Operating circuit arrangement for a discharge lamp

Abstract: An operating circuit arrangement for a discharge lamp has a chopper circuit and an inverter circuit. The inverter circuit generates a high frequency voltage to start and operate the discharge lamp. The chopper circuit supplies a d.c. voltage to the inverter circuit. The circuit arrangement has a chopper control circuit and an inverter control circuit which are coupled to the chopper circuit so that the operation of each control circuit is responded to the chopper circuit. In order to perform a soft starting operation, at which the inverter circuit generates a given high frequency voltage to start and operate the discharge lamp prior to the generation of a given level of said d.c. voltage by the chopper circuit, an inverter control circuit coupled to the inverter circuit is provided.

Description: The present invention relates to an operating circuit arrangement for a discharge lamp. More specifically, the present invention relates to an improved operating circuit arrangement for a fluorescent lamp which includes at least a chopper circuit and an inverter circuit. It is known from EP-A-0439240 for a dimmable operating circuit for a low pressure discharge lamp to include an inverter which feeds the lamp and which is controlled by a control circuit. An electronic harmonic filter which can be considered to be a chopper circuit supplies the inverter. EP-A-0059064 also discloses an operating circuit for a fluorescent lamp in which a converter produces dc output from a low frequency ac supply and an inverter for producing a high frequency ac supply from the dc output. Control means cause the inverter to operate at a frequency which is initially above the resonant frequency of a resonant circuit associated with the lamp and subsequently the frequency of operation is reduced towards resonance until the lamp strikes. Generally, a conventional inverter circuit is designed to start its operation when the output of the chopper circuit exceeds a given value. As long as the output of the chopper circuit is lower than the given value, the discharge is held in off-state. This operating condition for the chopper circuit is regarded as no-loaded condition. When the operating condition is changed from the no-load condition to loaded condition under which the discharge lamp is operated, a high output voltage is applied to a switching device of the inverter circuit, which is liable to damage the switching device. Accordingly, it is an object of the present invention to provide an improved operating circuit arrangement for a discharge lamp. According to the present invention an operating circuit arrangement for a discharge lamp, comprises a rectifier circuit for rectifying an a.c. voltage to a d.c. voltage, a chopper circuit coupled to the rectifier circuit for stepping up said d.c. voltage and generating a d.c. output voltage, the chopper circuit including a chopper control circuit for controlling the operation thereof, a controlled inverter circuit coupled to said chopper circuit for generating a high frequency voltage for application to the discharge lamp, characterised in provision of starting means which is coupled to the chopper control circuit for starting the chopper control circuit in a manner such that the inverter circuit is placed in a steady operation mode in which the discharge lamp is activated prior to the generation of a given level of the d.c. output voltage by the chopper circuit. In order that the invention may be more readily understood, it will now be described, by way of example only, with reference to the accompanying drawings, in which:- Figure 1 shows a fluorescent lamp device utilising an electric circuit arrangement of the present invention; Figure 2 shows a first embodiment of an electric circuit arrangement shown in Figure 1; Figure 3 shows a second embodiment, of an electric circuit arrangement according to the present invention; and Figure 4 shows a third embodiment of an electric circuit arrangement according to the present invention. Figure 1 shows a fluorescent lamp device. An elongate fluorescent lamp 1 is attached to a lamp fitting 2 in which an electric circuit arrangement 100 of the present invention described below is installed. Figure 2 shows a first embodiment of electric circuit arrangement 100 of the present invention. Circuit arrangement 100 shown in Figure 2 is composed of a power supply circuit 40, a chopper circuit 50, an inverter circuit 60, a chopper control circuit 70, an inverter control circuit 80 and a lighting circuit 90. Reference numerals 3, 4, denote input terminals which are intended to be connected to an a.c. voltage, such as 100 volts, 60Hz. A full-wave rectifier circuit 5 is connected to terminals 3, 4 through a transformer 6. Two output terminals 7,8 of rectifier circuit 5 are interconnected to a capacitor 9. The output voltage of power supply circuit 40 is applied to chopper circuit 50. A Field Effect Transistor 10 (hereinafter referred as FET) and a transformer 11 are provided in chopper circuit 50. The drain of FET 10 is connected to one end of a primary winding 11a of transformer 11. The other end of primary winding 11a is connected to one end of output terminals 7,8 of power supply circuit 40. Numeral 11b denotes a secondary winding of transformer 11. The junction point between FET 10 and primary winding 11a is connected to a diode 12. A capacitor 13 of which one end is connected to diode 12 is parallel with a resistor 14. The other end of capacitor 13 is connected to the source of FET 10. Namely, the drain of FET 10 is connected to one end of primary winding 11 while the source of FET 10 is connected to one end of capacitor 13. An output d.c. voltage of chopper circuit 50 is applied to a separately-excited oscillation type of inverter circuit 60. Inverter circuit 60 provides a pair of Field Effect transistors 15a,15b as switching means. Output terminals 16,17 of chopper circuit 50 is connected to the drain of FET 15a and the source of FET 15b, respectively. Each gate of FETs 15a,15b is driven by a drive circuit 18. One end of a transformer 19 is connected to a capacitor 20 while the other end is connected to the source of FET 15a (and the drain of FET15b). An a.c. voltage derived across capacitor 20 is the output of inverter circuit 60. The a.c output voltage is applied to a series circuit of a primary winding 21a of a transformer 21 and a capacitor 22 of lighting circuit 90. The a.c output voltage is also applied to coiled electrodes of fluorescent lamp 1. Numeral 23 denotes a capacitor connected to one of the electrodes of fluorescent lamp 1. Each of the coiled electrodes is connected to secondary windings 21b,21c of transformer 21, respectively. Neither of the chopper control circuit 70 and the inverter control circuit 80 has a separate power source. An a.c.voltage derived from secondary winding 11b of transformer 11 is applied to terminals 24,25 for control circuits 70,80. The a.c. voltage is rectified and smoothed to a d.c voltage by a rectifier circuit formed by capacitors 26,27 and diodes 28,29,30. The d.c. voltage thus obtained is applied to inverter control circuit 80 and chopper control circuit 70. Inverter control circuit 80 is connected to drive circuit 18 for adjusting frequency of the a.c.output voltage of inverter circuit 60. Chopper control circuit 70 is connected to the gate of FET 10 for controlling the chopper operation. A starting circuit 95 which is composed of a resistor 31 is connected to inverter control circuit 80. Starting circuit 95 is connected to chopper circuit so that the d.c.voltage derived at terminals 16,17 is supplied to inverter control circuit 80 therethrough. Starting circuit 95 may provide a switch device 32. Each operating principle of chopper circuit 50 and inverter circuit 60 is conventional, however inverter circuit 60 shown in this embodiment is started so that fluorescent lamp 1 is operated even before chopper circuit 50 starts the chopper operation. The output of chopper circuit 50 is applied to starting circuit 95. The d.c. voltage mentioned above is tentatively supplied to inverter control circuit 80 from starting circuit 95. Inverter control circuit 80 begins its operation in response to receiving the d.c. voltage. When chopper circuit 50 is out of the operation, the d.c.voltage applied to starting circuit 95 is equivalent to the output derived at terminals 7,8. The operation of drive circuit 18 connected to the gates of FETs 15a,15b is controlled by inverter control circuit 80. Inverter circuit 60 can start its operation in advance of the operation of chopper circuit 50 under low level of input voltage supplied from chopper circuit 50. Such starting is referred to a soft starting. To ensure the soft starting of inverter circuit 60, if necessary, another switch device 98 is provided as indicated by dotted line in Fig. 2. No voltage is applied to chopper control circuit 70 unless switch device 98 is held in the closed position, so that the operation of chopper control circuit 70 is delayed by the time where inverter circuit 60 goes in the steady mode. Inverter circuit 60 generates a high frequency voltage, which leads to fluorescent lamp 1 to be operated. Chopper control circuit 70 is also started in response to receiving the d.c.voltage from starting circuit 95. The gate of FET 10 is driven by chopper control circuit 70. Chopper circuit 50 is thus started and generates a predetermined d.c. voltage, for example 410 volts. Accordingly as the chopper circuit 50 is started, inverter circuit 60 goes in steady operation to increase the light output of fluorescent lamp 1. When lamp current flowing in lighting circuit 90 becomes larger than a predetermined value, it indicates that the operation of inverter circuit 60 is in the steady mode. Although a detailed lamp current detector is not shown, it will be easily obtained by detecting current flowing in lighting circuit 90. In response to the steady mode, switch device 32 of starting circuit 95 is opened and neither inverter control circuit 80 nor chopper control circuit 70 receives a voltage from the starting circuit 95. Instead, the output derived from secondary winding 11b of transformer 11 is supplied to both control circuits 70,80 through the rectifier circuit. The output voltage derived from transformer 11 of chopper circuit 50 is less dependent on the operating condition of inverter circuit 60 so that the output voltage is relatively constant. This is an advantage of this embodiment. Opening of switch device 32 prevents starting circuit 95 from consuming power at resistor 31, however such switch device 32 may be eliminated. Another embodiments in accordance with the present invention is shown in Fig.3 to Fig.4 and explained hereunder where like reference characters designate identical or corresponding elements of the above-mentioned first embodiment. Fig. 3 shows a second embodiment of a circuit arrangement according to the present invention, which is regared as a modification of the circuit arrangement shown in Fig.2. In this modification an output voltage derived from a secondary winding 11b of the transformer 11 in a chopper circuit is supplied only to a chopper control circuit 70 through a rectifier circuit. An inverter control circuit 80 shown in Fig.3 is equipped with a separate d.c.power source (not shown), which is regarded as a starting circuit corresponding to starting circuit 95 shown in Fig.2. A chopper control circuit 70 is connected to a starting circuit 95. An oscillation control circuit 85 which is connected to inverter control circuit 80 is designed to respond to the lamp current flowing lighting circuit 90 and is externally operated, generates a signal to stop the operation of inverter control circuit 80 when fluorescent lamp 1 is extinguished or a stop signal is externally applied thereto. Accordingly, the operation of inverter circuit 60 is stopped when discharge lamp is extinguished. Fig.4 shows a third embodiment of a circuit arrangement according to the present invention. A series circuit of a resistor 201 and a capacitor 202 is interconnected to the output terminals 16,17 of a chopper circuit 50. A diode 203 and a bidirectional diode-thyristor 204 are interposed between a junction point of the series circuit and the source of a FET 15a (and the drain of a FET 15b). An inverter circuit 60, which is called a self-excited type of inverter circuit, is provided with a saturatable transformer 205 having a pair of input windings 205a,205b. The gates of FETs are connected to resistors 206,207, respectively. Each one ends of input windings 205a,205b is connected to resistors 206,207, respectively while each other ends is connected to capacitors 208,209, respectively. Each gate and source of FETs 15a,15b is interconnected by resistors 210,211, respectively. An output winding 205c of transformer 205 is interposed between a fluorescent lamp 1 and the source of FET 15a (the drain of FET 15b). A series circuit of shunt capacitors 213,214 is interconnected between output terminals 16,17. Unlike other embodiments described above, the circuit arrangement shown in Fig. 4 has two starting circuits. One of the starting circuits is connected to a chopper control circuit 70, and is denoted by numeral 95. The other is formed with resistor 201, capacitor 202 and bidirectional diode-thyristor 204. An inverter control circuit in this embodiment is formed with resistors 206,207,210,211, capacitors 208,209 and output winding 205 of transformer 205. Inverter circuit 60 is ready to start with a relatively small input voltage and so-called soft starting is achieved.

Claims: An operating circuit arrangement for a discharge lamp (1), comprising a rectifier circuit (5) for rectifying an a.c. voltage to a d.c. voltage, a chopper circuit (50) coupled to the rectifier circuit (5) for stepping up said d.c. voltage and generating a d.c. output voltage, the chopper circuit (50) including a chopper control circuit (70) for controlling the operation thereof, a controlled inverter circuit (60) coupled to said chopper circuit for generating a high frequency voltage for application to the discharge lamp, characterised in provision of starting means (95) which is coupled to the chopper control circuit (70) for starting the chopper control circuit (70) in a manner such that the inverter circuit (60) is placed in a steady operation mode in which the discharge lamp is activated prior to the generation of a given level of the d.c. output voltage by the chopper circuit (50). An operating circuit arrangement as in claim 1, wherein the starting circuit (95) comprises a series circuit of a resistor (31) and a switching element (32), the switching element (32) being opened after the inverter circuit (60) reaches the given operation mode so that the starting circuit (95) is disconnected from the chopper control circuit (70). An operating circuit arrangement as in claim 2, wherein the starting circuit (95) is further coupled to an inverter control circuit (80), the switching element (32) being opened after said inverter circuit (60) reaches the given operation mode so that starting circuit (95) is disconnected from both the chopper control circuit (70) and the inverter control circuit (80). An operating circuit arrangement as in claim 3, wherein the starting circuit (95) includes delay means (98) coupled to chopper control circuit (70) for delaying the operation of the chopper control circuit (70) by an amount of the time required by the inverter circuit (60) to reach the given steady operation mode. An operating circuit arrangement as claimed in claim 2, wherein the chopper circuit (50) comprises a transformer (11) having a first winding (11a) and a second winding (11b), the second winding (11b) being coupled to the chopper control circuit (70) in order to utilise an a.c. voltage derived from the operation of the chopper circuit (50) as a source for the chopper control circuit whereby the chopper control circuit (70) is responsive to the operation of the chopper circuit (50). An operating circuit arrangement as claimed in claim 3 or 4, wherein the chopper circuit (50) comprises a transformer (11) having a first winding (11a) and a second winding (11b), the second winding (11b) being coupled to the chopper control circuit (70) and the inverter control circuit (80) in order to utilise an a.c. voltage derived from the operation of the chopper circuit (50) as a source for the chopper control circuit (70) and inverter control circuit whereby the chopper control circuit (70) and the inverter control circuit (80) are responsive to the operation of said chopper circuit. A device for lighting a discharge lamp comprising a fitting adapted to receive the discharge lamp and said fitting including an operating circuit arrangement as claimed in any preceding claim.

Inventors: OHSAKI HAJIME, SHIMIZU KEIICHI, OHSAKI, HAJIME, SHIMIZU, KEIICHI
Applicants: TOSHIBA LIGHTING & TECHNOLOGY, TOSHIBA LIGHTING & TECHNOLOGY CORPORATION
Application year: 1992
Main classification: H05B41
IPC codes: H05B41, H02M7