KR100531789B1 - Apparatus and method for driving againg of field emission display - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a field emission device, and in particular, converts a DC high voltage applied during an aging process into a high voltage pulse capable of duty cycle and frequency adjustment, and converts the converted high voltage pulse into a low energy high voltage pulse. The present invention relates to an aging driving apparatus and method for a field emission device capable of reducing aging time and preventing arcing as well as reducing energy consumed by converting and applying the same. In the aging method using a direct current high voltage, a large amount of energy is consumed because of applying a direct current high voltage to the field emission device, and a large amount of charge is charged to the device due to a large amount of energy input or arcing due to a high electric field. There is a problem in that damage to the device to reduce the life. In view of the above problems, the present invention generates a high voltage pulse having a variable pulse width or a constant frequency and duty cycle according to time, and converts the generated high voltage pulse into a low energy high voltage pulse to apply to the anode electrode. Aging can eliminate arcing and reduce energy consumption. In addition, by eliminating the damage that can be caused by the DC high voltage, it is possible to increase the life of the device, it is possible to improve the quality of the product.

Description

Aging driving apparatus and method of field emission device {APPARATUS AND METHOD FOR DRIVING AGAING OF FIELD EMISSION DISPLAY}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a field emission device, and in particular, converts a DC high voltage applied during an aging process into a high voltage pulse capable of duty cycle and frequency adjustment, and converts the converted high voltage pulse into a low energy high voltage pulse. The present invention relates to an aging driving apparatus and method for a field emission device capable of reducing aging time and preventing arcing as well as reducing energy consumed by converting and applying the same.

In general, a metal-insulator-metal (MIM) field emission display (FED) field is fixed to the data electrode 4 and the scan electrode 2, as shown in FIG. When the voltage Vd-s is applied, electrons are emitted from the scan electrode 2, and the electrons are emitted through the insulating layer 3 and the data electrode 4 by the quantum mechanical tunnel effect.

The emitted electrons (e) are accelerated toward the anode to which the phosphor is applied by the anode 5 voltage, which is a larger anode voltage, and energy is generated when these accelerated electrons collide with the phosphor. Due to the generated energy, electrons in the phosphor are excited and then fall off to emit light.

In addition, the region between the upper plate 5 and the lower plate 1 to which the high voltage of the MIM is applied, that is, between the anode and the cathode, has a high vacuum region for emitting electrons.

However, when fabricating a vacuum tube for making a high vacuum region, contaminats may be present on the surface of the tube or the element electrode surface.

In the case of contaminants in such a high vacuum region, when the field emission device is driven, electrons with sufficient energy are released, and the electrons collide with the contaminants, thereby causing particles of the contaminants to surface. Falling off.

When such a phenomenon occurs, a high ionization pressure region is formed inside the vacuum to promote electron emission between the scan electrode 2 and the data electrode 4, and the emitted electrons are discharged from the anode. The data electrode 4 is not emitted to the data electrode 4, thereby overheating the data electrode 4.

As such, when the data electrode 4 is overheated, a luminance discharge current exceeding an energy gap between the scan electrode 2 and the data electrode 4 is formed, which seriously damages the scan electrode 2. It causes the life of the field emission device to be shortened. This phenomenon is called arcing.

In order to prevent the arcing phenomenon, there should be no contaminants in the high vacuum, and the method of removing the contaminants of the conventional MIM field emission device is to insert a material capable of absorbing the contaminants to drive the field emission device. When adsorbed.

However, there is a problem in that a separate process is required to include the substances adsorbing contaminants in the upper and lower vacuum portions as described above.

In addition, the capacity of the adsorption material has a limit, and in particular, the capacity of the adsorption material varies depending on the size of the MIM field emission device. .

There is an aging method using a DC high voltage (DC HV) as a method to solve this problem, this method will be described with reference to FIG.

First, when a direct current high voltage (DC HV) gradually increasing up to the maximum voltage to be applied to the anode (5), the contaminants on the surface are released into the vacuum. Here, the vacuum state is not a sealed state (sealing), but a state in which a vacuum is made by continuously exhausting by the vacuum pump, the separated contaminants are exhausted by the vacuum pump.

After this process, voltage is applied to the data electrode 4 and the scan electrode 2 to emit electrons. The pollutants are separated again by the emitted electrons and exhausted by a vacuum pump.

However, the above-described aging method using the direct current high voltage has a problem in that a large amount of energy is consumed because the direct current high voltage is applied to the field emission device.

In addition, due to a large amount of energy input, a large amount of charge is charged in the device or arcing occurs due to a high electric field, which causes a problem of damaging the device and reducing its lifespan.

Therefore, in view of the above problems, the present invention generates a high voltage pulse having a variable pulse width or a constant frequency and duty cycle according to time, converting the generated high voltage pulse into a low energy high voltage pulse, and applying the same to the anode electrode. It is an object of the present invention to provide an aging driving apparatus and method for a field emission device capable of eliminating arcing through short aging and reducing energy consumption.

In addition, the object of the present invention is to provide an aging driving apparatus and method for a field emission device which can increase the life of the device and improve the quality of the product by eliminating the damage that may be caused by the DC high voltage.

The aging driving device of the field emission device of the present invention for achieving the above object is a aging driving device of the field emission device having a scan driver and a panel, the high voltage having a constant frequency and duty cycle Output by converting the pulse into a high voltage pulse whose pulse width gradually increases with time or outputting the DC high voltage, and converting the output high voltage pulse into a high energy pulse of low energy and applying it to the anode electrode of the panel And an airing driving control unit configured to apply a predetermined voltage to the scan driving unit when a high voltage pulse whose pulse width gradually increases with time is applied to the anode electrode.

In the aging driving method of the field emission device of the present invention for achieving the above object, in the aging driving method of the field emission device having a panel and a scan driver, the method comprising the steps of: receiving an anode voltage of a predetermined DC high voltage; Converting the applied DC high voltage into a high voltage pulse having a constant frequency and duty cycle for a preaging time, converting the converted high voltage pulse into a low energy high voltage pulse, and applying the applied voltage to an anode electrode of the panel; The DC high voltage is converted into a high voltage pulse whose pulse width gradually increases with time during the main aging time, and the converted high voltage pulse is converted into a low energy high voltage pulse and applied to the anode electrode, and at the same time, a predetermined predetermined value is set by the scan driver. Characterized in that the step of applying a voltage of The.

With reference to the accompanying drawings, a preferred embodiment of the aging driving apparatus and method of the field emission device of the present invention having the above characteristics will be described.

Prior to describing the present invention, terms to be used in the present invention will be defined. First of all, the process of eliminating the risk that may occur while purely aging with only the anode voltage without emitting electrons is called pre-aging, and after the anode voltage is supplied, the electron is released to discharge the current. The process of reducing the probability of arcing that can occur in the future by performing current aging is called main aging.

2 is a schematic cross-sectional view of a MIM element for performing aging in the present invention and a simple configuration of an aging drive device. As shown, a high voltage pulse output section 6 having a switching means SW1, which converts a direct current high voltage DC HV into a high voltage pulse by a predetermined switching control signal input from the outside, and a storage means. (C) and a switching means (SW2), and stores the energy of the high voltage pulse output from the high voltage pulse output section 6 in the storage means (C), and by the predetermined switching control signal input from the outside An energy converter 7 converts the high voltage pulse stored in the storage means C into a low energy high voltage pulse and applies it to the anode electrode 5 of the MIM element.

Fig. 3 is an overall block diagram showing the configuration of the aging drive device of the field emission small in accordance with the present invention. As shown in the drawing, the data driver 10 outputs a timing control signal and a data pulse, and the data IN and the clock signal CLK input from the outside by the timing control signal output from the data driver 10. A scan driver 20 that receives the scan pulse and outputs the scan pulse, a panel 30 that receives the data pulse output from the data driver 10 and the scan pulse output from the scan driver 20 and displays data IN; And converting the externally input DC high voltage (DC HV) into high voltage pulses, converting the converted high voltage pulses into low energy high voltage pulses, and applying the same to the anode electrode 5 of the panel 30, and the scan driver 20 And an aging drive control unit 40 for controlling the output voltage.

The data driver 10 includes a timing controller 10a, a memory and a buffer 10b, and a data driver IC 10c. The scan driver 20 includes a scan pulse shift register 20a and a scan. It comprises a drive IC 20b.

The aging drive control unit 40 is a power control unit 40a that applies a predetermined voltage to the scan drive unit 20 by an external power control signal, and the pulse width gradually increases with time or a constant frequency regardless of time. And a pulse controller 40c for outputting a plurality of pulse control signals having a duty cycle and a plurality of pulse control signals output from the pulse controller 40c. A pulse driver 40d for outputting the signals ① and ② and a switching means SW1, the switching means being turned on / off by the switching control signal ① output from the pulse driver 40d. And a high voltage pulse output unit 40e for converting an externally applied direct current high voltage DC HV into a high voltage pulse ③, and outputting the same, and storing means C and a switching means SW2. Classical output from section 40e The pulse is stored in the storage means, and the switching means SW2 is turned on / off by the switching control signal ② output from the pulse driver 40d to convert the high voltage pulse stored in the storage means into a low energy high voltage pulse. An energy converter 40f for converting and applying the converted low energy high voltage pulse ④ to the anode electrode 5 of the panel 30, and the voltage and current output from the high voltage pulse output unit 40e. And a program control unit 40b for comparing the detected current value with a preset limit current value and outputting a power control signal to the power control unit 40a.

As shown in FIG. 4, the pulse controller 40c converts the frequency of the oscillator 40c1 for outputting a pulse signal having a predetermined frequency and the frequency of the pulse signal output from the oscillator 40c1. A duty converter 40c4 that receives a pulse signal having a predetermined frequency output from the oscillator 40c1, converts the duty cycle of the pulse signal, and outputs the duty cycle 40c2; and the frequency converter 40c2. And a logic circuit portion 40c3 for receiving the pulse signal converted and output from the duty signal and the pulse signal output from the duty converter 40c4 and outputting two pulse control signals (out) that are opposite to each other to the pulse driver 40d. To configure.

The program control unit 40b controls and applies a DC high voltage DC HV to the high voltage pulse output unit 40e. That is, as illustrated in FIG. 5, the slope of the DC high voltage, the maximum DC high voltage, and the like are controlled in time by the program controller 40b and applied to the high voltage pulse output unit 40e. In addition, the slope and the DC high voltage data according to the time are stored in the form of a table in the program controller 40b or in a memory (not shown) included in the apparatus, and the DC high voltage applied by using the stored data can be controlled. This technique is known in the art and will not be described in detail.

In addition, the program controller 40b is connected to the high voltage pulse output unit 40e and the universal interface bus (GPIB or HPIB), detects the voltage and current output from the high voltage pulse output unit 40e, and detects the detected voltage. When the current value is larger than the preset limit current value, that is, when the excessive voltage is supplied to the anode voltage 5 or a large current flows or arcing occurs due to a certain effect, the high voltage pulse output unit 40e is applied. The aging is stopped by turning off the DC high voltage or stopping the program.

The power controller 40a is used for main aging, which is current aging, through a scan driving voltage, and the power controller 40a is also connected to the program controller 40b via a general-purpose interface bus.

An operation of the aging driving device of the field emission device of the present invention having such a configuration will be described by dividing it into a pre-aging process and a main aging process with reference to FIGS. 5, 6, and 7. Prior to the description, all operations of the present invention are performed by the program and the data driver 20 is grounded.

Then, the pre-aging process will be described. When the program controller 40b controls and applies the DC HV, which gradually increases as shown in FIG. 5, the frequency controller and the duty cycle are constant in the pulse controller 40c. Outputs two pulse control signals. That is, when the oscillator 40c1 outputs a pulse signal having a predetermined frequency, the frequency converter 40c2 receives the pulse signal output from the oscillator 40c1 and converts and outputs the frequency of the pulse signal. The duty converter 40c4 also receives the pulse signal output from the oscillator 40c1, converts the duty cycle of the pulse signal, and outputs it. The logic circuit 40c3 receives the pulse signal output from the frequency converter 40c2 and the pulse signal output from the duty converter 40c4 and outputs two opposing pulse control signals.

The pulse driver 40d receives two opposing pulse control signals output from the logic circuit unit 40c3 and outputs two switching control signals ① and ②, and switching means provided in the high voltage pulse output unit 40e. SW1 receives a DC high voltage gradually increased with time as shown in FIG. 5, and the switching means SW1 receiving the DC high voltage is turned on to the switching control signal output from the pulse driver 40d. On / off, as shown in Fig. 6, a high voltage pulse ③ having a constant frequency and duty cycle is output.

The energy conversion unit 40f stores the energy of the high voltage pulse output from the high voltage pulse output unit 40e in the condenser C, and the stored energy is output from the pulse driver 40d by the switching means SW2. It is turned on / off by the switching control signal ② and converted to a high energy pulse ④ of low energy. Then, the converted low energy high voltage pulse is applied to the anode electrode 5.

This process is performed during the preaging time, and the high voltage pulse applied to the anode electrode 5 during this preaging time is applied with a low energy high voltage pulse having a constant frequency and duty cycle regardless of time. The process is performed in an unsealed state, and contaminants emitted during the preaging process are exhausted by a vacuum pump.

After the preaging process, the current aging process, that is, the main aging process, is performed. Hereinafter, the main aging process will be described.

The pulse controller 40c outputs two opposing pulse control signals having a frequency and duty cycle which vary with time, and the two pulse control signals ①, by the pulse driver 40d by the two pulse control signals. 2), the switching means SW1 provided in the high voltage pulse output unit 40e receives the highest DC high voltage or a gradually decreasing DC high voltage applied to the switching control signal ① as shown in FIG. By outputting a high voltage pulse whose duty cycle (pulse width) gradually increases with time as shown in FIG. 6 or a high voltage pulse ③ whose duty cycle and frequency are variable.

The storage means provided in the energy conversion unit 40f receives the high voltage pulse ③ output from the high voltage pulse output unit 40e and stores the energy, and the switching means SW2 is output from the pulse driver 40d. A low-energy high voltage pulse ④ which is turned on / off by one switching control signal ② and discharged from the storage means is applied to the anode electrode 5. At this time, when a low-energy high voltage pulse is applied to the anode electrode 5, a power control signal is output from the program controller 40b to the power controller 40a, and the power controller 40a receives the power control signal to scan scan unit. The controller 20 is controlled to apply a predetermined power supply (for example, -5V) to the panel 30. That is, the current is emitted by emitting electrons from the scan electrode 2 of the device.

In this case, when the main aging is performed, the duty cycle of the high voltage pulse applied to the anode electrode 5 is gradually increased over time, thereby initially aging with a low current, and aging with a high current as time passes. By doing so, it is possible to reduce the overall aging time and prevent arcing. That is, as time passes, aging is performed under the condition that the actual panel 30 operates, thereby reducing the phenomenon of arcing when the actual panel 30 is driven. That is, as illustrated in FIG. 6, during main aging, aging is performed by applying a high voltage pulse whose width gradually increases with time.

Contaminants that fall off through the main aging are also exhausted by the vacuum pump, and after the pre-aging and main aging processes are completed, the vacuum part in the high vacuum state is sealed.

Then, a process of applying a low energy high voltage pulse to the anode electrode 5 during the preaging and main aging times will be described in more detail with reference to FIG. 7.

7 shows the two switching control signals ① and ② output from the pulse driver 40d, the high voltage pulse ③ output from the high voltage pulse output unit 40e, and the anode electrode 5 from the energy converter 40f. The timing diagram of the low energy high voltage pulse (4) to be output is shown. As shown, a DC high voltage (for example, 8 KV) applied during the time when the switching control signal ① applied to the high voltage pulse output unit 40e is turned on is output as a high voltage pulse ③, and the high voltage pulse. The energy of the high voltage pulse is stored in the storage means (capacitor) provided in the energy conversion section 40f for the time that is output.

The energy of the high voltage pulse stored in the storage means is converted into a low energy high voltage pulse during the time when the output of the high voltage pulse output unit 40e is turned off and the switching control signal ② applied to the energy conversion unit 40f is turned on. It is applied to the anode electrode 5. At this time, since the energy applied to the anode electrode 5 is only a discharged amount of energy, not all energy stored in the storage means, very low energy is applied to the input. That is, the switching means SW1 and SW2 provided in the high voltage pulse output unit 40e and the energy conversion unit 40f are turned on / off by the switching control signals ① and ② shown in FIG. 5) a low energy high voltage pulse is applied.

8 is a flowchart showing the flow of the aging driving method of the field emission device of the present invention. As shown, applying a DC high voltage of a predetermined type, converting the applied DC high voltage into a high voltage pulse by a pulse signal having a predetermined frequency and duty cycle, and converting the converted high voltage pulse to low energy Converting the high voltage pulse into a high voltage pulse and applying the same to the anode electrode of the panel during the preaging time, and by the pulse signal in which the duty cycle (pulse width) gradually increases with time after the preaging time passes. And converting the high voltage pulse whose pulse width increases with the time into a low energy high voltage pulse and applying it to the anode electrode of the panel during the main aging time, and simultaneously applying a predetermined voltage to the scan driver. .

The method may further include detecting current and voltage of the high voltage pulse applied to the anode electrode, comparing the detected current value with a preset limit current value, and if the detected current value is large, the anode electrode 5 The step of turning off the high voltage applied to).

The operation of the present invention consisting of these steps will be described by dividing the preaging and main aging processes. First, the preaging process will be described. When a DC high voltage of a predetermined type is applied to the switching means SW1 of the high voltage pulse output unit 40e (S10), the switching means SW1 is switched by a switching control signal having a constant frequency and duty cycle applied from the outside. On / off outputs a high voltage pulse with a constant frequency and duty cycle (S20, S30). Here, the preset high DC voltage is configured as shown in FIG. 5, and the high DC voltage gradually applied and the high DC voltage gradually decreased during the preaging and main aging times, respectively. Data about the slope and the like is stored in a table in a memory provided in the aging apparatus, and when a DC high voltage is applied, DC high voltage of the form as shown in FIG. 5 is applied using the data stored in the memory. That is, the DC high voltage is applied by the program.

The output high voltage pulse stores the energy of the high voltage pulse in a storage means provided in the energy converter 40f, and the switching means SW2 is turned on / off by a switching control signal having a constant frequency and duty cycle input from the outside. It turns off to output the energy of some of the energy stored in the storage means as a high voltage pulse (S50). That is, the high voltage pulse converted into low energy is applied to the anode electrode 5 of the panel.

At this time, the voltage and current of the high voltage pulse or the high voltage pulse output from the high voltage pulse output unit 40e converted into low energy are detected (S50), and the detected current value is compared with the limit current value for the preset voltage. It is determined whether damage can be caused to the device (S60). That is, when the detected current value is larger than the preset limit current value, the DC high voltage applied is turned off by turning off the switching means to which the DC high voltage is applied (S90, S100) or the program itself is down to the anode electrode 5 Stop the high voltage applied.

On the other hand, when the current value detected in the step S60 is smaller than the threshold current value for the preset voltage, a high voltage having a predetermined slope is applied using data stored in the memory up to the highest high voltage applied (S80). Of course, whenever a high voltage pulse is applied, the voltage and current applied to the anode electrode 5 are detected and compared.

When the highest value of the input DC high voltage is applied, preaging is performed by maintaining the highest high voltage pulse for a predetermined time period, for example, as shown in FIG. 6, for a time t2 (S110).

After the pre-aging process, the main aging process, which is current aging, is performed. At this time, the switching control signal applied to the high voltage pulse output unit 40e and the energy conversion unit 40f is a switching control signal in which the duty cycle of the pulse, that is, the pulse width gradually increases with time.

The high voltage pulse output unit 40e receives a switching control signal in which the pulse width gradually increases with time, and receives the highest DC high voltage applied from the outside or a DC high voltage gradually decreasing to receive a high voltage pulse as shown in FIG. 6. Output (S120).

The energy converter 40f converts a high voltage pulse whose pulse width increases with the time into a low energy high voltage pulse and applies it to the anode electrode 5 of the panel 30. In this case, when the low energy high voltage pulse is applied to the anode electrode 5, a predetermined voltage is applied to the scan electrode 2 of the panel 30 through the scan driver 20. That is, electrons are emitted by applying a predetermined voltage to the scan electrode 2, and current aging is performed using the emitted electrons.

Contaminants released during this preaging and main aging are evacuated by a vacuum pump.

In this way, by using a low-energy high voltage pulse in the present invention, it is possible to aging in less time than the conventional time required for aging by DC high voltage. In other words, if the aging time taken in the conventional method is 10 hours, the aging time taken in the present invention is possible in several tens of minutes.

As described in detail above, the present invention generates a high voltage pulse having a variable pulse width or a constant frequency and duty cycle with time, converting the generated high voltage pulse into a high energy pulse of low energy, and applying the same to the anode electrode. Short aging can eliminate arcing and reduce energy consumption.

In addition, by eliminating the damage that can be caused by the DC high voltage, it is possible to increase the life of the device, it is possible to improve the quality of the product.

1 is a schematic cross sectional view of a field emission device according to the prior art;

2 is a schematic cross-sectional view of a field emission device according to the present invention.

Figure 3 is a block diagram showing the configuration of the aging drive device of the field emission device of the present invention.

4 is a block diagram showing a detailed configuration of the pulse control unit of FIG.

Figure 5 illustrates a direct current high voltage applied to the present invention.

Figure 6 illustrates a high voltage pulse applied to the anode electrode of the panel in the present invention.

FIG. 7 is a diagram showing waveforms of output signals of respective units shown in FIG. 3; FIG.

8 is a flow chart showing a flow for the aging driving method of the field emission device of the present invention.

** Description of the symbols for the main parts of the drawings **

5: anode electrode 6, 40e: high voltage pulse output unit

7, 40f: energy conversion unit 20: scan drive unit

30: panel 40: aging drive control unit

40a: power control unit 40b: program control unit

40c: pulse controller 40d: pulse driver

40c1: Oscillator 40c2: Frequency converter

40c3: logic circuit 40c4: duty converter

Claims (5)

An aging drive device for a field emission device having a scan driver and a panel, The DC high voltage applied from the outside is converted into a high voltage pulse having a constant frequency and duty cycle, or the DC high voltage is converted into a high voltage pulse whose pulse width gradually increases with time and is output. The output high voltage pulse is low energy. And an air-driving control unit for applying a predetermined voltage to the scan driver when a high-voltage pulse is applied to the anode electrode of the panel and is applied to the anode electrode of the panel and the pulse width gradually increases with time to the anode electrode. An aging drive device for a field emission device, characterized in that the configuration. 2. The apparatus of claim 1, wherein the aging driving control unit comprises: a power control unit for applying a predetermined voltage to the scan driving unit by an external power control signal; A pulse controller for outputting a plurality of pulse control signals having a frequency or duty cycle that is constant or variable with time; A pulse driver for receiving a plurality of pulse control signals output from the pulse controller and outputting a plurality of switching control signals corresponding thereto; A high voltage pulse output unit having a switching means, the switching means being turned on / off by a switching control signal output from the pulse driver to convert a DC high voltage (DC HV) applied from the outside into a high voltage pulse; A storage means and a switching means, the high voltage pulse output from the high voltage pulse output unit is stored in the storage means, and the switching means is turned on / off by a switching control signal output from the pulse driver to the storage means. An energy converter converting the stored high voltage pulses into low energy high voltage pulses and applying the converted low energy high voltage pulses to an anode electrode of the panel; And a program controller configured to detect a voltage and a current output from the high voltage pulse output unit, compare the detected current value with a preset limit current value, and output a power control signal to the power control unit. Aging driving device of the emitting element. 3. The apparatus of claim 2, wherein the pulse controller comprises: an oscillator for outputting a pulse signal having a predetermined frequency; A frequency converter for converting and outputting a frequency of the pulse signal output from the oscillator; A duty converter which receives a pulse signal having a predetermined frequency output from the oscillator, and converts and outputs a duty cycle of the pulse signal; Aging of the field emission device, characterized in that it comprises a logic circuit for outputting a plurality of pulse control signals to the pulse driver by receiving the pulse signal converted by the frequency converter and the pulse signal output from the duty converter. drive. In the aging driving method of the field emission device having a panel and a scan driver, Receiving an anode voltage which is a preset DC high voltage; Converting the applied DC high voltage into a high voltage pulse having a constant frequency and duty cycle for a preaging time, converting the converted high voltage pulse into a low energy high voltage pulse and applying the same to an anode electrode of the panel; The applied DC high voltage is converted into a high voltage pulse whose pulse width gradually increases with time during the main aging time, and the converted high voltage pulse is converted into a low energy high voltage pulse and applied to the anode electrode, and simultaneously to the scan driver. An aging driving method of a field emission device, characterized in that the step of applying a predetermined predetermined voltage. The method of claim 4, further comprising: detecting a current and a voltage of a high voltage pulse applied to the anode electrode, and comparing the detected current value with a preset limit current value; And turning off the high voltage applied to the anode when the detected current value is greater than a preset threshold current value.