Electric lamp and discharge devices: systems – Surge generator or inductance in the supply circuit – Circuit interrupter in the inductance circuit
Reexamination Certificate
1999-10-22
2001-03-06
Philogene, Haissa (Department: 2821)
Electric lamp and discharge devices: systems
Surge generator or inductance in the supply circuit
Circuit interrupter in the inductance circuit
C315S240000, C315S2090SC, C315S307000, C315SDIG005
Reexamination Certificate
active
06198232
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
a first inductive element,
a first 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 first 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 first inductive element subsequently generates an ignition voltage. After ignition of the lamp and during stationary operation, the second switching element remains non-conducting and 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 low cost. A drawback of the known circuit arrangement is, however, that the first inductive element must be dimensioned in such a way that the lamp ignites reliably and rapidly. Since the first inductive element also conveys current during stationary operation of the lamp, the power losses occurring in the first inductive element during stationary operation should be relatively low. For these reasons, the first inductive element is often relatively large in practice and is expensive. Moreover, the ignition process-dictated dimensioning of the first inductive element is often not optimal for stationary lamp operation.
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 as described in the opening paragraph is therefore characterized in that the first circuit comprises a series arrangement of the second switching element, a second inductive element and a second unidirectional element, and the series arrangement of the second inductive element and the second unidirectional element is shunted by a second circuit comprising a third unidirectional element.
During the period when the second switching element is conducting, both the first and the second inductive element convey current. For this reason, the quantity of energy which is available for generating an ignition voltage across the lamp when the second switching element becomes non-conducting is equal to the sum of the energy in the first inductive element and the energy in the second inductive element. However, during stationary operation of the circuit arrangement, only the first inductive element conveys a current. For this reason, it is possible to choose the first inductive element optimally for stationary operation and independently of the energy required for ignition to be (relatively) small. The first and the second inductive element may be alternatively chosen to be such that the control circuit renders the first switching element conducting and non-conducting in the same way and at the same frequency f during the different phases of the lamp operation before and after ignition of the first switching element, so that the control circuit may be implemented in a relatively simple way. Moreover, only the first inductive element is to comply with the requirement that power losses occurring in this inductive element should be relatively small. The second inductive element may be dimensioned in such a way that a reliable ignition behavior is realized. Since the second inductive element conveys a current for a relatively short time only before ignition of the lamp, considerably less stringent requirements may be imposed with respect to the power losses occurring in the second inductive element than is the case for the first inductive element. A circuit arrangement according to the invention may thus be considerably cheaper at a given total inductance of both the first and the second inductive element.
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.
The amplitude of the ignition voltage is dependent on the instantaneous amplitude of the current in the inductive elements 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 first inductive element and the second inductive element in each period associated with the frequency f becomes substantially equal to zero during a given time interval and before the lamp is ignited. By rendering the first switching element conducting while the current in the first and the second 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. However, if the second switching element becomes non-conducting when the current in the inductive elements is substantially zero or has a relatively low instantaneous amplitude, the energy present in the inductive elements 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 elements 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. It has been found to be advantageous to provide the control
Eberson Etienne N. K. P. M.
Marinus Antonius A. M.
Oostvogels Ludovicus F. J.
Van Den Berg Arjan J.
Franzblau Bernard
Philogene Haissa
U.S. Philips Corporation
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