Circuit for power-factor correction

Details Circuit for power-factor correction Circuit for power-factor correction

2000-05-17

2001-03-27

Vu, David (Department: 2821)

Electric lamp and discharge devices: systems

Pulsating or a.c. supply

With power factor control device

C315S2090SC, C315S224000, C363S039000, C363S040000

Reexamination Certificate

active

06208085

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a circuit for power-factor correction, to be precise to a circuit having a bridge rectifier with a first and a second input connection in which case an AC voltage source can be arranged between the first and the second input connection, and having a first and a second output connection, an actuation and load circuit, at least one energy storage apparatus, whose first connection is connected to a connection in the actuation and load circuit, in which case the signal which can be tapped off at this connection in operation is at a considerably higher frequency than the output signal from the AC voltage source, and an energy storage capacitor.
BACKGROUND OF THE INVENTION
Circuits for power-factor correction are also referred to as charge pumps or pump circuits. They are used, for example, to satisfy IEC Standard 1000-3-2, in which the electricity supply organizations have defined the acceptable mains current harmonics. It is therefore undesirable to draw high-frequency energy from the power supply network. The mains current which is drawn from the mains is, optimally, proportional to the mains voltage. Proportionality between the mains current and the mains voltage allows the maximum power transfer for any given cable size. Reactive currents which would occur if the mains voltage and the mains current were not proportional would cause cable losses, which place additional loads on the cables and thus leading to interference with other loads.
Such circuits for power-factor correction are used, inter alia, for ballasts for operation of gas-discharge lamps.
The present invention is based on a prior art as is known, for example, from EP-A-0 253 224, DE-A-38 41 227 or U.S. Pat. No. 5,488,269. The prior art in these documents is illustrated in the outline circuit in FIG.
1
. In this circuit, an AC voltage source
10
, in general the mains voltage, is connected to the inputs
14
and
16
of a rectifier
18
which comprises the four diodes DG
1
, DG
2
, DG
3
and DG
4
.
First of all, reference will be made to the circuit arrangement illustrated by solid lines: an energy storage apparatus
20
is connected on the one hand to the junction point between two diodes DP
1
, DP
2
and on the other hand at the connection
28
to a high-frequency voltage source
22
, that is to say an AC voltage source which, in operation, provides a signal at a considerably higher frequency than the AC voltage source
10
. This AC voltage source
22
is part of the actuation and load circuit
24
, as is intended to be expressed by the double arrow
26
. Arranged in parallel with the actuation and load circuit
24
is an energy storage capacitor CS, which is used to store the energy drawn from the AC voltage source
10
in order to supply the actuation and load circuit
24
.
An alternative embodiment is shown by dashed lines in FIG.
1
. This comprises an energy storage apparatus
20
′ which is connected on the one hand to the high-frequency voltage source
22
and on the other hand to the junction point between two diodes DP
1
′, DP
2
′. The diodes DP
2
and DP
2
′ are used to prevent reactions from the actuation and load circuit
24
on the energy storage apparatus
20
or
20
′ respectively. The diodes, DP
1
, DP
1
′, which are in the form of so-called “fast diodes” in comparison with the diodes DG
1
to DG
4
in the rectifier
18
, are used to prevent energy from being pumped into the AC voltage source
10
.
Taking account of the fact that such pump circuits are used, for example, in ballasts for operation of gas discharge lamps which are mass-produced items, the cost aspect is of major importance.
SUMMARY OF THE INVENTION
The present invention is therefore based on the object of providing a circuit for power-factor correction, that is to say a pump circuit, which, as has already been achieved by the prior art, likewise prevents reactions from the actuation and load circuit on the energy storage apparatus, as well as suppressing pumping into the supplying power supply network, but which can be produced at lower cost than the pump circuits known from the prior art.
This object is achieved for a circuit of the type mentioned initially in that the energy storage capacitor is arranged in parallel with the output connections of the bridge rectifier, and the second connection of the at least one energy storage apparatus is connected to one of the two input connections of the bridge rectifier.
This circuit has the advantage that there is no need for the diodes denoted by DP
1
and DP
2
, or DP
1
′ and DP
2
′ in the prior art. The omission of these diodes not only avoids the material price for the diodes, but also the associated assembly costs.
The solution according to the invention is based on the idea that the diodes DG
1
to DG
4
(which are present in any case) in the bridge rectifier can be used twice, to be precise firstly in their known function in the bridge rectifier and then, in addition, for the pumping process.
The energy storage apparatus may comprise at least one inductance and/or at least one capacitor. The actuation part of the actuation and load circuit may comprise an inverter. The said connection in the actuation and load circuit which, in operation, provides a signal at a considerably higher frequency than the AC voltage source, may be formed by the junction point between two electrical switches in the inverter.
In one particularly advantageous development, the circuit has a first energy storage apparatus which is connected to one of the two input connections of the bridge rectifier, and a second energy storage apparatus which is connected to the other input connection of the bridge rectifier. In this case, a plurality of energy storage apparatuses may be connected to the same connection in the actuation and load circuit, but each energy storage apparatus may also be connected to a different connection in the actuation and load circuit.
One particularly advantageous embodiment provides for the voltage at the at least one connection in the actuation and load circuit to be clamped to the voltage of the energy storage capacitor.
In a further advantageous embodiment, which applies the teaching disclosed by the same inventors in DE 199 14 505.9 to the present invention, the energy storage apparatus comprises an inductance and at least one capacitor, in which case the first connection of each capacitor is connected to the inductance, and its second connection is connected to one of the two input connections of the bridge rectifier, and the junction point between the inductance and each capacitor is connected via in each case one diode to the first and the second output connection of the bridge rectifier.
It is advantageous to provide at least one filter, in particular a low-pass filter, between the first and the second input connection of the bridge rectifier, which filter is arranged connected in series or parallel with the AC voltage source.
Further advantageous developments of the invention are defined in the independent claims.
The invention will be described in more detail in the following exemplary embodiments with reference to the attached drawings, in which:


REFERENCES:
patent: 4808887 (1989-02-01), Fähnrich et al.
patent: 5008597 (1991-04-01), Zuchtriegel
patent: 5488269 (1996-01-01), El-Hamamsy et al.

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