JP5019503B2 - Discharge lamp lighting device - Google Patents

Description

  The present invention relates to a discharge lamp lighting device for lighting two or more discharge lamps connected in parallel at a high frequency.

As a discharge lamp lighting device provided with a discharge lamp, there is one as disclosed in Patent Document 1, for example, and such a discharge lamp lighting device is used for a backlight of an LCD (liquid crystal) panel or the like.
A discharge lamp lighting device in which two discharge lamps are connected in parallel is configured as follows. FIG. 2 is a circuit diagram showing a main part of a conventional discharge lamp lighting device, and the conventional discharge lamp lighting device will be described based on this circuit diagram.

The conventional discharge lamp lighting device includes two ballast capacitors 53 and 54 connected in parallel from the H side of the winding transformer 52 to limit the current, and each of the ballast capacitors 53 and 54 has two discharge lamps 55. , 56 are connected in series. A winding transformer 52 is connected to the discharge lamp lighting power source 51.
One of the current setting resistors 58 is connected in series to the discharge lamps 55 and 56, and the other is connected to the L side (GND) of the winding transformer 52. The anode side of the rectifier diode 59 is connected between the current setting resistor 58 and the discharge lamps 55 and 56.
The cathode side of the rectifier diode 59 is connected to one of a control IC 61 that controls the current and a smoothing capacitor 60 that smoothes the current control signal. The other side of the smoothing capacitor 60 is connected to GND.

While the two discharge lamps 55 and 56 are connected and lit, the tube current flows evenly by the ballast capacitors 53 and 54, but one of the discharge lamps, for example, the discharge lamp 55 is cut off (opened). ), About twice as much tube current flows through the other discharge lamp 56, so that there is a problem that the life of the discharge lamp 56 is shortened and heat generation is increased.
Also, since high voltage remains generated at the output terminal, there is a problem in safety.

  Therefore, the present applicant has applied for an invention of a discharge lamp lighting device that prevents a decrease in the life of other discharge lamps and improves safety even if any one of two or more discharge lamps is cut off ( Japanese Patent Application No. 2005-163610).

However, in the case of an LCD panel structure in which the L side (low pressure) of each discharge lamp cannot be connected to the overcurrent detection resistor (the L side is connected in the LCD panel), when one of the discharge lamps in the LCD panel is cut off The same effect cannot be obtained.
JP 2000-30881

  In view of the above-described problems, the problem to be solved by the present invention is a discharge lamp that can prevent a decrease in the life of other discharge lamps even when one of two or more discharge lamps is cut off, and improve safety. An object of the present invention is to provide a lighting device without changing a control circuit of a discharge lamp lighting power source.

In order to solve the above problems, a discharge lamp lighting device according to the present invention includes two or more discharge lamps connected in parallel to a secondary side of a transformer, and provided on the primary side of the transformer. A discharge lamp lighting power source for lighting at a high frequency, and a protection circuit that stops the discharge lamp lighting power source when any one of the discharge lamps is cut off, and one end sides of the discharge lamps are connected to each other is, the one end of the common tube current setting resistor to the discharge lamps are connected to the connection point, the protection circuit, the rectifying diode having an anode connected to a connection point of the discharge lamps, before Symbol discharge lamp lighting One end of a current path is connected to the control IC for controlling the power supply and the cathode of the rectifier diode, and the other end of the current path is connected to the other end of the tube current setting resistor, so that the primary voltage of the transformer is large. Control accordingly By child is controlled, and a switching element that is turned on / off control, the cathode of the rectifier diode is connected to the input side of the control IC, the discharge lamp lighting power to the output side of the control IC is When one or more of the two or more discharge lamps are disconnected and the switching element is switched from an off state to an on state due to a change in the primary voltage of the transformer, the tube current setting resistor And the driving of the discharge lamp lighting power source is stopped based on the control of the control IC.

Preferably, the protection circuit includes two voltage dividing resistors connected in series between the discharge lamp lighting power source and GND, and a positive input terminal connected to a connection point of the two voltage dividing resistors, and a negative input terminal. And an operational amplifier having an anode connected to the cathode of a constant voltage diode connected to GND and an output terminal connected to the control terminal of the switching element, and one of the two or more discharge lamps. When the above is cut, a signal is output from the operational amplifier, and the switching element is switched from the off state to the on state .

According to the discharge lamp lighting device of the present invention, when any one of two or more discharge lamps is cut off, the output of the discharge lamp lighting power supply is stopped by the protection circuit using the voltage fluctuation on the primary side of the winding transformer. It is configured to
Therefore, the current flowing through the other discharge lamps can be suppressed, the life of the discharge lamp can be prevented from being shortened, and it is safe without generating heat.
In either case, the LCD panel has a structure in which the L side (low pressure) of each discharge lamp is connected within the panel, and the LCD panel has a structure in which the L side (low pressure) of each discharge lamp is independent. Can be applied.

  Hereinafter, a discharge lamp lighting device according to the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a circuit diagram showing a discharge lamp lighting device according to the present invention.
As shown in FIG. 1, the discharge lamp lighting device includes a discharge lamp lighting power source 1 for lighting two discharge lamps 5 and 6 at a high frequency, and a winding transformer 2 is connected to the discharge lamp lighting power source 1.

Two ballast capacitors 3, 4 are connected in parallel to the H side of the winding transformer 2, discharge lamps 5, 6 are connected in series to the ballast capacitors 3, 4, and the low pressure side of the two discharge lamps 5, 6 They are connected in the panel.
One side of the tube current setting resistor 8 is connected to the connection point 18 of each discharge lamp 5, 6, and the other side of the tube current setting resistor 8 is connected to the L side (GND) of the winding transformer 2.
The tube current setting resistor 8 adjusts the tube current flowing to the discharge lamps 5 and 6 at the normal time.

The anode side of the rectifier diode 9 is connected between the tube current setting resistor 8 and the connection point of each of the discharge lamps 5, 6. The control IC 11 and the smoothing capacitor for smoothing the tube current control signal are connected to the cathode side of the rectifier diode 9. 10 is connected to the collector of the transistor 12, and the other side of the smoothing capacitor 10 and the emitter of the transistor 12 are connected to GND.
The control IC 11 is connected to the discharge lamp lighting power source 1 and controls the discharge lamp lighting power source 1.

  The discharge lamp lighting power source 1 and GND are connected by voltage dividing resistors 16 and 17, and one side of the second smoothing capacitor 15 and the positive input terminal of the operational amplifier 13 are connected between the voltage dividing resistors 16 and 17. Then, the other side of the smoothing capacitor 15 is connected to GND.

The cathode side of the constant voltage diode 14 and the negative input terminal of the operational amplifier 13 are connected, and the output of the operational amplifier 13 and the base of the transistor 12 are connected.
The anode side of the constant voltage diode 14 is connected to GND.

The discharge lamp lighting device according to the present invention is configured as described above, and in the normal state, the two discharge lamps 5 and 6 are lit, and the tube current flows evenly through the ballast capacitors 3 and 4.
When either one of the two discharge lamps 5 and 6 is cut off for some reason, about twice as much tube current flows to the other discharge lamp as normal.

At this time, since the discharge lamp connected in parallel with the two lamps becomes one lamp, the load impedance increases.
For this reason, the voltage on the H side of the winding transformer 2 increases as the tube current set by the tube current setting resistor 8 flows, and the primary side voltage, that is, the voltage of the discharge lamp lighting power source 1 also increases.

  Therefore, the voltage at both ends of the voltage dividing resistor 16 also rises, and when a predetermined voltage of the constant voltage diode 14 is exceeded, a signal is output from the output of the operational amplifier 13, and this signal drives the base of the transistor 12 to turn on the transistor 12 To do.

As a result, the voltage applied across the tube current setting resistor 8 is forcibly lowered, the timer latch function provided in the control IC 11 is activated, and the driving of the discharge lamp lighting power source 1 is stopped. ing.
This timer latch function compares the reference voltage (for example, 1 [V]) set in the control IC 11 with the voltage at both ends of the tube current setting resistor 8, and the voltage at both ends of the tube current setting resistor 8 is the reference voltage. When it becomes lower than (for example, 1 [V]) for a predetermined period, the output of the control IC 11 is stopped.

  In the discharge lamp lighting device according to the present invention, when one of the two discharge lamps is cut off during lighting or from the beginning, the control IC 11 of the protection circuit supplies the discharge lamp lighting power source 1. Is stopped and the tube current flowing through the other discharge lamp can be suppressed, so that the life of the other discharge lamp is not reduced.

  In the above embodiment, the case of two discharge lamps has been described. However, the present invention can also be applied to a discharge lamp lighting device including three or more discharge lamps. Further, the present invention can be applied to an LCD panel structure in which the L side (low pressure) of each discharge lamp is not connected inside the panel. Furthermore, the discharge lamp lighting power supply may be stopped when the control IC directly receives a predetermined signal output from the operational amplifier.

It is a circuit diagram which shows the discharge lamp lighting device which concerns on the Example of this invention. It is a circuit diagram which shows the conventional discharge lamp lighting device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Discharge lamp lighting power source 2 Winding transformers 3, 4 Ballast capacitor 5, 6 Discharge lamp 7 LCD panel 8 Tube current setting resistor 9 Rectifier diode 10 First smoothing capacitor 11 Control IC
12 transistor 13 operational amplifier 14 constant voltage diode 15 second smoothing capacitor 16, 17 voltage dividing resistor 18 connection point 51 of each discharge lamp discharge lamp lighting power source 52 winding transformer 53, 54 ballast capacitor 55, 56 discharge lamp 58 current setting resistance 59 Rectifier diode 60 Smoothing capacitor 61 Control IC

Claims (2)

Two or more discharge lamps connected in parallel to the secondary side of the transformer, a discharge lamp lighting power source for lighting each discharge lamp at a high frequency provided on the primary side of the transformer, and any of the discharge lamps In a discharge lamp lighting device comprising a protection circuit that stops the discharge lamp lighting power supply when one of them is cut off,
One end sides of each discharge lamp are connected to each other, and one end of a tube current setting resistor common to each discharge lamp is connected to the connection point,
The protection circuit is
A rectifier diode having an anode connected to a connection point of each discharge lamp ;
A control IC for controlling the pre-Symbol discharge lamp lighting power,
One end of a current path is connected to the cathode of the rectifier diode, the other end of the current path is connected to the other end of the tube current setting resistor, and a control terminal is controlled according to the magnitude of the primary side voltage of the transformer And having a switching element that is on / off controlled,
The cathode of the rectifier diode is connected to the input side of the control IC, and the discharge lamp lighting power source is connected to the output side of the control IC,
When one or more of the two or more discharge lamps are burned out, the switching element is switched from an off state to an on state due to a change in the primary voltage of the transformer, whereby the voltage across the tube current setting resistor is changed. And the driving of the discharge lamp lighting power supply is stopped based on the control of the control IC. The protection circuit is
Two voltage dividing resistors connected in series between the discharge lamp lighting power source and GND;
A positive input terminal is connected to a connection point of the two voltage dividing resistors, a negative input terminal is connected to a cathode of a constant voltage diode whose anode is connected to GND, and an output terminal is connected to a control terminal of the switching element. Operational amplifier
Further comprising
The discharge lamp according to claim 1 , wherein when one or more of the two or more discharge lamps are burned out, a signal is output from the operational amplifier to switch the switching element from an off state to an on state. Lighting device.

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