JPH0342535Y2 - - Google Patents

Description

[Detailed Description of the Invention] This invention relates to a mounting structure on a printed circuit board of a circuit section provided with a light-receiving element in a light receiver of a photodetector used in a burglar alarm or the like.

Conventionally, in this type of photodetector, a so-called light-interrupting photoelectric switch, the signal light is pulse-modulated and converted into pulses in order to distinguish between ambient steady light and signal light from a projector. FIG. 1 shows the circuit configuration of a conventional photoelectric switch. An oscillation circuit 1 activates an infrared light emitting diode 2 at a predetermined period to emit pulsed light 3, which is transmitted by a phototransistor 4 serving as a light receiving element. The phototransistor 4 is connected to the amplifier circuit 5 via the capacitor _C1 to cut out the signal caused by the stationary light and amplify only the signal light, and when this signal light is cut off, the signal processing starts. The circuit 6 sends out a theft alarm, etc. In this case, the output waveform of the phototransistor 4 of the light receiver becomes as shown in FIG. 2, and the signal level e _S of the signal light appears superimposed on the direct current signal level e _D of the ambient light. However, in burglar alarms and the like used outdoors, the steady light that enters the receiver changes greatly between day and night, so the DC signal level e _D from the phototransistor 4 changes, and the steady light in particular changes. If it becomes stronger, the DC signal level _eD increases and a masking phenomenon occurs in which the signal light level _eS is not detected. Therefore, in order to prevent the DC output level of the phototransistor from changing even if the ambient light changes, a circuit that applies bias using a phototransistor PTr with a base terminal has been put into practical use, as shown in Figure 3. has been done. That is, a bias circuit is provided in which the output of the phototransistor PTr is fed back to the base of the phototransistor PTr by a bias transistor Tr via an integrating circuit consisting of a capacitor _C2 and a resistor _R1 . The potential of ₂ increases, which increases the base current of the bias transistor Tr, lowers its collector potential, and the phototransistor Tr increases.
It operates by reducing the base bias current of the PTr so that the output DC level remains constant. Conversely, when the surroundings become dark, the collector potential of the bias transistor Tr rises, and the base bias current is increased to prevent the phototransistor's operating level from decreasing and maintain an efficient operating level.

On the other hand, in this type of photodetector, it is necessary to align the optical axes of the emitter and receiver, and in that case, it is impossible to move the entire device due to space constraints or angle adjustment. Only the optical system consisting of a lens or a reflecting mirror has a freely adjustable structure, and the light receiving element is placed at the focal point of the lens or reflecting mirror.

Figures 8a and 8b show an example of a conventional photodetector (Japanese Unexamined Patent Publication No. 53-2100), in which the printed circuit board 22
A light receiving unit housing 28 is attached to the upper part of the body 20 equipped with a mounting bracket 29 so that its optical axis can be freely adjusted. Element 4 is arranged.

For this reason, in the conventional photoreceiver, the phototransistor PTr is integrally supported at the focal point f of the lens 7, as shown in FIG. 4, along with its optical system, and the bias circuit section shown in FIG. It was mounted on a separately provided printed circuit board 8. However, since the bias circuit of the phototransistor PTr has a high impedance on the order of meg, the phototransistor PTr and the printed circuit board 8 must be connected by a shield wire 9. However, since the shield wire 9 has the same structure as a capacitor, it has a distributed capacitance between the core wire and the outer shield, and this distributed capacitance affects the response characteristics of the phototransistor PTr. A new problem arises in that the response characteristics to pulsed signal light deteriorate. In other words, the response of the phototransistor PTr is delayed with respect to the light emitting diode output of the floodlight shown in FIG.
As shown in the figure, the rise time of the phototransistor PTr output becomes longer, the output signal lens taken out becomes lower, and the detection sensitivity decreases.

In order to compensate for this, it is necessary to lengthen the time width of the light emitting diode output from the projector as shown by the dotted line, or to use a high output light emitting diode that can emit strong light. However, the power dissipation of light emitting diodes is limited to a certain value, and they are used in such a way that they allow a large current to flow for a short period of time and rest during the rest of the period to suppress the overall power dissipation.
There is a limit to the light emitting time, and if the response time of the phototransistor becomes long and exceeds the light emitting time of the light emitting diode, the phototransistor will not be able to obtain sufficient light receiving output.

Furthermore, if a high impedance bias circuit is placed on one printed circuit board together with a signal amplification processing circuit, it is likely to be influenced by other circuits, such as switching circuits or relay circuits, which may cause malfunctions.

The purpose of this invention was to mount the high impedance bias circuit used for the phototransistor with a base terminal together with the phototransistor on a printed circuit board that is separate from other amplification signal processing circuits, and to mount and mount it integrally with the optical system. By shortening the base terminal wiring of the transistor, the distributed capacitance is lowered and the response characteristics are improved.As a result, sufficient light receiving output can be obtained, the detection distance can be extended, and the high impedance bias circuit can be reduced from noise. The present invention provides a mounting structure for a light receiver in a photodetector that is less susceptible to noise because it is separated from other circuits that serve as sources.

Preferred embodiments of this invention will be described below with reference to the drawings.

FIG. 6 shows an embodiment of this invention in a lens condensing method using a convex lens in the optical system.
A bias circuit having the circuit configuration shown in FIG. 3 is also mounted, and the phototransistor PTr on the printed circuit board 11 is placed at the focal point f of the convex lens 10 as shown. Further, the printed circuit board 11 is integrally attached to the light receiver housing together with the optical system including the convex lens 10 so that the optical axis can be freely adjusted.
is located at the focal point f.

A main printed circuit board 13 on which other amplifier circuits and signal processing circuits 12 are mounted is provided separately from the printed circuit board 11 on which the phototransistor PTr and its bias circuit are mounted, and between this printed circuit board 13 and positive and negative power lines 14 and 14 are mounted. ' and output signal line 1
Connected with 5.

Due to this mounting structure in which the phototransistor PTr and its bias circuit are mounted on a printed circuit board separated from other circuit boards and integrated with the optical system of the photoreceiver, the distributed capacitance caused by the phototransistor's base terminal lead is minimized. This makes it possible to realize the response characteristics due to the junction capacitance of the phototransistor itself, and
Since the other amplified signal optical processing section is separated from the phototransistor bias circuit section, the high impedance circuit is less susceptible to noise from other circuit sections, and the received light signal output with high signal-to-noise ratio can be extracted. is now possible.

FIG. 7 shows another embodiment of this invention in a reflecting mirror type light receiver using a reflecting mirror 16 in the optical system. Phototransistor in f part
The PTr is mounted with a printed circuit board 11 on which its bias circuit is mounted, and is separated from the printed circuit board 11 to provide a printed circuit board 13 on which a subsequent stage amplifier circuit and signal processing circuit 12 are mounted, as shown in FIG. Similar to the embodiment, good response characteristics of the phototransistor PTr can be obtained, and the influence of noise on the high impedance bias circuit can be significantly suppressed.

Note that the bias circuit for the phototransistor PTr mounted on the printed circuit board 11 is not limited to the circuit configuration shown in FIG. 3, and a bias circuit having an appropriate circuit configuration can be used as necessary.

As explained above, the mounting structure of the photoreceiver in the photodetector of this invention is to maintain the change in the operating level of the phototransistor due to ambient light to a predetermined value.
A phototransistor with a base terminal is used, and a bias circuit is installed to suppress fluctuations in the operating level due to changes in ambient light.This bias circuit is mounted together with the phototransistor on a printed circuit board that is separated from the printed circuit board on which other circuits are mounted. By mounting it and integrating it with the optical system, it is possible to make the base terminal lead of the phototransistor extremely short, thereby preventing deterioration of response characteristics due to its distributed capacitance, and at the same time, it is possible to eliminate the amplification signal processing circuit that becomes a noise source. The high-impedance bias circuit is less susceptible to noise, and as a result, the detection distance can be extended compared to conventional methods for the same light-emitting diode output, and it is a reliable sensor with excellent detection sensitivity. This makes it possible to put a high-performance photodetector into practical use.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing an example of the basic configuration of a photodetector, Fig. 2 is an output signal waveform diagram of a phototransistor, Fig. 3 is a circuit diagram showing an example of a bias circuit of a phototransistor with a base terminal, and Fig. 4 is a block diagram showing an example of the basic configuration of a photodetector. Figure 5 is an explanatory diagram showing the mounting structure in a conventional light receiver, Figure 5 is a signal waveform diagram showing the light reception output of the phototransistor with respect to the light emitting diode output, and Figure 6 is an explanatory diagram showing an example of the mounting structure according to this invention. ,
FIG. 7 is an explanatory diagram showing another embodiment of the mounting structure according to this invention, and FIG. 8 is an explanatory diagram of the structure of a conventional photodetector. 1...Oscillation circuit, 2...Light emitting diode, 3...
...Pulsed light, 4...Phototransistor, 5...
Amplifier circuit, 6... Signal processing circuit, PTr... Photo transistor (with base terminal), 7, 10... Convex lens, 8, 11, 13... Printed circuit board, 9...
...Shield wire, 12...Amplification circuit and signal processing circuit, 14, 14'...Power supply line, 15...Output signal line, 16...Reflector.

Claims (1)

[Scope of Claim for Utility Model Registration] An optical system is provided on a light receiver housing so that it can be adjusted vertically and horizontally, a light receiving element is integrally mounted at the focal position of the optical system, and a substrate is placed separately from the light receiving element. In the mounting structure of the light receiver in a photodetector in which the output of the light receiving element is connected to the circuit section of the signal line, a phototransistor with a base terminal is used as the light receiving element, and the base terminal of the phototransistor is used to detect ambient light. A bias circuit is provided to set an operating level to a constant value depending on the illuminance of the optical system, and the phototransistor and bias circuit are mounted on the same substrate that is separated from a subsequent amplification signal processing mounting board, and are mounted integrally with the optical system. A mounting structure of a light receiver in a photodetector characterized by the following.