TWI420975B - Light-source driving circuit, back-light module and liquid crystal display - Google Patents

Description

Light source driving circuit, backlight module and liquid crystal display

The present invention relates to a light source driving circuit, and more particularly to a light source driving circuit capable of simultaneously improving a dimming range and brightness uniformity.

Liquid crystal displays use the optical activity and electro-optical properties of liquid crystal materials to display information. However, liquid crystal materials do not have illuminating properties. Therefore, an external backlight is required to provide a light source to make information visible, and other devices are A so-called backlight unit. Most of the current backlight modules use cold cathode fluorescent lamps (CCFLs) as light-emitting elements. The main reason is that cold cathode lamps are inexpensive and mature in technology.

On the other hand, dimming is a very important additional function of the backlight module, and its purpose is to enable the backlight module to save more power when the ambient brightness allows. The dimming methods of common cold cathode fluorescent lamps include analog dimming and burst dimming. The analog dimming changes the average current flowing through the lamp by adjusting the amplitude of the AC signal driving the lamp. Furthermore, as shown in FIG. 1A, the pulse dimming changes the length of time during which the lamp is turned on and off by adjusting the duty cycle of the AC signal S _AC11 , thereby controlling the average brightness of the lamp. effect.

Overall, analog dimming is simpler, but its disadvantage is that the dimming range is limited and the conversion efficiency of the lamp is poor at low brightness. Relatively speaking, pulse dimming has the advantage of a large dimming range, and as shown in FIG. 1B, recently, analog dimming is used together with pulse dimming to make the backlight module have a larger dimming range. . Referring to FIG. 1B, the dimming mode is to change the amplitude of the AC signal S _AC12 by using the level of the mode control signal S _ADIM1 . For example, when the level of the mode control signal S _ADIM1 is adjusted to 3.3V, 1.6V or 0V, the amplitude of the AC signal S _AC12 will be maintained at a different magnitude. In contrast, after the mode control signal S _ADIM1 is selected, the backlight module can adjust the duty cycle of the AC signal S _AC12 to achieve dimming control.

However, when the current flowing through the cold cathode fluorescent tube is low, that is, when the level of the mode control signal S _ADIM1 is adjusted to 0V, the cold cathode fluorescent tube will exhibit low temperature oscillation and lamp mura. Or leakage current (Lakage current) and other phenomena, which in turn cause uneven brightness provided by the backlight module and affect the picture quality of the liquid crystal display. In other words, how to improve the dimming range of the backlight module while taking into account the picture quality of the liquid crystal display has become a problem that various manufacturers have tried their best to solve.

The invention provides a light source driving circuit, which reduces the low temperature oscillation, the lamp defect or the leakage current of the light emitting element due to the low current by utilizing the method of increasing the current flowing through the light emitting element and reducing the duty cycle of the alternating current signal. .

The present invention provides a backlight module that utilizes a dimming mechanism provided by a light source driving circuit to cause a uniform light source to be emitted when the light emitting element is in a low current mode.

The invention provides a liquid crystal display, which can improve the dimming range of the backlight module while taking into consideration the quality of the display screen.

The invention provides a light source driving circuit comprising a voltage converter and a dimming control unit. The voltage converter is configured to convert the continuous stream signal into an alternating current signal to drive a light emitting element according to a mode control signal and a period control signal. The dimming control unit is used to adjust the mode control signal and the period control signal. Wherein, when the level of the mode control signal is switched to a first level to maintain the light-emitting element in a low current mode, the dimming control unit controls the signal level by adjusting the period control signal and the switching mode. The second level causes the light-emitting element to change the low current mode and maintain the overall brightness.

The present invention further provides a backlight module including a light emitting element and the above light source driving circuit. The light source driving circuit is configured to generate an alternating current signal to drive the light emitting element to generate a light source.

The invention further provides a liquid crystal display comprising a substrate and the above backlight module. The substrate includes a plurality of pixels to present an image. The backlight module is used to provide a light source required for displaying images on the substrate.

In one embodiment of the light source driving circuit, the backlight module and the liquid crystal display, the light emitting element is a cold cathode fluorescent tube.

The invention reduces the duty cycle of the alternating current signal by adjusting the impedance ratio of the periodic converter when the light emitting element is maintained in the low current mode, and uses the mode converter to adjust the feedback signal or the reference signal to improve the flow of the light. The current of the component. Thereby, compared with the prior art, the invention improves the dimming range of the backlight module, and also improves the brightness of the light-emitting element. Degree of uniformity.

The above described features and advantages of the present invention will be more apparent from the following description.

2 is a block diagram of a light source driving circuit in accordance with an embodiment of the present invention. The light source driving circuit 200 is configured to generate an alternating current signal S _AC to drive the light emitting element 201 to generate a light source. In addition, the light source driving circuit 200 includes a voltage converter 210, a feedback circuit 230, and a dimming control unit 220. In the present embodiment, the light-emitting element 201 is, for example, a cold cathode fluorescent lamp.

Referring to FIG. 2, the voltage converter 210 converts the _DC signal S _DC into an AC signal S _AC according to a mode control signal S _ADIM and a period control signal S _IE . The dimming control unit 220 is configured to adjust the mode control signal S _ADIM and the period control signal S _IE . When the level of the mode control signal S _ADIM is switched to a first level to maintain the light-emitting element 201 in a low current mode, the dimming control unit 220 will control the period control signal S _IE and the switching mode. The signal S _ADIM is at a second level, causing the light-emitting element 201 to change the low current mode and maintain the overall brightness.

Furthermore, the light source driving circuit 200 further includes a feedback circuit 230. In addition, the dimming control unit 220 includes a mode converter 221 and a period converter 222. The voltage converter 210 converts the DC signal S _DC into the AC signal S _AC according to the plurality of switching signals S21~S23. The feedback circuit 230 is configured to filter and rectify the AC signal S _AC to output the feedback signal S _FB to the mode converter 221. The mode converter 221 forms a loop with the voltage converter 210, the light-emitting element 201, and the feedback circuit 230 to generate switching signals S21-S23 to control the voltage converter 210.

In the operation mode of the loop, the mode converter 221 adjusts the integration of the feedback signal S _FB with reference signal S _RE based on the mode control signal S _ADIM , and generates an accumulated signal S _ACM . In addition, the mode converter 221 generates the switching signals S21 to S23 according to the accumulated signal S _ACM and the adjustment signal S _DIM . It is worth noting that, through the operation of the loop, the amplitude of the AC signal S _AC will be proportional to the level of the accumulating signal S _ACM , and the duty cycle of the AC signal S _AC will be proportional to the level of the adjustment signal S _DIM .

On the other hand, the cycle converter 222 may be generated based on an adjusted signal S _DIM impedance ratio, and according to the mode control signal S _ADIM cycle control signal and to control the level S _IE adjustment of the signal S _DIM. In this way, the light source driving circuit 200 will control the current flowing through the light emitting element 201 by the permeable mode control signal S _ADIM . When the current flowing through the light-emitting element 201 is selected, the light source driving circuit 200 can control the length of the light-emitting element 201 to be turned on and off according to the period control signal S _IE , thereby controlling the average brightness of the light-emitting element 201 .

However, it is worth noting that when the light source driving circuit 200 receives the mode control signal S _ADIM having the first level, the light emitting element 201 will remain in the low current mode. In addition, the period converter 222 will reduce the level of the adjustment signal S _DIM by adjusting the impedance ratio, and the mode converter 221 will increase the level of the accumulated signal S _ACM by adjusting the feedback signal S _FB or the reference signal S _RE . . Therefore, when the level of the mode control signal S _ADIM is switched to the first level, that is, when the light-emitting element 201 is maintained in the low current mode, the duty cycle of the AC signal S _AC will follow the level of the adjustment signal S _DIM . It decreases and becomes smaller, and the amplitude of the AC signal S _AC will become larger as the level of the accumulated signal S _ACM increases.

It is worth mentioning that the embodiment of FIG. 2 is compared with the prior art, FIG. 3A is a schematic diagram of the alignment of the dimming curve, and FIG. 3B is a schematic diagram of the waveform comparison of the alternating current signal, wherein the present case and the conventional method The dimming curves of the technology are denoted as 310 and 320, respectively, and the alternating signals generated by the _{prior art} and the _{prior art} are denoted as S _AC31 and S _{AC32 respectively} . Referring to FIG. 3A and FIG. 3B, it can be seen that when the light-emitting element is maintained in the low current mode, the amplitude of the alternating signal generated by the embodiment will be greater than that of the prior art. In addition, in order to satisfy the uniformity of the average brightness of the light-emitting elements, the present embodiment reduces the duty cycle of the alternating current signal by the period converter.

In other words, when the light-emitting element is maintained in the low current mode, the present embodiment will increase the current flowing through the light-emitting element and reduce the duty cycle of the alternating current signal. Therefore, the present embodiment can effectively reduce the phenomenon of low-temperature oscillation, lamp defect or leakage current of the light-emitting element due to low current, thereby improving the uniformity of the brightness of the light-emitting element.

In order to make the person skilled in the art more aware of the spirit of the embodiment, the internal architecture of the mode converter 221 and the period converter 222 will be further described below.

4 is a circuit diagram of a period converter in accordance with an embodiment of the present invention. Referring to FIG. 4, the period converter 222 includes an amplifier AMP ₁ , a switch SW ₁ , resistors R ₁ to R _{4 ,} and a capacitor C ₁ . The first input end of the amplifier AMP ₁ is used to receive the periodic control signal S _IE , and the second input end thereof is electrically connected to the reference voltage level LV ₁ . The first end of the resistor R ₁ is electrically connected to the first operating voltage V _CC , and the second end thereof is electrically connected to the output end of the amplifier AMP ₁ .

Furthermore, the first end of the resistor R ₂ is electrically connected to the output of the amplifier AMP ₁ . The first end of the switch SW ₁ is electrically connected to the second end of the resistor R ₂ , and the second end thereof is electrically connected to the second reference voltage (for example, a ground voltage). The resistor R _{3 is} electrically connected between the output of the amplifier AMP ₁ and the second reference voltage. The first end of the resistor R ₄ is electrically connected to the output end of the amplifier AMP ₁ , and the second end thereof is used to generate the adjustment signal S _DIM . The capacitor C ₁ is electrically connected between the second end of the resistor R ₄ and the ground.

In the overall operation, the period control signal S _IE of this embodiment is a Pulse-Width Modulation signal. This pulse width modulation signal is compared with the reference voltage level LV ₁ through the amplifier AMP ₁ . Thereafter, the signal output from the amplifier AMP ₁ is adjusted in the level by the impedance ratio formed by the resistors R ₁ to R ₃ . In other words, the impedance ratio depends on the resistance values of the resistors R ₁ to R ₃ . In addition, the signal outputted by the amplifier AMP ₁ charges and discharges the capacitor C ₁ through the resistor R ₄ , and generates the adjustment signal S _DIM at the second end of the resistor R ₄ .

It is worth noting that the impedance ratio formed by the resistors R ₁ to R ₃ is controlled by the mode control signal S _ADIM through the switch SW ₁ . Wherein, when the switch SW of the control terminal receives _a mode control signal S _ADIM having a first level, the switch SW ₁ is turned to its first and second ends. At this time, the resistors R ₂ and R ₃ will be connected in parallel to each other to lower the impedance ratio. In contrast, the level of the adjustment signal S _DIM will also decrease as the impedance ratio becomes smaller. In this way, when the level of the mode control signal S _ADIM is switched to the first level, that is, when the light-emitting element 201 is maintained in the low current mode, the duty cycle of the AC signal S _AC will be adjusted according to the adjustment signal S _DIM . The bit is reduced and becomes smaller.

FIG. 5 is a circuit diagram of a period converter according to another embodiment of the present invention. Referring to FIG. 5, the period converter 222 includes resistors R ₅ to R ₇ , a switch SW _{2 ,} and a diode D ₁ . The first end of the resistor R ₅ is configured to receive the periodic control signal S _IE . The first end of the resistor R ₆ is electrically connected to the second end of the resistor R ₅ . The first end of the switch SW ₂ is electrically connected to the second end of the resistor R ₆ , and the second end thereof is electrically connected to a third operating voltage (for example, a ground voltage). The diode D _{1 is} electrically connected between the first end of the resistor R ₅ and the third operating voltage, and the resistor R _{7 is} electrically connected between the second end of the resistor R ₅ and the third operating voltage.

In the overall operation, the period control signal S _IE of this embodiment is a DC voltage signal. The DC voltage signal is adjusted by the impedance ratio formed by the resistors R ₅ to R ₇ to transmit the adjustment signal S _DIM through the second end of the resistor R ₅ . In other words, the impedance ratio of the period converter 222 depends on the resistance values of the resistors R ₅ to R ₇ . In addition, the diode D ₁ functions as a voltage regulator and a rectification.

It is worth noting that the impedance ratio formed by the resistors R ₅ to R ₇ is controlled by the mode control signal S _ADIM through the switch SW ₂ . Wherein, when the control terminal of the switch SW ₂ receives the mode control signal S _ADIM having the first level, the switch SW ₂ will turn on the first end and the second end thereof. At this time, the resistors R ₆ and R ₇ are connected in parallel to each other to lower the impedance ratio. In contrast, the level of the adjustment signal S _DIM will also decrease as the impedance ratio becomes smaller. In this way, when the level of the mode control signal S _ADIM is switched to the first level, that is, when the light-emitting element 201 is in the low current mode, the duty cycle of the AC signal S _AC will be adjusted according to the adjustment signal S _DIM . The bit is reduced to become smaller, and the amplitude of the AC signal S _AC is simultaneously adjusted to maintain the overall brightness of the light-emitting element 201. The circuit design for adjusting the amplitude of the AC signal S _{AC will be} described below with reference to FIGS. 6 to 8.

6 is a partial circuit diagram of a mode converter in accordance with an embodiment of the present invention. Referring to FIG. 6, the mode converter 221 includes a resistor R ₈ , a capacitor C ₂ , a switch SW _{3 ,} and an amplifier AMP ₂ . The first end of the resistor is configured to receive the feedback signal S _FB . The first input of the amplifier AMP ₂ is electrically connected to the second end of the resistor R ₈ , and the second input thereof is used to receive the reference signal S _RE . The first end of the capacitor C ₂ is electrically connected to the first input of the amplifier AMP ₂ , and the second end thereof is electrically connected to the output end of the amplifier AMP ₂ . The first end of the switch SW ₃ is electrically connected to the second input end of the amplifier AMP ₂ , the second end thereof is electrically connected to the reference voltage level LV ₂ , and the third end thereof is electrically connected to the reference voltage level LV _{3 .} The fourth end is electrically connected to the reference voltage level LV ₄ , and the control end thereof is configured to receive the mode control signal S _ADIM .

In overall operation, resistor R ₈ , capacitor C ₂ and amplifier AMP ₂ form an integrator. Thereby, the mode converter 221 integrates the feedback signal S _FB with reference to the reference signal S _RE and generates an accumulated signal S _ACM through the output of the amplifier AMP ₂ . Since the mode converter 221 forms a loop with the voltage converter 210, the feedback circuit 230, and the light-emitting element 201, the level of the accumulated signal S _ACM will be proportional to the amplitude of the AC signal S _AC .

It is worth mentioning that, in this embodiment, the level of the reference signal S _RE received by the amplifier AMP ₂ is adjustable. For example, when the switch SW ₃ conducts its first end and the second end, the reference signal S _RE will be maintained at the reference voltage level LV ₂ . In contrast, when the switch SW ₃ conducts its first end and the third end, the reference signal S _RE will be maintained at the reference voltage level LV ₃ .

On the other hand, the on state of the switch SW ₃ is controlled by the mode control signal S _ADIM . When the mode converter 221 receives the mode control signal S _ADIM having the first level, the switch SW ₃ will adjust its conduction state and further cause the level of the reference signal S _RE to rise. In contrast, the level of the accumulated signal S _ACM will also increase as the level of the reference signal S _RE increases. In other words, when the level of the mode control signal S _ADIM is switched to the first level, that is, when the light-emitting element 201 is maintained in the low current mode, the amplitude of the AC signal S _AC will be in _accordance with the accumulating signal S _ACM . The bit rises and becomes larger.

7 is a partial circuit diagram of a mode converter in accordance with another embodiment of the present invention. Referring to FIG. 7, the mode converter 221 includes resistors R ₉ to R ₁₃ , a capacitor C _{3 ,} and amplifiers AMP ₃ to AMP ₄ . The first end of the resistor R ₉ is configured to receive the mode control signal S _ADIM having the first level. A first input terminal of the amplifier AMP ₃ is electrically connected to the second end of resistor R _9. The first end of the resistor R ₁₀ is electrically connected to the second input end of the amplifier AMP ₃ , and the second end thereof is electrically connected to the ground end.

Moreover, the first end of the resistor R ₁₁ is electrically connected to the first input end of the amplifier AMP ₃ , and the second end thereof is electrically connected to the output end of the amplifier AMP ₃ . A first end of the resistor R ₁₂ is electrically coupled to an output of the amplifier. The first input end of the amplifier AMP ₄ is electrically connected to the second ends of the resistors R ₁₂ and R ₁₃ , and the second input end thereof is electrically connected to the preset voltage level LV _PR . The first end of the capacitor C ₃ is electrically connected to the first input end of the amplifier AMP ₄ , and the second end thereof is electrically connected to the output end of the amplifier AMP ₄ .

Referring to FIG. 7, the resistor R ₁₃ , the capacitor C ₃ and the amplifier AMP ₄ form an integrator. Thereby, the mode converter 221 integrates the feedback signal S _FB with reference to the reference signal S _RE and generates an accumulated signal S _ACM through the output of the amplifier AMP ₄ . It should be noted that, in this embodiment, since the second input end of the amplifier AMP ₄ is electrically connected to the preset voltage level LV _PR , the reference signal S _RE received by the first input of the amplifier AMP ₄ is Its level will remain at the preset voltage level LV _PR .

On the other hand, the resistors R ₉ to R ₁₁ and the amplifier AMP ₃ constitute an inverting amplifier. Therefore, when the mode converter 221 receives the mode control signal S _ADIM having the first level, the output of the amplifier AMP ₃ will generate a negative voltage signal. The negative voltage signal is transmitted through the resistor R ₁₂ to the first input of the amplifier AMP ₄ , which in turn causes the level of the feedback signal S _FB to rise. In contrast, the level of the accumulated signal S _ACM will also increase as the level of the feedback signal S _FB increases. In other words, when the light-emitting element 201 is maintained in the low current mode, the amplitude of the alternating current signal S _AC will become larger as the level of the accumulated signal S _ACM rises.

FIG. 8 is a partial circuit diagram of a mode converter according to still another embodiment of the present invention. Referring to FIG. 8, the mode converter 221 includes resistors R ₁₄ to R ₁₇ , a capacitor C ₄ , switches SW ₄ to SW _{5 ,} and an amplifier AMP ₅ . The first end of the resistor R ₁₅ is electrically connected to the first end of the resistor R ₁₄ , and the second end thereof is electrically connected to the ground end. The first end of the switch SW ₄ is electrically connected to the first end of the resistor R ₁₅ , and the second end thereof is electrically connected to the first end of the resistor R ₁₆ .

Moreover, the first end of the switch SW ₅ is electrically connected to the first end of the resistor R ₁₅ , and the second end thereof is electrically connected to the first end of the resistor R ₁₇ . The second ends of the resistors R ₁₆ and R ₁₇ are electrically connected to the ground. The first input end of the amplifier AMP ₅ is electrically connected to the second end of the resistor R ₁₄ , and the second input end thereof is electrically connected to the preset voltage level LV _PR . The first end of the capacitor C ₄ is electrically connected to the first input end of the amplifier AMP ₅ , and the second end thereof is electrically connected to the output end of the amplifier AMP ₅ .

Referring to FIG. 8, the resistor R ₁₄ , the capacitor C ₄ and the amplifier AMP ₅ form an integrator. Thereby, the mode converter 221 integrates the feedback signal S _FB with reference to the reference signal S _RE and generates an accumulated signal S _ACM through the output of the amplifier AMP ₅ . It should be noted that, in this embodiment, since the second input end of the amplifier AMP ₅ is electrically connected to the preset voltage level LV _PR , the reference signal S _RE received by the first input of the amplifier AMP ₅ is Its level will remain at the preset voltage level LV _PR .

On the other hand, the equivalent resistance between node N1 and ground will be controlled by mode switch signal S _ADIM through switches SW ₄ and SW ₅ . For example, when the switch SW _{4 is} turned on, the resistor R ₁₆ and the resistor R _{15 are} electrically connected in parallel with each other. At this point, the equivalent resistance between node N1 and ground will decrease. In contrast, when the switch SW _{5 is} turned on, the equivalent resistance between the node N1 and the ground will decrease. It is known that when the equivalent resistance between the node N1 and the ground is lowered, the level of the feedback signal S _FB will also rise, thereby increasing the level of the accumulated signal S _ACM . Therefore, when the switches SW ₄ and SW ₅ turn on the first end and the second end according to the mode control signal S _ADIM having the first level, that is, when the light emitting element 201 is maintained in the low current mode, the AC signal S _AC The amplitude will increase as the level of the accumulated signal S _ACM rises.

FIG. 9 is a circuit block diagram of a liquid crystal display according to an embodiment of the invention. Referring to FIG. 9 , the liquid crystal display 900 of the present embodiment includes a substrate 910 and a backlight module 920 , and the backlight module 920 includes a light source driving circuit 921 and a light emitting element 922 . The light source driving circuit 921 can be the above-mentioned light source driving circuit 200 (shown in FIG. 2) or other light source driving circuits having the same technical features of the present invention. In addition, the substrate 910 includes a plurality of pixels (not shown), and the backlight module 920 is used to provide a light source required for the substrate 910 to display an image. The other members of the present embodiment and their arrangement relationships are similar to those of the above embodiments, and thus will not be described herein.

In summary, the present invention improves the duty cycle of the alternating current signal by adjusting the impedance ratio of the periodic converter when the light emitting element is switched to the low current mode, and uses the mode converter to adjust the feedback signal or the reference signal. The current flowing through the light-emitting element maintains the overall brightness of the light-emitting element. Therefore, the present embodiment can effectively reduce the phenomenon of low-temperature oscillation, lamp defect or leakage current of the light-emitting element due to low current, thereby improving the uniformity of the brightness of the light-emitting element.

Although the present invention has been disclosed in the above preferred embodiments, it is not intended to limit the invention, and any one of ordinary skill in the art can make some modifications and refinements without departing from the spirit and scope of the invention. Therefore, the scope of the invention is defined by the scope of the appended claims.

200, 921‧‧‧Light source drive circuit

201, 922‧‧‧Lighting elements

210‧‧‧Voltage Converter

230‧‧‧Return circuit

221‧‧‧Mode Converter

222‧‧‧cycle converter

310, 320‧‧‧ dimming curve

900‧‧‧LCD display

910‧‧‧Substrate

920‧‧‧Backlight module

AMP ₁ ~ AMP ₅ ‧ ‧ amplifier

SW ₁ ~SW ₅ ‧‧‧Switch

R ₁ ~R ₁₇ ‧‧‧resistance

C ₁ ~ C ₄ ‧‧‧ capacitor

D ₁ ‧‧‧ diode

S _DC ‧‧‧DC signal

S _AC11 , S _AC12 , S _AC , S _AC31 , S _AC32 ‧‧‧ AC signal

S _FB ‧‧‧Response signal

S _ADIM1 , S _ADIM ‧‧‧ mode control signals

S _DIM ‧‧‧Adjustment signal

S _IE ‧ ‧ cycle control signal

S _ACM ‧‧‧Accumulate signal

S21~S23‧‧‧Switch signal

LV ₁ ~LV ₄ ‧‧‧reference voltage level

LV _PR ‧‧‧Preset voltage level

FIG. 1A is a schematic diagram showing the waveform of pulse dimming.

FIG. 1B is a schematic diagram showing waveforms of analog dimming and pulse dimming.

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

FIG. 3A is a schematic diagram showing the alignment of the dimming curve of the embodiment of FIG. 2 and the prior art. FIG.

FIG. 3B is a schematic diagram showing the waveform comparison of the alternating signal of the embodiment of FIG. 2 and the prior art. FIG.

4 is a circuit diagram of a period converter in accordance with an embodiment of the present invention.

FIG. 5 is a circuit diagram of a period converter according to another embodiment of the present invention.

6 is a partial circuit diagram of a mode converter in accordance with an embodiment of the present invention.

7 is a partial circuit diagram of a mode converter in accordance with another embodiment of the present invention.

FIG. 8 is a partial circuit diagram of a mode converter according to still another embodiment of the present invention.

FIG. 9 is a circuit block diagram of a liquid crystal display according to an embodiment of the invention.

200‧‧‧Light source drive circuit

201‧‧‧Lighting elements

210‧‧‧Voltage Converter

230‧‧‧Return circuit

221‧‧‧Mode Converter

222‧‧‧cycle converter

S _DC ‧‧‧DC signal

S _AC ‧‧‧Communication signal

S _FB ‧‧‧Response signal

S _ADIM ‧‧‧ mode control signal

S _DIM ‧‧‧Adjustment signal

S _IE ‧ ‧ cycle control signal

S21~S23‧‧‧Switch signal

Claims (27)

A light source driving circuit comprising: a voltage converter for converting a constant current signal into an alternating current signal to drive a light emitting element according to a mode control signal and a period control signal; and a dimming control unit for adjusting the mode control a signal and the period control signal, wherein when the level of the mode control signal is switched to a first level to maintain the light emitting element in a low current mode, the dimming control unit adjusts the period control signal by Switching the mode control signal level to a second level causes the light emitting element to change the low current mode and maintain the overall brightness. The light source driving circuit of claim 1, wherein the dimming control unit further comprises a period converter, and when the period control signal is a pulse width modulation signal, the period converter comprises: a first An amplifier having a first input for receiving the periodic control signal, and a second input electrically coupled to a first reference voltage level; a first resistor electrically coupled to the first end Operating a voltage, and the second end thereof is electrically connected to the output end of the first amplifier; a second resistor, the first end of which is electrically connected to the output end of the first amplifier; a first switch, the first end thereof Electrically connected to the second end of the second resistor, and the second end thereof is electrically connected to a second operating voltage, wherein the operation of the first switch is based on the mode control signal; a third resistor is electrically connected At the output of the first amplifier and the a second resistor, a first end electrically connected to the output end of the first amplifier, and a second end of the output signal to adjust the period control signal; and a first capacitor, The connection is between the second end of the fourth resistor and the second operating voltage. The light source driving circuit of claim 2, wherein the periodic converter adjusts the periodic control signal according to an impedance ratio, wherein the impedance ratio is substantially according to the first resistance, the second resistance, and the The impedance value of the third resistor. The light source driving circuit of claim 1, wherein the dimming control unit further comprises a period converter, wherein when the period control signal is a DC voltage signal, the period converter comprises: a fifth resistor, The first end is configured to receive the periodic control signal; the sixth end is electrically connected to the second end of the fifth resistor; and the second end is electrically connected to the sixth end a second end of the resistor, and a second end thereof is electrically connected to a third operating voltage, wherein the operation of the second switch controls the signal according to the mode; a diode is electrically connected to the fifth resistor One end is connected to the third operating voltage; and a seventh resistor is electrically connected between the second end of the fifth resistor and the third operating voltage. The light source driving circuit as described in claim 4, wherein The period converter adjusts the period control signal according to an impedance ratio, and the magnitude of the impedance ratio is substantially based on impedance values of the fifth resistor, the sixth resistor, and the seventh resistor. The light source driving circuit of claim 1, wherein the dimming control unit further comprises a mode converter, the mode converter comprising: an eighth resistor, wherein the first end is configured to receive a feedback signal; a second amplifier having a first input electrically coupled to the second end of the eighth resistor, and an output signal for adjusting the mode control signal; a second capacitor having a first end electrically coupled to the second a first input end of the second amplifier, and a second end thereof is electrically connected to the output end of the second amplifier; and a third switch having a second input end electrically connected to the second amplifier, according to the second input end The mode control signal determines a reference signal. The light source driving circuit of claim 1, wherein the dimming control unit comprises a mode converter, the mode converter comprising: a ninth resistor, wherein the first end is configured to receive the mode control signal; a third amplifier having a first input electrically coupled to the second end of the ninth resistor; a tenth resistor having a first end electrically coupled to the second input of the third amplifier and a second end thereof Electrically connected to the ground; an eleventh resistor, the first end of which is electrically connected to the first input end of the third amplifier, and the second end of which is electrically connected to the output end of the third amplifier; a twelve resistor, the first end of which is electrically connected to the third amplifier An output end; a thirteenth resistor, the first end of which is configured to receive a feedback signal; and a fourth amplifier, the first input end of which is electrically connected to the twelfth resistor and the second end of the thirteenth resistor The second input is electrically connected to a predetermined voltage level, and the output signal is used to adjust the mode control signal; and a third capacitor is electrically connected to the first end of the fourth amplifier. The input terminal and the second end thereof are electrically connected to the output end of the fourth amplifier. The light source driving circuit of claim 1, wherein the dimming control unit further comprises a mode converter, the mode converter comprising: a fourteenth resistor, the first end of which is configured to receive a feedback signal a fifteenth resistor, the first end of which is electrically connected to the first end of the fourteenth resistor, and the second end thereof is electrically connected to the ground end; a sixteenth resistor, the second end of which is electrically connected a fourth switch, the first end of which is electrically connected to the first end of the fifteenth resistor, and the second end of which is electrically connected to the first end of the sixteenth resistor, wherein the first end The operation of the four switches is based on the mode control signal; a seventeenth resistor, the second end of which is electrically connected to the ground end; and a fifth switch, the first end of which is electrically connected to the first end of the fifteenth resistor And the second end is electrically connected to the first end of the seventeenth resistor, wherein the operation of the fifth switch is based on the mode control signal; a fifth amplifier, the first input is electrically connected to the The second end of the fourteenth resistor is electrically connected to a predetermined voltage Bit, and its output signal is used to adjust the mode control signal; a fourth capacitor having a first end electrically coupled to the first input of the fifth amplifier and a second end electrically coupled to the output of the fifth amplifier. The light source driving circuit of claim 1, wherein the light emitting element is a cold cathode fluorescent lamp. A backlight module includes: a light emitting component; and a light source driving circuit comprising: a voltage converter for converting a direct current signal into an alternating current signal to drive the light emitting component according to a mode control signal and a period control signal; and a dimming control unit configured to adjust the mode control signal and the period control signal; wherein when the level of the mode control signal is switched to a first level to maintain the light emitting element in a low current mode, the adjusting The light control unit adjusts the period control signal and switches the mode control signal to a second level, so that the light emitting element changes the low current mode and maintains the overall brightness. The backlight module of claim 10, wherein the dimming control unit further comprises a period converter, and when the period control signal is a pulse width modulation signal, the period converter comprises: a first An amplifier having a first input for receiving the periodic control signal, and a second input electrically coupled to a first reference voltage level; a first resistor electrically coupled to the first end Operating a voltage, and the second end thereof is electrically connected to the output end of the first amplifier; a second resistor, the first end of which is electrically connected to the input of the first amplifier a first switch, the first end of which is electrically connected to the second end of the second resistor, and the second end thereof is electrically connected to a second operating voltage, wherein the operation of the first switch is a mode control signal; a third resistor electrically connected between the output of the first amplifier and the second operating voltage; a fourth resistor having a first end electrically connected to the output of the first amplifier, And the second end is configured to output a signal to adjust the period control signal; and a first capacitor is electrically connected between the second end of the fourth resistor and the second operating voltage. The backlight module of claim 11, wherein the period converter adjusts the period control signal according to an impedance ratio, wherein the impedance ratio is substantially according to the first resistor, the second resistor, and the The impedance value of the third resistor. The backlight module of claim 10, wherein the dimming control unit further comprises a period converter, wherein when the period control signal is a DC voltage signal, the period converter comprises: a fifth resistor, The first end is configured to receive the periodic control signal; the sixth end is electrically connected to the second end of the fifth resistor; and the second end is electrically connected to the sixth end a second end of the resistor, and the second end thereof is electrically connected to a third operating voltage, wherein the operation of the second switch controls the signal according to the mode; a diode connected electrically between the first end of the fifth resistor and the third operating voltage; and a seventh resistor electrically connected to the second end of the fifth resistor and the third operating voltage between. The backlight module of claim 13, wherein the period converter adjusts the period control signal according to an impedance ratio, wherein the impedance ratio is substantially according to the fifth resistor, the sixth resistor, and the The impedance value of the seventh resistor. The backlight module of claim 10, wherein the dimming control unit further comprises a mode converter, the mode converter comprising: an eighth resistor, the first end of which is configured to receive a feedback signal; a second amplifier having a first input electrically coupled to the second end of the eighth resistor, and an output signal for adjusting the mode control signal; a second capacitor having a first end electrically coupled to the second a first input end of the second amplifier, and a second end thereof is electrically connected to the output end of the second amplifier; and a third switch having a second input end electrically connected to the second amplifier, according to the second input end The mode control signal determines a reference signal. The backlight module of claim 10, wherein the dimming control unit further comprises a mode converter, the mode converter comprising: a ninth resistor, the first end of which is configured to receive the mode control signal; a third amplifier having a first input electrically coupled to the second end of the ninth resistor; a tenth resistor having a first end electrically coupled to the third amplifier a second input end, wherein the second end is electrically connected to the ground end; an eleventh resistor, the first end is electrically connected to the first input end of the third amplifier, and the second end thereof is electrically connected to the An output end of the third amplifier; a twelfth resistor, the first end of which is electrically connected to the output end of the third amplifier; a thirteenth resistor, the first end of which is configured to receive a feedback signal; An amplifier, the first input end is electrically connected to the twelfth resistor and the second end of the thirteenth resistor, the second input end is electrically connected to the preset voltage level, and the output signal is used for adjusting The mode control signal; and a third capacitor, the first end of which is electrically connected to the first input end of the fourth amplifier, and the second end of which is electrically connected to the output end of the fourth amplifier. The backlight module of claim 10, wherein the dimming control unit further comprises a mode converter, the mode converter comprising: a fourteenth resistor, wherein the first end is configured to receive the feedback signal a fifteenth resistor, the first end of which is electrically connected to the first end of the fourteenth resistor, and the second end thereof is electrically connected to the ground end; a sixteenth resistor, the second end of which is electrically connected a fourth switch, the first end of which is electrically connected to the first end of the fifteenth resistor, and the second end of which is electrically connected to the first end of the sixteenth resistor, wherein the first end The operation of the four switches is based on the mode control signal; a seventeenth resistor, the second end of which is electrically connected to the ground end; and a fifth switch whose first end is electrically connected to the fifteenth resistor One end, and the second end thereof is electrically connected to the first end of the seventeenth resistor, wherein the operation of the fifth switch is based on; a fifth amplifier, the first input end of which is electrically connected to the fourteenth a second end of the resistor, the second input end is electrically connected to a predetermined voltage level, and an output signal is used to adjust the mode control signal; and a fourth capacitor is electrically connected to the first end The first input of the fifth amplifier, and the second end of the fifth amplifier is electrically connected to the output of the fifth amplifier. The backlight module of claim 10, wherein the light emitting element is a cold cathode fluorescent tube. A liquid crystal display comprising: a substrate comprising a plurality of pixels; and a backlight module for providing a light source required for displaying the image on the substrate, the backlight module comprising: a light emitting element; and a light source driving circuit comprising a voltage converter that converts a continuous stream signal into the alternating current signal to drive the light emitting element according to a mode control signal and a period control signal; and a dimming control unit for adjusting the mode control signal and the period control a signal; wherein when the level of the mode control signal is switched to a first level to maintain the light-emitting element in a low current mode, the dimming control unit adjusts the period control signal and switches the mode control signal a second level, causing the light emitting element to change the low current mode and maintaining the light emitting element The overall brightness does not change. The liquid crystal display according to claim 19, wherein the dimming control unit further comprises a period converter, and when the period control signal is a pulse width modulation signal, the period converter comprises: a first An amplifier, the first input end is configured to receive the periodic control signal, and the second input end is electrically connected to a first reference voltage level; a first resistor is electrically connected to the first end of the first operation a voltage, and a second end thereof is electrically connected to the output end of the first amplifier; a second resistor is electrically connected to the output end of the first amplifier; and a first switch is electrically connected to the first end Connected to the second end of the second resistor, and the second end thereof is electrically connected to the second operating voltage, wherein the operation of the first switch is based on the mode control signal; a third resistor is electrically connected to the a first resistor is coupled between the output terminal and the second operating voltage; a fourth resistor is electrically coupled to the output of the first amplifier, and a second terminal is configured to output a signal to adjust the period control Signal; and a first electric Electrically connected between the second terminal of the fourth resistor to the second operating voltage. The liquid crystal display according to claim 20, wherein the period converter adjusts the period control signal according to an impedance ratio, wherein the impedance ratio is substantially according to the first resistor, the second resistor, and the first The impedance value of the three resistors. The liquid crystal display of claim 20, wherein the dimming control unit further comprises a period converter, wherein when the period control signal is a DC voltage signal, the period converter comprises: a fifth resistor, The first end is configured to receive the periodic control signal; the sixth end is electrically connected to the second end of the fifth resistor; and the second end is electrically connected to the sixth resistor The second end is electrically connected to a third operating voltage, wherein the operation of the second switch controls the signal according to the mode; a diode is electrically connected to the first of the fifth resistor And between the terminal and the third operating voltage; and a seventh resistor electrically connected between the second end of the fifth resistor and the third operating voltage. The liquid crystal display according to claim 22, wherein the period converter adjusts the period control signal according to an impedance ratio, wherein the impedance ratio is substantially according to the fifth resistor, the sixth resistor, and the first The impedance value of the seven resistors. The liquid crystal display of claim 19, wherein the dimming control unit further comprises a mode converter, the mode converter comprising: an eighth resistor, the first end of which is configured to receive a feedback signal; a second amplifier having a first input electrically coupled to the second end of the eighth resistor, and an output signal for adjusting the mode control signal; a second capacitor having a first end electrically coupled to the second a first input of the amplifier, and a second end of the amplifier is electrically connected to the output of the second amplifier And a third switch having a second input electrically connected to the second amplifier for determining a reference signal according to the mode control signal. The liquid crystal display of claim 19, wherein the dimming control unit further comprises a mode converter, the mode converter comprising: a ninth resistor, the first end of which is configured to receive the mode control signal; a third amplifier having a first input electrically coupled to the second end of the ninth resistor; a tenth resistor having a first end electrically coupled to the second input of the third amplifier and a second end thereof Electrically connected to the ground; an eleventh resistor, the first end of which is electrically connected to the first input end of the third amplifier, and the second end of which is electrically connected to the output end of the third amplifier; a first resistor electrically coupled to the output of the third amplifier; a thirteenth resistor having a first end for receiving a feedback signal; and a fourth amplifier for first electrical input Connected to the twelfth resistor and the second end of the thirteenth resistor, the second input end is electrically connected to the predetermined voltage level, and the output signal thereof is used to adjust the mode control signal; a three capacitor, the first end of which is electrically connected to the fourth amplification A first input terminal, and a second end electrically connected to an output terminal of the fourth amplifier. The liquid crystal display of claim 19, wherein the dimming control unit further comprises a mode converter, the mode converter comprising: a fourteenth resistor, the first end of which is configured to receive a feedback signal; a fifteenth resistor, the first end of which is electrically connected to the first end of the fourteenth resistor, and the second end thereof is electrically connected a grounding end; a sixteenth resistor, the second end of which is electrically connected to the grounding end; a fourth switch, the first end of which is electrically connected to the first end of the fifteenth resistor, and the second end thereof is electrically Connected to the first end of the sixteenth resistor, wherein the operation of the fourth switch is based on the mode control signal; a seventeenth resistor, the second end of which is electrically connected to the ground; a fifth switch, The first end is electrically connected to the first end of the fifteenth resistor, and the second end thereof is electrically connected to the first end of the seventeenth resistor, wherein the operation of the fifth switch is controlled according to the mode a fifth amplifier having a first input electrically connected to the second end of the fourteenth resistor, a second input electrically coupled to a predetermined voltage level, and an output signal for adjusting the signal a mode control signal; and a fourth capacitor, the first end of which is electrically connected to the first input of the fifth amplifier End and a second end electrically connected to an output terminal of the fifth amplifier. The liquid crystal display of claim 19, wherein the light emitting element is a cold cathode fluorescent tube.