AU2013273732A1 - High Intensity Discharge Lamp Circuit - Google Patents

Abstract

3219G-AU A power control circuit for a high intensity discharge lamp L is disclosed in which a switch S2 interconnects a control reactor Z2, a bidirectional current controller, such as a triac T, and a tapped main ballast Z1D and Z1E. With the switch S2 in the position illustrated in Figs. 3 and 4, the triac T controls an additional shunt current which is added to the current through the main ballast to augment the lamp current and thus increase the lamp brightness. However, with the switch S2 in the other position, the lamp ballast is formed by the series parallel impedance combination of Z1D, Z1E and Z2. The power control circuit finds particular application in the progressive installation of electronic current control circuits in an installation of many lamps. 1(3 c~jt~oc.~cAIr Le 0LA T--ko1. cizc0 (opilgo(- cipgCOIT C

Description

3219G-AU AUSTRALIA Patents Act 1990 COMPLETE SPECIFICATION FOR A PATENT Name of Applicant(s): TRESTOTO PTY LIMITED Actual Inventor(s): Donat Witold MAJEWSKI Andrew Don MAJEWSKI Shane Peter MAJEWSKI Address for Service: FRASER OLD & SOHN Patent Attorneys PO Box 560 MILSONS POINT NSW 1565 Invention Title: High Intensity Discharge Lamp Circuit Details of Associated Provisional Applications: 2012 905 553 Dated 19 December 2012 The following statement is a full description of this invention, including the best method of performing it known to us: 1 3219G-AU HIGH INTENSITY DISCHARGE LAMP CIRCUIT Field of the Invention The present invention relates to high intensity discharge lamps and, in particular, to a power control circuit for controlling the power supplied to such lamps, and consequently their brightness. Background Art It is known to provide high intensity discharge lamps with a power control circuit and an electronic control circuit which controls the power supplied to the lamp. There is a simple changeover switch which reverts the lamp to the full power and which is used, for example, in the event of a failure of the electronics. Such power supply circuits are very desirable in the event of the refurbishment of a large installation with a large number of lamps where the refurbishment requires the lamps to be operated by the conventional reactor ballast until the whole conversion is completed, at which time the electronic control is implemented for the whole installation. Genesis of the Invention The genesis of the invention is a desire to simplify such power supply circuits. Summary of the Invention In accordance with an aspect of the present invention there is disclosed a power control circuit for a discharge lamp, said circuit comprising: a main reactor having a first and second windings connected in series, said series connection being connectable with said lamp across an AC supply; a control reactor, a switch having two positions, and a bidirectional current controller, said switch being connected to the junction of said first and second windings, to said current controller, and to said control reactor; whereby with said switch in its first position, said current controller and said control reactor are connected in series with each other and in parallel with said main reactor, and with said switch in its second position, said current controller is disconnected from said control reactor, and said control reactor is connected to said junction of said first and second windings, such that with said switch in said first 2 3219G-AU position said bidirectional current controller controls an additional shunt current supplied to said lamp to increase the brightness thereof, and with said switch in said second position, said first and second windings and said control reactor all conduct with only said first winding conducting all of the lamp current. Brief Description of the Drawings Preferred embodiments of the present invention will now be described with reference to the drawings in which: Fig. 1 is a circuit diagram of a first prior art power control circuit, Fig. 2 is a circuit diagram of a second prior art power control circuit, Fig. 3 is a circuit diagram of a power control circuit in accordance with a first embodiment of the present invention, Fig. 4 is a modification of the power control circuit of Fig. 3 in which the reactor interconnections are flipped over to form a mirror image, Fig. 5 is a circuit diagram of a still further embodiment in which the reactor windings are created as a single physical unit, and Fig. 6 is a schematic perspective view of the single physical unit. Detailed Description It is to be understood in relation to the circuit diagrams of Figs. 1-4 that for the sake of clarity various circuit components usually present have been omitted. Such omitted circuit components include an igniter, a power factor correction capacitor, control circuitry for the triac, and so on. In Fig. 1, a high intensity discharge lamp L is connected across an AC mains supply S in series with a main reactor or ballast Z1 which supplies the necessary impedance to operate the lamp L at the minimum lamp power required. A control reactor Z2 is connected in parallel with the main ballast Z1 via a bidirectional current controller in the form of a solid state switch such as a triac T. The current controller T allows the lamp wattage, and hence brightness, to be varied by allowing some additional shunt current to flow through the control reactor Z2 which is added to the lamp current. The amount of the additional current is governed by the impedance of the control reactor Z2 and by the turn on phase position of the triac T each half cycle. The control of the 3 3219G-AU triac T is in turn accomplished by means of a known control circuit C which derives its phase information and bias voltages from the mains supply S. Alternatively, the control circuit C can be isolated from the mains supply S by means of opto isolation, for example, as illustrated in Fig. 5. An alternative to the prior art circuit of Fig. 1, is the prior art circuit of Fig. 2. In this arrangement, the circuit of Fig. 1 is modified so that the main reactor incorporates two windings ZiA and Z1B. A two pole change-over switch Si as illustrated is connected to the first winding ZlA of the main reactor and to the triac T. With the switch Si in the position illustrated, the electronic control of the lamp wattage is as for the circuit of Fig. 1. However, with the switch Si in the other position, current only flows through the main reactor second winding ZiB for full power reactor ballasting. The prior art circuit of Fig. 2 has the advantage that the lamp can be switched between conventional operation using only ZiB as a ballast, and the electronic control of lamp power in the same manner as in the circuit of Fig. 1. This prior art circuit of Fig. 2 has a number of disadvantages including that the second winding ZiB of the main reactor is quite large as it must be dimensioned to meet the thermal limits of its insulation system and the starting and operating current requirements of the high intensity discharge lamp L when using only the winding ZiB for full power operation as a reactor ballast. In addition, the first winding ZiA needs to be provided on the same core to achieve the required impedance, that is the total impedance of ZiA and ZiB should be equivalent to the impedance of Z1 of Fig. 1. The overall effect, to provide the full power reactor operation using the circuit of Fig. 2, is that the size of the main ballast or reactor (ZiA and Z1B) has to be about 50% larger than the main ballast Z1 for just electronic control as in Fig. 1. Turning now to Fig. 3, here the main reactor again incorporates two windings ZiD and ZiE. The triac T, its control circuit C and the control reactor Z2 are the same as 4 3219G-AU for the circuit of Fig. 2. However, a single throw switch S2 is used to interconnect the triac T, the central tapping of the main reactor, and the control reactor Z2. With the switch S2 in the position illustrated in Fig. 3, the total impedance of the main reactor Z1D and Z1E is equivalent to the impedance of the second winding Z1B of the main reactor of the circuit of Fig. 2. That is, with the switch S2 in the position illustrated in Fig. 3, electronic control of the power supplied to the lamp L is accomplished via the triac T. Again additional shunt current flows through the control reactor Z2 and this is added to the current flowing through the main reactor Z1D and Z1E to increase the lamp current. However, with the switch S2 thrown to the other position, the impedances Z1E and Z2 are connected in parallel and the main reactor Z1D and Z1E also acts as an autotransformer. Thus under these conditions, all three windings Z1D, Z1E and Z2 are being used for the full power reactor ballasting. Although under these circumstances, the winding Z1D, which is only a small portion of the main reactor, must now carry full lamp current, the other winding Z1E carries a substantially reduced current (because it is in parallel with the control reactor Z2). The overall effect is to enable the main reactor to be made with lower losses and about the same material content as the main reactor Z1 of the circuit of Fig. 1. This is to be contrasted with the prior art arrangement of Fig. 2 where the main reactor must be made approximately 50% larger than the main reactor Z1 of the circuit of Fig. 1. In addition, there is also an added benefit in that only a single pole change-over switch or contactor S2 is required and it needs to carry only a reduced current (typically less than 50%) compared to the main reactor switching contacts of the switch Si in Fig. 2. This benefit is of particular importance if the switch is to be realised by electronic components rather than by a mechanical switch. Turning now to Fig. 4, this is essentially the same circuit as for Fig. 3 except that the 4 components interconnected by the switch S2 have been flipped over horizontally so as 5 3219G-AU to create a mirror image of the circuit of Fig. 3. However, the operation of the circuit of Fig. 4 is the same as the operation of the circuit of Fig. 3. Turning now to Figs. 4 and 5, it is possible to fabricate all the reactance is in a manner which enables them to be assembled as a single piece. The circuit diagram which illustrates this arrangement is provided in Fig. 4 and a schematic perspective view of the assembled completed unit is illustrated in Fig. 5. In this arrangement, the main reactor Z1 with its tapping and the smaller control reactor Z2 are joined having a combined magnetic circuit fabricated from laminations. During normal operation, the main reactor Z1D and Z1E and the control reactor Z2 have independent magnetic circuits even though the two parts are physically connected. During transient conditions, however, when one of the main cores can saturate, the stray magnetic field can utilise the steel from the other control component and thereby increase the inductance which reduces the transient peak currents. The foregoing describes only two embodiments of the present invention and modifications, obvious to those skilled in the art, can be made thereto without departing from the scope of the present invention. For example, whilst the current controlling device of Figs. 1-4 is shown as a triac T, many other types of current controlling devices such as SCRs, transistors, and the like can be used instead. The term "comprising" (and its grammatical variations) as used herein is used in the inclusive sense of "including" or "having" and not in the exclusive sense of "consisting only of'. 6

Claims (7)

1. A power control circuit for a discharge lamp, said circuit comprising: a main reactor having a first and second windings connected in series, said series connection being connectable with said lamp across an AC supply; a control reactor, a switch having two positions, and a bidirectional current controller, said switch being connected to the junction of said first and second windings, to said current controller, and to said control reactor; whereby with said switch in its first position said current controller and said control reactor are connected in series with each other and in parallel with said main reactor, and with said switch in its second position, said current controller is disconnected from said control reactor, and said control reactor is connected to said junction of said first and second windings, such that with said switch in said first position, said bidirectional current controller controls an additional shunt current supplied to said lamp to increase the brightness thereof, and with said switch in said second position, said first and second windings and said control reactor all conduct with only said first winding conducting all of the lamp current.

2. The circuit as claimed in claim 1 wherein said first winding is connected to one side of said current controller and said switch is connected to the other side of said current controller.

3. The circuit as claimed in claim 2 wherein said control reactor has one side connected to said second winding and the other side connected to said switch.

4. The circuit as claimed in claim 3 wherein the junction of said control reactor and said second winding is connected to said lamp.

5. The circuit as claimed in claim 4 wherein the junction of said control reactor and said second winding is connected to said AC supply.

6. The circuit as claimed in any one of claims 1-5 wherein said main reactor functions as an autotransformer with said switch in said second position. 7 3219G-AU

7. The circuit as claimed in any one of claims 1-6 wherein said main reactor and said control reactor are assembled as a single physical unit. Dated this 1 9 th day of December 2013 TRESTOTO PTY LIMITED By: FRASER OLD & SOHN Patent Attorneys for the Applicant 8