Constant Current Smoke Alarm Circuit With Zero Standby Power
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Solution Overview
Problem
Existing constant current driving circuits for photoelectric smoke alarms face challenges in maintaining consistent output characteristics over varying power supply voltage and temperature ranges, with high power consumption and large area requirements, especially in low power consumption CMOS technology-based devices.
Innovation Solution
A compact constant current driving circuit integrated into a chip, comprising a reference voltage source module, linear voltage regulator module, level conversion module, and current mirror module, along with a NMOS transistor, which eliminates voltage coefficient and reduces standby power consumption, ensuring consistent current and luminous intensity across temperature and voltage variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If built-out linear voltage regulators are used to maintain stable voltage, then voltage stability is improved, but static power consumption increases and cost increases
Solution Approach 1:
The patent employs periodic pulsed action by controlling the infrared light emitting diode to emit light in short intervals (100μs-200μs every 8 seconds) rather than continuously. This periodic operation dramatically reduces static power consumption while maintaining detection functionality, eliminating the need for continuously operating linear voltage regulators that would consume excessive power in low-power smoke alarm applications
2Stability of the object's composition
If single-chip machine with discrete devices is used for constant current driving, then current stability is improved, but device area increases
Solution Approach 1:
The patent merges multiple discrete components (voltage regulator, current mirror, level conversion modules) into a single integrated chip. This integration maintains the current stability functionality while dramatically reducing the overall device area, as the integrated circuit occupies minimal space compared to discrete components and their interconnections on the PCB
3Adaptability or versatility
If built-in DC-DC boost voltage modules are used, then voltage conversion capability is improved, but device area increases and EMI interference increases
Solution Approach 1:
The patent extracts and eliminates the DC-DC boost voltage module from the circuit design. By using a simplified voltage regulation approach that does not require complex switching conversion, the design removes the source of EMI interference and reduces device area, while still achieving the necessary voltage adaptation through alternative means
4Stability of the object's composition
If constant current is provided to infrared LED, then luminous efficiency consistency is improved, but circuit complexity increases
Solution Approach 1:
The patent combines voltage regulation and constant current driving functions into a single integrated circuit. This merging approach maintains the luminous efficiency consistency through precise current control while reducing overall circuit complexity by eliminating the need for separate regulation stages and external components
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 provides a compact, low-power consumption constant current driving circuit that maintains consistent output characteristics over a wide temperature range without voltage coefficient, reducing area occupation and power consumption, while ensuring accurate smoke detection.
Implementation Method 1
A constant current I1 that does not vary with the power supply voltage, temperature and time is provided to the infrared light emitting diode D1. The constant current I1 flows in from a first port 1 in FIG. 1 and flows out from the second port 2, thereby generating infrared light with constant luminous efficiency.
Implementation Method 2
When smoke enters into the optical labyrinth, the photodiode D2 receives the infrared light by refraction and reflection, thereby generating a photocurrent I0.
Data Source
AI summary
A constant current driving circuit and a corresponding photoelectric smoke alarm circuit are provided. The constant current driving circuit includes a reference voltage source module (1), a linear voltage regulator module (3), a level conversion module (2), a current mirror module (4) and a first NMOS transistor. The linear voltage regulator module (3) may control turning on and turning off thereof according to actual requirements, thus electrical energy loss may effectively be reduced for some periodically used devices. The constant current driving circuit and the corresponding photoelectric smoke alarm circuit may provide a constant current source, so that auxiliary output performance remains stable within a full temperature range, a certain timing sequence requirement is met, no standby power is consumed when not working, performance is stable, power consumption is low, and application range is wide.