KR20040068014A - Controller and driving method for power circuits, electrical circuit for supplying energy and display device having the electrical circuit - Google Patents

Abstract

PURPOSE: A control device of a power circuit and a driving method thereof, an electric circuit for supplying energy and a display device having the electric circuit are provided to supply an improved electric circuit having plural power circuits such as DC/AC inverters to drive plural loads such as CCFL(Cold Cathode Fluorescent Lamp) loads, thereby reducing noise caused by an instantaneous high circuit ripple. CONSTITUTION: A phase selector(44) generates a reference signal according to a variable input signal. In the case that four power circuits(10,12) is connected to at least two power circuit(10,12), the selector(44) outputs the reference signal showing the four power circuits connected by the variable input signal(s). A pulse generator(46) generates the first pulse signal, which is connected to the first power circuit(10) among at least the two power circuits(10,12) to initialize an operation of the first power circuit(10). The first power circuit(10) outputs the second pulse signal, and initializes an operation of the second power circuit(12) of at least the two power circuits(10,12). At least the two power circuits(10,12) supply energy to plural loads.

Description

CONTROLLER AND DRIVING METHOD FOR POWER CIRCUITS, ELECTRICAL CIRCUIT FOR SUPPLYING ENERGY AND DISPLAY DEVICE HAVING THE ELECTRICAL CIRCUIT}

BACKGROUND OF THE INVENTION Field of the Invention The present invention generally relates to electrical circuits for energizing multiple loads, such as Cold-Cathode-Fluorescent-Lamp (CCFL) loads, and more particularly to electrical circuits for providing phase shifts to multiple loads. It is about. Generally, the electric circuit is applied to a display device such as a liquid crystal display monitor, a liquid crystal display computer or a liquid crystal display television.

Cold cathode tube loads are widely used to provide backlighting for liquid crystal displays (LCDs), and in particular for backlighting liquid crystal display monitors and liquid crystal display televisions. However, these existing applications require a separate DC / AC power inverter to drive each cold cathode tube. This existing application is shown in FIG. 1. Referring to FIG. 1, each cold cathode tube 20, 22,..., 24 is supplied with power from an individual DC / AC inverter 10, 12,..., 14. Is synchronous. Each DC / AC inverter includes an A / C switched A / C network and a power supply circuit. The power supply driving circuit may include a resonant tank circuit for a cold cathode tube. The A / C switching network of each inverter is driven on / off synchronously. Thus, a lot of ripple occurs in the power line. Much current is supplied from the power supply V _Batt when the switches in the A / C switching network are turned on, and the supplied current is released when the switch is turned off. Simultaneous turn-on and turn-off of all inverters introduce noise in the power lines, which degrades the signal / noise integrity of the system.

One method of reducing ripple is to increase the filtering at the power line, but this method has the disadvantage of increasing the cost of the system because the size of the circuit is increased.

2 shows another circuit according to the prior art for driving a plurality of cold cathode loads. The circuit comprises a control device for driving a plurality of DC / AC inverters 10, 12, 14,..., 16 and a plurality of cold cathode loads 20, 22, 24,. 40). The clock generator 42 of the control device 40 generates a string of phase shifted clock signals to the respective DC / AC inverters 10, 12, 14, ..., 16 to delay the phase. . Since the switches in the network of all DC / AC inverters 10, 12, 14, ..., 16 are turned on and off with the same phase shift between neighboring inverters, the ripple on the power line is shown in FIG. It effectively reduces up to 1 / N of the ripple. Where N is the number of connected DC / AC inverters.

However, a problem is that the control device 40 is fixed to the number of loads initially required. That is, the number of cold cathode tube loads is equal to the number of lines transferring the phase shift from the control device 40 to the respective inverters 10, 12, 14,. Therefore, when the number of cold cathode tube loads changes, the configuration of the control device 40 must also change. As a result, the control device 40 has a disadvantage of generating a high frequency clock signal having a frequency N times the operating frequency of each DC / AC inverter.

It is an object of the present invention to provide a simple control device employing a simpler phase shift circuit technology than the prior art. The number of phases can be programmed according to the number of inverters used to obtain high power, low cost and many smaller inverter systems.

Another object of the present invention is to provide an instantaneous high current ripple by providing an improved electrical circuit with a plurality of power supply circuits such as direct current / AC inverters for driving a plurality of loads such as cold cathode tube loads. ripple) and to reduce noise caused by simultaneous turn on and turn off in the power supply circuit.

Another object of the present invention is to provide a display device including at least two loads such as cold cathode tube loads. The display device may be a liquid crystal display monitor, a liquid crystal display computer or a liquid crystal display television.

It is yet another object of the present invention to provide a method for driving an electrical circuit having a plurality of power supply circuits, such as direct current / AC inverters, for driving a plurality of loads such as cold cathode tube loads. It is to reduce noise caused by simultaneous turn on and turn off in the power supply circuit.

The control device of the present invention includes a pulse generator for generating a clock signal for initializing the operation of the connected DC / AC inverters, and a phase selector for generating a reference signal indicative of a plurality of connected DC / AC inverters.

In addition, the electrical circuit according to the invention provides a phase shift of switching on and off between DC / AC inverters for driving cold cathode tube loads. Here, the number of phase shifts is programmed according to the number of connected DC / AC inverters. According to the present invention, the first DC / AC inverter receives a first pulse signal from the phase generator and a reference signal indicating the number of phases from the phase selector, and generates a second pulse signal to the second DC / AC inverter. The second DC / AC inverter receives a second pulse signal having a phase shift with respect to the first pulse signal input to the first DC / AC inverter. Similarly, the second DC / AC inverter generates a third pulse signal having the same phase shift amount to the third DC / AC inverter with respect to the second pulse signal input to the second DC / AC inverter, thereby all DC / AC inverters. The inverters are turned on and off with the same phase shift between neighboring inverters. Thus, according to the present invention, the ripple on the power line is effectively reduced, the circuit can be programmed and simplified, and the cost is reduced.

1 is a schematic illustration of a conventional circuit for driving multiple cold cathode loads, showing that all direct current / AC inverters are synchronized when driving the cold cathode loads.

FIG. 2 is a schematic view of a conventional circuit for driving a plurality of cold cathode loads, the circuit comprising a control device and a plurality of DC / AC inverters, the control device comprising a sequence of phase delay clock signals. To generate a plurality of DC / AC inverters.

3 is a block diagram of an electrical circuit according to the present invention for driving multiple cold cathode loads.

4 shows an input clock signal and an output clock signal for DC / AC inverters.

5 shows an embodiment of a selector circuit, in which the inputs connected to the selector circuit are digital signals and the outputs connected to the DC / AC inverters are analog signals.

6 is an exemplary diagram schematically showing input signals connected to the selector circuit and output signals corresponding to the input signals.

FIG. 7 shows an embodiment of a selector circuit wherein the input connected to the selector circuit is an analog signal and the output connected to the DC / AC inverters is an analog signal.

8 is an exemplary view schematically showing the selector circuit shown in FIG.

9 is an exemplary diagram schematically illustrating a delay circuit of a DC / AC inverter including a ramp signal generated based on an input clock signal.

10 (a) is a schematic diagram showing a delay cell according to the present invention.

10 (b) shows one embodiment of a delay circuit of a direct current / alternating current inverter including the delay cell of FIG. 10 (a) operating in accordance with an input clock signal and an output signal of the selector circuit.

11 (a) to 11 (e) show one embodiment of direct current / AC inverters for implementing an electrical circuit according to the present invention.

3 shows an electrical circuit according to the invention used to drive a plurality of loads such as light source loads or cold cathode loads. The electrical circuit comprises a control device 40 and at least two power supply circuits 10, 12, such as a DC / AC inverter. The control device 40 comprises a selector 44, such as a phase selector, and a pulse generator 46, such as an oscillator.

The selector 44 generates a reference signal according to the variable input signal, and the reference signal indicates the number of phases to be transitioned or the number of power supply circuits connected to and controlled with the at least two power supply circuits 10 and 12. That is, when four power supply circuits are connected, the selector 44 will output a reference signal representing the four power supply circuits connected by the variable input signal (s). Thus, the power supply circuits to be controlled can be programmed according to the input signal (s) without changing the circuit arrangement of the control device 40 and the power supply circuits 10, 12. The selector 44 may be a digital-to-digital converter or an analog-input-analog-output circuit.

The pulse generator 46 generates a first pulse signal, and the first pulse signal is connected to the first power circuit 10 among at least two power circuits 10 and 12 so that the first power circuit 10 Initializes the operation of. Then, the first power supply circuit 10 outputs a second pulse signal to initialize the operation of the second power supply circuit 12 among the at least two power supply circuits 10 and 12. The at least two power supply circuits 10 and 12 are connected to a load such as a transformer and a light source or a cold cathode tube, respectively, to supply energy to the loads.

Hereinafter, for the sake of simplicity, the operation of the electric circuit according to the present invention including two power supply circuits will be described.

The selector 44 generates a reference signal to the two power supply circuits 10, 12 in accordance with the input signal (s) connected to the selector 44 to indicate the number of controlled power supply circuits (in this case, two). Let's do it. The pulse generator 46 then generates a first pulse signal to the first power supply circuit 10 to initialize the operation of the first power supply circuit 10. The first power supply circuit 10 is connected to a first transformer connected to a first load such as a light source or a cold cathode tube, and controls the operation of the first load. The first power supply circuit 10 outputs a second pulse signal to the second power supply circuit 12 to initialize the operation of the second power supply circuit 12, and the second pulse signal is sent to the first power supply circuit 10. The delay is with respect to the transmitted first pulse signal. The second power supply circuit 12 is connected to a second transformer connected to a second load such as a light source or a cold cathode tube and controls the operation of the second load. Similarly, the second power supply circuit 12 outputs a third pulse signal to the first power supply circuit 10 for a second operation cycle. The third pulse signal is delayed with respect to the second pulse signal transmitted to the second power supply circuit 12. Then, the first power supply circuit 10 outputs a fourth pulse signal, and the fourth pulse signal is delayed with respect to the third pulse signal transmitted to the first power supply circuit 10. In general, this signal is a pulse signal output from the last power supply circuit as an input pulse signal to the first power supply circuit 10. According to the invention, the two power supply circuits 10, 12 are turned on and off with the same phase shift. Thus, the ripple on the power line is effectively reduced, the circuit can be programmed and simplified, and the cost is reduced. The greater the number of power supply circuits, the more clear the advantages of the present invention.

The electric circuit according to the present invention can be applied to a display device such as a liquid crystal display monitor, a liquid crystal display computer or a liquid crystal display television. The display device may include not only a control device but also at least two power supply circuits, at least two transformers, at least two light sources, and a display panel.

4 is a diagram illustrating signals of an input clock and an output clock for a power supply circuit. There is a time delay ΔT between the input clock signal and the output clock signal. The time delay is a kind of phase shift delay and is caused by the delay circuit described later.

5 illustrates one embodiment of the selector circuit 70. Input signals 60, 62, 64, ..., 66 connected to the selector circuit 70, such as a digital-to-analog converter, are digital signals and connected to the power supply circuits 10, 12, ..., 14. The output signal is an analog signal Vaa. Input signals connected to the selector circuit 70 and output signals corresponding to the input signals are shown in FIG. 6. That is, when there are four input terminals of the selector 70, 16 power circuits to be controlled may be programmed.

FIG. 7 illustrates another embodiment of a selector circuit 72, such as a scaled analog selector. The input signal connected to the selector circuit 72 is an analog signal (Vain), and the output signal connected to the power supply circuits (10, 12, ..., 14) is an analog signal (Vaa). FIG. 8 is a schematic illustration of one embodiment of the selector circuit 72 shown in FIG. Reference numeral “Vain” denotes an analog input signal of the selector circuit 72 and reference numeral “Vaa” denotes an analog output signal of the selector circuit 72. The value of Vaa can be obtained using the superposition method based on the values of Vain, Vref and three resistors 80, 82, 84.

FIG. 9 is a diagram schematically illustrating an embodiment of a delay circuit of a power supply circuit including a ramp signal generated based on an input clock signal and a reference signal. The time delay DELTA T is caused by a delay circuit between each phase. 9 is a diagram showing a series of signals sequentially connected to each cold cathode tube. Here, the delay of the starting point is generated by the ramp generator based on the first pulse signal and the reference signal.

FIG. 10 (a) schematically illustrates a delay cell according to the present invention, in which a delay generated by the delay cell 92 between a clock in signal CLOCK IN and a clock out signal CLOCK OUT is shown. (ΔT) is shown. FIG. 10B is a diagram showing an embodiment of a delay circuit of a power supply circuit including the delay cell 92 shown in FIG. The delay ΔT is mainly determined by the reference signal Vaa. First, when the clock in signal CLOKC IN is first connected to the delay cell 92, the transistor 93 is turned on and the voltage Vc drops to zero volts. On the other hand, when the clock in signal CLOCK IN drops down until the voltage of the capacitor 94 becomes higher than the reference voltage Vref and the transistor 93 is turned off (start of the delay time), the capacitor 94 is a current. It is charged by (Ic). When the voltage of capacitor 94 is higher than Vref, comparator 95 changes state to generate a pulse signal through capacitor 96 to the next stage (end of delay time). The current Ic is determined by the difference between Vaa and Vcc. For example, as the value of Vaa increases, the current Ic decreases and the charging time increases. That is, the delay time is increased. As another example, the higher the value of Vaa, the larger the current Ic, thereby reducing the charging time. In other words, the delay time is reduced.

11 (a) to 11 (e) are diagrams showing one embodiment of DC / AC inverters implementing an electric circuit according to the present invention. FIG. 11A shows a full-bridge DC / AC inverter. FIG. 11B shows a half-bridge DC / AC inverter. FIG. 11C shows a full-bridge DC / AC inverter. ) Is a view showing a fly-back forward DC / AC inverter, Figure 11 (d) is a view showing a push-pull DC / AC inverter, Figure 11 (E) A diagram showing a class D direct current / AC inverter.

In the above description, the present invention is not limited to the above-described embodiments and the accompanying drawings, and it is common in the art that various substitutions, modifications, and changes can be made without departing from the technical spirit of the present invention. It will be evident to those who have knowledge of.

The control device of the present invention is used to control the energy supplied to an electrical circuit comprising a plurality of inverters, in particular to provide a phase shift in the electrical circuit. In addition, the electric circuit of the present invention is generally applied to a display device such as a liquid crystal display monitor, a liquid crystal display computer or a liquid crystal display television.

Claims (65)

A control device for controlling at least two power supply circuits, A pulse generator for generating a pulse signal coupled to a first power circuit of the at least two power circuits to initialize operation of the at least two power circuits; And And a selector for generating a reference signal coupled to each of said at least two power supply circuits to indicate the number of controlled power supply circuits. The method of claim 1, And the pulse generator is an oscillator. The method of claim 1, And the selector is a phase selector, a digital-to-analog converter or an analog-to-analog-output circuit. The method of claim 1, And the reference signal indicates the number of phases that are transitioned. The method of claim 1, And the selector comprises at least one input terminal for programming the number of controlled power supply circuits and an output for outputting a reference signal in accordance with an input signal coupled to the at least one input terminal. The method of claim 5, And the input signal is an analog signal or a digital signal for selecting the number of phases. In an electrical circuit for supplying energy, A control device having a pulse generator for generating a first pulse signal and a selector for generating a reference signal; And At least two power supply circuits, The reference signal is connected to each of the at least two power supply circuits to indicate the number of controlled power supply circuits, and the first pulse signal is connected to a first power supply circuit among the at least two power supply circuits to connect the first power supply circuit. Initialize the operation of the power circuit, The first power supply circuit outputs a second pulse signal to a second power supply circuit among the at least two power supply circuits to initialize an operation of the second power supply circuit, and the second pulse signal corresponds to the And delayed with respect to the first pulse signal. The method of claim 7, wherein The pulse generator is an oscillator. The method of claim 7, wherein The selector is a phase selector, a digital-to-analog converter or an analog-input-analog-output circuit. The method of claim 7, wherein The reference signal is indicative of the number of phases that are transitioned. The method of claim 7, wherein The selector comprises at least one input for programming the number of controlled power supply circuits and an output for outputting the reference signal in accordance with an input signal coupled to the at least one input. The method of claim 11, The input signal is an analog signal or a digital signal for selecting the number of phases. The method of claim 7, wherein The power circuit is a DC / AC inverter. The method of claim 13, The DC / AC inverter is a full-bridge inverter, a half-bridge inverter, a fly-back forward inverter, a push-pull inverter or a class D inverter. The method of claim 7, wherein The delay is a phase shift delay. The method of claim 7, wherein The power circuit further comprises a transformer. The method of claim 16, The power supply circuit further comprises a light source. The method of claim 17, The light source is a cold-cathode-fluorescent-lamp. The method of claim 7, wherein The power supply circuit further comprises a ramp generator for generating the delay, wherein a starting point of the ramp generator is generated based on the first pulse signal and the reference signal. The method of claim 7, wherein The power supply circuit further comprises a delay circuit for generating the delay, wherein the delay amount is generated based on the first pulse signal and the reference signal. A control device having a pulse generator for generating a first pulse signal and a selector for generating a reference signal; At least two power supply circuits; At least two transformers each connected to the at least two power circuits; At least two light sources respectively connected to the at least two transformers; And Including the display panel, The reference signal is coupled to each of the at least two power supply circuits to indicate the number of controlled power supply circuits, and the first pulse signal is configured to turn on the first light source among the at least two light sources. Connected to a first power circuit among power circuits to initialize an operation of the first power circuit, The first power supply circuit outputs a second pulse signal to a second power supply circuit among the at least two power supply circuits to turn on a second light source among the at least two light sources, and the second pulse signal is output to the first power supply circuit. And a delay with respect to said first pulse signal of a power supply circuit. The method of claim 21, The display device is a liquid crystal display television, a liquid crystal display monitor or a liquid crystal display computer. The method of claim 21, And the pulse generator is an oscillator. The method of claim 21, And the selector is a phase selector, a digital-to-analog converter or an analog-input-analog-output circuit. The method of claim 21, And the reference signal indicates the number of phases that are transitioned. The method of claim 21, And the selector includes at least one input terminal for programming the number of controlled power supply circuits and an output for outputting the reference signal in accordance with an input signal connected to the at least one input terminal. The method of claim 26, And the input signal is an analog signal or a digital signal for selecting the number of phases. The method of claim 21, And the power supply circuit is a DC / AC inverter. The method of claim 28, The DC / AC inverter may be a full-bridge inverter, a half-bridge inverter, a fly-back forward inverter, a push-pull inverter, or a class D inverter. The method of claim 21, And wherein the delay is a phase shift delay. The method of claim 21, And the light source is a cold cathode tube. The method of claim 21, The power supply circuit further includes a ramp generator for generating the delay, wherein a start point of the ramp generator is generated based on the first pulse signal and the reference signal. The method of claim 21, The power supply circuit further includes a delay circuit for generating the delay, wherein the delay amount is generated based on the first pulse signal and the reference signal. A method for driving at least two power supply circuits, Generating a reference signal from the selector; Connecting the reference signal to each of the at least two power supply circuits to indicate a number of controlled power supply circuits; Generating a first pulse signal from a pulse generator; Connecting the first pulse signal to the first power circuit to initialize an operation of a first power circuit among the at least two power circuits; And Outputting the second pulse signal having a delay with respect to the first pulse signal from the first power circuit to the second power circuit to initialize an operation of a second power circuit among the at least two power circuits; And at least two power supply circuits. The method of claim 34, wherein The reference signal is generated according to input signals coupled to the selector in the first step. The method of claim 34, wherein And said fourth step further comprises coupling said first power circuit to a first transformer. The method of claim 36, Connecting the first transformer to a first light source. The method of claim 34, wherein The fifth step further comprises coupling the second power supply circuit to a second transformer. The method of claim 38, Connecting the second transformer to a second light source. The method of claim 34, wherein In the fifth step, the delay is generated by a ramp generator, and a starting point of the ramp generator is generated based on the first pulse signal and the reference signal. The method of claim 34, wherein In the fifth step, the delay is generated by a delay circuit, and the delay amount is generated based on the first pulse signal and the reference signal. A control device for controlling at least two cold cathode tube power supply circuits, A phase shift selector for generating a reference signal programmed to indicate a phase delay amount according to the number of connected cold cathode tube power supply circuits; And A pulse generator configured to receive the reference signal and generate a pulse signal coupled to the at least two cold cathode tube power circuits in response to the input reference signal to initiate operation of the at least two cold cathode tube power circuits. Control device, characterized in that configured to. The method of claim 42, wherein And the phase shift selector comprises at least one input terminal for programming the number of connected cold cathode tube power circuits and an output for outputting the reference signal in accordance with an input signal coupled to the at least one input terminal. The method of claim 43, And the input signal is an analog signal or a digital signal for selecting the number of phases. In an electrical circuit for supplying energy to cold cathode loads, At least two cold cathode tubes comprising a phase delay selector for programming the phase delay of the cold cathode tube power supply circuit, wherein the amount of phase delay for each cold cathode tube power supply circuit is increased stepwise in accordance with the order of operation of the cold cathode tube power supply circuits; Power supply circuits; And A phase shift selector for generating a reference signal in accordance with the number of connected cold cathode tube power circuits; A control device having a pulse generator for generating a pulse signal coupled to the cold cathode tube power supply circuits, A first cold cathode tube power circuit among the at least two cold cathode tube power circuits is initialized immediately after receiving the pulse signal, and a second cold cathode tube power circuit among the at least two cold cathode tube power circuits has a predetermined positive phase. Electrical circuit which is initialized immediately after a delay. The method of claim 45, The phase shift selector comprises at least one input terminal for programming the number of connected cold cathode tube power supply circuits and an output for outputting the reference signal in accordance with an input signal coupled to the at least one input terminal. 47. The method of claim 46 wherein The input signal is an analog signal or a digital signal for selecting the number of phases. The method of claim 45, An electrical circuit further comprising a transformer. The method of claim 48, An electrical circuit further comprising cold cathode tube loads. The method of claim 45, And the cold cathode tube power supply circuit further comprises a lamp generator for generating the phase delay, wherein a starting point of the lamp generator is generated based on the pulse signal. The method of claim 45, The cold cathode tube power supply circuit further comprising a delay circuit for generating the programmed phase delay. In a display device having cold cathode tube loads, At least two cold cathode tubes comprising a phase delay selector for programming the phase delay of the cold cathode tube power supply circuit, wherein the amount of phase delay for each cold cathode tube power supply circuit is increased stepwise in accordance with the order of operation of the cold cathode tube power supply circuits; Power supply circuits; A phase shift selector for generating a reference signal according to the number of connected cold cathode tube power circuits, and the at least two cold cathode tube power circuits for initializing operation of the at least two cold cathode tube power circuits in response to the reference signal received from the reference signal; A control device having a pulse generator for generating a pulse signal coupled to the cold cathode tube power supply circuits; At least two transformers each connected to the at least two cold cathode tube power circuits; At least two cold cathode tube loads respectively connected to the at least two transformers; And Including the display panel, A first cold cathode tube power circuit among the at least two cold cathode tube power circuits is initialized immediately after receiving a pulse signal to turn on a first cold cathode tube load among the at least two cold cathode tube loads, and the at least two cold cathode tube power circuits. And a second cold cathode tube power circuit among the cathode tube power circuits is initialized after a predetermined amount of phase delay to turn on a second cold cathode tube load of the at least two cold cathode tube loads. The method of claim 52, wherein The display device is a liquid crystal display television, a liquid crystal display monitor or a liquid crystal display computer. The method of claim 52, wherein And the phase shift selector includes at least one input terminal for programming the number of connected cold cathode tube power circuits and an output for outputting the reference signal according to an input signal connected to the at least one input terminal. The method of claim 54, And the input signal is an analog signal or a digital signal for selecting the number of phases. The method of claim 52, wherein The cold cathode tube power supply circuit further includes a lamp generator for generating the phase delay, wherein a starting point of the lamp generator is generated based on the pulse signal. The method of claim 52, wherein And the cold cathode tube power supply circuit further comprises a delay circuit for generating the programmed phase delay. A method for driving at least two cold cathode tube power supply circuits, the method comprising: Generating a reference signal from a phase shift selector; Coupling the reference signal to a pulse generator; Generating a pulse signal from the pulse generator in response to the reference signal and coupling the pulse signal to each of the at least two cold cathode tube power supply circuits; A fourth step of initializing an operation of a first cold cathode tube power circuit after receiving the pulse signal; And And a fifth step of initiating operation of the second cold cathode tube power circuit after a predetermined amount of phase delay. The method of claim 58, In the first step, the reference signal is generated in accordance with input signals coupled to the phase shift selector. The method of claim 58, And said fourth step further comprises connecting said first cold cathode tube power supply circuit to a first transformer. The method of claim 60, Connecting the first transformer to a first cold cathode load. The method of claim 58, And said fifth step further comprises connecting said second cold cathode tube power supply circuit to a second transformer. The method of claim 62, Connecting the second transformer to a second cold cathode load. The method of claim 58, In the fifth step, a phase delay is generated by a ramp generator, and a starting point of the ramp generator is generated based on the pulse signal. The method of claim 58, In the fifth step, a phase delay is generated by a delay circuit, and the phase delay amount is programmed by a phase delay selector in the cold cathode tube power supply circuit.