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EP-4325459-B1 - LIGHT EMITTER DRIVER CIRCUIT FOR SMOKE DETECTOR

EP4325459B1EP 4325459 B1EP4325459 B1EP 4325459B1EP-4325459-B1

Inventors

  • PATEL, VIPUL

Dates

Publication Date
20260506
Application Date
20230816

Claims (15)

  1. A driver circuit (100) for a light emitter (202) of a smoke detector (200), the driver circuit comprising: a transistor (102) comprising a base terminal, a collector terminal, and an emitter terminal, wherein the collector terminal of the transistor is adapted to be operatively connected to the light emitter of the smoke detector; a resistor (106) of a predefined resistance configured to be connected to the emitter terminal of the transistor; and a controller (104) operatively connected to the base terminal, wherein the controller is configured to: determine, at a manufacturing stage of the driver circuit, a first base voltage to be supplied to the base terminal of the transistor to enable the transistor to supply a predefined current to the light emitter; determine, at the manufacturing stage, a first resistor voltage across the resistor when the first base voltage is supplied to the base terminal; set, before each smoke detection process, a value of the base voltage supplied to the base terminal to the first base voltage; correspondingly determine a second resistor voltage across the resistor; compare the first resistor voltage with the second resistor voltage; determine a difference between the first resistor voltage and the second resistor voltage based on the comparison; and adjust the value of the base voltage supplied to the base terminal based on the determined difference to enable the transistor to supply the predefined current to the light emitter.
  2. The driver circuit of claim 1, wherein: the predefined current corresponds to a constant current to be supplied to the light emitter at a predefined temperature; and/or the predefined temperature is room temperature.
  3. The driver circuit of any preceding claim, wherein the transistor is a Darlington pair transistor or single transistor.
  4. The driver circuit of any preceding claim, wherein, based on one or more of the second resistor voltage across the resistor, the adjusted base voltage to be supplied to the base terminal to supply the predefined current to the light emitter, and the predefined resistance of the resistor, the controller is configured to determine a temperature at an area of interest (AOI) where the driver circuit or the smoke detector is installed.
  5. The driver circuit of any of any preceding claim, wherein the controller of the driver circuit is a computing unit of the smoke detector, wherein the smoke detector comprises the light emitter and a light receiver.
  6. The driver circuit of any of claims 1 to 4, wherein the controller of the driver circuit is different from a computing unit of the smoke detector, wherein the controller of the driver circuit is in communication with a computing unit of the smoke detector.
  7. The driver circuit of claim any preceding claim, wherein the controller comprises: an analog to digital converter (ADC) (114) to monitor voltage across the resistor; and a digital to analog converter (DAC) (112) to supply an analog voltage to the base terminal of the transistor; and/or a processor (108); and a memory (110) coupled to the processor and configured to store the values of the first base voltage and the first resistor voltage.
  8. A smoke detection and alarm device comprising: a light emitter; a light receiver; the driver circuit according to any preceding claim.
  9. The device of claim 8, wherein the light emitter and the light receiver are enclosed within a hollow enclosure having a smoke chamber that is adapted to receive smoke therewithin.
  10. The device of claim 9, wherein the controller is configured to: enable the transistor to supply the predefined current to the light emitter to enable the light emitter to emit photons within the smoke chamber (208); detect smoke within the smoke chamber based on a count of photons received by the light receiver (204) upon getting reflected from particles of the smoke within the smoke chamber; and optionally wherein the controller is configured to generate alarm signals when the count of reflected photons within the smoke chamber exceeds a predefined value.
  11. The device of any of claims 8 to 10, wherein the device is adapted to be installed in one or more areas of interest (AOI) comprising one or more of an HVAC duct, room, hall, staircase, vehicle interior, and storage space.
  12. A method for supplying a constant current to a light emitter of a smoke detector, the method comprising the steps of: connecting a collector terminal of a transistor to the light emitter of the smoke detector, a resistor of a predefined resistance to an emitter terminal of the transistor, and a controller at the base terminal; determining, at a manufacturing stage, a first base voltage to be supplied to the base terminal of the transistor to enable the transistor to supply a predefined current to the light emitter; determining, at the manufacturing stage, a first resistor voltage across the resistor when the first base voltage is supplied to the base terminal; setting, before each smoke detection process, a value of the base voltage supplied to the base terminal to the first voltage; correspondingly determining a second resistor voltage across the resistor; comparing the first resistor voltage with the second voltage; determining a difference between the first resistor voltage and the second resistor voltage based on the comparison; and adjusting the value of the base voltage supplied to the base terminal based on the determined difference to enable the transistor to supply the predefined current to the light emitter.
  13. The method of claim 12, wherein the method comprises the step of determining a temperature at an area of interest (AOI) where the driver circuit or the smoke detector is installed, based on one or more of the second resistor voltage across the resistor, the adjusted base voltage to be supplied to the base terminal to supply the predefined current to the light emitter, and the predefined resistance of the resistor.
  14. The method of any of claims 12 or 13, wherein: when the difference between the first resistor voltage and the second resistor voltage is zero, the method comprises the step of: supplying the first base voltage to the base terminal of the transistor; and/or when the difference between the first resistor voltage and the second resistor voltage is positive, the method comprises the steps of: computing, by the controller, a first compensation value that corresponds to the difference between the first resistor voltage and the second resistor voltage, divided by a first correction factor ranging from 0.1 to 16; adjusting, by the controller, the base voltage to be supplied to the base terminal to a value equal to a sum of the first base voltage and the first compensation value; and supplying, by the controller, the adjusted base voltage to the base terminal
  15. The method of any of claims 12, 13 or 14, wherein: when the difference between the first resistor voltage and the second resistor voltage is negative, the method comprises the steps of: computing, by the controller, a second compensation value that corresponds to the difference between the second resistor voltage and the first resistor voltage, divided by a second correction factor ranging from 0.1 to 16; adjusting the base voltage to be supplied to the base terminal to a value equal to a difference between the first base voltage and the second compensation value; and supplying, by the controller, the adjusted base voltage to the base terminal.

Description

TECHNICAL FIELD This invention relates to the field of smoke detectors, and more particularly, to a driver circuit for smoke detectors. BACKGROUND Smoke detectors are generally subjected to wide temperature swings and are required to perform consistently and accurately without having any false alarms or going into a non-operative/trouble state. Photoelectric smoke detectors are widely used smoke detectors that typically include a driver circuit that is required to supply constant current to the light emitter of the smoke detector, regardless of the temperature around the smoke detector, such that the photon count or smoke count detected by the light receiver of the smoke detector does not vary with varying temperature. However, the driver circuits involve semiconductor devices that may generally be affected by varying temperatures. As a result, the driver circuits may fail to provide a constant current to the light emitter. For instance, at higher temperatures, the driver circuit may supply a higher current to the light emitter which may increase the photon count, leading to false alarm generation by the smoke detector. Similarly, at lower temperatures, the driver circuit may supply less current to the light emitter which may decrease the photon count, thereby causing the smoke detector to go into a non-operative or troubled state. There is, therefore, a need to compensate for the effect of temperature on the driver circuit and enable the driver circuit to supply constant current to the light emitter of the smoke detector, independent of the temperature around the smoke detector. JP H09-223281 discloses a circuit to suppress the fluctuation of light emission due to temperature variations of a light emitting element by adjusting the size of a driving current. EP 3819741 discloses a current driving circuit for a photoelectric smoke alarm including a constant current source, so that auxiliary output performance remains stable within a full temperature range. WO 2011/131937 discloses an optical smoke detector provided with a light source, a light receiver and a control circuit configured to generate a smoke detection signal. The control circuit generates a ratio signal representative of the ratio of monitored currents of the light source and light receiver; and compares the ratio signal with a reference value to generate the smoke detection signal. BRIEF SUMMARY According to a first aspect of the invention, a driver circuit for a light emitter of a smoke detector is provided. 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. The driver further comprises a resistor of a predefined resistance configured to be connected to the emitter terminal of the transistor; and a controller operatively connected to the base terminal. The controller is configured to determine, at a manufacturing stage of the driver circuit, a first base voltage to be supplied to the base terminal of the transistor to enable the transistor to supply a predefined current to the light emitter, and further determine, at the manufacturing stage, a first resistor voltage across the resistor when the first base voltage is supplied to the base terminal. The controller is configured to set, before each smoke detection process, a value of the base voltage supplied to the base terminal to the first base voltage, determine a second resistor voltage across the resistor, compare the first resistor voltage with the second resistor voltage, determine a difference between the first resistor voltage and the second resistor voltage based on the comparison, and adjust the value of the base voltage supplied to the base terminal based on the determined difference to enable the transistor to supply the predefined current to the light emitter. The predefined current may correspond to a constant current to be supplied to the light emitter at a predefined temperature. The predefined temperature may be room temperature. The transistor may be a Darlington pair transistor or single transistor. The controller may be configured to determine a temperature at an area of interest (AOI) where the driver circuit or the smoke detector is installed based on one or more of the second resistor voltage across the resistor, the adjusted base voltage to be supplied to the base terminal to supply the predefined current to the light emitter, and the predefined resistance of the resistor. The controller of the driver circuit may be a computing unit of the smoke detector, wherein the smoke detector comprises the light emitter and a light receiver. The controller of the driver circuit may be different from a computing unit of the smoke detector, and wherein the controller of the driver circuit is in communication with a computing unit of the smoke detector. The controller may comprise an