Electric lamp and discharge devices: systems – Current and/or voltage regulation – Automatic regulation
Reexamination Certificate
1999-04-08
2001-02-27
Vu, David (Department: 2821)
Electric lamp and discharge devices: systems
Current and/or voltage regulation
Automatic regulation
C315S289000, C315S100000, C315S103000
Reexamination Certificate
active
06194846
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a starter circuit comprising a series arrangement of a glowswitch and a safety switch, which glowswitch and safety switch are each provided with an enclosed space, with a pair of current conductors which enter the respective enclosed space. A bimetal element is arranged in the enclosed space and is connected to one of the current conductors, the enclosed space of the glowswitch being provided with an ionizable filling. The glowswitch is open in the cold state, and the safety switch is closed in the cold state, while in addition the starter circuit comprises a heat source for opening the safety switch and a heat source for keeping the safety switch open.
Such a starter circuit is known from DE 815 365. The glowswitch is the heat source for opening the safety switch in the known starter circuit. The glowswitch and the safety switch are thermally coupled to one another for this purpose. A resistor shunting the safety switch acts as a heat source for keeping the safety switch open.
The known starter circuit serves for igniting a low-pressure discharge lamp with preheatable electrodes. The known starter circuit for this purpose forms part of a circuit in which the low-pressure discharge lamp is connected in series with an inductive impedance having connection terminals and in which the starter circuit shunts the discharge lamp and is connected in series with the electrodes.
When the connection terminals are connected to a supply source, the glowswitch alternately enters an open and a closed state. In the closed state, a current flows through the electrodes via the starter circuit. This current brings the electrodes of the discharge lamp to a temperature at which a sufficient degree of electron emission occurs for enabling the discharge lamp to ignite.
A transition from the closed state to the open state of the glowswitch interrupts the current through the electrodes of the lamp, so that the inductive element connected in series with the lamp will generate an ignition voltage pulse. If this ignition voltage pulse effects a discharge between the electrodes of the discharge lamp, the voltage across the discharge lamp, and accordingly the voltage between the current conductors of the glowswitch, drops so strongly that the glowswitch remains in its open state. The contact between the current conductors and the glowswitch remains broken then.
If, however, repeated ignition efforts do not lead to a discharge in the low-pressure discharge lamp, the safety switch is heated owing to the thermal coupling to the glowswitch to such an extent that the bimetal element of the safety switch is bent. The safety switch thus assumes an open position. As a result of this, a current will start to flow through the resistive impedance which shunts the safety switch. The heat generated in this resistive impedance keeps the safety switch in its open state, so that no further ignition pulses are generated. It is a disadvantage that the time elapsing until the moment the safety switch enters a closed state again after switching-off of the supply source, called recovery time hereinafter, is comparatively long. This renders it more difficult to determine whether it is sufficient to replace the lamp or whether there is another defect.
SUMMARY OF THE INVENTION
It is an object of the invention to provide a starter circuit which has a shorter recovery time. According to the invention, the starter circuit of the kind described in the opening paragraph is for this purpose characterized in that the heat source for keeping the safety switch open is formed by an ionizable filling in the enclosed space of the safety switch. The ionizable filling of the safety switch is, for example, a rare gas or a mixture of rare gases, as is the filling of the glowswitch, for example a mixture of the rare gases Ne and Xe, for example Ne95Xe5 (mole %), Ne99Xe1, or, for example, a mixture of the rare gases Ne and Ar, for example Ne99Ar1, or Ne25Ar75. The filling pressure may lie in a range from 10 to 100 mbar.
A glow discharge will arise between the current conductors of the safety switch when the heat source for opening the safety switch causes the safety switch to open in the case of an ignition failure of the lamp. The heat generated in the glow discharge keeps the bimetal element of the safety switch in the open state. Since the ionizable filling of the safety switch has a negligibly small heat capacity, in contrast to a resistive impedance, the bimetal element of the safety switch can cool down quickly after the supply source has been switched off.
The heat source for opening the safety switch is, for example, the glowswitch, in which case the glowswitch is thermally coupled to the safety switch. In a practical embodiment, the heat source for opening the safety switch is a resistive impedance which is thermally coupled to the bimetal element of the safety switch and which is connected in series with the glowswitch. To enhance the thermal coupling, the resistive impedance may be fastened to the safety switch, for example, by means of a thermally conductive glue or a metal strip. Preferably, the resistive impedance is a power resistor, for example a wire
5
wound resistor. The moment at which the safety switch opens in the case of a defective lamp may be readily chosen by means of the resistance value of the resistive impedance. In practice, the resistive impedance will have a value which lies in a range from 5 to 100 &OHgr;.
In a favorable embodiment, the glowswitch is shunted by a branch which comprises an impedance. The voltage available for maintaining a glow discharge between the current conductors of the safety switch is made higher thereby. This widens the range of possibilities for choosing the safety switch.
Preferably, the impedance is a capacitive impedance. so as to counteract malfunctions in the switching of the glowswitch. It is favorable when the branch comprises a series arrangement of the capacitive impedance and the resistive impedance. The resistive impedance limits currents through the capacitive impedance, so that less stringent requirements need be imposed on the capacitive impedance and on the current conductors of the glowswitch starter.
Unlike the glowswitch, the safety switch is closed in the cold state. Apart from this difference, the safety switch may be realized by means of technologies and materials which are usual in the field of glowswitches and are accordingly familiar to those skilled in the art.
REFERENCES:
patent: 2464748 (1949-03-01), Hodgkins
patent: 5059870 (1991-10-01), Choon
patent: 5420479 (1995-05-01), Iida et al.
patent: 5886481 (1999-03-01), Flory, IV
patent: 815365 (1949-07-01), None
Lee Wilson
U.S. Philips Corporation
Vu David
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