Electric lamp and discharge devices: systems – Periodic switch in the supply circuit – Impedance or current regulator in the supply circuit
Reexamination Certificate
2000-01-17
2001-05-01
Vu, David (Department: 2821)
Electric lamp and discharge devices: systems
Periodic switch in the supply circuit
Impedance or current regulator in the supply circuit
C315S2090SC, C315S247000
Reexamination Certificate
active
06225753
ABSTRACT:
BACKGROUND OF THE INVENTION
(a) Field of the Invention
The present invention relates to an electronic ballast. More specifically, the present invention relates to an electronic ballast that has a small number of components and a high degree of efficiency.
(b) Description of the Related Art
An electronic ballast provides stable power to lighting apparatuses such as fluorescent lamps and discharge tubes.
Since the fluorescent lamp and discharge tube emit light via a discharge process, the polarity of the supplied power must be switched at predetermined periods. To supply such power, the electronic ballast is implemented with a converter. Typically, a boost converter, half bridge converter, and flyback converter are used.
A conventional electronic ballast will now be described with reference to the drawings.
Referring to
FIG. 1
, the conventional electronic ballast using the boost converter and half bridge converter comprises a rectifier
10
, a boost converter
20
, a diode D
1
, a capacitor C
1
, a half bridge converter
30
, a resonance circuit
40
, and a lamp Rlamp.
The rectifier
10
receives, rectifies, and outputs an alternating current (AC).
The boost converter
20
comprises a coil L
1
and a switch S
1
, and receives the rectified power to boost the power to a predetermined level, after which the boost converter
200
outputs the result.
One end of the diode D
1
is coupled to the coil L
1
and the switch S
1
and its other end is coupled to one end of the capacitor C
1
, the other end of the capacitor C
1
being grounded. The diode D
1
and capacitor C
1
smooth the output of the boost converter
20
.
The half bridge converter
30
is coupled to both ends of the capacitor C
1
and comprises two switches S
2
and S
3
. The half bridge converter
30
changes the polarities of the power by performing the switching operation on the voltage at the capacitor C
1
at a predetermined period, and outputs the result so that AC power is supplied to the discharge tube.
The resonance circuit
40
comprises capacitors C
2
and C
3
and a coil L
2
, and resonates the output power of the half bridge converter
30
to convert the output power to AC power having a predetermined frequency. After this conversion, the resonance circuit
40
supplies the AC power to the lamp Rlamp.
As shown in
FIG. 2
, the electronic ballast using the conventional flyback converter and half bridge converter comprises a rectifier
10
, a flyback converter
50
, a diode D
1
, a capacitor C
1
, a half bridge converter
30
, a resonance circuit
40
, and a lamp Rlamp.
The flyback converter
50
, by the on and off operation of a switch S
1
, receives an output power of the rectifier
10
from a primary coil of a transformer T
1
, performs conversion of the power, then transmits the result to a secondary coil of the transformer T
1
.
In the above-noted conventional electronic ballast, a system having a boost converter connected to a half bridge converter, and another system having a flyback converter connected to a half bridge converter are described. The overall performance of such systems decreases as a result of these inefficient interconnections. Also, since the elements are physically coupled, the size of the circuit increases with an increase in the number of components, and overall reliability decreases. Manufacturing costs also go up with such configurations.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an electronic ballast that has a small number of components and obtains a high level of performance.
In one aspect of the present invention, an electronic ballast comprises a a rectifier receiving and rectifying an alternating current (AC) power and outputting a resulting output current; a first converter receiving the output current of the rectifier and changing levels of the voltage by the on and off operations of a first switch and outputting a resulting output current; a half bridge converter coupled to the first converter in parallel and comprising first and second switches shared with the first converter, the half bridge converter receiving the output current of the first converter and changing a flow direction of the current according to on and off states of the first and second switches; and a resonance circuit, coupled to the half bridge converter, resonating an output current of the half bridge converter to convert the current into a sine wave current and outputting the current to a discharge lamp.
The electronic ballast further comprises a first diode that is coupled between the first converter and the half bridge converter in the forward direction of the half bridge converter and prevents reverse flow from the half bridge converter to the first converter; and a first capacitor that is coupled to the first diode, the half bridge converter, and the ground, and smoothes and maintains the output current of the first converter.
The first converter is a boost converter or a flyback converter.
The second switch of the half bridge converter is coupled to the first capacitor, first diode, and first switch, and shares the first switch with the first converter, the first and second switches performing opposite on and off operations such that when the first switch is controlled to on the second switch is controlled to off and vice versa.
The resonance circuit comprises a second capacitor coupled to the first and second switches; a second inductor coupled to the second capacitor; and a third capacitor coupled between the second inductor and the ground.
REFERENCES:
patent: 5936357 (1999-08-01), Crouse et al.
Blakely & Sokoloff, Taylor & Zafman
Fairchild Korea Semiconductor Ltd.
Vu David
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