Electronic ballast for a fluorescent lamp

Details Electronic ballast for a fluorescent lamp Electronic ballast for a fluorescent lamp

2000-11-29

2002-02-26

Wong, Don (Department: 2821)

Electric lamp and discharge devices: systems

Current and/or voltage regulation

C315S2090SC, C315S219000, C315S307000, C315S20000A

Reexamination Certificate

active

06351082

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to an electronic ballast for a fluorescent lamp with low-voltage power supply comprising a wave filter connected with its output to the input of a rectifier circuit which is connected with its output to the input of a generation and control circuit of high frequency the output end of which is connected to a resonance circuit composed of a choke and a capacitor and an ignition circuit; the generation and control circuit including two solid state switches and a feedback transformer means which is put with its primary circuit into the output of the generation and control circuit. Mainly the present invention relates to a circuit for the ignition and control of a fluorescent lamp.
The electronic ballast of fluorescent lamps is composed of a rectifier circuit, a wave filter circuit, a generation and control circuit of high frequency, an ignition circuit of the lamp tube, etc. In a fluorescent lamp with discharge in low-voltage mercury vapor using the electronic ballast, the direct current voltage that is supplied to the converting transistor of the generation and control circuit will be too low when the voltage of the power supply is 120 V or lower and the circuit of the electronic ballast works under cheap and reliable direct rectification. Thus the voltage after conversion will be also too low. Because of this, the fluorescent lamp cannot work stably and normally. In order to solve the problem of the insuffucient low-voltage of high frequency, one of the methods is to add a resonance circuit to the output end of high frequency so that the voltage of high frequency that is supplied to the lamp tube can be raised.
In
FIG. 1
of the drawing there is shown the principle diagram of a circuit of the electronic ballast for a fluorescent lamp. A wave filter comprising capacitor C
1
and choke L
0
is connected to the low-voltage mains. The output of the wave filter circuit is connected to the input of a rectifier circuit composed of diodes D
1
-D
4
. The output of the rectifier circuit is connected to the input of a generation and control circuit of high frequency comprising two transistors V
1
, V
2
, resistors R
2
, R
3
, R
4
, R
5
, capacitors C
4
, C
5
, diode D
5
, and feedback transformer B
1
. Connected to the output of the rectifier circuit is a filtering capacitor C
2
. Resistor R
1
and capacitor C
3
are connected in series to the output of the rectifier circuit. The collector of transistor V
1
is connected to the positive output of the rectifier circuit. The emitter of transistor V
2
is connected to the negative output of the rectifier circuit. The emitter of transistor V
1
is connected to the collector of transistor V
2
. Connected to the joint point of emitter of transistor V
1
and collector of transistor V
2
is the primary coil B
1
-
1
of feedback transformer B
1
. Secondary coil B
1
-
2
of feedback transformer B
1
is connected in series with resistor R
3
which is connected to the base of transistor V
1
. Resistor R
4
is connected to the base of transistor V
2
and the secondary coil B
1
-
3
of feedback transformer B
1
. One end of the secondary coil B
1
-
3
is connected to the negative output of the rectifier circuit. One end of secondary coil B
1
-
2
is connected to the joint point of emitter of transistor V
1
and collector of transistor V
2
. The second end of capacitor C
5
is connected to one tap or contact respectively of the lamp F. The other plug-in pin or contact of the lamp F is connected to one end of a choke L and one end of a capacitor C
7
which is connected with its other end to the negative output of the rectifier circuit. One end of the choke L is connected to the primary coil B
1
-
1
of feedback transformer B
1
. The starting circuit of the fluorescent lamp F includes a capacitor C
3
in series with resistor R
1
and DIAC DB
3
.
In the electronic ballast circuit shown in
FIG. 1
capacitor C
7
and choke L form a resonant circuit. Because the capacity of C
2
and C
5
is relatively big, the voltage of high frequency on C
7
is mainly supplied to the two ends of the lamp tube so that the lamp tube can work normally. There are great defects in this circuit if the lamp tube is a part that can be changed. Firstly, the resonance circuit C
7
and L will work under the idle situation and the transistor will be burnt out quickly if the plug-in pins of the lamp tube have a loose contact and the lamp tube itself does not work normally. Secondly, the safety regulation requirements of the changeable lamp tube cannot be fulfilled.
SUMMARY OF THE INVENTION
It is an object of the present invention to overcome the above mentioned defects and to provide an electronic ballast which will not fail if the lamp tube has a loose contact or the lamp tube is removed from its lampholder.
An electronic ballast for a fluorescent lamp with low-voltage power supply according to the invention comprises a wave filter connected with its output to the input of a rectifier circuit, which is connected with its output to the input of a generation and control circuit of high frequency, the output end of which is connected to the resonance circuit composed of a choke and a capacitor, and an ignition circuit, the generation and control circuit including two solid state switches and feedback transformer means which is put with its primary circuits into the output of the generation and control circuit; at least one coil of the primary circuit of the feedback transformer means for supplying feedback to one of the solid state switches is connected between the joint of the choke and the capacitor of the resonance circuit and one contact of the fluorescent lamp. The normal work of the generation and control circuit of high frequency is maintained by the positive feedback that is formed through each group of coils in the feedback transformer. Thus the primary feedback coil will have no feedback current in the feedback transformer if the lamp tube has a loose contact or an open circuit. Thereby the solid state switch, for instance a transistor, stops working and the safety regulation requirements of the changeable lamp tube are fulfilled. Preferably the feedback transformer means comprises two transformers and the primary feedback coil is connected on the two transformers between the joint of the choke and the capacitor of said resonance circuit and said one contact of the fluorescent lamp.
In another preferred embodiment of the present invention the feedback transformer means comprises one primary feedback coil connected with a two holes transformer. In still another preferred embodiment of the present invention the primary feedback means comprises two transformers; one transformer being connected in the front and one at the back of the choke.
In another preferred embodiment of the present invention the primary feedback transformer means comprises one transformer including two primary feedback coils one coil being connected in the front and one coil being connected to the back of the choke. The invention will be further explained hereinafter by reference to the drawings.


REFERENCES:
patent: 4954754 (1990-09-01), Nilssen
patent: 4959591 (1990-09-01), Hirschmann
patent: 5402043 (1995-03-01), Nilssen
patent: 5512801 (1996-04-01), Nilssen
patent: 5677601 (1997-10-01), Zuchtriegel
patent: 5898278 (1999-04-01), Muessli
patent: 5925984 (1999-07-01), Fisher et al.
patent: 00 99 474 (1984-02-01), None

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