JP4624282B2 - Cold cathode tube drive - Google Patents

Description

  The present invention relates to a cold cathode tube driving device.

  For example, in a liquid crystal display or the like, a plurality of cold cathode tubes are arranged as a backlight on the back of the liquid crystal panel, and these cold cathode tubes are turned on to serve as a light source for illuminating the liquid crystal panel.

  When a cold cathode tube is used as a backlight, the brightness of each cold cathode tube needs to be constant. This is because, when the luminance is not constant, luminance unevenness occurs in the liquid crystal display, and the brightness does not become constant depending on the location of the display. Note that the main cause of luminance unevenness is considered to be a variation in parasitic capacitance generated between the cold cathode fluorescent lamp and the panel.

  Conventionally, as a technique for preventing the luminance unevenness of the backlight, for example, there is a technique shown in Patent Document 1.

JP 2006-41468 A (abstract, claims)

  By the way, in the technique shown in Patent Document 1, a transformer is used to balance the currents flowing through the plurality of cold cathode tubes. However, since the transformer is composed of a core and a coil and has a certain size, there is a problem that it is difficult to reduce the size and cost.

  In addition, in order to balance the current flowing in the cold cathode tube, it is necessary to make the element values (for example, the number of turns) of each winding the same. However, since the element values vary from transformer to transformer, they are balanced. There is also a problem that it is difficult to take.

  The present invention has been made based on the above circumstances, and an object of the present invention is to provide a cold-cathode tube driving device capable of making the luminance of a plurality of cold-cathode tubes uniform.

In order to achieve the above object, a cold cathode tube driving device according to the present invention includes a power supply circuit for supplying AC power to a plurality of cold cathode tubes in a cold cathode tube driving device for driving a plurality of cold cathode tubes. A first current mirror circuit for equalizing a positive alternating current flowing from each cold cathode tube to ground, and a second current mirror circuit for equalizing a negative alternating current flowing from ground to each cold cathode tube; A resistor is connected between the base terminal or gate terminal of the transistors constituting the first current mirror circuit and the second current mirror circuit and the ground, and both the first current mirror circuit and the second current mirror circuit are connected to each other. Different transistors are connected to each other.

Therefore, according to the present invention, it is possible to provide a cold-cathode tube driving device capable of making the luminance of a plurality of cold-cathode tubes uniform in a small size and at low cost. In addition, the operation of the circuit can be stabilized by discharging the charge accumulated in the transistors or rectifying diodes constituting the current mirror circuit.

According to another aspect of the present invention, there is provided a cold-cathode tube driving device, in addition to the above-described invention, wherein the first current mirror circuit and the second current mirror circuit are base current compensation type current mirror circuits using different transistors. It is. As a result, the balance of the output current can be increased by reducing the base current flowing through the transistors constituting the first current mirror circuit. Further, since the negative feedback by the transistor constituting the first current mirror circuit is applied to the emitter of another transistor and the impedance is lowered, the influence of the mirror effect due to the resistance can be reduced. Thereby, switching operation can be performed reliably. In addition to the above-mentioned invention, the cold-cathode tube driving device of another invention is a Wilson type current mirror circuit in which the first current mirror circuit and the second current mirror circuit described above use different transistors. . Thereby, negative feedback is applied so that the emitter voltage of another transistor becomes equal to the base voltage of the transistor of the second current mirror circuit. At this time, the transistors of the first current mirror circuit are diode-connected, and the base voltages of the transistors of the first current mirror circuit and the second current mirror circuit are equal. The voltages are equal. Therefore, according to such a configuration, it is possible to make the currents flowing through the cold-cathode tubes more equal as compared with a normal current mirror circuit. In addition to the above-mentioned invention, the cold cathode tube driving device of another invention is a high-precision Wilson type current mirror circuit in which the first current mirror circuit and the second current mirror circuit described above use different transistors. It is. As a result, the operating conditions of the transistors constituting the first current mirror circuit and the transistors constituting the second current mirror circuit become equal, so that the temperature drift is reduced and the balance of the output currents can be made equal.

  In the cold cathode tube driving device of another invention, in addition to the above-mentioned invention, the first current mirror circuit and the second current mirror circuit are constituted by monolithic ICs. For this reason, the currents flowing through the cold cathode tubes can be made to coincide with each other by matching the characteristics of the transistors constituting the first and second current mirror circuits and making the temperature characteristics uniform. In addition, the cost can be reduced by reducing the number of parts.

  The present invention can provide a cold-cathode tube drive device that can be made compact and low-cost, and can uniformize the luminance of a plurality of cold-cathode tubes.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 is a diagram showing a configuration example of a liquid crystal display device having a cold cathode tube driving device according to an embodiment of the present invention. As shown in this figure, the liquid crystal display device includes a liquid crystal panel 1, a liquid crystal driving circuit 2, a cold cathode tube driving circuit 10, and a plurality of cold cathode tubes 15 as main components.

  Here, the liquid crystal panel 1 transmits or blocks light emitted from the cold cathode tube 15 by changing the arrangement state of some molecules of the liquid crystal according to the control of the liquid crystal driving circuit 2. Display text and images.

  The liquid crystal driving circuit 2 is a driving circuit that displays a desired character or image by driving a TFT (Thin Film Transistor) provided on the back surface of the liquid crystal panel 1, for example.

  The cold cathode tube driving circuit 10 is a circuit for driving and lighting a plurality of cold cathode tubes 15 as backlights provided on the back surface of the liquid crystal panel 1. The detailed configuration of the cold cathode tube driving circuit 10 will be described later.

  In the cold cathode tube 15, a phosphor is applied to the inner wall of the tube, electrodes are attached to both ends of the tube, and argon as a buffer gas and an appropriate amount of mercury are enclosed. When a high voltage is applied between the electrodes at both ends of the tube, electrons remaining in the tube are attracted by the anode and collide with argon molecules while moving at high speed, and the cations that have undergone impact ionization collide with the cathode. The next electron is knocked out and discharge starts. Electrons flowing through the discharge collide with mercury atoms, and the excited mercury emits ultraviolet rays. This ultraviolet light excites the phosphor and emits visible light unique to the phosphor. In the example of FIG. 1, the plurality of cold cathode fluorescent lamps 15 are arranged in the vertical direction, but this is an example, and it is also possible to arrange them in the horizontal direction. Hereinafter, when the individual cold cathode tubes 15 are shown, they are referred to as cold cathode tubes 15-1 to 15-n. Each of the cold cathode fluorescent lamps 15-1 to 15-n has substantially the same current-luminance characteristics.

  FIG. 2 is a diagram showing a detailed configuration example of the cold cathode tube driving circuit 10 shown in FIG. As shown in this figure, the cold cathode tube drive circuit 10 includes a controller 11, a switching circuit 12, a transformer 13, capacitors 14-1 to 14-n, diodes 16-1 to 16-n, and diodes 17-1 to 17-. n, transistors 18-1 to 18-n, transistors 19-1 to 19-n, resistors 20-1 to 20-n, and resistors 21-1 to 21-n are main components.

  Here, the controller 11 as a part of the power supply circuit controls the switching operation of the switching circuit 12 based on, for example, PWM (Pulse Width Modulation) control, and a predetermined alternating current is applied to the cold cathode tubes 15-1 to 15-1. Control to flow to 15-n. In the control, the controller 11 detects a voltage generated in the resistor 20-1, and controls the switching circuit 12 based on the voltage.

  The switching circuit 12 as a part of the power supply circuit is configured by, for example, a bipolar transistor or an FET (Field Effect Transistor), etc., and switches DC power supply power (not shown) according to the control of the controller 11. AC power of about 50 kHz is generated.

  The transformer 13 as a part of the power supply circuit is a step-up transformer, and boosts and outputs the output voltage (AC voltage) of the switching circuit 12 according to the turn ratio of the windings. The primary winding of the step-up transformer is connected to the switching circuit 12, one of the secondary windings is grounded, and the other is connected to one terminal of the capacitors 14-1 to 14-n.

  Capacitors 14-1 to 14-n have one terminal connected to the high voltage side of the secondary winding of transformer 13, and the other connected to one terminal of cold cathode fluorescent lamps 15-1 to 15-n. Capacitors 14-1 to 14-n have negative resistance characteristics when the cold cathode fluorescent lamp 15-1 is lit, and the system becomes unstable. Therefore, the capacitors 14-1 to 14-n are inserted to cancel the negative resistance characteristics and stabilize the system. ing.

  The diodes 16-1 to 16-n have anodes connected to one terminals of the cold cathode fluorescent lamps 15-1 to 15-n and cathodes connected to collectors of the transistors 18-1 to 18-n, respectively. The diodes 17-1 to 17-n have cathodes connected to one terminal of the cold cathode tubes 15-1 to 15-n and anodes connected to collectors of the transistors 19-1 to 19-n, respectively. . These diodes 16-1 to 16-n and diodes 17-1 to 17-n are diodes 16-1 to 16-1 when a positive voltage is applied to the cold cathode tubes 15-1 to 15-n. 16-n is forward biased and turned on, and diodes 17-1 to 17-n are reverse biased and turned off. When a negative voltage is applied to the cold cathode fluorescent lamps 15-1 to 15-n, the diodes 17-1 to 17-n are forward biased and turned on, and the diodes 16-1 to 16- n becomes a reverse bias and is turned off. As a result, when a positive voltage is applied to the cold cathode fluorescent lamps 15-1 to 15-n, a current is passed to the positive current mirror circuit constituted by the transistors 18-1 to 18-n. When a negative voltage is applied, a current is passed to the negative current mirror circuit constituted by the transistors 19-1 to 19-n.

  The transistors 18-1 to 18-n as a part of the first current mirror circuit constitute a multi-output current mirror circuit (positive side current mirror circuit). Therefore, the currents flowing through the collectors of the transistors 18-1 to 18-n are almost equal. The transistors 19-1 to 19-n as a part of the second current mirror circuit similarly constitute a multi-output current mirror circuit (negative current mirror circuit). Therefore, the currents flowing through the collectors of the transistors 19-1 to 19-n are almost equal.

  The resistors 20-1 to 20-n as a part of the first current mirror circuit are emitter resistors having the same resistance value so that the current flowing through the positive current mirror circuit does not fluctuate due to temperature characteristics or the like. It has a function. Similarly, the resistors 21-1 to 21-n as a part of the second current mirror circuit are emitter resistors having the same resistance value, and the current flowing through the negative-side current mirror circuit does not vary depending on temperature characteristics or the like. Has the function of The element values of the resistors 20-1 to 20-n and the resistors 21-1 to 21-n are, for example, about 100Ω. Note that a voltage detection terminal of the controller 11 is connected to the resistor 20-1, and a positive current flowing through the cold cathode tube 15-1 is detected by detecting the voltage.

  Next, the operation of the above embodiment will be described.

  When the power of the liquid crystal display device shown in FIG. 1 is turned on, the liquid crystal driving circuit 2 applies a driving voltage to the TFT of the liquid crystal panel 1 based on the input video signal to display an image on the liquid crystal panel 1.

  At this time, the controller 11 of the cold cathode tube driving circuit 10 starts an operation of driving the switching circuit 12. That is, the controller 11 switches the switching circuit 12 according to the voltage generated in the resistor 20-1, and generates a sine wave having a predetermined voltage. For example, when the voltage generated in the resistor 20-1 is low, the output voltage is increased by increasing the ON time of the switching circuit 12 (increasing the duty ratio). Further, when the voltage is high, the output voltage is lowered by shortening the ON time (decreasing the duty ratio).

  The sine wave output from the switching circuit 12 is input to the transformer 13. The transformer 13 boosts and outputs the sine wave output from the switching circuit 12 according to the turn ratio.

  The sine wave output from the transformer 13 is applied to the cold cathode fluorescent lamps 15-1 to 15-n via the capacitors 14-1 to 14-n. When the applied voltage exceeds the discharge voltage, the cold cathode tubes 15-1 to 15-n start discharging. When the discharge starts, visible light (white light) is emitted from the cold cathode fluorescent lamps 15-1 to 15-n. The emitted visible light is transmitted or blocked according to the liquid crystal state of the liquid crystal panel 1. As a result, it is displayed as a predetermined character or visible video according to the driving of the liquid crystal driving circuit 2.

  By the way, when a positive voltage (a positive voltage with respect to the ground) is applied to the cold cathode tubes 15-1 to 15-n, as described above, the diodes 16-1 to 16-n are in the forward bias state. The diodes 17-1 to 17-n are in a reverse bias state and turned off. As a result, current flows to the collectors of the transistors 18-1 to 18-n. The transistors 18-1 to 18-n constitute a multi-output current mirror circuit. That is, since the bases of the transistors 18-1 to 18-n are connected to each other, the base voltages are equal. Here, the resistors 20-1 to 20-n have the same value, and the voltages between the bases and the emitters of the transistors 18-1 to 18-n are substantially equal. The voltages applied to 20-n are approximately equal. For this reason, the currents flowing through the collectors of the transistors 18-1 to 18-n are substantially equal.

  On the other hand, when a negative voltage (a negative voltage with respect to the ground) is applied to the cold cathode fluorescent lamps 15-1 to 15-n, as described above, the diodes 16-1 to 16-n are in a reverse bias state. The diodes 17-1 to 17-n are in a forward bias state and turned on. As a result, current flows to the collectors of the transistors 19-1 to 19-n. The transistors 19-1 to 19-n constitute a multi-output current mirror circuit. That is, since the bases of the transistors 19-1 to 19-n are connected to each other, the base voltages are equal. Here, the resistors 21-1 to 21-n have the same value, and the voltages between the bases and the emitters of the transistors 19-1 to 19-n are substantially equal. The voltages applied to 21-n are approximately equal. For this reason, the currents flowing through the collectors of the transistors 19-1 to 19-n are substantially equal.

  That is, when a positive voltage is applied to the cold cathode fluorescent lamps 15-1 to 15-n, the cold cathode fluorescent lamps 15 are connected to the respective cold cathode fluorescent lamps 15 by the positive-side current mirror circuit constituted by the transistors 18-1 to 18-n. -1 to 15-n are controlled to be equal to each other, and when a negative voltage is applied to the cold cathode fluorescent lamps 15-1 to 15-n, the transistors 19-1 to 19-n Are controlled so that the currents flowing in the cold cathode fluorescent lamps 15-1 to 15-n are equal. As a result, the currents flowing through the cold cathode fluorescent lamps 15-1 to 15-n are substantially equal on both the positive side and the negative side. Since the cold cathode fluorescent lamps 15-1 to 15-n have substantially the same current-luminance characteristics, the cold cathode fluorescent lamps 15-1 to 15-n have substantially the same luminance. Since uniform light is projected onto the liquid crystal panel 1, the viewer can view a uniform image.

  As described above, according to the embodiment of the present invention, the currents flowing in the cold cathode fluorescent lamps 15-1 to 15-n are balanced using the positive and negative current mirror circuits. The occurrence of uneven brightness in the liquid crystal panel 1 can be reduced.

  Further, in the above embodiment, since a current mirror circuit using transistors is used, the size of the device can be reduced and the cost can be further reduced as compared with the case where a transformer is used as in the prior art. I can plan. In the current mirror circuit, since the current value can be determined by the emitter resistance, the current balance accuracy can be improved as compared with the case of using a transformer. As a result, the occurrence of uneven brightness can be further suppressed.

  In the above embodiment, since the positive and negative current mirror circuits are inserted into the low voltage side of the cold cathode fluorescent lamps 15-1 to 15-n, the transistors 18-1 to 18-n and the transistors Since transistors with low withstand voltage can be used as 19-1 to 19-n, cost can be reduced. In addition, a transistor with a low breakdown voltage has better high-frequency characteristics than a transistor with a high breakdown voltage, and thus it is possible to maintain a current balance up to a high frequency.

  In the above embodiment, the currents are balanced by the current mirror circuit using the transistors. However, the transistors 18-1 to 18-n and the transistors 19-1 to 19-n are formed into a monolithic IC (Integrated Circuit). As a result, the apparatus can be further miniaturized. In addition, by making an IC, the relative characteristics of the transistors 18-1 to 18-n and the transistors 19-1 to 19-n can be made uniform. Can be increased. In addition, since the transistors 18-1 to 18-n and the transistors 19-1 to 19-n can be thermally coupled by using a monolithic IC, current balance can be prevented from being lost due to temperature changes. .

  FIG. 3 is a diagram showing another configuration example of the cold cathode tube driving circuit 10 shown in FIG. In this figure, portions corresponding to those in FIG. 2 are denoted by the same reference numerals, and description thereof is omitted. In the example of FIG. 3, resistors 22 and 23 are newly added as compared with FIG. The other configuration is the same as that of FIG.

  The resistor 22 has one terminal connected to the bases of the transistors 18-1 to 18-n constituting the positive-side current mirror circuit, and the other terminal connected to the ground. The resistor 23 has one terminal connected to the bases of the transistors 19-1 to 19-n constituting the negative current mirror circuit, and the other terminal connected to the ground.

  The resistor 22 discharges the electric charge accumulated in the junction capacitance of the diode 16-1 when the negative voltage is reversed to the positive voltage from the state where the negative voltage is applied to the cold cathode tubes 15-1 to 15-n. To speed up switching in the forward direction.

  The resistor 22 discharges charges accumulated between the base and the collector when the transistors 18-2 to 18-n are switched from the on state to the off state, thereby speeding up the switching in the forward direction. .

  The resistor 23 discharges the electric charge accumulated in the junction capacitance of the diode 17-1 when the positive voltage is inverted from the state in which the positive voltage is applied to the cold cathode tubes 15-1 to 15-n to the positive voltage. To speed up switching in the forward direction.

  The resistor 23 discharges the charge accumulated between the base and the collector when the transistors 19-2 to 19-n are switched from the on state to the off state, thereby speeding up the switching in the forward direction. .

  That is, in the present embodiment, a sine wave having a frequency of about 50 kHz is output from the transformer 13. Therefore, the positive-side current mirror circuit and the negative-side current mirror circuit are repeatedly turned on and off at a frequency of about 50,000 times per second. The diodes 16-1 and 17-1 are repeatedly turned on and off in the same cycle. Here, when the diodes 16-1 and 17-1 are switched from the reverse bias to the forward bias, the charge is accumulated in the diffusion capacitor, and the charge needs to be discharged. The resistors 22 and 23 have a role of discharging the charge through the base. Thereby, switching operation can be performed reliably.

  In addition, when an emitter resistor is added to the transistor constituting the current mirror circuit, the stability increases, but the stray capacitance (for example, the capacitance between the base and the collector) increases due to the mirror effect. For this reason, in the embodiment shown in FIG. 3, by adding resistors 22 and 23 to the base, the charge accumulated in the capacitor is discharged, and the switching operation of the transistor is performed quickly. That is, in the embodiment shown in FIG. 3, by adding the resistors 22 and 23, capacitances that are equivalently generated on the input side of the transistors 18-1 to 18-n and the transistors 19-1 to 19-n (for example, base By discharging the charge accumulated in the capacitor between the collectors, the switching operation can be performed reliably.

  The above-described embodiments are preferred examples of the present invention, but the present invention is not limited to these, and various modifications and changes can be made without departing from the scope of the present invention. is there.

  For example, in the above embodiment, bipolar transistors are used as the transistors 18-1 to 18-n and the transistors 19-1 to 19-n. However, for example, an FET (Field Effect Transistor) or A MOS (Metal-Oxide Semiconductor) -FET may be used. Since these transistors have a large input resistance (gate resistance), it is possible to improve the balance of the output current of the current mirror circuit.

  Further, as the current mirror circuit, for example, as shown in FIG. 4A, a base current compensation type current mirror circuit to which a transistor 30 is added may be used. Specifically, the base-collector connection of the transistor 18-1 shown in FIG. 2 or FIG. 3 is excluded, the base of the transistor 30 is connected to the collector of the transistor 18-1, and the emitter of the transistor 30 is connected to the transistor 18 -1 to 18-n are connected to the bases, and the collector of the transistor 30 is connected to the cathode of the diode 16-2. Similarly, a transistor (not shown) is connected to the negative-side current mirror circuit. According to such a configuration, the balance of the output current can be increased by reducing the base current flowing through the transistor 18-1. Further, since the negative feedback by the transistor 18-1 is applied to the emitter of the transistor 30 and the impedance is lowered, the influence of the mirror effect due to the resistors 20-2 to 20-n can be reduced. Thereby, switching operation can be performed reliably.

Further, as shown in FIG. 4 (B), may be used a current mirror circuit of Wilson added transistor 31. According to such a configuration, negative feedback is applied so that the emitter voltage of the transistor 31 becomes equal to the base voltage of the transistor 18-2. At this time, the transistor 18-1 is diode-connected, and the base voltages of the transistors 18-1 and 18-2 are equal. Therefore, when the characteristics of the transistors 18-1 and 18-2 are equal, the output voltages are equal. . Therefore, according to such a configuration, the currents flowing through the cold cathode fluorescent lamps 15-1 to 15-n can be made more equal as compared with the circuits shown in FIGS.

Furthermore, as shown in FIG. 4 (C), by adding the transistors 32 and 33, may be configured with high accuracy Wilson current mirror circuit. According to such a configuration, since the operating conditions of the transistors 18-1 and 18-2 are equal, the temperature drift is reduced and the balance of output currents can be equalized.

  In the above embodiment, the transistors 18-1 to 18-n and the transistors 19-1 to 19-n have discrete configurations. For example, as described above, these transistors can be configured as a monolithic IC. It is. In that case, since the relative characteristics of the transistors 18-1 to 18-n and the transistors 19-1 to 19-n can be made uniform, the balance of output currents can be made uniform. In addition, since it is arranged in a region close to the monolithic IC, thermal characteristics can be made uniform, so that variations in characteristics due to heat can be suppressed. Note that it is not necessary to make all of the transistors 18-1 to 18-n and the transistors 19-1 to 19-n monolithic ICs, and at least the transistors 18-1 to 18-n and the transistors 19-1 to 19-n, respectively. What is necessary is just to make monolithic IC about.

  Further, in the embodiment shown in FIG. 3, resistors 22 and 23 are added to discharge electric charges. For example, instead of these resistors, a semiconductor switch (for example, MOS-FET) is provided. The charge may be discharged by performing a switching operation. Such a configuration can also prevent malfunction of the circuit.

  In the above embodiment, both the positive side and negative side current mirror circuits are provided. However, for example, only one of the positive side and negative side current mirror circuits may be provided. According to such an embodiment, the bidirectional current flowing to the cold cathode fluorescent lamps 15-1 to 15-n cannot be balanced, but the balance can be achieved in one direction. Compared to the case where no current is provided, the current balance characteristic can be improved.

  In the above embodiment, the controller 11 controls the output current by detecting the voltage drop generated in the resistor 20-1. For example, between the secondary winding of the transformer 13 and the ground. A resistor may be added to control the voltage drop generated in the resistor.

  The present invention can be used for a liquid crystal display, for example.

It is a block diagram which shows the structural example of the liquid crystal display which concerns on embodiment of this invention. FIG. 2 is a block diagram illustrating a configuration example of a cold cathode tube driving circuit illustrated in FIG. 1. It is a block diagram which shows the other structural example of the cold cathode tube drive circuit shown in FIG. It is a figure which shows the other structural example of a current mirror circuit, (A) shows a base current compensation type | mold current mirror circuit, (B) shows a Wilson type | mold current mirror circuit, (C) is a high-precision Wilson type | mold current mirror. The circuit is shown.

Explanation of symbols

  10 cold cathode tube drive circuit, 11 controller (part of power supply circuit), 12 switching circuit (part of power supply circuit), 13 transformer (part of power supply circuit), 18-1 to 18-n transistor ( Part of the first current mirror circuit), 19-1 to 19-n transistors (part of the second current mirror circuit), 20-1 to 20-n resistors (part of the first current mirror circuit) , 21-1 to 21-n resistors (part of the second current mirror circuit)

Claims (5)

In a cold cathode tube driving device for driving a plurality of cold cathode tubes,
A power supply circuit for supplying AC power to the plurality of cold cathode tubes;
A first current mirror circuit for equalizing a positive alternating current flowing from each cold cathode tube to the ground;
A second current mirror circuit for equalizing negative alternating current flowing from the ground to the cold cathode tubes ,
A resistor is connected between a base terminal or a gate terminal of a transistor constituting the first current mirror circuit and the second current mirror circuit and the ground;
2. A cold-cathode tube driving device, wherein different transistors are connected to both the first current mirror circuit and the second current mirror circuit . 2. The cold cathode tube driving device according to claim 1, wherein the first current mirror circuit and the second current mirror circuit are base current compensated current mirror circuits using the other transistors . 2. The cold cathode tube driving device according to claim 1, wherein the first current mirror circuit and the second current mirror circuit are Wilson type current mirror circuits using the other transistors. 2. The cold cathode tube driving device according to claim 1, wherein the first current mirror circuit and the second current mirror circuit are high-accuracy Wilson current mirror circuits using the other transistors. 5. The cold cathode tube driving device according to claim 1, wherein the first current mirror circuit and the second current mirror circuit are configured by a monolithic IC. 6.

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