JPH0799431A - Photoelectric smoke sensor - Google Patents

Abstract

PURPOSE:To reduce the current consumption of a light emitting element. CONSTITUTION:The photoelectric smoke sensor provided with a light emitting circuit 1 having a light emitting element L, a photoelectric conversion circuit 2, a sample-and-hold circuit 3, an analog output circuit 4 and a timing control circuit 5 driving intermittently the light emitting circuit 1 and the photoelectric conversion circuit 2 and controlling the operating timing of the sample-and-hold circuit 3 is provided with a light emission control circuit 10 providing an output of a light emitting timing at which the light emission of the light emitting element L is finished almost at the same time of the end of the operation of the sample-and-hold circuit 3. Thus, the current consumption of the light emitting element L is reduced without degrading the operating accuracy of the sample- and-hold circuit 3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photoelectric smoke detector that senses smoke by detecting scattered light from the smoke.

[0002]

2. Description of the Related Art FIG. 3 shows a circuit diagram of a conventional photoelectric smoke detector. In the figure, the photoelectric smoke detector is a light emitting circuit 1 including a light emitting element L that emits light in the photoelectric smoke detector housing.
A photoelectric conversion circuit 2 for receiving scattered light generated by scattering light emitted from the light emitting circuit 1 by smoke and converting it into an electric signal, and a sample for holding an output signal of the photoelectric conversion circuit 2 by sampling Hold circuit 3, analog output circuit 4 for converting the signal held by sample hold circuit 3 into an analog output signal, and light emitting circuit 1
And a timing control circuit 5 for intermittently driving the photoelectric conversion circuit 2 and controlling the operation timing of the sample hold circuit 3.

The light emitting circuit 1 includes a light emitting element L such as a light emitting diode, a switching element (NPN transistor Q1) for supplying a drive current to the light emitting element L, a current limiting resistor R1, and a drive signal to the NPN transistor Q1. It is composed of a light emission drive circuit 6 for giving. Light emission drive circuit 6
Are controlled by the timing control circuit 5.

In order to intermittently drive the above light emitting circuit 1,
In the timing control circuit 5, the signal output from the oscillation circuit 7 is frequency-divided by the frequency dividing circuit 8 to obtain a clock signal, an intermittent drive signal is generated based on the clock signal, and the intermittent drive signal is supplied to the light emission drive circuit 6 of the light emission circuit 1. is doing. Further, the frequency dividing circuit 8 controls the photoelectric conversion circuit drive signal for controlling the operations of the differential amplifiers A1 to A4 of the photoelectric conversion circuit 2 and the electronic switch S provided in the sample hold circuit 3 to perform the sampling operation. It is configured to output a sample hold circuit drive signal for switching the holding operation.

The photoelectric conversion circuit 2, when receiving light, converts the photocurrent generated in the light receiving element PD into differential amplifier circuits A1 to A3 and resistors R2 to R6.
And, the DC amplification is performed by the amplification circuit composed of 3 stages with the capacitor C1 and the DC component is cut by the capacitor C2, and then output to the sample hold circuit 3 of the next stage via the buffer circuit composed of the differential amplification circuit A4. It is a circuit to do. The reference voltage source 9 is provided to supply an offset voltage.

The sample and hold circuit 3 includes a resistor R7 for limiting current, a capacitor C3 for holding an input voltage,
It is composed of a differential amplifier circuit A5 which functions as a buffer and an electronic switch S whose opening and closing is controlled by a sample and hold circuit drive signal output from the frequency divider circuit 8. When the sample and hold circuit drive signal is at a high level, the photoelectric conversion circuit 2 Is sampled and the sampled and held circuit is configured to hold the sampled voltage when the drive signal is at a low level. The voltage applied to the non-inverting input terminal is directly output to the output of the sample hold circuit 3.

The analog output circuit 4 is a level conversion circuit composed of a differential amplifier A6, resistors R8 to R12, and an NPN transistor Q2. This is a circuit that adds an offset voltage to the output voltage of the sample hold circuit 3 input to the inverting input terminal, converts the level of the signal into a predetermined signal, and outputs the signal to a receiver (not shown).

When smoke enters the photoelectric smoke detector housing constructed as described above, the light emitted from the light emitting element L of the light emitting circuit 1 is scattered by the smoke and received by the photoelectric conversion circuit 2. . When the light receiving element PD is irradiated with light, a weak photocurrent flows. This photocurrent is DC-amplified by the amplifier circuit of the photoelectric conversion circuit 2, and its DC component is cut by the capacitor C2. After that, the output voltage of the photoelectric conversion circuit 2 is sampled and held by the sample hold circuit 3 and converted into a predetermined output signal by the analog output circuit 4. The operation timing at this time is shown in FIG. In the figure, (a) shows a clock signal obtained by dividing the output of the oscillation circuit 7 by the frequency dividing circuit 8, and (b) shows a drive signal of the photoelectric conversion circuit 2, which indicates an operating state at a high level. ing. (C) is an intermittent drive signal of the light emitting circuit 1, which indicates that the light emitting state is in a high level. (D) shows the sampling operation signal of the sample hold circuit 3, and shows that the sampling operation state is at the high level and the holding operation state is at the low level. As shown in the figure, first, the photoelectric conversion circuit 2 is driven by the timing control circuit 5. With the photoelectric conversion circuit 2 stable,
The light emitting circuit 1 is driven, and the light emitting element L 1 is in a light emitting state.
After that, in the sample hold circuit 3, the electronic switch S is opened by the sampling operation signal of the timing control circuit 5 becoming High level, and the sampling operation state is maintained for 1/2 cycle. Sampling operation signal is L
At the ow level, the electronic switch S is closed and the sample hold circuit 3 shifts to the holding operation state, and the output voltage of the photoelectric conversion circuit 2 is held. In order to accurately sample and hold the stable output voltage of the photoelectric conversion circuit 2, the light emitting circuit 1 must be in the light emitting state at least during the sampling operation state of the sample hold circuit. In the example shown in the figure, the light emitting circuit 1 is driven 1/2 cycle ahead of the start of the sampling operation of the sample and hold circuit 3 and emits light 1/2 cycle after the completion of the sampling operation of the sample and hold circuit 3. It is controlled by the timing control circuit 5 to stop.

[0009]

However, in the circuit described above, the intermittent drive signal supplied to the light emitting circuit 1 and the sampling operation signal supplied to the sample hold circuit 3 are separated from the signal output from the oscillation circuit 7. Since it is created based on the clock signal divided by the frequency circuit 8, in order to bring the light emitting circuit 1 into the driving state during the sampling operation,
It is necessary to make the period for driving the light emitting circuit 1 longer than the sampling operation period, and in the above-mentioned conventional example, the driving of the light emitting circuit 1 was completed with a delay of 1/2 cycle after the completion of the sampling operation. Therefore, the driving time of the light emitting circuit 1 becomes long, and there is a problem in that originally unnecessary power is consumed.

The present invention has been made in view of the above problems, and an object thereof is to provide a structure of a photoelectric smoke detector capable of reducing the current consumption of a light emitting element.

[0011]

In order to solve the above problems, the photoelectric smoke detector according to claim 1 is a photoelectric smoke detector housing, and a light emitting circuit having a light emitting element for emitting light, A photoelectric conversion circuit that receives scattered light due to smoke of light emitted from the light emitting circuit and converts it into an electric signal, a sample hold circuit that samples and holds an output signal of the photoelectric conversion circuit, and a sample hold circuit Photoelectric smoke including an analog output circuit that converts and outputs the generated analog signal, and a timing control circuit that intermittently drives the light emitting circuit and the photoelectric conversion circuit and controls the operation timing of the sample hold circuit In the sensor, the drive signal of the sample hold circuit and the intermittent drive signal supplied to the light emitting circuit are input,
A light emission control circuit for outputting a signal for terminating the light emission of the light emitting element substantially at the same time when the operation of the sample and hold circuit is completed is provided.

A photoelectric smoke detector according to a second aspect is the photoelectric smoke detector according to the first aspect, wherein the light emission control circuit inputs the intermittent drive signal output from the timing control circuit to one input. At the same time, the drive signal of the sample-hold circuit is input to the other input via the NOT circuit and the two-input type exclusive NOR circuit and the output of the exclusive NOR circuit are divided and output to the light emitting circuit. And a flip-flop circuit that changes the output by detecting the rising edge of the clock input.

[0013]

In the photoelectric smoke detector of the present invention, the light emission control circuit 10
Receives the sampling operation signal of the timing control circuit 5 and the intermittent drive signal for controlling the light emitting circuit 1, and detects the rising edge of the intermittent drive signal for controlling the light emitting circuit 1,
The output is changed from the low level to the high level, the rising edge of the sampling operation signal is detected, and the output is changed from the high level to the low level. Therefore, as shown in the timing chart of FIG. The output of the light emission control circuit 10 is
Immediately after the fall of the sampling operation signal of (3), it falls. By using the output of the light emission control circuit 10 as a new intermittent drive signal of the light emitting circuit 1, the intermittent drive operation time of the light emitting circuit 1 can be shortened, and the light emitting element
The current consumption due to L can be reduced.

[0014]

1 is a circuit diagram of an embodiment of the present invention. The photoelectric smoke detector of the present invention is configured such that a light emission control circuit 10 is added to the circuit of the conventional photoelectric smoke detector shown in FIG. 3 and the light emission circuit 1 is driven by its output. Therefore, the same components as those of the conventional example will be denoted by the same reference numerals and detailed description thereof will be omitted.

First, the structure of the light emission control circuit 10 will be described. In the figure, 11 is a NOT circuit, 12 is a two-input type exclusive NOR circuit, and 13 is a level state of the input D when the signal input to the clock signal input rises.
Is a D flip-flop circuit configured to output to the output QB and to the output QB in a level opposite to the level of the output Q. The sampling operation signal is supplied from the frequency dividing circuit 8 to the one input terminal of the exclusive NOR circuit 12 via the NOT circuit 11, and the intermittent driving signal from the frequency dividing circuit 8 is supplied to the other input terminal. Is configured to be supplied. The output of the exclusive NOR circuit 12 is
The D flip-flop circuit 13 is connected to the clock signal input CLK, the output QB of the D flip-flop circuit 13 is connected to the input D 1, and the output Q is connected to the input terminal of the intermittent drive signal of the light emission drive circuit 6.

The operation of the light emission control circuit 10 configured as described above will be described below with reference to the timing chart of FIG. In the figure, (a) is a clock signal output from the frequency dividing circuit 8, (b) is a drive signal of the photoelectric conversion circuit 2, (c) is an intermittent drive signal of the light emitting circuit 1, and (d) is a sample and hold circuit 3. Sampling operation signal, (e) output of exclusive NOR circuit 12, (f) light emission control circuit 10
Shows the output of. Only when the sampling operation signal shown in (d) is in a state different from the intermittent drive signal shown in (c), the output of the exclusive NOR circuit 12 is as shown in (e).
High level.

Next, when the output signal of the exclusive NOR circuit 12 shown in (e) is divided by one stage by the D edge flip-flop circuit 13 for detecting the rising edge, the signal shown in (f) becomes D.
From the output Q of the flip-flop circuit 13 to the light emission drive circuit 6
Will be output to. The light emission control circuit output shown in (f) is Hi with the intermittent drive signal of the light emitting circuit 1 shown in (c).
It is a signal that shifts to the Low level after shifting to the gh level together with the sampling operation signal shown in (d). By supplying this light emission control circuit output to the light emitting circuit 1 as a new intermittent drive signal, As described above, after the sampling operation is completed, it is not necessary to drive the light emitting circuit 1 for 1/2 cycle, and the current consumption of the light emitting element L 1 can be reduced. Further, the operation of the light emitting circuit 1 is as described above.
Since the sampling operation is completed when the sampling operation is completed, it is ensured that the sampling operation is performed during the operation of the light emitting circuit 1.

[0018]

As described above, according to the photoelectric smoke detector of the present invention, the light emission control circuit is configured to end the intermittent driving of the light emitting circuit when the sampling operation is completed. It is possible to reduce the current consumption of the light emitting element without lowering the operation accuracy.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of a photoelectric smoke detector of the present invention.

FIG. 2 is a time chart of the photoelectric smoke detector of the present invention.

FIG. 3 is a circuit diagram showing an example of a conventional photoelectric smoke detector.

FIG. 4 is a time chart of a conventional photoelectric smoke detector.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 light emitting circuit 2 photoelectric conversion circuit 3 sample hold circuit 4 analog output circuit 5 timing control circuit 6 light emission drive circuit 7 oscillation circuit 8 frequency divider circuit 9 reference voltage source 10 light emission control circuit 11 NOT circuit 12 exclusive NOR circuit 13 D flip-flop circuit

Claims (2)

[Claims] 1. A light emitting circuit having a light emitting element for emitting light in a photoelectric smoke detector housing, and a photoelectric device for receiving scattered light of smoke emitted from the light emitting circuit and converting it into an electric signal. A conversion circuit, a sample hold circuit for sampling and holding an output signal of the photoelectric conversion circuit, an analog output circuit for converting and outputting an analog signal held by the sample hold circuit, the light emitting circuit and the photoelectric conversion circuit And a timing control circuit for controlling the operation timing of the sample and hold circuit, in the photoelectric smoke detector, the drive signal of the sample and hold circuit and the intermittent drive signal supplied to the light emitting circuit are Light emission control for inputting and outputting a signal for ending the light emission of the light emitting element substantially at the same time as the operation of the sample hold circuit is completed. A photoelectric smoke detector comprising a circuit. 2. The light emission control circuit inputs the intermittent drive signal output from the timing control circuit to one input and also outputs the drive signal to the sample hold circuit.
Two-input type exclusive input to the other input through the circuit
A NOR circuit and a flip-flop circuit that divides the output of the exclusive NOR circuit and outputs it to the light emitting circuit, and detects the rising edge of the clock input to change the output. The photoelectric smoke detector according to claim 1.