Light emitter driver circuit for smoke detector

A smoke detection and alarm device comprising:

• a light emitter;
• a light receiver;
• a driver circuit comprising a transistor having a base terminal, a collector terminal, and an emitter terminal,
• wherein the collector terminal of the transistor is operatively connected to the light emitter of the smoke detector;
• a resistor of a predefined resistance configured to be connected to the emitter terminal of the transistor;
• and
• a controller operatively configured at the base terminal,
• wherein the controller is configured to:
• set, before each individual smoke detection process, a base voltage supplied to the base terminal to a predetermined base voltage value;
• determine a resistor voltage across the resistor;
• compare the determined resistor voltage to a predetermined resistor voltage value;
• and
• adjust the base voltage supplied to the base terminal based on the comparison;
• wherein the predetermined base voltage value is configured to enable the transistor to supply a constant current to the light emitter at room temperature, and wherein the predetermined resistor voltage is voltage across the resistor when the predetermined base voltage value is supplied to the base terminal.

A method for supplying a constant current to a light emitter of a smoke detector, the method comprising:

• 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;
• 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;
• wherein when the difference between the first resistor voltage and the second resistor voltage is negative, the method comprises:
• 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.