Radiant energy – Photocells; circuits and apparatus – Photocell controlled circuit
Reexamination Certificate
2000-05-30
2003-12-30
Allen, Stephone B. (Department: 2878)
Radiant energy
Photocells; circuits and apparatus
Photocell controlled circuit
C250S2140SW, C315S159000
Reexamination Certificate
active
06670597
ABSTRACT:
BACKGROUND OF INVENTION
1. Field of Invention
This invention relates to an illumination sensor for turning on and off a separately provided switch element in response to the brightness of ambient light and an electronic automatic on/off switch for turning on and off power supply to a load in response to the brightness of ambient light.
2. Related Art
Conventionally, an automatic on/off switch for detecting the brightness of ambient light and lighting a load when the ambient light becomes stipulated brightness or less has been provided. With an automatic on/off switch of this kind, a CdS cell has been widely used as an illumination sensor for detecting the brightness of ambient light. The automatic on/off switch of this kind is called a thermal type; a bimetal heater as a switch element is connected in series to the CdS cell and a contact inserted between a load and a power supply is opened and closed by means of the bimetal. Such a thermal-type automatic on/off switch has the advantage that it can be provided at low cost. However, cadmium is used for the CdS cell and therefore the automatic on/off switch using the CdS cell as the illumination sensor has a problem of a large load on the environment when it is manufactured and is discarded.
Then, a device using a photodiode array in place of the CdS cell to detect the brightness of ambient light is proposed to reduce the load on the environment when it is manufactured and is discarded. For example, JP-A-5-152924 describes a configuration wherein a photodiode array
1
is used as an illumination sensor for detecting the brightness of ambient light and a switching element
2
comprising two depletion-type MOSFETs connected in series is used as a switch element for turning on and off the feeding path from a power supply E to a load L, as shown in FIG.
81
.
In the configuration, the load of cadmium on the environment is eliminated because the CdS cell is not used to detect the brightness and no power is required for controlling the switching element
2
and the number of parts is lessened because the photodiode array
1
of photovoltaic element is used.
By the way, the switching element
2
comprising two depletion-type MOSFETs is inserted between the power supply E and the load L in the configuration shown in FIG.
81
and thus the switching element
2
needs to have a large rated current capacity to use a load consuming large power. To drive the switching element
2
of a large rated current capacity, the electromotive force of the diode array
1
must also be enlarged. Since the electromotive force of one photodiode is constant, the number of photodiodes needs to be increased to provide a large electromotive force and consequently, the occupation area of the photodiode array
1
becomes large. That is, in addition to use of a high-cost switching element of a large rated current capacity as the switching element
2
, a high-cost photodiode array
1
of a large area is also used as the photodiode array
1
.
JP-A-5-152924 describes the fact that if the load capacity is large, the MOSFETs making up the switching element
2
are connected in parallel, thereby enlarging the current capacity of the switching element
2
; however, if the gates and sources of two or more MOSFETs are connected in parallel, the capacity components of the gates and sources are also connected in parallel and thus it is feared that the capacity components may form a feedback path, resulting in an oscillation state. Moreover, if two or more MOSFETs are connected in parallel, the costs are increased as with use of MOSFET of a large rated current capacity and the MOSFET occupation area becomes large, leading to upsizing.
SUMMARY OF INVENTION
It is therefore an object of the invention to provide an electronic automatic on/off switch that can lessen a load on the environment, of course, and provide a comparatively large current capacity at low costs and an illumination sensor forming a part of the electronic automatic on/off switch with a switch element.
Illumination Sensor
According to a first aspect of the present invention, there is provided an illumination sensor comprising a photovoltaic element made of a solar battery for generating a voltage responsive to brightness of ambient light and a switching element comprising MOSFET being turned on or off in response to the output voltage of the photovoltaic element for opening or closing a separately provided switch element. According to the configuration, a solar battery is used as the photovoltaic element, whereby a circuit for applying a bias voltage as with a photodiode need not be provided and moreover a power supply is not required for controlling the switching element. Moreover, MOSFET is used as the switching element, so that low power is consumed and the switching element can be turned on and off by output of a small-sized solar battery. Further, CdS cells are not used and thus the ill effect of cadmium on the environment is not produced.
According to a second aspect of the present invention, in the illumination sensor as the first aspect of the present invention, the switching element is made up of two MOSFETs with sources connected and gates connected in common. In the configuration, the switching element can be used for an AC power supply.
According to the third aspect of the present invention, in the illumination sensor as the first aspect of the present invention, the photovoltaic element is a solar battery comprising a plurality of cells each having a pin structure connected in series on a single plane, the cells being formed on a single substrate. According to the configuration, the output voltage of the photovoltaic element can be enlarged without increasing the number of parts at the assembling time.
According to a fourth aspect of the present invention, in the illumination sensor as the first aspect of the present invention, an amorphous silicon solar battery having a sensitivity wavelength range of 400 to 700 nm, a peak wavelength in the vicinity of 500 nm, and a spectral sensitivity characteristic closely similar to the luminosity characteristic of a human being is used as the solar battery. According to the configuration, the operation of the switching element in response to the brightness of ambient light can be matched with the luminosity characteristic of a human being and control with no sense of incongruity is enabled. Moreover, an amorphous silicon solar battery is used, so that easy formation is enabled at comparatively low temperature on a comparatively inexpensive substrate of glass, silicon, etc., and costs can be reduced.
According to a fifth aspect of the present invention, the illumination sensor as the first aspect of the present invention further includes a light quantity adjustment member being placed in at least a part of an incidence path of ambient light on a light reception face of the photovoltaic element and having transmittance controlled by an external signal generated in response to opening or closing the switch element. According to the configuration, the light quantity adjustment member having transmittance controlled by an external signal responsive to turning on or off the switching element controlled in response to the brightness of ambient light is placed in the incidence path of ambient light on the photovoltaic element, so that it is made possible to give hysteresis to the relationship between the brightness of the ambient light and turning on/off the switching element. That is, an external signal is given so as to decrease the transmittance of the light quantity adjustment member when the ambient light is decreased, whereby it is made possible to lower the sensitivity when the quantity of the ambient light is small, and it is made possible to set so as to prevent a malfunction if light of headlights of an automobile, etc., is incident in the night. Since a delay element need not be placed between the solar battery and the switching element, when light quantity change of the ambient light is sufficiently large, the transmittance of the light quantity adjustmen
Akinari Yoshinori
Ishigami Yoshihisa
Kitamura Nobuhiro
Murata Yukihiro
Allen Stephone B.
Matsushita Electric & Works Ltd.
Nixon & Vanderhye P.C.
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