WO2005051050A1

WO2005051050A1 - The apparatus and method for synchronous lighting by one ballast with two bulb

Info

Publication number: WO2005051050A1
Application number: PCT/KR2003/002633
Authority: WO
Inventors: Young-Rok Kang
Original assignee: K.D.G. Eng
Priority date: 2003-11-21
Filing date: 2003-12-03
Publication date: 2005-06-02
Also published as: AU2003284707A1; KR100446102B1; CN1879455A

Abstract

Disclosed are an apparatus for lighting two bulbs with one ballast and a rnethod for controlling the same. In order to allow one ballast, not two ballasts, to control two bulbs or left and right lamps in an M (High Intensity Discharge) system used as car headlights, the apparatus is provided with two inverters having sensing functions, a step down chopper for controlling an unbalanced load between the two bulbs and an igniter including a double layer foil having a capacitor layer shape, so that an unbalanced load between the two bulbs or lamps is controlled, making it possible to simultaneously light the two bulbs or the left and right lamps with one ballast.

Description

THE APPARATUS AND METHOD FOR SYNCHRONOUS LIGHTING BY ONE BALLAST WITH TWO BULB

BACKGROUND OF THE INVENTION Field ofthe Invention

The present invention relates to an apparatus for lighting two bulbs with one ballast and a method for controlling the same, and more particularly to an apparatus for lighting two bulbs with one ballast and a method for controlling the same, wherein in order to allow one ballast to control two bulbs or left and right lamps, there are provided with two inverters, a step down chopper and an igniter including a double layer foil having a capacitor layer shape, so that an unbalanced load between the two bulbs or lamps is controlled to simultaneously light the two bulbs or the left and right lamps.

Description ofthe Related Art

A ballast generally provides a high starting voltage required to start a lamp, and limits a current in the lamp to a predetermined value after the lamp is turned on. For this reason, it is required for the ballast to provide a high voltage ignition pulse for lighting Hie lamp and provide an instantaneous current and an open circuit voltage suitable for transitioning the discharge state after the ignition, and further to perfonn a lighting control suitable for rapidly turning on the lamp in the case of a cold start. In addition, a uniform power must be supplied to the lamp to achieve a stabilized light output and a long life in the steady state. However, it is difficult to control the lamp power and design a controller since the bulb voltage ofthe lamp varies greatly depending on individual lamps and it increases as the lamp continues to operate. In the prior art, in order to operate two FHD (High Intensity Discharge) lamps for vehicles that are unbalanced control targets as described below, two ballasts are used to independently control the operations ofthe HID lamps. However, since there is difficulty in securing a space in a vehicle for installing the two ballasts and also since two igniters are provided at different places to generate a high voltage, the equipment costs increase and a safety problem occurs. In addition, left and right lamps attached to a front portion of a vehicle are under different conditions and the internal bulb voltage unifonnities of the bulbs thereof do not correctly coincide with each other. For this reason, in order to operate the conventional HID lamps for vehicles, one ballast is required for each lamp and is independently controlled. In this case, there is a problem in that in temis ofthe vehicle lamp configuration, upward and downward lamps for vehicles are configured together and the upward and downward lamps are composed of a conventional halogen lamp and a HID lamp, respectively.

SUMMARY OF THE hNVENπON

Therefore, the present invention has been made in view ofthe above problems, and it is an object of the present invention to provide an apparatus for simultaneously lighting two independent bulbs or left and right lamps with one ballast in an HID (High Intensity Discharge) system used as car headlights, wherein two inverters, a step down chopper and an igniter including a double layer foil having a capacitor layer shape are provided so that an unbalanced load between the two bulbs or the left and right lamps are controlled to simultaneously light the two bulbs or the left and right lamps. In accordance with one aspect ofthe present invention, the above and other objects can be accomplished by the provision of an apparatus for simultaneously lighting two bulbs with one ballast, said apparatus comprising: a flyback converter; a power supply unit; a P WM controller; first and second gate drivers; a full bridge inverter including a first inverter and a second inverter, said first inverter detecting and sensing an output voltage and an output current, outputted when a left lamp operates, througli 5th, 7th and 8th sensing resistors and an 11th sensing resistor, which are coupled to one side ofthe full bridge inverter, said second inverter detecting and sensing an output voltage and an output current, outputted when a right lamp operates, through 12th, 14th and 15th sensing resistors and a 16th sensing resistor; a controller for receiving an input voltage from the power supply unit and receiving an input current through a 10th resistor to maintain an output power at a uniform level and thus stabilize a power supplied to each load, and detecting an output voltage and an output current, outputted when the first and second inverters operate, to control an unbalanced load between the two lamps; a step down chopper connected to one side ofthe controller, said step down chopper controlling a bulb voltage of one of the two bulbs having a lower resistance after firstly adjusting a power ofthe other having a higher resistance to a reference power so as to make powers of the two bulbs uriiform, thereby controlling an unbalanced load caused when the lamps initially operate; and an igniter connected to one side ofthe first and second inverters, said igniter being capable of simultaneously applying a high voltage pulse to the left and right lamps so that Hie lamps are ignited with a high voltage power at a cold or hot start ofthe lamps. In accordance with another aspect of the present invention, there is provided a method for simultaneously lighting two bulbs with one ballast, comprising the steps of: a) perfonning a voltage control operation by measuring a value of an input and output voltage, and then maxiinizing a duty rate at a flyback converter and applying a high voltage to a secondary side of a transfonner until the bulbs start to light so that an igniter can operate in a time section when the bulbs do not start to light after power is applied to the ballast; b) allowing first and second gate drivers to simultaneously light two independent lamps or a lamp having two bulbs in a single body under control of a controller; c) perfoiining a current control operation to allow the ballast to cause a large amount of current to flow in with free movement of electric charges between a lighting start time section and a transition time section of the bulbs so that a DC operation is stabilized; and d) perfoπriing a power control operation to allow the ballast to measure an input voltage and current and an output voltage and current until it enters a stabilized state after the transition time section and then to control all the voltages and currents so that the bulbs are kept nonnally lit.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and other advantages ofthe present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which: Fig. 1 is a circuit diagram showing an apparatus for simultaneously lighting two bulbs with one ballast according to the present invention; Fig. 2 is a graph illustrating the operation ofthe apparatus for simultaneously lighting two bulbs with one ballast according to the present invention; Fig. 3 illustrates the operation of a flyback converter when voltage control is perfonned according to an embodiment ofthe present invention; Fig. 4 illustrates the operation of a flyback converter when current control is perfonned according to an embodiment ofthe present invention; Fig. 5 shows an igniter having an "LT'-shaped coil configuration according to an embodiment ofthe present invention; Fig. 6 shows an igniter having a double-layer coil configuration according to an embodiment ofthe present invention; Fig. 7 shows an igniter having a serial-type coil configuration according to an embodiment ofthe present invention; Fig. 8 is a flow chart showing a method for simultaneously lighting two bulbs with one ballast according to the present invention; and Fig.9 is a detailed flow chart showing a simultaneous Ughting control operation in the method for simultaneously Ughting two bulbs with one ballast according to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Now, preferred embodiments ofthe present invention will be described in detail with reference to the annexed drawings. Fig. 1 is a circuit diagram showing an apparatus for simultaneously Ughting two bulbs with one baUast according to the present invention. As shown in this figure, the apparatus includes a flyback converter 10, a full bridge inverter 20/30, a controUer 40, a PWM (Pulse Width Modulation) controUer 16, a step down chopper 15, gate drivers 23 and 33, and an igniter 70. In particular, in order to simultaneously turn on left and right lamps 50 and 60 of a vehicle, Hie full bridge inverter 20/30 includes a first half bridge inverter 20 for operating the left lamp 50 and a second half bridge inverter 30 for operating the right lamp 60. The configurations and operations ofthe PWM controller 16 and tlie gate drivers 23 and 33 are well known in the art and thus a detailed description thereof will be omitted. The flyback converter 10 is connected to an input voltage detector 12, an input cuirent detector 13, a transformer TI, and diodes Dl, D2, D3 and D4. The input voltage detector 12 is connected to the circuit ofthe flyback converter 10 at one side thereof to detect an input voltage inputted from a battery and a generator, as a power supply unit for a vehicle, according to a predetei ined resistance ratio between a register R3 and a register R.4. The input current detector 13 is connected to the circuit at one side ofthe input voltage detector 12 to detect an input current inputted to switching transistors S3 and S4 that are turned on/off by a control signal of the PWM controUer 16 at the initial operation. The transformer TI is connected to the circuit at the top thereof to boost and output voltages V+ and V- ofthe battery and generator as the switching transistors S3 and S4 are turned on off. The diodes Dl and D2 rectify a high voltage of 1500V outputted from the transformer TI, and provide it to the igniter 70. The diodes D3 and D4 rectify a DC voltage outputted from the transformer TI, which varies depending on the ignition state ofthe lamp, and provide it to the first and second inverters 20 and 30. An electrolytic capacitor C5, resistors R6 and Rl 1 and an electrolytic capacitor C6 are connected in paraUel between the ground and a cathode of the diode D3. Likewise, an electrolytic capacitor C8, resistors R13 and R16 and an electrolytic capacitor C9 are connected in parallel between the ground and a cathode ofthe diode D4. The input voltage detector 12 detects whether a uniform voltage of 12V is suppUed to each load. By using a sensing resistor R10, the input current detector 13 detects whether a unifonn current flows in the transfonner TI on the basis of a current command value provided from the controller 40. The first inverter 20 includes sensing resistors coupled to a portion of the flyback converter 10 and thus has a sensing function to control any one of two independent lamps or a lamp having two bulbs to operate as a left lamp 50. As shown in Fig. 1, the first inverter 20 includes sensing resistors R5, R7 and R8, an electrolytic capacitor C7 and a sensing resistor Rl l. The first inverter 20 is connected to an output voltage detector 22, an output current detector 21 and switching transistors SI, S2, S5 and S6. The output voltage detector 22 is connected between the two sensing resistors R7 and R8 to detect a voltage outputted when the left lamp 50 operates. By using the sensing resistor Rll, the output current detector 21 detects a DC current flowing in through the igniter 70 when the lamp initially operates. The switching transistors SI, S2, S5 and S6 are switched on/off based on a drive signal outputted from the gate driver 23. The second inverter 30 includes sensing resistors coupled to a portion ofthe flyback converter 10 and thus has a sensing function to control any one of two independent lamps or a lamp having two bulbs to operate as a right lamp 60. As shown in Fig. 1, the second inverter 30 includes sensing resistors R12, R14 and R15, an electrolytic capacitor CIO and a sensing resistor R16. The second inverter 30 is connected to an output voltage detector 32, an output current detector 31 and switching transistors S7, S8, S9 and S10. The output voltage detector 32 is connected between the two sensing resistors R14 and R15 to detect a voltage outputted when the right lamp 60 operates. By using the sensing resistor R16, the output current detector 31 detects a DC current flowing in it through the igniter 70 when the lamp initiaUy operates. The switching transistors SI, S2, S5 and S6 are switched on/off based on a drive signal outputted from the gate driver 33. The controUer 40 has features including a PWM generator, a lamp power stabilizer, a lamp temperature compensator, and an overall fault protection circuit. The controller 40 receives an input voltage from the power supply unit and controls a voltage provided to each load by keeping the input current at a unifonn or constant level through the resistor R10 at the initial operation. In addition, the controller 40 controls an unbalanced load between the two lamps or bulbs by detecting an output current and an output voltage produced when the first and second inverters 20 and 30 operate. As shown in Fig. 1, the controller 40 is connected to the input voltage detector 12, the input current detector 13, the output current detector 21, the output voltage detectors 22 and 32, the PWM controller 16, and the gate driver 23. The input voltage detector 12 is used to adjust the initial voltage to a unifonn or constant voltage of 12V. The input current detector 13 is connected to the input voltage detector 12 at one side thereof to obtain a unifonn voltage on the basis of a current command value provided from the controUer 40. The output current detector 21 is used to control a DC cunent in the igniter 70 that varies depending on the ignition state of the lamp. The output voltage detectors 22 and 32 detect output voltages, respectively, outputted when the left and right lamps operate. The PWM controUer 16 allows the flyback converter 10 to output a DC voltage of a predetennined level and a DC voltage whose level varies depending on the ignition state ofthe lamp. The gate driver 23 provides a gating signal as a control signal to aUow the first and second inverters 20 and 30 to output a rectangular AC voltage. The step down chopper 15 as a buck converter is connected to the controller 40 and operates in the Mowing manner. In order to control an unbalanced load occurring when the lamp initially operates, the step down chopper 15 firstly adjusts a power of one of the two bulbs having a higher resistance to a reference power and then controls a bulb voltage ofthe other bulb having a lower resistance, so as to maintain the powers ofthe two bulbs uniformly. According to the present invention, the igniter 70 has a primary portion in a capacitor layer fonn and has two secondary portions provided at one side ofthe primary portion, and the two secondary portions are connected respectively to the left and right lamps 50 and 60. In particular, the igniter 70 having one primary coil and two secondary coils is based on the following coiling scheme. As shown in Fig. 5. a primary portion 71 is foπned in the igniter 70 at one side thereof, and two secondary portions 72 and 73 are vertically arranged at one side ofthe primary portion 71 so that the two primary and secondary portions have a "TI" shape. Alternatively, as shown in Fig. 6, a primary portion 71 is fonned in the igniter 70 at one side thereof, and two secondary portions 72 and 73 are fonned as a double layer at one side ofthe primary portion 71 so that one ofthe secondary portions 72 is arranged at an inner side and the other 73 is arranged at an outer side. Further, alternatively, as shown in Fig. 7, a primary portion 71 is formed in the igniter 70 at one side Uiereof, and two secondary portions 72 and 73 are seriaUy arranged in a line at one side ofthe primary portion 71. One ofthe two secondary portions configured as described above is connected to the left lamp 50 and the other is connected to the right lamp 60, so that any one of two bulbs or left and right lamps can be controUed with a single baUast, instead of using two baUasts. It is preferable that the coU be made of an aluminum foU that has high thermal and electric conductivity and also has high corrosion resistance in the air. Similarly to an apparatus for simultaneously Ughting two bulbs with two ballasts in the prior art, an apparatus for simultaneously Ughting two bulbs with one baUast according to the present invention includes a flyback converter 10, a full bridge inverter 20/30, a power supply unit 11, a PWM controUer 16, and gate drivers 23 and 33, as described above, and also has the following features. The flyback converter 10 includes an input voltage detector 12, an input current detector 13, a step down chopper 15 and output current detectors 21 and 31. The fuU bridge inverter 20/30 includes a first inverter 20 having a sensing function for operating the left lamp 50 and a second inverter 30 having a sensing function for operating the right lamp 60. In addition, a foil-shaped igniter 70 provided in the apparatus includes two secondary portions 72 and 73, fonned as a double layer having a capacitor layer shape, so that it is connected to both the left and right lamps 50 and 60. A description will now be given ofthe operation ofthe apparatus for simultaneously lighting two bulbs with one ballast according to the present invention. As shown in Fig. 2, the lamp operating state is divided into a breakdown time section in which discharge starts, a glow discharge time section in which glow discharge occurs due to ion coUision, a glow-to-arc transition time section in which the lamp is transitioned from a glow discharge state to an arc discharge state, and an arc discharge time section in which arc discharge occurs due to thermionic emission. First, in the breakdown time section where discharge starts, a high voltage pulse for ignition is applied across two electrodes of a lamp to break an internal insulating state thereof. To break the internal insulating state, 2 KV is required in the case of a cold start (initial ignition), and 25 KV is required in the case of a hot start (re-ignition). It is required to cool tlie lamp in order to avoid the necessity of having to apply a high ignition voltage in the case of . the hot start, but it takes 10 minutes or more to return to the cold state with natural cooling. Accordingly, the present invention adopts an igniter 70 capable of outputting a high ignition voltage of 25 KV or more. Next, a voltage for mamtaining the glow discharge state after the lamp has been ignited is appUed to the lamp in the glow discharge time section in which the glow discharge occurs due to ion collision, hi the present invention, a voltage of about 600V is applied to the lamp before the lamp is ignited, so that the lamp maintains the glow state after the ignition. Next, a take-over current circuit is provided for the glow-to-arc transition time section in which the lamp is transitioned from the glow discharge state to the arc discharge state after it is ignited. Unless a sufficient take-over cunent is supplied to the lamp, the lamp fails to light. This is because the lamp voltage is lowered right after the lamp is fransitioned to the arc discharge state and the lamp maintains the arc discharge state by a current provided from tlie ballast. Thus, in tl e present invention, tlie take-over cuιτent circuit causes a cuitent to flow to the lamp until a sufficient current is supplied from the ballast to the lamp. Next, in the arc discharge time section in which tlie arc discharge is caused by thennionic emission, the internal temperature and pressure ofthe lamp increases due to power. suppUed from the baUast after the lamp has been transitioned from the glow discharge state to the arc discharge state. At this time, the voltage and optical output ofthe lamp also increases to reach a steady state. Since a curcent supplied in this operating time section determines a warm-up time ofthe lamp, and also determines optical-output response characteristics thereof at the transition state, the lamp power is adjusted to a desired power under the control ofthe controUer in the present invention. Finally, in order to attain a predetermined optical output in the steady state, the power , suppUed to the lamp is uniformly controlled to a rated value to prevent both flickering ofthe lamp and reduction in the lamp Ufe. Detailed operations of the controUer 40, the step down chopper 15, the first and second inverters 20 and 30 and the igniter 70 included in the apparatus according to the present invention wUl now be described with reference to the above-described operation of the apparatus. First, the operation of the controller 40 is described with reference to Fig. 1. The controUer 40 has features including a PWM generator, a lamp power stabilizer, a lamp temperature compensator, and an overaU fault protection circuit. The controller 40 receives an input voltage and an input αurent respectively from a battery and a generator, and maintains the output power at a unifonn level to control a power supplied to each load, and also controls an output voltage and an output current that are suppUed to the first and second inverters 20 and 30. Especially, tl e controller allows the output voltage detectors 22 and 32 to detect an output voltage applied between the sensing resistors R7 and R8 and an output voltage applied between the sensing resistors R14 and R15 when the left and riglit lamps 50 and 60 operate. If the detection result is that an unbalanced load is increased in one of the two lamps, the controller 40 increases the system short capacity and thus maintains the output voltage at a uniform level so as to control the unbalanced load. In addition, when the step down chopper 15 operates, the controller 40 produces a control signal to control the input voltage and the input current of a uniform level inputted to the step down chopper 15, so as to control the unbalanced load caused between the two bulbs when the lamp initiaUy operates. Further, the controUer 40 controls the gate driver 23 ofthe first inverter 20 and the gate driver 33 ofthe second inverter 30 so as to simultaneously light the left and right lamps 50 and 60. The operation ofthe first inverter 20 w l now be described. Using four switches S 1 , S2, S5 and S6, the first inverter 20 is operated by repeatedly turning on and off a pair of switches alternately. That is, it can be seen from the operating waveforms ofthe switches that the switches have flie same voltage stress as the input voltage, but it can be seen from the primary voltage wavefonn ofthe transformer that the maximum value is twice as high as that ofthe half bridge. This means that the output is doubled and it is possible to obtain an output twice as high as that ofthe half bridge under the same condition. In other words, since tlie voltage is inversely proportional to the current, the input current becomes the switch curcent, so that the intensity ofthe output current ofthe inverter is a half of that ofthe switch current under the same output condition. The current in the circuit of the first inverter 20 is expressed by the foUowing equation.

[Expression 1]

The switching operation ofthe circuit is perfonned in Hie sequence of (SI, S6) and (S2, S5), and the signal has a rectangular wavefonn. In this manner, the first inverter 20 receives a DC voltage of 20 ~ 100V outputted from the flyback converter 10, and converts it to a rectangular AC voltage of 150 ~ 200 Hz. The first inverter 20 has sensing resistors coupled to one side thereof and thus has a sensing function to aUow any one of two independent lamps or a lamp having two bulbs in a single body to operate as the left lamp 50. hi other words, when the lamp operates, the first inverter 20 senses an output voltage of 50V through the sensing resistors R5, R7 and R8 and the sensing resistor Rl 1 at a predetermined ratio, and applies it to the left lamp 50 through the gate driver 23 or decreases a current flowing from the igniter 70 to the sensing resistor Rl 1 as the lamp resistance increases, thus decreasing the sensed intensity, so as to control the unbalanced load between the two lamps. Here, tlie output voltage detector 22 detects an output voltage between the sensing resistor R7 and the sensing resistor R8, and the transistors SI, S2, S5 and S6 are switched on/off with a drive signal outputted from the gate driver 23, so as to light the left lamp 50. Next, the operation of the first inverter 20 is described as follows. In the same manner as the first inverter 20, the second inverter 30 receives a DC voltage of 20 ~ 100V outputted from the flyback converter 10, and converts it to a rectangular AC voltage of 150 ~ 200 Hz. The second inverter 30 has sensing resistors coupled to one side thereof and thus has a sensing function to aUow any one of two independent lamps or a lamp having two bulbs in a single body to operate as the right lamp 60. hi other words, when the lamp operates, the second inverter 30 senses an output voltage of 50V through the sensing resistors R12, R14 and R15 and the sensing resistor R16 at a predetennined ratio, and applies it to the right lamp 60 through the gate driver 33 or decreases a current flowing from the igniter 70 to the sensing resistor Rl 6 as the lamp resistance increases, thus decreasing the sensed intensity, so as to control the unbalanced load between the two lamps. Here, the output voltage detector 32 detects an output voltage between the sensing resistor R14 and the sensing resistor R15, and the transistors S7, S8, S9 and S10 are switched on/off with a drive signal outputted from the gate driver 33, so as to Ught the right lamp 60. Next, the operations ofthe igniter 70 and the step down chopper 15 are described as foUows. When a voltage applied from the power supply unit reaches a predetermined voltage in the range of 400V ~ 600V, it is suppUed to tlie igniter 70 through a self-transferred electronic spark gap. Then, the igniter 70 starts discharge ofthe bulb by producing discharge electricity required to cause the initial glow discharge ofthe bulb. At this time, the inverter opens the current pass in one direction to continuously supply the power, and the two secondary portions according to the present invention are connected respectively to the two bulbs to supply a voltage required for the discharge. However, since a smoothed voltage at that time (prior to the inverter) is constant, a larger current flows in one of tlie bulbs having a lower resistance whereas a smaller current flows in the other having a higher resistance, thereby causing unbalanced power to be supplied to the bulbs. To prevent the unbalanced power, the present invention makes the powers supplied to the two bulbs unifonn through the step down chopper 15 that controls the bulb voltage of one bulb having a lower resistance after adjusting a power of the other bulb having a higher resistance to a reference power, and ttius makes it possible to reach a rated value. In other words, when unbalanced power occurs between the two bulbs at the initial operation ofthe lamp, the controller 40 transfers a control signal through the PWM controller 16. A control signal from the PWM controller serves to control an input current and an input voltage of a predetermined level inputted to the step down chopper 15, so as to control the bulb voltage of one bulb having a lower resistance after adjusting the power ofthe other having a higher resistance to a reference power and thus to control the unbalanced load caused between the two bulbs. A description will now be given of a control method for simultaneously Ughting two bulbs with one baUast according to the present invention with reference to Fig. 8. First, in order that the igniter can operate in the time section when the Ughting has not yet started after power is applied to the baUast, the controller performs a voltage control operation in such a manner that it measures the value ofthe input and output voltage, and then maximizes the duty rate at the flyback converter and applies a high voltage to the secondary side ofthe transfonner until the Ughting starts ("voltage control step" SI 10). In an embodiment of the present invention, as shown in Fig. 3, a power supply voltage of 12V of a battery as a power supply for vehicles is increased in voltage and smoothed at the flyback converter. At this time, if the transistors S3 and S4 are turned off by a control signal of the PWM controller outputted from the controUer 40, the input current, which was flowing in the primary side ofthe transfoi er, cannot flow any longer and thus a magnetic field is no longer induced in the core, h the secondary side ofthe transfoimer, the polarity of the electromotive force E_s is reversed, while an output diode D is biased in the forward direction. At this time, the energy induced in the secondary side ofthe transformer core inversely induces a voltage in the primary side according to the turn ratio ofthe primary and secondary coils. This reflected voltage V^ is caUed a "flyback voltage", which can be expressed by the following equation.

[Expression 2]

Here, when the transistors S3 and S4 are turned off, the voltage V_& is applied between the drain and source, and a withstanding voltage is deteimined and the duty rate is maximized to perfonn voltage control so that a high voltage is applied to the secondary side of the transfonner. Next, under the control ofthe controUer, the gate drivers 23 and 33 simultaneously light two independent lamps or a lamp having two bulbs in a single body (S 120). As described above, the apparatus according to the present invention includes two inverters, a step down chopper for controlling an unbalanced load between two bulbs and an igniter including a double layer foil having a capacitor layer shape, so that it controls the unbalanced load between the two bulbs, thereby making it possible to simultaneously Ught two bulbs or left and right independent lamps with one baUast. In an embodiment ofthe present invention, as shown in Fig. 9, a check is performed on chattering of power applied by the power supply unit (S200), and then it is checked whether the bulb condition is a hot or cold start condition (S210). If the bulb condition is the hot start condition, a full bridge converter duty rate D₂ is determined by the following equation (S220).

[Expression 3]

where D₂ denotes a full bridge converter duty rate in the case of a hot start.

On the other hand, if the bulb condition is the cold start condition, a full bridge converter duty rate Di is determined (S230) as expressed in the following equation.

[Expression 4]

where Di denotes a fuU bridge converter duty rate in the case of a cold start.

The duty rates Dl and D2 determined in such a manner are added to determine an optimal duty rate, so as to apply a DC voltage in the range of 400V to 600V suitable for the operations ofthe first and second inverters (S240). The DC voltage produced in such a manner is automaticaUy provided to the igniter througli tlie electronic spark gap. As the DC voltage is provided to the igniter, a voltage required for the initial glow discharge is produced to start the discharge (S250). Thereby, the bulbs are simultaneously lit (S260). At this time, if an unbalanced load occurs between the two bulbs, the respective powers ofthe left and right lamps are compared with each other (S270). If one ofthe left and right lamps has a large power, the controller controls the step down chopper to operate so that the bulb voltage of one bulb having a lower resistance is controlled after the power of tlie other bulb having a higher resistance is firstly adjusted to a reference power, thereby making the powers of the two bulbs unifonn (S290). The first inverter detects and senses an output voltage and an output cuirent outputted when the left lamp operates, through the sensing resistors R5, R7 and R8 and the sensing resistor Rll, whereas the second inverter detects and senses an output voltage and an output cuirent outputted when the right lamp operates, tiirough the sensing resistors R12, R14 and R15 and the sensing resistor R16, so that alternate control between tlie first and second inverters is perfonned (S300). If one of the left and right lamps has a smaU power, alternate control between the inverters is performed in the same manner as described above (S280) to keep the bulbs Ut with a unifonn constant power (S310). Next, the baUast causes a large amount of current to flow in with free movement of electric charges between the Ughting start time section and the transition time section ofthe bulb, so that the DC operation is stabUized ("current control step" S 130). In an embodiment ofthe present invention, as shown in Fig. 4, if the transistors S3 and S4 are turned on, a Vj_n is directly appUed to the primary side ofthe transfonner having an inductance L_p. Here, it is assumed that the input voltage is an ideal DC voltage, and a period of time t for which the transistors S3 and S4 are turned on is equal to a duty cycle D ofthe switching period T. At that time, the input current increases as expressed in the foUowing equation.

[Expression 5]

h this equation, as H e input cuirent i_in(t) increases, tlie magnetic energy of the transformer also increases. If a varying input c rent i_in(t) flows through the primary coil of the transformer, the magnetic flux Φ(t) occurs inside the core of the fransfonner, and an electromotive force is induced between the two ends of each coil according to Faraday's law as expressed in the foUowing equation.

[Expression 6] dΦ(t) E P„ = N P,s dt

In other words, if an electromotive force E_p is induced in the primary side, an electromotive force E_s with polarity opposite to it is induced, so that the output diode D is inversely biased. Accordingly, the input voltage's energy is accumulated only in the core and is not transferred to the secondary side, and only the energy ofthe output capacitor is suppUed to the load. The input ciurent increases in such a manner, and at a time (t=DT) when it does not increase any more, the input current has a maximum value so that the DC operation can be stabilized. Next, until it enters a stabilized state after the transition time section, the baUast measures the input voltage and cunent and the output voltage and current, and controls all the voltage and current so that Hie bulbs are kept nonnally lit ("power control step" S140). In an embodiment ofthe present invention, if a power is supplied to the first inverter 20 and the left lamp 50 is nonnally lit, the first inverter 20 detects and senses an output voltage and an output current produced from a high voltage ofthe igniter, which vary depending on the ignition state ofthe left lamp 50, through the sensing resistors R5, R7 and R8 and the sensing resistor Rll. At this time, in order to allow the left lamp to be kept nonnally lit through the step down chopper 15, tlie controller 40 compares the value of an output current ofthe transformer TI with a predetermined cuurent value, and controls the frequency and Hie pulse width ofthe PWM control signal if the compared value is out of a predetennined range so that the output current ofthe transfonner TI can be kept unifonn. In the same manner as in the first inverter 20, if a power is supplied to the second inverter 30, the second inverter 30 detects and senses an output voltage and an output current produced from a high voltage ofthe igniter, which vary depending on the ignition state ofthe right lamp 60, through the sensing resistors R12, R14 and R15 and the sensing resistor R16. At this time, in order to allow the right lamp to be kept normally Ut through the step down chopper 15, the controUer 40 compares the value of an output current ofthe transformer TI with a predetermined current value, and controls the frequency and the pulse width ofthe PWM control signal if the compared value is out of a predetermined range, so that the output current ofthe transfonner TI can be kept unifonn. As described above, the apparatus according to the present invention includes two inverters, a step down chopper and an igniter including a double layer foil having a capacitor layer shape, so that it effectively controls the unbalanced load between two bulbs or left and right lamps, thereby making it possible to simultaneously light the two bulbs or the left and right lamps with one baUast. Industrial AppUcability

As apparent from the above description, an apparatus for simultaneously lighting two bulbs with one ballast and a method for controlling the same according to the present invention have the following advantages. Compared to the conventional apparatus and method in which two ballasts are used to independently control the FflD lamps for vehicles that are unbalanced control targets, the apparatus and method according to the present invention can reduce the production cost and effectively control the unbalanced load, and further can achieve size and weight reduction and simpUfy circuit configuration, thus improving reUabUity. Although the preferred embodiments ofthe present invention have been disclosed for iUustrative purposes, those skilled in the art wUl appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.

Claims

WHAT IS CLAIMED IS:

1. An apparatus for simultaneously lighting two bulbs with one baUast, said apparatus comprising: a flyback converter; a power supply unit; a PWM controller; first and second gate drivers; a full bridge inverter including a first inverter and a second inverter, said first inverter detecting and sensing an output voltage and an output current, outputted when a left lamp operates, through 5th, 7th and 8th sensing resistors and an 11th sensing resistor, which are coupled to one side ofthe full bridge inverter, said second inverter detecting and sensing an output voltage and an output current, outputted when a right lamp operates, through 12th, 14th and 15th sensing resistors and a 16th sensing resistor; a controller for receiving an input voltage from the power supply unit and receiving an input current through a 10th resistor to maintain an output power at a uniform level and thus stabUize a power supplied to each load, and detecting an output voltage and an output current, outputted when the first and second inverters operate, to control an unbalanced load between the two lamps; a step down chopper connected to one side of the controller, said step down chopper controlling a bulb voltage of one of the two bulbs having a lower resistance after firstly adjusting a power of H e other having a higher resistance to a reference power so as to make powers ofthe two bulbs unifonn, thereby controlling an unbalanced load caused when the lamps initially operate; and an igniter connected to one side ofthe first and second inverters, said igniter being capable of simultaneously applying a high voltage pulse to the left and right lamps so that the lamps are ignited with a high voltage power at a cold or hot start ofthe lamps.

2. The apparatus according to claim 1, wherein the first inverter is connected to a first output voltage detector, positioned between the 7th and 8th sensing resistors, for detecting a voltage outputted when the left lamp operates, wherein the first inverter is also connected to a first output current detector for detecting a DC current flowing in through the igniter when the left lamp initially operates, and wherein the first inverter is further connected to 1st, 2nd, 5th and 6th switching transistors that are switched on/off by a drive signal outputted from the first gate driver.

3. The apparatus according to claim 1, wherein the second inverter is connected to a second output voltage detector, positioned between the 14th and 15th sensing resistors, for detecting a voltage outputted when the right lamp operates, wherein the second inverter is also connected to a second output current detector for detecting a DC current flowing in through the igniter when the right lamp initially operates, and wherein the second inverter is further connected to 7th, 8th, 9th and 10th switching transistors that are switched on/off by a drive signal outputted from the second gate driver.

4. The apparatus according to claim 1, wherein the controller is connected to an input voltage detector, an input current detector, the PWM controller, first and second output cuirent detectors, and the first and second gate drivers.

5. Tlie apparatus according to claim 1, wherein the igniter includes a primary portion fonned in the igniter at one side thereof and two secondary portions vertically arranged at one side of the primary portion so that the primary and secondary portions have a " F " shape.

6. The apparatus according to claim 1, wherein the igniter includes a primary portion formed in the igniter at one side thereof and two secondary portions fonned as a double layer at one side ofthe primary portion so tiiat one ofthe secondary portions is arranged at an inner side and the other is arranged at an outer side.

7. The apparatus according to claim 1, wherein the igniter includes a primary portion fonned in the igniter at one side thereof and two secondary portions seriaUy formed in a line at one side ofthe primary portion.

8. A method for simultaneously lighting two bulbs with one baUast, comprising the steps of: a) perfonning a voltage control operation by measuring a value of an input and output voltage, and then maximizing a duty rate at a flyback converter and applying a high voltage to a secondary side of a fransfonner until the bulbs start to light so that an igniter can operate in a time section when the bulbs do not start to light after power is applied to the ballast; b) aUowing first and second gate drivers to simultaneously Ught two independent lamps or a lamp having two bulbs in a single body under control of a controUer; c) peifoiming a current control operation to allow the ballast to cause a large amount of cuirent to flow in with free movement of electric charges between a lighting start time section and a transition time section ofthe bulbs so that a DC operation is stabilized; and d) peifoiming a power control operation to allow the ballast to measure an input voltage and cuirent and an output voltage and cuirent until it enters a stabilized state after the transition time section and then to control aU tlie voltages and cmrents so that the bulbs are kept nonnaUy Ut.

9. The method according to claim 8, wherein said step b) includes the steps of: b- 1) perfonning a check on chattering of power appUed with a power supply unit; b-2) checking whether the bulbs are in a hot or cold start condition; b-3) determining a first fuU bridge converter duty rate if the bulbs are in the hot start condition; b-4) determining a second full bridge converter duty rate if the bulbs are in the cold start condition; b-5) determining an optimal duty rate by adding up the first and second duty rates and then applying a DC voltage in the range of 400V to 600V suitable for operations of first and second inverters; and b-6) allowing the DC voltage to be provided to the igniter so that the igniter produces a voltage required for initial glow discharge and thus starts the discharge; b-7) simultaneously Ughting the bulbs by ignition ofthe igniter; b-8) comparing respective powers of left and right lamps with each other when the corresponding bulbs are simultaneously lit; b-9) if one ofthe left and right lamps has a small power, allowing tlie first inverter to detect and sense an output voltage and an output current, outputted when the left lamp operates, througli 5th, 7th and 8th sensing resistors and an 11th sensing resistor, and aUowing the second inverter to detect and sense an output voltage and an output current, outputted when the right lamp operates, through 12th, 14th and 15th sensing resistors and a 16th sensing resistor, so that alternate control between the first and second inverters are perfonned; b- 10) if one ofthe left and right lamps has a large power, allowing the controUer to control a step down chopper to operate so that a bulb voltage of one ofthe two bulbs having a lower resistance is controlled after a power of the other having a higher resistance is firstly adjusted to a reference power, thereby making the powers ofthe two bulbs unifonn; b-11) performing alternate control between the first and second inverters after the control ofthe step down chopper has been completed; and b- 12) keeping the bulbs Ut with a uniform constant power.