JP2006286260A - Discharge lamp lighting device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent breakdown due to overvoltage of a switching element of a preheating control circuit of a discharge lamp lighting device. <P>SOLUTION: The device 6 is provided with an inverter circuit 2 lighting hot-cathode discharge lamps 1a, 1b with high-frequency voltage generated from an alternate current power source E driven by a pair of switches Q1, Q2, an inverter control circuit 3 controlling operation states of preheating/driving/lighting of the discharge lamps by driving the switching elements of the inverter circuits, a series circuit of a coupling capacitor C6, a primary winding of a preheating transformer T2 without any gaps at the core, and a preheating switching element Q3, and a capacitor C7 connected in parallel with both ends of the preheating switching elements. The device is further provided with a preheating control circuit 4 passing current to filaments of the discharge lamp at its operating state of preheating/driving with control of the inverter circuit to preheat it, and restraining current flowing in the filaments of the discharge lamp at its operating state of lighting. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a discharge lamp lighting device for high-frequency lighting of a hot cathode type discharge lamp, and in particular, prevents a switching element of a preheating control circuit from being damaged due to overvoltage.

  A conventional discharge lamp lighting device includes an inverter circuit for lighting a hot cathode discharge lamp with a high-frequency voltage generated from a DC power source by driving a pair of switching elements, and driving the switching element of the inverter circuit to drive the discharge lamp. An inverter control circuit for controlling a preheating / starting / lighting operation state; and preheating by supplying a current to a filament of the discharge lamp in the preheating / starting operation state of the discharge lamp under the control of the inverter control circuit; And a preheating control circuit that suppresses a current flowing through the filament of the discharge lamp in a lighting operation state, and the preheating control circuit includes a series circuit of a capacitor, a primary winding of a preheating transformer, and a preheating switch. .

When the power is turned on, the inverter control circuit controls a pair of switching elements of the inverter circuit so as to apply a resonance voltage that cannot be lit to the discharge lamp. At this time, the preheating switch of the preheating control circuit is turned on, and a rectangular high frequency voltage is applied to the preheating transformer, which is applied from the secondary winding of the preheating transformer to the filament of the discharge lamp to heat the filament. The discharge lamp is preheated.
After a predetermined time has elapsed, the inverter control circuit drives the pair of switching elements of the inverter circuit so as to apply a resonance voltage that can light the discharge lamp, starts the discharge lamp, and then starts the inverter circuit. The discharge lamp is normally lit by changing the drive frequency of the pair of switching elements. At this time, since the preheating switch of the preheating control circuit is turned off and the application of the high frequency voltage to the primary side of the preheating transformer is interrupted, the filament current flowing on the secondary side becomes almost zero (see, for example, Patent Document 1). ).
Japanese Unexamined Patent Publication No. 2004-193075 (first page, FIG. 1)

In a conventional discharge lamp lighting device, when a MOSFET is used as a preheating switch of a preheating control circuit, the discharge lamp is preheated and started, and then the preheating switch MOSFET is turned off when the discharge lamp is turned on. At that time, due to the leakage inductance of the preheating transformer and the resonance of the combined capacitance between the drain and source of the MOSFET and between the drain and gate, between the drain and source of the MOSFET every cycle of the oscillation frequency of the inverter circuit Since a surge voltage is applied, a high withstand voltage preheating switch element is required. In some cases, the preheating switch element is broken by overvoltage.
The present invention has been made to solve such problems, and an object of the present invention is to provide a discharge lamp lighting device that can prevent the preheating switch element of the preheating control circuit from being damaged due to overvoltage.

  A discharge lamp lighting device according to the present invention includes an inverter circuit for lighting a hot cathode discharge lamp with a high-frequency voltage generated from a DC power source by driving a switching element, and driving the switching element of the inverter circuit to drive the discharge lamp. Inverter control circuit for controlling the operation state of preheating, starting and lighting, a coupling capacitor, a primary circuit of a preheating transformer without a gap in the core and a series circuit of a preheating switch element, and both ends of the preheating switch element A capacitor connected in parallel, preheated by flowing a current through the filament of the discharge lamp in the preheating / starting operation state of the discharge lamp under the control of the inverter control circuit, and in the lighting operation state of the discharge lamp. A preheating control circuit for suppressing a current flowing in the filament of the discharge lamp.

  As described above, since the preheating transformer that constitutes a part of the preheating control circuit has a structure without a gap in the core, the leakage flux corresponding to the leakage inductance on the primary side of the preheating transformer is not lost. Since the LC resonance element of the preheating control circuit is eliminated, when the preheating switch element of the preheating control circuit is turned from on to off, a surge high voltage generated every cycle of oscillation of the inverter circuit is suppressed. The preheating switch element that forms part of the preheating control circuit does not need to be selected with a higher withstand voltage than is necessary, and there is no risk of destruction due to overvoltage, and capacitors are connected in parallel across the preheating switch element. Therefore, the voltage is divided by the coupling capacitor in the preheating control circuit, and the voltage across the preheating switch element is further reduced. But there is an effect of improving.

Embodiment 1 FIG.
FIG. 1 is a circuit diagram showing a configuration of a discharge lamp lighting device according to Embodiment 1 of the present invention, FIG. 2 shows a voltage waveform between the drain and source of a MOSFET of a preheating control circuit, and FIG. FIG. 4B is a waveform diagram of the first embodiment.
In FIG. 1, a discharge lamp lighting device according to Embodiment 1 of the present invention lights hot cathode discharge lamps 1a and 1b with a high-frequency voltage generated from a DC power supply E by driving a pair of switching elements Q1 and Q2. The inverter circuit 2 and the inverter control circuit 3 for controlling the operating state of the discharge lamps 1a and 1b by alternately driving the switching elements Q1 and Q2 of the inverter circuit 2 and the current flowing through the filaments of the discharge lamps 1a and 1b are controlled. The preheating control circuit 4 is generally provided.

A series circuit of a pair of switching elements Q1 and Q2 of the inverter circuit 2 is connected to the DC power source E. A series circuit of a coupling capacitor C6, a primary winding P2 of the preheating transformer T2, a preheating switch element Q3, and a voltage dividing capacitor connected in parallel to both ends of the preheating switch element Q3 are connected to both ends of the switching element Q2. A preheating control circuit 4 composed of C7 is connected in parallel. The preheating switch element Q3 is driven on and off by the inverter control circuit 3.
The secondary winding S1 of the preheating transformer T2 of the preheating control circuit 4 is connected to both terminals of the filament F1 of the discharge lamp 1a via the capacitor C4, and the terminal not connected to the capacitor C4 of the filament F1 is a ballast choke. It is connected to one end of the switching element Q2 via the primary winding P1 of T1.

Further, the secondary winding S2 of the preheating transformer T2 is connected to both terminals of the filament F4 of the discharge lamp 1b via the capacitor C5, and the terminal not connected to the capacitor C5 of the filament F4 is connected via the capacitor C3. The other end of the switching element Q2 is connected.
Further, the secondary winding S3 of the preheating transformer T2 is connected to a series circuit of the filament F2 of the discharge lamp 1a and the filament F3 of the discharge lamp 1b via the secondary winding S4 of the ballast choke T1. Both ends of the capacitor C2 are connected to a terminal connected to the capacitor C4 of the filament F1 and a terminal connected to the capacitor C5 of the filament F4.

Next, the operation of the discharge lamp lighting device according to Embodiment 1 of the present invention will be described with reference to FIG.
In the inverter circuit 2, the switching elements Q1 and Q2 are alternately turned on and off by a drive signal from the inverter control circuit 3 to the switching elements Q1 and Q2, and the primary winding P1 and the discharge lamps 1a and 1b of the ballast choke T1 A rectangular wave-shaped high-frequency voltage is applied to a load circuit composed of a capacitor C2 and a capacitor C3 connected in parallel to this, and the discharge lamps 1a and 1b are lit at a sinusoidal high-frequency.

  When the power is turned on, the inverter control circuit 3 drives the pair of switching elements Q1 and Q2 of the inverter circuit 2 at a high frequency to start oscillation, and the discharge lamps 1a and 1b have a low resonance voltage that does not light up. Applied. At this time, the inverter control circuit 3 turns on the preheating switch element Q3 of the preheating control circuit 4, and a rectangular high frequency voltage is applied to the primary winding P2 of the preheating transformer T2, which is converted into the preheating transformer. The filaments F1 and F4 are preheated by being applied to the filaments F1 and F4 of the discharge lamps 1a and 1b from the secondary windings S1 and S2 of the vessel T2 via the capacitors C4 and C5. Further, the voltage generated in the secondary winding S3 of the preheating transformer T2 and the secondary winding S4 of the ballast choke T1 is applied to the filaments F2 and F3 of the discharge lamps 1a and 1b to preheat the filaments F2 and F3.

Then, after preheating for a predetermined time, the inverter control circuit 3 changes the drive frequency of the inverter circuit 2 to a low frequency, applies a high resonance voltage for lighting the discharge lamps 1a and 1b, and sets the discharge lamps 1a and 1b. Light up.
Thereafter, the inverter control circuit 3 changes the drive frequency of the inverter circuit 2 to the lighting frequency and shifts to the normal lighting state. At this time, the inverter control circuit 3 turns off the preheating switch element Q3 of the preheating control circuit 4. Then, since the application of the high frequency voltage to the primary winding P2 of the preheating transformer T2 is interrupted, the filament current flowing from the secondary side of the preheating transformer T2 becomes almost zero. Thereby, the loss by the filament current at the time of lighting of the discharge lamps 1a and 1b can be almost eliminated.

  In the first embodiment, as described above, the pre-heating / starting of the discharge lamps 1a, 1b is performed, the discharge lamps 1a, 1b are turned on, and pre-heating is performed when the pre-heating switch element Q3 of the pre-heating control circuit 4 is turned off. A surge voltage is generated at every cycle of the oscillation frequency of the inverter circuit 2 due to the leakage magnetic flux corresponding to the leakage inductance of the transformer T2, but the preheating transformer T2 constituting a part of the preheating control circuit 4 is provided in the core. Since the structure has no gap, the leakage magnetic flux corresponding to the leakage inductance of the preheating transformer T2 is eliminated, and the LC resonance element is eliminated in the preheating control circuit 4. Therefore, a surge high voltage for each cycle of oscillation of the inverter circuit 2 is suppressed, and it is not necessary to select a high-voltage product more than necessary for the preheating switch element constituting a part of the preheating control circuit 4. There is no longer any risk of destruction.

Further, by using a MOSFET as the preheating switch element Q3 of the preheating control circuit 4, the preheating switch element Q3 is driven by voltage, so that the on / off drive control of the preheating switch element Q3 is easily performed. I was able to do it.
Further, the capacitor C7 is connected in parallel to both ends of the preheating switch element Q3 of the preheating control circuit 4, so that the voltage is divided by the coupling capacitor C6 in the preheating control circuit 4, and the voltage across the preheating switch element Q3 is further increased. Since it was kept low, the reliability against overvoltage was further improved.

  Referring to FIG. 2A, the voltage waveform between the drain and the source of the MOSFET of the preheating control circuit of the conventional example shows the rectangular wave of the inverter circuit 2 when the preheating switch element Q3 of the preheating control circuit 4 is off. Although it can be seen that a surge voltage is generated at the rising edge, when looking at FIG. 2B, the voltage waveform between the drain and source of the MOSFET according to the first embodiment of the present invention shows the preheating of the preheating control circuit 4. It can be seen that the generation of surge voltage is suppressed when the rectangular wave of the inverter circuit 2 rises when the switching element Q3 is turned off.

Embodiment 2. FIG.
3 is a circuit diagram showing a configuration of a discharge lamp lighting device according to Embodiment 2 of the present invention, FIG. 4 shows voltage waveforms of respective parts of the discharge lamp lighting device, (a) is a waveform diagram of a conventional example, b) is a waveform diagram of the second embodiment.
In the second embodiment, the same components as those in the first embodiment are denoted by the same reference numerals, and the description of the overlapping components is omitted.
In the second embodiment, a diode D1 is connected in parallel to both ends of a coupling capacitor C6 constituting a part of the preheating control circuit 4 so that the output terminal side of the inverter circuit 2 becomes a cathode.

In the second embodiment, the discharge lamps 1a and 1b are preheated and started, the discharge lamps 1a and 1b are turned on, and the preheating switch element Q3 of the preheating control circuit 4 is turned off. When the filaments F1 and F4 of 1a and 1b are disconnected, the secondary side of the preheating transformer T2 of the preheating control circuit 4 is opened and becomes only the primary side, so the preheating transformer T2 has an equivalently small inductance value. Become.
In this case, since the voltage between both ends of the preheating control circuit 4, that is, the drain-source (DS) of the switching element Q2, is a rectangular wave, the primary winding P2 of the preheating transformer T2 connected to the coupling capacitor C6 The voltage at both ends of the series circuit of the preheating switch element Q3 is also a rectangular wave, but the voltage between the drain and source (DS) of the preheating switch element Q3, that is, the both ends of the capacitor C7 is the voltage of the preheating transformer T2. The slope of the rectangular wave changes due to the above-described reduced inductance value of the primary winding P2 and the capacitance of the capacitor C7, resulting in a triangular wave shape.

In this case, the voltage of the capacitor C7 (between D and S of the preheating switch element Q3) can be expressed by the following equation.
C7 voltage = Q2 DS voltage -C6 voltage -T2 P1 voltage In the above equation, the Q2 DS voltage is constant, and the T2 P1 voltage is also substantially constant.
Considering charging / discharging of the coupling capacitor C6 at this time, in the case of charging, the voltage of the coupling capacitor C6 is charged in the minus direction. Therefore, the capacitor C7 (preheating switch element Q3) is used to establish the above equation. Therefore, a voltage higher than that of the switching elements Q1 and Q2 may be applied to the preheating switch element Q3. For this reason, the preheating switch element Q3 requires components having a higher breakdown voltage than the switching elements Q1 and Q2.
Therefore, in the second embodiment, since the diode D1 is connected in parallel to both ends of the coupling capacitor C6 so that the output terminal side of the inverter circuit 2 becomes the cathode, the diode D1 charges the coupling capacitor C6 in the negative direction. Therefore, the preheating switch element Q3 does not have to have a higher withstand voltage than necessary.

4A, it can be seen that a high voltage is generated in the triangular waveform of the voltage between the drain and source of the MOSFET of the preheating control circuit of the conventional example, but FIG. 4B is seen. It can be seen that a low voltage is generated in the triangular waveform of the drain-source voltage of the MOSFET according to the second embodiment of the present invention.
Note that the voltage of the coupling capacitor C6 is also lower in the second embodiment than in the conventional example, and it can be seen that the voltage of the primary winding P2 of the preheating transformer T2 is not changed between the conventional example and the second embodiment. .

Embodiment 3 FIG.
In the third embodiment, preheating / starting of the discharge lamps 1a, 1b is performed, and then the preheating switch element Q3 of the preheating control circuit 4 is turned off when the discharge lamps 1a, 1b are turned on. This relates to the operation time of the switch element Q3.
In the third embodiment, the inverter control circuit 3 turns on the MOSFET that is the preheating switch element Q3 of the preheating control circuit 4 before the inverter circuit 2 starts oscillating. It is possible to suppress the application of an overvoltage.
Further, preheating is performed by controlling the MOSFET from on to off in a time (eg, over 0.3 seconds) that is longer than one period of the oscillation frequency of the inverter circuit 2 by gradually decreasing the gate voltage of the MOSFET. Even if an LC resonance circuit is formed with the capacitor C7 in the control circuit 4 and an inductance component such as the wiring pattern of the printed circuit board constituting the inverter circuit 2, the preheating control circuit 4, etc., generation of back electromotive force is suppressed. Since no resonance voltage is generated, it is possible to suppress an overvoltage from being applied between the drain and the source when the MOSFET is turned on and off.

  5A, the voltage waveform between the drain and source of the MOSFET of the preheating control circuit according to the first embodiment of the present invention shows an inverter circuit when the preheating switch element Q3 of the preheating control circuit 4 is off. It can be seen that a surge voltage is generated at the rise of the rectangular wave 2, but when FIG. 5B is seen, the voltage waveform between the drain and source of the MOSFET according to the third embodiment of the present invention is preheated. It can be seen that the occurrence of surge voltage is suppressed when the rectangular wave of the inverter circuit 2 rises when the preheating switch element Q3 of the control circuit 4 is off.

The circuit diagram which shows the structure of the discharge lamp lighting device which concerns on Embodiment 1 of this invention. The voltage waveform between the drain-source of MOSFET of a preheating control circuit is shown, (a) is a wave form diagram of a prior art example, (b) is a wave form diagram of Embodiment 1. FIG. The circuit diagram which shows the structure of the discharge lamp lighting device which concerns on Embodiment 2 of this invention. The voltage waveform of each site | part of a discharge lamp lighting device is shown, (a) is a waveform diagram of a prior art example, (b) is a waveform diagram of Embodiment 2. FIG. The voltage waveform between the drain-source of MOSFET of a preheating control circuit of a discharge lamp lighting device, and the waveform figure of a filament current are shown, (a) is the waveform diagram of Embodiment 1, (b) is the waveform diagram of Embodiment 3. FIG. .

Explanation of symbols

1a, 1b Discharge lamp, 2 inverter circuit, 3 inverter control circuit, E DC power supply, Q1 switching element, Q2 switching element, Q3 preheating switch element (MOSFET), T1 ballast choke, P1, P2 primary winding, S1 to S4 Secondary winding, T2 preheating transformer, C6 coupling capacitor, C7 capacitor.

Claims (4)

An inverter circuit for lighting a hot cathode discharge lamp with a high-frequency voltage generated from a DC power source by driving a switching element;
An inverter control circuit that drives the switching element of the inverter circuit to control the operation state of preheating, starting, and lighting of the discharge lamp;
A coupling capacitor, a primary winding of the preheating transformer with no gap in the core and a series circuit of the preheating switch element, and a capacitor connected in parallel to both ends of the preheating switch element;
The current is supplied to the filament of the discharge lamp in the pre-heating / starting operation state of the discharge lamp by the control of the inverter control circuit to pre-heat, and the current flowing to the filament of the discharge lamp is suppressed in the operating state of the discharge lamp. A preheating control circuit to perform,
A discharge lamp lighting device comprising:   The preheating control circuit is connected between output terminals of the inverter circuit, and diodes are connected in parallel to both ends of a coupling capacitor of the preheating control circuit so that the output terminal side of the inverter circuit becomes a cathode. Item 2. A discharge lamp lighting device according to Item 1.   The inverter control circuit turns on the preheating switch element of the preheating control circuit before the inverter circuit starts oscillating, and controls the preheating switch element from on to off of the oscillation frequency of the inverter circuit. The discharge lamp lighting device according to claim 1 or 2, wherein the discharge lamp lighting device is operated in a time longer than one cycle. The discharge lamp lighting device according to any one of claims 1 to 3, wherein the preheating switch element of the preheating control circuit is a MOSFET.

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