Induction circuits for lighting

Details Induction circuits for lighting Induction circuits for lighting

1998-04-03

2001-02-13

Vu, David (Department: 2821)

Electric lamp and discharge devices: systems

Condenser in the supply circuit

Inductance in the condenser circuit

C315S242000, C315S243000, C363S024000

Reexamination Certificate

active

06188179

ABSTRACT:

TECHNICAL FIELD OF THE INVENTION
This invention relates to the field of inductive power transfer to negative-resistance devices such as gas-discharge and filament lamps, (including means to start the discharge) and in particular the invention relates to a resonant secondary circuit adapted to pick up power from an alternating magnetic field and provide power in a form matched to the requirements of a gas discharge lamp.
BACKGROUND
An example gas discharge lamp is the type commonly referred to as a fluorescent lamp. This is generally a mercury vapour plus inert or rare gas (argon or a mixture of similar gases) at low pressure, sealed into an elongated glass tube that is provided with electrodes at each end. As the name suggests, visible light is emitted from fluorescing phosphors coating the inside of the glass tube when excited by ultraviolet light. A fluorescent lamp is normally driven from the AC mains (110 V, 60 Hz or 240 V, 50 Hz etc) and must be used in series with a ballast (to limit current; the lamp having a negative “resistance” when in its running mode) and must be used with starting gear, to heat the electrodes during startup and to provide a high-voltage starting pulse. (The term “resistance” here applies to a voltage, temperature, and history-dependent property (are ions present?) which is rather an impure resistance). This ancillary circuitry results in a high capital cost for a fluorescent lamp installation and the starter device is at least as likely to fail during use as is the lamp itself.
Furthermore, it is difficult to provide brightness control of a fluorescent lamp. Yet an easily dimmable lamp would be useful in controlled illumination arrangements, in “intelligent buildings” and in lecture theatres, for example.
Another example gas discharge lamp is widely known as the neon tube as used in a neon sign. These devices comprise long and usually specially bent glass tubes terminated with electrodes and containing various rare gas fillings (including but not limited to the gas neon) at low pressure, optionally made of coloured glass and sometimes also with coating phosphors hence providing a wide variety of colours.
Typically each lamp is driven at mains frequency (50/60 Hz) by a potentially lethal 15 kV, 30 mA current limiting transformer. This voltage is used to ionise the gas filling and start the lamps. Once started, these lamps run at a lower voltage and, being gas-filled, also exhibit a negative resistance.
Furthermore, brightness control of a neon sign is very difficult to achieve. AC power control at the primary of the transformer is the usual method, resulting in on/off control only.
An isolated lamp power supply has likely safety benefits. Applications for the operation of gas discharge lamps under adverse (wet) conditions include lighting for environments where salty water exists—such as on board ship, in wharves, fish processing plants, meat processing plants, farm dairies, hotel kitchens, in coal or other mines, and the like.
Another “wet” application is in illumination of spaces or in illuminated signs used outdoors, where contact by the public with a wet sign, perhaps in a case which has deteriorated, is likely to result in lethal shock. Condensation in a window of a restaurant for example is likely whenever the weather outside is cold, or humid.
A further “wet” application is a swimming pool.
A yet further “wet” application is in the sterilisation of liquids—actually using biocidal wavelengths and substantial doses of ultraviolet light in order to sterilise liquids that may contain micro-organisms harmful to life. The working conditions under which lamps of this type are used would benefit from the use of simple, reliable, isolated lamp power supplies.
Yet another application is in testing products for resistance to ultraviolet degradation where existing accelerated test methods prescribe a certain type, positioning, and number of lamps but at present cannot prescribe that they emit a controlled amount of light.
OBJECT
It is an object of the present invention to provide an improved means for the transfer and conditioning of electricity obtained from across a space in order to energise a device having a negative resistance, such as a gas-discharge lamp, or a means which will at least provide the public with a useful choice.
These and other objects of the invention will be apparent to the ordinary artisan upon consideration of the specification as a whole.
STATEMENT OF THE INVENTION
In a first broad aspect the invention provides a circuit for collecting inductively transferred electric power and supplying the power to a load having a negative resistance, the circuit comprising:
(a) at least one first, pickup inductor having a core oriented so that it is capable of intercepting the magnetic flux radiating from a powered primary conductor in a loosely coupled fashion, thereby causing a voltage to be induced in the windings of the at least one first inductor,
(b) at least one second, current-limiting inductor in series with the at least one first inductor, the second inductor having a core substantially incapable of intercepting the magnetic flux radiating from the primary conductor,
(c) at least one capacitor connected across the series of inductors, thereby forming in combination with the series of inductors a circuit capable of resonance at or about a supply frequency,
(d) an output from across the at least one capacitor,
so that in use the circuit provides
(a) when not under load, an alternating output at a high voltage—and then
(b) when under load, a supply of alternating current of the constant-current type, supplying a current substantially proportional to the magnetic flux about the primary conductor yet substantially independent of the resistance of the load, and having an upper current level limited by the second inductor.
In a related aspect the current limiting inductor and the pickup inductor may be amalgamated.
In a further related aspect the invention provides a circuit as described above, wherein the load having a negative resistance is a gas discharge lamp, the lamp having a relatively high striking voltage, and a negative resistance within the arc, when struck; the circuit providing a high-voltage alternating output adapted for striking the arc when the current drawn from it is substantially zero and the circuit consequentially exhibits a high Q, and a constant-current alternating output when the current drawn is high and the Q of the circuit is low.
In a yet further related aspect the invention provides a circuit further including a saturated inductor capable of detuning the resonant circuit if the circulating voltage rises above a predetermined limit, so that an open circuit in the load has a minimal effect on a system of more than one circuit as claimed driven from one primary conductor.
In a second broad aspect the invention comprises means for converting or conditioning inductively transferred electric power to the requirements of a gas-discharge lamp, including means to provide a first striking voltage to the lamp and then to provide a second running voltage; the running voltage being supplied at substantially a constant current, the means including a circuit capable of resonance substantially at a supply frequency.
In a related aspect the invention comprises a circuit as above, wherein the circuit capable of resonance includes at least one inductive means which comprises at least a first inductive unit adapted to receive an alternating magnetic flux; the flux having the effect of inducing a voltage within the windings of the first inductive unit, and at least a second inductive unit in series, the second inductive unit having an effect of providing a limit on the current output.
In a further related aspect the invention comprises a circuit as above, further including a saturated inductor capable of detuning the resonant circuit if the circulating voltage rises above a predetermined limit.
In a second broad aspect the invention provides a system for energizing one or more lamps; the system providing a high-frequency c

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