Electric lamp and discharge devices: systems – Periodic switch in the supply circuit – Periodic switch in the primary circuit of the supply...
Reexamination Certificate
1999-03-26
2001-01-30
Wong, Don (Department: 2821)
Electric lamp and discharge devices: systems
Periodic switch in the supply circuit
Periodic switch in the primary circuit of the supply...
C315S362000, C315S313000, C315S307000
Reexamination Certificate
active
06181074
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to an operating circuit for a load. Discharge lamps, chiefly compact fluorescent lamps, come into consideration as the load.
Use is made in discharge lamps of operating circuits and electronic ballasts which can, for example, have a half-bridge oscillator with mains supply via a rectifier and a smoothing capacitor. In this case, the half-bridge oscillator generates a high-frequency AC voltage supply for the flicker-free and low-noise operation of the discharge lamp.
A substantial disadvantage of discharge lamps as against incandescent lamps and halogen incandescent lamps has hitherto consisted in that it has not been possible to implement a dimming function in the case of operating units of discharge lamps. At this juncture, a proposal belonging to the prior art has provided an improvement in which interruptions in the power supply of an operating circuit for a discharge lamp are evaluated and serve to some extent as a trigger signal in order to cause the operating circuit when restarting to operate further in another operating state with a larger or smaller lamp current. It is possible thereby to distinguish and switch two operating states which permit the lamp power to be reduced in a way similar to a dimming function if required. For this prior art, reference is made to EP 0 488 002 B1 and the associated priority application DE 40 37 948.
SUMMARY OF THE INVENTION
Starting from the outlined state of the art, this invention is based on the technical problem of specifying an operating circuit, in particular for discharge lamps, having operating states which can be switched by power supply interruptions, and having a circuit design which is further developed with respect to the properties of use by comparison with the cited prior art.
According to the invention, this problem is solved by a circuit for operating a load, in particular a discharge lamp, having an operating state storage device for storing a variable representing an operating state of the load, and having a changeover device for switching over between a plurality of operating states of the load, which is activated in the case of each relatively short interruption of the power supply of the operating circuit, and switches over into an operating state other than that represented by the stored variable, defined by a timer circuit separate from the operating state storage device, for defining a specific time for distinguishing relatively long interruptions of the power supply from the relatively short ones, the changeover device being activated by relatively long interruptions so as to switch into a fixed initial operating state.
Thus, it is provided according to the invention to distinguish power supply interruptions in accordance with their period. In this case, unlike the relatively short ones, relatively long interruptions do not lead to a changeover operation into another operating state, but to restarting in an operating state uniquely fixed independently of the previous operating state.
It is true that the cited EP 0 488 002 B1 already mentions such a stipulated aim, specifically switching over the bistable changeover system there into the initial state. However, this document provides no data on an approach to a technical solution for implementing this function.
Proceeding from this known stipulated aim, it could be considered obvious to start by attempting to design the store, which is intended to store the last operating state via a power supply interruption, in such a way that, starting from a certain time threshold, it loses the last operating state as its store contents. It would have to be ensured in this case that the loss of the store contents led to a defined initial state of the store. It would therefore be obvious to make use as operating state store of a capacitor which discharged in the case of a power supply interruption and which always had the “empty” state starting from a certain period of power supply interruptions.
The invention is based on the idea that in the case of this obvious approach two functions which should advantageously be realized separately are combined in one device. Consequently, the invention provides to separate the function of “store operating state” and the function of “define time threshold for power supply interruptions”, that is to say to provide a timer circuit separate from an operating state storage device.
Advantages of this solution consist, for example, in that it is possible to make use for the operating state storage device of a store which emits a discrete, and thus always well defined output signal, relating to the operating state. This cannot be done straight away with a storage device which is intended to implement the timer function simultaneously and whose store contents must therefore “decay” with time.
A further advantage can be yielded when the output variable of the operating state storage device is used as desired value or to generate a desired value. If the timer function were then to be integrated in the operating state storage device, the outcome would be that in the case of short power supply interruptions the variable stored in the operating state storage device would scarcely have altered. However, since the aim is to switch over into another operating state after a short power supply interruption, this stored variable would no longer be suitable as desired value or for forming such a value.
In the solution according to the invention, by contrast, the separation of the timer circuit from the operating state storage device may have the effect, for example, of simultaneously making the timer circuit into a store for the operating state which comes after a short power supply interruption in the future, it being the case, however, that the variable stored in the actual operating state storage device serves for forming the desired value. However, it is also possible for a device which is switched over automatically by a trigger signal in the event of any power supply interruption to be used as the operating state storage device. By means of a defined resetting signal, said device can then hold as store contents the variable corresponding to the initial operating state. The resetting signal is triggered when the timer circuit determines a relatively long interruption of the power supply.
Overall, the solution according to the invention yields improved possibilities of circuit design which lead via the unique initial operating state after relatively long power supply interruptions to a greater convenience of operation and, in the way just outlined, to more reliable and more serviceable circuit designs.
It is preferably provided in the case of this invention that the timer circuit is of capacitive design and, specifically, has a smoothing electrolytic capacitor which is provided in many instances in any case on the output side of a mains rectifier and supplies the operating circuit. This smoothing electrolytic capacitor is then recharged in any case during operation by the mains rectifier and discharged in the event of power supply interruptions, with the result that its state of charge can be used to define time.
The discharging of the smoothing electrolytic capacitor in the event of interruption of the power supply can be performed in the case of a simple circuit variant by consumption currents of circuit components which are present in any case, for example by a consumption current of the operating state storage device. This discharging operation is prescribed in any case by the circuit design, and therefore offers an advantageous configuration—if the simplicity of the circuit is a leading concern.
On the other hand, the consumption currents are frequently relatively poor reference variables, because they are affected by manufacturing tolerances or can be strongly dependent on temperature, for example owing to the temperature dependence of the leakage currents. An improved variant of the invention therefore provides a separate discharge resistor which, together with the smoothing electrolytic capacit
Bessone Carlo S.
Patent-Treuhand-Gesellschaft Fuer Elektrische Gluehlampen MBH
Vo Tuyet T.
Wong Don
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