Electric lamp and discharge devices: systems – Current and/or voltage regulation
Reexamination Certificate
2001-11-08
2004-06-01
Clinger, James (Department: 2821)
Electric lamp and discharge devices: systems
Current and/or voltage regulation
C315S294000, C315S307000
Reexamination Certificate
active
06744222
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a discharge lamp lighting apparatus that is powered by the commercial ac power source and lights up discharge lamps at high power factors.
BACKGROUND OF THE PRESENT INVENTION
FIG. 6
illustrates a circuit configuration of a prior art discharge lamp lighting apparatus disclosed in Japanese Patent Laid-Open Publication No. Hei. 9-45490. In this figure, denoted
1
is a commercial ac power source,
42
rectifier circuit,
43
step-up inverter,
44
step-down inverter,
45
rectangular wave circuit,
46
starter circuit,
8
discharge lamp,
48
step-up inverter control circuit,
49
step-down inverter control circuit,
50
rectangular wave control circuit, and
11
controlled power source circuit.
In the discharge lamp lighting apparatus of this configuration, the controlled power source circuit
11
generates controlled power when the commercial power source
1
is supplied, and then the step-up inverter control circuit
48
, the step-down inverter control circuit
49
and the rectangular wave control circuit
50
initiate operation.
The step-up inverter
43
converts an output, which is made by rectifying ac voltage provided by the commercial power source
1
in the rectifier circuit
42
, into a predetermined dc voltage. In this time, the step-up inverter control circuit
48
corrects the waveform distortion of the input current supplied to the step-up inverter
43
and controls the step-up inverter
43
so that the input power factor becomes almost 100%.
The step-down inverter
44
is a DC-to-DC converter that converts the dc voltage provided by the step-up inverter
43
into another dc voltage. The step-down inverter control circuit
49
controls the output voltage of the step-down inverter
44
so that the current running through the discharge lamp
8
becomes a predetermined current.
The rectangular wave circuit
45
converts the dc voltage of the step-down inverter
44
into ac voltage. The rectangular wave control circuit
50
controls the rectangular wave circuit
45
so that the current running through the discharge lamp
8
becomes a rectangular alternating current of a predetermined frequency.
The starter circuit
46
generates high voltage pulses to start up the discharge lamp
8
.
FIG. 7
is a block diagram illustrating the conventional lamp lighting apparatus, called magnetic type lighting apparatus, where denoted
1
is a commercial power source,
51
capacitor,
52
choke coil,
53
high voltage pulse generator and
8
discharge lamp. The high voltage pulse generator
53
applies high voltage pulses to the discharge lamp
8
. When the discharge lamp
8
lights up, a current runs from the commercial power source
1
to the discharge lamp
8
. The choke coil
52
limits the current flowing to the discharge lamp
8
. The capacitor
51
raises the power factor by improving the lagging in current caused by the choke coil
52
.
Electric appliances are required to have high power factors in order to reduce negative effects on power system facilities for the ac commercial power. In order to raise the power factor of an electric appliance, it is necessary to convert ac voltage into dc voltage at high power factors by the use of a step-up inverter, as shown in the example of the prior art. Thus, the discharge lamp lighting apparatus becomes large and costly as such a step-up inverter is installed.
On the order hand, it is possible, as shown in
FIG. 7
, to control the current running through the discharge lamp by the use of a choke coil of large inductance. However, the employment of a large choke coil leads to a large lamp lighting apparatus. In addition, as shown in FIG.
8
(
a
), since the discharge lamp current presents the same sinusoidal wave as that of the commercial ac voltage of the commercial power source, the period of time when the discharge lamp current is near zero becomes long. Then as shown in FIG.
8
(
b
), restriking voltage appears when the discharge lamp current is low. The occurrence of restriking voltage leads to turn-off of the discharge lamp and lowers illumination efficiency.
DISCLOSURE OF THE INVENTION
It is, therefore, the object of this invention to provide an inexpensive, small, high power factor discharge lamp lighting apparatus that can reduce the generation of restriking voltage.
According to a first embodiment of the present invention, in a discharge lamp lighting apparatus for controlling electric power supplied to the discharge lamp by a step-up/step-down converter comprising a transformer, a first switching element serially connected to the transformer on a side of a commercial ac power source, a first diode and a first capacitor connected to the transformer on the load side, the discharge lamp lighting apparatus includes a zero-cross detection means for detecting the zero-cross of voltage of the commercial ac power source; a supplemental power circuit comprising a second diode connected to a junction between the transformer and the first switching element, a second capacitor for charging energy stored in the coil of the transformer on a side of the commercial ac power source via the second diode, and a second switching element, a third diode and an inductance through which the energy charged in the second capacitor is supplied to the discharge lamp; and a control circuit that calculates the voltage cycle of the commercial ac power source based on the output from the zero-cross detection means and then operates the second switching element in the supplemental power circuit at a high frequency during a predetermined period of time around the zero-cross.
As described above, the supplemental power circuit supplies electric power to the discharge lamp during the period before and after zero-cross of the commercial ac power source voltage and thus the duration of time the current running through the discharge lamp is zero becomes short. Therefore, no restriking voltage appears in the discharge lamp, turn-off of the lamp can be prevented, and decrease of the illumination efficiency can be prevented.
When the first switching device of the step-up/step-down converter is turned off, the energy stored in the leakage inductance of the transformer in the step-up/step-down converter is discharged to the second switching element in the power amplification circuit, and then a high voltage is applied to the second switching element. Thus it becomes possible to use energy efficiently and raise the conversion rate since the high voltage is stored in the capacitor via the diode and then supplied to the discharge lamp.
In addition, since the voltage applied to the switching element can be lowered, a low withstand voltage switching element can be used and the system cost is thereby reduced.
In a second embodiment of the invention, the discharge lamp lighting apparatus according to the first embodiment further includes current detection means for detecting current running through the discharge lamp; wherein the control circuit has calculation means for calculating a target current to be provided to the discharge lamp, the calculation means provides a constant target current during the period of time when the second switching element in the supplemental power circuit is operated at a high frequency and another target current of an arched waveform having peaks at around 90° and 270° of voltage of the commercial ac power source during the period of time when the second switching element is not operated, and the control circuit controls the current running through the discharge lamp detected by the current detection means so as to make it equal to the calculated target current.
As a result, since the input current presents a sinusoidal a waveform similar to that of the commercial ac power source voltage, an inexpensive system with high power factor can be provided without adding a step-up converter for improving power factor.
According to a third embodiment, in the discharge lamp lighting apparatus set forth in the second embodiment, the target current of an arched waveform having peaks at around 90° and 270° of
Asayama Masatomi
Kisaichi Hiroyasu
Clinger James
Mitsubishi Denki & Kabushiki Kaisha
Vu Jimmy T.
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