LED backlight driving circuit and liquid crystal display

Embodiments of the disclosure disclose a LED backlight driving circuit, including a power source, LED strings, a buck circuit, and a LED controller. The LED strings include at least one string of LED lamps, a positive terminal thereof and the power source are electrically connected. The buck circuit and the LED strings are electrically connected. The LED controller and the buck circuit are electrically connected. The LED controller controls the power source to provide electricity to the LED strings and controls the buck circuit to store energy during a first period. The LED controller controls the buck circuit to provide electricity to the LED strings during a second period. The disclosure further provides a liquid crystal display. The disclosure has the advantage of preventing the LED backlight driving circuit from being damaged easily.

This disclosure claims priority to Chinese patent application No. 201710004506.3, entitled “LED BACKLIGHT DRIVING CIRCUIT AND LIQUID CRYSTAL DISPLAY” filed on Jan. 4, 2017, which is incorporated by reference in its entirety.

FIELD OF THE DISCLOSURE

The disclosure relates to a liquid crystal display technical field, and more particularly to a LED backlight driving circuit and a liquid crystal display.

BACKGROUND

The backlight technology of LCD is developed continuously as the display technique is improved constantly. A backlight source of a conventional liquid crystal display adopts a cold cathode fluorescent lamp (CCFL). But the CCFL backlight source has disadvantages such as relatively poor color rendition ability, low luminous efficiency, high discharge voltage, poor discharge property at low temperature, long time for heating till stable gray scale and so on. The backlight source technology using a light emitting diode (LED) backlight source has been developed.

FIG. 1is a conventional LED backlight driving circuit applied in a liquid crystal display. As shown inFIG. 1, the LED backlight driving circuit includes a boost circuit, a LED controller, a capacitor C1′ and a LED strip. The boost circuit includes an inductance L′, a diode D′, a first transistor Q1′ and a first resistor R1′. One end of the inductance L′ receives a direct-current voltage Vin input from a power source, the other end of the inductance L′ is connected to an anode of the diode D′ and a drain electrode of the first transistor Q1′. A gate electrode (control end) of the first transistor Q1′ is driven by a first control signal provided by the LED controller. The source electrode of the first transistor Q1′ and the ground are electrically connected by the first resistor R1′. A cathode of the diode D′ is electrically connected to a positive terminal of the LED strip. The cathode of the diode D′ is further connected with the ground by the capacitor C′. A negative terminal of the LED strip is further connected with a second transistor Q2′. A drain electrode of the second transistor Q2′ is connected to the negative terminal of the LED strip. A source electrode of the second transistor Q2′ and the ground are electrically connected by a second resistor R2′. A gate electrode of the second transistor Q2′ is driven by a second control signal provided by the LED controller. The operational current of the LED strip can be increased or decreased by adjusting a duty ratio of the second control signal to control brightness of the LED strip.

The inventor of the disclosure discovers the number of required LED lamps is increasing with enlargement of panels, demands of outdoor display or commercial display in the process of the LED backlight driving circuit above, such as the number of LED lamps included in the LED strip exceeds 16. The LED lamps are series connection, which lead to increase of an output voltage Vout of the inductance L′ to drive the LED strip after boosting the voltage, such as over 90V or 100V, so that the first transistor Q1′ and the diode D′ experience a high level of stress, resulting in shortening life of the first transistor Q1′ and the diode D′, or even causing damage of the LED backlight driving circuit. Moreover, conversion efficiency of the boost circuit is inversely proportional to boost voltage, which means the conversion efficiency is lower while the voltage is higher. The conversion efficiency of the boost circuit will be reduced, energy is wasted.

SUMMARY

An embodiment of the disclosure provides a LED backlight driving circuit and a liquid crystal display. Which can prevent circuit damage and save energy.

In order to solve the technical problem above, the disclosure provides a LED backlight driving circuit, including a power source, LED strings, a buck circuit, and a LED controller. The LED strings include at least one string of LED lamps, a positive terminal thereof and the power source are electrically connected. The buck circuit and the LED strings are electrically connected. The LED controller and the buck circuit are electrically connected. The LED controller controls the power source to provide electricity to the LED strings and controls the buck circuit to store energy during a first period. The LED controller controls the buck circuit to provide electricity to the LED strings during a second period.

In an embodiment of the disclosure, the buck circuit includes an inductance element, a diode element, a capacitor element and a transistor element. A first terminal of the inductance element and a negative terminal of the LED strings are electrically connected. An anode of the diode element and a second terminal of the inductance element are electrically connected, a cathode of the diode element and positive terminals of the LED strings are electrically connected. One end of the capacitor element and the cathode of the diode element are electrically connected, the other end thereof and a first terminal of the inductance element are electrically connected. A drain electrode of the transistor element is electrically connected with the second terminal of the inductance element, a source electrode of the transistor element is electrically connected to ground, and a control end thereof is electrically connected with the LED controller.

In an embodiment of the disclosure, the LED strings include a first LED string and a second LED string. The first LED string is on a first branch. A positive terminal of the first LED string and the power source are electrically connected. The first LED string includes at least two LED lamps. The second LED string is on a second branch. The second branch and the first branch are parallel connected. A positive terminal of the second LED string and the power source are electrically connected. The second LED string includes at least two LED lamps. The inductance element includes a first inductance and a second inductance. A first terminal of the first inductance and a negative terminal of the first LED string are electrically connected. A first terminal of the second inductance and a negative terminal of the second LED string are electrically connected. The diode element includes a first diode and a second diode. An anode of the first diode and a second terminal of the first inductance are electrically connected. A cathode of the first diode and a positive terminal of the first LED string are electrically connected. An anode of the second diode and a second terminal of the second inductance are electrically connected. A cathode of the second diode and a positive terminal of the second LED string are electrically connected. The capacitor element includes a first capacitor and a second capacitor. One end of the first capacitor and the cathode of the first diode are electrically connected. The other end of the first capacitor and the first terminal of the first inductance are electrically connected. One end of the second capacitor and the cathode of the second diode are electrically connected, the other end thereof and the first terminal of the second inductance are electrically connected. The transistor element includes a first transistor and a second transistor. A drain electrode of the first transistor is electrically connected with the second terminal of the first inductance. A source electrode of the first transistor is electrically connected to the ground. A control end of the first transistor is electrically connected with the LED controller. A drain electrode of the second transistor is connected with the second terminal of the second inductance. A source electrode of the second transistor is electrically connected to the ground. A control end of the second transistor is electrically connected with the LED controller.

In an embodiment of the disclosure, in the first period, the LED controller controls the first transistor and the second transistor to communicate, the first diode and the second diode are cut-off. The power source provides electricity to the first LED string and the second LED string. The power source further provides electricity to the first inductance and the second inductance to store energy in the first inductance and the second inductance. In the second period, the LED controller controls the first transistor and the second transistor to cut-off, the first diode and the second diode are communicated. The first inductance and the second inductance provide electricity to the first LED string and the second LED string respectively through the first diode and the second diode.

In an embodiment of the disclosure, the LED strings include a first LED string and a second LED string. The first LED string is on a first branch, a positive terminal thereof and the power source are electrically connected. The first LED string includes at least two LED lamps. The second LED string is on a second branch. The second branch and the first branch are parallel connected. A positive terminal of the second LED string and the power source are electrically connected. The second LED string includes at least two LED lamps. The inductance element includes a first inductance. A first terminal of the first inductance, a negative terminal of the first LED string and a negative terminal of the second LED string are electrically connected. The diode element includes a first diode. An anode of the first diode and a second terminal of the first inductance are electrically connected. A cathode of the first diode and a positive terminal of the first LED string as well as the second LED string are electrically connected. The capacitor element includes a first capacitor. One end of the first capacitor and the cathode of the first diode are electrically connected, the other end thereof and the first terminal of the first inductance are electrically connected. The transistor element includes a first transistor. A drain electrode of the first transistor is connected with the second terminal of the first inductance. A source electrode of the first transistor is electrically connected to the ground. A control end of the first transistor is electrically connected with the LED controller.

In an embodiment of the disclosure, in the first period, the LED controller controls the first transistor to be communicated and the first diode to be cut-off. The power source provides electricity to the first LED string and the second LED string. The power source further provides electricity to the first inductance to store energy in the first inductance. In the second period, the LED controller controls the first transistor to cut-off, the first diode is communicated. The first inductance provides electricity to the first LED string and the second LED string respectively through the first diode.

In an embodiment of the disclosure, the at least two LED lamps on the first LED string are series connection. The at least two LED lamps on the second LED string are series connection. The number of the LED lamps on the first LED string and that on the second LED string are equal.

In an embodiment of the disclosure, a range of inductance values of the first inductance and the second inductance is 47 μh-100 μh.

In an embodiment of the disclosure, the first period and the second period are included in one cycle.

The disclosure further provides a liquid crystal display, including a liquid crystal panel and a backlight module disposed opposite. The backlight module provides light to the liquid crystal panel to display images on the liquid crystal panel. The backlight module adopts a LED backlight source. The LED backlight source is driven by the LED backlight driving circuit described above.

The embodiments of the disclosure have following beneficial effects.

Stress loaded on devices in the embodiments is relatively small due to replacement of the boost circuit in the prior art by the buck circuit, which will not reduce lift of the devices, or damage the devices. So that the LED backlight driving circuit will not be destroyed easily. Moreover, the problem of low conversion efficiency of the boost circuit in the prior art can be prevented due to absence of the conventional boost circuit, which is benefit for saving energy. And the LED driving circuit in the embodiments can drive a large amount of LED lamps.

ILLUSTRATION ON LABELS

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Embodiments of the disclosure will be described in detail with reference to the accompanying drawings as follows. Obviously, the described embodiments are part of embodiments of the disclosure rather than all of them. Based on the embodiments of the disclosure, all other embodiments obtained by a person skilled in the art without creativity should be considered within the scope of protection of the disclosure.

Terms “comprise”, “have” and other forms thereof in embodiments, claims and figures of the disclosure indicate exclusive inclusion. Such as processes, methods, systems, products or devices containing a series of steps or elements are not restricted to the listed steps or elements, steps or elements out of list are optionally included. Or other steps or elements inherent in the process, methods, products or devices are optionally included. Moreover, terms “first”, “second”, “third” are used to distinguish different objects, rather than describing a certain order.

First Embodiment

Referring toFIG. 2,FIG. 2is a circuit diagram of a LED backlight driving circuit according to a first embodiment of the disclosure. The LED backlight driving circuit includes a power source110, LED strings, a buck circuit200and a LED controller140.

Specifically, the power source110is configured to provide electricity to the LED backlight driving circuit. The power source110provided by the embodiment needs to output the higher voltage compared with the power source110provided by the prior art. Output voltages such as 36V, 48V, 60V, 72V, etc. are provided to drive the LED string.

The LED strings include at least one string of LED lamps, a positive terminal thereof and the power source are electrically connected. In the embodiment, the LED includes a first LED string120and a second LED string130.

The first LED string120is on a first branch. The first LED string120includes at least two LED lamps, such as 2 LED lamps, 4 LED lamps, 6 LED lamps, 8 LED lamps, 9 LED lamps, 10 LED lamps, etc. The at least two LED lamps in the embodiment are series connection. However, in other embodiments of the disclosure, the at least two LED lamps can further be parallel connection.

The second LED string130is on a second branch. The second branch and the first branch are parallel connected. The second LED string130includes at least two LED lamps, such as 2 LED lamps, 4 LED lamps, 6 LED lamps, 8 LED lamps, 9 LED lamps, 10 LED lamps, etc. The at least two LED lamps in the embodiment are series connection. However, in other embodiments of the disclosure, the at least two LED lamps can further be parallel connection. In the embodiment, the number of LED lamps included in the first LED string120and the number of LED lamps included in the second LED string130are the same, which can balance brightness. Obviously, in other embodiments of the disclosure, the number of LED lamps included in the first LED string and the number of LED lamps included in the second LED string can also be different.

The buck circuit200is electrically connected with the first LED string120and the second LED string130respectively. The buck circuit200provides an output voltage lower than that of the power source110. The voltage provided by the buck circuit200is an output voltage such as 30V, 40V, 50V, 60V, etc. The voltage lower than that of the power source110is output, resulting in reducing the voltage.

The LED controller140and the buck circuit200are electrically connected to control the buck circuit200. The LED controller140controls the power source110to provide electricity to the first LED string120and the second LED string130respectively during a first period. The buck circuit200stores energy at the moment. The LED lamps in the first LED string120and the second LED string130can be lit by the power source110in the first period. The LED controller controls the buck circuit200to provide electricity to the first LED string120and the second LED string130respectively during a second period. The voltage is lower than the voltage output from the power source110. The LED lamps in the first LED string120and the second LED string130can be lit by the buck circuit200in the second period. The first period and the second period are different. The first period and the second period are substituted, such as X axis represents time, in sequence of first period-second period-first period-second period . . . , so on and so forth.

Accordingly, in the embodiment, stress loaded on devices in the embodiments is relatively small due to replacement of the boost circuit in the prior art by the buck circuit200, which will not reduce lift of the devices, or damage the devices. So that the LED backlight driving circuit will not be destroyed easily. Moreover, the problem of low conversion efficiency of the boost circuit in the prior art can be prevented due to absence of the conventional boost circuit, which is benefit for saving energy. And the LED driving circuit in the embodiment can drive a large amount of LED lamps. Brightness of the LED lamps is balanced.

Referring toFIG. 2, the buck circuit200includes an inductance element210, a diode element220, a capacitor element230and a transistor element240.

The inductance element210has a first terminal and a second terminal. The first terminal is electrically connected with negative terminals of the first LED string120and the second LED string130respectively. An anode of the diode element220and a second terminal of the inductance element210are electrically connected. A cathode of the diode element220is electrically connected with positive terminals of the first LED string120and the second LED string130respectively. The capacitor element230is configured to bootstrap, one end thereof and the cathode of the diode element220are electrically connected. The other end thereof and a first terminal of the inductance element210are electrically connected. A drain electrode of the transistor element240is electrically connected with the second terminal of the inductance element210, a source electrode thereof is electrically connected to ground. Optionally, in the embodiment, the source electrode of the transistor element240is electrically connected to the ground indirectly, a control end thereof (gate electrode) is electrically connected with the LED controller140. Therefore, the LED controller140can control the transistor element240to communicate or cut-off.

Specifically, in the embodiment, the inductance element210includes a first inductance L1and a second inductance L2. A first terminal of the first inductance L1and a negative terminal of the first LED string120are electrically connected. A first terminal of the second inductance L2and a negative terminal of the second LED string130are electrically connected. The diode element220includes a first diode D1and a second diode D2. An anode of the first diode D1and a second terminal of the first inductance L1are electrically connected. A cathode of the first diode D1and a positive terminal of the first LED string120are electrically connected. An anode of the second diode D2and a second terminal of the second inductance L2are electrically connected. A cathode of the second diode D2and a positive terminal of the second LED string130are electrically connected. The capacitor element230includes a first capacitor C1and a second capacitor C2. The first capacitor C1and the second capacitor C2are configured to bootstrap. One end of the first capacitor C1and the cathode of the first diode D1are electrically connected, the other end thereof and the first terminal of the first inductance L1are electrically connected. One end of the second capacitor C2and the cathode of the second diode D2are electrically connected, the other end thereof and the first terminal of the second inductance L2are electrically connected. The transistor element240includes a first transistor Q1and a second transistor Q2. A drain electrode of the first transistor Q1is electrically connected with the second terminal of the first inductance L1, a source electrode thereof is electrically connected to the ground. The source electrode is electrically connected to the ground indirectly in the embodiment. The source electrode is specifically connected to the ground electrically by a resistor. A control end of the first transistor Q1is electrically connected with the LED controller140. A drain electrode of the second transistor Q2is connected with the second terminal of the second inductance L2, a source electrode thereof is electrically connected to the ground. The source electrode is electrically connected to the ground indirectly in the embodiment. The source electrode is specifically connected to the ground electrically by a resistor. A control end of the second transistor Q2is electrically connected with the LED controller140.

Accordingly, the LED controller140controls the buck circuit200by communicating or cutting off the first transistor Q1and the second transistor Q2. Specifically, the LED controller140controls the first transistor Q1and the second transistor Q2to communicate during the first period. The first diode D1and the second diode D2are cut-off at the time. Electricity from the power source110is output to branches where the first LED string120and second LED string130are. Therefore, the power source110provides electricity to the first LED string120and the second LED string130, as well as storing energy in the first inductance L1and the second inductance L2. Referring to current flow paths CH1and CH2inFIG. 3, the path of current flow is: power source110→first LED string120→first inductance L1-first transistor Q1→resistor→ground, and power source110→second LED string130→second inductance L2→second transistor Q2→resistor→ground. The LED controller140controls the first transistor Q1and the second transistor Q2to cut-off during the second period. The first diode D1and the second diode D2are communicated at the time. The energy stored in the first inductance L1and the second inductance L2is released to be provided to the first LED string120and the second LED string130respectively. Referring to current flow paths CH3and CH4inFIG. 4, the path of current flow is: second terminal of first inductance L1→first diode D1→first LED string120→first terminal of first inductance L1, and second terminal of second inductance L2→second diode D2→second LED string130→first terminal of second inductance L2. As the first transistor Q1, the second transistor Q2, the first diode D1and the second diode D2are respectively on the negative terminals of the first LED string120and the second LED string130, voltages are relatively low. Stress loaded on the first transistor Q1, the second transistor Q2, the first diode D1and the second diode D2is relatively small, which will not reduce lift of the first transistor Q1, the second transistor Q2, the first diode D1and the second diode D2, or damage the first transistor Q1, the second transistor Q2, the first diode D1and the second diode D2. So that the LED backlight driving circuit will not be destroyed easily.

In the embodiment, inductance values of the first inductance L1and the second inductance L2are required to be relatively large. A range of the first inductance L1and the second inductance L2is 47 μh-100 μh, such as 47 μh, 50 μh, 55 μh, 60 μh, 65 μh, 70 μh, 75 μh, 80 μh, 86 μh, 90 μh, 95 μh, 100 μh, etc. So that the ripple current is small. Brightness of the first LED string120and the second LED string130is even. The problem of LED lamp flashing will not occur.

In the embodiment, the first transistor Q1and the second transistor Q2are NMOS transistors. Obviously, in other embodiments of the disclosure, the first transistor and the second transistor can further be switch components equal to the NMOS transistors.

In the embodiment, the first period and the second period form a cycle. In other words, a sum of the first period and the second period is time of a cycle. Specifically, the first period and the second period form the cycle of the first transistor Q1and the second transistor Q2. For instance, time for the first transistor Q1and the second transistor Q2to communicate and cut-off once is one cycle. The sum of the first period and the second period is one cycle of the first transistor Q1and the second transistor Q2. The cycle is for example 50 microseconds. The first transistor Q1and the second transistor Q2repeat periodic actions. But in other embodiments of the disclosure, the first period and the second period can also be shorter than one cycle, which means one cycle can also include a third period or so on. In the disclosure, the first period and the second period are included in one cycle.

In the embodiment, the LED backlight driving circuit further includes a third capacitor C3. One end of the third capacitor C3and the power source110are electrically connected. The other end of the third capacitor C3is electrically connected to the ground. The third capacitor C3is configured to filter.

The embodiment further provides a liquid crystal display. The liquid crystal display includes a liquid crystal panel and a backlight module disposed opposite. The backlight module provides light to the liquid crystal panel to display images on the liquid crystal panel. The backlight module adopts a LED backlight source. The LED backlight source is driven by the LED backlight driving circuit described above.

Furthermore, in other embodiments of the disclosure, the LED driving circuit can include a third LED string, a fourth LED string, etc. besides the first LED string and the second LED string. Correspondingly, the buck circuit adds such as a third inductance, a fourth inductance, a third diode, a fourth diode, a third capacitor, a fourth capacitor, etc.

Furthermore, in other embodiments of the disclosure, the LED strings can further include three strings of LED strings, four strings of LED strings, five strings of LED strings, etc.

Second Embodiment

FIG. 5is a circuit diagram of a LED backlight driving circuit according to a second embodiment of the disclosure. As the circuit ofFIG. 5and the circuit ofFIG. 2are similar, an identical symbol represents an identical element. The difference of the embodiment and the first embodiment is mainly the buck circuit300.

Referring toFIG. 5, in the embodiment, the buck circuit300includes an inductance element310, a diode element320, a capacitor element330and a transistor element340.

The inductance element310has a first terminal and a second terminal. The first terminal is electrically connected with negative terminals of the first LED string120and the second LED string130respectively. An anode of the diode element320and a second terminal of the inductance element310are electrically connected. A cathode of the diode element320are electrically connected with positive terminals of the first LED string120and the second LED string130respectively. The capacitor element330is configured to bootstrap, one end thereof and a pin of the diode element320are electrically connected. The other end thereof and a first terminal of the inductance element310are electrically connected. A drain electrode of the transistor element340is electrically connected with the second terminal of the inductance element310, a source electrode thereof is electrically connected to the ground. The source electrode is electrically connected to the ground indirectly in the embodiment. The source electrode of the transistor element340is electrically connected to the ground by a resistor, a control end thereof (gate electrode) is electrically connected with the LED controller140. Therefore, the LED controller140can control the transistor element340to communicate or cut-off.

Specifically, in the embodiment, the inductance element310includes a first inductance L1. A first terminal of the first inductance L1is electrically connected with the negative terminal of the first LED string120and the negative terminal of the second LED string130respectively. The range of inductance values of the first inductance L1is 47 μh-100 μh. The diode element320includes a first diode D1. An anode of the first diode D1and a second terminal of the first inductance L1are electrically connected. A cathode of the first diode D1is electrically connected with the positive terminal of the first LED string120and the positive terminal of the second LED string130respectively. The capacitor element330includes a first capacitor C1. The first capacitor C1is configured to bootstrap. One end of the first capacitor C1and the cathode of the first diode D1are electrically connected, the other end thereof and the first terminal of the first inductance L1are electrically connected. The transistor element340includes a first transistor Q1. A drain electrode of the first transistor Q1is electrically connected with the second terminal of the first inductance L1, a source electrode thereof is electrically connected to the ground. The source electrode thereof is electrically connected to the ground indirectly in the embodiment. The source electrode is specifically connected to the ground electrically by a resistor. A control end of the first transistor Q1is electrically connected with the LED controller140.

Accordingly, the LED controller140controls the buck circuit300by communicating or cutting off the first transistor Q1. Specifically, the LED controller140controls the first transistor Q1to communicate during the first period. The first diode D1is cut-off at the time. Electricity from the power source110is output to branches where the first LED string120and second LED string130are. Therefore, the power source110provides electricity to the first LED string120and the second LED string130, as well as storing energy in the first inductance L1. The LED controller140controls the first transistor Q1to cut-off during the second period. The first diode D1is communicated at the time. The energy stored in the first inductance L1is released to be provided to the first LED string120and the second LED string130respectively.

In the embodiment, as the number of components applied in the buck circuit300is reduced compared with the first embodiment, costs can be reduced as well.

Third Embodiment

FIG. 6is a circuit diagram of a LED backlight driving circuit according to a third embodiment of the disclosure. As the circuit ofFIG. 6and the circuit ofFIG. 5are similar, an identical symbol represents an identical element. The difference of the embodiment and the first embodiment is mainly the number of LED strings.

Referring toFIG. 6, in the embodiment, the LED strings include a first LED string420, which includes at least one string of LED lamps, a positive terminal thereof and the power source are electrically connected.

The buck circuit300includes the inductance element310, the diode element320, the capacitor element330and the transistor element340. The inductance element310has a first terminal and a second terminal. The first terminal is electrically connected with the negative terminal of the first LED string420. An anode of the diode element320and a second terminal of the inductance element310are electrically connected. A cathode of the diode element320is electrically connected with the positive terminal of the first LED string420. The capacitor element330is configured to bootstrap, one end thereof and the pin of the diode element320are electrically connected. The other end thereof and a first terminal of the inductance element310are electrically connected. A drain electrode of the transistor element340is electrically connected with the second terminal of the inductance element310, a source electrode thereof is electrically connected to the ground. The source electrode is electrically connected to the ground indirectly in the embodiment. The source electrode of the transistor element340is electrically connected to the ground by a resistor, a control end thereof (gate electrode) is electrically connected with the LED controller140. Therefore, the LED controller140can control the transistor element340to communicate or cut-off.

Specifically, in the embodiment, the inductance element310includes a first inductance L1. A first terminal of the first inductance L1and a negative terminal of the first LED string420are electrically connected. The range of inductance values of the first inductance L1is 47 μh-100 μh. The diode element320includes the first diode D1. An anode of the first diode D1and a second terminal of the first inductance L1are electrically connected. A cathode of the first diode D1is electrically connected with the positive terminal of the first LED string420. The capacitor element330includes the first capacitor C1. The first capacitor C1is configured to bootstrap. One end of the first capacitor C1and the cathode of the first diode D1are electrically connected, the other end thereof and the first terminal of the first inductance L1are electrically connected. The transistor element340includes a first transistor Q1. A drain electrode of the first transistor Q1is electrically connected with the second terminal of the first inductance L1, a source electrode thereof is electrically connected to the ground. The source electrode thereof is electrically connected to the ground indirectly in the embodiment. The source electrode is specifically connected to the ground electrically by a resistor. The control end of the first transistor Q1is electrically connected with the LED controller140.

Accordingly, the LED controller140controls the buck circuit300by communicating or cutting off the first transistor Q1. Specifically, the LED controller140controls the first transistor Q1to communicate during the first period. The first diode D1is cut-off at the time. Electricity from the power source110is output to the branch where the first LED string420is. Therefore, the power source110provides electricity to the first LED string420and stores energy in the first inductance L1. The LED controller140controls the first transistor Q1to cut-off during the second period. The first diode D1is communicated at the time. The energy stored in the first inductance L1is released to be provided to the first LED string420.

The problem of low conversion efficiency of the boost circuit in the prior art can be prevented due to absence of the boost circuit in the embodiment, which is benefit for saving energy. Moreover, stress loaded on components in the embodiment is relatively small due to replacement of the boost circuit in the prior art by the buck circuit, which will not reduce lift of the components, or damage the components. So that the LED backlight driving circuit will not be destroyed easily.

It needs to be illustrated that each of the embodiments in the disclosure is described in a sequence of progression. The emphasis of each of the embodiments is the difference from the other embodiments. Same or similar sections among the embodiments can be referred mutually. As the embodiments on devices are almost the same with the embodiments on methods, description will be simple. Related sections can be referred to illustration in the embodiments on methods.

The disclosure has following advantages by description of the embodiment above.

Stress loaded on components in the embodiments is relatively small due to replacement of the boost circuit in the prior art by the buck circuit, which will not reduce lift of the components, or damage the components. So that the LED backlight driving circuit will not be destroyed easily. Moreover, the problem of low conversion efficiency of the boost circuit in the prior art can be prevented due to absence of the conventional boost circuit, which is benefit for saving energy. And the LED driving circuit in the embodiment can drive a large amount of LED lamps. Brightness of the LED lamps is balanced.

The disclosed above is merely preferred embodiments of the disclosure, which cannot limit the protection scope of the disclosure. Equivalent modification within the spirit of the claims of the disclosure should be covered by the protected scope of the disclosure.