Photoelectric switch

Details Photoelectric switch Photoelectric switch

1995-05-22

1997-11-04

Fleming, Fritz

Electricity: electrical systems and devices

Electric charging of objects or materials

Particulate matter

361235, H03K 1778, H05F 302

Patent

active

056846665

DESCRIPTION:

BRIEF SUMMARY
This invention relates to electronic switching means for use in applications involving high voltages of at least 1 kV and more usually at least 5 kV ranging up to 50 kV.
Although not limited thereto, the invention has particular application to devices for affecting electrostatic spraying of materials, especially liquids. Typical devices of the type that the present invention is concerned with are disclosed in EP-A-120633, EP-A-441501, EP-A-468735 and EP-A-468736.
According to one aspect of the present invention there is provided electronic switching means comprising a series of radiation sensitive semiconductor junctions collectively having a maximum dc reverse voltage of at least 1 kV (preferably at least 5 kV and often at least 10 kV), terminal means for the application of high voltage to the junctions such that the junctions permit current flow in one direction only when forwardly biased by an applied voltage, and selectively operable, radiation producing means associated with said junctions for selectively irradiating the same so as to produce current flow in the reverse direction when the junctions are reverse biased by an applied voltage, said junctions and the radiation producing means being supported in fixed predetermined relation within a mass of encapsulating material transmissive to the radiation emitted from the radiation producing means.
Preferably said junctions collectively have a maximum dc reverse voltage of at least 5 kV and more preferably at least 10 kV.
It is to be understood that, when said series of junctions are reverse biased and not exposed to radiation from said radiation producing means, there may nevertheless be a small current flow as in the case of a conventional diode (dark current) but the reverse current flow is neglible compared with that produced when the junctions are forwardly biased with a voltage of the same amplitude but opposite polarity. In contrast, when the junctions are reverse biased and subjected to irradiation, the current flow is substantially greater than that occurring in the absence of such irradiation.
The encapsulating mass may be such as to provide reflective surfaces in the vicinity of the junctions so that radiation which is not directly incident on the junctions is reflected thereby increasing the efficiency with which the Junctions is irradiated. Such reflective surfaces may be constituted by a specific layer or layers of material reflective to radiation at the wavelength or wavelengths emitted by the radiation producing means; or reflectivity may be obtained as a result of changes in refractive index within the mass of encapsulating material.
It is widely known that silicon diodes having a pn junction are photosensitive and that, when reverse biased and exposed to near infrared radiation, such diodes are rendered conductive and permit current flow substantially in excess of the dark current. This is the principle underlying photodiode operation. In contrast with conventional photodiodes which have an architecture or layout consistent with making effective use of incident light, the switching means according to said one aspect of the invention is designed to operate at voltages substantially in excess of those at which conventional photodiodes are intended to operate. Thus, conventional photodiodes are designed with maximum dc reverse voltages ranging up to 600 volts (see "Optoelectronics", D.A.T.A. Digest 1992 (Edition 25) published by D.A.T.A. Business Publishing of Englewood, Colo., USA--"Photodiodes", Page 613) whereas the switching means of this aspect of the invention is intended for use in applications involving high voltages of at least 1 kV, and more usually at least 5 kV ranging up to for example 50 kV.
In a preferred embodiment of the invention, said series of semiconductor junctions constitute a high voltage semiconductor diode, preferably a high voltage silicon diode having a series of stacked pn junctions.
The radiation producing means conveniently comprises a light-emitting diode. As used herein, references to "light" are to be und

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