Radiant energy – Photocells; circuits and apparatus – Temperature control of photocell
Reexamination Certificate
1999-05-11
2001-12-04
Le, Que T. (Department: 2878)
Radiant energy
Photocells; circuits and apparatus
Temperature control of photocell
C062S003700, C136S203000, C165S104330, C257S930000
Reexamination Certificate
active
06326610
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical sensor having a multistage type thermoelectric cooling section.
2. Related Background Art
For example, in a CCD image sensor or the like, a number of photosensors, such as photodiodes, for example, are arranged in parallel as a photosensitive section, whereas the photosensors are provided with a thermoelectric cooling section for cooling the photosensors. As the thermoelectric cooling section, there has been known the one in which Peltier devices are stacked on each other in a plurality of stages for effecting forcible air cooling.
In the thermoelectric cooling section in which Peltier devices are stacked on each other in a plurality of stages, it is necessary that, in order to improve the heat radiation efficiency, a Peltier device having a higher output (greater current consumption) than that of a Peltier device on the heat absorption side nearer the photosensors is disposed on the heat radiation side. Consequently, Peltier devices having different output characteristics [I (current)−V (voltage) characteristics] are disposed on the heat absorption side and the heat radiation side, respectively.
When the Peltier devices having different output characteristics are thus stacked on each other, it is necessary for each Peltier device to operate at its optimum operating point, i.e., the point where the cooling performance of the Peltier device is maximized with respect to its consumed power, in order to exhibit the characteristics of the individual Peltier devices at maximum.
For this reason, the individual Peltier devices have conventionally been driven at their optimum operating points by their respective power sources independent from each other.
SUMMARY OF THE INVENTION
When the above-mentioned individual Peltier devices are driven by power sources independent from each other, as mentioned above, while the cooling efficiency is excellent since each Peltier device can be driven at its optimum operating point, there is such a problem that the apparatus has a larger size since the power sources are needed by the number corresponding to that of Peltier devices.
On the other hand, when the individual Peltier devices are driven by a single common power source, there is such a problem that only one of the Peltier devices can operate at its optimum operating point.
In order to overcome such problems, it is an object of the present invention to provide an optical sensor which can reduce its size and improve its cooling efficiency.
The optical sensor in accordance with the present invention is an optical sensor comprising: a temperature sensor; a current control section; a thermoelectric cooling section; and a bypass circuit, said temperature sensor being disposed in said optical sensor, said current control section supplying a driving current to said thermoelectric cooling section according to an output of said temperature sensor, said thermoelectric cooling section being constituted by a multistage structure in which a first Peltier device on a heat radiation side, and a second Peltier device, on a heat absorption side, having a current consumption lower than that of said first Peltier device are stacked on each other, and said Peltier devices being electrically connected to each other in series and being driven by the driving current from said current control section, and said bypass circuit being connected to said second Peltier device in parallel, and diverting an excess current with respect to said second Peltier device.
In the optical sensor in accordance with the present invention, since the first Peltier device on the heat radiation side and at least one second Peltier device, on the heat absorption side, having a current consumption lower than that of the first Peltier device, are connected to each other in series, while a bypass circuit for diverting an excess current with respect to the second Peltier device is connected to the second Peltier device in parallel, the first Peltier device is driven at its optimum operating point (the point at which the cooling performance of the Peltier device is maximized with respect to its consumed power) by the driving current from the current control section, and the excess current with respect to the second Peltier device is diverted into the bypass circuit, whereby the second Peltier device can also be driven at its optimum operating point. Consequently, the cooling efficiency can be improved. Also, since the first and second Peltier devices are stacked on each other while all the Peltier devices are driven by a single common power source (current control section), a smaller size can be attained.
The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not to be considered as limiting the present invention.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.
REFERENCES:
patent: 5385020 (1995-01-01), Gwilliam et al.
patent: 5515683 (1996-05-01), Kessler
patent: 9-219475 (1997-08-01), None
Muramatsu Satoru
Suzuki Hidetaka
Hamamatsu Photonics K.K.
Le Que T.
Luu Thanh X.
Pillsbury & Winthrop LLP
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