Electric lamp and discharge devices: systems – Condenser in the supply circuit – Inductance in the condenser circuit
Reexamination Certificate
2002-10-22
2004-09-21
Philogene, Haissa (Department: 2821)
Electric lamp and discharge devices: systems
Condenser in the supply circuit
Inductance in the condenser circuit
C315S307000, C315S291000, C315S312000, C315S324000, C315SDIG007
Reexamination Certificate
active
06794828
ABSTRACT:
The present invention relates to high intensity discharge lighting systems, and to high intensity discharge lamps and controls therefor.
BACKGROUND OF THE INVENTION
High intensity discharge lighting systems comprising a high intensity discharge lamp and a control for regulating the electrical power to the lamp are known. In this specification, references to “high intensity discharge lamps” are to lamps having a sealed envelope containing at least two electrodes for an electrical discharge, and are arranged to be used for lighting when an arc is established across the electrodes. Such lamps have a high impedance before they are lit, and a low impedance while they are lit. Before the lamp is lit, it is necessary to apply a high voltage (typically 2-5 kV) across the lamp to start the lamp to conduct electricity. High intensity discharge lamps are characterised by a short arc length, typically less than 20 mm for a 70 watt lamp, and typically have a high internal pressure when hot. The envelope is filled with fill materials that may not be fully evaporated and hence have a low pressure when the lamp is cold and before the lamp has started conducting. However, when the lamp is operating and is hot, the said fill materials have a high pressure. High intensity discharge lamps are further characterised in that as a result of this increase in pressure of the fill material an ignition voltage required to start such lamps may increase sharply as the lamp becomes hot. For example, a lamp with a cold ignition voltage of 2,000 volts may when hot require an ignition voltage of 30,000 volts to restart the lamp. Additional electrodes may be provided in such lamps for particular applications to meet particular operating requirements.
Such known controls may comprise an electro-magnetic inductance to regulate the power, and a capacitor and switch arrangement to generate the high starting voltage. Such electromagnetic controls provide an electrical output to the lamp at the same frequency as the electrical supply to the control. Alternatively, electronic controls are known, where an electronic circuit is arranged to provide both the regulation and generate the high starting voltage. Such electronic controls normally provide an electrical output to the lamp at a higher frequency than that of the electrical supply to the control. Typical electronic controls for operating a high intensity discharge lamp produce a square wave voltage output at a frequency of up to 400 Hz with an electrical supply having a sinusoidal waveform and a frequency of 50 Hz or 60 Hz. These are hereinafter referred to as “square wave” technology controls.
The arrangement for producing a high voltage for starting or igniting the lamp, being known hereinafter as an “ignitor”, and the means for regulating the power when the lamp is operating in the lit state to provide a desired operating power for the lamp being known hereinafter as a “ballast”.
In electronic controls known means to generate high voltage includes resonant circuits and suddenly discharged capacitor circuits. Known electronic controls having a self oscillating circuit operate at a frequency determined by the resonance of power handling components in the control circuit. A benefit of these self oscillating circuits is simplicity and low cost, however a disadvantage is that it is difficult to vary the operating frequency of such a control circuit as the operating frequency is determined solely by the values of fixed components, the values of which are determined by the power of the circuit it is arranged to control. Also known are electronic controls where the operating frequency is determined solely by a frequency generator such that the operating frequency can be arranged to be independent of the characteristics of power handling components in the circuit.
The electronic controls employed to date have, as a result of their complexity, a disadvantage of cost that has prevented their widespread use.
One of the reasons for the complex design of square wave technology controls, (which operate lamps at relatively low frequencies 50-400 Hz for example), is that discharge lamps exhibit undesirable instabilities when operated in the frequency range of 1 kHz-300 kHz depending on lamp type and geometry. Consequently, elaborate electronic topologies are required to generate low frequencies with power levels and control characteristics suited to discharge lamps.
Should the operating frequency (or some harmonic or sub harmonic of the operating frequency) be such as to excite standing waves of pressure within a lamp then undesirable movement or even extinction of the arc can occur. This can be damaging to the lamp since arc movement can cause the arc to impinge upon an inner surface of the envelope forming burner walls with consequent lamp failure. At the very least, these movements of the arc spoil the quality of illumination obtained.
The above mentioned instability and standing waves of pressure are manifestations of a phenomenon known as “acoustic resonance”. Acoustic resonance arises as a result of pressure variations in the lamp caused by the operating frequency or some harmonic or sub harmonic of the operating frequency. A lamp has an acoustic resonant frequency range that is the range of frequencies which will excite acoustic resonance within the lamp. Hence a particular lamp would be likely to exhibit acoustic resonance when operated with a power input frequency within the acoustic resonant frequency range.
For a particular lamp, the acoustic resonance conditions during the starting of the lamp will be different to those when the lamp is operating in a stable lit condition. Since the starting of the lamp is a transient phase of operation lasting a very short time interval such acoustic resonance phenomena that might otherwise occur during this transient phase do not normally have time to become established. Hence the acoustic resonant frequency range is defined with reference only to the conditions when the lamp is operating in a stable lit condition.
A high intensity discharge lighting system having a control and at least two high intensity discharge lamps is described in U.S. Pat. No. 5,986,412 to Collins. FIG. 1 of Collins' Patent shows that the operation of the two lamps 12 and 14 is by means of an electromagnetic control, referred to as ballast circuit 10 which has a shared portion of the circuit comprising principally transformer 16, and two ignitor pulse circuits 30 and 50 for starting lamps 12 and 14 respectively. In operation lamp 12 must start before lamp 14 in order to conduct the electrical power necessary to operate the second ignitor pulse circuit 50. A disadvantage of the Collins system is that it is necessary to duplicate the ignitor circuit.
U.S. Pat. No. 5,982,109 to Konopka shows in his FIG. 4 two lamps 10 and 20 connected to an electronic control 120, and in FIG. 6 two lamps 10 and 20 connected to a control 160. In each case the lamps are connected in parallel current paths, and the only shared part of the control is the inverter 200, each lamp having its own output circuit 300, 500 and 400, 600 inductor 310, 510 and 410, 610 and other ignitor components. The Konopka arrangement has similar disadvantages to the Collins system in that it requires considerable duplication of expensive components.
U.S. Pat. No. 5,900,701 to Guhilot in FIG. 4C shows a plurality of lamps 16 connected in parallel across a secondary winding 111 of an inverter transformer 115. For each lamp so connected it is necessary to duplicate a ballast filter comprising capacitor 112 and inductor 113. A reason that it is necessary to duplicate the ballast filter components is to ensure stable and safe operation of each lamp, since being in parallel if one lamp failed to start all the output power from the transformer would pass through the single lit lamp. Hence, as in the previous examples duplication of expensive components is required.
U.S. Pat. Nos. 5,828,185 and 5,998,939 to Philips Electronics in FIG. 8 shows two light emitting elements, a first and a second discharge dev
Merchant & Gould P.C.
MicroLights Limited
Philogene Haissa
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