Electric lamp and discharge devices: systems – Pulsating or a.c. supply
Reexamination Certificate
2000-05-11
2001-09-25
Wong, Don (Department: 2821)
Electric lamp and discharge devices: systems
Pulsating or a.c. supply
C315S247000, C315S224000, C315S2090SC, C315S291000
Reexamination Certificate
active
06294882
ABSTRACT:
The invention relates to a circuit arrangement for feeding a discharge lamp, comprising
input terminals to be connected to a power supply source supplying a low-frequency alternating voltage,
rectifier means coupled to the input terminals for rectifying the low-frequency alternating voltage, and provided with a first output terminal and a second output terminal,
a first branch which comprises a series arrangement of a first buffer capacitance and a second buffer capacitance, and which interconnects said output terminals,
a load branch which comprises a series arrangement of a first inductive element and clamps for holding a discharge lamp, and a first end of which is coupled to a common point of the two buffer capacitances,
a first switching element coupled to the load branch,
a second switching element coupled to the load branch,
a control circuit coupled to a control electrode of the first switching element and to a control electrode of the second switching element for rendering the first switching element alternately conducting and non-conducting, while the second switching element is non-conducting, and for rendering the second switching element alternately conducting and non-conducting, while the first switching element is non-conducting,
a first unidirectional element and a second unidirectional element coupled to the load branch.
Such a circuit arrangement is well known. The known circuit arrangement is a full half bridge. The lamp current generated by the known circuit arrangement is a low-frequency square-wave alternating current. During a first half period of the low-frequency square-wave alternating current, the control circuit renders the first switching element alternately conducting and non-conducting with a frequency which is much higher than that of the low-frequency alternating current, while the second switching element is maintained non-conducting by the control circuit. As a result thereof, a part of the components, namely the first switching element, the first inductive element and the first unidirectional element, of the full half bridge circuit function as a down-converter type DC-DC converter. As a result, the lamp current during this first half period of the low-frequency square-wave alternating current is a direct current in a first direction with a substantially constant amplitude. During a second half period of the low-frequency square-wave alternating current, the control circuit renders the second switching element alternately conducting and non-conducting with a frequency which is much higher than that of the low-frequency direct current, and the first switching element is maintained non-conducting. During this second half period, the second switching element, the second unidirectional element and the first inductive element jointly form a down-converter type DC-DC converter. As a result, the lamp current during the second half period of the low-frequency square-wave alternating current is a direct current of substantially constant amplitude in a second direction opposed to the first direction. It has been found that the low-frequency square-wave alternating current yields a favorable lamp operation without visible flicker, particularly in the case of HID lamps, while also the electrodes of the lamp are uniformly loaded. A drawback of the known circuit arrangement resides in that the circuit arrangement almost only takes current from the voltage supply source if the alternating current supplied by the voltage supply source has a high amplitude. As a result, the known circuit arrangement has a low power factor.
It is an object of the invention to provide a circuit arrangement with which a discharge lamp can be fed by means of a low-frequency square-wave current, and which circuit arrangement has a relatively high power factor.
To achieve this, a circuit arrangement as mentioned in the opening paragraph is characterized in accordance with the invention in that the circuit arrangement is further provided with
a third unidirectional element coupled between the first output terminal and the first buffer capacitance,
a fourth unidirectional element coupled between the second output terminal and the second buffer capacitance,
a second inductive element a first end of which is coupled to a first end of the first inductive element, which end faces the lamp clamps,
a first capacitive element coupled between a first tapping point of the first conductive element and the second output terminal,
a second capacitive element coupled between a tapping point of the second inductive element and the first output terminal, and wherein the first switching element is coupled between a second end of the first inductive element and a common point of the third unidirectional element and the first buffer capacitance, wherein the second switching element is coupled between a second end of the second inductive element and a common point of the fourth unidirectional element and the second buffer capacitance, and wherein the first unidirectional element is coupled between the second end of the first inductive element and a common point of the fourth unidirectional element and the second buffer capacitance, and the second unidirectional element is coupled between the second end of the second inductive element and a common point of the third unidirectional element and the first buffer capacitance.
The first and the second capacitive element serve as power feedback capacitors. If the first switching element is rendered alternately conducting and non-conducting with a frequency f
1
by the control circuit, the first capacitance is charged with the same frequency by means of a current supplied by the supply voltage source and, subsequently, discharged by means of a current charging the first buffer capacitance. If the second switching element is rendered alternately conducting and non-conducting with a frequency f
1
by the control circuit, the second capacitance is charged with the same frequency by means of a current supplied by the supply voltage source and, subsequently, discharged by means of a current charging the first buffer capacitance. As a result thereof, current is continuously taken from the supply voltage source and hence the circuit arrangement has a relatively high power factor. During the second half period of the low-frequency square-wave current, the second inductive element in combination with the second switching element and the second unidirectional element form a second downconverter. This second downconverter consists completely of components which differ from the components which, during the first half period of the square-wave low-frequency current, form the first downconverter, namely the first switching element, the first inductive element and the second unidirectional element. This is necessary to bring about the proper power feedback.
In a preferred embodiment of a circuit arrangement in accordance with the invention, a third inductive element is coupled between the first output terminal and the third unidirectional element. This inductive element limits the current with which the first and the second capacitive element are charged and hence also limits the power dissipation in different components of the circuit arrangement.
It has also been found that the performance of the circuit arrangement is further improved if the clamps for holding a discharge lamp are connected to each other by means of a second branch comprising a third capacitive element.
In a further preferred embodiment, a fifth unidirectional element is coupled between the first output terminal and the second capacitive element, and a sixth unidirectional element is coupled between the second output terminal and the first capacitive element. In this further preferred embodiment, the fifth and the sixth unidirectional element are chosen in such a manner that they can become conducting and non-conducting with a frequency f
1
without too much power dissipation. In this further preferred embodiment, less high requirements are imposed on the unidirectional elements forming part of the recti
U.S. Philips Corporation
Vo Tuyet T.
Wong Don
LandOfFree
Circuit arrangement with improved power-factor for feeding a... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Circuit arrangement with improved power-factor for feeding a..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Circuit arrangement with improved power-factor for feeding a... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2467033