JPH0294395A - Discharge lamp lighting device - Google Patents

Abstract

PURPOSE:To start a lamp after fully preheating of a filament at the time of soft starting, by interposing a resonance capacitor between the non-power supply side terminal of one of the filaments of a discharge lamp, and furnishing a changeover means to vary the capacitance of this resonance capacitor at the starting time of the discharge lamp. CONSTITUTION:Circuit setting is so made that a changeover means 63 enlarges the capacitance of a resonance capacitor 53 during the period after turning-on of a power supply and before starting of a lamp. Accordingly the impedance of the resonance capacitor 53 becomes lower during this period, and the voltage between cathodes 65a, 65b of a discharge lamp 65 does not attain the lamp starting voltage to leave the lamp 65 out of lighting, but a current flows through its filament as preheating. The abovementioned changeover means 63 changed over the circuit so that the capacitance of the resonance capacitor 53 becomes smaller a certain while after turning-on of the power supply. Accordingly the voltage between the two cathodes 65a, 65b of the discharge lamp 65 rises to cause starting of the lamp 65. This enables starting of the lamp after full preheating of the lamp filament at the time of soft starting.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a discharge lamp lighting device, and in particular to a discharge lamp lighting device that enables accurate soft start operation by lighting the lamp after sufficiently preheating the lamp filament. The present invention relates to a discharge lamp lighting device.

[Prior Art] FIG. 2 shows a conventional lighting device including a soft start circuit for lighting a discharge lamp such as a fluorescent lamp. The device in the figure includes a switching transistor 3, a current limiting inductor 7
, a base feedback inductor 11 magnetically coupled to the current limiting inductor 7, a collector resonant circuit composed of the inductor 9 and the capacitor 17, and a series circuit of the inductor 11, 13 and the capacitor 19. It has an inverter circuit including a base resonant circuit and the like. The collector of the switching transistor 3 is connected to one electrode of a discharge lamp 31 via a current-limiting inductor 7, and the other electrode of the discharge lamp 31 is connected to a DC power source. Further, a capacitor 15 that forms a resonant circuit with the inductor 7 is connected between both electrodes of the discharge lamp 31. Furthermore, a time constant circuit constituted by a resistor 25 and a capacitor 23 is connected to the output of the DC power supply 1. The output of this time constant circuit is connected to the base of transistor 5 via a voltage dividing circuit constituted by resistors 27 and 29.

In addition, the collector of the transistor 5 is connected to the inductor 13 of the base resonant circuit and the capacitor 19 via the capacitor 21.
connected to the connection point.

In the lighting device shown in FIG. 2, when the DC power supply 1 is initially applied, the output of the time constant circuit constituted by the resistor 25 and the capacitor 23, that is, the voltage at the node N1, is sufficiently low.
Transistor 5 is therefore cut off. Therefore, the capacitance of the series resonant circuit connected to the base of the switching transistor 3 is due only to the capacitor 19, and the resonant frequency becomes relatively high. Therefore, the on-time of the switching transistor 3 of the inverter circuit is considerably shortened, and the output voltage of the inverter circuit is also relatively low. Therefore, the discharge lamp 31 is not lit and the filament is preheated during this time.

When a predetermined period of time elapses after the power supply 1 is supplied and the voltage at the node N1 rises to a predetermined value or higher, the transistor 5 is turned on. Thereby, the capacitor 21 is connected in parallel with the capacitor 19 of the base resonant circuit, and the resonant frequency of the base resonant circuit is lowered. Therefore, the on time of the switching transistor 3 becomes longer and the output voltage of the inverter circuit increases.

Therefore, the discharge lamp 31 is turned on after the filament is preheated as described above, and a so-called soft start is performed.

This increases the lamp life of the discharge lamp and prevents half-wave discharge and the like.

[Problems to be Solved by the Invention] In the discharge lamp lighting device shown in FIG. 2, during the last start, it is necessary to output a high-frequency voltage that does not cause the discharge lamp to light up while flowing a sufficient preheating current to the filament. For this reason, it is necessary to set the on-time of the switching transistor 3 to be quite small, but if this on-time is made too short, the operation of the inverter circuit may become unstable, such as intermittent oscillation. Furthermore, transistor 3
If you reduce the on time of the discharge lamp 3 during soft start,
There was a problem in that the preheating current for the filament No. 1 was reduced, making it impossible to perform sufficient preheating.

SUMMARY OF THE INVENTION In view of the above-mentioned problems in the discharge lamp lighting device, an object of the present invention is to provide a discharge lamp lighting device that can start the lamp after sufficiently preheating the lamp filament at the last start.

[Means for Solving the Problems] A discharge lamp lighting device according to the present invention includes an inverter means for generating a high frequency power source for lighting the discharge lamp, and a power source for one output terminal of the inverter means and one filament of the discharge lamp. an inductor inserted in series between the side terminal and the resonant capacitor connected between the non-power side terminal of the one filament and the non-power side terminal of the other filament;
It is characterized by comprising a switching means for changing the capacitance of the resonance capacitor at the time of starting the discharge lamp.

[Operation] In the above configuration, after the power is turned on and before the lamp is started, the circuit is set so that the capacitance of the resonance capacitor is increased by the switching means. therefore,
During this time, the impedance of the resonance capacitor is low, and the voltage between the cathodes of the discharge lamp does not reach the lamp starting voltage, so the discharge lamp does not light up. Therefore, during this period, current flows through the filament of the discharge lamp to preheat it. Since the impedance of the resonance capacitor is low during this preheating, the output power of the inverter circuit is sufficiently supplied to the filament, and the preheating current of the filament can be increased.

Further, in the above-described configuration, when a predetermined period of time has elapsed after the power is turned on, the switching means switches the circuit so that the capacitance of the resonance capacitor decreases. As a result, the voltage between both cathodes of the discharge lamp increases and the discharge lamp is properly started.

[Example] Hereinafter, the present invention will be explained in detail with reference to the drawings.

FIG. 1 shows a circuit configuration of a discharge lamp lighting device according to an embodiment of the present invention. The device shown in the figure includes a collector resonant circuit composed of a switching transistor 43, a capacitor 57, and an inductor 47, a current-limiting inductor 45, and a current-limiting inductor 45 connected to the base of the switching transistor 43 and magnetically coupled to the current-limiting inductor 45. The inverter circuit includes an inductor 49, an inductor 51 and a capacitor 59, which together with the inductor 49 form a base series resonant circuit, a resonant capacitor 53 connected between the non-power supply side terminals of both filaments of the discharge lamp 65, and the like. In addition,
Resistor 67, diode 73, and resistor 69 constitute a base bias circuit of switching transistor 43. The collector of the switching transistor 43 is connected between one end of a capacitor 57 and the center tap point of the inductor 47, and one end of the inductor 47 and the other end of the capacitor 57 are connected to the positive voltage side terminal of the DC power supply 41. Further, the other end of the inductor 47 is connected to the power supply side terminal of one filament of the discharge lamp 65 via the current limiting inductor 45. Other filament 65b
The power supply side terminal is connected to the positive voltage terminal of the DC power supply 41. A resonance capacitor 53 is connected between the non-power supply side terminals of each filament 65a and 65b, and a series circuit of another capacitor 55 and a contact of a relay 63 is connected to both ends of the capacitor 53. There is. A time constant circuit formed by a resistor 71 and a capacitor 61 is connected between both output terminals of the DC power supply 41, and the output of this time constant circuit, that is, the connection point (node N2) between the resistor 71 and the capacitor 61, and the negative polarity of the power supply 41. Relay 6 is connected between the terminal and
3 coils are connected.

In the discharge lamp lighting device having the above configuration,
Immediately after the DC power supply 41 is applied, the capacitor 61 is not charged, so the voltage at the connection point between the resistor 71 and the capacitor 61, that is, the node N2 is approximately zero. and,
As time passes, the voltage at this node N2 increases
1 and a time constant determined by the value of capacitor 61. If the voltage at node N2 is not high enough to operate relay 63, the contacts of relay 63 are closed, so that capacitor 55 is connected in parallel with capacitor 53. In this state, the inverter circuit oscillates due to positive feedback due to the magnetic coupling between the inductors 45 and 49, and the transistor 43 is turned on and off.

A high frequency voltage is output from one end of the inductor 47 in accordance with the on/off state of the transistor 43 and is applied to the discharge lamp 65 via the current limiting inductor 45. In this case, the on-time of transistor 43 is determined primarily by the series resonant circuit of inductor 49, 51 and capacitor 59 connected to the base circuit.

Further, the off time of the transistor 43 is mainly determined by the resonant frequency of the parallel resonant circuit constituted by the capacitor 57 and the inductor 47 connected to the collector.

In this way, the inverter circuit outputs a high frequency voltage, but since the contacts of the relay 63 are closed as described above, the impedance between the filaments of the discharge lamp 65 is low, and therefore the voltage between the filaments is also low. ing. For this reason, the discharge lamp 65 is not lit and enters a so-called preheating state in which current flows through its filament. In this preheating state, a high frequency voltage is applied between the power supply side terminals of each filament of the discharge lamp 65, but since the capacitance of the capacitor connected between the non-power supply side terminals of each filament is large, the high frequency voltage is applied from the inverter circuit. A larger portion of the generated high-frequency power is applied to the fiment, and the discharge lamp is sufficiently preheated.

After a predetermined period of time has elapsed after the power is turned on, the voltage at node N2 increases and relay 63 operates. As a result, the contacts of the relay 63 are opened, and the capacitor 5 is connected from both ends of the capacitor 53.
5 is separated. Therefore, the voltage between both cathodes of the discharge lamp 65 increases and the discharge lamp lights up.

Thus, according to the configuration shown in FIG. 1, the discharge lamp can be started properly after the filament has been sufficiently preheated.

[Effects of the Invention] As described above, according to the present invention, a sufficient preheating current can be supplied to the filament during preheating, so the soft start operation can be performed accurately, thus extending the lamp life and reducing the half-wave discharge characteristic of discharge lamps. It can be prevented. Furthermore, since there is no need to take measures such as extremely shortening the on-time of the switching transistor, the inverter circuit does not cause intermittent oscillation (an extremely stable and highly reliable lighting device can be obtained).

[Brief explanation of the drawing]

FIG. 1 is an electric circuit diagram showing the general configuration of a discharge lamp lighting device according to an embodiment of the present invention, and FIG. 2 is an electric circuit diagram showing the configuration of a conventional discharge lamp lighting device. 1.41; DC power supply, 3.5.43;) Transistor, 7.45; Current-limiting inductor, 9.11, 13, 47, 49; Inductor, 15.17
．． ......, 23, 53, 55.・・・・・・6
1; Capacitor, 25.27, 29, 67.69, 71, Resistor, 31.
65; Discharge lamp, 33.35.73. diode, 63; relay

Claims (1)

[Scope of Claims] Inverter means for generating a high frequency power source for lighting a discharge lamp, an inductor inserted in series between one output terminal of the inverter means and a power supply side terminal of one filament of the discharge lamp; a resonant capacitor connected between a non-power terminal of the one filament and a non-power terminal of the other filament of the discharge lamp; and switching to change the capacitance of the resonant capacitor when starting the discharge lamp. A discharge lamp lighting device characterized by comprising: means.