Smoke Detector Light Emitter Driver Circuit Temperature Compensation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Smoke detectors face issues with temperature variations affecting the driver circuit's ability to supply a constant current to the light emitter, leading to false alarms or non-operative states due to fluctuations in photon count.
Innovation Solution
A driver circuit with a transistor and a controller that adjusts the base voltage based on pre-determined resistor voltage values to maintain a constant current to the light emitter, independent of temperature, using a predefined resistance and analog/digital converters for precise voltage monitoring and adjustment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a driver circuit uses semiconductor devices to supply current to the light emitter, then the circuit can provide current control capability, but the driver circuit fails to maintain constant current due to temperature variations
Solution Approach 1:
The patent implements a feedback mechanism where the controller monitors the voltage across the emitter resistor and adjusts the base voltage of the transistor accordingly. The controller determines a difference between the monitored voltage and a reference voltage, then adjusts the base voltage to compensate for temperature-induced variations, ensuring constant current supply to the light emitter regardless of temperature changes.
Solution Approach 2:
The patent changes the operating parameters of the transistor by dynamically adjusting the base voltage based on temperature conditions. The controller modifies the base voltage parameter in response to temperature variations detected through voltage monitoring across the emitter resistor, thereby maintaining constant collector current despite environmental temperature changes.
2Power
If the driver circuit supplies higher current at higher temperatures, then the transistor remains in active region, but the photon count increases leading to false alarms
Solution Approach 1:
The feedback mechanism monitors the actual current through the light emitter by measuring voltage across the emitter resistor and adjusts the base voltage to prevent current increase at higher temperatures. This closed-loop control ensures the current remains constant, preventing photon count variations that would cause false alarms.
Solution Approach 2:
The controller takes preliminary anti-action by anticipating temperature-induced current increases and adjusting the base voltage in advance to counteract the effect. The system proactively compensates for the inherent positive temperature coefficient of the transistor, preventing the harmful effect of false alarms before they occur.
3Power
If the driver circuit supplies less current at lower temperatures, then the transistor operates safely, but the photon count decreases causing non-operative state
Solution Approach 1:
The feedback mechanism detects current decreases at lower temperatures through voltage monitoring and adjusts the base voltage upward to compensate. This ensures the light emitter receives sufficient current to maintain operational photon count, preventing the smoke detector from entering a non-operative state.
Solution Approach 2:
The controller takes preliminary anti-action by anticipating temperature-induced current decreases and adjusting the base voltage in advance to prevent photon count drops. This proactive compensation ensures the system remains in a reliable operational state across the full temperature range.
4Reliability
If the driver circuit is designed for constant current supply, then the photon count should be stable, but semiconductor devices are affected by temperature causing current variation
Solution Approach 1:
The feedback mechanism continuously monitors the actual current through voltage measurement across the emitter resistor and adjusts the base voltage to compensate for temperature effects. This closed-loop control eliminates the direct relationship between temperature and current that exists in open-loop designs, maintaining constant current despite temperature sensitivity of the semiconductor devices.
Solution Approach 2:
The controller acts as an intermediary between the temperature environment and the transistor current. It decouples the temperature influence from the current supply by introducing a control element that actively compensates for temperature effects, thereby protecting the constant current supply function from temperature variations.
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 ensures a consistent photon count across varying temperatures, preventing false alarms and maintaining operational stability of the smoke detector, as the driver circuit supplies a constant current to the light emitter, regardless of temperature changes.
Implementation Method 1
The driver circuit comprises a transistor. The transistor comprises a base terminal, a collector terminal, and an emitter terminal. The collector terminal of the transistor is adapted to be operatively connected to the light emitter of the smoke detector.
Implementation Method 2
The driver further comprises a resistor of a predefined resistance configured to be connected to the emitter terminal of the transistor
Data Source
AI summary
A driver circuit and a method of supplying a constant current to the light emitter of the smoke detector are disclosed. The driver circuit includes a transistor, and a controller. The collector terminal of the transistor is connected to the light emitter and a resistor is connected to the emitter terminal. During the manufacturing stage, the controller monitors and stores the values of first base voltage to be supplied to the base terminal to supply a constant current to the light emitter, and first resistor voltage across the resistor when the first base voltage is supplied to the base terminal. Before each smoke detection process, the controller processes the stored data and adjusts the base voltage to be supplied to the base terminal to enable the transistor to supply the constant current to the light emitter, regardless of the temperature around the smoke detector.