Lamp Driving Circuit for a Discharge Lamp and a Control Method Thereof

Abstract

A lamp driving circuit includes a step-up transformer, a detector, and a controller. The step-up transformer includes a primary winding, and a secondary winding adapted to cooperate with a discharge lamp to form a tank circuit that generates a tank current. The detector is adapted for detecting current magnitude of current flowing through the discharge lamp, and outputs a detecting signal corresponding to the current magnitude. The controller receives the detecting signal from the detector, and generates a drive signal for driving the step-up transformer. The controller includes a capacitor, and configures a waveform of the drive signal by controlling charging of the capacitor based on a calculation value that corresponds to a frequency of the drive signal, a start-setting value, and a difference between the detecting signal and a current-setting signal.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

Other features and advantages of the present invention will become apparent in the following detailed description of the preferred embodiments with reference to the accompanying drawings, of which:

FIG. 1 is a circuit block diagram of a conventional drive circuit adapted for driving a discharge lamp;

FIG. 2 is a timing diagram, illustrating waveforms of a tank current and a first detecting signal in the conventional drive circuit;

FIG. 3 is a timing diagram, illustrating waveforms of a set of control sub-signals, a drive signal, and current flowing through a primary winding in the conventional drive circuit;

FIG. 4 is a timing diagram, illustrating waveforms of the control sub-signal corresponding to a third switch and the first detecting signal in the conventional drive circuit in a situation where a phase-setting value is smaller than a first calculation value;

FIG. 5 is a timing diagram, illustrating waveforms of the control sub-signal corresponding to the third switch and the first detecting signal in the conventional drive circuit in a situation where the phase-setting value is greater than the first calculation value;

FIG. 6 is a circuit block diagram, illustrating the first preferred embodiment of a lamp driving circuit according to the present invention;

FIG. 7 is a timing diagram, illustrating waveforms of a set of control sub-signals, a drive signal, and voltage across a capacitor in the first preferred embodiment;

FIG. 8 is a circuit block diagram of a first implementation of an adjustment control unit of the first preferred embodiment;

FIG. 9 is a circuit block diagram of a second implementation of the adjustment control unit of the first preferred embodiment;

FIG. 10 is a circuit block diagram, illustrating the second preferred embodiment of a lamp driving circuit according to the present invention; and

FIG. 11 is a timing diagram, illustrating waveforms of the set of control sub-signals, the drive signal, and the voltage across the capacitor in the second preferred embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Before the present invention is described in greater detail, it should be noted that like elements are denoted by the same reference numerals throughout the disclosure.

As shown in FIG. 6, a lamp driving circuit according to the present invention is adapted for driving at least one discharge lamp 4. When the lamp driving circuit is for driving a plurality of the discharge lamps 4, the discharge lamps 4 need to be connected in parallel. The following description is presented using an illustrative example where the lamp driving circuit drives a single discharge lamp 4.

The first preferred embodiment of a lamp driving circuit according to the present invention includes a step-up transformer 1, a detector 2, and a controller 3.

The step-up transformer 1 includes a primary winding 11, and a secondary winding 12 adapted to be coupled electrically to the discharge lamp 4 and adapted to cooperate with the discharge lamp 4 to form a tank circuit that generates a tank current. More particularly, the tank current is generated by resonance among distributed capacitance of the secondary winding 12, stray capacitance around the discharge lamp 4, a suitably added auxiliary capacitance 5, and leakage inductance 121 of the secondary winding 12.

The detector 2 is adapted for detecting current magnitude of current flowing through the discharge lamp 4, and outputs a first detecting signal that corresponds to the current magnitude detected thereby. In this embodiment, the detector 2 is further adapted to detect phase of the tank current and voltage magnitude of voltage of the secondary winding 12, and further outputs a second detecting signal that corresponds to the phase of the tank current, and a third detecting signal that corresponds to the voltage magnitude of the voltage of the secondary winding 12.

The controller 3 is coupled electrically to the primary winding 11 of the step-up transformer 1, and to the detector 2 for receiving the first detecting signal therefrom. The controller 3 generates a drive signal for driving the step-up transformer 1. Referring to FIG. 8, the controller 3 includes a capacitor 363, and further receives a current-setting signal. The controller 3 configures a waveform of the drive signal by controlling charging of the capacitor 363 based on a first calculation value that corresponds to a frequency of the drive signal, a start-setting value, and a difference between the first detecting signal and the current-setting signal. In this embodiment, start of the charging of the capacitor 363 is controlled according to the start-setting value, and a charging period of the capacitor 363 is controlled according to the difference between the first detecting signal and the current-setting signal duty ratio of the drive signal corresponds to the charging period of the capacitor 363.

In this embodiment, the controller 3 further receives the second detecting signal from the detector 2, and adjusts the first calculation value according to the second detecting signal. Preferably, the controller 3 adjusts the first calculation value such that a phase difference between the drive signal and the tank current is approximately zero. Preferably, the controller 3 further determines a phase difference between the drive signal and the tank current with reference to a phase-setting value. In addition, the controller 3 outputs an abnormal signal when the charging period of the capacitor 363 exceeds a reasonable range.

Referring once again to FIG. 6, according to the first preferred embodiment of the present invention, the controller 3 includes a switching unit 31, an analog-to-digital converting unit 32, an oscillator unit 33, a processing unit 34, a burst unit 35, a waveform generating unit 37, and an adjustment control unit 36. The switching unit 31 is coupled electrically to the primary winding 11 of the step-up transformer 1, and to the waveform generating unit 37 for receiving a control signal therefrom. The switching unit 31 further receives a direct-current (DC) power signal from a DC power source, and generates the drive signal for driving the step-up transformer 1 from the direct-current power signal based on the control signal. The drive signal is a periodic alternating-current (AC) signal.

In this embodiment, the switching unit 31 is a full bridge circuit, includes four switches, namely a first switch 311, a second switch 312, a third switch 313, and a fourth switch 314. In addition, the control signal includes a set of control sub-signals that respectively correspond to the first to fourth switches 311˜314. The first switch 311 is coupled electrically between a first end of the primary winding 11 and ground. The second switch 312 is coupled electrically between the first end of the primary winding 11 and the DC power source. The third switch 313 is coupled electrically between a second end of the primary winding 11 and ground. The fourth switch 314 is coupled electrically between the second end of the primary winding 11 and the DC power source.

Example waveforms of the control sub-signals for controlling opening and closing of the first to fourth switches 311˜314, and of the drive signal generated by the switching unit 31 are shown in FIG. 7, the horizontal axis denoting a time axis (t). In FIG. 7, waveforms 61˜64 respectively represent control sub-signals for the first to fourth switches 311˜314, and waveform 65 represents the drive signal, where T_drive denotes a period of the drive signal, T_start denotes lag of positive or negative pulses of the drive signal from a start of a half period of the drive signal, T_duty denotes duration of the positive or negative pulses of the drive signal, and T_overlap denotes a discharge duration to release energy stored by the primary winding 11. It should be noted herein that since T_overlap is much smaller than T_drive, T_overlap is enlarged in FIG. 7 for illustrative purposes.

High voltage levels of the waveforms 61˜64 respectively represent closing (i.e., a conducting state) of the first to fourth switches 311˜314, while low voltage levels of the waveforms 61˜64 respectively represent opening (i.e., a non-conducting state) of the first to fourth switches 311˜314.

The phase difference between the current flowing through the primary winding 11 and the voltage across the primary winding 11 can be adjusted by adjusting T_drive. Starting times of the positive and negative pulses of the drive signal are adjusted by adjusting T_start. Current flowing through the discharge lamp 4 can be adjusted by adjusting T_duty, where T_duty is adjusted by varying duration of the positive/negative pulse of the drive signal from a starting time of the positive/negative pulse. Since the first switch 311 and the third switch 313 are disposed in the conducting state simultaneously for a period of time (i.e., during T_overlap), both the first and second ends of the primary winding 11 are grounded simultaneously, and energy stored by the primary winding 11 can be discharged to facilitate reversal of the direction of the current flowing through the primary winding 11. T_overlap needs to be large enough for the primary winding 11 to be sufficiently discharged. Discharging of the primary winding 11 can also be achieved by closing the second switch 312 and the fourth switch 314 simultaneously such that the two ends of the primary winding 11 are coupled electrically and simultaneously to the DC power source.

Referring back to FIG. 6, the analog-to-digital converting unit 32 is coupled electrically to the detector 2 for receiving the third detecting signal therefrom, and further receives a first burst signal (i.e., a DC voltage signal) from an external source. The analog-to-digital converting unit 32 converts the third detecting signal and the first burst signal respectively into corresponding digital values, namely a third detecting value and a first burst value.

The oscillator unit 33 is coupled electrically to the waveform generating unit 37 and is for generating and outputting an oscillating signal to the waveform generating unit 37. Frequency of the oscillating signal is greater than frequency of the drive signal.

The processing unit 34 records the first calculation value and the start-setting value, and is coupled electrically to the waveform generating unit 37 for providing the first calculation value and the start-setting value thereto. In this embodiment, the processing unit 34 further records a voltage-setting value and an overlap-setting value, and further provides the voltage-setting value and the overlap-setting value to the waveform generating unit 37. The processing unit 34 is further coupled electrically to the detector 2 for receiving the second detecting signal therefrom, to the analog-to-digital converting unit 32 for receiving the third detecting value therefrom, and to the oscillator unit 33 for receiving the oscillating signal therefrom.

The first calculation value, the start-setting value and the overlap-setting value are defined by the following relations:

$N_1=\frac{T_{\mathrm{drive}}}{T_{\mathrm{osc}}}$ $N_{\mathrm{start}}=\frac{T_{\mathrm{start}}}{T_{\mathrm{osc}}}$ $N_{\mathrm{overlap}}=\frac{T_{\mathrm{overlap}}}{T_{\mathrm{osc}}}$

wherein N₁ denotes the first calculation value, N_start denotes the start-setting value, N_overlap denotes the overlap-setting value, T_drive denotes the period of the drive signal, T_start denotes lag of positive or negative pulses of the drive signal from a start of a half period of the drive signal, T_overlap denotes the discharge duration to release energy stored by the primary winding 11, and T_osc denotes a period of the oscillating signal. The first calculation value, the start-setting value, the overlap-setting value, and the oscillating signal are used to configure the waveform of the drive signal (for example, as shown in FIG. 7 by waveform 65).

The first calculation value has a preset value. The processing unit 34 adjusts the first calculation value from the preset value according to the second detecting signal. Since the first calculation value is adjusted in the same manner as the prior art, further details of the same are omitted herein for the sake of brevity.

As with the prior art, a difference between the third detecting value and the voltage-setting value is used to determine whether the processing unit 34 needs to output a warning signal, and further details of the same are also omitted herein for the sake of brevity.

The start-setting value and the overlap-setting value are determined by the user.

The adjustment control unit 36 is coupled electrically to the detector 2 for receiving the first detecting signal therefrom, is further coupled electrically to the waveform generating unit 37 for receiving a start signal therefrom and for outputting a termination signal thereto, and includes the capacitor 363 (as shown in FIG. 8). The adjustment control unit 36 further receives the current-setting signal from the external source, controls start of the charging of the capacitor 363 based on the start signal, and controls a charging period of the capacitor 363 based on the difference between the first detecting signal and the current-setting signal. The adjustment control unit 36 outputs the termination signal upon termination of the charging of the capacitor 363.

Two implementations of the adjustment control unit 36 are presented in this text.

As shown in FIG. 6, according to a first implementation of the adjustment control unit 36, in addition to the capacitor 363, the adjustment control unit 36 further includes a differential amplifier 361, a current adjuster 362, and a comparator 364.

The differential amplifier 361 is coupled electrically to the detector 3 for receiving the first detecting signal therefrom, and further receives the current-setting signal. Each of the first detecting signal and the current-setting signal is a voltage signal in this embodiment. The differential amplifier 361 determines and amplifies the difference between the first detecting signal and the current-setting signal so as to generate a difference signal.

The current adjuster 362 is coupled electrically to the differential amplifier 361 for receiving the difference signal therefrom, is further coupled electrically to the waveform generating unit 37 for receiving the start signal therefrom, is further coupled electrically to the capacitor 363, and generates a charging current for charging the capacitor 363. The current adjuster 362 starts charging the capacitor 363 according to the start signal. The current adjuster 362 decreases the charging current when the difference signal indicates that the first detecting signal is smaller than the current-setting signal (i.e., T_duty is too small), such that charging rate of the capacitor 363 is decreased. The current adjuster 362 increases the charging current when the difference signal indicates that the first detecting signal is greater than the current-setting signal (i.e., T_duty is too large), such that the charging rate of the capacitor 363 is increased. The current adjuster 362 terminates the charging of the capacitor 363 and starts to discharge the capacitor 363 upon receipt of the termination signal, until a voltage across the capacitor 363 becomes zero.

The comparator 364 is coupled electrically to the capacitor 363 for comparing the voltage across the capacitor 363 with a reference voltage, and is further coupled electrically to the current adjuster 362 and the waveform generating unit 37 for generating and outputting the termination signal thereto when the voltage across the capacitor 363 is greater than the reference voltage.

As shown in FIG. 9, according to a second implementation of the adjustment control unit 36′, in addition to the capacitor 366, the adjustment control unit 36 further includes a current generator 365, a differential integrator 367, and a comparator 368.

The current generator 365 is coupled electrically to the waveform generating unit 37 for receiving the start signal therefrom, is further coupled electrically to the capacitor 366, and generates a charging current for charging the capacitor 366. The current generator 365 starts charging the capacitor 363 according to the start signal, and terminates the charging of the capacitor 366 and starts to discharge the capacitor 366 upon receipt of the termination signal, until a voltage across the capacitor 366 becomes zero.

The differential integrator 367 is coupled electrically to the detector 2 for receiving the first detecting signal therefrom, and further receives the current-setting signal. Each of the first detecting signal and the current-setting signal is a voltage signal in this embodiment. The differential integrator 367 integrates and amplifies the difference between the first detecting signal and the current-setting signal so as to generate a reference voltage. The differential integrator 367 increases the reference voltage when the first detecting signal is smaller than the current-setting signal (i.e., T_duty is too small), such that the charging period of the capacitor 366 is lengthened. The differential integrator 367 decreases the reference voltage when the first detecting signal is greater than the current-setting signal (i.e., T_duty is too large), such that the charging period of the capacitor 366 is shortened.

The comparator 368 is coupled electrically to the differential integrator 367 for receiving the reference voltage therefrom, is further coupled electrically to the capacitor 366 for comparing the voltage across the capacitor 366 with the reference voltage, and is further coupled electrically to the current generator 365 and the waveform generating unit 37 for generating and outputting the termination signal thereto when the voltage across the capacitor 366 is greater than the reference voltage.

As shown in FIG. 7, waveform 66 represents the voltage across the capacitor 363, 366.

It should be noted herein that one end of the capacitor 363, 366 is coupled electrically to a DC voltage (not shown), which can have a value ranging from a ground voltage to the DC voltage as provided by the DC power source.

Referring back to FIG. 6 the waveform generating unit 37 receives the oscillating signal from the oscillator unit 33, receives the first calculation value, the start-setting value, the overlap-setting value and the warning signal from the processing unit 34, and receives the termination signal from the adjustment control unit 36. The waveform generating unit 37 outputs the start signal to the adjustment control unit 36, and outputs the control signal to the switching unit 31. The waveform generating unit 37 generates the start signal according to the first calculation value, the start-setting value, the overlap-setting value and the oscillating signal by counting the oscillating signal, and further generates the control signal with reference to the termination signal. The control signal is one such that a starting time for conduction of the second and fourth switches 312, 314 of the step-up transformer 31 corresponds to a starting time for charging of the capacitor 363, 366. The waveform generating unit 367 stops operating upon receipt of the warning signal.

In particular, the start-setting value and the termination signal are used to determine the duration of the positive pulse or the negative pulse of the drive signal, which is identical to the charging time of the capacitor 363, 366. In addition, the termination signal is generated as an analog signal. Consequently, the smallest variation gradient in T_duty is not limited by the period of the oscillating signal T_osc. In other words, T_duty can vary in a continuous manner, such that the brightness of the light provided by the discharge lamp 4 changes in a continuous manner as well.

The burst unit 35 is coupled electrically to the oscillator unit 33 for receiving the oscillating signal therefrom, to the analog-to-digital converting unit 32 for receiving the first burst value therefrom, and to the processing unit 34 for receiving the warning signal therefrom. The burst unit 35 further receives a second burst signal and a select signal from an external source. The burst unit 35 generates and outputs a burst control signal to the waveform generating unit 37. Since operation of the burst unit 35 is identical to that of the prior art, further details of the same are omitted herein for the sake of brevity.

The waveform generating unit 37 controls output of the control signal to the switching unit 31 according to the burst control signal. The burst control signal is further used to control whether the current adjuster 362 or the current generator 365 of the adjustment control unit 36, 36′ is to operate. When the burst control signal is one such that the waveform generating unit 37 does not output the control signal to the switching unit 31, the current adjuster 362 or the current generator 365 of the adjustment control unit 36, 36′ also stops operating, thereby avoiding ripple interference.

As shown in FIG. 6, preferably, the processing unit 34 is further coupled electrically to the adjustment control unit 36 for receiving the termination signal therefrom, and further receives the start signal from the waveform generating unit 37. The processing unit 34 generates a second calculation value based on the start signal, the termination signal and the oscillating signal, the second calculation value corresponding to the charging period of the capacitor 363, 366, which is the same as the duration of the positive pulse or negative pulse of the drive signal. The processing unit 34 outputs an abnormal signal when the charging period of the capacitor 363, 366 exceeds a reasonable range, which is indicated by the second calculation value being too large or too small.

The second calculation value is defined by the following relation:

$N_2=\frac{T_{\mathrm{duty}}}{T_{\mathrm{osc}}}$

where N₂ represents the second calculation value, T_duty denotes the duration of the positive pulse or the negative pulse of the drive signal, and T_osc denotes the period of the oscillating signal.

As shown in FIG. 10, the second preferred embodiment of the lamp driving circuit according to the present invention differs from the first preferred embodiment in the configuration of the switching unit 31′.

In the second preferred embodiment, the switching unit 31′ is a 3-FET (field effect transistor) circuit, and includes three switches, namely a fifth switch 315, a sixth switch 316, and a seventh switch 317. The fifth switch 315 is coupled electrically between the first end of the primary winding 11 of the step-up transformer 1 and ground. The sixth switch 316 is coupled electrically between the second end of the primary winding 11 and ground. The seventh switch 317 is coupled electrically between a center tap of the primary winding 11 and the DC power source.

Waveforms of control sub-signals for the fifth to seventh switches 315˜317 of the switching unit 31′, of the drive signal provided to the primary winding 11, and of the voltage across the capacitor 363, 366 (shown in FIG. 8 and FIG. 9) of the adjustment control unit 36, 36′ are shown in FIG. 11, the horizontal axis denoting a time axis (t). Waveforms 71˜73 respectively represent control sub-signals for the fifth to seventh switches 315˜317, waveform 74 represents the drive signal, and waveform 75 represents the voltage across the capacitor 363, 366, where T_drive denotes the period of the drive signal, T_start, denotes lag of positive or negative pulses of the drive signal from a start of a half period of the drive signal, T_duty denotes the duration of a positive pulse or a negative pulse of the drive signal, and T_overlap denotes a discharge duration to release energy stored by the primary winding 11. It should be noted herein that since T_overlap is much smaller than T_drive, T_overlap is enlarged in FIG. 11 for illustrative purposes.

High voltage levels of the waveforms 71˜73 respectively represent closing (i.e., a conducting state) of the fifth to seventh switches 315˜317, while low voltage levels of the waveforms 71˜73 respectively represent opening (i.e., a non-conducting state) of the fifth to seventh switches 315˜317.

In sum, the present invention uses an analog adjustment method for generating the termination signal, such that the smallest variation gradient in T_duty is not limited by the period of the oscillating signal T_osc, thereby alleviating discontinuous change in lighting of the discharge lamp 4. In addition, the present invention utilizes the charging period of the capacitor 363, 366 and the first detecting signal, which corresponds to the current magnitude of the current flowing through the discharge lamp 4, and which is not converted into a corresponding digital value, to adjust T_duty in real time, thereby avoiding circuit malfunction, and stabilizing the brightness of the light provided by the discharge lamp 4.

While the present invention has been described in connection with what are considered the most practical and preferred embodiments, it is understood that this invention is not limited to the disclosed embodiments but is intended to cover various arrangements included within the spirit and scope of the broadest interpretation so as to encompass all such modifications and equivalent arrangements.

Claims

1. A lamp driving circuit adapted for driving at least one discharge lamp, said lamp driving circuit comprising: a step-up transformer including a primary winding, and a secondary winding adapted to be coupled electrically to the discharge lamp and adapted to cooperate with the discharge lamp to form a tank circuit that generates a tank current;a detector adapted for detecting current magnitude of current flowing through the discharge lamp, and outputting a first detecting signal that corresponds to the current magnitude detected thereby; anda controller coupled electrically to said primary winding of said step-up transformer, and to said detector for receiving the first detecting signal therefrom, said controller generating a drive signal for driving said step-up transformer;wherein said controller includes a capacitor, and further receives a current-setting signal, said controller configuring a waveform of the drive signal by controlling charging of said capacitor based on a first calculation value that corresponds to a frequency of the drive signal, a start-setting value, and a difference between the first detecting signal and the current-setting signal.

2. The lamp driving circuit as claimed in claim 1, wherein start of the charging of said capacitor is controlled according to the start-setting value, and a charging period of said capacitor is controlled according to the difference between the first detecting signal and the current-setting signal, a duty ratio of the drive signal corresponding to the charging period of said capacitor.

3. The lamp driving circuit as claimed in claim 1, wherein said detector is further adapted to detect phase of the tank current, and further outputs a second detecting signal that corresponds to the phase of the tank current, said controller further receiving the second detecting signal from said detector, the first calculation value being adjusted by said controller according to the second detecting signal.

4. The lamp driving circuit as claimed in claim 3, wherein said controller adjusts the first calculation value such that a phase difference between the drive signal and the tank current is approximately zero.

5. The lamp driving circuit as claimed in claim 3, wherein said controller further determines a phase difference between the drive signal and the tank current with reference to a phase-setting value.

6. The lamp driving circuit as claimed in claim 1, wherein said controller outputs an abnormal signal when a charging period of said capacitor exceeds a reasonable range.

7. The lamp driving circuit as claimed in claim 1, wherein: said controller includes a switching unit, an oscillator unit, a processing unit, an adjustment control unit, and a waveform generating unit;said switching unit is coupled electrically to said primary winding of said step-up transformer, and to said waveform generating unit for receiving a control signal therefrom, said switching unit further receiving a direct-current power signal, and generating the drive signal for driving said step-up transformer from the direct-current power signal based on the control signal, the drive signal being a periodic alternating-current signal;said oscillator unit is coupled electrically to said waveform generating unit and is for generating and outputting an oscillating signal to said waveform generating unit, frequency of the oscillating signal being greater than frequency of the drive signal;said processing unit records the first calculation value and the start-setting value, and is coupled electrically to said waveform generating unit for providing the first calculation value and the start-setting value thereto;said adjustment control unit is coupled electrically to said detector for receiving the first detecting signal therefrom, is further coupled electrically to said waveform generating unit for receiving a start signal therefrom and for outputting a termination signal thereto, and includes said capacitor, said adjustment control unit further receiving the current-setting signal, controlling start of the charging of said capacitor based on the start signal, and controlling a charging period of said capacitor based on the difference between the first detecting signal and the current-setting signal, said adjustment control unit outputting the termination signal upon termination of the charging of said capacitor; andsaid waveform generating unit receives the oscillating signal from said oscillator unit, receives the first calculation value and the start-setting value from said processing unit, receives the termination signal from said adjustment control unit, outputs the start signal to said adjustment control unit, and outputs the control signal to said switching unit, said waveform generating unit generating the start signal according to the first calculation value, the start-setting value and the oscillating signal, and further generating the control signal with reference to the termination signal.

8. The lamp driving circuit as claimed in claim 7, wherein: said detector further detects phase of the tank current, and further outputs a second detecting signal that corresponds to the phase of the tank current, said processing unit being further coupled electrically to said detector for receiving the second detecting signal; andthe first calculation value has a preset value, said processing unit adjusting the first calculation value from the preset value according to the second detecting signal.

9. The lamp driving circuit as claimed in claim 7, wherein said processing unit is further coupled electrically to said oscillator unit for receiving the oscillating signal therefrom, and to said adjustment control unit for receiving the termination signal therefrom, and further receives the start signal from said waveform generating unit, said processing unit generating a second calculation value based on the start signal, the termination signal and the oscillating signal, and outputting an abnormal signal when the charging period of said capacitor exceeds a reasonable range.

10. The lamp driving circuit as claimed in claim 7, wherein: each of the first detecting signal and the current-setting signal is a voltage signal, said adjustment control unit further including a differential amplifier, a current adjuster, and a comparator;said differential amplifier is coupled electrically to said detector for receiving the first detecting signal therefrom, and further receives the current-setting signal, said differential amplifier determining and amplifying the difference between the first detecting signal and the current-setting signal so as to generate a difference signal;said current adjuster is coupled electrically to said differential amplifier for receiving the difference signal therefrom, is further coupled electrically to said waveform generating unit for receiving the start signal therefrom, is further coupled electrically to said capacitor, and generates a charging current for charging said capacitor, said current adjuster decreasing the charging current when the difference signal indicates that the first detecting signal is smaller than the current-setting signal, said current adjuster increasing the charging current when the difference signal indicates that the first detecting signal is greater than the current-setting signal, said current adjuster terminating the charging of said capacitor and starting to discharge said capacitor upon receipt of the termination signal, until a voltage across said capacitor becomes zero; andsaid comparator is coupled electrically to said capacitor for comparing the voltage across said capacitor with a reference voltage, and is further coupled electrically to said current adjuster and said waveform generating unit for generating and outputting the termination signal thereto when the voltage across said capacitor is greater than the reference voltage.

11. The lamp driving circuit as claimed in claim 7, wherein: each of the first detecting signal and the current-setting signal is a voltage signal, said adjustment control unit further including a current generator, a differential integrator, and a comparator;said current generator is coupled electrically to said waveform generating unit for receiving the start signal therefrom, is further coupled electrically to said capacitor, and generates a charging current for charging said capacitor, said current generator terminating the charging of said capacitor and starting to discharge said capacitor upon receipt of the termination signal, until a voltage across said capacitor becomes zero;said differential integrator is coupled electrically to said detector for receiving the first detecting signal therefrom, and further receives the current-setting signal, said differential integrator integrating and amplifying the difference between the first detecting signal and the current-setting signal so as to generate a reference voltage, said differential integrator increasing the reference voltage when the first detecting signal is smaller than the current-setting signal, said differential integrator decreasing the reference voltage when the first detecting signal is greater than the current-setting signal; andsaid comparator is coupled electrically to said differential integrator for receiving the reference voltage therefrom, is further coupled electrically to said capacitor for comparing the voltage across said capacitor with the reference voltage, and is further coupled electrically to said current generator and said waveform generating unit for generating and outputting the termination signal thereto when the voltage across said capacitor is greater than the reference voltage.

12. A control method to be implemented using a lamp driving circuit that is adapted for driving at least one discharge lamp, and that includes a step-up transformer, the step-up transformer including a primary winding and a secondary winding adapted to be coupled electrically to the discharge lamp and adapted to cooperate with the discharge lamp to form a tank circuit that generates a tank current, the control method comprising the steps of: detecting current magnitude of current flowing through the discharge lamp, and outputting a first detecting signal that corresponds to the current magnitude thus detected; andconfiguring a waveform of a drive signal used to drive the step-up transformer by controlling charging of a capacitor based on a first calculation value that corresponds to a frequency of the drive signal, a start-setting value, and a difference between the first detecting signal and a current-setting signal.

13. The control method as claimed in claim 12, wherein start of the charging of the capacitor is controlled according to the start-setting value, and a charging period of the capacitor is controlled according to the difference between the first detecting signal and the current-setting signal, a duty ratio of the drive signal corresponding to the charging period of the capacitor.

14. The control method as claimed in claim 12, further comprising the steps of: detecting phase of the tank current, and outputting a second detecting signal that corresponds to the phase of the tank current; andadjusting the first calculation value according to the second detecting signal.

15. The control method as claimed in claim 14, wherein the first calculation value is adjusted such that a phase difference between the drive signal and the tank current is approximately zero.

16. The control method as claimed in claim 14, further comprising the step of determining a phase difference between the drive signal and the tank current with reference to a phase-setting value.

17. The control method as claimed in claim 12, further comprising the step of outputting an abnormal signal when a charging period of the capacitor exceeds a reasonable range.