CN105263209B - controller and method for dimming light emitting diode - Google Patents

Abstract

The present invention discloses a controller and method for dimming a light emitting diode. The controller includes a pulse width modulation pin, a low-pass filter, a frequency detection unit and a control signal generation module. The low-pass filter generates a DC signal according to a pulse width modulation signal generated by a microcontroller. The frequency detection unit generates a logic value according to a critical value and the pulse width modulation signal. The control signal generation module generates a switch control signal to a first switch connected in series with the light emitting diode according to the DC signal, the logic value, a reference voltage and the pulse width modulation signal. When the frequency of the pulse width modulation signal is lower than the critical value, the controller enters a digital dimming mode; when the frequency of the pulse width modulation signal is higher than the critical value, the controller enters an analog dimming mode. Therefore, the present invention does not need to modify the printed circuit board accordingly, and the present invention does not add additional burden.

Description

Controller and method for dimming light-emitting diodes

technical field

The present invention relates to a controller and method for dimming light-emitting diodes, in particular to a controller and method for dimming light-emitting diodes that can realize digital dimming mode and analog dimming mode on the same pin according to the frequency of pulse width modulation signals controller and method.

Background technique

The digital dimming mode and the analog dimming mode applied to light-emitting diode dimming have their own advantages. For example, the analog dimming mode has the following advantages: first, better color saturation in the analog dimming mode; ), there is a large product design space; third, the analog dimming mode will not produce water ripples, so the analog dimming mode is more friendly to the human eye, that is to say, it has a marketing theme; fourth, the analog dimming mode produces The frequency of electromagnetic waves falls within the range (1Hz-30kHz) regulated by the Swedish Federation of Professional Employees (TCO); and the digital dimming mode has the following advantages: First, the digital dimming mode has better contrast; Second, the digital dimming mode is easier to control the color temperature and color gamut; third, the brightness and driving current of the light-emitting diodes generated by the digital dimming mode change linearly.

In the prior art, because the digital dimming mode and the analog dimming mode applied to light-emitting diode dimming have their own advantages, although the user can set the driving circuit of the light-emitting diode to operate in digital dimming mode or Analog dimming mode, but the driving circuit of the light emitting diode must have different pins to receive the external signal corresponding to the digital dimming mode and the analog dimming mode, or the printed circuit board should be modified accordingly, causing the existing technology to be difficult for users Not a good choice.

Contents of the invention

The first embodiment of the present invention discloses a controller for dimming LEDs. The controller includes a pulse width modulation pin, a low-pass filter, a frequency detection unit and a control signal generation module. The PWM pin is used for receiving a PWM signal generated by a microcontroller. The low-pass filter is used to generate a DC signal according to the PWM signal. The frequency detection unit is used for generating a logic value according to a threshold value and the PWM signal. The control signal generation module is coupled to the low-pass filter and the frequency detection unit, and is used to generate A switch control signal is sent to the first switch connected in series with the LEDs, wherein the first switch is turned on and off according to the switch control signal. When the frequency of the PWM signal is lower than the threshold, the controller enters a digital dimming mode, and when the frequency of the PWM signal is higher than the threshold, the The controller is in an analog dimming mode.

The second embodiment of the present invention discloses a method for dimming a light-emitting diode, wherein a controller applied to the method includes a pulse width modulation pin, a low-pass filter, a frequency detection unit and A control signal generation module. The method comprises that the pulse width modulation pin receives a pulse width modulation signal generated by a microcontroller; the low-pass filter generates a DC signal according to the pulse width modulation signal; the frequency detection The unit generates a logic value according to a critical value and the pulse width modulation signal; the control signal generation module generates a logic value according to the DC signal, the logic value, a reference voltage and the pulse width modulation signal switch control signal to the first switch connected in series with the light emitting diodes, wherein the first switch is turned on and off according to the switch control signal; when the frequency of the pulse width modulation signal is lower than the critical value, the The controller enters a digital dimming mode, and when the frequency of the PWM signal is higher than the critical value, the controller enters an analog dimming mode.

A third embodiment of the present invention discloses a method for dimming a light-emitting diode, wherein the light-emitting diode is applied to a liquid crystal display, and a controller applied to the method includes a pulse width modulation pin, A low-pass filter, a frequency detection unit and a control signal generation module, wherein the control signal generation module includes a multiplexer, a logic unit, a transmission unit, a second switch and a comparator. The method comprises that the pulse width modulation pin receives a pulse width modulation signal generated by a microcontroller according to the image signal received by the liquid crystal display; the low-pass filter according to the pulse width modulation signal, generating a DC signal; the frequency detection unit generates a logic value according to a critical value and the pulse width modulation signal; the control signal generating module generates a logic value according to the DC signal, the logic value, a reference voltage and The pulse width modulation signal generates a switch control signal to the first switch connected in series with the LEDs, wherein the first switch is turned on and off according to the switch control signal; when the pulse width modulation signal When the frequency is lower than the threshold value, the controller is in a digital dimming mode, and when the frequency of the PWM signal is higher than the threshold value, the controller is in an analog dimming mode model.

The invention discloses a controller and method for dimming light-emitting diodes. The controller and the method determine whether the controller operates in a digital dimming mode or an analog dimming mode according to a pulse width modulation signal generated by a microcontroller and a threshold value, so the present invention only needs to One pin receives a pulse width modulation signal generated by the microcontroller, which enables the controller to switch between the digital dimming mode and the analog dimming mode. Therefore, compared with the prior art, the present invention determines whether the controller operates in the digital dimming mode or the analog dimming mode according to the pulse width modulation signal generated by the microcontroller and the critical value. light mode, so the present invention does not require a corresponding modification of a printed circuit board. In addition, the present invention determines whether the controller operates in the digital dimming mode or the analog dimming mode according to the pulse width modulation signal generated by the microcontroller and the critical value, so the present invention does not will add an additional burden.

Description of drawings

FIG. 1 is a schematic diagram of a controller for dimming LEDs according to the first embodiment of the present invention.

FIG. 2 is a schematic diagram illustrating the relationship between the pulse width modulation signal and the driving current flowing through the LED. 3A and 3B are flowcharts of a method for dimming LEDs according to the second embodiment of the present invention.

4A and 4B are flowcharts of a method for dimming LEDs according to the third embodiment of the present invention.

Wherein, the reference signs are explained as follows:

100 LEDs

200 controllers

202 Pulse Width Modulation Pins

204 low pass filter

206 frequency detection unit

208 control signal generation module

210 microcontroller

212 First switch

214 Gate pins

216 power converter

2082 Multiplexer

2084 logical units

2086 transfer unit

2088 Second switch

2090 Comparator

DS DC signal

ILED drive current

ILEDMAX maximum drive current

LV logical value

first logical value

PWMS pulse width modulation signal

Inverted PWM signal

SEC secondary side

SCS switch control signal

SV sense voltage

VOUT output voltage

VREF Reference voltage

300-328, 400-428 steps

Detailed ways

Please refer to FIG. 1. FIG. 1 is a schematic diagram of a controller 200 for dimming a light-emitting diode 100 according to a first embodiment of the present invention, wherein a secondary side SEC of a power converter 216 is used to generate an output voltage VOUT is used to drive the LED 100 , and the controller 200 is located at the secondary side SEC of the power converter 216 . As shown in FIG. 1 , the controller 200 includes a PWM pin 202 , a low-pass filter 204 , a frequency detection unit 206 and a control signal generation module 208 . As shown in FIG. 1 , the pulse width modulation pin 202 is used to receive a pulse width modulation signal PWMS generated by a microcontroller 210 . The low-pass filter 204 is coupled to the PWM pin 202 for generating a DC signal DS according to the PWM signal PWMS. The frequency detection unit 206 is coupled to the pulse width modulation pin 202 for generating a logic value LV according to a threshold value and the pulse width modulation signal PWMS. For example, when the frequency of the pulse width modulation signal PWMS is lower than the threshold value, the frequency detection unit 206 generates a logic value “0”, and when the frequency of the pulse width modulation signal PWMS is higher than the threshold value, the frequency detection unit 206 206 generates a logic value "1". But the present invention is not limited to when the frequency of the pulse width modulation signal PWMS is lower than the critical value, the frequency detection unit 206 generates a logic value "0", and when the frequency of the pulse width modulation signal PWMS is higher than the critical value , the frequency detection unit 206 generates a logic value “1”. The control signal generation module 208 is coupled to the low-pass filter 204 and the frequency detection unit 206, and is used to generate a switch control signal SCS according to the DC signal DS, the logic value LV, a reference voltage VREF and the pulse width modulation signal PWMS To the first switch 212 of the LEDs 100 connected in series, wherein the first switch 212 is turned on and off according to the switch control signal SCS, and the switch control signal SCS is transmitted to the first switch 212 through a gate pin 214 .

As shown in FIG. 1 , the control signal generation module 208 includes a multiplexer 2082 , a logic unit 2084 , a transmission unit 2086 , a second switch 2088 and a comparator 2090 . As shown in FIG. 1, the multiplexer 2082 is coupled to the low-pass filter 204 and the frequency detection unit 206, and is used to output the reference voltage VREF or the DC signal DS according to the logic value LV, wherein when the pulse width modulation signal PWMS When the frequency is lower than the critical value, the multiplexer 2082 outputs the reference voltage VREF, and when the frequency of the pulse width modulation signal PWMS is higher than the critical value, the multiplexer 2082 outputs the DC signal DS; the logic unit 2084 is coupled to the frequency detection Unit 206, for receiving the pulse width modulation signal PWMS and the logic value LV, and outputting an inverted pulse width modulation signal or the first logical value that is the inverse of logical value LV Wherein when the frequency of the pulse width modulation signal PWMS is lower than the critical value, the logic unit 2084 outputs an inverted pulse width modulation signal And when the frequency of the pulse width modulation signal PWMS is higher than the critical value, the logic unit 2084 outputs the first logic value The transmission unit 2086 is coupled to the multiplexer 2082 and the logic unit 2084 for outputting one of the reference voltage VREF and the DC signal DS, and outputting an inverted pulse width modulation signal with the first logical value One of them; the second switch 2088 is coupled to the transmission unit 2086 for modulating the signal according to the inverted pulse width or the first logical value Execute a corresponding action, wherein when the second switch 2088 is turned on (ON), the first switch 212 is turned off (OFF), and when the second switch 2088 is turned off, the first switch 212 is turned on; the comparator 2090 is coupled to the transmission unit 2086, for generating a switch control signal SCS to the first switch 212 according to one of the reference voltage VREF and the DC signal DS and a sensing voltage SV.

As shown in FIG. 1, when the frequency of the pulse width modulation signal PWMS is lower than the critical value, the multiplexer 2082 outputs the reference voltage VREF, and the frequency detection unit 206 generates Logical value "0". The logic unit 2084 outputs an inverted pulse width modulation signal according to the logic value "0" and the pulse width modulation signal PWMS The transmission unit 2086 outputs the reference voltage VREF, and outputs the inverted pulse width modulation signal The second switch 2088 modulates the signal according to the inverted pulse width On and off, wherein when the second switch 2088 is turned on, the first switch 212 is turned off, and when the second switch 2088 is turned off, the first switch 212 is turned on; the comparator 2090 generates switch control according to the reference voltage VREF and the sensing voltage SV The signal SCS is sent to the first switch 212 . Because the second switch 2088 is based on the inverted pulse width modulation signal is turned on and off, so the first switch 212 will also modulate the signal according to the inverted pulse width Turning on and off causes the controller 200 to enter a digital dimming mode. Therefore, when the frequency of the pulse width modulation signal PWMS is lower than the critical value, the controller 200 enters the digital dimming mode, that is, when the comparator 2090 generates the switch control signal SCS to When the first switch 212 is on, the controller 200 enters the digital dimming mode.

As shown in FIG. 1, when the frequency of the pulse width modulation signal PWMS is higher than the critical value, the multiplexer 2082 outputs a DC signal DS, and the frequency detection unit 206 generates Logical value "1". The logic unit 2084 outputs the first logic value "0" which is the inversion of the logic value "1" according to the logic value "1" and the pulse width modulation signal PWMS; the transmission unit 2086 outputs the DC signal DS, and outputs the first logic value " 0"; the second switch 2088 is turned off according to the first logic value "0", wherein when the second switch 2088 is turned off, the first switch 212 is turned on; the comparator 2090 generates a switch control signal SCS according to the DC signal DS and the sensing voltage SV to the first switch 212 . Since the second switch 2088 is continuously turned off according to the first logic value “0”, the first switch 212 is continuously turned on according to the switch control signal SCS (corresponding to the DC signal DS), causing the controller 200 to enter an analog dimming mode. Therefore, when the frequency of the pulse width modulation signal PWMS is higher than the critical value, the controller 200 enters the analog dimming mode, that is, when the comparator 2090 generates the switch control signal SCS to When the first switch 212 is turned on, the controller 200 enters the analog dimming mode.

Please refer to FIG. 2 . FIG. 2 is a schematic diagram illustrating the relationship between the pulse width modulation signal PWMS and the driving current ILED flowing through the light emitting diode 100 . As shown in FIG. 2 , when the frequency of the pulse width modulation signal PWMS is lower than a threshold value, the controller 200 enters the digital dimming mode. If the duty cycle (duty cycle) of the pulse width modulation signal PWMS is 50%, the duty cycle of the driving current ILED is also 50%; when the frequency of the pulse width modulation signal PWMS is higher than the critical value, the controller 200 enters Analog dimming mode. If the duty cycle of the pulse width modulation signal PWMS is 50%, the driving current ILED will be 50% of the maximum driving current ILEDMAX

In addition, the present invention is not limited to the controller 200 having only two dimming modes, that is to say, the frequency detection unit 206 can generate a corresponding logic value according to more than one critical value and the frequency of the pulse width modulation signal PWMS . For example, when the frequency of the pulse width modulation signal PWMS is lower than a first critical value, the frequency detection unit 206 may generate a logic value “00”; when the frequency of the pulse width modulation signal PWMS is between the first critical value and When between the second critical value, the frequency detection unit 206 can generate a logic value “01”; and when the frequency of the pulse width modulation signal PWMS is higher than a second critical value, the frequency detection unit 206 can generate a logic value Value "10". At this time, the multiplexer 2082 and the logic unit 2084 can be correspondingly modified according to the logic values ("00", "01", "10") generated by the frequency detection unit 206, so that the controller 200 has three kinds of dimming model.

In addition, in the present invention, when the controller 200 is turned on, the controller 200 enters the digital dimming mode or the analog dimming mode by default, or when the controller 200 is in normal operation, the controller 200 is based on the pulse width modulation signal PWMS , switch from digital dimming mode to analog dimming mode, or switch from analog dimming mode to digital dimming mode.

Please refer to FIG. 1 and FIG. 3A and FIG. 3B . FIG. 3A and FIG. 3B are flowcharts of a method for dimming a light emitting diode according to a second embodiment of the present invention. The method of FIG. 3A and FIG. 3B is illustrated by using the controller 200 of FIG. 1, and the detailed steps are as follows:

Step 300: start;

Step 302: the pulse width modulation pin 202 receives the pulse width modulation signal PWMS generated by the microcontroller 210;

Step 304: the low-pass filter 204 generates a DC signal DS according to the pulse width modulation signal PWMS;

Step 306: the frequency detection unit 206 generates a logic value LV according to a threshold value and the frequency of the pulse width modulation signal PWMS;

Step 308: Whether the frequency of the pulse width modulation signal PWMS is lower than a critical value; if yes, go to step 310; if not, go to step 320;

Step 310: the multiplexer 2082 outputs a reference voltage VREF;

Step 312: Logic unit 2084 outputs an inverted PWM signal

Step 314: The transmission unit 2086 outputs the reference voltage VREF and the inverted PWM signal

Step 316: The second switch 2088 modulates the signal according to the inverted pulse width Turn on and off; step 318: the comparator 2090 generates a switch control signal SCS to the first switch 212 according to the reference voltage VREF and a sensing voltage SV, and jumps to step 308;

Step 320: the multiplexer 2082 outputs a DC signal DS;

Step 322: The logic unit 2084 outputs the first logic value which is inverted from the logic value LV

Step 324: The transmission unit 2086 outputs the DC signal DS and the first logic value

Step 326: The second switch 2088 according to the first logical value closure;

Step 328 : The comparator 2090 generates a switch control signal SCS to the first switch 212 according to the DC signal DS and the sensing voltage SV, and skips to step 308 .

In step 306, the frequency detection unit 206 generates a logic value LV according to a threshold value and the pulse width modulation signal PWMS. For example, when the frequency of the pulse width modulation signal PWMS is lower than the threshold value, the frequency detection unit 206 generates a logic value “0”, and when the frequency of the pulse width modulation signal PWMS is higher than the threshold value, the frequency detection unit 206 yields a logical value "1". But the present invention is not limited to when the frequency of the pulse width modulation signal PWMS is lower than the critical value, the frequency detection unit 206 generates a logic value "0", and when the frequency of the pulse width modulation signal PWMS is higher than the critical value , the frequency detection unit 206 generates a logic value “1”.

In step 310, when the frequency of the pulse width modulation signal PWMS is lower than the critical value, the multiplexer 2082 outputs the reference voltage VREF, and the frequency detection unit 206 generates a logic value "" according to the critical value and the pulse width modulation signal PWMS 0". In step 312, the logic unit 2084 outputs an inverted pulse width modulation signal according to the logic value "0" and the pulse width modulation signal PWMS In step 316, the second switch 2088 modulates the signal according to the inverted pulse width On and off, wherein when the second switch 2088 is turned on, the first switch 212 is turned off, and when the second switch 2088 is turned off, the first switch 212 is turned on; in step 318, the comparator 2090 is based on the reference voltage VREF and the sensing voltage SV, to generate a switch control signal SCS to the first switch 212 . Because the second switch 2088 is based on the inverted pulse width modulation signal is turned on and off, so the first switch 212 will also modulate the signal according to the inverted pulse width Turning on and off causes the controller 200 to enter the digital dimming mode. Therefore, when the frequency of the pulse width modulation signal PWMS is lower than the critical value, the controller 200 enters the digital dimming mode, that is, when the comparator 2090 generates the switch control signal SCS to When the first switch 212 is on, the controller 200 enters the digital dimming mode.

In step 320, when the frequency of the pulse width modulation signal PWMS is higher than the threshold value, the multiplexer 2082 outputs the DC signal DS, and the frequency detection unit 206 generates logic according to the threshold value and the frequency of the pulse width modulation signal PWMS Value "1". In step 322, the logic unit 2084 outputs the first logic value "0" which is the inversion of the logic value "1" according to the logic value "1" and the pulse width modulation signal PWMS; in step 326, the second switch 2088 outputs The first logic value "0" is off, wherein when the second switch 2088 is off, the first switch 212 is on; in step 328, the comparator 2090 generates a switch control signal SCS to the first Switch 212. Since the second switch 2088 is kept closed according to the first logic value “0”, the first switch 212 is kept turned on according to the switch control signal SCS (corresponding to the DC signal DS), causing the controller 200 to enter the analog dimming mode. Therefore, when the frequency of the pulse width modulation signal PWMS is higher than the critical value, the controller 200 enters the analog dimming mode, that is, when the comparator 2090 generates the switch control signal SCS to When the first switch 212 is turned on, the controller 200 enters the analog dimming mode.

Please refer to FIG. 1 and FIG. 4A and FIG. 4B . FIG. 4A and FIG. 4B are flowcharts of a method for dimming light emitting diodes according to a third embodiment of the present invention. The method of FIG. 4A and FIG. 4B is illustrated by using the controller 200 of FIG. 1, and the detailed steps are as follows:

Step 400: start;

Step 402: the pulse width modulation pin 202 receives the pulse width modulation signal PWMS generated by the microcontroller 210 according to the image signal received by the liquid crystal display;

Step 404: the low-pass filter 204 generates a DC signal DS according to the pulse width modulation signal PWMS;

Step 406: the frequency detection unit 206 generates a logic value LV according to a threshold value and the frequency of the pulse width modulation signal PWMS;

Step 408: Whether the frequency of the pulse width modulation signal PWMS is lower than a critical value; if yes, go to step 410; if not, go to step 420;

Step 410: the multiplexer 2082 outputs a reference voltage VREF;

Step 412: Logic unit 2084 outputs an inverted PWM signal

Step 414: The transmission unit 2086 outputs the reference voltage VREF and the inverted PWM signal

Step 416: The second switch 2088 modulates the signal according to the inverted pulse width on and off;

Step 418: The comparator 2090 generates a switch control signal SCS to the first switch 212 according to the reference voltage VREF and a sensing voltage SV, and jumps to step 408;

Step 420: the multiplexer 2082 outputs a DC signal DS;

Step 422: The logic unit 2084 outputs the first logic value which is inverted from the logic value LV

Step 424: The transmission unit 2086 outputs the DC signal DS and the first logic value

Step 426: The second switch 2088 according to the first logical value closure;

Step 428 : The comparator 2090 generates a switch control signal SCS to the first switch 212 according to the DC signal DS and the sensing voltage SV, and then jumps to step 408 .

The difference between the embodiment of FIG. 4A and FIG. 4B and the embodiment of FIG. 3A and FIG. 3B is that in step 402, the microcontroller 210 generates a pulse width modulation signal PWMS according to the image signal received by the liquid crystal display, wherein the pulse width The modulating signal PWMS corresponds to various playback modes, various contrast ratios, or various white balances of the liquid crystal display, and the various playback modes of the liquid crystal display include a movie mode, a game mode, and a three-dimensional (3D) mode. mode and a two-dimensional (2D) mode. In the embodiment shown in FIG. 4A and FIG. 4B , the microcontroller 210 can generate the pulse width modulation signal PWMS according to the image signal received by the liquid crystal display, that is to say, the microcontroller 210 can generate the pulse width modulation signal PWMS according to the image signal received by the liquid crystal display. The corresponding driving current ILED flowing through the LED 100 generates a pulse width modulation signal PWMS. For example, when the image signal received by the liquid crystal display requires a large driving current ILED, the microcontroller 210 can generate a low-frequency pulse width modulation signal PWMS. In addition, the remaining operating principles of the embodiment of FIG. 4A and FIG. 4B are the same as those of the embodiment of FIG. 3A and FIG. 3B , and will not be repeated here.

In summary, the controller and method for dimming light-emitting diodes disclosed in the present invention determine whether the controller operates in digital dimming mode or analog dimming mode according to the pulse width modulation signal generated by the microcontroller and a threshold value. light mode, so the present invention only needs one pin to receive the pulse width modulation signal generated by the microcontroller, so that the controller can switch between the digital dimming mode and the analog dimming mode. Therefore, compared with the prior art, because the present invention determines whether the controller operates in the digital dimming mode or the analog dimming mode according to the pulse width modulation signal and the critical value generated by the microcontroller, the present invention does not need to correspondingly Modify the printed circuit board. In addition, the present invention determines whether the controller operates in the digital dimming mode or the analog dimming mode according to the pulse width modulation signal and the critical value generated by the microcontroller, so the present invention does not add additional burden.

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and changes. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims (12)

1. It is 1. a kind of dimming the controller of light emitting diode, it is characterised in that including：

   One pulse width modulation pin, to receive the pulse width modulation signal of microcontroller generation；

   One low-pass filter, according to the pulse width modulation signal, to generate a direct current signal；

   One frequency detecting unit, according to a critical value and the pulse width modulation signal, to generate a logical value；And

   One control signal generator module, is coupled to the low-pass filter and the frequency detecting unit, to according to described straight Signal, the logical value, a reference voltage and the pulse width modulation signal are flowed, generates a switch control signal to connecting State the first switch of light emitting diode, wherein the first switch be according to the switch control signal open and close and The control signal generator module includes：

   One multiplexer is coupled to the low-pass filter and the frequency detecting unit, to according to the logical value, output The reference voltage or the direct current signal, wherein when the frequency of the pulse width modulation signal is less than the critical value, The multiplexer exports the reference voltage and when the frequency of the pulse width modulation signal is higher than the critical value When, the multiplexer exports the direct current signal；

   One logic unit is coupled to the frequency detecting unit, to receive the pulse width modulation signal and the logic Value and one rp pulse width modulation signal of output or the first logical value with the logical value reverse phase, wherein when the arteries and veins When rushing the frequency of width modulation signal less than the critical value, the logic unit exports the rp pulse width modulation letter Number and when the frequency of the pulse width modulation signal is higher than the critical value, logic unit output described first Logical value；

   One transmission unit is coupled to the multiplexer and the logic unit, to export the reference voltage with it is described straight Flow one of signal and output one of the rp pulse width modulation signal and first logical value；

   One second switch is coupled to the transmission unit, to according to the rp pulse width modulation signal or described first Logical value performs a corresponding action, wherein when the second switch is opened, the first switch closes and when described When second switch is closed, the first switch is opened；And

   One comparator is coupled to the transmission unit, to according to one of the reference voltage and the direct current signal and One sensing voltage generates the switch control signal to the first switch；

   Wherein when the comparator is according to the reference voltage and the sensing voltage, the switch control signal is generated to described During first switch, the controller be into a digital dimming mode and when the comparator according to the direct current signal with The sensing voltage,

   When generating the switch control signal to the first switch, the controller is to enter an analog dimming mode；

   Wherein when the frequency of the pulse width modulation signal is less than the critical value, the controller is to enter the number Light-modulating mode and when the pulse width modulation signal frequency be higher than the critical value when, the controller be enter institute State analog dimming mode.
2. 2. controller as described in claim 1, it is characterised in that：When the controller is switched on, the controller is acquiescence Into the digital dimming mode or the analog dimming mode.
3. 3. controller as described in claim 1, it is characterised in that：When the controller normal operation,

   The controller is according to the pulse width modulation signal and the critical value, switches the digital dimming mode to institute Analog dimming mode or the switching analog dimming mode are stated to the digital dimming mode.
4. 4. controller as described in claim 1, it is characterised in that：The switch control signal is transmitted by a grid pin To the first switch.
5. 5. it is a kind of to dim the method for light emitting diode, wherein the controller applied to the method includes

   One pulse width modulation pin, a low-pass filter, a frequency detecting unit and a control signal generator module, wherein institute It states control signal generator module and includes a multiplexer, a logic unit, a transmission unit, a second switch and a comparator, The method is characterized in that including：

   The pulse width modulation pin receives the pulse width modulation signal that a microcontroller generates；

   The low-pass filter generates a direct current signal according to the pulse width modulation signal；

   The frequency detecting unit generates a logical value according to a critical value and the pulse width modulation signal；

   When the frequency of the pulse width modulation signal is less than the critical value, the multiplexer exports a reference voltage；

   When the frequency of the pulse width modulation signal is less than the critical value, it is wide that the logic unit exports a rp pulse Spend modulating signal；

   The transmission unit exports the reference voltage and the output rp pulse width modulation signal；

   The second switch opens and closes, according to the rp pulse width modulation signal wherein when the second switch is opened Qi Shi, the first switch for the light emitting diode of connecting are closed and when the second switch is closed, and the first switch is opened It opens；And

   The comparator generates a switch control signal to the first switch according to the reference voltage and a sensing voltage, Wherein described first switch is opened and closed according to the switch control signal；

   Wherein when the frequency of the pulse width modulation signal is less than the critical value, the controller is to enter a number to adjust Optical mode, when the frequency of the pulse width modulation signal is higher than the critical value, the controller is to enter a simulation to adjust Optical mode and when the comparator is according to the reference voltage and the sensing voltage, generates the switch control signal extremely During the first switch, the controller is to enter the digital dimming mode.
6. 6. method as claimed in claim 5, it is characterised in that：When the controller is switched on, the controller be give tacit consent into Enter the digital dimming mode or the analog dimming mode.
7. 7. method as claimed in claim 5, it is characterised in that：When the controller normal operation, the controller is root According to the pulse width modulation signal and the critical value, switch the digital dimming mode to the analog dimming mode or Switch the analog dimming mode to the digital dimming mode.
8. 8. it is a kind of to dim the method for light emitting diode, wherein the controller applied to the method includes

   One pulse width modulation pin, a low-pass filter, a frequency detecting unit and a control signal generator module, wherein institute It states control signal generator module and includes a multiplexer, a logic unit, a transmission unit, a second switch and a comparator, The method is characterized in that including：

   The pulse width modulation pin receives the pulse width modulation signal that a microcontroller generates；

   The low-pass filter generates a direct current signal according to the pulse width modulation signal；

   The frequency detecting unit generates a logical value according to a critical value and the pulse width modulation signal；

   When the frequency of the pulse width modulation signal is higher than the critical value, the multiplexer exports the direct current letter Number；

   When the frequency of the pulse width modulation signal is higher than the critical value, the logic unit output and the logical value First logical value of reverse phase；

   The transmission unit exports the direct current signal and output first logical value；

   The second switch is closed according to first logical value, wherein when the second switch is closed,

   Connect the light emitting diode first switch open；And

   The comparator generates a switch control signal to the first switch according to the direct current signal and a sensing voltage；

   Wherein when the comparator is according to the direct current signal and the sensing voltage, the switch control signal is generated to described During first switch, the controller is to enter an analog dimming mode, when the frequency of the pulse width modulation signal is less than institute When stating critical value, the controller is into a digital dimming mode and when the frequency of the pulse width modulation signal is high When the critical value, the controller is to enter the analog dimming mode.
9. 9. it is a kind of to dim the method for light emitting diode, wherein the light emitting diode is to be applied to a liquid crystal display, with And the controller applied to the method includes a pulse width modulation pin, a low-pass filter, a frequency detecting unit And one control signal generator module, wherein it is described control signal generator module include a multiplexer, a logic unit, one transmission Unit, a second switch and a comparator, the method are characterized in that including：

   The pulse width modulation pin receives a microcontroller according to produced by the video signal that the liquid crystal display receives Pulse width modulation signal；

   The low-pass filter generates a direct current signal according to the pulse width modulation signal；

   The frequency detecting unit generates a logical value according to a critical value and the pulse width modulation signal；

   When the frequency of the pulse width modulation signal is less than the critical value, the multiplexer exports a reference voltage；

   When the frequency of the pulse width modulation signal is less than the critical value, it is wide that the logic unit exports a rp pulse Spend modulating signal；

   The transmission unit exports the reference voltage and the rp pulse width modulation signal；

   The second switch opens and closes, according to the rp pulse width modulation signal wherein when the second switch is opened Qi Shi, the first switch for the light emitting diode of connecting are closed and when the second switch is closed, and the first switch is opened It opens；And

   The comparator generates a switch control signal to the first switch according to the reference voltage and a sensing voltage, Wherein described first switch is opened and closed according to the switch control signal；

   Wherein when the comparator is according to the reference voltage and the sensing voltage, the switch control signal is generated to described During first switch, the controller is to enter a digital dimming mode, when the frequency of the pulse width modulation signal is less than institute When stating critical value, the controller is to enter the digital dimming mode and the frequency when the pulse width modulation signal During higher than the critical value, the controller is to enter an analog dimming mode.
10. 10. method as claimed in claim 9, it is characterised in that：The pulse width modulation signal corresponds to the liquid crystal Various play mode, various contrasts or various white balances possessed by display.
11. 11. method as claimed in claim 10, it is characterised in that：The various play mode include a film mode, an electricity Object for appreciation pattern, a three dimensional pattern and a two-dimensional model.
12. 12. it is a kind of to dim the method for light emitting diode, wherein the light emitting diode is to be applied to a liquid crystal display, with And the controller applied to the method includes a pulse width modulation pin, a low-pass filter, a frequency detecting unit And one control signal generator module, wherein it is described control signal generator module include a multiplexer, a logic unit, one transmission Unit, a second switch and a comparator, the method are characterized in that including：

    The pulse width modulation pin receives a microcontroller according to produced by the video signal that the liquid crystal display receives Pulse width modulation signal；

    The low-pass filter generates a direct current signal according to the pulse width modulation signal；

    The frequency detecting unit generates a logical value according to a critical value and the pulse width modulation signal；

    When the frequency of the pulse width modulation signal is higher than the critical value, the multiplexer exports the direct current letter Number；

    When the frequency of the pulse width modulation signal is higher than the critical value, the logic unit output and the logical value First logical value of reverse phase；

    The transmission unit exports the direct current signal and first logical value；

    The second switch is closed according to first logical value, wherein when the second switch is closed,

    Connect the light emitting diode first switch open；And

    The comparator generates a switch control signal to the first switch according to the direct current signal and a sensing voltage；

    Wherein when the comparator is according to the direct current signal and the sensing voltage, the switch control signal is generated to described During first switch, the controller is to enter an analog dimming mode, when the frequency of the pulse width modulation signal is less than institute When stating critical value, the controller is into a digital dimming mode and when the frequency of the pulse width modulation signal is high When the critical value, the controller is to enter the analog dimming mode.