TWI683595B - System and method for LED backlight driving dual controller cascade - Google Patents

Abstract

The invention relates to a system and method for cascading LED backlight driving dual controllers. Provided is a LED driving system, including: a power stage for converting an input voltage into a regulated voltage and supplying to a plurality of LED lamp bead strings; a voltage selector for selecting a plurality of LED lamp bead string first feedback points The lowest voltage input at the controller is configured to: if the first lowest voltage first becomes greater than the first reference voltage, then take the second reference voltage as the first feedback signal and the second lowest voltage as the second feedback signal, the first The second lowest voltage is finally stabilized at the difference between twice the first reference voltage and the second reference voltage; the pulse width modulator is used to adjust the operating factor of the driving signal based on the first lowest voltage and the second lowest voltage; and the driver , Used to drive the LED system according to the drive signal.

Description

System and method for LED backlight driving dual controller cascade

Some embodiments of the invention relate to integrated circuits. More specifically, some embodiments of the present invention provide a method of cascade control applied to a dual controller of a light emitting diode (LED) backlight system.

As a new energy-saving and environmentally friendly light source, LED is widely used in various fields due to its advantages of high brightness, low power consumption and long life. In LED backlight applications for large-size liquid crystal display devices such as Liquid-crystal Display (LCD) LCD TV, in order to make the brightness of the entire screen uniform, it is often used to provide backlight illumination by means of multi-channel LED lamp beads to produce uniform backlight brightness. A multi-channel backlight system architecture often requires more LED backlight lamp bead strings as the size of the liquid crystal display device increases.

2)。功率轉換單元功率級110採用DC-DC或AC-DC的開關電源控制架構用於為LED燈珠串提供穩定的輸出電壓VOUT。控制器單元控制器108通過偵測輸出電壓的變化進行誤差放大並產生脈寬調變(Pulse Width Modulation,PWM)或脈衝頻率調變(Pulse Frequency Modulation,PFM)信號。輸出控制功率級110功率開關的驅動信號閘極GATE。最小LEDx電壓選擇器106用於判斷選擇燈珠串的回饋點LED1至LEDN的最低電壓LEDx_min並將其作為控制器108的輸入信號。N個 電流平衡器，用於為N串LED燈珠串提供穩定的LED輸出電流。 FIG. 1 is a diagram showing a typical application diagram of a conventional multi-channel LED lamp bead string driving circuit. The traditional multi-channel LED lamp string driving circuit mainly includes a power conversion unit power stage 110, a controller unit controller 108, a minimum controller LEDx voltage selector 106, and N current balancers (N

2). The power stage 110 of the power conversion unit adopts a DC-DC or AC-DC switching power supply control architecture to provide a stable output voltage VOUT for the LED lamp bead string. The controller unit controller 108 performs error amplification by detecting changes in the output voltage and generates pulse width modulation (Pulse Width Modulation, PWM) or pulse frequency modulation (Pulse Frequency Modulation, PFM) signals. Output the drive signal gate GATE of the power stage 110 power switch. The minimum LEDx voltage selector 106 is used to determine the minimum voltage LEDx_min of the feedback points LED1 to LEDN of the selected lamp bead string and use it as the input signal of the controller 108. N current balancers are used to provide stable LED output current for N strings of LED lamp beads.

Figure 2 is the circuit block diagram of the current balancer. Including amplifier 201, adjustment transistor Q1, resistor RSEN. The amplifier 201 has a non-inverting input receiving the reference signal VREF, an inverting input connected to the resistor RSEN to receive the feedback voltage VS, and an output connected to the base of the adjustment transistor Q1. One end of the resistor RSEN is connected to the inverting input of the amplifier 201, and one end is grounded. The base of the adjustment transistor Q1 is connected to the output of the amplifier 201, the emitter is connected to the resistor RSEN, and the collector is connected to the LED lamp bead. The formed negative feedback circuit makes the feedback terminal voltage VS equal to the reference signal VREF, then the current flowing through the adjustment transistor Q1 is the set LED current, as shown in Equation 1: ILED = VREF / RSEN (Equation 1)

In order to make the negative feedback circuit work normally, the LED current adjustment transistor Q1 needs to work in the saturation region, so the controller LEDx voltage needs to be greater than a certain value. Therefore, the design controller LEDx reference voltage VREF_EA, through the system in Figure 1, the minimum voltage of the N string LED lamp string is LEDx_min equal to the reference voltage VREF_EA, which can ensure that all current balancers can reach the designed LED current value.

FIG. 3 shows the internal circuit of the controller 108. It includes an error amplifier 301 and an output capacitor Ccmp, which are used to amplify and integrate the difference between the reference voltage VREF_EA and the lowest voltage LEDx_min; a ramp generating circuit 304, which outputs a ramp signal Vslope; and a PWM comparator unit 302, which is used to compare the error amplifier output CMP and Vslope generates a PWM signal; the signal driving unit driver 303 outputs a gate GATE signal for driving the power stage control switch. When the LED driving circuit system works stably, the minimum LEDx voltage LEDx_min in each string of lamp beads is equal to the reference voltage VREF_EA.

In LED backlight applications for large-size liquid crystal display devices, multi-channel LED lamp strings are often used to provide uniform backlight brightness to provide backlight illumination, and the number of LEDx current paths of the controller is relatively fixed due to limitations such as packaging, cost, and heat dissipation. The traditional control method is to connect multiple systems controlled by multiple controllers in parallel to generate multiple LED lamp beads. This solution requires multiple sets of power devices (such as inductors, power switches, etc.), which has high cost and volume. Big.

Therefore, there is a great need for an improved LED backlight driving dual controller cascade system and method.

Some embodiments of the invention relate to integrated circuits. More specifically, some embodiments of the present invention provide a system and method for LED backlight driving a dual controller cascade. Merely by way of example, some embodiments of the invention are applied to LED-backlit displays. However, it will be recognized that the present invention has a broader scope of application.

The present invention introduces a system and method for LED backlight driving dual controller cascade. Control method In the application of high-power backlight systems, two controllers share a set of DC-DC or AC-DC LED backlight power supply control system and expand the number of LED backlight lamp beads, saving system costs, further can also be based on The difference of LED lamp bead string adjusts the master-slave controller to optimize the system efficiency.

According to an embodiment, there is provided a driving system for an LED, including: a power stage for converting an input voltage into a regulated voltage to provide to a plurality of LED lamp bead strings; a first voltage selector and a second voltage selector, Used to select the first lowest voltage input at the first feedback point and the second lowest voltage input at the second feedback point of multiple LED lamp bead strings, the first lowest voltage and the second lowest voltage increase as the adjusted voltage increases The controller is configured to: if the first lowest voltage first becomes greater than the first reference voltage, then take the second reference voltage as the first feedback signal and the second lowest voltage as the second feedback signal, the second lowest voltage finally stabilizes At the difference between twice the first reference voltage and the second reference voltage, otherwise if the second lowest voltage first becomes greater than the first reference voltage, the first lowest voltage is taken as the first feedback signal and the second reference voltage as the first Two feedback signals, the first lowest voltage is finally stabilized at the difference between twice the first reference voltage and the second reference voltage; the pulse width modulator is used to adjust the driving signal based on the first lowest voltage and the second lowest voltage Working factor; and driver, used to drive the LED system according to the driving signal.

According to another embodiment, a driving method for an LED system is provided The method includes: converting the input voltage into an adjusted voltage and providing it to a plurality of LED lamp bead strings; selecting the first lowest voltage input at the first feedback point and the second lowest voltage at the second feedback point of the plurality of LED lamp bead strings Input, the first lowest voltage and the second lowest voltage increase as the adjusted voltage increases; if the first lowest voltage first becomes greater than the first reference voltage, the second reference voltage is taken as the first feedback signal and the second lowest voltage As the second feedback signal, the second lowest voltage finally stabilizes at the difference between twice the first reference voltage and the second reference voltage, otherwise if the second lowest voltage first becomes greater than the first reference voltage, the first lowest voltage is taken As the first feedback signal and the second reference voltage as the second feedback signal, the second lowest voltage finally stabilizes at the difference between twice the first reference voltage and the second reference voltage; based on the first lowest voltage and the second lowest voltage Adjust the working factor of the driving signal; and drive the LED system according to the driving signal.

According to an embodiment, one or more benefits may be obtained. With reference to the detailed description and drawings that follow, these benefits and various additional objects, features, and advantages of the present invention can be thoroughly understood.

110, 505‧‧‧ power level

304‧‧‧slope generating circuit

VIN‧‧‧Input voltage

Vslope‧‧‧output ramp signal

VOUT‧‧‧Output voltage

302‧‧‧PWM comparator unit

LED1_1~LEDN_1‧‧‧‧Feedback point of lamp string

303‧‧‧Signal drive unit driver

201‧‧‧Amplifier

CMP‧‧‧Error amplifier output

Q1‧‧‧Adjust transistor

V _CS ‧‧‧CS sampling resistor voltage

RSEN‧‧‧Resistor

V _ramp ‧‧‧slope compensation voltage

VREF‧‧‧Reference signal

5041_1~504N_1‧‧‧LED string

VS‧‧‧Feedback voltage

601‧‧‧Drive

VREF_EA, VREF_EA’‧‧‧reference voltage

S1 607, S2 608‧‧‧Controller switch

104_i‧‧‧circuit frame of current balancer

604‧‧‧Comparator

VFB‧‧‧Error amplifier feedback input

606‧‧‧Adder

301, 603‧‧‧ error amplifier

602‧‧‧PWM

Ccmp‧‧‧ Output capacitance

702~716‧‧‧frame

GATE, GATE_1, GATE_2 ‧‧‧ gate

100‧‧‧Traditional multi-channel LED lamp string drive circuit

500‧‧‧Double controller cascaded LED drive circuit application

503_i‧‧‧Schematic simplified box of the controller

108、LEDx、503_1、503_2‧‧‧‧controller

106、502_1、502_2‧‧‧Minimal controller LEDx voltage selector

700‧‧‧LED backlight drive dual controller cascade method

104_1~104_N, 5011_1~501N_N‧‧‧‧ current balancer

LEDx_min, LEDx_min_1~LEDx_min_N‧‧‧Minimum voltage

OUT‧‧‧Minimum voltage LED_min and reference voltage VREF_EA determine the comparator output

OUT_b‧‧‧Minimum voltage LED_min and reference voltage VREF_EA determine the reverse of the output of the comparator

Fig. 1 is a diagram showing a typical application diagram of a conventional single-controller multi-channel LED lamp string drive circuit.

Figure 2 is a schematic simplified block diagram of the current balancer.

Figure 3 is a schematic simplified block diagram of the controller.

FIG. 4 is an application diagram of a dual-controller cascaded LED driving circuit according to an embodiment of the present invention.

Fig. 5 is a schematic simplified block diagram of a controller according to an embodiment of the present invention.

FIG. 6 is a flowchart of internal operations of a two-chip IC (Integrated Circuit) cascade controller according to an embodiment of the present invention.

The features and exemplary embodiments of the various aspects of the invention will be described in detail below. In the following detailed description, many specific details are proposed in order to provide a comprehensive view of the present invention understanding. However, it is obvious to those skilled in the art that the present invention can be implemented without some of these specific details. The following description of the embodiments is merely to provide a better understanding of the present invention by showing examples of the present invention. The present invention is by no means limited to any specific configurations and algorithms proposed below, but covers any modification, replacement, and improvement of elements, components, and algorithms without departing from the spirit of the present invention. In the drawings and the following description, well-known structures and techniques are not shown in order to avoid unnecessarily obscuring the present invention.

FIG. 4 is an application diagram of a dual-controller cascaded LED driving circuit according to an embodiment of the present invention. The LED driving circuit includes a power stage 505, two controllers 503_1 and 503_2, minimum LEDx voltage selectors 502_1 and 502_2 corresponding to the two controllers, 2N strings of LED lamp beads, and 2N current balancers (for example, N is greater than An integer of 1). Figure 4 is only an example, which should not unduly limit the scope of patent application. Those of ordinary skill in the art will recognize many variations, replacements, and modifications.

According to one embodiment, after the system is powered on, for example, an AC input voltage is received and subjected to full-wave rectification to generate a rectified voltage, and the power stage 505 outputs the rectified voltage as the input voltage of the system. For example, the power stage 505 is used to provide a stable output voltage for the LED lamp bead string. Although an AC circuit is given as an example, the system of the present invention can be applied to a DC-DC or AC-DC scenario.

The output terminals CMP of the error amplifiers of the two controllers 503_1 and 503_2 are connected together and connected to the ground through an external capacitor Ccmp. The output gate GATE_1 of the controller 503_1 is used to control the output gate GATE of the power switch of the power stage Signal, the gate GATE_2 of the output terminal of the controller 503_2 is suspended.

The minimum LEDx voltage selectors 502_1 and 502_2 corresponding to the two controllers. The minimum LEDx voltage selector 502_1 is used to select the lowest voltage input of the LED lamp string feedback points LED1_1 to LEDN_1 to the controller 503_1, and the minimum LEDx voltage selector 502_2 is used to Select the lowest voltage of LED1_2 to LEDN_2 as the feedback point of the lamp bead string to the controller 503_2. In the 2N string of LED lamp bead strings, the feedback terminal of the 5041_1 to 504N_1 N string of lamp bead strings is input The minimum LEDx voltage selectors 502_1 and 5041_2 to 504N_2 are connected to the feedback terminals of the N string lamp string to the minimum LEDx voltage selector 502_2.

2N current balancers are used to provide stable LED output current for the 2N string of LED lamp beads. According to one embodiment, an exemplary current balancer may include an amplifier, a tuning transistor, and a resistor RSEN. The amplifier non-inverting input receives the reference signal VREF, the inverting input is connected to the resistor RSEN to receive the feedback voltage VS, and the output is connected to the base of the adjustment transistor. One end of the resistor RSEN is connected to the inverting input of the amplifier 201, and one end is grounded. The base of the adjustment transistor is connected to the output of the amplifier 201, the emitter is connected to the resistor RSEN, and the collector is connected to the LED lamp bead.

In one example, the adjustment transistor is a field-effect transistor (for example, a metal oxide semiconductor field effect transistor (Metal-Oxide-Semiconductor Field-Effect Transistor, MOSFET)). In another example, the power adjustment transistor is an insulated gate bipolar junction transistor (IGBT). In another example, the power adjustment transistor is a bipolar junction junction transistor. In various examples, the system 300 may include more or fewer elements, where the value of the reference voltage VREF may be set by those skilled in the art as needed.

When the two controller systems work in cascade, the power stage input voltage VIN and the output gate GATE of any one of the controllers 503_1 and 503_2 are used to generate a stable output voltage VOUT. The minimum controller LEDx voltage selector 502_1 is used to select the lowest voltage input LEDx_min_1 of the lamp bead feedback point LED1_1 to LEDN_1, and the minimum controller LEDx voltage selector 502_2 is used to select the lowest voltage LEDx_min_2 of the lamp bead feedback point LED1_2 to LEDN_2 ; VREF_EA and VREF_EA' are fixed reference voltages inside the controller. In this example, it is assumed that the lowest voltage LEDx_min_1 first becomes greater than the reference voltage VREF_EA, and the controller 503_1 does not use the lowest voltage LEDx_min_1 as the feedback input, but uses the reference voltage VREF_EA' as the feedback input. The reference voltage VREF_EA' is equal to the reference voltage VREF_EA plus a fixed 'S offset. At this time, the minimum voltage LEDx_min_2 does not reach the reference voltage VREF_EA, the controller 503_2 still uses the minimum voltage LEDx_min_2 as the feedback input, The reference voltage VREF_EA' is not used as the feedback input. After the action of the loop, the minimum voltage LEDx_min_2 cannot always reach the reference voltage VREF_EA, and the controller 503_2 always uses the minimum voltage LEDx_min_2 as the feedback input. The minimum voltage LEDx_min_1 first becomes greater than the reference voltage VREF_EA, which represents that the minimum value of the feedback point LED1_1 to LEDN_1 of the lamp bead string is greater than the minimum value of the feedback point LED2_1 to LED2_N of the lamp bead string, that is, the maximum LED voltage drop of the 2N string LED Appears in the feedback points LED2_1 to LED2_N of the lamp bead string. Therefore, the circuit ensures that the lowest value of all LED feedback points is used as the feedback point.

Fig. 5 is a schematic simplified block diagram of a controller according to an embodiment of the present invention. The controller has two switches S1 607 and S2 608, a comparator 604, an error amplifier 603, an adder 606, a pulse width modulator PWM 602, and a driver 601.

Switches S1 607 and S2 608 are used to gate reference voltage VREF_EA or reference voltage VRER_EA'. The comparator 604 is used to compare the minimum voltage LEDx_min_i and the reference voltage VREF_EA. If the minimum voltage LEDx_min_i is greater than the reference voltage VREF_EA, the minimum voltage LED_min and the reference voltage VREF_EA determine that the comparator output OUT is high, and the minimum voltage LED_min and the reference voltage VREF_EA determine the comparator output The reverse OUT_b is low, the control switch S1 607 is turned on, S2 608 is not turned on, the reference voltage VRER_EA' is gated; if the minimum voltage LEDx_min_i is less than the reference voltage VREF_EA, the minimum voltage LED_min and the reference voltage VREF_EA judge that the comparator output OUT is low, the minimum The voltage LED_min and the reference voltage VREF_EA determine that the reverse OUT_b of the comparator output is high, the control switch S1 607 is not turned on, S2 608 is turned on, and the reference voltage VRER_EA is gated.

The error amplifier 603 is used to convert the difference between the reference voltage VREF_EA and the error amplifier feedback terminal input VFB into a current to charge and discharge the output capacitor Ccmp. The reference voltage VREF_EA is greater than the error amplifier feedback terminal input VFB, generating source current, which is The capacitor Ccmp is charged, and the reference voltage VREF_EA is less than the input of the error amplifier feedback terminal VFB, which generates a sink current to discharge the output capacitor Ccmp. The adder 606 adds the slope compensation voltage V _ramp and the CS sampling resistor voltage Vcs by a certain ratio for slope compensation, and outputs a slope signal Vslope. The PWM 602 is used to compare the error amplifier output CMP and the output ramp signal Vslope to generate a PWM signal. The driver 601 is used to PWM amplify the output of the PWM 602 and output a gate GATE signal.

In this embodiment, assuming that the lowest voltage LEDx_min_1 is first higher than the reference voltage VREF_EA, in the controller 603, the lowest voltage LEDx_min_1 is greater than the reference voltage VREF_EA, the lowest voltage LED_min and the reference voltage VREF_EA determine that the comparator output OUT is high, and the lowest voltage LED_min Judging from the reference voltage VREF_EA that the reverse OUT_b of the comparator output is low, the control switch S1 607 is turned on, S2 608 is not turned on, and VREF_EA' is selected as the feedback input, and the minimum voltage LEDx_min_1 is not used as the feedback input; the reference voltage VREF_EA' is equal to the reference voltage VREF_EA plus a fixed offset.

The error amplifier feedback terminal input VFB of the error amplifier 603 is equal to the reference voltage VRER_EA', which is greater than the reference voltage VREF_EA, generates sink current, and discharges the output capacitor Ccmp; while the minimum voltage LEDx_min_2 does not reach the reference voltage VREF_EA at this time, it is in the error amplifier 603, The minimum voltage LEDx_min_2 is less than the reference voltage VREF_EA, the minimum voltage LED_min and the reference voltage VREF_EA determine the comparator output OUT is low, the minimum voltage LED_min and the reference voltage VREF_EA determine the comparator output OUT_b is high, the control switch S1 607 is not turned on, S2 608 Turn on, select the lowest voltage LEDx_min_2, then use the lowest voltage LEDx_min_2 as the feedback input instead of the reference voltage VREF_EA' as the feedback input. The loop is balanced and the output capacitor Ccmp is charged and discharged balanced, so the loop automatically adjusts the minimum voltage LEDx_min_2 to always be less than the reference voltage VREF_EA.

LEDx _min_2=2* VREF _ EA - VREF _ EA '(Equation 2)

The minimum voltage LEDx_min_2 is the lowest value of the 2N string LED voltage. The minimum value of the circuit design LED voltage 2*VREF_EA-VRER_EA’ is greater than the voltage required by the output current of the current balancer to ensure that all current balancers can output the design current.

FIG. 6 is a flowchart of the internal operation of the two-chip IC cascade controller according to an embodiment of the present invention. Figure 6 is only an example, which should not unduly limit the scope of patent application. Those of ordinary skill in the art will recognize many variations, replacements, and modifications.

At block 702, the power stage converts the input voltage to a regulated voltage.

At block 704, the minimum voltage LEDx_min_1 and the minimum voltage LEDx_min_2 gradually increase as the output voltage increases.

At block 706, it is determined whether the lowest voltage LEDx_min_1 first becomes greater than the reference voltage VREF_EA.

At block 708, the lowest voltage LEDx_min_1 first becomes greater than the reference voltage VREF_EA, then VFB_1=VREF_EA', VFB_2=LEDx_min_2.

At block 710, the lowest voltage LEDx_min_1 first becomes greater than the reference voltage VREF_EA, and finally the lowest voltage LEDx_min_2 stabilizes at 2*VREF_EA-VREF_EA'.

At block 712, the lowest voltage LEDx_min_1 first becomes greater than the reference voltage VREF_EA, then VFB_1=LEDx_min_1, VFB_2=VREF_EA'.

At block 714, the lowest voltage LEDx_min_2 first becomes greater than the reference voltage VREF_EA, and finally LEDx_min_1 stabilizes at 2*VREF_EA-VREF_EA'.

At block 716, the loop adjusts the output voltage according to the last selected lowest voltage LEDx_min_i.

According to one embodiment, a method 700 for cascading a dual-controller LED backlight drive includes: converting an input voltage into a regulated voltage to provide up to a plurality of LED lamp bead strings; selecting the first A lowest voltage input and a second lowest voltage input at the second feedback point, the first lowest voltage and the second lowest voltage increase as the adjusted voltage increases; if the first lowest voltage changes first If it is greater than the first reference voltage, the second reference voltage is taken as the first feedback signal and the second lowest voltage is used as the second feedback signal. The second lowest voltage is finally stabilized at twice the first reference voltage and At the difference of the second reference voltage, otherwise if the second lowest voltage first becomes greater than the first reference voltage, the first lowest voltage is taken as the first feedback signal and the second reference The voltage is used as the second feedback signal, and the first lowest voltage finally stabilizes at the difference between twice the first reference voltage and the second reference voltage; based on the first lowest voltage and the second Adjust the operating factor of the drive signal with the lowest voltage; and drive the system according to the drive signal System.

Some embodiments of the invention relate to integrated circuits. More specifically, some embodiments of the present invention provide a system and method for LED backlight driving a dual controller cascade. Merely by way of example, some embodiments of the invention are applied to LED-backlit displays. However, it will be recognized that the present invention has a broader scope of application.

For example, using one or more software components, one or more hardware components, and/or one or more combinations of software and hardware components, some or all of the components of various embodiments of the present invention are individually and/or It is implemented in combination with at least another element. In another example, some or all elements of various embodiments of the present invention are each implemented individually, and/or in combination with at least another element, such as one or more analog circuits and/or one or more digital Circuits in one or more circuits. In another example, various embodiments and/or examples of the invention may be combined.

Although specific embodiments of the present invention have been described, those skilled in the art should understand that there are other embodiments equivalent to the described embodiments. Therefore, it should be understood that the present invention is not limited to the specific embodiments shown, but only by the scope of the attached patent application.

505‧‧‧Power stage

5041_1~504N_1‧‧‧LED string

503_1、503_2‧‧‧‧Controller

VREF_EA, VREF_EA’‧‧‧reference voltage

VIN‧‧‧Input voltage

LED1_1~LEDN_1‧‧‧‧Feedback point of lamp string

VOUT‧‧‧Output voltage

GATE_1, GATE_2 ‧‧‧ gate

Ccmp‧‧‧ Output capacitance

5011_1~501N_N‧‧‧ current balancer

CMP‧‧‧Error amplifier output

V _CS ‧‧‧CS sampling resistor voltage

500‧‧‧Double controller cascaded LED drive circuit application

502_1、502_2‧‧‧Minimal controller LEDx voltage selector

LEDx_min, LEDx_min_1~LEDx_min_N‧‧‧Minimum voltage

Claims (5)

An LED driving system includes: a power stage for converting an input voltage into a regulated voltage and providing it to a plurality of LED lamp bead strings; a first voltage selector and a second voltage selector for selecting the plurality The first lowest voltage input at the first feedback point and the second lowest voltage input at the second feedback point of the LED lamp bead string, the first lowest voltage and the second lowest voltage increase as the adjusted voltage increases Increase; the controller is configured to: if the first lowest voltage first becomes greater than the first reference voltage, then take the second reference voltage as the first feedback signal and the second lowest voltage as the second feedback signal, so The second lowest voltage eventually stabilizes at the difference between twice the first reference voltage and the second reference voltage, otherwise if the second lowest voltage first becomes greater than the first reference voltage, then take The first lowest voltage is used as the first feedback signal and the second reference voltage is used as the second feedback signal, the first lowest voltage is finally stabilized at twice the first reference voltage and the second The difference of the reference voltage; a pulse width modulator for adjusting the operating factor of the driving signal based on the first lowest voltage and the second lowest voltage; and a driver for driving the driving signal according to the driving signal LED system. The system according to item 1 of the patent application scope, further includes a plurality of current balancers respectively connected to the plurality of LED lamp bead strings, each of the plurality of current balancers is configured to output current to the LED Perform stable operation. The system according to item 1 of the patent application scope, wherein the controller includes a first control module and a second control module, wherein the first control module is connected to the first voltage selector, the The second control module is connected to the second voltage selector, the corresponding error amplifier output terminals of the first control module and the second control module are connected together, and through an external capacitor Grounding. The system of claim 3, wherein the error amplifier is configured to convert the difference between twice the first reference voltage and the second reference voltage into a current to charge and discharge the external capacitor . A driving method for an LED system includes: converting an input voltage into a regulated voltage and providing it to a plurality of LED lamp bead strings; selecting the first lowest voltage input and the first voltage at the first feedback point of the plurality of LED lamp bead strings The second lowest voltage input at the second feedback point, the first lowest voltage and the second lowest voltage increase as the adjusted voltage increases; if the first lowest voltage first becomes greater than the first reference voltage , Then take the second reference voltage as the first feedback signal and the second lowest voltage as the second feedback signal, the second lowest voltage finally stabilizes at twice the first reference voltage and the second reference voltage Difference, otherwise if the second lowest voltage first becomes greater than the first reference voltage, then take the first lowest voltage as the first feedback signal and the second reference voltage as the second Feedback signal, the first lowest voltage is finally stabilized at the difference between twice the first reference voltage and the second reference voltage; the driving signal is adjusted based on the first lowest voltage and the second lowest voltage Operating factor; and drive the LED system according to the drive signal.

Images