TWI420958B - Circuits and methods for driving light sources, and controllers for controlling dimming of light source - Google Patents

Description

Light source driving circuit, light source driving method, and light source dimming controller

The invention relates to a circuit, in particular to a light source driving circuit, a driving method and a controller.

Light sources such as light-emitting diodes (LEDs) or cold cathode fluorescent lamps (CCFLs) are widely used in the lighting industry, particularly in liquid crystal display (LCD) backlights, street lighting, and household appliances. The light source driving circuit can adjust the energy transmitted to the light source according to a dimming signal (for example, a pulse width modulation signal).

FIG. 1 is a schematic diagram of a prior art light source driving circuit 100. The light source driving circuit 100 includes an AC/DC converter 104, a power converter 106, and a dimming module 112. The AC/DC converter 104 converts an input AC voltage provided by an AC power source 102 into a first DC voltage. Power converter 106 converts the first DC voltage to a second DC voltage suitable for powering LED string 108. The dimming module 112 can operate in a burst dimming mode. In the pulse dimming mode, the dimming module 112 generates a pulse width modulation signal 120 to adjust the energy transmitted to the LED string 108, thereby adjusting the brightness of the LED string 108. More specifically, the light source driving circuit 100 further includes a switch 110 coupled to the LED string 108 for controlling the current I _LIGHT flowing through the LED string 108 according to the pulse width modulation signal 120, thereby further The brightness of the LED string 108 is determined.

2 is a signal timing diagram 200 generated by a prior art light source driving circuit 100. Figure 2 will be described in conjunction with Figure 1. In the embodiment of FIG. 2, timing diagram 200 depicts pulse width modulation signal 120 and current I _LIGHT flowing through LED string 108. When the pulse width modulation signal 120 is at a high potential, for example, in the time interval T _ON from time t1 to time t2, the switch 110 is turned on. The current I _LIGHT flows through the LED string 108 and has a preset current value I ₁ . When the pulse width modulation signal 120 to a low level, for example: at time interval t2 to t3 T _OFF, the switch 110 is off. Current I _LIGHT drops to zero amps. Therefore, by adjusting the duty cycle of the pulse width modulation signal 120, the average current value of the current I _LIGHT changes, and the brightness of the LED string 108 can be adjusted.

However, according to the characteristics of the semiconductor component (for example, the power converter 106), after the switch 110 is turned on (for example, at time t1 or time t3), the current I _LIGHT needs to pass a delay time T _DELAY to reach the preset current value I _{1 .} . Therefore, the dimming control of the LED string 108 is affected by the frequency noise of the light source driving circuit 100. For example, when the duty cycle is relatively small (eg, the duty cycle is in the range of 0 to 5%) and the frequency of the pulse width modulation signal 120 is greater than the preset threshold F _MAX , the time interval T _{ON is} close to or even less than the delay. Time T _DELAY . Therefore, the average current value of the current I _LIGHT does not change according to the duty cycle of the pulse width modulation signal 120, thereby causing an error in the dimming control of the light source driving circuit 100.

An object of the present invention is to provide a light source driving circuit, comprising: a frequency controller, receiving a first dimming signal to control a light source to reach a predetermined brightness, and when a frequency of the first dimming signal is between When the preset range is within, the frequency controller generates a second dimming signal according to the first dimming signal, wherein a frequency of the second dimming signal is outside the preset range; and a switch module, And being coupled to the frequency controller, wherein when the frequency of the first dimming signal is within the preset range, the switch module is alternately turned on and off according to the second dimming signal, and when When the frequency of the first dimming signal is outside the preset range, the switch module is alternately turned on and off according to the first dimming signal, so that the light source reaches the preset brightness.

The present invention also provides a method for driving a light source, comprising: receiving a first dimming signal to control a light source to reach a predetermined brightness; and when a frequency of the first dimming signal is within a predetermined range, according to the The first dimming signal generates a second dimming signal, wherein a frequency of the second dimming signal is outside the preset range; when the frequency of the first dimming signal is within the preset range Controlling the light source according to the second dimming signal to achieve the preset brightness; and when the frequency of the first dimming signal is outside the preset range, controlling the first dimming signal according to the first dimming signal Light source to achieve the preset brightness.

The invention also provides a light source dimming controller, comprising: a frequency controller, receiving a first dimming signal to control energy transmitted to a light source, so that the light source reaches a preset brightness, when the first tone When the frequency of one of the optical signals is within a predetermined range, generating a second dimming signal according to the first dimming signal and one of the frequencies outside the preset range, and alternating according to a selected dimming signal Turning on and off a switch coupled to the light source to cause the light source to reach the predetermined brightness, wherein when the frequency of the first dimming signal is outside the preset range, the selected tone The optical signal includes the first dimming signal, when the frequency of the first dimming signal is within the preset range, the selected dimming signal includes the second dimming signal; and a logic module, Coupling to the frequency controller, detecting the selected dimming signal, and stopping the operation of the power converter when the selected dimming signal indicates that the switch is off, wherein the operation of the power converter includes providing a Voltage to drive the source.

A detailed description of the embodiments of the present invention will be given below. While the invention will be described in conjunction with the embodiments, it is understood that the invention is not limited to the embodiments. Rather, the invention is to cover various modifications, equivalents, and equivalents of the invention as defined by the scope of the appended claims.

In addition, in the following detailed description of the embodiments of the invention However, it will be understood by those of ordinary skill in the art that the present invention may be practiced without these specific details. In other instances, well-known methods, procedures, components, and circuits have not been described in detail in order to facilitate the invention.

Embodiments of the present invention provide a light source driving circuit. The light source driving circuit includes a frequency controller and a switch module. The frequency controller receives the first dimming signal (eg, a pulse width modulation signal), and controls the light source according to the first dimming signal, and the light source emits a preset brightness. The advantage is that when the frequency of the first dimming signal is within one or more preset ranges, the frequency controller generates a second dimming signal according to the first dimming signal, wherein the frequency of the second dimming signal is between One or more of the above preset ranges. For example, the preset range can be greater than a maximum frequency threshold. In addition, the duty cycle of the first dimming signal and the second dimming signal are the same.

Therefore, when the frequency of the first dimming signal is within one or more preset ranges, the switch module is alternately turned on and off according to the second dimming signal to achieve a preset brightness; when the first dimming signal When the frequency is outside one or more preset ranges, the switch module is alternately turned on and off according to the first dimming signal to achieve a preset brightness. Therefore, the dimming control of the light source is not affected by the frequency noise, thereby improving the accuracy of the light source driving circuit.

3 is a schematic diagram of a light source driving circuit 300 in accordance with an embodiment of the present invention. In an embodiment, the light source driving circuit 300 includes an AC/DC converter 304, a power converter 306, a switch 310, a dimming module 312, and a frequency controller 320. The AC power source 302 provides an input AC voltage to the light source drive circuit 300, for example, a 120 volt commercial voltage. The light source may include one or more light source strings, for example, a plurality of light emitting diode strings 308 formed by a plurality of light emitting diodes coupled in series with each other. Although only one source string is employed in the example of Figure 3, the source may also include other numbers of strings of sources. An AC/DC converter 304 coupled to the AC power source 302 converts the input AC voltage to a first DC voltage. Power converter 306 converts the first DC voltage to a second DC voltage suitable for powering LED string 308. The operation of AC/DC converter 304 and power converter 306 will be further described in FIG.

In one embodiment, the switch 310 is coupled to the LED string 308, and controls the energy transmitted to the LED string 308 according to the dimming signal, thereby causing the LED string 308 to emit a predetermined brightness. More specifically, in an embodiment, the dimming signal can be a pulsed signal, such as a pulse width modulated signal. When the dimming signal has a logic high potential, the switch 310 is turned "on". Therefore, the current I _LIGHT flows through the light-emitting diode string 308, and the light-emitting diode string 308 is illuminated. This is called the conductive state of the light-emitting diode string 308. When the dimming signal has a logic low potential, switch 310 is turned off. Therefore, the current I _LIGHT drops to approximately zero amperes, and therefore, the light emitting diode string 308 stops emitting light, which is referred to as the off state of the light emitting diode string 308. When the switching frequency of the switch 310 is greater than a predetermined minimum threshold F _MIN , the human eye does not perceive the blinking of the LED string 308 (eg, the LED string 308 is in an on state and an off state). Blinking caused by switching between). At this time, the duty cycle of the dimming signal can be adjusted to adjust the average current value of the current I _LIGHT to further adjust the brightness of the LED string 308.

In an embodiment, the dimming module 312 can be a signal generator for generating a dimming signal DIM1 (eg, a PWM signal) to control the power transmitted to the LED string 308 to achieve the LED. The preset brightness of the body string 308. For example, the user can set the preset brightness by setting the duty cycle of the dimming signal DIM1.

The frequency controller 320 coupled between the dimming module 312 and the switch 310 receives the dimming signal DIM1 and determines whether the frequency F _{DIM1 of the} dimming signal DIM1 is within one or more preset ranges. For example, the preset range may be greater than a preset maximum threshold F _MAX . In some cases, if the frequency F _{DIM1 of the} dimming signal DIM1 is within a preset range (eg, greater than F _MAX ), the frequency noise will affect the accuracy of the dimming control. For convenience of description, this article will be described in combination with a preset range greater than F _MAX . However, the invention is not limited thereto. In other embodiments, the one or more preset ranges may further include other ranges, such as a range smaller than F1 and/or a range larger than F2 and smaller than F3, where F1 < F2 < F3.

In an embodiment, if the frequency F _{DIM1 of the} dimming signal DIM1 is within a preset range (eg, greater than F _MAX ), the frequency controller 320 generates another dimming signal DIM2 according to the dimming signal DIM1. Frequency F. F. _{DIM2 DIM1} frequency dimming signal is a dimming signal DIM2 DIM1 different (e.g., F _DIM2 less than the maximum threshold value F _MAX). Therefore, F _DIM2 is outside the preset range. Further, the frequency controller 320 maintains the duty cycle of the dimming signal DIM1 and the dimming signal DIM2 to be the same. Therefore, the preset brightness can also be obtained according to the power transmitted to the LED string 308 under the control of the dimming signal DIM2. In this case, the frequency controller 320 transmits the dimming signal DIM2 to the switch 310. The switch 310 controls the power transmitted to the LED string 308 according to the dimming signal DIM2, for example, through the control current I _LIGHT .

If the frequency F _{DIM1 of the} dimming signal DIM1 is outside the preset range (eg, less than F _MAX ), the frequency controller 320 transmits the dimming signal DIM1 to the switch 310. In this case, the switch 310 controls the current I _LIGHT according to the dimming signal DIM1 to control the power transmitted to the LED string 308 to reach a preset brightness.

Therefore, based on the frequency F _{DIM1 of the} dimming signal DIM1, the switch 310 controls the power transmitted to the LED string 308 based at least on the dimming signal DIM1 or the dimming signal DIM2. Therefore, the frequency of the dimming signal (DIM1 or DIM2) controlling the LED string 308 is always less than F _MAX . Therefore, the frequency noise does not affect the current I _LIGHT flowing through the LED string 308. For example, although the current I _LIGHT needs to go through a delay time T _DELAY after the switch 310 is turned on, it can rise to the preset current value I1, and although the duty cycle of the dimming signal (DIM1 or DIM2) may be relatively small, for example: 0 ～5%, the duration T _{ON of the} on-state of the LED string 308 can always be greater than the delay time T _DELAY . Therefore, the accuracy of the light source driving circuit 300 is improved.

4 is a schematic diagram of a light source driving circuit 400 in accordance with an embodiment of the present invention. Elements labeled the same as in Figure 3 have the same function. Figure 4 will be described in conjunction with Figure 3.

In an embodiment, the AC/DC converter 304 includes a rectifier circuit and a filter. The rectifier circuit may include a half wave rectifier, a full wave rectifier or a bridge rectifier, but is not limited thereto. The rectifier circuit rectifies the input AC voltage to provide a first DC voltage. For example, the rectifier circuit can delete the negative voltage waveform of the input AC voltage or convert the negative voltage waveform into a corresponding positive voltage waveform. Therefore, the output of the rectifier circuit obtains a first DC voltage having a positive voltage waveform. Alternatively, AC power source 302 and AC/DC converter 304 may be replaced by a DC power source. For example, the first DC voltage can be provided by a DC power source (eg, a battery pack).

Power converter 306 converts the first DC voltage to a second DC voltage suitable for powering LED string 308. In the embodiment of FIG. 4, the power converter 306 can be a boost converter including an inductor L1, a diode D1, a capacitor C1, and a switch S1. By adjusting the on-time and off-time of switch S1 (eg, adjusted according to PWM signal CP), power converter 306 can regulate the electrical energy stored in inductor L1 and capacitor C1. In one embodiment, power converter 306 generates a second DC voltage that is greater than the first DC voltage in this manner. When the switch 310 is turned on, the second DC voltage can forward bias the LED string 308. Power converter 306 can have other configurations, such as a buck converter, a buck-boost converter, or a flyback converter, and is not limited to the embodiment of FIG.

The dimming module 312 generates a dimming signal DIM1. For example, DIM1 can be a pulse signal (eg, a PWM signal), and the duty cycle of dimming signal DIM1 represents a preset brightness of light emitting diode string 308. The user can set the duty cycle of the dimming signal DIM1. The frequency controller 320 receives the dimming signal DIM1. In an embodiment, frequency controller 320 includes frequency detector 402, frequency converter 404, and logic circuit 406.

The frequency detector 402 detects the frequency F _{DIMI of the} dimming signal DIM1 to determine whether the F _DIM1 is within a preset range, for example, the preset range is F _MAX to infinity. In an embodiment, the frequency detector 402 includes a counter 420 for calculating the frequency F _{DIM1 of the} dimming signal _DIM1 . More specifically, the dimming signal DIM1 is synchronized with a predetermined sampling clock signal. In an embodiment, the preset sampling clock signal may be a periodic square wave signal having a fixed period T _CLOCK . In operation, the counter 420 calculates the number M of revolutions of the preset sampling clock signal occurring within one cycle of the dimming signal DIM1. The frequency F _DIM1 of the dimming signal DIM1 can be calculated according to the number of loops M and the fixed period T _{CLOCK of the} sampling clock signal, which can be expressed by the equation (1):

F _DIM1 =1/(M*T _CLOCK )----(1)

In addition, the frequency detector 402 further includes a comparator 422 for comparing the magnitude between the detected frequency F _DIM1 and one or more preset thresholds to determine whether the frequency F _DIM1 is within a preset range. In an embodiment, the comparator 422 compares the frequency F _DIM1 with a preset maximum threshold F _MAX . If F _{DIM1 is} greater than F _MAX , it means that F _DIM1 is within the preset range. At this time, the comparator 422 transmits the dimming signal DIM1 to the frequency converter 404. If F _{DIM1 is} less than F _MAX , it means that F _DIM1 is outside the preset range. At this time, the comparator 422 transmits the dimming signal DIM1 to the logic circuit 406. Logic circuit 406 transmits dimming signal DIM1 to switch 310. The switch 310 thereby adjusts the current I _LIGHT flowing through the LED string 308. Frequency detector 402 may include other components and is not limited to the embodiment of FIG.

The frequency converter 404 generates a dimming signal DIM2 based on the dimming signal DIM1. In one embodiment, frequency converter 404 converts frequency F _{DIM1 of} dimming signal _DIM1 and maintains its duty cycle D _DIM1 to produce dimming signal DIM2. The dimming signal DIM2 has a frequency F _DIM2 and a duty cycle D _DIM2 . The frequency F _{DIM2 is} less than F _MAX . And, the duty cycle D _DIM2 is equal to the duty cycle D _DIM1 of the dimming signal _DIM1 . Therefore, the preset brightness indicated by the dimming signal DIM1 can also be represented by the dimming signal DIM2.

More specifically, the frequency converter 404 can generate the dimming signal DIM2 using the first sampling clock signal SIGNAL1 and the second sampling clock signal SIGNAL2, wherein the frequency F _DIM2 of the dimming signal _DIM2 is the fraction of the frequency F _{DIM1 of the DIM1} . (fraction). In an embodiment, the first sampling clock signal SIGNAL1 and the second sampling clock signal SIGNAL2 may be periodic square wave signals having a fixed frequency. SIGNAL2 frequency clock signal when the second sampling clock frequency is F _CLOCK2 F _CLOCK1 signal SIGNAL1 of the first fraction sampled, as shown in equation (2):

F _CLOCK2= (1/N)*F _CLOCK1 ----(2)

The frequency converter 404 calculates the number of loops of the first sampling clock signal SIGNAL1 to obtain the result data indicating the period and duty cycle of the DIM1, and then generates the dimming signal DIM2 according to the data and the second sampling clock signal SIGNAL2.

In the embodiment of FIG. 4, frequency converter 404 includes multiplexer 414 and one or more counting modules (eg, counting module 410 and counting module 412). In one embodiment, when one of the counting modules detects the period and duty cycle of the dimming signal DIM1, the other counting module determines the period and duty cycle of the dimming signal DIM2. In one embodiment, each of the counting module 410 and the counting module 412 includes a cycle counter and a duty cycle counter (not shown). When the corresponding counting module (taking the counting module 410 as an example) detects the dimming signal DIM1, the period counter in the counting module 410 calculates the first sampling clock signal SIGNAL1 in one cycle of the dimming signal DIM1. The number of N1A. In this way, the period counter obtains period data indicating the period of the dimming signal DIM1. In addition, the duty cycle counter calculates the number of loops N1B of the first sample clock signal SIGNAL1 in the time interval T _STATE1 , where T _STATE1 indicates that one cycle of the dimming signal DIM1 and the DIM1 is in a preset state (eg: Time interval of logic high or logic low). In this way, the duty cycle counter acquires the duty cycle data indicating the duty cycle of the dimming signal DIM1. For example, if T _STATE1 represents the duration of the logic high of the dimming signal DIM1, the duty cycle data representing the duty cycle D _DIM1 of the DIM1 can be obtained in combination with N1A and N1B, for example: D _DIM1 = N1B / N1A. If T _STATE1 represents the duration of the logic low of the dimming signal DIM1, the duty cycle data representing the duty cycle D _DIM1 of the DIM1 can be obtained in combination with N1A and N1B, for example: D _DIM1 =1-(N1B/N1A). Therefore, the result data including the cycle data and the responsibility cycle data is obtained. The operation of the counting module to detect the dimming signal DIM1 will be further described in FIG.

When the corresponding counting module (taking the counting module 412 as an example) is used to generate the dimming signal DIM2, the period counter in the counting module 412 calculates the back of the second sampling clock signal SIGNAL2 according to the period data (for example, N1A). The number of turns is used to determine the period T _{DIM2 of the} dimming signal _DIM2 . For example, T _DIM2 is equal to N1A times the period of the second sampling clock signal SIGNAL2. In addition, the duty cycle counter of the counting module 412 calculates the number of loops of the second sampling clock signal SIGNAL2 according to the duty cycle data (for example, N1B) to determine the duty cycle D _{DIM2 of the} dimming signal _DIM2 . For example, the duration T _STATE2 of the corresponding preset state (eg, logic high potential and logic low potential) of the dimming signal DIM2 is equal to N1B times the period of the second sampling clock signal SIGNAL2. The duty cycle D _{DIM2 of the} dimming signal DIM2 can be expressed as D _DIM2 =T _STATE2 /T _DIM2 (when T _STATE2 corresponds to the logic high of _DIM2 ) or D _DIM2 =1-T _STATE2 /T _DIM2 (when T _STATE2 corresponds to DIM2 Logic low potential). The operation of the counting module for generating the dimming signal DIM2 will be further described in FIG.

As a result, the dimming signal DIM1 _DIM1 of T and T _STATE1 are multiplied by the same value N, and thus to obtain the dimming signal DIM2 _DIM2 T and T _STATE2, wherein, according to formula (2) obtained N. Therefore, the frequency F _DIM2 is a fraction of the frequency F _DIM1 , which can be expressed by the equation (3):

F _DIM2 = (1/N) * F _DIM1 ---- (3)

As shown in equation (3), the fraction 1/N is also determined by the ratio between the frequency of the second sampling clock signal SIGNAL2 obtained according to equation (2) and the frequency of the first sampling clock signal SIGNAL1. In addition, the duty cycle D _DIM1 is equal to the duty cycle D _DIM2 , which can be derived from equation (4):

D _DIM2 =T _STATE2 /T _DIM2 =(N*T _STATE1 )/(N*T _DIM1 )=T _STATE1 /T _DIM1 =D _DIM1 ----(4)

5 is a timing diagram 500 of signals received and generated by a frequency converter (e.g., frequency converter 404 shown in FIG. 4) in accordance with an embodiment of the present invention. In the embodiment of FIG. 5, timing diagram 500 depicts dimming signal DIM1, first sampling clock signal SIGNAL1, and second sampling clock signal SIGNAL2. Further, when the frequency of the second sampling clock signal SIGNAL2 F _CLOCK2 is the first sampling clock frequency F _CLOCK1 signal SIGNAL1 is 1 / N. For example, in Figure 5, F _CLOCK2 = 1/2 * F _CLOCK1 .

During the time interval from t1 to t7, one or more counting modules obtain result data by performing a counting operation. At time t1, the corresponding counting module calculates the number of loops of the first sampling clock signal SIGNAL1. In the embodiment of FIG. 5, the first sampling clock signal SIGNAL1 has five loop periods during one period (for example, t1 to t3 or t3 to t5) of the dimming signal DIM1. Therefore, the cycle counter gets a cycle data of 5. And, in one period of the dimming signal DIM1, the duration of the dimming signal DIM1 is at a logic high level (for example, t1 to t2, t3 to t4 or t5 to t6), and the first sampling clock signal SIGNAL1 has 2 Cycle cycle. Therefore, the duty cycle data indicating the duty cycle of the dimming signal DIM1 is 40%.

In the time interval from t1' to t6', the one or more counting modules generate the dimming signal DIM2 by using the result data (including the period data and the duty cycle data) and the second sampling clock signal SIGNAL2. In the embodiment of Fig. 5, the period of the dimming signal DIM2 (e.g., t1' to t3' or t3' to t5') is equal to 5 times the period of the second sampling clock signal SIGNAL2. Further, the duration of the logic high of the dimming signal DIM2 (e.g., t1' to t2', t3' to t4' or t5' to t6') is equal to twice the period of the second sampling clock signal SIGNAL2. Therefore, the duty cycle of the dimming signal DIM2 is also 40%.

Therefore, in order to generate the dimming signal DIM2, the period of the dimming signal DIM1 and the duration of the logic high potential are multiplied by the same preset value N (for example, N is equal to 2 in FIG. 5). The preset value N is determined by the first sampling clock signal SIGNAL1 and the second sampling clock signal SIGNAL2 according to equation (2). As a result, the frequency of the dimming signal DIM2 is 1/N of the frequency of the dimming signal DIM1.

In an embodiment, the dimming signal DIM1 and the dimming signal DIM2 have a fixed frequency that is preset or programmed by the user. For example, the user can set the value N to a substantially constant value. Alternatively, the first sampling clock signal SIGNAL1 and the second sampling clock signal SIGNAL2 may be generated by a signal generator. At this time, the value N or the fraction 1/N can be determined according to the frequency F _{DIM1 of the} dimming signal DIM1. That is to say, the value N can vary according to the frequency F _DIM1 . For example, if the frequency F _{DIM1 is} greater than F _MAX and less than F1, for example: F _MAX <F _DIM1 <F1, the value N is equal to N1. If the frequency F _{DIM1 is} greater than F1, for example: F _MAX >F1, the value N is equal to N2, where N2 is greater than N1.

Description will be made in conjunction with FIGS. 4 and 5. In an embodiment, the counting module 410 and the counting module 412 can alternately calculate the number of loops of the first sampling clock signal SIGNAL1 (acquisition result data) and calculate the second sampling clock signal SIGNAL2 according to the result data. Dimming signal DIM2). For example, in the time interval from t1 to t3, the counting module 410 detects the dimming signal DIM1 by calculating the number of loops of the first sampling clock signal SIGNAL1. At time t3, the counting module 410 obtains the cycle data and the responsibility cycle data. Then, the counting module 410 enters the time interval of t1' to t3', that is, the counting module 410 generates the dimming signal DIM2 by calculating the number of loops of the second sampling clock signal SIGNAL2. In this embodiment, the time t1' corresponds to the time t3, and the time t3' corresponds to the time t7. Therefore, at time t3 or t1', the counting module 412 starts detecting the dimming signal DIM1 by calculating the number of loops of the first sampling clock signal SIGNAL1. Similarly, at time t5, the counting module 412 obtains the cycle data and the responsibility cycle data. At time t3' or t7, when the counting module 410 completes the operation of generating the dimming signal DIM2, the counting module 410 starts detecting the dimming signal DIM1, and the counting module 412 starts generating the dimming signal DIM2. In this way, the dimming signal DIM2 can be a continuous PWM signal.

The multiplexer 414 transmits the dimming signal DIM2 generated by the counting module 410 or the counting module 412 to the logic circuit 406. The logic circuit 406 transmits the dimming signal DIM2 whose frequency is outside the preset range to the switch 310.

FIG. 6 shows another schematic diagram of frequency controller 320 in accordance with an embodiment of the present invention. Elements labeled the same as in Figure 4 have the same function. Figure 6 will be described in conjunction with Figures 3 through 5.

In the embodiment of FIG. 6, the frequency converter 404 includes a counting module 510, a register 514, and a counting module 512. The counting module 510 detects the dimming signal DIM1 by calculating the number of loops of the first sampling clock signal SIGNAL1 (for example, at times t1 to t7 in FIG. 5), and includes the result of the period data and the duty cycle data. The data is stored in a register 514 coupled to the counting module 510. The counting module 512 coupled to the register 514 reads the result data, and generates the dimming signal DIM2 by calculating the number of loops of the second sampling clock signal SIGNAL2 (for example, at time t1' in FIG. 5 to T6' is performed). Therefore, in this embodiment, the time t1' corresponds to the time t1 and the time t3' corresponds to the time t5.

Frequency controller 320 can have other configurations and is not limited to the embodiments of Figures 4 and 6. In another embodiment, the counting module 510 can be removed from the frequency controller 320 and the functionality of the counting module 510 incorporated into the frequency detector 402. For example, the frequency detector 402 can detect the frequency and duty cycle of the dimming signal DIM1 by counting the first sample clock signal SIGNAL1. If the frequency of the detected dimming signal DIM1 is greater than F _MAX , the frequency detector 402 stores the period data and the duty cycle data to the register 514. The counting module 512 generates the dimming signal DIM2 using the second sampling clock signal SIGNAL2 and the result data, and transmits the DIM2 to the frequency detector 402. If the frequency of the dimming signal DIM1 is less than F _MAX , the frequency detector 402 transmits the dimming signal DIM1 to the logic circuit 406.

FIG. 7 is a schematic diagram of a light source driving circuit 700 in accordance with another embodiment of the present invention. Elements labeled the same as in Figures 3 and 4 have the same function. Figure 7 will be described in conjunction with Figures 3, 4 and 6. In the embodiment of FIG. 7, drive circuit 700 includes an AC/DC converter 304, a power converter 306, a switch 310, a dimming module 312, and a controller 702. The controller 702 is coupled between the switch 310 and the power converter 306 and can be integrated on an integrated circuit chip. The controller 702 controls dimming of the LED string 308 through the control switch 310 and the power converter 306.

In an embodiment, the controller 702 includes a frequency controller 320, a conversion controller 704, and a logic module 706. Frequency controller 320 employs an architecture similar to that of Figures 4 and 6. Therefore, the controller 702 can turn on or off the switch 310 according to the selected dimming signal DIM1/DIM2 to control the current I _LIGHT flowing through the LED string 308, thereby causing the LED string 308 to have a preset brightness. . When the frequency F _{DIM1 of the} dimming signal DIM1 is outside the preset range, for example, less than F _MAX , the selected dimming signal is DIM1. When the frequency F _{DIM1 of the} dimming signal DIM1 is within a preset range, for example, greater than F _MAX , the selected dimming signal is DIM2.

The conversion controller 704 is operative to generate a PWM signal CP to drive the power converter 306. A logic module 706 coupled to the conversion controller 704 and the frequency controller 320 detects the selected dimming signal (eg, DIM1 or DIM2) to obtain the switching state of the switch 310 and control the power converter 306 accordingly. More specifically, in one embodiment, logic module 706 transmits PWM signal CP to power converter 306 when the selected dimming signal indicates that switch 310 is conducting. Then, the power converter 306 adjusts the on and off times of the switch S1 according to the PWM signal CP to adjust the energy stored in the inductor L1 and the capacitor C1. In conjunction with the description in FIG. 4, the first DC voltage is converted to a second DC voltage to forward bias the LED string 308.

When the selected dimming signal indicates that switch 310 is open, current I _LIGHT drops to approximately zero amps. At this time, the logic module 706 generates an end signal (for example, logic 1) and transmits an end signal to the switch S1 for stopping the operation of the power converter 306. For example, the switch S1 is kept turned on according to the end signal whose state is logic 1, thereby depleting the energy stored in the inductor L1 and the capacitor C1. Thus, power converter 306 stops converting the first DC voltage to the second DC voltage. Moreover, the power converter 306 no longer consumes the energy absorbed from the AC power source 302, thereby reducing the power consumption of the light source driving circuit 700.

In summary, when switch 310 is turned on, power converter 306 provides a second DC voltage to drive LED string 308; and when switch 310 is turned off, power converter 306 stops operating. Therefore, the energy efficiency of the light source driving circuit 700 is improved.

FIG. 8 shows an operational flow diagram 800 of a light source driving circuit 300, 400 or 700 in accordance with an embodiment of the present invention. FIG. 8 will be described in conjunction with FIGS. 3 through 7. The specific steps covered in Figure 8 are merely examples. That is, the present invention is applicable to other reasonable processes or steps for improving FIG. In step 802, a first dimming signal (eg, dimming signal DIM1) is received. In step 804, the first dimming signal is detected to determine whether the frequency of the first dimming signal (eg, F _DIM1 ) is within a predetermined range (eg, greater than F _MAX ). If the frequency of the first dimming signal is outside of the preset range, flowchart 800 proceeds to step 806. In step 806, a light source is controlled according to the first dimming signal to achieve a predetermined brightness. Conversely, when the frequency of the first dimming signal is within a predetermined range, the flowchart 800 proceeds to step 808.

In step 808, a second dimming signal is generated according to the first dimming signal, wherein the frequency of the second dimming signal is outside a preset range. In an embodiment, the first dimming signal and the second dimming signal are pulse width modulation signals. The duty cycle of the first dimming signal and the second dimming signal remains the same. In one embodiment, the period and on-time of the first dimming signal are multiplied by an identical value to produce a second dimming signal. In an embodiment, the value is adjusted based on the frequency of the first dimming signal. In one embodiment, the number of loops of the first sampled clock signal (eg, SIGNAL1) is calculated to obtain a result data representative of the period and duty cycle of the first dimming signal. And, calculating the number of loops of the second sampling clock signal according to the result data to generate a second dimming signal. Wherein the frequency of the second dimming signal is a fraction of the frequency of the first dimming signal, and the fraction is determined by a ratio between a frequency of the second sampling clock signal and a frequency of the first sampling clock signal.

In step 810, the light source is controlled according to the second dimming signal to achieve a preset brightness.

The above detailed description and the accompanying drawings are only typical embodiments of the invention. It is apparent that various additions, modifications and substitutions are possible without departing from the spirit and scope of the invention as defined by the appended claims. It should be understood by those skilled in the art that the present invention may be changed in form, structure, arrangement, ratio, material, element, element, and other aspects without departing from the scope of the invention. Therefore, the embodiments disclosed herein are intended to be illustrative and not restrictive, and the scope of the invention is defined by the appended claims

100. . . Light source driving circuit

102. . . AC power

104. . . AC/DC converter

106. . . Power converter

108. . . Light-emitting diode string

110. . . switch

112. . . Dimming module

120. . . Pulse width modulation signal

200. . . Timing diagram

300. . . Light source driving circuit

302. . . AC power

304. . . AC/DC converter

306. . . Power converter

308. . . Light-emitting diode string

310. . . switch

312. . . Dimming module

320. . . Frequency controller

400. . . Light source driving circuit

402. . . Frequency detector

404. . . Frequency converter

406. . . Logic circuit

410, 412. . . Counting module

414. . . Multiplexer

420. . . counter

422. . . Comparators

500. . . Timing diagram

510, 512. . . Counting module

514. . . Register

700. . . Light source driving circuit

702. . . Controller

704. . . Conversion controller

706. . . Logic module

800. . . flow chart

802, 804, 806, 808, 810. . . step

The technical method of the present invention will be described in detail below in conjunction with the accompanying drawings and specific embodiments to make the features and advantages of the present invention more obvious. among them:

FIG. 1 is a schematic diagram of a light source driving circuit of the prior art.

FIG. 2 is a timing diagram of signals generated by a prior art light source driving circuit.

3 is a schematic diagram of a light source driving circuit in accordance with an embodiment of the present invention.

4 is a schematic diagram of a light source driving circuit in accordance with an embodiment of the present invention.

Figure 5 is a timing diagram of signals received and generated by a frequency converter in accordance with an embodiment of the present invention.

6 is another schematic diagram of a frequency controller in accordance with an embodiment of the present invention.

FIG. 7 is a schematic diagram of a light source driving circuit according to another embodiment of the present invention.

FIG. 8 is a flow chart showing the operation of a light source driving circuit according to an embodiment of the present invention.

300. . . Light source driving circuit

302. . . AC power

304. . . AC/DC converter

306. . . Power converter

308. . . Light-emitting diode string

310. . . switch

312. . . Dimming module

320. . . Frequency controller

Claims (22)

A light source driving circuit includes: a frequency controller that receives a first dimming signal to control a light source to reach a predetermined brightness, and when a frequency of the first dimming signal is within a predetermined range, The frequency controller generates a second dimming signal according to the first dimming signal, wherein a frequency of the second dimming signal is outside the preset range; and a switch module coupled to the frequency control The switch module is alternately turned on and off according to the second dimming signal when the frequency of the first dimming signal is within the preset range, and when the first dimming signal is When the frequency is outside the preset range, the switch module is alternately turned on and off according to the first dimming signal, so that the light source reaches the preset brightness. The light source driving circuit of claim 1, wherein the first dimming signal and the second dimming signal comprise a pulse width modulation signal, wherein the first dimming signal and the second dimming Signals have the same duty cycle. The light source driving circuit of claim 1, wherein the frequency controller comprises: a frequency converter, multiplying a period of the first dimming signal and an on-time by a same value to generate the first Two dimming signals. The light source driving circuit of claim 3, wherein the value is adjusted according to the frequency of the first dimming signal. The light source driving circuit of claim 1, wherein the frequency controller comprises: a frequency converter, calculating a number of loops of a first sampling clock signal to obtain a result data indicating a period and a duty cycle of the first dimming signal, and calculating a second according to the result data The number of turns of the clock signal is sampled to generate the second dimming signal. The light source driving circuit of claim 5, wherein a frequency of the second dimming signal is a fraction of the frequency of the first dimming signal, wherein the fraction is determined by the second sampling clock signal The ratio of the frequency to the frequency of the first sampled clock signal is determined. The light source driving circuit of claim 5, wherein the frequency converter further comprises: two counting modules, alternately calculating the number of the loops of the first sampling clock signal and the second sampling clock The number of loops of the signal. The light source driving circuit of claim 5, wherein the frequency converter further comprises: a first counting module, calculating the number of the loops of the first sampling clock signal, and storing the result data to And a second counting module coupled to the register, and calculating the number of the loops of the second sampling clock signal according to the result data to generate the second dimming signal. The light source driving circuit of claim 1, wherein the light source comprises one or more light emitting diodes. The light source driving circuit of claim 1, further comprising: a power converter coupled to the light source to convert a first DC voltage And switching to a second DC voltage to drive the light source; and a logic module coupled to the power converter and the frequency controller, detecting the switch mode according to the first dimming signal and the second dimming signal Group, when the switch module is disconnected, the operation of the power converter is stopped. A light source driving method includes: receiving a first dimming signal to control a light source to reach a predetermined brightness; and when a frequency of the first dimming signal is within a predetermined range, according to the first dimming The signal generates a second dimming signal, wherein a frequency of the second dimming signal is outside the preset range; when the frequency of the first dimming signal is within the preset range, according to the The second dimming signal controls the light source to achieve the preset brightness; and when the frequency of the first dimming signal is outside the preset range, the light source is controlled according to the first dimming signal to achieve The preset brightness. The method of claim 11, further comprising: maintaining a duty cycle of the first dimming signal and the second dimming signal, wherein the first dimming signal and the second dimming signal comprise a pulse Wave width modulation signal. The method of claim 11, further comprising: multiplying a period of the first dimming signal and an on-time by the same value to generate the second dimming signal. The method of claim 13, further comprising: adjusting the value according to the frequency of the first dimming signal. The method of claim 11, further comprising: calculating a number of loops of a first sampling clock signal to obtain a result data indicating a period and a duty cycle of the first dimming signal; Calculating a number of loops of a second sampling clock signal according to the result data, to generate the second dimming signal, wherein the frequency of the second dimming signal is the frequency of the first dimming signal The score, and the score is determined by a ratio between a frequency of the second sampled clock signal and a frequency of the first sampled clock signal. The method of claim 11, further comprising: converting a first DC voltage to a second DC voltage by using a power converter to drive the light source; and according to the first dimming signal and the second tone The optical signal stops the operation of the power converter. A light source dimming controller includes: a frequency controller that receives a first dimming signal to control energy transmitted to a light source to cause the light source to reach a predetermined brightness, when the first dimming signal is one of the first dimming signals When the frequency is within a predetermined range, generating a second dimming signal that is one of the frequencies outside the preset range according to the first dimming signal, and alternately turning on and off according to a selected dimming signal Coupling to a switch of the light source to enable the light source to reach the preset brightness, wherein when the frequency of the first dimming signal is outside the preset range, the selected dimming signal includes the a first dimming signal, when the frequency of the first dimming signal is within the preset range The selected dimming signal includes the second dimming signal; and a logic module coupled to the frequency controller to detect the selected dimming signal, and when the selected dimming signal indicates the switch is off When turned on, operation of a power converter is stopped, wherein operation of the power converter includes providing a voltage to drive the light source. The light source dimming controller of claim 17, wherein the first dimming signal and the second dimming signal comprise a pulse width modulation signal, wherein the first dimming signal and the second Dimming signals have the same duty cycle. The light source dimming controller of claim 17, wherein the frequency controller comprises: a frequency converter, calculating a number of loops of a first sampling clock signal to obtain the first dimming A result of a period of the signal and a period of the duty cycle, and calculating a number of loops of the second sample clock signal according to the result data to generate the second dimming signal. The light source dimming controller of claim 19, wherein the frequency of the second dimming signal is a fraction of the frequency of the first dimming signal, and the fraction is determined by the second sampling A ratio between a frequency of the pulse signal and a frequency of the first sampled clock signal is determined. The light source dimming controller of claim 17, wherein the light source comprises one or more light emitting diodes. The light source dimming controller of claim 17, wherein the power converter is a combination of a buck converter, a boost converter, a buck-boost converter, or a flyback converter. Among them one.