CN102196619A - Driving circuit and driving method of light emitting diode - Google Patents

Abstract

The invention provides a driving circuit and a driving method of a light emitting diode. The driving circuit of the light emitting diode comprises a driving unit, a current pre-charging unit and a feedback selection unit. The driving unit outputs a driving power to drive the light emitting diode and outputs at least one first feedback signal according to the current conducted by the light emitting diode. The current pre-charging unit is coupled to the output of the driving unit to provide a current path to the driving unit and generate a second feedback signal according to the current conducted by the current pre-charging unit. The feedback selection unit selects one of the at least one first feedback signal or the second feedback signal as an output according to the enable signal, and the driving unit adjusts the driving power according to the output of the feedback selection unit. Therefore, the driving circuit can maintain the current driving capability to drive the light emitting diode.

Description

Driving circuit and driving method of light emitting diode

technical field

The present invention relates to a driving circuit and a driving method of a light emitting diode (Light Emitting Diode, LED), and in particular to a driving circuit and a driving method capable of maintaining current driving capability.

Background technique

With the increasing awareness of environmental protection and energy saving and the small size, power saving and durable characteristics of light-emitting diodes, they have gradually replaced traditional light sources and become a new generation of light sources. LEDs emit light by converting electrical energy into light energy. The composition material of LED grain is semiconductor, and the wavelength of light can be determined according to the energy level of the material used, so it will emit light of different colors. Therefore, LED can not only be used as a white light source, but also can be used in automotive headlights, traffic lights, text displays, billboards and large-screen video displays, as well as general and architectural lighting and LCD backlighting.

Since the luminance of an LED is related to the magnitude of the current it conducts, its current driving capability is very important when driving the LED. Especially for large-scale LED signage, because it is used to display images or text, the response speed of LED is very important. Large-scale LED signages have a large number of LEDs and require a considerable amount of current to be driven. If the current of the drive circuit cannot provide sufficient current immediately, the LEDs cannot display the correct brightness and image quality. Therefore, the current driving capability of the LED driving circuit is a very important issue for LED displays or signage. However, most of the current LED driving circuits focus on the stability of the current or the control of the driving voltage, and seldom focus on the improvement of the driving ability of the driving current.

Contents of the invention

The invention relates to a driving circuit and a driving method of an LED. A current pre-charging unit is arranged in the driving circuit so that the driving circuit can maintain its current driving capability so as to provide sufficient current to drive the LED when the LED is switched. In this way, the switching speed of the LED can be accelerated, and the display speed of the LED can be avoided due to insufficient instantaneous current.

Based on the above, the present invention proposes a driving circuit for a light emitting diode, which is suitable for driving at least one light emitting diode unit, the light emitting diode unit includes at least one light emitting diode, and the driving circuit includes a driving unit, a current pre-charging unit and a feedback selection unit. The driving unit outputs a driving power to the LED unit, and outputs at least a first feedback signal according to the conduction current of the LED unit. The current pre-charging unit is coupled to the output of the driving unit to provide a current path to the driving unit and generate a second feedback signal according to the driving power. The feedback selection unit is coupled to the driving unit and the current pre-charging unit, and selects one of the first feedback signal or the second feedback signal as an output according to an enable signal. Wherein, the driving unit adjusts the driving power according to the output of the feedback selection unit.

In an embodiment of the present invention, when the enable signal is disabled to turn off the LED unit, the feedback selection unit selects the second feedback signal as an output to maintain the output current of the driving unit at a specific value. When the enable signal enables the LED unit to be turned on, the feedback selection unit selects one of the enabled first feedback signals with the minimum voltage as an output.

In an embodiment of the present invention, the current pre-charging unit includes a first resistor, a second resistor, an inverter and a switch. The first resistor and the second resistor are coupled in series between the output of the driving unit and a switch, the input end of the inverter is coupled to the enabling signal, and the output end of the inverter is coupled to the switch. When the enabling signal is disabled, the switch is turned on; when the enabling signal is enabled, the switch is turned off.

In an embodiment of the present invention, the current pre-charging unit includes a first resistor, an adjustable current source, a control unit and a delay unit. One end of the first resistor is coupled to the output of the drive unit, the adjustable current source is connected between the other end of the first resistor and a ground end, the control unit is coupled to the adjustable current source and adjusted according to an original enabling signal The on-current of the adjustable current source. The delay unit is coupled between the feedback selection unit, the current control circuit and the original enable signal, and is used for delaying the original enable signal for a preset time to output the enable signal to the feedback selection unit and the current control circuit. Wherein, the common contact between the adjustable current source and the first resistor outputs the second feedback signal, and the control unit changes the current value of the adjustable current source according to the original enable signal during the preset delay time to improve the driving unit output current, and automatically shuts off the current of the adjustable current source when the LED is turned on (after a preset delay time has elapsed).

The present invention further proposes a driving method of a light emitting diode, which includes the following steps: first, outputting a driving power to drive a light emitting diode unit and generating at least a first feedback signal, and then providing a current path to the driving power and according to the current path The conducted current generates a second feedback signal. Then it is determined whether to turn on the at least one light emitting diode according to an enabling signal. When the light emitting diode unit is turned off, the driving power is adjusted according to the second feedback signal; when the light emitting diode unit is turned on, the driving power is adjusted according to the first feedback signal. For the rest of the operation details of the driving method, please refer to the description of the driving circuit above, and will not be repeated here.

Based on the above, the present invention maintains the current driving capability of the driving circuit by adjusting the current in advance, so that the LED can obtain enough current to accelerate its turn-on speed when switching. At the same time, the present invention uses the current pre-charging unit to provide a feedback signal, so that the driving circuit can also adjust the output of the power conversion unit according to the feedback signal when the LED is turned off.

In order to make the above-mentioned features and advantages of the present invention more comprehensible, the following specific embodiments will be described in detail in conjunction with the accompanying drawings.

Description of drawings

FIG. 1A is a driving circuit according to a first embodiment of the present invention.

FIG. 1B is a circuit structure of the driving unit 105 according to the first embodiment of the present invention.

FIG. 2A is a detailed circuit diagram of the driving circuit according to the first embodiment of the present invention.

FIG. 2B is a driving circuit according to the first embodiment of the present invention.

FIG. 3A is a driving circuit according to a second embodiment of the present invention.

FIG. 3B is a driving circuit according to a second embodiment of the present invention.

FIG. 3C is a driving circuit according to a third embodiment of the present invention.

4A-4C are various circuit structures of the current control circuit according to the present invention.

5A-5F are various circuit structures of the current pre-charging unit according to the present invention.

FIG. 6 is a flowchart of a driving method of a light emitting diode according to a fourth embodiment of the present invention.

Description of main component symbols:

105: drive unit; 110: power conversion unit;

120: Pulse width modulation unit; 122: Pulse width modulation signal generator;

124, 430, 510: operational amplifiers; 130: feedback selection unit;

140: current adjustment unit; 142, 144: current control circuit;

150, 350, 355: current pre-charging unit; 160: light-emitting diode unit;

310: inverter; 320, 560: adjustable current source;

360: control unit; 370: delay unit;

420, 520, 530: current mirror; GND: ground terminal;

VOUT: drive power; F1～Fn: first feedback signal;

FS: second feedback signal; EN: enable signal;

OEN: original enable signal; VIN: input voltage;

PWMS: pulse width modulation signal; I1, I2: current;

Vref: reference voltage; R51: variable resistor;

EN1: the first enabling signal; EN2: the second enabling signal;

S610～S650: steps;

410, 551, 552, 553, 554, 555: current source;

R21, R22, R41, R42, R52, R53: resistance;

M21, M41, M42, M51, M52: NMOS transistors;

SW51, SW52, SW53, SW54, SW55: Switches.

Detailed ways

first embodiment

Please refer to FIG. 1A . FIG. 1A is a driving circuit according to a first embodiment of the present invention, suitable for driving at least one light-emitting diode. The driving circuit includes a driving unit 105 , a feedback selection unit 130 and a current pre-charging unit 150 . The driving unit 105 is coupled to the light emitting diode unit 160, wherein the light emitting diode unit 160 includes at least one light emitting diode, and the light emitting diodes can be connected in series to form a light emitting diode string. The driving unit 105 outputs a driving power VOUT to the LED unit 160 and outputs first feedback signals F1˜Fn according to the conduction current of the LED string (not shown). The first feedback signals F1-Fn can reflect the divided voltage of individual LED strings to infer their conduction currents. The current pre-charging unit 150 is coupled to the output of the driving unit 105 , provides a current path to the driving unit and generates a second feedback signal FS according to the current conducted by the current pre-charging unit 150 or the voltage level of the driving power VOUT. The feedback selection unit 130 is coupled to the driving unit 105 and the current pre-charging unit 150, and selects one of the first feedback signals F1-Fn or the second feedback signal FS as an output according to the enable signal EN. Then, the driving unit 105 adjusts the driving power VOUT according to the output of the feedback selection unit 130 .

When the light-emitting diode string in the light-emitting diode unit 160 is turned on, the feedback selection unit 130 will select one of the first feedback signals F1-Fn as an output (for example, the feedback signal with the smallest voltage), and the driving unit 105 will The feedback signals F1˜Fn adjust the driving power VOUT. At this time, the operation of the overall driving circuit is similar to that of the existing LED driving circuit, which adjusts the driving power VOUT according to the feedback signal generated by the LED element. Generally speaking, the first feedback signals F1˜Fn are related to the current conducted by the corresponding LED. When the LED elements in the LED unit 160 are turned off, the feedback selection unit 130 will select the second feedback signal FS as an output. The driving unit 105 adjusts the driving power VOUT according to the second feedback signal FS. That is to say, when the LED unit 160 is turned off, the driving unit 105 still maintains the output current to prepare for the LED unit 160 to be turned on.

The current pre-charging unit 150 can be regarded as the second output current path of the driving unit 105. When the light-emitting diode element in the light-emitting diode unit 160 is temporarily turned off (that is, when it is switched due to the enable signal EN), the current pre-charging unit 150 The current output of the driving unit 105 is maintained to prevent its output current from dropping to zero. In this way, when the LED element is turned on again, the driving unit 105 can immediately provide a momentary high current to the LED element, so as to avoid the delayed turn-on of the LED element and affect the normal display. At this time, the current pre-charging unit 150 can be temporarily turned off in conjunction with the conduction of the light emitting diode element to reduce current consumption, and then determine its turn-on time according to the enable signal EN.

Next, the circuit structure of the driving unit 105 is further described, please refer to FIG. 1B , which is a circuit structure of the driving unit 105 according to the first embodiment of the present invention. The driving unit 105 includes a power conversion unit 110 , a pulse width modulation unit 120 and a current adjustment unit 140 . The power conversion unit 110 is coupled to the LED unit 160 composed of several LED strings for converting the input voltage VIN into a driving power VOUT to the LED strings (respectively composed of several LEDs) in the LED unit 160 . The other ends of the LED strings are respectively coupled to the current adjustment unit 140 . The current adjustment unit 140 has the function of controlling the conduction current of individual LED strings, and can selectively conduct individual LED strings to make them emit light or not emit light according to the enable signal EN. The current pre-charging unit 150 is coupled to the output of the power conversion unit 110 , and the feedback selection unit 130 is coupled to the current pre-charging unit 150 and the pulse width modulation unit 120 , and can receive multiple signals returned by the current adjusting unit 140 . The first feedback signals F1 ˜ Fn and the second feedback signal FS returned by the current pre-charging unit 150 . Among them, the first feedback signals F1-Fn are the voltage signals of the connection ends of the individual LED strings and the current adjustment unit 140, and the second feedback signal FS returned by the current pre-charging unit 150 will vary according to the magnitude of the conducted current. And change.

The pulse width modulation unit 120 can adjust the pulse width modulation signal PWMS according to the feedback signal selected by the feedback selection unit 130 , so that the power conversion unit 110 can output the corresponding driving power VOUT. In another embodiment of the present invention, the driving unit 105 can also use a pulse frequency modulation unit to adjust its driving power VOUT, that is, use a pulse frequency modulation unit to replace the pulse width modulation unit 120 .

When the enable signal EN is enabled, the current adjustment unit 140 will turn on the LED string to make it emit light. At this time, the feedback selection unit 130 will select from the first feedback signals F1-Fn corresponding to the turned-on LED string. One of them (eg, the feedback signal of the specific node with the minimum voltage) is output to the PWM unit 120 . The pulse width modulation unit 120 adjusts the output of the power conversion unit 110 according to the received feedback signal, so that the LED string can obtain sufficient driving current. When the enable signal EN is disabled, the current adjustment unit 140 turns off the LED string, that is, stops the conduction current of the LED string. At this time, the feedback selection unit 130 selects the second feedback signal FS and outputs it to the PWM unit 120 . The pulse width modulation unit 120 adjusts the output of the power conversion unit 110 according to the received feedback voltage, so as to maintain the output current or voltage of the power conversion unit 110 at a specific value.

In other words, in this embodiment, a current path is added in the LED driving circuit, so that the power conversion unit 110 can maintain the output value of the current without stopping the output current due to whether the LED is turned on or not. In this embodiment, when the LED is turned off, the current pre-charging unit 150 maintains the turned-on current, so that the power conversion unit 110 continues to output current. In this way, when the enable signal EN is enabled, as long as the current pre-charging unit 150 stops conducting the current, the power conversion unit 110 can directly supply the current required for the LED to be turned on, and no insufficient driving current will occur. The magnitude of the current conducted by the current pre-charging unit 150 can be controlled by the feedback selection unit 130 or directly set according to design requirements, and the present invention is not limited thereto. As long as the current pre-charging unit 150 can provide the current path of the power conversion unit 110 . In addition, the current pre-charging unit 150 does not need to be turned on all the time, it can be turned on before the LED is turned on to maintain the current driving capability, which can save power.

The current pre-charging unit 150 can be formed by connecting resistors in series, please refer to FIG. 2A , which is a detailed circuit diagram of the driving circuit according to the first embodiment of the present invention. The light-emitting diode unit 160 is illustrated with a single string of LEDs as an example, and the current adjustment unit 140 is configured with a corresponding current control circuit 142 according to individual LED strings to control the amount of current conducted by the LED strings. Taking FIG. 2A as an example, the current control circuit 142 is coupled to one end of the LED string to generate the current I1 according to the enable signal EN, and the common end of the current control circuit 142 and the LED string generates the first feedback signal F1. It should be noted that the current control circuit 142 and the LED string may be separated by MOS elements according to circuit design requirements, but it does not affect the generation of the first feedback signal F1.

The current control circuit 142 is composed of, for example, a structure of a current source and a current mirror, which is not limited in this embodiment. The current pre-charging unit 150 is connected in series between the driving power supply VOUT and the ground terminal GND through resistors R21 and R22. The pulse width modulation unit 120 includes a pulse width modulation (Pulse Width Modulation, PWM) signal generator 122 and an operational amplifier 124, and the input terminals of the operational amplifier 124 are respectively coupled to the output of the feedback selection unit 130 and the reference voltage Vref , the output end of the operational amplifier 124 is coupled to the PWM signal generator 122 .

When the enable signal EN is enabled, the LED string is in a normal display state (conduction state), and the feedback selection unit 130 will select the first feedback signal F1 as an output. The PWM unit 120 judges whether the voltage and current of the driving power VOUT are sufficient to drive the LED string according to the voltage of the first feedback signal F1 , and then outputs the PWM signal PWMS to the power conversion unit 110 accordingly. The power conversion unit 110 is, for example, a boost circuit or a buck circuit, which can adjust the voltage value of the driving power VOUT by using the duty cycle of the pulse width modulation signal PWMS. When the LED string is turned off, in the prior art, the power conversion unit 110 will drop the voltage of the driving power VOUT to zero, so when the LED string is turned on again, the power conversion unit 110 cannot provide a large current to supply the LEDs immediately. At this time, the LED string will be delayed or the brightness will be inaccurate. To solve this problem, the present embodiment adds a current pre-charging unit 150 in the driving circuit, which provides another current path for the power conversion unit 110 to maintain the current output of the power conversion unit 110 . When the LED string is turned on again, the required driving current can be obtained instantly to enhance its driving speed.

When the LED string is turned off, the feedback selection unit 130 will switch the feedback path to the current pre-charging unit 150 to output the second feedback signal FS, and the pulse width modulation unit 120 adjusts the pulse width according to the second feedback signal FS The active period of the signal PWMS is modulated to adjust the output voltage of the power conversion unit 110 . The current pre-charging unit 150 can set the resistance values of the resistors R21 and R22 according to the current I1 when the LED string is turned on, so that the power conversion unit 110 can also make the output current correspond to a specific value when the LED string is turned off. In this way, the power conversion unit 110 can maintain its current driving capability at any time to apply whether the LED string is turned on or not.

In this embodiment, the number of LED strings driven by the power conversion unit 110 is not limited, and multiple LED strings can also be driven, taking two as an example. Please refer to FIG. 2B . FIG. 2B is a driving circuit according to a first embodiment of the present invention. Wherein, the power conversion unit 110 is used to drive two LED strings, and the LED strings are coupled between the output of the power conversion unit 110 and the current control circuits 142 , 144 . The common contacts of the current control circuits 142, 144 and the LED strings respectively output the first feedback signals F1, F2 to the feedback selection unit 130, and determine whether to turn on the LED strings according to the enable signal EN. In this embodiment, the enable signal EN may include a first enable signal EN1 and a second enable signal EN2 for controlling the current control circuits 142 and 144 respectively.

Similarly, when the enable signal EN is enabled, the feedback selection unit 130 will return one of the first feedback signals F1-F2 to the PWM unit 120, and when the enable signal EN is disabled, The feedback selection unit 130 feeds back the second feedback signal FS to the PWM unit 120 . The PWM unit 120 adjusts the output of the power conversion unit 110 according to the received feedback signal. The rest of the circuit structure of FIG. 2B is the same as that of FIG. 2A , and will not be repeated here.

second embodiment

It should be noted that the above-mentioned current pre-charging unit 150 can add a switch (for example realized by NMOS transistor M21 ) to save energy. Please refer to FIG. 3A , which is a driving circuit according to the second embodiment of the present invention. The main difference between FIG. 3A and FIG. 2A lies in the NMOS transistor M21. The current pre-charging unit 350 in FIG. 3A includes resistors R21 and R22 and the NMOS transistor M21. The NMOS transistor M21 is coupled between the resistor R22 and the ground terminal GND, and is controlled by the inverting enable signal EN, which can selectively turn on the current pre-charging unit 350 . In addition, the current pre-charging unit 350 can close the current path to save power when the LED string needs to be turned off for a longer period of time or the display power is turned off. In normal operation, when the enable signal EN is enabled, the NMOS transistor M21 is turned off, and when the enable signal EN is disabled, the NMOS transistor M21 is turned on. In addition, the NMOS transistor M21 can be controlled by the feedback selection unit 130 according to the enable signal EN, or an independent control circuit, such as the inverter 310 , can also be set, and this embodiment is not limited. The rest of the circuit structures and operations in FIG. 3A and FIG. 2A are the same, and will not be repeated here.

Similarly, FIG. 3A is also suitable for driving multiple LED strings, as shown in FIG. 3B , which is a driving circuit according to the second embodiment of the present invention. FIG. 3B includes two LED strings. For the driving method, please refer to the above-mentioned FIG. 2B and FIG. 3A , which will not be repeated here.

third embodiment

Next, please refer to FIG. 3C , which is a driving circuit according to a third embodiment of the present invention. The main difference between FIG. 3C and FIG. 3A lies in the current pre-charging unit 355 . The current pre-charging unit 355 includes a resistor R21 , an adjustable current source 320 , a control unit 360 and a delay unit 370 . The resistor R21 and the adjustable current source 320 are coupled between the driving power VOUT and the ground terminal GND. The common contact between the resistor R21 and the adjustable current source 320 outputs the second feedback signal FS. The control unit 360 is coupled between the original enable signal OEN and the adjustable current source 320 , and adjusts the conduction current of the adjustable current source 320 according to the original enable signal OEN. The delay unit 370 is coupled to the feedback selection unit 130 and the current control circuit 142 for delaying the original enable signal OEN to generate the enable signal EN to the feedback selection unit 130 and the current control circuit 142 . During the preset time when the original enable signal OEN is delayed, the control unit 360 pre-adjusts the adjustable current source 320 according to the amount of current to be conducted by the LED string, so that the output current of the power conversion unit 110 is increased in advance. After a preset time, the control unit 360 disables the adjustable current source 320, so that the current that was originally turned on through the current pre-charging unit 355 flows to the LED string to be turned on instead. Similarly, the current pre-charging unit 355 can also be applied in FIG. 3B to replace the current pre-charging unit 350 .

The above-mentioned current control circuits 142 and 144 are mainly used to control the conduction current of the LED strings, and its implementation mode can be implemented by various circuit structures according to the design requirements, as shown in Figures 4A to 4C, which are according to the present invention Various circuit structures of the current control circuit. Taking the current control circuit 142 as an example, please refer to FIGS. 4A-4C . In FIG. 4A , the current control circuit 142 can be composed of a current source 410 and a current mirror 420 to determine the current conducted by the LED string. It should be noted that the current mirror 420 is controlled by the enable signal EN to determine whether to be enabled, for example, by using a switch disposed in the current conduction path of the current mirror 420 .

In FIG. 4B , the current control circuit 142 is realized by connecting the resistor R41 and the NMOS transistor M41 in series between the first feedback signal F1 and the ground terminal GND. The NMOS transistor M41 is controlled by the enable signal EN, which can be The conduction current is determined according to the voltage of the enable signal EN. In FIG. 4C, the current control circuit 142 can be composed of an operational amplifier 430, an NMOS transistor M42, and a resistor R42. The output terminals of the operational amplifier 430 are respectively coupled to the enable signal EN and the source of the NMOS transistor M42. The resistor R42 is It is coupled between the drain of the NMOS transistor M42 and the ground terminal GND. It should be noted that the above circuit structures in FIGS. 4A-4C are only exemplary embodiments of the current control circuit 142 , and the present invention is not limited thereto.

The current pre-charging unit 150 is mainly used to provide another current path of the power conversion unit 110 and is suitable for maintaining the output current of the power conversion unit 110 when the LED is turned off. In addition, in another embodiment of the present invention, the current pre-charging unit 150 can dynamically adjust the output current of the power conversion unit 110 according to the current corresponding to the enable signal EN when the LED is about to be turned on, so that the LED can obtain the required current immediately. required current. For example, when the enable signal EN is about to turn on the LED string and requires the current I1, the current pre-charging unit 150 will first increase the output current of the power conversion unit 110 by the current I1. When the enable signal EN needs twice the current I1 to turn on the LED string, the current pre-charging unit 150 first increases the output current of the power conversion unit 110 by twice the current I1. That is to say, the current pre-charging unit 150 dynamically adjusts the conduction current according to the enable signal EN, so that the output current of the power conversion unit 110 can be adjusted in advance according to the enable signal EN.

The adjustable current source 320 in the current pre-charging unit 355 can be implemented by various circuit structures according to design requirements, as shown in FIG. 5A-FIG. 5F, and FIG. 5A-FIG. 5F are various circuits of the current pre-charging unit according to the present invention structure. Referring to FIG. 5A , the current pre-charging unit 150 is coupled in series between the driving power VOUT and the ground terminal GND through a resistor R21 and a variable resistor R51 . The current pre-charging unit 150 can adjust the output current of the power conversion unit 110 by adjusting the resistance value of the variable resistor R51. In another embodiment of the present invention, the variable resistor R51 can be directly set by the feedback selection unit 130 with reference to the enable signal EN to dynamically adjust the output current of the power conversion unit 110 .

Next, please refer to FIG. 5B , the main difference between it and FIG. 5B is the NMOS transistor M51 , which is coupled between the resistor R52 and the ground terminal GND. The gate of the NMOS transistor M51 is coupled to the control unit 360. When the system needs to enter the power saving mode, the current path of the current pre-charging unit 355 can be closed to save power consumption. FIG. 5C is another constant current circuit architecture, including a resistor R21, an NMOS transistor M52, an operational amplifier 510, and a resistor R53. The resistor R21, the NMOS transistor M52 and the resistor R53 are coupled between the driving power VOUT and the ground terminal GND. The negative input terminal of the operational amplifier 510 is coupled to the source of the NMOS transistor M52. The amount of current conducted by the current pre-charging unit 355 can be controlled through the positive input terminal of the operational amplifier 510 .

Next, please refer to FIG. 5D . FIG. 5D is composed of a resistor R21 and a plurality of current mirrors 520 , 530 . The resistor R21 is connected to the current mirrors 520 , 530 through switches SW51 , SW52 . The current mirrors 520 and 530 respectively map the current I1 and the current I2 of the current sources 551 and 552 . The current flowing through the resistor R21 can be adjusted by controlling the conduction of the switches SW51 and SW52. The switches SW51 and SW52 can also be controlled by the control unit 360 . The current mirrors 520 and 530 in FIG. 5D can be directly integrated with the current source in the current adjustment unit 140 to map the current of each LED string when it is turned on. The current mirrors 520 and 530 can adopt the structure design of a general current mirror, and the aspect ratio of the elements can be designed according to the current ratio, which will not be repeated here. In addition, the above current mirrors 520 and 530 in FIG. 5D can be directly expressed as current sources, as shown in FIG. 5E . In FIG. 5E , the resistor R21 is coupled to the current sources 553 , 554 and 555 through the switches SW53 , SW54 and SW55 . The current of the resistor R21 can be adjusted by controlling whether the switches SW53, SW54, and SW55 are turned on or not. The switches SW51 , SW51 , SW551 can also be controlled by the feedback selection unit 130 .

5A to 5E above, it can be concluded that the circuit structure of the current pre-charging unit 150 can be composed of a resistor and an adjustable current source, as shown in FIG. 5F, the resistor R21 and the adjustable current source 560 are coupled in series to the driving power supply Between VOUT and ground GND. The circuit architecture of the adjustable current source 560 can be realized with reference to the circuit architectures in FIG. 5A to FIG. 5E , but the present invention is not limited thereto. The adjustable current source 560 can adjust the current value according to the enable signal EN, or set the current value at a specific value according to the design requirement to maintain the current output value of the power conversion unit 110 .

Based on the above, the present invention adds a current pre-charging unit (150, 350 or 355) at the output end of the power conversion unit 110. This current pre-charging unit can be pre-conducted before the light-emitting diode is turned on, so that the output of the power conversion unit 110 The current is pre-boosted to enhance its drive capability. When the LED is turned on, this current path is automatically turned off, allowing the LED to quickly obtain the required amount of current. During the dynamic display process, the current pre-charging unit can cooperate with the adjustable current source to delay the enable signal of the LED for a period of time, and increase the output current of the power conversion unit 110 in advance during the delay time. When the light-emitting diode is turned on, it will also be automatically turned off to allow the light-emitting diode to obtain the required amount of current. By setting the current pre-charging unit, the output current of the power conversion unit 110 can be adjusted in advance, so that the LED can be turned on quickly.

In addition, the current adjustment unit 140 and the current pre-charging unit 150 , 350 , 355 are mainly used to control the magnitude of the current and generate a feedback signal to adjust the output of the power conversion unit 110 . The above circuit structures in FIGS. 4A-4C and FIGS. 5A-5F are only exemplary embodiments of the current adjustment unit 140 and the current pre-charging unit 150, the present invention is not limited thereto, and those skilled in the art Other feasible circuit structures can be easily deduced after the disclosure of the present invention, which will not be repeated here. The above NMOS transistors in FIGS. 4a-4c and FIGS. 5a-5f can also be implemented with PMOS transistors according to design requirements, but the circuit structure needs to be adjusted accordingly.

Fourth embodiment

From another point of view, the above embodiments can be summarized as a driving method of a light emitting diode, please refer to FIG. 6 , which is a flowchart of a driving method of a light emitting diode according to a fourth embodiment of the present invention. Firstly, output the driving power to drive the LED unit and generate a first feedback signal (step S610 ). In this step, the first feedback signal is used to adjust the voltage and current of the driving power so that the LED can obtain sufficient driving current. Then, another current path is provided to the driving power supply and a second feedback signal is generated according to the current conducted by the current path (step S620 ). During the driving process of the LED unit, it is determined whether to turn on the LED in the LED unit according to the enable signal (step S630), and when the LED in the LED unit is turned on, the driving power is adjusted according to the first feedback signal (step S640), when the LED unit is turned off, adjust the driving power according to the second feedback signal (step S650). Since the driving power is adjusted according to the second feedback signal when the LED unit is turned off, the driving power can be adjusted by adjusting the current conducted by the above-mentioned current path so that it has sufficient current driving capability in advance.

The above-mentioned driving method provides an additional current path in the driving circuit of the light-emitting diode, and through this current path, the current size of the driving power supply is adjusted in advance, so that its current driving capability can meet the current demand required to turn on the light-emitting diode to speed up the switching of the light-emitting diode speed. For the rest of the operation details in the above-mentioned driving method, please refer to the description of the above-mentioned FIGS.

To sum up, the present invention proposes an improved method for the driving capability of the LED driving circuit. An additional current path is set in the driving circuit to maintain its current output capability, or it is pre-set according to the amount of current required by the LED string to be turned on. By adjusting the output current of its driving circuit, the LED can switch quickly and obtain the required driving current in real time.

Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: it can still be Modifications are made to the technical solutions described in the foregoing embodiments, or equivalent replacements are made to some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims (20)

1. A driving circuit for a light emitting diode, suitable for driving at least one light emitting diode unit, the light emitting diode unit comprising at least one light emitting diode, the driving circuit comprising: A driving unit, outputting a driving power supply to the light emitting diode unit, and outputting at least a first feedback signal according to the current conducted by the light emitting diode unit; a current pre-charging unit, coupled to the output of the driving unit to provide a current path to the driving unit and generate a second feedback signal according to the driving power; and a feedback selection unit, coupled to the drive unit and the current pre-charging unit, selects one of the at least one first feedback signal or the second feedback signal as an output according to an enabling signal; Wherein, the driving unit adjusts the driving power according to the output of the feedback selection unit. 2. The driving circuit of the light emitting diode according to claim 1, wherein the driving unit comprises: A power conversion unit, coupled to the light emitting diode unit, converts an input voltage into the driving power, and outputs the driving power to the light emitting diode unit; A current adjustment unit, coupled to the LED unit, selectively turns on the at least one LED in the LED unit according to the enabling signal and generates the at least one first feedback signal; and A pulse width modulation unit is coupled to the feedback selection unit and the power conversion unit, and adjusts the output of the power conversion unit according to the output of the feedback selection unit. 3. The driving circuit of the light emitting diode according to claim 1, wherein when the enabling signal is disabled to turn off the light emitting diode unit, the feedback selection unit selects the second feedback signal as an output, so that the driving unit The output current is maintained at a specific value. 4. The driving circuit of the light emitting diode according to claim 1, wherein when the enable signal enables the light emitting diode unit to be turned on, the feedback selection unit selects one of the at least one first feedback signal as output. 5. The driving circuit of LED according to claim 2, wherein the at least one LED in the LED unit is connected in series to form at least one LED string, and the at least one LED string is coupled to the Between the output of the power conversion unit and the current adjustment unit, the common contact between the at least one LED string and the current adjustment unit generates the at least one first feedback signal. 6. The driving circuit of the light emitting diode according to claim 5, wherein when the enable signal enables the current adjustment unit to selectively turn on the at least one light emitting diode string, the feedback selection unit selects the corresponding to the at least one light emitting diode string. One of the at least one first feedback signal of the at least one LED string that is turned on is used as an output. 7. The driving circuit of the light emitting diode according to claim 6, wherein the feedback selection unit selects a signal having a minimum voltage from the at least one first feedback signal corresponding to the turned on at least one light emitting diode string one of them as output. 8. The driving circuit of a light emitting diode according to claim 1, wherein the current pre-charging unit comprises: a first resistor; and a second resistor; Wherein, the first resistor and the second resistor are coupled in series between the output of the driving unit and a ground terminal, and the common junction of the first resistor and the second resistor generates the second feedback signal. 9. The driving circuit of a light emitting diode according to claim 1, wherein the current pre-charging unit comprises: a first resistor; A second resistor, the first resistor and the second resistor are coupled in series between the output of the drive unit and a switch, the other end of the switch is coupled to a ground terminal, the first resistor and the second resistor The common contact of generates the second feedback signal; and an inverter, the input end of the inverter is coupled to the enabling signal, and the output end of the inverter is coupled to the switch; Wherein, when the enabling signal is disabled, the switch is turned on; when the enabling signal is enabled, the switch is turned off. 10. The driving circuit of a light emitting diode according to claim 1, wherein the current pre-charging unit comprises: a first resistor, one end of the first resistor is coupled to the output of the drive unit; and an adjustable current source, coupled between the other end of the first resistor and a grounding end; a control unit, coupled to the adjustable current source and adjusting the conduction current of the adjustable current source according to an original enabling signal; and a delay unit, coupled between the feedback selection unit, the current control circuit and the original enabling signal, the delay unit delays the original enabling signal for a preset time to output the enabling signal to the feedback selection unit and the current control circuit; Wherein, the common contact between the adjustable current source and the first resistor outputs the second feedback signal, and the control unit changes the current value conducted by the adjustable current source according to the original enable signal during the preset time . 11. The LED driving circuit according to claim 10, wherein the control unit disables the adjustable current source after the preset time. 12. The driving circuit of LED according to claim 10, wherein the adjustable current source comprises: At least one current mirror circuit is coupled to the first resistor through several switches, and selectively maps the corresponding current when the at least one LED is turned on according to the original enabling signal. 13. The driving circuit of LED according to claim 10, wherein the adjustable current source comprises: an operational amplifier, the positive input terminal of the operational amplifier is coupled to a reference voltage output by the control unit; An NMOS transistor, the drain of which is coupled to the other end of the first resistor, the source of which is coupled to the negative input terminal of the operational amplifier, and the gate of the NMOS transistor is coupled to the output terminal of the operational amplifier; and A second resistor is coupled between the source of the NMOS transistor and a ground terminal. 14. The driving circuit of LED according to claim 10, wherein the adjustable current source comprises: Several switches are coupled between the first resistor and several current sources, wherein the several switches are controlled by the control unit. 15. The driving circuit of LED according to claim 2, wherein the power conversion unit is a boost circuit. 16. The driving circuit of the light emitting diode according to claim 2, wherein the current adjustment unit comprises a plurality of current control circuits respectively coupled to the at least one light emitting diode and respectively controlling the at least one light emitting diode according to the enabling signal The current conducted by the diode. 17. A driving method for a light emitting diode, comprising: Outputting a driving power to drive a LED unit and generate at least a first feedback signal; providing a current path to the drive power supply and generating a second feedback signal according to the current conducted by the current path; and determining whether to turn on the at least one light emitting diode according to an enabling signal; Wherein, when the light emitting diode unit is turned off, the driving power is adjusted according to the second feedback signal; when the light emitting diode unit is turned on, the driving power is adjusted according to the first feedback signal. 18. The driving method of the light emitting diode according to claim 17, further comprising: when the light emitting diode unit is turned off, adjusting the current of the driving power according to the second feedback signal, so that the current of the driving power is maintained at a specific value . 19. The driving method of a light emitting diode according to claim 17, wherein the step of determining whether to turn on the light emitting diode unit according to the enabling signal further comprises: receiving an original enabling signal; delaying the original enable signal for a preset time to generate the enable signal; and During the preset time, the current conducted by the current path is adjusted according to the original enabling signal. 20. The driving method of a light emitting diode according to claim 17, wherein the light emitting diode unit comprises at least one light emitting diode string.

Images