Electric lamp and discharge devices: systems – Current and/or voltage regulation – Automatic regulation
Reexamination Certificate
1999-10-22
2001-02-13
Philogene, Haissa (Department: 2821)
Electric lamp and discharge devices: systems
Current and/or voltage regulation
Automatic regulation
C315S291000, C315S2090SC, C315SDIG005, C315S058000
Reexamination Certificate
active
06188184
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a circuit arrangement for igniting and supplying a lamp with a DC current, comprising
input terminals for connection to terminals of a power supply source supplying a DC voltage,
a DC-DC converter coupled to the input terminals and provided with
an inductive element,
a unidirectional element,
a first switching element,
a control circuit coupled to a control electrode of the first switching element for rendering the first switching element conducting and non-conducting at a frequency f,
output terminals for connecting the lamp, and
a first circuit which connects the output terminals during operation and comprises a second switching element and means for rendering the second switching element conducting and non-conducting.
The invention also relates to a compact lamp.
A circuit arrangement as described in the opening paragraph is known from U.S. Pat. No. 5,581,161. In the known circuit arrangement, the DC-DC converter is constituted by a down-converter. The second switching element is conducting immediately after the known circuit arrangement is put into operation. The control circuit renders the first switching element conducting and non-conducting at a frequency f. During operation of the known circuit arrangement, both a first and a second lamp electrode form a part of the first circuit. The inductive element and the first circuit convey current during a first time interval, so that the electrodes of the lamp connected to the circuit arrangement are preheated. At the end of the first time interval, the second switching element is rendered non-conducting, so that the first circuit no longer conveys current. The inductive element subsequently generates an ignition voltage. After ignition of the lamp and during stationary operation, the control circuit renders the first switching element high-frequency conducting and non-conducting, and a lamp connected to the circuit arrangement is fed with a DC current supplied by the down-converter. Since the down-converter consists of only a small number of components, the known circuit arrangement can be manufactured relatively easily and thus also at a low cost.
The amplitude of the ignition voltage is dependent on the instantaneous amplitude of the current in the inductive element when the second switching element becomes non-conducting. In practice, the DC-DC converter is often operated in the discontinuous mode so as to limit switching losses. This means that the current through the inductive element in each period associated with the frequency f becomes substantially equal to zero during a given time interval. By rendering the first switching element conducting while the current in the inductive element is substantially zero, a considerable power dissipation in the unidirectional element is prevented so that the circuit arrangement has a relatively high efficiency. If the second switching element becomes non-conducting when the current in the inductive element is substantially zero or has a relatively low instantaneous amplitude, the energy present in the inductive element is insufficient to generate an ignition voltage with a sufficiently high amplitude. This problem could be solved by implementing the means for rendering the second switching element conducting and non-conducting in such a way that these means render the second switching element non-conducting when the instantaneous amplitude of the current in the inductive element has a relatively high value. Such an implementation of the means for rendering the second switching element conducting and non-conducting would, however, render the circuit arrangement relatively complicated and expensive.
SUMMARY OF THE INVENTION
It is an object of the invention to provide a relatively simple and, hence, low-cost circuit arrangement for igniting and supplying a lamp with a DC current, with which the lamp can be ignited in an efficient and reliable manner.
According to the invention, a circuit arrangement of the type described in the opening paragraph is therefore characterized in that the control circuit is provided with a circuit section I for decreasing the frequency f after ignition of the lamp.
A relatively high value of the frequency for igniting the lamp causes the DC-DC converter to be operated in the continuous mode in this phase of the lamp operation, and the current in the inductive element is constituted by the sum of a DC component having a relatively high amplitude and an AC component having a relatively low amplitude. At such a shape of the current in the inductive element, the instantaneous value of the amplitude of this current is high enough at any instant to generate an ignition pulse having a sufficiently high amplitude for igniting the lamp in the case when the second switching element becomes non-conducting at that instant.
By choosing the frequency f for igniting the lamp to be relatively high, it is also ensured that, if breakdown of the plasma of the lamp occurs during the period when the first switching element is non-conducting, this first switching element is rendered conducting again for only a relatively short time interval after the occurrence of the breakdown, so that the lamp can convey a current while the charge carriers formed by the breakdown are still present in the plasma. This results in a satisfactory take-over behavior of the lamp. After igniting the lamp, the circuit section I decreases the frequency f. The frequency f after ignition of the lamp may be chosen such that the DC-DC converter is operated in the discontinuous mode so that the switching losses during stationary supply of the lamp are relatively low. The highest efficiency is achieved if the current in the inductive element becomes zero for a very short time during each period associated with the frequency f. Since the time interval between the instant when the circuit arrangement is put into operation and the ignition of the lamp is often relatively short in practice, the switching losses occurring in the DC-DC converter upon operation in the continuous mode do not give rise to the occurrence of relatively high temperatures which might damage components of the DC-DC converter.
Satisfactory results have been obtained with embodiments of a circuit arrangement according to the invention, in which the DC-DC converter comprises a down-converter.
The unidirectional element may be realized in a relatively simple and, hence, low-cost manner if the unidirectional element comprises a diode.
It is possible to implement the second switching element as a semiconductor switching element and to realize the means for rendering this semiconductor switching element consecutively conducting and non-conducting with the aid of a second control circuit which is coupled to a control electrode of the semiconductor switching element. However, if the second switching element is implemented as a glow discharge starter, a separate control circuit is not necessary for realizing the consecutive conductance and non-conductance of the second switching element. The circuit arrangement thus comprises a relatively small number of components and can therefore be manufactured in a relatively simple way and at low cost.
To enhance the ignition behavior of a lamp operated by means of a circuit arrangement according to the invention, it is possible to implement the circuit arrangement in such a way that the first circuit comprises a lamp electrode during operation.
When the second switching element is conducting, the current flowing through the first circuit also flows through this lamp electrode so that it is preheated. Since the lamp is fed with a DC current after ignition, a considerable improvement of the ignition behavior can be achieved if only the lamp electrode, which constitutes the cathode of the lamp during stationary operation, is preheated.
It has been found that the circuit arrangement according to the invention is particularly suitable for use in the ballast circuit of a compact lamp comprising
a light-transmissive discharge vessel having a filling comprising
Eberson Etienne N. K. P. M.
Marinus Antonius A. M.
Franzblau Bernard
Philogene Haissa
U.S. Philips Corporation
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