JP2004119206A - Discharge lamp lighting device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a discharge lamp lighting device in which a long-length cold cathode tube for a backlight such as a large-sized liquid crystal monitor can be driven by reducing hardware scale and manufacturing cost while this is constituted of a less number of components without requiring a triangular wave generating circuit. <P>SOLUTION: This device is provided with a direct-current power source 1, a PNP type bipolar transistor 2 as a switch means, a diode 3 for current reflux, an inductor 4 for choking, a Royer type inverter 5, a ballast capacitor 6, a discharge lamp 7 such as a cold cathode tube or a rare gas discharge lamp, a resistor 8 as a current detecting means, a voltage conversion circuit 9 as a voltage conversion means, a diode 10 as a voltage limiting element, a comparator 11 as a comparing means, the reference voltage source 12, and a resistor 13 and a resistor 14 for base biases. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a discharge lamp lighting device, and more particularly to a discharge lamp lighting device for driving a backlight cold cathode tube for a large liquid crystal monitor or the like.
[0002]
[Prior art]
A long cold-cathode tube having a length of 1 m is used for a backlight of a large liquid crystal monitor or a wall-mounted liquid crystal television. In general, a discharge lamp such as a cold-cathode tube is desirably driven at a constant current because the tube current sharply increases after the lighting start voltage.Conventionally, an inverter that obtains a high voltage using a transformer represented by a Royer-type inverter is conventionally used. Since the output impedance is low and the output is driven at a constant voltage, a small-capacity, high-withstand-voltage ballast capacitor, which is an impedance element, is inserted in series between the inverter and the discharge lamp to increase the apparent output impedance of the inverter. Lighting was performed close to driving. Since the capacity of the ballast capacitor needs to be sufficiently larger than the impedance of the discharge lamp, the value of the cold-cathode tube ranges from several pF to several tens pF. The output voltage of the transformer of the inverter is the vector sum of the tube voltage at both ends of the discharge lamp and the voltage at both ends of the ballast capacitor, and generally requires a voltage 2.5 times or more the tube voltage. Since the tube voltage required for lighting the long cold cathode tubes in the 1 m class is 1 KV or more, the output voltage of the inverter, that is, the output voltage of the transformer, needs to be 2.5 kV or more. However, a general-purpose inexpensive small transformer has a withstand voltage of about 1.5 kV and thus has a short withstand voltage. A transformer with a withstand voltage of 2.5 kV or more is expensive and large and cannot be used. Therefore, in the conventional discharge lamp lighting device, the output current of the inverter is increased by feeding back the tube current of the discharge lamp, and the output voltage of the inverter is reduced to about the tube voltage required for lighting. A small transformer can be used. (For example, refer to Patent Document 1.)
As shown in FIG. 3, a conventional discharge lamp lighting device includes a DC power supply 101, a PNP type bipolar transistor 102 as a switch, a current return diode 103, a choke inductor 104, and a lower type. An inverter 105, a ballast capacitor 106, a discharge lamp 107, a resistor 108 for detecting a tube current, a rectifying and smoothing circuit 109, a comparator 110, a triangular wave generating circuit 111, and a resistor 112 are provided.
[0003]
The inverter 105 includes a transformer 1051, a capacitor 1052 for resonance, NPN-type bipolar transistors 1053 and 1054 for push-pull switching, and a resistor 1055 for base bias.
[0004]
Then, the voltage of the DC power supply 101 is turned on and off by the PNP type bipolar transistor 102 and the diode 103, the output current is smoothed by the inductor 104, supplied as the power supply voltage of the inverter 105, and the ballast capacitor 106 is supplied by the AC output voltage of the inverter 105. The discharge lamp 107 is turned on through the lamp, the tube current flowing through the discharge lamp 107 is converted into a voltage by the resistor 108, converted into a DC voltage by the rectifying / smoothing circuit 109, and output by the triangular wave generation circuit 111 and the comparator 110. The comparison is performed, and the comparison result output signal of the comparator 110 is supplied to the base of the PNP-type bipolar transistor 102 via the resistor 112. If the tube current increases, the output voltage of the inverter 105 decreases. Output power There is increasing, so that the output impedance of the inverter 105 is increased.
[0005]
[Patent Document 1]
JP-A-8-78180 (FIG. 1)
[0006]
[Problems to be solved by the invention]
However, the conventional discharge lamp lighting device shown in FIG. 3 converts a tube current into a DC voltage, compares the DC voltage with a triangular wave, generates a pulse width modulation signal, and opens and closes the switch means by the pulse width modulation signal. Therefore, a triangular wave generating circuit for generating a triangular wave is required as a function block, and there is a problem in that the number of elements is large and the hardware scale and cost are increased.
[0007]
The present invention has been made in view of such a problem, and does not require a triangular wave generating circuit, is configured with a smaller number of elements, has a small hardware scale, reduces costs, and has a large liquid crystal monitor and the like. An object of the present invention is to provide a discharge lamp lighting device that can drive a long cold cathode tube for a backlight.
[0008]
[Means for Solving the Problems]
The discharge lamp lighting device according to the present invention includes a switch unit that intermittently outputs a power supply voltage, an inverter that converts an output voltage of the switch unit into an AC voltage and lights the discharge lamp with the AC voltage, A current detecting means for converting a flowing current into a voltage and outputting the voltage; a voltage converting means for converting an output voltage of the current detecting means into a pulsating voltage and outputting the pulsating voltage; Comparing means for controlling the intermittent operation of the switch means based on the result.
[0009]
Further, the comparing means performs the control such that the AC voltage decreases when the current flowing through the discharge lamp increases, and the AC voltage increases when the current flowing through the discharge lamp decreases. The above control is performed.
[0010]
Further, the voltage conversion means includes a half-wave rectifier circuit.
[0011]
Further, the voltage conversion means includes a voltage limiting element connected to an output terminal of the half-wave rectifier circuit.
[0012]
Further, the comparison means has a non-inverting input terminal and an inverting input terminal, and further includes a voltage limiting element connected between the non-inverting input terminal and the inverting input terminal.
[0013]
Further, the invention is characterized in that the inverter includes a switching transistor whose input bias voltage is supplied from the power supply voltage.
[0014]
BEST MODE FOR CARRYING OUT THE INVENTION
Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a configuration diagram of a discharge lamp lighting device according to a first embodiment of the present invention. As shown in FIG. 1, a discharge lamp lighting device according to a first embodiment of the present invention comprises a DC power supply 1, a PNP bipolar transistor 2 as a switch, a current return diode 3, and a choke diode. An inductor 4, a lower-type inverter 5, a ballast capacitor 6, a discharge lamp 7 such as a cold cathode tube or a rare gas discharge lamp, a resistor 8 as current detection means, and a voltage conversion circuit 9 as voltage conversion means. , A diode 10 as a voltage limiting element, a comparator 11 as comparison means, a reference voltage source 12, and resistors 13 and 14 for base bias.
[0015]
An inverter 5 includes a transformer 51 having a push-pull primary winding, a secondary winding, and a feedback winding, a resonance capacitor 52 connected in parallel to the primary winding to perform a resonance operation, and a push-pull switching. , An NPN bipolar transistor 53 and an NPN bipolar transistor 54, and a base bias resistor 55 and a resistor 56.
[0016]
The voltage conversion circuit 9 includes a half-wave rectification circuit 95 and a constant voltage diode 94 as a voltage limiting element. The half-wave rectification circuit 95 includes a diode 91, a capacitor 92, and a resistor 93.
[0017]
The low-potential output terminal of the DC power supply 1 is connected to the ground as the low-potential power supply voltage, the high-potential output terminal of the DC power supply 1 is connected to the emitter of the PNP bipolar transistor 2, and the collector of the PNP bipolar transistor 2 Is connected to one end of the inductor 4, a resistor 14 is connected between the base and the emitter of the PNP bipolar transistor 2, and a resistor 13 is connected between the output terminal of the comparator 11 and the base of the PNP bipolar transistor 2. , The anode of the diode 3 is connected to the ground, and the cathode of the diode 3 is connected to the collector of the PNP bipolar transistor 2.
[0018]
In the inverter 5, the collector of the NPN-type bipolar transistor 53 and the collector of the NPN-type bipolar transistor 54 are connected to the primary push-pull winding, and the midpoint of the primary push-pull winding is connected to the other end of the inductor 4. A capacitor 52 is connected in parallel with the primary winding of the push-pull, an emitter of the NPN bipolar transistor 53 and an emitter of the NPN bipolar transistor 54 are connected to the ground, and a base of the NPN bipolar transistor 53 and the NPN bipolar transistor 54 are connected. The base is connected to the feedback winding, the resistor 55 is connected between the base of the NPN bipolar transistor 53 and the high potential output terminal of the DC power supply 1, and the resistor 56 is connected to the base of the NPN bipolar transistor 54 and the DC power supply. 1 with the high potential side output terminal It is connected to.
[0019]
The switching operation is stabilized by supplying the input bias voltage of the base of the NPN bipolar transistor 53 and the base of the NPN bipolar transistor 54 from the power supply voltage of the DC power supply 1.
[0020]
One end of the secondary winding is connected to one end of the discharge lamp 7 via the ballast capacitor 6, the other end of the secondary winding is connected to the ground, and the other end of the discharge lamp 7 is connected to the ground via the resistor 8. Connected to the anode of a diode 91 as an input terminal of a half-wave rectifier circuit 95, a capacitor 92 is connected between the cathode of the diode 91 and ground, and a resistor 93 is connected in parallel with the capacitor 92. The cathode of the constant voltage diode 94 is connected to the cathode of the diode 91 as the output terminal of the half-wave rectifier circuit 95, and the anode of the constant voltage diode 94 is connected to the ground.
[0021]
The comparator 11 has a non-inverting input terminal and an inverting input terminal. The non-inverting input terminal is connected to the cathode of a diode 91 as an output terminal of the voltage conversion circuit 9. The output terminal of the reference voltage source 12 is connected to the ground, the anode of the diode 10 is connected to the non-inverting input terminal, and the cathode of the diode 10 is connected to the inverting input terminal.
[0022]
In the above configuration, the PNP-type bipolar transistor 2 and the diode 3 intermittently output the power supply voltage of the DC power supply 1, and the output current is smoothed by the inductor 4 and supplied as the power supply voltage of the inverter 5. The output voltage of the collector of the bipolar transistor 2 is converted into an AC voltage via the inductor 4, and the discharge lamp 7 is turned on by the AC voltage.
[0023]
The resistor 8 converts the tube current flowing through the discharge lamp 7 into a voltage (V1) and outputs the voltage, and the half-wave rectifier circuit 95 of the voltage conversion circuit 9 pulsates the output voltage (V1) of the resistor 8 by half-wave rectification. The output is converted to a voltage (V2), and the comparator 11 compares the pulsation voltage (V2) with the reference voltage (VREF) of the reference voltage source 12 and outputs a comparison result output signal (V3) which is a result of the comparison from the output terminal. And controls the intermittent operation of the PNP bipolar transistor 2 based on the comparison result output signal (V3).
[0024]
The comparison result output signal (V3) of the comparator 11 becomes the power supply voltage level when the pulsation voltage (V2) is higher than the reference voltage (VREF), and the ground level (0 V) when the pulsation voltage (V2) is lower than the reference voltage (VREF). It becomes.
[0025]
The constant voltage diode 94 is a diode for preventing the capacitor 92 from being overcharged and unstable operation when a large current flows into the discharge lamp 7 instantaneously. This is a diode for preventing the operation from becoming unstable due to excessive input. As for the constant voltage diode 94 and the diode 10, both may be provided, or only one of them may be provided.
[0026]
Next, the operation will be described with reference to FIG. When the discharge lamp 7 is turned on, the output voltage (V1) of the resistor 8 has an AC voltage waveform as shown in FIG. Since the output voltage (V1) of the resistor 8 is rectified by the diode 91 and charged in the capacitor 92 while the voltage of the capacitor 92 is discharged by the resistor 93, the output from the voltage conversion circuit 9 is shown in FIG. Thus, the pulsating voltage (V2) in which the pulsating component voltage (ΔV) is superimposed on the DC voltage is output.
[0027]
As shown in FIGS. 2C and 2D, when the pulsation voltage (V2) is equal to or higher than the reference voltage (VREF), the comparison result output signal (V3) becomes the power supply voltage level, and the PNP bipolar transistor 2 Turns off and opens, the collector voltage (V4) of the PNP bipolar transistor 2 becomes the ground level (0 V), and when the pulsation voltage (V2) is lower than the reference voltage (VREF), the comparison result output signal (V3) becomes the ground level (V3). 0V), the PNP bipolar transistor 2 turns on and closes, and the collector voltage (V4) of the PNP bipolar transistor 2 becomes the power supply voltage level.
[0028]
Note that, as shown in FIG. 2B, the resistor 8, the capacitor 92, the resistor 93, and the resistor 93 are arranged such that the reference voltage (VREF) falls within the range of the pulsating component voltage (ΔV) of the pulsating voltage (V2) in a steady state. Each constant of the reference voltage (VREF) is determined.
[0029]
Since the waveform of the pulsation voltage (V2) has a slope, when the tube current increases, the amplitude of the pulsation voltage (V2) increases, and a period (toff) in which the pulsation voltage (V2) becomes equal to or higher than the reference voltage (VREF). And the duty ratio of the collector voltage (V4) of the PNP-type bipolar transistor 2 serving as the power supply voltage of the inverter 5 decreases as compared with the period (ton) during which the pulsating voltage (V2) is lower than the reference voltage (VREF). The output voltage of the inverter 5 decreases, and an increase in tube current is suppressed.
[0030]
Conversely, when the tube current decreases, the amplitude of the pulsation voltage (V2) decreases, and the period (toff) in which the pulsation voltage (V2) is equal to or higher than the reference voltage (VREF) is equal to the pulsation voltage (V2). ), The duty ratio of the collector voltage (V4) of the PNP bipolar transistor 2 serving as the power supply voltage of the inverter 5 increases, the output voltage of the inverter 5 increases, and the tube current decreases. Reduction is suppressed.
[0031]
As described above, the comparator 11 performs control so that the AC voltage decreases when the tube current flowing through the discharge lamp 7 increases, and controls the AC voltage to increase when the tube current flowing through the discharge lamp 7 decreases. Do.
[0032]
Therefore, the output impedance of the inverter 5 apparently increases, and the impedance value can be reduced by increasing the capacitance value of the ballast capacitor 6 by the increased impedance.
[0033]
When the impedance of the ballast capacitor 6 decreases, the voltage generated at both ends of the ballast capacitor 6 decreases for the same tube current, and the output voltage of the transformer 51 obtained by vector-adding the tube voltage of the discharge lamp 7 can also be reduced.
[0034]
Since the output voltage of the transformer 51 of the inverter 5 can be set low, insulation measures can be simplified, the transformer 51 and the circuit board can be downsized, and the cost can be reduced.
[0035]
Further, in the conventional discharge lamp lighting device, it is necessary to convert the tube current into a pulsating DC voltage, so that the time constant of the rectifying and smoothing circuit must be increased. In the electric lamp lighting device, since the pulsating voltage can be maintained, the time constant of the half-wave rectifier circuit can be reduced. Therefore, in the discharge lamp lighting device according to the present embodiment, since the response time to the change in the tube current is short, the oscillation phenomenon and the like hardly occur, and the stable operation can be performed.
[0036]
As described above, according to the discharge lamp lighting device of the first embodiment of the present invention, not only can an inexpensive small transformer with low withstand voltage and a ballast capacitor be used, but also a triangular wave generation circuit conventionally required is unnecessary. A discharge lamp lighting device which is configured with a smaller number of elements, has a small hardware scale, reduces costs, and can drive a long cold cathode tube for a backlight such as a large liquid crystal monitor is realized. The effect that it can be obtained is obtained.
[0037]
In the discharge lamp lighting device of the present embodiment, a lower type inverter has been described as an example of an inverter.
[0038]
Also, the PNP type bipolar transistor has been described as an example of the switch means, but it is easy to change the polarity of the comparison result output signal to the NPN type bipolar transistor, and further to change to another element such as MOSFET, JFET and the like. It is also easy to do.
[0039]
【The invention's effect】
Advantageous effects of the present invention are that a triangular wave generation circuit is not required, the number of elements is small, the hardware scale is small, the cost is reduced, and a long cold cathode tube for a backlight such as a large liquid crystal monitor is driven. It is possible to realize a discharge lamp lighting device capable of performing the above.
[0040]
[Brief description of the drawings]
FIG. 1 is a configuration diagram of a discharge lamp lighting device according to a first embodiment of the present invention.
2 (a) is a waveform diagram of a voltage (V1) in FIG. 1, FIG. 2 (b) is a waveform diagram of a voltage (V2), and FIG. V3) is a waveform diagram, and FIG. 2D is a waveform diagram of the voltage (V4).
FIG. 3 is a configuration diagram of a conventional discharge lamp lighting device.
[Explanation of symbols]
Reference Signs List 1 DC power supply 2 PNP bipolar transistor 3 Diode 4 Inductor 5 Inverter 51 Transformer 52 Capacitor 53 NPN bipolar transistor 54 NPN bipolar transistor 55 Resistance 56 Resistance 6 Ballast capacitor 7 Discharge lamp 8 Resistance 9 Voltage conversion circuit 91 Diode 92 Capacitor 93 Resistance 94 constant voltage diode 95 half-wave rectifier circuit 10 diode 11 comparator 12 reference voltage source 13 resistor 14 resistor 101 DC power supply 102 PNP bipolar transistor 103 diode 104 inductor 105 inverter 1051 transformer 1052 capacitor 1053 NPN bipolar transistor 1054 NPN bipolar transistor 1055 Resistance 106 Ballast capacitor 107 Discharge lamp 108 Resistance 109 Rectifier smoothing circuit 110 Comparator 111 Triangular wave generation circuit 112 Resistance

Claims (6)

Switch means for intermittently outputting a power supply voltage, an inverter for converting an output voltage of the switch means to an AC voltage and lighting a discharge lamp by the AC voltage, and converting a current flowing through the discharge lamp to a voltage for output Current detecting means, a voltage converting means for converting the output voltage of the current detecting means into a pulsating voltage, and outputting the pulsating voltage. And a comparing means for controlling the discharge lamp lighting device. The comparing means performs the control so that the AC voltage decreases when the current flowing through the discharge lamp increases, and performs the control such that the AC voltage increases when the current flowing through the discharge lamp decreases. The discharge lamp lighting device according to claim 1, wherein: The discharge lamp lighting device according to claim 1, wherein the voltage conversion means includes a half-wave rectifier circuit. The discharge lamp lighting device according to claim 3, wherein the voltage conversion means includes a voltage limiting element connected to an output terminal of the half-wave rectifier circuit. 2. The discharge lamp according to claim 1, wherein said comparing means has a non-inverting input terminal and an inverting input terminal, and further comprises a voltage limiting element connected between said non-inverting input terminal and said inverting input terminal. Lighting device. The discharge lamp lighting device according to claim 1, wherein the inverter includes a switching transistor whose input bias voltage is supplied from the power supply voltage.

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