Electric lamp and discharge devices: systems – Periodic switch in the supply circuit – Impedance or current regulator in the supply circuit
Reexamination Certificate
2000-11-16
2002-03-26
Philogene, Haissa (Department: 2821)
Electric lamp and discharge devices: systems
Periodic switch in the supply circuit
Impedance or current regulator in the supply circuit
C315S291000, C315S307000, C315S244000, C315S312000, C315S2090SC, C315SDIG007
Reexamination Certificate
active
06362575
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to an electronic ballast apparatus for the ignition and operation of a plurality of gas discharge lamps, and more particularly to an improved high frequency electronic ballast for multiple discharge lamps which regulates the output voltage supplied to the discharge lamps despite the absence or inoperation of one or more of the discharge lamps of a bank of parallel connected lamps. The invention further relates to a method of igniting and operating multiple discharge lamps with a regulated lamp output voltage, i.e. multiple lamp independent lamp operation (ILO).
One form of high frequency electronic ballast for the operation of multiple gas discharge lamps is described in the copending U.S. application Ser. No. 09/467,596 filed Dec. 20, 1999 in the name of Chang et al, issued on Jan. 30, 2001 as U. S. Pat. No. 6,181,079 B1, and which is shown in the accompanying
FIG. 1
of the drawings. This electronic ballast circuit basically consists of two building blocks. The front end is a boost converter for power factor correction and universal input line voltage regulation. The main components are a transistor power switch Q
1
, an inductor L
1
, a diode D
5
and the DC storage capacitor C
1
along with an EMI filter and the diode bridge rectifier interposed between the AC supply voltage (e.g. 60 Hz) and the boost converter. The transistor switch Q
1
is periodically switched on and off by a control circuit
7
as a function of the voltage across capacitor C
1
and the current flowing through the transistor switch Q
1
and a series connected sensing resistor
6
.
The back end is a typical voltage-fed half-bridge inverter loaded with a group of parallel connected discharge lamps via a resonant tank circuit L
2
-C
3
. The main components are the power switches Q
2
and Q
3
, resonant components including capacitor C
3
, inductor L
2
and possibly the magnetizing inductance of the output transformer T
1
. The capacitors Clp in the secondary circuit of the transformer T
1
are usually provided in order to ballast the lamp current and to protect against possible lamp rectification at the end of lamp life. The operation of the power switches Q
2
and Q
3
is controlled by a high voltage control IC
11
as a function of current flow in the transistor switch Q
3
and of the voltage on capacitor C
3
.
In order to achieve multiple lamp independent operation (ILO) in a circuit such as that shown in
FIG. 1
, the output voltage (Vo) applied across the multiple parallel connected discharge lamps is usually kept constant at an rms value that exceeds the ignition voltage of the loaded gas discharge lamps. The level of the lamp ignition voltage is higher than the lamp operating voltage and presents the hazard of electric shock in the case where one or more of the multiple discharge lamps is (are) absent from a multiple lamp fixture.
For example, in the case of a fixture supporting multiple fluorescent TL lamps such as those with the manufacturers designation F32T8/TL735, the reliable ignition voltage is about 550 V (rms). In order to achieve independent lamp operation (ILO), the output (lamp) voltage is usually regulated to about 550 V in the normal steady state operation mode of the lamps even when less than all of the discharge lamps are operating, i.e. in a four-lamp fixture, even if one, two or three of the lamps are inoperative or are removed from the lamp fixture, the output voltage is still regulated at the ignition voltage value of 550 V (rms). In this case, the open circuit voltage across the lamp connector terminals will be the ignition voltage, 550 V (rms) which is required for the ignition of a newly inserted lamp or lamps. This presents the electric shock hazard mentioned above, especially during the removal of a discharge lamp or the insertion of a new lamp in the lamp fixture.
This problem is further exacerbated in Europe where the IEC 928 safety requirement, e.g. Section 12 concerning protection against electric shock, states that “For ballasts whose output terminals are to be connected to 250 V rated components, the voltage between any output terminals and between any output terminal and neutral or earth shall decrease within 5s after switching on or beginning of the starting process to a value less than 700 V (peak), under both normal and abnormal conditions . . .”. This 700 V peak value translates to 495 V (rms) for sinusoidal waveforms. Therefore, the steady state output voltage exceeds the open circuit safety voltage. A ballast that operates with a 550 V (rms) lamp output voltage during steady state operation would clearly violate the European electric shock safety requirements of IEC 928.
Attention is also directed to the Japanese abstract 5-283183 by the Toshiba Corp. for a Discharge Lamp Lighting Device and Lighting System. This abstract describes a multiple lamp apparatus which detects if one lamp is removed from a bank of two parallel lamps by the use of a voltage detection circuit and a lamp filament detection circuit. This is but one of several known schemes for lamp insertion/removal detection based upon the detection of filament current. Most of these prior art circuits provide circuit protection when a lamp is removed by turning off the electronic ballast or putting the ballast into a standby mode. It appears that JP-A5-283,183 falls into this category of ballasts because of the use of the AND logic gate circuit
30
. This circuit is not applicable for determining the number of inoperative lamps in a multiple lamp apparatus.
SUMMARY OF THE INVENTION
It is therefore an object of the invention to provide a high frequency electronic ballast for operation of multiple discharge lamps with a regulated lamp output voltage irrespective of the number of lamps actually in operation (ILO).
It is another object of the invention to provide a high frequency electronic ballast for operation of multiple discharge lamps which simultaneously provides independent lamp operation while satisfying the electric shock safety requirements that are desirable in this type of apparatus.
Another object of the invention is to provide an electronic ballast of the type mentioned which also regulates, e.g. makes constant, the lamp current in the case where the number of operating lamps is variable, thereby extending the useful lamp life and improving the ballast efficacy for partial load conditions.
A still further object of the invention is an electronic ballast of simple and inexpensive construction that nevertheless makes possible the objects and advantages mentioned above.
Another object of the invention is to provide an improved method of operating multiple gas discharge lamps which achieves the objects of the invention described above.
The above and other objects and advantages are achieved in accordance with the present invention by independently operating a plurality of discharge lamps in parallel by means of a high frequency electronic ballast that regulates the output lamp voltage even if one or more of the total number of lamps is inoperative or is removed from its connection terminals.
The regulation of lamp output voltage is achieved by monitoring and detecting the level of total lamp filament current flowing in the circuit, which then provides an indication of the actual number of discharge lamps that are in operation. A reference voltage is generated that is determined by the level of the detected total lamp filament current. By means of a feedback loop, the lamp output voltage is compared with the generated reference voltage and the frequency of the lamp output voltage is automatically adjusted so as to maintain a fixed (constant) output voltage level irrespective of the number of discharge lamps in operation at any given moment in time.
When a discharge lamp is inserted into a fixture that holds the multiple lamp configuration, there will be a rise or jump in the total filament current which is sensed. A short higher reference voltage is generated and the feedback loop responds to momentarily generate a higher lamp output voltage at a
Chang Chin
Stommen Theo
Halajian Dicran
Philips Electronics North America Corporation
Philogene Haissa
LandOfFree
Voltage regulated electronic ballast for multiple discharge... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Voltage regulated electronic ballast for multiple discharge..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Voltage regulated electronic ballast for multiple discharge... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2880686