Arrangement for the ignition and alternating current supply for a gas-and/or vapor discharge lamp

Abstract

Abstract The invention relates to an arrangement for igniting and supplying a discharge lamp, particularly a long low-pressure mercury vapor discharge lamp of about 2.5 meter. Said lamp has a relatively high ignition voltage so that it can not be ignited with the aid of a normal glow discharge starter. According to the invention a circuit is used in which with the aid of a diode branch a voltage doubling is effected at which the lamp can be ignited. In addition this circuit includes a resistor having a positive temperature characteristic which, after ignition of the lamp, renders the diode branch inoperative. By using the voltage doubling, a glow discharge starter can be used which must, however, be proportioned for a voltage which is generally higher than the conventional voltage. The invention relates to an arrangement for the ignition and alternating current supply of at least one gas and/or vapor discharge lamp which includes two electrodes. An arrangement of this kind is generally provided with a stabilizing capacitor which, in the operating condition, is connected in series with the lamp, a series arrangement of a diode and a resistor being provided which in that condition is shunted by a branch including the lamp and is connected in series with the capacitor. A known arrangement of the kind mentioned above is described, for example, in U.S. Pat. No. 2,134,439. A drawback of this known arrangement is that once the value of the resistor arranged in series with the diode is adjusted, the so-called dark period of the lamp is rather long (at a low resistive value of the resistor), or the lamp starts with difficulty (at a high resistive value of this resistor). A long dark period means that the lamp does not emit light during a fairly large fraction of a period of the alternating supply voltage. This is detrimental as regards the luminous value of such a lamp, hence for considerations of efficiency. A difficult or very slow starting discharge lamp is likewise a drawback. An object of the present invention is to obviate or at least to mitigate the mentioned drawbacks. According to the invention an arrangement for the ignition and alternating current supply of at least one gas and/or vapor discharge lamp which includes two electrodes comprises a stabilizing capacitor which in the operating condition is connected in series with the lamp and in which a series arrangement of a diode and a resistor is present which in that condition is shunted by a branch including the lamp and which is connected in series with the capacitor. The invention is characterized in that the resistor is of the type having a positive temperature characteristic which in case of the arrangement being switched on, but the lamp not yet being ignited, has a resistive value which is at most twice the resistance of the shunting lamp branch in the ignited condition of the lamp, and in which in the situation of the lamp being ignited the resistive value of the resistor having a positive temperature characteristic is at least twenty times the resistance of the shunting lamp branch. An advantage of this arrangement is that during the starting operation the resistor having a positive temperature characteristic (P.T.C. resistor) has a relatively low resistive value. As a result the capacitor is charged quickly. This is effected through the diode. A voltage doubling across the lamp electrodes, thus occurring in a next half period of the supply voltage, may then lead to a quick ignition of this lamp. When, however, the lamp is ignited the P.T.C. resistor will exhibit a relatively high resistance value. Consequently, with the lamp ignited, the current flowing through the diode branch is then very low relative to the lamp current. As a result, the situation in the operating condition of the lamp is not much different from that of an ordinary capacitively stabilized lamp circuit. This means that the dark period of the lamp is relatively short and that substantially no direct current components in the operating condition are present in the lamp current. It is feasible that the lamp is not only stabilized through a stabilizing capacitor but through a combination of a capacitor and a coil. This coil might be located, for example, between the capacitor and a supply terminal. It is also feasible that this coil is present in series with the lamp, namely in the so-called shunting lamp branch which is connected in parallel with the series arrangement of the diode and the P.T.C. resistor. One solution to bring the P.T.C. resistor to a highly resistive condition when the lamp is ignited is to utilize the fact that upon the ignition of the lamp the current flowing through the diode branch and hence the current flowing through the P.T.C. resistor is slightly increased. This leads to an extra heating of this resistor so that it achieves a relatively high resistive value. Furthermore it is feasible to realize the high resistive value of the P.T.C. resistor in the operating condition of the lamp is realized by bringing this resistor into close heat contact with the lamp. It can be achieved that in the operating condition the hot lamp heats the P.T.C. resistor in such a manner that it is in the high resistive condition. The gas and/or vapor discharge lamp is, for example, a lamp which is not provided with preheated electrodes. It is, for example, a high-pressure discharge lamp. An arrangement according to the invention preferably serves for igniting and supplying a lamp whose two electrodes are of the preheated type and that those ends of the two lamp electrodes which are remote from the supply are connected together through a glow discharge starter, the ignition voltage of the glow discharge starter being greater than 90 percent of the effective value of the supply voltage. An advantage of this preferred embodiment is that special discharge lamps such as, for example, low-pressure mercury vapor discharge lamps of a type having a relatively high ignition voltage, can be ignited by means of a glow discharge starter. As a rule other provisions, for example, transformers or electronic starters are required for the ignition of this kind of lamp. In a given embodiment of the above-mentioned preferred arrangement the glow discharge starter is proportioned in such a manner that its contact (formed by two electrodes) already close at a power of less than 0.5 Watt. An advantage thereof is that in the situation when the arrangement is switched on but when the lamp is not yet ignited the current flowing through the glow discharge starter and hence the current flowing through the P.T.C. resistor can be maintained low. This has the advantage that the P.T.C. resistor can readily be maintained in its relatively low resistive condition. The following may serve to explain this. In a situation in which a lamp, having preheated electrodes, and a glow discharge starter are used the capacitor charged through the diode and the P.T.C. resistor in the starting situation will always discharge to a slight extent through the glow discharge in the glow discharge starter. Since a balanced state is reached in which the additional charge of the capacitor, is always equal to the discharge of the capacitor the current flowing through the glow discharge starter is actually the same as the current flowing through the P.T.C. rEsistor in that situation. In a special arrangement according to the invention relating to the ignition and supply of a discharge lamp provided with preheated electrodes and a glow discharge starter which connects those ends of the two lamp electrodes which are remote from the supply together and in which the ignition voltage of the glow discharge starter is more than 90 percent of the effective value of the supply voltage and in which the glow discharge starter already closes at a power of less than 0.5 Watt, the arrangement is preferably intended for connection to a voltage supply of approximately 220 Volts and the lamp is a low-pressure mercury vapor discharge lamp having an operating voltage of approximately 180 Volts while the ignition voltage of the glow discharge starter is more than 230 Volts. An advantage of the last-mentioned preferred arrangement is that such a known low pressure mercury vapor discharge lamp, having a length of about 2.5 meters, can be ignited and supplied in a simple manner. In a further preferred embodiment of an arrangement according to the invention the thermal capacity of the P.T.C. resistor is so small that when the arrangement is switched on, but after the lamp is extinguished, within 5 seconds after said extinguishment the temperature of the resistor will have decreased so far that the resistive value of said resistor is at most twice the resistance of the shunting lamp branch in the ignited condition of the lamp. An advantage of this prefered embodiment becomes manifest when considering the case where the operating lamp is switched off and is immediately thereafter switched on again. In that case the temperature of the P.T.C. resistor still has a high value so that this resistor is in the so-called high resistive range. When it is ensured that in this situation with the lamp extinguished this resistor has decreased so rapidly in temperature, i.e., within 5 seconds, to a resistive value which is suitable to start the lamp again, an arrangement is obtained which causes the lamp to ignite rapidly after the arrangement has been switched on again. An arrangement according to the invention may be used, for example, for igniting and supplying one discharge lamp. However, it is alternatively possible to ignite and supply a plurality of series-arranged discharge lamps with the aid of an arrangement according to the invention. In a special embodiment of an arrangement according to the invention intended for the ignition and supply of a plurality of series-arranged discharge lamps which are provided with preheated electrodes, each lamp is shunted by a glow discharge starter whose ignition voltage is larger than 0.9.(1/n) times the supply voltage, where n represents the number of series-arranged lamps. An advantage of the last-mentioned embodiment is that when the sum of the ignition voltages of a plurality of discharge lamps closely approximates or exceeds the value of the supply voltage, a simple ignition with the aid of glow discharge starters also is possible. For obtaining a relatively high ignition voltage of the glow discharge starter the electrodes of this starter may consist of, for example, a material having a high work function. In an arrangement according to the invention a glow discharge starter is preferably used whose filler gas mainly consists of hydrogen. An advantage of this starter is that the electrodes need not be

Inventors

• 👤 J Moerkens

Bibliographic Details