Smoke detector with regulated constant-current circuit for driving optical sources

Patent metadata

Field	Value
Publication number	US-9622301-B2
Application number	US-201514717739-A
Country	US
Kind code	B2
Filing date	May 20, 2015
Priority date	May 20, 2015
Publication date	Apr 11, 2017
Grant date	Apr 11, 2017

Abstract

Systems and methods for driving optical sources operating at different wavelengths within a smoke sensor are described herein. Multiple optical sources such as light emitting diodes may be used in a photoelectric smoke sensor to detect particles of different sizes. Photoelectric smoke sensors can operate by pulsing the LEDs and measuring a response in a light sensor. The signal measured at the light sensor changes based on the quantity of particles existing in a smoke chamber. Each optical source may have different operational characteristics and thus require different drive currents to operate. LED driving circuitry according to embodiments discussed herein provide a consistent and reliable drive current to each optical source, while maximizing efficiency of power consumption across a range of possible voltages provided by different power sources.

First claim

What is claimed is:

1. A method for powering first and second light emitting diodes (LEDs) in a smoke sensor of a hazard detection system, the system comprising a power source signal ranging between a first signal value and a second signal value, the method comprising:
managing a first LED power signal for use by the first LED, wherein managing the first LED power signal comprises:
down converting the power source signal to the first LED power level, wherein the first LED power signal has a value less than the first and second signal values; and

managing a second LED power signal for use by the second LED, wherein managing the second LED power signal comprises:
up converting the power source signal to the second LED power signal, wherein the second LED power signal has a value greater than the first and second signal values.

2. The method of claim 1 , wherein managing the first LED power signal comprises filtering the first LED power signal with a RC filter to produce a filtered first LED power signal.

3. The method of claim 2 , wherein managing the first LED power signal comprises using a first low dropout regulator to supply a substantially constant-current to the first LED, wherein the first low dropout regulator receives the filtered first LED power signal.

4. The method of claim 2 , wherein the first LED is characterized by a first forward voltage drop, wherein the first dropout regulator is characterized a first LDO feedback voltage, and wherein the first LED power signal exceeds the summation of the first forward voltage drop and the first LDO feedback voltage.

5. The method of claim 2 , further comprising:
supplying the first LED power signal to at least one circuit other than the first LED.

6. The method of claim 5 , further comprising:
driving the first LED according to a known pulse profile, where the RC filter is tuned based on the known pulse profile to ensure that a simultaneous load demand of the at least one circuit and the first LED does not exceed a maximum current output of the power source signal.

7. The method of claim 1 , wherein managing a second LED power signal comprises using a second low dropout regulator to supply a substantially constant-current to the second LED, wherein the second low dropout regulator receives the second LED power signal.

8. The method of claim 7 , wherein the second LED is characterized by a second forward voltage drop, wherein the second dropout regulator is characterized a second LDO feedback voltage, and wherein the second LED power signal exceeds the summation of the second forward voltage drop and the second LDO feedback voltage.

9. The method of claim 1 , further comprising:
selectively activating the first LED with the first LED power signal;
monitoring for scattered electromagnetic energy derived from electromagnetic energy being emitted by the selectively activated first LED;
selectively activating the second LED with the second LED power signal; and
monitoring for scattered electromagnetic energy derived from electromagnetic energy being emitted by the selectively activated second LED.

10. A hazard detection system, comprising:
a smoke chamber comprising first and second light emitting diodes (LEDs);
a power input configured to receive a power signal ranging between first and second values;
first LED driving circuitry coupled to receive the power signal from the power input and operative to provide a first LED power signal to the first LED, the first LED power signal characterized as having a value lower than the first and second values and a first substantially constant current value; and
second LED driving circuitry coupled to receive the power signal from the power input and operative to provide a second LED power signal to the second LED, the second LED power signal characterized as having a value higher than the first and second values and a second substantially constant current.

11. The hazard detection system of claim 10 , wherein the first LED driving circuitry comprises:
a buck converter coupled to the power input and operative to generate the first LED power signal;
an RC filter coupled to the buck converter and operative to filter the first LED power signal;
a first low dropout regulator coupled to the RC filter and both terminals of the first LED, the first low dropout regulator operative to provide the first substantially constant current value to the first LED; and
a current setting resistor coupled to the first low dropout regulator and the first LED.

12. The hazard detection system of claim 11 , further comprising:
wireless circuitry coupled to the buck converter and powered by the first power signal, wherein the RC filter sets a ceiling on current draw from the power input when the wireless circuitry and first LED are simultaneously operating.

13. The hazard detection system of claim 10 , wherein the second LED driving circuitry comprises:
a boost converter coupled to the power input and operative to generate the second LED power signal;
a second low dropout regulator coupled to the boost converter and both terminals of the second LED, the second low dropout regulator operative to provide the second substantially constant current value to the second LED; and
a current setting resistor coupled to the second low dropout regulator and the second LED.

14. The hazard detection system of claim 13 , further comprising:
a speaker coupled to the boost converter and operative to be powered by the second LED power signal.

15. The hazard detection system of claim 10 , wherein the smoke chamber further comprises at least one energy detector, the system further comprising a processor operative to:
selectively activate the first LED with the first LED power signal;
monitor the at least one energy detector for scattered electromagnetic energy derived from electromagnetic energy being emitted by the selectively activated first LED;
selectively activate the second LED with the second LED power signal; and
monitor the at least one energy detector for scattered electromagnetic energy derived from electromagnetic energy being emitted by the selectively activated second LED.

16. The hazard detection system of claim 10 , wherein the first LED is an infrared LED, and where the second LED is a blue LED.

17. The hazard detection system of claim 10 , wherein the power input is coupled to a battery, and wherein the first LED driving circuitry further comprises:
a first low dropout regulator coupled to the battery and both terminals of the first LED, the first low dropout regulator operative to provide the first substantially constant current value to the first LED; and
a current setting resistor coupled to the first low dropout regulator and the first LED.

18. The hazard detection system of claim 17 , further comprising: wireless circuitry coupled to the battery and powered by the first power signal, wherein the RC filter sets a ceiling on current draw from the power input when the wireless circuitry and first LED are simultaneously operating.

19. A particle detector for use in a hazard detection system that is powered by one of a plurality of different power sources, wherein a power signal supplied by the plurality of power source ranges between first and second values, the particle detector comprising:
a particle detection chamber comprising an infrared light emitting diode (IR LED), a blue light emitting diode (LED), and a photodetector;
a power input for receiving the power signal; and
LED driving circuitry coupled to the IR LED, the blue

Assignees

• Google Inc

Inventors

• Warren Daniel Adam
• Smith Ian C
• Conner Brian Jonathan

Classifications

• G08B5/36 Primary

  using visible light sources · CPC title

• G01N21/53

  within a flowing fluid, e.g. smoke · CPC title

• G08B17/107

  for detecting light-scattering due to smoke · CPC title

• G01N2201/06153

  the sources being LED's · CPC title

• G01N2201/0692

  Regulated sources; stabilised supply · CPC title