KR100886663B1 - Driving apparatus for Cold Cathode Flat Fluorescent Lamp - Google Patents

Abstract

The present invention relates to a driving apparatus for a cold cathode flat fluorescent lamp equipped with a resonance type inverter of a high voltage direct current input type for driving a flat type cold cathode fluorescent lamp and includes a filter unit for removing a surge from an AC input power source, ; A rectifying unit for rectifying the AC power input through the filter unit to DC power; A power factor circuit for improving the power factor of the rectified power output from the rectifier and for increasing the input voltage; An inverter unit that oscillates the DC voltage output from the power factor circuit unit to a square-wave type high frequency AC voltage; A frequency control unit for controlling an oscillation frequency of the switching element provided in the inverter unit; And a high voltage generator for boosting the square wave AC voltage output from the inverter to a sinusoidal AC voltage to generate a driving voltage of the cold cathode flat fluorescent lamp. The frequency controller outputs two square waves having a phase difference of 180 degrees with each other The inverter unit includes a pair of switching elements that are alternately switched by a square wave signal generated in a frequency control unit, and has an effect of stably and stably lighting the CCFFL replacing the conventional HCFL.

 CCFFL, driving device, power factor circuit part, inverter part, frequency control part, high voltage generation part, protection circuit part, auxiliary power part

Description

[0001] The present invention relates to a cold cathode flat fluorescent lamp,

1 is a block diagram schematically showing a driving apparatus according to the present invention;

Fig. 2 is a circuit diagram showing the configuration of a rectifying part in the present invention

3 is a circuit diagram showing the configuration of a power factor circuit portion and an auxiliary power portion in the present invention.

4 is a circuit diagram showing the configuration of the inverter unit and the frequency control unit in the present invention.

5 is a circuit diagram showing the configuration of a high voltage generating portion in the present invention

6 is a circuit diagram showing the configuration of a protection circuit portion in the present invention

FIG. 7 is a waveform diagram of each part of the inverter section and the high voltage generating section according to the present invention

Description of the Related Art

10: filter section 12: rectifying section

14: power factor circuit part 16: inverter part

18: Frequency control unit 20: CCFFL

22: High voltage generating unit 24: Brightness adjusting means

26: Protection circuit part 28:

The present invention relates to a driving apparatus for a cold cathode flat fluorescent lamp, and more particularly to a driving apparatus for a cold cathode flat fluorescent lamp including a resonant inverter of a high voltage direct current input type for driving a flat cold cathode fluorescent lamp will be.

Generally, the conventional illumination device has a filament electrode at both ends of a glass tube, and argon (Ar), neon (Ne), and a small amount of mercury (Hg) are sealed in the glass tube and a fluorescent material And a hot cathode fluorescent lamp (HCFL) coated on a glass substrate. Such a hot-cathode fluorescent lamp induces thermoelectrons emission by applying a high tube current to the filament electrode, and thermoelectrons emitted from the filament react with the enclosed gas in the glass tube to generate ultraviolet rays, which ultraviolet rays excite the phosphor to emit visible light do.

However, in order to emit thermoelectrons from the filament electrode, a high tube current must be applied. Such a high tube current deteriorates the phosphor or damages the emulsion powder deposited on the filament surface, thereby causing the lamp to terminate early. Therefore, it is required to develop a fluorescent lamp that replaces the cold cathode fluorescent lamp (CCFL), and the cold cathode fluorescent lamp (CCFL) is a method of making light with a low tube current, and is being watched as a fluorescent lamp to overcome the shortcomings of the hot cathode fluorescent lamp.

Meanwhile, in recent years, as a liquid crystal display (LCD) has become widespread, a backlight unit (BLU) for lighting an LCD mounted on the back of the LCD has been developed in order to secure visibility of the LCD, ought. Conventionally, the backlight unit of an LCD includes a light guide plate for diffusing linear light of CCFL and CCFL in a plane. However, due to the problem that the efficiency of light is lowered and it is difficult to cope with the enlargement of the LCD, various types of planar fluorescent lamps are being developed in various aspects in recent years.

As an example, research and development of CCFL (Cold Cathode Flat Flourescent Lamp), which flattens CCFL by making use of the advantage of CCFL against HCFL, are undergoing various aspects. The CCFFL has a structure in which cathodes are arranged on a plane, and requires a high-voltage DC driving power source (approximately 400 V DC) as compared with the CCFL. That is, in order to accelerate the development of a planar lighting device for solving the advantages of the HCFL, it is necessary to use a ballast suitable for driving the CCFFL, that is, a cold cathode flat fluorescent lamp having high efficiency, high power factor, long life, Development of a driving apparatus for a lamp is urgently required.

It is an object of the present invention to provide a driving apparatus for a cold cathode flat fluorescent lamp in which the CCFFL replacing the conventional HCFL can be stably and stably turned on as described above.

Further, the present invention aims to provide a body diode in the switching element of the inverter section so that the switching elements achieve zero voltage switching.

The present invention also aims to protect the switching elements of the inverter section from high voltage switching.

According to another aspect of the present invention, there is provided a cold cathode flat fluorescent lamp driving apparatus including: a filter unit for removing a surge from an AC input power source and filtering noise; A rectifying unit for rectifying the AC power input through the filter unit to DC power; A power factor circuit for improving the power factor of the rectified power output from the rectifier and for increasing the input voltage; An inverter unit that oscillates the DC voltage output from the power factor circuit unit to a square-wave type high frequency AC voltage; A frequency control unit for controlling an oscillation frequency of the switching element provided in the inverter unit; And a high voltage generator for boosting the square wave AC voltage output from the inverter to a sinusoidal AC voltage to generate a driving voltage of the cold cathode flat fluorescent lamp. The frequency controller outputs two square waves having a phase difference of 180 degrees with each other And the inverter unit includes a pair of switching elements that are alternately switched by a square wave signal generated in a frequency control unit.

Preferably, the pair of switching elements is a MOSFET.

More preferably, a reverse diode (Body Diode) for switching the zero voltage of the MOSFET is installed in each of the MOSFETs.

Further, a protective resistor for protecting the MOSFET is connected between each MOSFET gate terminal and the source terminal.

A capacitor for DC partial pressure is connected in parallel between the MOSFET source terminal and the drain terminal.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings and embodiments.

First, a driving apparatus for a cold cathode flat fluorescent lamp (hereinafter referred to as CCFFL) of the present invention is a driving apparatus specialized for driving the CCFFL. Unlike the conventional HCFL driving device or the CCFL driving device, the driving device of the present invention to be described below receives an AC power source and boosts the voltage to a high-voltage DC power source (approximately DC 400V) to light the CCFFL. In the following description, a detailed description of parts similar to those of a conventional driving device for a fluorescent lamp will be omitted, and a circuit configuration specialized in the present invention will be mainly described.

1 is a block diagram schematically showing a driving apparatus according to the present invention. The driving apparatus for a CCFFL of the present invention includes a filter unit 10 for filtering surge and noise by receiving a commercial AC power source (AC 220 V, 60 Hz), a rectifying unit 12 for rectifying AC power to a DC power source, A power factor circuit portion 14 including a boost converter for improving a power factor of the rectified power source and boosting an input voltage, an inverter portion 14 for oscillating the DC voltage output from the power factor circuit portion 14 into a square-wave high- A frequency control unit 18 for controlling the oscillation frequency of the switching element provided in the inverter unit 16 and a control unit 18 for boosting the square wave AC voltage outputted from the inverter unit 16 to a sinusoidal AC voltage, And a high voltage generating unit 22 for generating a driving voltage.

The frequency control unit 18 may control the dimming of the CCFFL 20 by controlling the oscillation frequency of the inverter unit 16 according to a signal input from the external brightness adjusting unit 24, The secondary auxiliary winding L5-1 of the resonance inductor L5 provided in the unit 22 is connected to a protective circuit portion 26 for blocking the driving power applied to the abnormal voltage generating power factor circuit portion 14 and the frequency control portion 18 ). The power factor circuit portion 14 may further include an auxiliary power portion 28 for generating driving power of an integrated circuit provided in the power factor circuit portion 14 and the frequency control portion 18.

The filter unit 10 filters surges and noise inputted through a commercial AC power source (220 V, 60 Hz) and is composed of a generally known EMI filter. In this embodiment, the commercial AC power source is used as the input power source of the CCFFL driving apparatus. However, the present invention can be driven by various other input power source schemes, and the configuration of the filter unit 10 It can also be different.

2 is a circuit diagram showing a configuration of a rectifying section in the present invention. As shown in the figure, the rectifying unit 12 includes a rectifying circuit unit 12a for rectifying input AC power to a DC power source, and a filter circuit unit 12b for removing harmonic components from the DC voltage rectified by the rectifying circuit unit 12a . The rectifier circuit portion 12a is based on full-wave rectification by a bridge diode D1 composed of four diodes. In order to make the circuit size as compact as possible, the bridge diode D1 is provided in a form integrated on a single chip . The power source rectified by the bridge diode D1 includes harmonic noise that can not be removed by the filter unit 10. [ The filter circuit portion 12b includes two capacitors C1 and C2 connected in parallel to the output terminal of the bridge diode D1 in order to remove such harmonics components and a capacitor C1 and C2 connected in series to one end of each of the capacitors C1 and C2 Inductor L1. The filter circuit portion 12b constitutes an LC resonance circuit to remove the harmonic components and smoothen the output of the rectifying circuit portion 12a.

3 is a circuit diagram showing a configuration of a power factor circuit portion and an auxiliary power portion in the present invention. In the present invention, the power factor circuit portion 14 boosts the DC voltage output from the rectifying portion 12 to generate a high-voltage DC voltage for lighting the CCFFL 20 while suppressing reactive power to improve the power factor . 3, the power factor circuit portion 14 includes a power factor correction (PFC) IC U1, a switching element Q1 driven by the output signal of the PFC IC U1, And an inductor L2 connected to the switching element Q1 and to which the output of the rectifying part 12 is selectively applied by the driving of the switching element Q1. Preferably, the switching element Q1 is a metal oxide semiconductor field effect transistor (MOSFET). As shown in the figure, the power factor circuit portion 14 is configured such that the input power applied across the inductor L2 is turned on / off by the switching of the MOSFET Q1, thereby raising the output voltage by the current charge / Boost Converter.

More specifically, the PFC IC U1 supplies a starting power source from a plurality of resistors R1, R2, and R3 connected in parallel to an output terminal of the rectifying unit 12 and a Zener diode D3 connected in series to the resistors R1, R2, and R3, Receive. And is driven by the constant voltage supplied from the auxiliary power supply unit 28, which will be described later. The PFC IC U1 collects input voltage information, current information flowing in the inductor L2, output voltage information, and current information flowing through the MOSFET Q1. Each information is provided on the input terminal side of the PFC IC U1 through the following circuit configuration. As shown in the figure, a voltage dividing circuit formed by connecting a plurality of resistors R4, R5, R6 and R7 to the output terminal of the rectifying part 12 is connected to the third pin of the PFC IC U1, And collects input voltage information from the voltage dividing circuit. The first auxiliary winding L2-1 of the inductor L2 and the resistor R9 connected in series to the first auxiliary winding L2-1 are connected to the fifth pin of the PFC IC U1 and the PFC IC U1 collects current information flowing from the first auxiliary winding L2-1 of the inductor L2 to the inductor L2. A voltage dividing circuit formed by connecting a plurality of resistors R11, R12, R13 and R14 to both ends of the output terminal of the power factor circuit portion 14 is connected to the first pin of the PFC IC U1. Collect the output voltage information. A plurality of resistors R15, R16, R17, R18, and R19 are connected in parallel between the source terminal and the ground of the MOSFET Q1 at the fourth pin of the PFC IC U1, and a resistor R8 connected in series to the node And collects current information flowing from the resistor R8 to the MOSFET Q1. The PFC IC U1 computes the information collected through the above-described circuit configuration to generate the gate driving signal of the MOSFET Q1. That is, the PFC IC U1 controls the drive voltage of the MOSFET Q1 to improve the power factor of the input power source, and interrupts the power source supplied to the inductor L2 to boost the input voltage.

The auxiliary power supply unit 28 smoothes the voltage induced in the second auxiliary winding L2-2 of the inductor L2 and supplies the PFC IC U1 of the power factor circuit unit and the frequency control IC of the frequency control unit 18 And generates driving power for the U2. The auxiliary power supply unit 28 includes a smoothing circuit portion composed of an inductor L3 connected in series to the second auxiliary winding L2-2 of the inductor L2 and a capacitor C9 connected in parallel. The inductor L3 and the capacitor C9 smooth the auxiliary power applied to the second auxiliary winding L2-2 of the inductor L2. A linear voltage regulator which is a combination of a zener diode D5 and a transistor Q2 for generating a constant voltage is connected to the rear end of the capacitor C9 to supply stable power to each of the ICs U1 and U2 .

4 is a circuit diagram showing the configuration of an inverter unit and a frequency control unit in the present invention. The inverter unit 16 has a half bridge structure and includes a pair of switching elements Q11 and Q12 that are switched at a 180 degree phase difference by a switching frequency generated by the frequency control unit 18 . Preferably, the pair of switching elements Q11 and Q12 are MOSFETs. Capacitors C14 and C15 are connected in parallel to each MOSFET Q11 and Q12 for DC partial pressure. In addition, a reverse diode (Body Diode) is installed in each of the MOSFETs Q11 and Q12 for zero voltage switching. This reverse diode (Body Diode) serves to eliminate the switching loss that may occur when each MOSFET Q11 and Q12 is turned on by the current flowing in the resonance inductor L5 of the high voltage generating portion 22 . The MOSFET is very vulnerable to high currents. If an abnormality occurs in any one of the MOSFETs Q11 and Q12 of the inverter unit 16, the driving apparatus of the present invention may cause a fatal failure. Therefore, in the present invention, in order to protect each of the MOSFETs Q11 and Q12 from an abnormal current, protective resistances R27 and R28 are provided between the gate terminal and the source terminal of each of the MOSFETs Q11 and Q12 as shown in the figure .

The frequency control unit 18 includes a frequency control IC U2 for generating a switching frequency for alternately switching the MOSFETs Q11 and Q12 of the inverter unit 16. Resistors R21 and R22 and a capacitor C13 are connected between the input terminal of the frequency control IC U2 and the output terminal of the power factor circuit portion 14. The frequency control IC U2 is connected between the resistors R12 and R22, And the constant time constant of the capacitor C13. The frequency control IC U2 generates two square wave signals having a phase difference of 180 degrees from the oscillation frequency and a duty ratio of 50%. These two square wave signals are supplied to MOSFET Q1 and MOSFET Q2, respectively.

The frequency control unit 18 of the present invention can selectively implement the fixed frequency control and the variable frequency control using the frequency control IC U2 unlike the conventional method using the oscillation inductor. First, a fixed oscillation frequency can be set by adjusting the variable resistor R21 connected to the input terminal of the frequency control IC U2. Further, the brightness control means 24 may be further connected to the input terminal of the frequency control IC U2 via a photocoupler (PC). For example, the brightness adjusting means 24 may be an external manual volume switch. As another example, the brightness adjustment means 24 may be a photosensor that senses the ambient illumination. The input terminal of the frequency control IC U2 is provided with a switch SW1 for selectively switching the connection of the optical coupler PC. The frequency control unit 18 operates the switch SW1 to select the fixed frequency control by the RC time constant and the variable frequency control by the brightness control unit 24 so that the MOSFETs Q11 and Q12 of the inverter unit 16 Can be controlled. On the other hand, since the external brightness adjusting means 24 is connected to the frequency control IC U2 via the optical coupler PC, it can electrically isolate the external signal from the external signal and remove noise that may be generated from the external signal .

5 is a circuit diagram showing a configuration of a high voltage generating portion in the present invention. The high voltage generating unit 22 supplies the high frequency AC voltage generated by the inverter unit 16 to the CCFFL 20. The high voltage generating unit 22 of the present invention uses two high voltage transformers in a conventional CCFL driving apparatus and converts a square wave voltage into a sine wave voltage by using a leakage inductance inside the transformer, (TR1) is used to reduce transformer losses, and a resonance inductor is employed to set the maximum power transfer point for driving the CCFFL (20).

5, the high voltage generating section 22 includes a resonance inductor L5 and a boosting circuit section 22a for boosting the sinusoidal voltage converted by the resonance inductor L5 to a high voltage. The boosting circuit portion 22a is constituted by one high voltage transformer TR1 and two capacitors C21 and C22 and the primary winding of the high voltage transformer TR1 is connected in series with the resonance inductor L5 and the high voltage transformer TR1 ) Are connected to the CCFFL 20 by constituting a parallel resonant circuit with two capacitors C21 and C22.

The resonance inductor L5 of the high voltage generating portion 22 includes a first auxiliary winding L5-1 for detecting an abnormal state signal of the drive apparatus of the present invention and the first auxiliary winding L5 of the resonance inductor L5 -1) may further be connected to the protection circuit portion 26.

6 is a circuit diagram showing a configuration of a protection circuit portion in the present invention. The protection circuit portion 26 detects the current flowing from the resonance inductor auxiliary winding L5-1 of the high voltage generating portion 22 to the resonance inductor L5 and when the detected current rises above the set value, 14 and the frequency control unit 18, as shown in FIG. Accordingly, when the abnormal current is generated due to the opening or burning of the CCFFL 20, the driving apparatus of the present invention can be prevented from malfunction and secondary accident such as fire.

6, the protection circuit unit 26 includes an abnormal signal detection unit 26a for detecting an abnormal signal induced in the resonance inductor auxiliary winding L5-1, And a processing unit 26c for cutting off power supplied to the power factor circuit unit 14 and the frequency control unit 18 when it is determined that the comparison signal is an abnormal signal in the comparison unit 26b.

The comparator 26b includes a Zener diode D31 connected in reverse bias to one side of the resonance inductor auxiliary winding L5-1. The abnormality signal detecting unit 26a is installed at the front end of the Zener diode D31 and includes a diode D32 for converting a signal of an AC component induced in the resonance inductor auxiliary winding L5-1 into a signal of a DC component, And a resistor R33 and a resistor R34 for generating the operation reference potential of the Zener diode D31. The processing unit 26c is configured to allow the driving power supplied to the PFC IC U1 of the power factor circuit unit 14 and the frequency control IC U2 of the frequency control unit 18 to be bypassed to the ground side when the Zener diode D31 is surrendered Lt; / RTI > Preferably, the processing section 26c is configured by a combination of the two-stage transistors Q31 and Q32 and the resistors R31 and R32 and the capacitors C31 and C32. The processing section 26c greatly reduces the holding current loss as compared with the SCR which is mainly used in the conventional protection circuit.

7 is an operation waveform diagram of each part of the inverter unit and the high voltage generating unit according to the present invention. Each of the waveforms shown in FIG. 7 sequentially includes the gate drive waveforms Vgs1 and Vgs2 applied between the gate terminal and the source terminal of the MOSFETs Q11 and Q12 of the inverter section 16, the gate drive waveforms Vgs1 and Vgs2 of the MOSFETs Q11 and Q12 of the inverter section 16 The voltages Vds1 and Vds2 between the drain terminal and the source terminal of the MOSFETs Q11 and Q12 according to the gate driving signal and the output voltage waveform Vuv of the inverter section 16 and the waveform shown by the dotted line in the output voltage waveform of the inverter section 16 is the high voltage And the current waveform iL flowing through the resonance inductor L5 of the generating section 22. [

For convenience of explanation, the operation timings of the respective operation waveforms are divided into t0 to t6, and operation modes between the respective timings are divided into mode1 to mode6.

7, the MOSFET Q11 is turned on at a time point t0 of the mode 1, and the resonant inductor L5 current iL flows through the MOSFET Q12 during the mode1 period in the negative direction. When the MOSFET Q12 is turned off at the time point t1 of mode2, the capacitor of the MOSFET Q12 is charged by the resonant inductor L5 current iL, and the voltage Vds2 between the drain terminal and the source terminal of the MOSFET Q12 increases by Vs / 2 during the period Tc. The reverse diode (Body Diode) provided inside the MOSFET Q11 which has already been turned off is turned on by the resonant inductor L5 current iL, and the voltage Vds1 between the drain terminal and the source terminal of the MOSFET Q11 changes from Vs / (0 V) during the Tc period.

As described above, since the voltage Vds1 between the drain terminal and the source terminal of the MOSFET Q11 can be made 0V by the resonance inductor L5 current iL, that is, the resonance inductor L5 is provided inside the MOSFET Q11 by the resonance inductor L5 current iL The MOSFET Q11 is turned on by applying a gate driving signal between the gate terminal and the source terminal of the MOSFET Q11 during the period from the mode 2 to the mode 3 in which the reverse diode (Body Diode) is turned on so that the switching loss Thereby achieving zero voltage switching. Then, MOSFET Q12 goes through the same process as above during mode4 to mode6.

Further, a constant delay time Td is secured to prevent the MOSFETs Q11 and Q12 from being turned on at the same time. However, since a delay time longer than necessary acts as a loss in the inverter circuit, the internal capacitor of the MOSFETs (Q11 and Q12) is set to a minimum time considering the time Tc required for charging.

The driving apparatus for the cold cathode flat fluorescent lamp of the present invention as described above is a driving apparatus specialized for stable lighting of the CCFFL 20. Each component of the present invention has the following features.

The power factor circuit portion 14 of the present invention is configured with a boost converter structure to improve the power factor of the input power source and generate a high voltage DC voltage for lighting the CCFFL 20. [ The power factor circuit portion 14 switches and drives the switching element Q1 using the PFC IC U1 as an active integrated circuit and interrupts the power source applied to the inductor L2 by the switching element Q1, And the output of the rectifying section 12 is boosted to a high-voltage direct-current voltage. Therefore, it becomes possible to provide a drive device for a CCFFL having a high power factor.

The inverter unit 16 of the present invention has a half-bridge structure and achieves zero voltage switching using MOSFETs Q11 and Q12 with a built-in reverse diode. Thus, switching losses that can be generated by switching the high voltage input power supply are minimized. Further, since the MOSFET Q11 and Q12 may be damaged by switching the input power of a high voltage, the protection between the gate terminal and the source terminal of each MOSFET Q11 and Q12 for protection of the MOSFETs Q11 and Q12 Install a resistor.

The frequency control unit 18 of the present invention supplies a square wave signal having a phase difference of 180 degrees to the gate terminals of the MOSFETs Q11 and Q12 of the inverter unit 16. In the present invention, It is possible to control the switching frequency of the MOSFETs Q11 and Q12 using the frequency control IC U2 to control the fixed frequency system based on the RC time constant and to control the brightness of the external brightness adjusting means 24 It is possible to selectively perform the control of the inter-variable frequency system. At this time, the external brightness adjusting means 24 is connected to the input terminal of the frequency control IC U2 through the optical coupler PC, thereby controlling the dimming of the CCFFL 20 while suppressing the noise due to the external signal Can be realized.

The high voltage generating unit 22 of the present invention uses a resonant inductor L5 to convert a square wave voltage into a sine wave voltage and uses a single high voltage transformer TR1 to light the CCFFL 20. [ Therefore, compared with the conventional method using two high-voltage transformers, loss of the transformer is greatly reduced, and inverter efficiency is greatly improved.

The protection circuit portion 26 of the present invention is not a method of detecting the output of the CCFFL 20 but a method of detecting an abnormal current flowing through the resonance inductor L5 with the auxiliary winding L5-1 of the resonance inductor L5 . Therefore, the failure of the initial lamp lighting and the abnormal current on the load side are detected without interfering with the driving of the CCFFL 20, and the MOSFETs Q11 and Q12 of the inverter unit 16 as well as the MOSFETs of the power factor circuit unit 14 Q1) to protect the entire circuit components. Preferably, the protection circuit unit 26 bypasses the PFC IC U1 of the power factor circuit unit 14 and the driving power supplied to the frequency control IC U2 of the frequency control unit 18 to the ground side during abnormal current detection , So as to more safely protect the entire drive circuit.

Furthermore, the driving apparatus for CCFFL of the present invention makes it possible to design a compact and lightweight product by using a plurality of active integrated circuits, which has an advantage that a driving device can be integrally designed in CCFFL.

It will be apparent that the present invention described above can be used in various lighting apparatus fields such as LCD backlight units or independent lighting apparatuses driven by the present invention as CCFFL dedicated driving apparatuses for driving CCFFLs. Further, the driving device for the CCFFL of the present invention is not limited to the above-described embodiment and the accompanying drawings, and various substitutions, modifications and changes are possible according to the use of the CCFFL within the scope of the technical idea of the present invention Will be apparent to those skilled in the art to which the present invention pertains.

As described above, the driving apparatus for the cold cathode flat fluorescent lamp according to the present invention improves the power factor of the rectified power source in the power factor circuit section, boosts the rectified power factor to a high-voltage direct current power and supplies it to the inverter section, And a reverse diode is provided inside each MOSFET of the inverter unit to minimize the switching loss that may be caused by high frequency switching of the high voltage input power supply.

Further, according to the present invention, a protection resistor is provided between each MOSFET gate terminal and a source terminal of the inverter section, thereby protecting the MOSFET safely even in high-voltage switching.

Claims (5)

A filter unit for removing surge from the AC input power source and filtering the noise; A rectifying unit for rectifying the AC power input through the filter unit to DC power; A power factor circuit for improving the power factor of the rectified power output from the rectifier and for increasing the input voltage; An inverter unit that oscillates the DC voltage output from the power factor circuit unit to a square-wave type high frequency AC voltage; A frequency controller for outputting two rectangular waves having a phase difference of 180 degrees with each other to control an oscillation frequency of a switching element provided in the inverter; And And a high voltage generator for boosting the square wave AC voltage output from the inverter to a sinusoidal AC voltage to generate a driving voltage for the cold cathode flat fluorescent lamp, Wherein the frequency control unit includes an optical coupler to which a photo sensor for sensing the illuminance of the outside of the driving unit for the fluorescent lamp is connected to control an oscillation frequency of the inverter unit according to a signal input from the photosensor, Wherein the inverter unit includes a pair of switching elements that are alternately switched by a square wave signal generated in a frequency control unit. delete delete The method according to claim 1, Wherein the switching element is a MOSFET, and a protective resistor for protecting the MOSFET is connected between each of the MOSFET gate terminals and the source terminal of the cold cathode flat type fluorescent lamp. The method according to claim 1, Wherein the switching element is a MOSFET and a capacitor for DC partial pressure is connected in parallel between the MOSFET source terminal and the drain terminal.

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