CN105530720A - Driving device and method thereof - Google Patents

Abstract

The present invention discloses a driving method and a driving device using the method. The method comprises the following steps: generating a selection signal according to the power output by a triode current switch; generating a voltage regulation signal by a linear voltage regulator; generating a modulation signal by a pulse width modulator; and selecting one of the voltage regulation signal and the modulation signal according to the selection signal to control the output current provided to a light emitting diode circuit, wherein the light emitting diode circuit is coupled to the triode current switch.

Description

Driving device and method thereof

technical field

The present invention relates to a driving device and its method, in particular to a driving device and its method suitable for a light-emitting diode circuit driven by a triode current switch.

Background technique

Light emitting diodes (light emitting diodes, LEDs) are widely used in daily life as a light-emitting element with high luminous efficiency. Among them, LED circuits directly applicable to alternating current power (AC power) are widely used. Usually, in order to stabilize the luminous intensity of the LED circuit, a pulse-width modulation (PWM) technology is used with specific passive electronic components to roughly stabilize the current flowing through the LED.

On the other hand, in the lighting field, a dimming circuit is used in various specific environments to create a special atmosphere because it can be used to adjust the luminous intensity of the light emitting element. In a traditional dimming circuit, a triode for alternating current (TRIAC) is a common component.

However, when the light-emitting diode circuit uses pulse width modulation technology to stabilize the luminous intensity at the same time, and uses the triode current switch as the brightness adjustment element, there will be flickering problems. The problem is that after the triode current switch is ignited (conducted), if its output current is less than a holding current (holding current), the triode current switch will stop operating, and it has to wait until the next input power supply voltage/current is high enough , the triode current switch will be ignited again. When the pulse width modulation technology and the triode current switch are applied to the light-emitting diode circuit at the same time, the pulse width modulation technology may make the output current of the triode current switch too small. In this way, the triode current switch will always be re-ignited repeatedly, so that the current flowing through the LED is actually unstable, resulting in the problem of flash.

Contents of the invention

Since the pulse width modulation technology and the triode current switch are applied to the light-emitting diode circuit at the same time, the pulse width modulation technology may make the output current of the triode current switch too small. As a result, the triode current switch will always be repeatedly re-ignited, so that the current flowing through the LED is actually unstable, causing the problem of flash. In order to solve this problem, the present invention proposes a new driving device, which does not use pulse width modulation to stabilize the current of the LED when the current of the triode current switch drops to a certain level. Instead, a linear voltage regulator is used to stabilize the LED current. In this way, the current output from the triode current switch can be limited above the holding current, thus avoiding repeated refiring of the triode current switch, and finally solving the problem of flicker.

A driving device according to one or more embodiments of the present invention has a current control module, a linear voltage regulator, a pulse width modulator, a selection module and a multiplexing module. The current control module is coupled to a LED circuit, and is used for controlling the output current provided to the LED circuit according to the control signal, and generating a feedback signal according to the output current, wherein the LED circuit is coupled to a triode current switch. The linear voltage regulator is coupled to the current control module, and is used to generate a voltage-stabilizing signal according to the power output by the triode current switch and the feedback signal. The pulse width modulator is coupled to the current control module and used for generating modulation signals according to the feedback signal and the reference voltage. The selection module is used for generating a selection signal according to the power output by the triode current switch. The multiplexing module is respectively coupled to the selection module, the linear voltage regulator and the pulse width modulator for selecting one of the voltage stabilization signal and the modulation signal as a control signal according to the selection signal.

A driving method according to one or more embodiments of the present invention includes the following steps: generating a selection signal according to the power output by the triode current switch. Generate a regulated signal with a linear regulator. The modulated signal is generated with a pulse width modulator. According to the selection signal, one of the voltage regulation signal and the modulation signal is selected to control the output current provided to the LED loop, wherein the LED loop is coupled to the triode current switch.

The driving method and its device disclosed in one or more embodiments of the present invention selectively use pulse-width modulation (pulse-width modulation) or linear voltage regulation (low-dropout) according to the power output by the triode current switch. Control the current supplied to the light emitting diode circuit, so as to avoid the problem of repeated re-ignition caused by the output current of the triode current switch being less than the holding current.

The above description of the content of the present invention and the following description of the implementation are used to demonstrate and explain the spirit and principle of the present invention, and to provide further explanation of the protection scope of the patent application claims of the present invention.

Description of drawings

FIG. 1 is a schematic diagram of a system architecture of a driving device used in a triode for alternating current (TRIAC) driven light emitting diode circuit according to an embodiment of the present invention.

FIG. 2A is a schematic circuit diagram of a current control module according to an embodiment of the invention.

FIG. 2B is a schematic current diagram of a current control module according to another embodiment of the present invention.

FIG. 3 is a schematic circuit diagram of controlling a current control module with a voltage stabilizing signal of a linear regulator according to an embodiment of the invention.

FIG. 4A is a functional block diagram of a pulse width modulator according to an embodiment of the invention.

FIG. 4B is a timing diagram corresponding to each signal in FIG. 4A.

FIG. 5A is a schematic diagram of a selection module circuit according to an embodiment of the invention.

FIG. 5B is a schematic diagram of a selection module circuit according to another embodiment of the present invention.

FIG. 5C is a functional block diagram of a selection module according to yet another embodiment of the present invention.

FIG. 6 is a schematic diagram of a multiplexing module circuit according to an embodiment of the present invention.

FIG. 7 is a signal timing diagram corresponding to FIG. 1 .

FIG. 8 is a flowchart of a driving method according to an embodiment of the invention.

Among them, reference signs:

100 drive unit

110 current control module

111 switch unit

111a first end

111b second end

111c control terminal

113 current voltage conversion unit

113a first impedance element

113b second impedance element

120 linear regulator

121 amplifier

130 Pulse Width Modulator

131 comparators

133 clock generator

135S-R latch

137 buffers

140 selection modules

141 comparators

143 amplifier

145 Analog to Digital Converter

147 digital signal processing unit

150 multiplex modules

151, 153 channel units

200 triode current switch

300 LED loop

301 first end

302 second end

310 LED array

311 first end

312 second end

320 capacitance

321 first end

322 second end

330 inductance

331 first end

332 second end

340 diode

341 first end

342 second end

I _O output current

I _IN current value

I _TH threshold

P ₀ Power

P1, P2 time interval

R resistance

SEL selection signal

T ₁ ~ T ₃ time point

V _C control signal

V _CLK clock signal

V _COMP comparison signal

V _F feedback signal

V _LATCH latch signal

V _LDO regulation signal

V _PWM modulation signal

V _REF1 , V _REF2 reference voltage

_VTH threshold voltage

detailed description

The detailed features and advantages of the present invention are described in detail below in the implementation manner, and its content is enough to make any person skilled in the art understand the technical content of the present invention and implement it accordingly, and according to the content disclosed in this specification, the scope of protection of the claims and With the accompanying drawings, any person skilled in the art can easily understand the related objects and advantages of the present invention. The following examples further illustrate the concept of the present invention in detail, but do not limit the scope of the present invention in any way.

Regarding a driving device according to an embodiment of the present invention, please refer to FIG. 1 , which is a schematic diagram of a system architecture of a driving device according to an embodiment of the present invention for a light-emitting diode circuit driven by a triode for alternating current (TRIAC). As shown in FIG. 1 , a driving device 100 implemented according to an embodiment of the present invention is coupled to a triode current switch 200 and an LED circuit 300 , and the LED circuit 300 and the triode current switch 200 are coupled to each other. The driving device 100 has a current control module 110 , a linear voltage regulator 120 , a pulse width modulator 130 , a selection module 140 and a multiplexing module 150 . The current control module 110 is coupled to the LED loop 300, the linear regulator 120 is coupled to the current control module 110, the pulse width modulator 130 is coupled to the current control module 110, the selection module 140 is coupled to the triode current switch 200, and the multiplexing module 150 is respectively coupled to the selection module 140 , the linear regulator 120 and the pulse width modulator 130 .

The LED circuit 300 has a first end 301 and a second end 302 , wherein the first end 301 is coupled to the triode current switch 200 , and the second end 302 is coupled to the current control module 110 . The light emitting diode includes a light emitting diode array 310 , a capacitor 320 , an inductor 330 and a diode 340 . As shown in FIG. 1 , the first terminal 311 of the LED array 310 , the first terminal 321 of the capacitor 320 and the first terminal 341 of the diode 340 in this embodiment are all coupled to the first terminal 301 of the LED circuit 300 . Both the second terminal 312 of the LED array 310 and the second terminal 322 of the capacitor 320 are coupled to the first terminal 331 of the inductor 330 . Both the second terminal 332 of the inductor 330 and the second terminal 342 of the diode 340 are coupled to the second terminal 302 of the LED circuit 300 .

The current control module 110 is used for controlling the output current I _O provided to the LED circuit 300 according to the control signal V _C and generating a feedback signal V _F according to the output current I _O. In one embodiment, please refer to FIG. 2A and FIG. 2B , wherein FIG. 2A is a schematic circuit diagram of a current control module according to an embodiment of the present invention, and FIG. 2B is a schematic current diagram of a current control module according to another embodiment of the present invention. . As shown in FIG. 2A, the current control module 110 has a switch unit 111 and a current-voltage conversion unit 113, wherein the current-voltage conversion unit 113 is implemented as a resistor or other two-terminal voltage difference corresponding to the flowing current (one -to-oneandonto), that is to say, the current flowing through the voltage conversion unit 113 and the feedback voltage V _F provided by the current voltage conversion unit 113 are strictly increasing or decreasing.

The switch unit 111 has a first end 111 a , a second end 111 b and a control end 111 c , wherein the control end 111 c is coupled to the multiplexing module 150 . Therefore, whether an electric path is formed between the first terminal 111 a and the second terminal 111 b of the switch unit 111 can be determined by the control signal V _C sent from the multiplexing module 150 . And the first end 111a is coupled to the light emitting diode circuit 300, and the two ends of the current-voltage conversion unit 113 are respectively coupled to the second end 111b and a voltage reference end (for example, it can be the ground end of the entire system structure or the current the ground terminal of the control module 110 itself). In this embodiment, the feedback signal V _F is generated from the second terminal 111 b of the switch unit 111 .

In the embodiment of FIG. 2A, the switch unit 111 is an N-type metal-oxide semiconductor field effect transistor (N-type metal-oxide semiconductor field effect transistor, N-MOSFET), an npn bipolar transistor (npnbipolarjunctiontransistor, npnBJT) or other elements with similar characteristics. . In this way, when the voltage level of the control signal V _C is a high voltage, the switch unit 111 is turned on, so that a power channel is formed between the first terminal 111 a and the second terminal 111 b. When the voltage level of the control signal _VC is low, the switch unit 111 is not turned on, so that no power channel is formed between the first terminal 111a and the second terminal 111b.

In another embodiment, as shown in FIG. 2B , the current-to-voltage conversion unit 113 has a first impedance element 113 a and a second impedance element 113 b connected in series. That is to say, compared with the embodiment of FIG. 2A , the feedback signal V _F of FIG. 2B is not generated at the second end 111b of the switch unit 111, but is generated at the phase between the first impedance element 113a and the second impedance element 113b. Junction. In one embodiment, the circuit designer adjusts the relationship between the feedback signal V _F and the output current I _O by properly selecting the first impedance element 113 a and the second impedance element 113 b.

The linear voltage regulator 120 is used for generating a voltage regulation signal V _LDO according to the power P ₀ output by the triode current switch 200 and the feedback signal V _F . Please refer to FIG. 3 , which is a schematic circuit diagram of controlling the current control module with the voltage regulation signal of the linear regulator according to an embodiment of the present invention. As shown in FIG. 3 , in one embodiment, the linear regulator 120 has an amplifier 121, its positive input end is used to receive a reference voltage V _REF1 , its negative input end is used to receive a feedback signal V _F , and its The output end is used to output the voltage-stabilizing signal V _LDO , wherein when the voltage-stabilizing signal V _LDO is used as the control signal V _C as described later, the voltage level of the feedback signal V _F is substantially equal to the reference voltage V _REF1 . In this way, the output current I _O provided by the current control module 110 to the LED circuit 300 is determined by the reference voltage V _REF1 and the current-to-voltage conversion module 113 .

The pulse width modulator 130 is used for generating the modulation signal V _PWM according to the feedback signal V _F and the reference voltage V _REF2 . Specifically, please refer to FIG. 4A and FIG. 4B , wherein FIG. 4A is a functional block diagram of a pulse width modulator according to an embodiment of the present invention, and FIG. 4B is a timing diagram corresponding to each signal in FIG. 4A . As shown in FIG. 4A , the pulse width modulator 130 in one embodiment of the present invention has a comparator 131 , a clock generator 133 , an SR latch 135 (set-reset latch, SRlatch) and a buffer 137 . The positive input terminal of the comparator 131 is used to receive the feedback signal V _F , and the negative input terminal is used to receive a reference voltage V _REF2 . When the voltage level of the feedback signal V _F is substantially greater than the reference voltage V _REF2 , the comparator 131 The voltage level of the comparison signal V _COMP output by the output end is a high voltage, otherwise it is a low voltage. The clock generator 133 is used to generate the clock signal V _CLK . The setting terminal (Sterminal) of the SR latch 135 is used to receive the clock signal V _CLK , and its reset terminal (Rterminal) is used to receive the comparison signal V _COMP , and the output terminal (Qterminal) of the latch 135 outputs The latch signal V _LATCH obeys the rules in Table 1 below. The input end of the buffer 137 is coupled to the output end of the latch 135 to receive the latch signal V _LATCH , and the output end of the buffer 137 is used to output the modulation signal V _PWM . In this embodiment, the modulation signal V _PWM is substantially equal to the latch signal V _LATCH .

Table 1

Set terminal voltage level Reset terminal voltage level Latch signal voltage level Low Low no change

Low high Low high Low high high high undefined (should not happen)

Next, please refer to FIG. 4A and FIG. 4B together. In the embodiment of FIG. 4B , corresponding to FIG. 4A , the modulation signal V _PWM is used as the control signal V _C to control the output current I _O . As shown in FIG. 4B, before the _first time point T1, the voltage level of the feedback signal V _F is lower than the reference voltage V _REF2 , so the voltage level of the comparison signal V _COMP is a low voltage, and the voltage of the clock signal V _CLK The voltage level is a low voltage. If the voltage levels of the latch signal V _LATCH , the modulation signal V _PWM and the control signal V _C are all high voltages, the switch unit 111 in the current control module 110 is turned on. Then at the first time point T ₁ , the output current I _O is large enough to cause the voltage level of the feedback signal V _F to be higher than the reference voltage V _REF , so the voltage level of the comparison signal V _COMP output by the comparator 131 changes to a high voltage. . And the voltage level of the clock signal V _CLK is a low voltage, so the latch signal V _LATCH and the modulating signal V _PWM both change to a low voltage. Therefore, the control signal V _C is also pulled to a low voltage, and the switch unit 111 is turned off to make it non-conductive. In this way, the voltage level of the feedback signal V _F is reduced to a low voltage, and the voltage level of the comparison signal V _COMP is also reduced to a low voltage. At this time, since the voltage level of the clock signal V _CLK is still low, the voltage levels of the latch signal V _LATCH , the modulation signal V _PWM and the control signal V _C are all still low.

Then, at the _second time point T2, the voltage level of the clock signal V _CLK rises to a high voltage, so that the voltage levels of the latch signal V _LATCH , the modulation signal V _PWM and the control signal V _C are all raised to a high voltage. Voltage. In this way, the switch unit 111 is turned on, so that the output current I _O is provided to the LED circuit 300 again. At the third time point T ₃ , since the output current I _O is large enough, the voltage level of the feedback signal V _F is higher than the reference voltage V _REF , so the voltage level of the comparison signal V _COMP output by the comparator 131 turns high. Voltage. And the voltage level of the clock signal V _CLK is a low voltage, so the latch signal V _LATCH and the modulating signal V _PWM both change to a low voltage. Therefore, the control signal V _C is also pulled to a low voltage, and the switch unit 111 is turned off to make it non-conductive. In this way, the voltage level of the feedback signal V _F is reduced to a low voltage, and the voltage level of the comparison signal V _COMP is also reduced to a low voltage. At this time, since the voltage level of the clock signal V _CLK is still low, the voltage levels of the latch signal V _LATCH , the modulation signal V _PWM and the control signal V _C are all still low. That is to say, the pulse width modulator 130 controls the conduction of the switch unit 111 so that in a long enough time interval, the average value of the output current _I0 is approximately equal to the preset current value, so that the light can be emitted. The energy consumed by the diode circuit 300 within this time interval is roughly in line with expectations.

The selection module 140 is used for generating the selection signal SEL according to the power P ₀ output by the triode current switch 200 . Specifically, please refer to FIG. 5A and FIG. 5B , wherein FIG. 5A is a schematic circuit diagram of a selection module according to an embodiment of the present invention, and FIG. 5B is a schematic circuit diagram of a selection module according to another embodiment of the present invention. As shown in FIG. 5A, the selection module 140 in one embodiment has a comparator 141, the positive input terminal of the comparator 141 is used to receive a threshold voltage V _TH , and the negative input terminal of the comparator 141 is used to receive the triode current For the power P ₀ output by the switch 200 , the comparator 141 compares the threshold voltage V _TH with the voltage level of the power P ₀ to generate a selection signal SEL at the output terminal. When the voltage level of the power P ₀ is lower than the threshold voltage V _TH , the voltage level of the selection signal SEL is a high voltage, otherwise it is a low voltage. Conceptually, the current value is estimated according to the voltage level of the power supply P ₀ , and the current value is compared with the current value corresponding to the threshold voltage V _TH to generate the selection signal SEL. The current value (threshold value) corresponding to the threshold voltage V _TH in this embodiment is greater than the holding current (I _H ) of the triode current switch 200 . For example, the current value (threshold value) corresponding to the threshold voltage V _TH is twice the holding current (I _H ) of the triode current switch 200 .

In addition, in another embodiment, as shown in FIG. 5B , the power P0 output by the triode current switch ₂₀₀ flows through a resistor R before being sent to the LED circuit 300, and the voltage difference between the two ends of the resistor R is amplified 143 is read and amplified, and is compared with the threshold voltage V _TH by the comparator 141 to generate the selection signal SEL. The method is roughly as described in FIG. 5A , and will not be repeated here.

In addition, in other embodiments, please refer to FIG. 5C , which is a functional block diagram of a selection module according to another embodiment of the present invention. As shown in FIG. 5C , the selection module 140 has an analog-to-digital converter 145 (analog-to-digital converter, ADC) and a digital signal processing unit 147 (digital signal processing unit, DSP). The analog-to-digital converter 145 converts the voltage and/or current of the power supply P0 into a digital signal, and the digital signal processing unit 147 _judges the phase characteristic of the power supply P0 output by the triode current switch ₂₀₀ according to the digital signal, and outputs according to the phase characteristic Selection signal SEL.

The multiplexing module 150 is used for selecting one of the voltage regulation signal V _LDO and the modulating signal V _PWM as the control signal V _C according to the selection signal SEL. In an embodiment, please refer to FIG. 6 , which is a circuit diagram of a multiplexing module according to an embodiment of the present invention. As shown in Figure 6, the multiplexing module 150 is an analog multiplexer, which has a channel unit 151 and a channel unit 153, wherein the channel unit 151 is respectively coupled to the linear voltage regulator 120 and the switch unit 111, and the channel unit 153 is respectively coupled to The pulse width modulator 130 and the switch unit 111 . According to the selection signal SEL, at most one of the channel unit 151 and the channel unit 153 is turned on at any point in time, so that one of the regulation signal V _LDO and the modulation signal V _PWM is used as the control signal V _C . Specifically, with the embodiment shown in FIG. 5A , when the voltage level of the selection signal SEL is a high voltage, the multiplexing module 150 selects the voltage regulator signal V _LDO as the control signal V _C . And when the voltage level of the selection signal SEL is a low voltage, the multiplexing module 150 selects the modulation signal V _PWM as the control signal V _C .

Therefore, overall, please refer to FIG. 1 and FIG. 7 together, wherein FIG. 7 is a signal timing diagram corresponding to FIG. 1 . As shown in FIG. 7 , in the first time interval P1 , the selection module 140 determines that the current value I _IN of the power supply P ₀ is greater than the threshold value I _TH , and thus uses the modulation signal V _PWM as the control signal V _C . When the first time interval P1 ends and the second time interval P2 enters, the selection module 140 judges that the current value I _IN of the power supply P ₀ is smaller than the threshold value I _TH , so the voltage regulator signal V _LDO is used as the control signal V _C . Since when the current value I _IN is smaller than the threshold value I _TH , the voltage regulator signal V _LDO is used as the control signal, and the current value I _IN is still greater than the holding current of the triode current switch 200, and the linear voltage regulator 120 is properly designed, The output current _I0 is also greater than the holding current of the triode current switch 200, so the problem that the triode current switch 200 needs to be re-ignited does not occur in the first time interval P1 and the second time interval P2.

Therefore, the operation mode of the driving device in one or more of the foregoing embodiments can be summarized as a driving method. Please refer to FIG. 8 , which is a flowchart of a driving method according to an embodiment of the present invention. As shown in FIG. 8 , the driving method implemented according to an embodiment of the present invention includes the following steps: as described in step S810 , generating a selection signal according to the power output by the triode current switch. As described in step S830, according to the selection signal, it is selected to generate the voltage stabilization signal according to the feedback signal or to generate the modulation signal according to the feedback signal, and use the generated voltage stabilization signal or the feedback signal as the control signal. As described in step S850, the output current provided to the LED circuit is controlled according to the control signal.

The driving device and method thereof according to an embodiment of the present invention are suitable for a light-emitting diode circuit driven by a triode current switch. When it is judged that the current output by the triode current switch is less than the threshold value, choose to control the current flowing through the LED circuit in the form of linear voltage regulation, and when it is judged that the current output by the triode current switch is greater than or equal to the threshold value, choose to use pulse width modulation way to control the current flowing through the LED circuit. In this way, when the triode current switch and pulse width modulation are applied to drive the LED circuit at the same time, the probability that the triode current switch needs to be re-ignited repeatedly is reduced, thereby avoiding the flickering problem of the light-emitting diode circuit caused by the triode current switch re-ignition.

Claims (18)

1. A driving device, characterized in that, comprising: A current control module, coupled to a light-emitting diode circuit, is used to selectively provide an output current to the light-emitting diode circuit according to a control signal, and generate a feedback signal according to the output current, wherein the light-emitting diode circuit is coupled to A triode current switch; a linear voltage regulator, coupled to the current control module, for generating a voltage-stabilizing signal according to the power output by the triode current switch and the feedback signal; a pulse width modulator, coupled to the current control module, for generating a modulation signal according to the feedback signal and a reference voltage; a selection module, used to generate a selection signal according to the power output by the triode current switch; and A multiplexing module is coupled to the selection module, the linear voltage regulator and the pulse width modulator respectively, and is used for selecting one of the voltage stabilization signal and the modulation signal as the control signal according to the selection signal. 2. The driving device according to claim 1, wherein the current control module comprises: A switch unit has a first terminal, a second terminal and a control terminal, the first terminal is coupled to the light emitting diode circuit, and the control terminal is coupled to the multiplexer module for determining the whether a power channel is formed between the first terminal and the second terminal to allow the output current to pass; and A current-voltage conversion unit is electrically connected to the second terminal of the switch unit and ground respectively, and is used for generating the feedback signal according to the output current passing through the switch unit. 3 . The driving device according to claim 1 , wherein the selection module generates the corresponding selection signal according to a phase characteristic of the power outputted by the triode current switch. 4 . 4. The driving device according to claim 1, wherein the selection module generates the corresponding selection signal according to a voltage value of the power outputted by the triode current switch. 5 . The driving device according to claim 4 , wherein the selection module obtains a current value of the power outputted by the triode current switch according to the voltage value, so as to generate the corresponding selection signal. 6 . The driving device according to claim 1 , wherein the selection module generates the corresponding selection signal according to a current value of the power source output by the triode current switch. 7. The driving device according to claim 5 or 6, wherein the selection module generates the corresponding selection signal according to the current value and a threshold value, wherein the threshold value is related to the triode current switch a sustaining current. 8. The driving device according to claim 7, wherein when the current value is substantially greater than the threshold value, the selection signal controls the multiplexing module to select the modulation signal as the control signal. 9. The driving device according to claim 7, wherein when the current value is substantially smaller than the threshold value, the selection signal controls the multiplexer module to select the voltage stabilization signal as the control signal. 10. A driving method, characterized in that, comprising: Generate a selection signal according to the power output by a triode current switch; According to the selection signal, select to generate a voltage-stabilizing signal according to a feedback signal or generate a modulation signal according to the feedback signal, and use the generated voltage-stabilizing signal or the feedback signal as a control signal; and An output current selectively provided to a light emitting diode circuit according to the control signal; Wherein the LED circuit is coupled to the transistor current switch, and the feedback signal is related to the output current. 11. The method according to claim 10, wherein in the step of generating the voltage stabilization signal, the voltage stabilization signal is generated according to the feedback signal and the power supply, and in the step of generating the modulation signal, the feedback signal is used and a reference voltage to generate the modulation signal. 12. The method of claim 10, wherein the selection signal is generated according to a phase characteristic of the power supply. 13. The method of claim 10, wherein the selection signal is generated according to a voltage value of the power supply. 14. The method of claim 13, wherein a current value of the power supply is obtained according to the voltage value, and the selection signal is generated according to the current value. 15. The method of claim 10, wherein the selection signal is generated according to a current value of the power supply. 16. The method according to claim 14 or 15, wherein the selection signal is generated according to the current value and a threshold value, and the threshold value is related to a holding current of the triode current switch. 17. The method according to claim 16, wherein in the step of selecting one of the voltage regulation signal and the modulating signal to control the output current according to the selection signal, when the current value is substantially greater than the threshold value, choose to control the output current with the modulating signal. 18. The method according to claim 16, wherein in the step of selecting one of the voltage regulation signal and the modulating signal to control the output current according to the selection signal, when the current value is substantially smaller than the threshold value, choose to control the output current with the regulated signal.