KR20100045170A - Inverter system and its operating method - Google Patents

Abstract

PURPOSE: An inverter system and an operation method thereof are provided to improve power efficiency of an inverter system by making a freewheeling current flow in a switch instead of a body diode. CONSTITUTION: An inverter system includes a switch controller(50). A switch controller is comprised of a diode controller(100) and a logic controller(150). The diode controller generates a signal corresponding to a conduction period of the body diode. The diode controller includes a delay time controller. The delay time controller controls the signal corresponding to the conduction period of the body diode by an external input signal. The logic controller generates the control signal for controlling the on/off of each switch during the freewheeling period from the output signal of the diode controller.

Description

Inverter system and its operating method

The present invention relates to an inverter system of a display device and a method of operating the same. More particularly, in an inverter system for generating an alternating voltage, a control is performed to reduce power consumption generated by a freewheeling current and improve efficiency. An inverter system and a method of operating the same.

LCD (Liquid Crystal Display) is a display device is widely used in TVs, monitors. According to the operation principle of the LCD, a back light is required to display an image through the LCD.

A cold cathode tube (CCFL) is used as the back light. The cold cathode tube is a fluorescent lamp that is turned on at a low temperature without heating the filament. The cold cathode tube includes a glass tube containing a predetermined amount of a mixed gas such as mercury, argon, and neon, and an electrode disposed at both ends of the glass tube. Electrons are emitted by the high-voltage electric field applied to the two electrodes, mercury is excited by the emitted electrons, and ultraviolet rays are emitted. The emitted ultraviolet rays collide with the phosphor on the inner wall of the glass tube to emit visible light.

In order to emit light, a cold cathode tube requires an AC voltage of several hundred V or more, and an inverter system is required. Such an inverter system includes a half bridge, a full bridge, and a push pull method. The half-bridge or push-pull method uses only two power semiconductors as switch elements, so it is used for LCD monitors with lower output power than large LCDs such as TVs.

FIG. 1 is a diagram illustrating a configuration of an inverter system implemented by a general half-bridge method, assuming an inverter system when driving one lamp.

A typical half-bridge inverter system uses a pulse width modulation (PWM) control method to control the lamp current to a desired value while converting an input DC voltage into an alternating voltage of several hundred V to drive a CCFL lamp.

More specifically, as shown in FIG. 1, the inverter system compares the smoothed voltage VF with the reference voltage Vref to output an error voltage Verr and an error amplifier output Verr by comparing a triangular wave with a lamp current. PWM comparator 12 for outputting the PWMO signal for controlling the signal, oscillator 30 for generating the triangular wave for PWM comparison, Logic Controller 14 for making the PWMO signal to drive the switch, Switch A switch block 16 for outputting an input voltage VIN or ground in response to an on / off control signal, an AC amplifier 18 for receiving an output OUT of the switch block 16 as an input and amplifying the signal to a bipolar voltage for driving a lamp; And a CCFL lamp load 20.

In addition, the gate driver 15 for amplifying the output signals DrvH and DrvL of the logic controller 14 and transferring them to the switch block 16, and the rectifier 22 for converting the lamp current into a voltage and smoothing the AC voltage to a DC voltage. It includes.

FIG. 2 is a circuit diagram showing a power stage circuit in FIG. 1, FIG. 2 (a) is a diagram showing the configuration of a switch block and an AC amplifier, and FIG. 2 (b) is a circuit diagram of FIG. Equivalent circuit equivalently converted to the primary side of a transformer. 3 is a diagram illustrating waveforms of voltage and current according to the operation of the switch block in FIG. 2.

The two switch elements M1 and M2 constituting the switch block may be provided with a semiconductor such as a MOSFET, and as a result, the parasitic capacitances C1 and C2 may be included in a circuit as shown in FIG. do.

In FIG. 2 (b) where the equivalent circuit is shown, Cb, the primary capacitor of the transformer, has a relatively large capacity, and thus Cb is represented as a voltage source of VIN / 2, and a load Ro connected to the secondary side is a transformer turn ratio. Converted to the primary side as a function of. In the primary equivalent circuit, the equivalent inductance Leq is approximately equal to the leakage inductance of the transformer primary side, the equivalent capacitance Ceq is equal to the secondary side capacitance capacitance Cr multiplied by the squared n ² of the turn ratio, and the equivalent load resistance Req is the secondary side load resistance Ro Is divided by n ² .

Referring to Figures 2 (b) and 3 will be described in more detail the operation of the switch block and the AC amplifier as follows. At this time, it is assumed that the turn-on voltages of the body diodes D1 and D2 of the switch elements M1 and M2 are the same as VD. When the first switch element M1 is turned on at t = 0, OUT = VIN and Vp = VIN / 2. Therefore, the current Ip of the inductor Leq is increased by resonance due to the inductor Leq and the equivalent capacitance Ceq, and the voltage Vo of the equivalent capacitance Ceq is also increased by the resonance. At this time, the parasitic capacitance C1 of the first switch element is zero and the parasitic capacitance C2 of the second switch element is charged to VIN.

When t = t1, when the first switch element M1 is turned off, the parasitic capacitance C2 of the second switch element is discharged at the VIN voltage by the inductor current Ip, and the parasitic capacitance C1 of the first switch element is 0 ( starts charging at zero). Therefore, the voltages OUT and Vp decrease gradually. When the OUT voltage gradually decreases and becomes the OUT = -VD voltage at t = t2, the body diode D2 of the second switch element is turned on and Vp = -VIN / 2-VD. Therefore, the inductor Leq receives the maximum voltage of VL = -VIN / 2-VD-Vo and the inductor current Ip starts to decrease rapidly.

At t = t3, the inductor current Ip becomes zero and thus the body diode D2 of the second switch element is turned off. However, although the body diode D2 of the second switch element is turned off, the second switch element M2 is not yet turned on, and thus resonates due to parasitic capacitances C1 and C2 and the inductor Leq of each switch element. Equivalent capacitance (Ceq) is relatively large compared to the parasitic capacitance (C1, C2), so the resonant frequency is much higher frequency than the resonance caused by the inductor (Leq) and equivalent capacitance (Ceq) and also equivalent load (Req) Since the resonance is small, the resonance disappears quickly.

When the second switch element M2 is turned on at t = t4, OUT = 0, and the parasitic capacitance C1 of the first switch element is charged to VIN and C2 is charged to zero. Since OUT = 0V, Vp = -VIN / 2, and thus the inductor current Ip starts to increase in the opposite direction to the previous one due to the resonance caused by the inductor Leq and the equivalent capacitance Ceq. The subsequent operation is the same as the operation after the first switch element M1 is turned on, and consequently becomes the same as the waveform shown in FIG.

As described above, in a general inverter system configuration and PWM control scheme, the body diodes D1 and D2 of the switch element are automatically turned on during a freewheeling period in which the inductor current Ip direction is maintained as it is. Since the current flows to the body diodes D1 and D2 and consumes power at the body diode side, the efficiency of the inverter system is lowered and the heat generation of the switch element is increased.

On-resistance of MOSFET switches used in inverter systems, such as LCD monitors, is typically on the order of tens of milliohms, and the on-voltage of the body diode is about 0.5V. The maximum current flowing through the switch of the inverter increases in proportion to the size of the LCD panel and the number of CCFL lamps used, and usually more than a few amps of current flow. At this time, when comparing the conduction loss caused by the MOSFET switch-on resistance with the diode loss, which is the power consumed when the diode is turned on, the power consumed by the diode cannot be ignored.

For example, assuming that the maximum current of a switch with an on resistance of 20 mΩ and a body diode on voltage of 0.5 V is 7 A and freewheeling with the diode at this current, the maximum instantaneous power consumption by the switch on resistance is 0.98 W. The diode is very large, 3.5W.

The present invention is to improve the above-mentioned problems, by controlling the freewheeling current to flow to the switch during the period of flow to the body diode of the switch element to improve the power efficiency of the inverter system and reduce heat generation of the switch element to improve durability An inverter system and a method of operating the same are provided.

More specifically, the inverter system of the display device according to an embodiment of the present invention, a period in which the freewheeling current flows by automatically turning on the body diode of each switch while each switch performs an inverting operation. A switch controller for generating a control signal to temporarily turn on or off the respective switches during operation, thereby allowing the freewheeling current to flow to the switch instead of the body diode, thereby reducing power consumption and increasing efficiency Can be reduced.

In addition, the operating method of the inverter system according to an embodiment of the present invention, the first step of generating an on / off control signal for a plurality of switches using the error amplifier output voltage and a triangular wave, the generated on / off control signal In accordance with the method of operation of the inverter system comprising a second step of the switch to perform an on / off operation to generate an AC voltage, and applying the generated AC voltage to the lamp to emit light. And a third step of generating a control signal for temporarily turning on each switch in a period during which the freewheeling current flows to the body diode of the switch, thereby improving the power efficiency of the inverter system.

Hereinafter, exemplary embodiments of the present invention will be described with reference to the accompanying drawings.

4 is a diagram illustrating an operation concept of the present invention.

Inverter system according to the present invention is a method for reducing the power loss consumed by a diode in a general inverter control method, by turning on the corresponding switch element during the period in which the body diode is on, the inductor current (Ip) is not a diode switch Control to flow. As a result, efficiency can be improved by lowering power consumption and heat can be reduced to increase durability.

In more detail, after the first switch is turned off, the second switch is turned on in accordance with the freewheeling period in which the body diode of the second switch is turned on so that the inductor current maintains the direction of the current, and the second switch in a similar manner. After turning off, the first switch is turned on in accordance with the freewheeling period during which the body diode of the first switch is turned on.

5 is a diagram illustrating a configuration of an inverter system implemented according to the first embodiment of the present invention.

In the inverter system of the display device according to the first embodiment of the present invention implemented according to the operation concept shown in FIG. 4, as shown in FIG. 5, the smoothed voltage VF is compared with the reference voltage Vref. Error amplifier 10 for outputting error voltage Verr, PWM comparator 12 for outputting signal PWMO for PWM control of lamp current by comparing output voltage Verr of error amplifier with triangle wave CT, PWM control An oscillator 30 for generating a triangular wave for the switch controller 50 and a switch controller 50 for generating a control signal for turning on a corresponding switch instead of a diode in the freewheeling period in addition to the general PWM duty control signal of the switch. And a gate driver 60 that amplifies the switch so that it can be driven by the output signal. In addition, according to the switch control output signal of the gate driver 60, the CCFL lamp is received by receiving the switch block 16 which connects the output signal OUT to the input voltage VIN or the ground, and OUT which is the output signal of the switch block 16. It is an inverter system which consists of an AC amplifier 18 which amplifies to AC of more than several hundred V to drive, a CCFL lamp 20 as a load, and a rectifier 22 which converts lamp current into voltage and smoothes AC voltage into DC voltage. .

The switch controller 50 according to an embodiment of the present invention has a signal corresponding to the freewheeling period so that the corresponding switches M1 and M2 can be turned on in accordance with the freewheeling period in which the body diodes D1 and D2 are turned on. It includes a diode controller (Diode On-Time Controller) 100 for outputting the logic controller 150 to make a separate signal for the PWM control of the switches.

At this time, the diode controller 100 according to the embodiment of the present invention output signal PWMAd corresponding to the period in which the body diode (D1, D2) of each switch element (M1, M2) constituting the switch block 16 is turned on You can output

That is, the logic controller 14 of the general inverter system as shown in FIG. 1 receives the PWMO which is the output signal of the PWM comparator 12 and the charge / discharge control signal of the oscillator 30 to control the first switch for PWM control. While outputting the signal DrvH and the second switch control signal DrvL, the logic controller 150 included in the switch controller 50 according to the embodiment of the present invention is a PWM control signal from the PWM comparator 12. The PWMO and the charge / discharge control signal CK of the oscillation controller 32 and the control signal PWMAd corresponding to the freewheeling period are input from the diode controller 100 to perform PWM control and simultaneously switch the switch according to the freewheeling period. The control signals DrvH and DrvN are controlled to be turned on and supplied to the gate driver 60.

The error amplifier 10 amplifies the difference between the output voltage VF and the reference voltage Vref of the rectifier 22 to output the output signal Verr so that the PWM duty can be increased or decreased, and the capacitor Cc is Stabilize the inverter system. In the present specification, the error amplifier 10 is illustrated as a transconductance amplifier that outputs a difference in input voltage as an output current, but is not limited thereto, and may also be configured as a voltage amplifier.

Oscillator 30 is a circuit for making a triangular wave for PWM control is composed of an oscillation controller 32 and an oscillation capacitor (Cosc). The oscillation controller 32 outputs the charge / discharge control signal CK, and the triangular wave is generated by charging or discharging the oscillation current source Iosc with the oscillation capacitor Cosc as this signal becomes high or low. The gate driver 60 drives the gate-source voltage of the switch elements M1 and M2 constituting the switch block 16 to a sufficiently large voltage so that the switch-on resistance is reduced while simultaneously switching It is composed of a first gate driver (not shown) and a second gate driver (not shown) for driving with a large current to charge and discharge the input capacitors of the elements M1 and M2 sufficiently fast. The first gate driver amplifies the first driving control signal DrvH of the logic controller 150 to output the GP signal, and the second gate driver amplifies the second driving control signal DrvL of the logic controller 150. Output the GN signal.

The switch block 16 alternately connects the output signal OUT to the input voltage VIN and ground. The switch block 16 includes a first switch element M1 located above and a second switch element M2 located below. The switch element includes body diodes D1 and D2, respectively.

In the present specification, the first switch device M1 is described with an example in which a P-type MOSFET is applied, but is not limited thereto. An N-type MOSFET may be used.

The first switch element M1 may be turned on / off according to the first gate driving signal GP of the gate driver 60, and when turned on, the first switch element M1 may connect OUT to an input voltage VIN. The second switch element M2 operates on / off according to the second gate driving signal GN and, when on, connects OUT to ground. Therefore, OUT becomes a square wave AC voltage having a voltage of VIN or ground (0V).

The AC amplifier 18 amplifies the input signal into an AC signal of several hundred volts or more so as to drive the CCFL lamp 20, and more specifically, OUT, which is an output signal output from the square wave AC voltage of the switch block 16, is output. The LC resonance converts the output to a sine wave output VAC with positive and negative voltages. To this end, the AC amplifier may include a DC blocking capacitor Cb, a transformer T1 and a resonant capacitor Cr that amplify at a turn ratio of 1: n.

In the DC blocking capacitor Cb, a large value capacitor is usually used for DC blocking. Therefore, when the symmetric PWM control method is used, the DC blocking capacitor Cb is charged with a DC voltage of VIN / 2. Accordingly, the input voltage Vx of the transformer T1 becomes an AC voltage having voltages of + VIN / 2 and -VIN / 2.

The rectifier 22 senses and rectifies the lamp current and performs a filtering operation to enable PWM control. Specifically, the rectifier 22 includes a sense resistor (Rs), a half-wave rectifier diode (D3), and a smoothing resistor ( Rf) and a capacitor Cf. At this time, the rectifier 22 may be a circuit configuration in a variety of ways according to the designer as an example shown when one CCFL lamp 20 is provided, and also in the case of a plurality of lamps are connected in various ways depending on the designer The configuration of the circuit may vary.

FIG. 6 is an exemplary diagram showing a configuration of a switch controller in FIG. 5, and FIG. 7 is a diagram showing an operation waveform of a circuit constructed according to FIG. 6.

As shown in FIG. 6, in the inverter system according to the first embodiment of the present invention, the diode controller 100 of the switch controller 50 includes at least one rising-edge-delay-circuit. 102, 108 and logic circuits 104, 106, 110. The PWMO_Ax signal output from the first rising-edge-delay-circuit 102 and the PWMOB signal output as the PWMO passes through the inverter 104 and charge / discharge of the oscillation controller are delayed by the PWMO signal by a freewheeling period. When the control signal CK is input to the NOR gate 106, a PWMOA signal corresponding to the freewheeling period can be obtained. The second rising-edge-delay that delays the PWMOA from the rising edge by a certain time, i.e., dead time (Td), since the switching element should not be turned on at the same time even if the corresponding switching element is turned on instead of the diode during the freewheeling period. After passing through the circuit 108 and the inverter 110, an output signal PWMOAd corresponding to a period for turning on corresponding switches instead of a diode during the freewheeling period can be obtained.

The logic controller 150 according to the embodiment of the present invention shown in FIG. 6 is a diode in the PWM duty control signal PWMO for the PWM duty control from the PWM comparator 12 to implement an inverter system of high efficiency. Instead, the control signal PWMOAd corresponding to the freewheeling period and the charge / discharge control signal CK for generating a signal capable of driving the gate driver separately are received from the diode controller 100 to turn on the corresponding switch. . That is, when the charge / discharge control signal CK passes through the T-type flip-flop (TFF) 152, the frequency is 1/2 of the charge / discharge control signal CK, and at the oscillation maximum voltage VH of the oscillation waveform CT. The transitional complementary square wave signals VFD and BVFD can be obtained, and these signals can pass through a logic gate to output switch control signals for symmetric PWM control. In addition, if the PWM duty control signal PWMO and the square wave signal BVFD are input terminals of the NOR gate 154, a DrvP signal corresponding to the PWM duty control period of the first switch element M1 can be obtained. When the output signal PWMAd and the square wave signal VFD are input terminals of the NOR gate 156, the DrvPA signal corresponding to the freewheeling period of the body diode D1 of the first switch element M1 can be obtained. In addition, when the DrvP signal and the DrvPA signal are input to the NOR gate 162, the first switch element M1 is turned on during the PWM duty control period of the first switch element M1 and the freewheeling period of the body diode D1. DrvH can be obtained.

In a similar manner, if the PWM duty control signal PWMO and the square wave signal VFD are input terminals of the NOR gate 160, DrvN corresponding to the PWM duty control period of the second switch element is obtained, and the PWMAd output signal of the diode controller 100 is obtained. When the square wave signal BVFD is an input terminal of the NOR gate 158, a DrvNA signal corresponding to the freewheeling period of the body diode D2 of the second switch element M2 can be obtained. Therefore, when the DrvN signal and the DrvNA signal pass through the OR gate 164, a control signal DrvL for turning on the second switch element M2 in the PWM duty control period of the second switch element M2 and the freewheeling period of the body diode can be obtained. have.

The oscillator 30 is a circuit which generates or oscillates the waveform CT by charging or discharging the oscillation capacitor Cosc with the charge / discharge current source Iosc according to the charge / discharge control signal CK of the oscillation controller 32. In more detail, the oscillation controller 32 causes the charge / discharge control signal CK to go low when the oscillation waveform CT becomes smaller than the oscillation minimum voltage VL, thereby driving the oscillation capacitor Cosc to the current source Iosc. To charge. In addition, the charge / discharge control signal CK becomes high at the moment when the oscillation waveform CT becomes larger than the oscillation maximum voltage VH so that the oscillation capacitance Cosc is discharged. Therefore, the frequency of the CK waveform is equal to the frequency of the CT waveform.

8 is an exemplary view showing the configuration of a switch controller implemented according to a second embodiment of the present invention.

As shown in FIG. 8, the switch controller implemented according to the second embodiment of the present invention further includes a delay time controller 202 capable of changing the diode on period by an external signal in the diode controller 200. The logic controller 250 further includes a duty limiter 270 that limits only the specific PWM duty to be switched on instead of the diode in the freewheeling period. The diode on period depends on the design of the power stage circuit, such as the inductance of the transformer T1. Therefore, it is advantageous for system design to be able to vary by external signal rather than fixing diode on period. The delay time controller 202 is preferably for varying the freewheeling period to achieve this characteristic, so that the delay time of the first rising-edge-delay-circuit 204 varies according to the FWT pin state.

In PWM control, as the PWM duty increases, the inductor current (Ip) decreases beyond the maximum point of resonance, thus reducing the diode on-period as the current magnitude decreases at the beginning of freewheeling. Therefore, if the duty is increased to a certain degree, the effect of improving efficiency by turning on the switch instead of the diode during the diode freewheeling period can be reduced. However, since the switch controller 50 implemented according to the first embodiment of the present invention turns on the switch in the freewheeling period at a fixed time regardless of the PWM duty, the switch is turned on longer than the freewheeling period as the duty gradually increases. This causes distortion of the current waveform.

The switch controller according to the second embodiment of the present invention is configured to ignore the output of the diode controller 200 when a certain PWM duty is exceeded.

In addition, as the PWM duty decreases gradually, the power supplied to the CCFL lamp 20 decreases. As a result, the switch current also decreases, so that the period during which the switch remains on is gradually reduced. Therefore, if the PWM duty is gradually reduced when the switch is turned on instead of the diode for a fixed time, such as the switch controller 50 implemented according to the first embodiment of the present invention, any signal of PWMO and PWMAd is a PWM duty control signal. It is not known which signal is the diode on time control signal. Therefore, as a solution to this problem, the switch controller can be configured to ignore the output of the diode controller 200 when the PWM duty is lowered below.

In order to perform the above-described function, the switch controller 50 ′ according to the second embodiment of the present invention provides a duty limiter 270 for operating the output PWMAd of the diode controller 200 only in any region of the PWM duty. It may be further included in the logic controller 250. Duty limiter 270 may comprise at least one comparator 272, 274 and a NAND gate 276. Since the PWM duty is determined by the output voltage Verr of the error amplifier 10, the output voltage Verr and the duty limit voltage Vmax and Vmin of the error amplifier may be compared to limit the maximum and minimum of the PWM duty. Where Vmax is the reference voltage that sets the maximum PWM duty and Vmin is the reference voltage that sets the minimum PWM duty.

In the duty limiter 270, the output FWD goes low only when the output voltage Verr of the error amplifier is greater than Vmin and less than Vmax so that the output PWMAd of the diode controller 200 operates. Also, if the error amplifier's output voltage (Verr) is less than Vmin or greater than Vmax, FWD will be high and DrvPA and DrvNA will always be low regardless of PWMAd. Therefore, the output PWMAd of the diode controller 200 is ignored and the switch controller 50 'performs only the PWM duty control.

Meanwhile, the diode controller implemented according to the first and second embodiments of the present invention controls the diode on time to be constant regardless of the PWM duty.

Although the duration of turning on the switch instead of the diode during the freewheeling period by the diode controller is shorter than the actual freewheeling period, there is no problem in the PWM control operation, but in terms of efficiency, It's a bit worse in terms of efficiency.

On the contrary, if the diode controller turns on the switch instead of the diode in the freewheeling period longer than the actual freewheeling period, the distortion of the current waveform is generated, and the distortion increases as the period for turning on the switch is longer. In PWM duty control, the diode freewheeling period becomes shorter as the PWM duty increases. Therefore, as the PWM duty increases, shortening the diode-on time generated by the diode controller will improve the efficiency when the PWM duty is small and improve the current waveform when the PWM duty is high. .

9 is an exemplary diagram showing an internal configuration of a switch controller implemented according to the third embodiment of the present invention.

The switch controller implemented according to the third embodiment of the present invention is to achieve the above object, and is implemented so that the output PWMAd of the diode controller 300 changes according to the PWM duty. More specifically, as shown in FIG. 9, when the variable pulse width generator 302 outputs a signal PWMO_Ax1 whose pulse width is changed according to the PWM duty, the output signal passes through a logic circuit to the variable diode on time. It is output with the corresponding PWMAd.

When the PWM duty is lowered, the minimum duty limiter instead of the duty limiter in the configuration of the logic controller implemented according to the second embodiment of the present invention in order to ignore the output of the diode controller 300 and to operate as simple PWM duty control. 370. Therefore, if the output voltage Verr of the error amplifier is less than Vmin, FWDm becomes high so that DrvPA and DrvNA always go low regardless of PWMAd, and the output PWMAd of diode controller 300 is ignored and the switch controller 50 ″. Will only control the PWM duty.

In the switch controller implemented according to the third embodiment of the present invention, the configuration of the variable pulse width generator is as follows.

FIG. 10 is a diagram illustrating a diode freewheeling period in an inverter system according to the present invention. FIG. 10 (a) illustrates a model of the freewheeling period as a linear function according to PWM duty. The relationship between the PWM duty and the diode freewheeling period T _FW is shown.

Referring to FIG. 10 (a), T _FW may be represented by the following equation.

In order to reduce the diode freewheeling period generated by the diode controller 300 according to the PWM duty, the diode controller 300 may operate as shown in Equation 1 below. In PWM control, the error amplifier output voltage (Verr) represents the current PWM duty. Therefore, if the voltage V _FW higher than the error amplifier output voltage Verr is compared with the triangular CT, the diode freewheeling period can be obtained and if the V _FW voltage is decreased as the PWM duty increases, the diode controller 300 increases the PWM duty. When satisfying the equation (1) can be made a signal that reduces the diode freewheeling period.

Also, referring to FIG. 10 (b) in which the relationship between the PWM duty and the diode freewheeling period T _FW is shown in comparison with the triangular CT with a voltage V _FW higher than the error amplifier output voltage Verr, the following equation 2 is derived. Can be.

Substituting Equation 1 into Equation 2 derived as described above may obtain the following equation.

In Equation 3, K ₁ , V _{FW, OFFSET} are derivable values, and Verr is an error amplifier output voltage, so a circuit satisfying Equation 3 can be designed and applied to the variable pulse width generator.

FIG. 11 is a circuit diagram illustrating an example of implementing a variable pulse width generator in FIG. 10.

In the switch controller according to the third embodiment of the present invention, the variable pulse width generator may include a variable voltage generator 410 and a comparator 420. The variable voltage generator 410 is implemented as a circuit to satisfy Equation 3 so that the variable voltage V _FW gradually decreases as the PWM duty increases. At this time, since V _FW is always greater than the error amplifier output voltage Verr, when V _FW is compared with the triangular CT in the comparator 420, a PWMO_Ax1 signal in which the pulse width gradually decreases as the PWM duty increases.

In more detail, the variable voltage generator 410 receives a voltage-current converter 412 that outputs an output current I ₁ proportional to an error amplifier output voltage Verr, and receives the output as an input sourcing current. The current mirror 416 includes a voltage-current converter 414 for outputting an output current I ₂ proportional to an offset voltage Voff, and a current mirror 418 for receiving the output as an input and outputting a sourcing current. Moreover, it consists of the resistor R3 which adds the output current of the current mirrors 416 and 418, and converts it into a voltage. In this case, when the gains of the current mirrors 416 and 418 are 1, the output V _FW of the variable voltage generator 410 may be represented by the following equation.

Comparing Equations 3 and 4, it can be seen that K ₁ = R ₃ / R ₁ and V _{FW, OFFSET} = (R ₃ / R ₂ ) * V _off . Therefore, comparing the VFW with a triangular CT, we can obtain a signal PWMO_Ax1 whose pulse width decreases as the PWM duty increases.

As described above, the inverter system of the display device and the operation method thereof according to the present invention have been described with reference to the illustrated drawings. However, by turning on the corresponding switch in a period in which current flows through the body diode of the switch element, the power efficiency of the inverter system is improved. It is apparent that the technical idea of the present invention, which enables to enhance the durability of the switch element, can be easily applied by those skilled in the art within the scope of protection.

1 is a view showing the configuration of an inverter system implemented in a general half-bridge method,

FIG. 2 is a circuit diagram showing a power stage circuit in FIG. 1;

FIG. 3 is a diagram illustrating waveforms of voltage and current according to a switch operation in FIG. 2;

4 is a diagram illustrating an operation concept of the present invention;

5 is a diagram showing the configuration of an inverter system implemented according to the first embodiment of the present invention;

6 is an exemplary view showing the configuration of a switch controller in FIG. 5;

7 shows an operating waveform of a circuit constructed in accordance with FIG. 6;

8 is an exemplary view showing the configuration of a switch controller implemented according to a second embodiment of the present invention;

9 is an exemplary diagram showing an internal configuration of a switch controller implemented according to the third embodiment of the present invention;

10 is a diagram illustrating a diode freewheeling period in an inverter system according to the present invention; and

FIG. 11 is a circuit diagram illustrating an example of implementing a variable pulse width generator in FIG. 10.

<Description of the symbols for the main parts of the drawings>

16: switch block 18: AC amplifier

20: CCFL lamp 14, 150, 250, 350: logic controller

50, 50 ', 50 ”: switch controller

100, 200, 300: diode controller 202: delay time controller

270: duty limiter 302: variable pulse width generator

370: minimum duty limiter

Claims (10)

In the inverter system of the display device to cause the lamp to emit light when the AC voltage generated by the on / off operation of the multiple switches, The control signal is prevented from flowing to the body diode of each switch during a freewheeling period in which the direction of the current is maintained after each switch is turned off, and the control signal is temporarily turned on. Generating switch controller Inverter system of the display device comprising a. The method of claim 1, The switch controller may include a diode controller generating a signal corresponding to a period during which the body diode conducts during the freewheeling period; And Logic controller for generating a control signal for controlling the on / off operation of each switch during the freewheeling period from the signal output from the diode controller Inverter system of the display device comprising a. The method of claim 2, And the diode controller comprises a delay time controller which adjusts a signal corresponding to the time that the body diode is conducted by an external input signal. The method of claim 2, The switch controller includes a duty limiter for controlling the operation of the delay time controller to generate a control signal and transmit the control signal to the logic controller during the freewheeling period during a freewheeling period only at a specific PWM duty. . The method of claim 1, The switch controller includes a diode controller for generating a signal corresponding to a freewheeling period according to the PWM duty of the inverter system; And Logic controller to ignore the output signal of the diode controller to generate the on / off control signal of each switch when the PWM duty is lowered below a certain value Inverter system of the display device comprising a. The method of claim 5, The diode controller includes a variable pulse width generator for varying the output pulse width in accordance with the PWM duty. The method of claim 6, The variable pulse width generator is an inverter system of a display device that satisfies the following equation.

(Verr; Error Amplifier Output Voltage, T _FW ; Freewheeling Period, V _OFFSET ; Offset Voltage) The method of claim 5, The logic controller includes a minimum duty limiter to ignore the output signal of the diode controller when the PWM duty is lower than a predetermined value. The first step of generating an on / off control signal for a plurality of switches using the error amplifier output voltage and a triangular wave, the switch is turned on / off according to the generated on / off control signal to generate an AC voltage, In the operating method of the inverter system consisting of a second step of applying light to the lamp to emit light, The first step is a third step of generating a control signal to temporarily turn on each switch so as to prevent freewheeling current from flowing to the body diode of each switch while the switches are turned off. Method of operation of the inverter system comprising a. The method of claim 9, The third step is to generate a signal corresponding to a freewheeling period, which is a period in which the direction of current is maintained after each switch is turned off, and controls to perform an on / off operation of the switch from the generated signal. A method of operating an inverter system comprising generating a signal.

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