Method 1
The temperature compensated current generating circuit includes a temperature detecting circuit
Implementation Method 2
by gradually increasing the temperature compensated current using a charging/discharging function of a capacitor
Data Source
AI summary
An LED driving circuit can improve characteristics. A first current increasing circuit 10i4 is constituted of a first slow regulating unit 10i41 and a post-stage first supplying circuit 10i43 and, from a point in time of output switching of a first comparator 10i2, that is, when a set temperature exceeding a reference potential Va is attained, gradually increases a temperature compensated current IT1 (ΔI1) and thereby suppresses the lowering of emission output. Here, by gradually increasing the temperature compensated current IT1 by making use of charging/discharging functions of a capacitor, etc., that is, by increasing the temperature compensated current IT1 over a longer time than a pulse width that a photodetecting element, onto which light from an LED 11 is made incident, can respond within, pulse width distortion and jitter can be suppressed.