Electricity: power supply or regulation systems – In shunt with source or load – Using choke and switch across source
Reexamination Certificate
1997-05-23
2001-11-20
Riley, Shawn (Department: 2838)
Electricity: power supply or regulation systems
In shunt with source or load
Using choke and switch across source
C323S224000, C323S266000
Reexamination Certificate
active
06320357
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a circuit arrangement for supplying a load which comprises a lamp, comprising means for generating a DC voltage provided with
input terminals for connection to a supply voltage source,
rectifying means coupled to the input terminals for rectifying an AC voltage supplied by the supply voltage source,
output terminals for connection to the load,
a DC-DC converter connected between the rectifying means and the output terminals and provided with first inductive means, a first unidirectional element, and a switching element, and
first capacitive means coupled to the output terminals.
Such a circuit arrangement is known from European Patent 0323676. In the switching arrangement described therein, the output terminals are coupled to a DC-AC converter for generating a current of alternating polarity from the DC voltage, which current can be used for supplying a lamp. The switching element of the DC-DC converter is rendered in turn conducting and non-conducting with high frequency during lamp operation. As a result, a DC voltage is present across the first capacitive means, with which the DC-AC converter is supplied. The known circuit arrangement is highly suitable for operating lamps, more in particular discharge lamps such as low-pressure mercury lamps. A disadvantage of the known circuit arrangement, however, is that the first capacitive means are charged with a comparatively strong current when the circuit arrangement is switched on at a moment at which the supply voltage has a comparatively high value. This comparatively strong current, also called inrush current hereinafter, can adversely affect the life of the first capacitive means and the life of other components which carry this current. If the supply voltage source comprises a safety cut-out, a comparatively high inrush current may also cause the safety cut-out to interrupt the supply voltage.
SUMMARY OF THE INVENTION
The invention has for its object to provide a circuit arrangement with which the amplitude of the current charging the first capacitive means immediately after switching-on of the circuit arrangement can be limited.
According to the invention, a circuit arrangement as described in the opening paragraph is for this purpose characterized in that the output terminals are interconnected by a circuit branch which comprises a series arrangement of an impedance and the first capacitive means, which impedance is shunted by a further unidirectional element. When a circuit arrangement according to the invention is switched on, the current charging the first capacitive means flows through the impedance. Since this inrush current flows in the reverse direction of the further unidirectional element, the first unidirectional element carries no current. It is possible to limit said current to a desired value in that the impedance value is suitably chosen. It is achieved thereby that the inrush current is comparatively low. This comparatively low inrush current has a favourable effect on the life of the first capacitive means and of other components of the circuit arrangement which carry this inrush current. The comparatively low inrush current also prevents any safety cut-out which forms part of the supply voltage source from interrupting the supply voltage. If power is transmitted to the load from the first capacitive means, the current supplying this power flows substantially through the further unidirectional element, so that comparatively little power is dissipated in the impedance. During stationary operation, a periodic charging current with a frequency twice the frequency of the AC voltage flows through the first capacitive means and the impedance, so that a finite power dissipation takes place in the impedance. It was found, however, that this power dissipation is comparatively small when the AC voltage is sinusoidal and the switching element of the DC-DC converter is so controlled that also a sinusoidal current is taken up from the supply voltage source in phase with the AC voltage.
It should be noted that circuit arrangements are known, for example from Japanese Patent Applications 59-191476 and 63-107457, which also comprise rectifying means and output terminals for connecting a load interconnected by a first circuit comprising a series arrangement of an impedance and capacitive means, while the impedance is shunted by a unidirectional element. In these circuit arrangements, however, no DC-DC converter is coupled between the rectifying means and the output terminals, as it is in a circuit arrangement according to the invention. When such circuit arrangements are supplied with a sinusoidal supply voltage, a peak-shaped periodic current is taken up from the supply voltage source. When a circuit arrangement according to the invention is supplied with a sinusoidal AC voltage, however, it is possible to cause the current taken up from the supply voltage source to be also approximately sinusoidal in shape and approximately in phase with the supply voltage through adjustment of the duty cycle of the switching element of the DC-DC converter. The peak shape of the current during stationary lamp operation leads to a comparatively high power dissipation in the impedance, in contrast to stationary lamp operation when a circuit arrangement according to the invention is used. The circuit arrangements described in Japanese Patent Applications 59-191476 and 63-107457 use the power supplied by the supply voltage source less efficiently than does a circuit arrangement according to the invention.
Good results were achieved with circuit arrangements according to the invention in which the impedance comprises an ohmic resistor or an inductive element.
An advantageous embodiment of a circuit arrangement according to the invention is characterized in that the DC-DC converter comprises a boost converter, also referred to as an up-converter. If the DC voltage present during stationary lamp operation between the output terminals is higher than the maximum amplitude of the AC voltage supplied by the supply voltage source, the boost converter is active over the entire range of the instantaneous amplitude of the full-wave rectified AC voltage which forms the input voltage for the DC-DC converter, so that the DC-DC converter may be of a comparatively simple construction. It can also be realised in a comparatively simple manner through adjustment of the duty cycle of the switching element that the current taken up from the supply voltage source is also approximately sinusoidal and approximately in phase with the AC voltage. The advantageous embodiment as a result has a high power factor, while the power dissipation in the impedance is comparatively low during stationary operation.
A further advantageous embodiment of a circuit arrangement according to the invention is characterized in that the circuit arrangement in addition comprises a DC-AC converter, coupled to the output terminals, for generating a current of alternating polarity. Since the load comprises a lamp, it is often desirable to supply this load with a current of alternating polarity. This prevents, for example, cataphoresis or an unequal load on the lamp electrodes in the case of discharge lamps. Especially when the frequency of this current of alternating polarity is comparatively high, it is advantageous when the circuit branch in addition comprises further inductive means, and the circuit arrangement comprises further capacitive means shunting the circuit branch. These further inductive means and further capacitive means together form a filter by which the quantity of power dissipated in the impedance and in the first capacitive means by the current of alternating polarity is limited to a comparatively small quantity. If the impedance comprises an inductive element, it is possible to integrate this inductive element with the further inductive means into one component. If the impedance comprises an ohmic resistor, an integration of this ohmic resistor with the further inductive means into one component is also possible. This
Peters Henricus P. M.
Stout Arnold P.
Veldman Paul R.
Franzblau Bernard
Riley Shawn
U.S. Philips Corporation
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