The present invention relates in general to the field of drivers for gas discharge lamps, more specifically high-intensity discharge (HID) lamps.
Conventionally, gas discharge lamps are driven by CuFe ballasts. Also, electronic drivers have been developed, which offer advantages such as higher operational frequency and improved efficiency.
Gas discharge lamps are designed for a specific nominal power, and drivers for such lamps need to be designed for the required power specification. Up till now, electronic drivers for gas discharge lamps having nominal power of, for instance, 50 W, 150 W, 250 W, 400 W, 600 W are available. Gas discharge lamps having very high power, for instance 1800 W, are nowadays still driven by CuFe ballasts. However, it is desirable that these lamps are also driven by electronic drivers. Thus, there is a need for high-power electronic drivers for gas discharge lamps, specifically HID lamps.
Although low-power or medium-power electronic drivers for gas discharge lamps have been developed, it is not easily possible to develop a high-power electronic driver. For instance, it is not simply possible to scale-up existing designs. A high-power electronic driver should be developed from the basic drawing board, which takes a lot of time and is quite costly. Further, components to be used for such high-power electronic driver involve high-power components, which are expensive.
An objective of the present invention is to provide an electronic driver apparatus for high-power gas discharge lamps. According to an important aspect of the present invention, an electronic driver apparatus is designed as an electronic driver assembly comprising a plurality of low-power electronic drivers connected in parallel. Thus, the present invention advantageously uses existing low-power electronic drivers, which are relatively low-cost since they are manufactured in large volumes. Further, development of low-power electronic drivers has advanced very far already, so that these components are very reliable.
These and other aspects, features and advantages of the present invention will be further explained by the following description with reference to the drawings, in which same reference numerals indicate same or similar parts, and in which:
FIGS. 4B-D are block diagrams schematically illustrating synchronisation details of specific embodiments of a driver assembly in accordance with the present invention;
FIGS. 5A-D are block diagrams schematically illustrating safety control details of specific embodiments of a driver assembly in accordance with the present invention;
A second stage 3 has an input receiving the DC voltage from the pre-conditioner, and has an output connected to the lamp L. This second stage, also indicated as forward commutator, is designed for generating an alternating DC current at its output, i.e. a current having substantially constant magnitude but alternating direction.
The first driver 1A has input terminals 11a and 11b. The second driver 1B has input terminals 12a and 12b. The third driver 1C has input terminals 13a and 13b. In a first variation, the three drivers are fed from the same mains, for instance 230 V one-phase mains, so that terminals 11a, 12a, 13a are connected together and terminals 11b, 12b, 13b are connected together. An advantage of this variation is that the assembly 10 can be powered from common one-phase mains. It is also possible that terminals 11a, 12a, 13a are connected to one phase of a three-phase mains, and that terminals 11b, 12b, 13b are connected to another phase of this three-phase mains; an advantage is that the voltage available between two phases of a three-phase mains is higher than the voltage available between one phase and neutral.
In a second variation, the three drivers are fed from the three phases of a three-phase mains. In the following, the three phases of a three-phase mains will be indicated as P1, P2, P3, respectively, while the neutral conductor will be indicated as N. In one implementation, the drivers are always connected between one phase and neutral (star configuration); for instance, terminals 11a, 12a, 13a are connected to phases P1, P2, P3, respectively, whereas terminals 11b, 12b, 13b are connected to N. In another implementation, the drivers are always connected between two subsequent phases (triangle configuration); for instance, terminals 11a, 12a, 13a are connected to phases P1, P2, P3, respectively, whereas terminals 11b, 12b, 13b are connected to phases P2, P3, P1, respectively.
Using more than one phase has the advantage of increased reliability. If one of the phases fails, the system can continue operating at a lower power level. The star configuration has the advantage that the mains current is sinusoidal and that, during normal operation, the neutral line carries no current. The triangle configuration has the advantage that the resulting pre-conditioner output voltage is substantially higher, which makes this implementation specifically suitable to operate high voltage burners.
It is to be noted, however, that the present invention is not limited to an assembly design comprising three drivers. A driver assembly in accordance with the present invention may have two, or four or more drivers connected in parallel. In the case of the first variation, all pre-conditioner inputs are connected in parallel. In the case of the second variation, it is preferred that the number of drivers can be written as 3·N, wherein N is an integer, and that always N pre-conditioner inputs are connected in parallel.
In the simplest implementation, the individual drivers 1A, 1B, 1C, . . . are operating autonomously, i.e. independent from each other. However, since such independent operation may lead to problems and even failure, such is not preferred. Preferably, there is some operative coupling between the individual drivers 1A, 1B, 1C, This operative coupling may relate to one or more of the following aspects:
As is known to persons skilled in the art, drivers 1A, 1B, 1C, . . . are normally provided with a built-in ignitor device (not shown in
In one possibility, only one ignitor of only one of said individual drivers is active, while all other ignitors are made inactive. One problem of this solution is, however, that now one single ignitor needs to be capable of handling the overall current of the entire driver assembly circuit.
In another possibility, individual ignitor devices are disconnected, and their outputs are connected together, such that these ignitor device together define one large ignitor.
In a preferred embodiment, the individual drivers 1A, 1B, 1C, . . . are designed without individual ignitors, i.e. they are ignitorless drivers, and the driver assembly 10 is provided with a common ignitor 41 between the lamp L and the output node 40 of the forward commutator stages 31, 32, 33 . . . , as illustrated in
Synchronisation
The individual pre-conditioners need not be mutually synchronised, mainly because, at least under normal circumstances, their output is a constant output voltage, wherein internal timings within the individual pre-conditioners do not play any role of importance. In contrast, the individual forward commutator stages 31, 32, 33 provide individual AC current contributions to the overall lamp current, each of such individual AC current contributions being characterised by the current curve of
For driving the switches, the switch driver 54 can operate in several possible modes. Hereinafter, one possible mode of operation will be explained by way of example only. In this one mode of operation, the switch driver 54 is either in a first operative state or in a second operative state. In the first operative state, the switch driver 54 generates its output signals such that second switch 52 is continuously non-conductive while first switch 51 is switched from its conductive state to its non-conductive state at a relatively high frequency, in which case current flows from high voltage level supply line VH via output filter 58 into lamp output terminal 55. In the second operative state, the switch driver 54 generates its output signals such that first switch 51 is continuously non-conductive while second switch 52 is switched from its conductive state to its non-conductive state at a relatively high frequency, in which case current flows from lamp output terminal 55 via output filter 58 to low voltage level supply line VL. The switch driver also has an OFF state, in which both switches 51 and 52 are continuously non-conductive. The switch driver 54 in turn has a control input 54a coupled to a control output 53b of a timing controller 53, which generates a control signal Sc for the switch driver 54, the control signal Sc having two signal values causing the switch driver 54 to operate in either its first operative state or in its second operative state, respectively. The timing of this control signal Sc determines the timing of the positive and negative commutation periods of the output current.
FIGS. 4B-D illustrate various embodiments in which synchronisation is implemented. In these Figures, individual switches 51, 52, switch drivers 54, and timing controllers 53 of the three commutators 31, 32, 33 are shown, distinguished by indexes 1, 2, 3, respectively.
In the embodiment of
In the embodiment of
In the embodiment of
An advantage of the embodiment of
An advantage of the embodiments of
Distribution of Power
Ideally, each individual driver 1A, 1B, 1C provides the same current magnitude. If manufacturing tolerances are such that one or more drivers provide substantially less than nominal power, one or more of the other drivers need to provide substantially more than their nominal power in order to meet the demand of the lamp L. However, in well-designed drivers which are well-set, mutual deviations in current magnitude are not severe, and control measures are not needed in this respect.
Safety
Typically, a driver for a gas discharge lamp is provided with safety control circuitry, which monitors one or more operational parameters of the driver, and which is capable of switching OFF such driver in case it finds that anomalies exist. Typical operational parameters which are monitored are, for example, temperature and current magnitude. For instance, the driver is switched OFF if the current magnitude is so high that a short circuit must be present, or if the temperature of the driver rises beyond a safety level. Also, if the driver does not generate current at all, it is decided that something is wrong and the driver is switched OFF.
Such switching OFF is intended to prevent (further) damage to the driver. However, in a driver assembly comprising two or more driver units, switching OFF one driver unit may be very disadvantageous to one or more of the other driver units, because now these other driver units need to generate more current than nominal current. Typically, driver units are provided with protection means for limiting the output current to a certain maximum. Depending on the total number of driver units, the drivers may be caused to generate their maximum output current, and the overall current as received by the lamp may be less than nominal lamp current, which may lead to failure of the lamp.
According to the present invention, this problem is solved by designing safety control circuitry for drivers in a driver assembly such that all drivers are automatically switched OFF if the safety control circuitry decides that even one individual driver should be switched OFF.
Several configurations are possible, which will be explained in the following with reference to FIGS. 4A and 5A-D. By way of example, the parameter “temperature” will be discussed, but it should be clear that the same discussion applies, mutatis mutandis, to other parameters like current magnitude etc.
In a case where all forward commutators 31, 32, 33 would have such individual safety control circuitry including an individual temperature sensor and an individual safety controller, and where all individual safety controllers would be operating independently, the above-mentioned disadvantages would arise.
Thus, in the configuration of
The overall SWITCH-OFF signal SOFF of the main safety controller 70 may be sent to corresponding inputs 62a1, 62a2, 62a3 of the individual safety controllers 621, 622, 623, which are designed, in response to receiving the overall SWITCH-OFF signal SOFF, to generate their individual SWITCH-OFF signals for the corresponding switch drivers 541, 542, 543, as also illustrated in
It is noted that the OR-gates 631, 632, 633 may be omitted, and that the safety control inputs 54d1, 54d2, 54d3 of the switch drivers 541, 542, 543 may only receive the overall SWITCH-OFF signal SOFF from the main safety controller 70, in which case the safety control of the assembly 10 is performed solely by the single main safety controller 70. In this case, also the individual safety controllers may be omitted.
It is further noted that, as an alternative to the embodiment of
In another embodiment, illustrated in
It is noted that, from the above-discussed embodiments of
It should be clear to a person skilled in the art that the present invention is not limited to the exemplary embodiments discussed above, but that various variations and modifications are possible within the protective scope of the invention as defined in the appending claims.
In the above, the present invention is explained for an exemplary embodiment wherein each individual driver has a two-stage design of pre-conditioner and forward commutator. However, instead of the individual drivers 1A, 1B, 1C having a two-stage design of pre-conditioner and forward commutator, it is also possible that the individual drivers have a three-stage design of pre-conditioner, down-converter and commutator.
Further, in the above exemplary embodiment, the forward commutator is shown as a half-bridge embodiment (HBCF). The present invention can, however, also be implemented as a full-bridge embodiment (FBCF). This is illustrated specifically in
The same variation also applies to the embodiments of
In the above, the present invention has been explained with reference to block diagrams, which illustrate functional blocks of the device according to the present invention. It is to be understood that one or more of these functional blocks may be implemented in hardware, where the function of such functional block is performed by individual hardware components, but it is also possible that one or more of these functional blocks are implemented in software, so that the function of such functional block is performed by one or more program lines of a computer program or a programmable device such as a microprocessor, microcontroller, etc.
Number | Date | Country | Kind |
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03102007.6 | Jul 2003 | EP | regional |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/IB04/51068 | 6/30/2004 | WO | 12/29/2005 |