TWI761028B - Multi-channel LED backlight system and its constant current control circuit and method - Google Patents

Abstract

A multi-channel light emitting diode (Light Emitting Diode, LED) backlight system and a constant current control circuit and method thereof are provided. The constant current control circuit includes: a channel setting current generator, which generates multiple channel setting currents according to the size of the reference voltage and external resistance; multiple channel voltage generators, which generate multiple channel voltages according to multiple channel setting currents; multiple LEDs A channel driver that generates multiple LED drive currents for multiple LED channels based on multiple channel voltages. Each LED channel driver includes an operational amplifier. The operational amplifier includes an op amp input pair tube, an offset voltage storage pair tube, and an offset voltage storage capacitor. The offset voltage storage pair tube stores the op amp input pair tube’s offset voltage on the offset voltage storage capacitor before the op amp generates the LED drive current. , when the op amp generates the LED drive current, the offset voltage of the op amp input pair tube is superimposed on the op amp input pair tube to eliminate the influence of the op amp input pair tube offset voltage on the LED drive current, thereby improving the channel current. match.

Description

Multi-channel LED backlight system and its constant current control circuit and method

The invention relates to the field of circuits, in particular to a multi-channel light emitting diode (Light Emitting Diode, LED) backlight system and a constant current control circuit and method thereof.

In a multi-channel light-emitting diode (LED) backlight system, in order to ensure uniform brightness throughout the screen, it is required that the LED drive currents for each LED channel must be precisely matched.

In an LED backlight system that adopts a low-frequency (eg, 100Hz to 1000Hz) pulse width modulation (PWM) dimming method, after setting the maximum LED drive current for each LED channel, by adjusting the maximum LED drive current for each LED channel The operating factor of the LED drive current of the LED channel to adjust the brightness of the LED. Current matching is done for the maximum LED drive current for each LED channel. When the brightness of the LED is small, increasing the LED brightness by increasing the operating factor of the LED driving current for each LED channel will not affect the matching of the maximum LED driving current for each LED channel, but the screen will flicker. , which has a certain impact on the health of the eyes.

In the LED backlight system using the analog dimming method, the brightness of the LED is adjusted by adjusting the LED driving current for each LED channel. When the brightness of the LED is small, reducing the brightness of the LED by reducing the LED driving current for each LED channel will not cause the screen to flicker, but it is necessary to ensure the matching between the LED driving currents for each LED channel, so that Ensure that the brightness of the entire screen is uniform.

In view of one or more of the above problems, the present invention provides a novel multi-channel LED backlight system and a constant current control circuit and method thereof.

A constant current control circuit for a multi-channel LED backlight system according to an embodiment of the present invention includes: a channel setting current generator operable to a plurality of channel voltage generators operable to generate a plurality of channel voltages for each of the plurality of LED channels based on the plurality of channel set currents; and a plurality of LEDs a channel driver operable to generate a plurality of LED drive currents for the plurality of LED channels, respectively, based on the plurality of channel voltages, wherein each LED channel driver of the plurality of LED channel drivers includes an operational amplifier and a drive current generating resistor, the operation The amplifier generates an LED drive current for a corresponding one of the multiple LED channels according to a corresponding one of the multiple channel voltages and the size of the drive current generating resistor. The operational amplifier includes an op amp input pair tube and an offset voltage storage pair. tube, and the offset voltage storage capacitor. The offset voltage storage pair tube stores the offset voltage of the op amp input pair tube on the offset voltage storage capacitor before the op amp generates the LED drive current, and stores the offset voltage when the op amp generates the LED drive current. The offset voltage of the op amp input pair tube stored on the storage capacitor is superimposed on the op amp input pair tube to eliminate the influence of the op amp input pair tube offset voltage on the LED drive current.

A constant current control circuit for an LED backlight system according to another embodiment of the present invention includes: a channel setting current generator, operable to generate a channel setting current according to a reference voltage and the magnitude of an external resistance; a channel voltage converter, which can a plurality of LED channel drivers operable to generate a plurality of LED drive currents for each of the plurality of LED channels based on the plurality of channel voltages , wherein each LED channel driver in the plurality of LED channel drivers includes an operational amplifier and a driving current generating resistor, and the operational amplifier generates a voltage for a plurality of LEDs according to a corresponding one of the plurality of channel voltages and the size of the driving current generating resistor The LED drive current of a corresponding LED channel in the channel. The operational amplifier includes an op amp input pair tube, an offset voltage storage pair tube, and an offset voltage storage capacitor. The offset voltage storage pair tube connects the op amp input to the op amp before generating the LED drive current. The offset voltage of the pair of tubes is stored on the offset voltage storage capacitor, and when the op amp generates the LED drive current, the offset voltage of the op amp input pair tube stored on the offset voltage storage capacitor is superimposed on the op amp input pair tube to eliminate the op amp input pair. The effect of the input-to-tube offset voltage on the LED drive current.

A constant current control method for a multi-channel LED backlight system according to an embodiment of the present invention includes: generating by a channel setting current generator according to a reference voltage and the size of an external resistor Multiple channel setting currents for multiple LED channels respectively; multiple channel voltage generators generating multiple channel voltages for multiple LED channels respectively according to multiple channel setting currents; and multiple LED channel drivers according to multiple channel setting currents; The channel voltages generate a plurality of LED driving currents for the plurality of LED channels respectively, wherein each LED channel driver in the plurality of LED channel drivers includes an operational amplifier and a driving current generating resistor, and the operational amplifier is based on the corresponding one of the plurality of channel voltages. One channel voltage and the size of the drive current generating resistor generate the LED drive current for a corresponding one of the multiple LED channels. The operational amplifier includes an op amp input pair tube, an offset voltage storage pair tube, and an offset voltage storage capacitor. The offset voltage storage pair tube stores the offset voltage of the op amp input pair tube on the offset voltage storage capacitor before the op amp generates the LED drive current, and stores the op amp input on the offset voltage storage capacitor when the op amp generates the LED drive current The offset voltage of the pair of tubes is superimposed on the op amp input pair tube to eliminate the influence of the offset voltage of the op amp input pair tube on the LED drive current.

A constant current control method for a multi-channel LED backlight system according to an embodiment of the present invention includes: generating a channel setting current by a channel setting current generator according to the reference voltage and the size of an external resistor; converting the channel setting current by a channel voltage converter Converted into a plurality of channel voltages respectively used for a plurality of LED channels; a plurality of LED drive currents respectively used for a plurality of LED channels are generated by a plurality of LED channel drivers according to the plurality of channel voltages, wherein the plurality of LED channel drivers are Each LED channel driver includes an operational amplifier and a driving current generating resistor. The operational amplifier generates an LED driver for a corresponding one of the plurality of LED channels according to a corresponding one of the multiple channel voltages and the size of the driving current generating resistor. Current, the operational amplifier includes an op amp input pair tube, an offset voltage storage pair tube, and an offset voltage storage capacitor. The offset voltage storage pair tube stores the op amp input pair tube’s offset voltage in the offset voltage storage before the op amp generates the LED drive current. On the capacitor, and when the op amp generates the LED drive current, the offset voltage of the op amp input pair stored on the offset voltage storage capacitor is superimposed on the op amp input pair tube, so as to eliminate the op amp input pair tube offset voltage to the LED drive current. Impact.

The multi-channel LED backlight system according to the embodiment of the present invention includes the above-mentioned constant current control circuit.

Through the constant current for the multiplex LED backlight system according to the embodiment of the present invention The control system and method can improve the current matching accuracy between each LED channel in a multi-channel LED backlight system.

100: Multi-channel LED backlight system

102: Switch Mode Power Systems

104,104': constant current control circuit

1042, 1042': Channel current control module

1042-1, 1042-1’: Channel setting current generator

1042-2: Channel Voltage Converter

1042-21~1042-2n, 1042-2m: Channel voltage generator

1044-1~1044-n, 1044-1’~1044-n’, 1044-m, 1044-m’: LED channel driver

106: Dynamic headroom control module

C1: Offset voltage storage capacitor

I1,Ich1~Ichn,Ichm: Channel setting current

Ic: Channel setting source current

ISET: pin

LED1~LEDn,LEDm: LED pins

OP1~OPn,OPC31,OP31~OP3n,OP3m,OPC51,OPm: Operational amplifier

PM31, PM32: P-channel metal oxide semiconductor field effect (PMOS) current mirror

PM1~PMn, PM51, PMm: PMOS transistor

PM62, PM63: Offset voltage storage pair tube

PM65, PM66: Op amp input pair tube

Q1~Qn, Q51, Qm: bipolar junction transistor

R1~Rm, R3m: drive current generation resistor

R3C, R5c: External resistors

R30, R31~R3n: resistance

R51, R53-1~R53-n, R53-m: negative feedback resistance

Rc1~Rcn, Rcm: channel voltage generation resistance

SW1, SW2, SW3, SW4, SW5: switch

V1~Vn, V1’~Vn’, Vm, Vm’: channel voltage

VLED: minimum voltage

Vout: output voltage

Vref: reference (reference) voltage

The present invention can be better understood from the following description of specific embodiments of the present invention in conjunction with the drawings, wherein:

FIG. 1 shows an example system block diagram of a multi-channel LED backlight system according to an embodiment of the present invention;

FIG. 2 shows an example system block diagram of a constant current control circuit for a multi-channel LED backlight system according to an embodiment of the present invention;

FIG. 3 shows an example circuit diagram of the constant current control circuit shown in FIG. 2;

FIG. 4 shows an example system block diagram of a constant current control circuit for a multi-channel LED backlight system according to an embodiment of the present invention;

FIG. 5 shows an example circuit diagram of the constant current control circuit shown in FIG. 4;

FIG. 6 shows an example circuit diagram of an LED channel driver for a constant current control circuit according to an embodiment of the present invention.

Features and exemplary embodiments of various aspects of the invention are described in detail below. In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. However, it will be apparent to one skilled in the art that the present invention may be practiced without some of these specific details. The following description of the embodiments is only intended to provide a better understanding of the present invention by illustrating examples of the invention. The present invention is in no way limited to any specific configurations and algorithms set forth below, but covers any modification, substitution and improvement of elements, components and algorithms without departing from the spirit of the invention. In the drawings and the following description, well-known structures and techniques have not been shown in order to avoid unnecessarily obscuring the present invention.

FIG. 1 shows an example system block diagram of a multiplexed LED backlight system 100 according to an embodiment of the present invention. In the multi-channel LED backlight system 100 shown in FIG. 1, when the output voltage Vout of the switch mode power supply system 102 rises above the turn-on voltage of the LEDs, current begins to flow The constant current control circuit 104 includes a channel current control module 1042 and n LED channel drivers 1044-1 to 1044-n (n is an integer greater than 0), the channel current control module 1042 being operable to The magnitude of the LED drive current of the LED channel is set, and the LED channel drivers 1044-1 to 1044-n are operable to generate n LED drive currents for the n LED channels respectively; the headroom control module 106 is operable to sense The voltages at the LED pins LED1 to LEDn respectively connected to each LED channel are measured and the sensed lowest voltage VLED is fed back to the switch mode power system 102 to control the output voltage Vout to optimize system efficiency.

FIG. 2 shows an example system block diagram of the constant current control circuit 104 for the multiplexed LED backlight system 100 according to an embodiment of the present invention. As shown in FIG. 2, in some embodiments, the constant current control circuit 104 includes a channel setting current generator 1042-1, a channel voltage converter 1042-2, and n LED channel drivers 1044-1 to 1044-n, wherein : the channel setting current generator 1042-1 is operable to generate the channel setting current I1 according to the magnitude of the reference voltage Vref and the external resistance of the pin ISET; the channel voltage converter 1042-2 is operable to convert the channel setting current I1 to the respective n channel voltages V1 to Vn for the plurality of LED channels; LED channel drivers 1044-1 to 1044-n are operable to generate n LED drive currents for the n LED channels respectively from the n channel voltages V1 to Vn . Here, it should be understood that the channel setting current generator 1042-1 and the channel voltage converter 1042-2 are components of the channel current control module 1042, that is, the channel current control module 1042 includes the channel setting current generator 1042-1 and channel voltage converter 1042-2.

FIG. 3 shows an example circuit diagram of the constant current control circuit 104 shown in FIG. 2 . As shown in FIG. 3, in some embodiments, the operational amplifier OPC31 is used to realize the function of the channel setting current generator 1042-1, that is, the channel setting current I1 is generated according to the reference voltage Vref and the size of the external resistor R3C of the ISET pin ; P-channel type metal oxide semiconductor field effect (P type metal oxide semiconductor, PMOS) current mirrors PM31 and PM32 and resistor R30 are used to realize the function of the channel voltage converter 1042-2, that is, the PMOS current mirrors PM31 and PM32 pair the channel The mirror current generated by setting the current I1 for mirroring is converted into n channel voltages V1 to Vn on the resistor R30; the operational amplifiers OP31 to OP3n and the resistors R31 to R3n are used to realize The function of the LED channel drivers 1044-1 to 1044-n is to generate n LED channel currents for the n LED channels respectively according to the n channel voltages V1 to Vn.

m

n。 Specifically, as shown in FIG. 3 , each of the LED channel drivers 1044-1 to 1044-n, for example, the LED channel driver 1044-m includes an operational amplifier OP3m and a driving current generating resistor R3m, wherein the operational amplifier The OP3m generates an LED for a corresponding one of the n LED channels (ie, the LED channel to which the LED pin LEDm is connected) according to the corresponding one of the channel voltages V1 to Vn and the size of the driving current generating resistor R3m. drive current. Here, m is an integer, and 1

m

n.

In the constant current control circuit 104 shown in FIG. 3 , the matching of the LED driving current between the LED channels is mainly affected by the matching of the resistor R30 and the resistors R31 to R3n and the offset voltage of the operational amplifiers OP31 to OP3n. Since it is difficult to balance the matching of resistor R30 and resistors R31 to R3n, and the voltage on resistors R31 to R3n is too low when the channel setting current I1 is small, the offset voltage of operational amplifiers OP31 to OP3n will affect the LED output to each LED channel. The influence of the drive current is very large, and the traditional metal-oxide-semiconductor field-effect transistor (Metal-Oxide-Semiconductor Field-Effect Transistor, MOSFET) operational amplifier is difficult to achieve extremely low offset voltage (within 1mV), which will lead to LED The matching consistency of the LED drive currents between channels deteriorates.

In view of one or more of the above problems, the present invention provides a novel constant current control circuit and method for a multi-channel LED backlight system, so as to improve the matching accuracy of LED drive currents between each LED channel.

Figure 4 shows an example system block diagram of a constant current control circuit 104' for a multiplexed LED backlight system 100 according to an embodiment of the present invention. As shown in FIG. 4, in some embodiments, the constant current control circuit 104' includes a channel setting current generator 1042-1', n channel voltage generators 1042-21 to 1042-2n, and n LED channel drivers 1044 -1' to 1044-n', wherein: the channel setting current generator 1042-1' is operable to generate n channel settings for n LED channels respectively according to the reference voltage Vref and the magnitude of the external resistance of the ISET pin currents Ich1 to Ichn; channel voltage generators 1042-21 to 1042-2n operable to generate n channel voltages V1' to Vn' according to the n channel set currents Ich1 to Ichn; LED channel drivers 1044-1' to 1044-n' is operable to generate n LED drive currents for each of the n LED channels from the n channel voltages V1' to Vn'. Similarly, it should be understood that the channel setting current generator 1042-1' and the channel voltage generators 1042-21 to 1042-2n are components of the channel current control module 1042', that is, the channel current control module 1042' includes The channel setting current generator 1042-1' and the channel voltage generators 1042-21 to 1042-2n.

FIG. 5 shows an example circuit diagram of the constant current control circuit 104' shown in FIG. 4 . As shown in FIG. 5, in some embodiments, operational amplifier OPC51 and bipolar junction transistors Q51 and Q1 through Qn including PMOS transistors PM51 and PM1 through PMn, emitters of these PMOS transistors, and these PMOS transistors The negative feedback resistors R51 of the emitter of the crystal and the n bipolar junction transistor current mirrors of R53-1 to R53-n are used to realize the function of the channel setting current generator 1042-1', that is, the operational amplifier OPC51 according to the reference voltage The size of Vref and the external resistor R5c of the ISET pin generates the channel setting source current Ic, and the channel setting source current Ic generates the channel setting current Ich1 to Ichn through the mirror image of the n bipolar junction transistor current mirrors; the channel voltage generating resistor Rc1 to Rcn are used to realize the functions of the channel voltage generators 1042-21 to 1042-2n, that is, the channel voltage generation resistors Rc1 to Rcn generate the channel voltages V1' to Vn' according to the channel setting currents Ich1 to Ichn respectively; the operational amplifiers OP1 to OPn and The driving current generating resistors R1 to Rm are used to realize the functions of the LED channel drivers 1044-1' to 1044-n', that is, to generate n LED driving currents for the n LED channels respectively according to the channel voltages V1' to Vn'.

Specifically, as shown in FIG. 5 , the bipolar junction transistors Q51 and Qm including the emitters of the PMOS transistor PM51, any one of the PMOS transistors PM1 to PMn, the PMOS transistor PM51 and PMm, the PMOS transistor PM51 and PMm, As well as the negative feedback resistors R51 and R53-m of the emitters of the PMOS transistors PM51 and PMm, the bipolar junction transistor current mirror m generates the channel setting current Ichm by mirroring the channel setting source current Ic; the channel voltage generating resistors Rc1 to Any one of the channel voltage generation resistors Rcm in Rcn generates the channel voltage Vm' according to the channel setting current Ichm; The current generating resistor Rm, the operational amplifier OPm generates the LED driving current for the LED channel connected to the LED pin LEDm according to the channel voltage Vm' and the size of the driving current generating resistor Rm.

Compared with the constant current control circuit 104, the constant current control circuit 104' has the following technical advantages: 1) using a bipolar junction transistor current mirror, accurate current mirror matching can be achieved; 2) in the bipolar junction transistor The negative feedback resistor of the emitter is added to the current mirror, which can further improve the matching accuracy of the current mirror; 3) For any LED channel m in the LED channels 1 to n, only the channel voltage generation resistor Rcm and the drive current generation resistor need to be implemented Precise resistance distribution between Rm.

It should be understood that it is not necessary to realize all of the above three technical advantages of the constant current control circuit 104' to improve the matching accuracy of the LED drive currents between the various LED channels. On the contrary, in some embodiments, the matching accuracy of the LED driving current between the various LED channels can be improved to a certain extent by realizing one or more of the above three technical advantages of the constant current control circuit 104 ′ according to the needs. .

In some embodiments, the matching accuracy of the LED driving currents between the LED channels can also be improved by improving the LED channel driver. FIG. 6 shows an example circuit diagram of an LED channel driver for a constant current control circuit according to an embodiment of the present invention. It should be understood that by applying the LED channel driver shown in FIG. 6 in the constant current control circuit 104 shown in FIG. 2 and the constant current control circuit 104 ′ shown in FIG. Matching accuracy between LED drive currents. That is, each of the LED channel drivers 1044-1 to 1044-n (eg, the LED channel driver 1044-m) and each of the LED channel drivers 1044-1' to 1044-n' ( For example, the LED channel driver 1044-m') can be implemented in the form of the LED channel driver shown in FIG. 6 to improve the matching accuracy of the LED driving currents between the respective LED channels.

Here, it is assumed that FIG. 6 shows an example circuit diagram of any one of the LED channel drivers 1044-m or 1044-m'. As shown in FIG. 6, the LED channel driver 1044-m or 1044-m' includes an op-amp input pair of tubes PM65 and PM66 and an offset voltage storage pair of tubes PM62 and PM63; the op-amp input pair of the VR terminals of the tubes PM65 and PM66 (ie, The positive input terminal of the operational amplifier OP3m or OPm in the LED channel driver 1044-m or 1044-m') is connected to the channel voltage Vm or Vm'. Normally, the operational amplifier OP3m or OPm has the following two stages of operation: The first stage, that is, before generating the LED drive current, the switch SW1 is closed to Connect the VN terminal of the op amp input pair tubes PM65 and PM66 (ie, the inverting input terminal of the op amp OP3m or OPm in the LED channel driver 1044-m or 1044-m') and the VR terminal together, while switching SW2 and SW5 is turned off to disconnect the resistance feedback loop, and switches SW3 and SW4 are closed to allow the offset voltage storage capacitor C1 to store the offset voltage of the op amp input pair tube; in the second stage, when the LED drive current is generated, the switch SW1 is turned off , the switches SW2 and SW5 are closed to form a resistance feedback loop to control the LED drive current with constant current, while the switches SW3 and SW4 are turned off to store the offset voltage stored on the offset voltage storage capacitor C1 in the first stage to the tube through the offset voltage storage. PM62 and PM63 are converted into currents and superimposed on the Drain terminals of the op amp input pair tubes PM65 and PM66, thereby eliminating the influence of the offset voltage of the op amp OP3m or OPm on the LED drive current output to the LED channel m.

That is to say, the operational amplifier OP3m or OPm includes an operational amplifier input pair tube, an offset voltage storage pair tube, and an offset voltage storage capacitor. The offset voltage storage pair tube inputs the op amp input pair tube’s offset voltage before the operational amplifier generates the LED drive current. Stored on the offset voltage storage capacitor, and when the op amp generates the LED drive current, the offset voltage of the op amp input pair tube stored on the offset voltage storage capacitor is superimposed on the op amp input pair tube to eliminate the op amp input pair tube offset The effect of voltage on LED drive current.

In realizing all of the above three technical advantages of the constant current control circuit 104' and the constant current control circuit of the operational amplifier shown in Figure 6, the matching of the LED drive currents between all channels can be optimized for a wide range of currents. For example, the matching of the LED drive current of about 5mA can be done less than 3%.

To sum up, the constant current control circuit 104 ′ according to the embodiment of the present invention can implement a constant current control method, which includes: the channel setting current generator generates, according to the reference voltage and the size of the external resistance, a current generator for a plurality of LED channels respectively. The multiple channel setting currents are generated by the multiple channel voltage generators according to the multiple channel setting currents for the multiple LED channels respectively; Multiple LED drive currents for multiple LED channels, wherein each LED channel driver in the multiple LED channel drivers includes an operational amplifier and a drive current generating resistor, and the operational amplifier is based on a corresponding one of the multiple channel voltages and the drive current. The size of the generating resistor is generated for multiple The LED drive current of a corresponding one of the LED channels. The operational amplifier includes an op amp input pair tube, an offset voltage storage pair tube, and an offset voltage storage capacitor. The offset voltage storage pair tube will operate before the op amp generates the LED drive current. The offset voltage of the amplifier input pair tube is stored on the offset voltage storage capacitor, and when the operational amplifier generates the LED drive current, the offset voltage of the op amp input pair tube stored on the offset voltage storage capacitor is superimposed on the op amp input pair tube to eliminate the The influence of the op amp input to the tube's offset voltage on the LED drive current.

In addition, the constant current control circuit 104 according to the embodiment of the present invention can implement a constant current control method, including: generating a channel setting current by a channel setting current generator according to the reference voltage and the size of an external resistance; converting the channel setting current by a channel voltage converter The set current is converted into a plurality of channel voltages respectively used for a plurality of LED channels; a plurality of LED drive currents respectively used for a plurality of LED channels are generated by a plurality of LED channel drivers according to the plurality of channel voltages, wherein the plurality of LED channel drivers Each LED channel driver in includes an operational amplifier and a driving current generating resistor, and the operational amplifier generates a corresponding one of the plurality of LED channels according to the size of the corresponding one of the plurality of channel voltages and the driving current generating resistor. LED drive current. The operational amplifier includes an op amp input pair tube, an offset voltage storage pair tube, and an offset voltage storage capacitor. The offset voltage storage pair tube stores the op amp input pair tube’s offset voltage in the offset before the op amp generates the LED drive current. On the voltage storage capacitor, and when the op amp generates the LED drive current, the offset voltage of the op amp input pair tube stored on the offset voltage storage capacitor is superimposed on the op amp input pair tube to eliminate the op amp input pair tube. Influence of drive current.

Other aspects of the constant current control method according to the embodiment of the present invention are the same as or similar to the corresponding aspects of the constant current control circuit described above with reference to FIGS. 2 to 6 , so they are not repeated here.

The present invention may be embodied in other specific forms without departing from its spirit or essential characteristics. For example, the algorithms described in particular embodiments may be modified without departing from the basic spirit of the invention in system architecture. Accordingly, the present embodiments are to be considered in all respects as illustrative and not restrictive, the scope of the present invention is defined by the appended claims rather than the foregoing description, and the meanings and equivalents falling within the claims all changes within the scope of Therefore, they are all included in the scope of the present invention.

104': constant current control circuit

1042': Channel current control module

1042-1’: Channel setting current generator

1042-21~1042-2n, 1042-2m: Channel voltage generator

1044-1'~1044-n',1044-m': LED channel driver

Ich1~Ichn,Ichm: Channel setting current

ISET: pin

LED1~LEDn,LEDm: LED pins

V1'~Vn',Vm,Vm': channel voltage

Vref: reference (reference) voltage

Claims (8)

A constant current control circuit for a multi-channel light emitting diode (Light Emitting Diode, LED) backlight system, comprising: a channel setting current generator operable to generate a plurality of channel setting currents respectively for the plurality of LED channels according to the reference voltage and the magnitude of the external resistance; a plurality of channel voltage generators operable to generate a plurality of channel voltages for the plurality of LED channels, respectively, based on the plurality of channel setting currents; and a plurality of LED channel drivers operable to generate a plurality of LED drive currents for the plurality of LED channels, respectively, based on the plurality of channel voltages, wherein Each LED channel driver in the plurality of LED channel drivers includes an operational amplifier and a driving current generating resistor, and the operational amplifier generates a corresponding one of the plurality of channel voltages and the size of the driving current generating resistor according to a corresponding one of the plurality of channel voltages. LED drive current for a corresponding one of the plurality of LED channels, The operational amplifier includes an op amp input pair tube, an offset voltage storage pair tube, and an offset voltage storage capacitor. The offset voltage storage pair tube connects the op amp input pair tube to the op amp input pair tube before the operational amplifier generates the LED drive current. The offset voltage is stored on the offset voltage storage capacitor, and when the operational amplifier generates the LED drive current, the offset voltage of the op amp input pair tube stored on the offset voltage storage capacitor is superimposed on the The op amp input to the tube can eliminate the influence of the offset voltage of the op amp input to the tube on the LED driving current. The constant current control circuit of claim 1, wherein the channel setting current generator is further operable to: generating a channel setting source current according to the reference voltage and the size of the external resistor; and The channel setting source currents are mirrored with a plurality of bipolar junction transistor current mirrors to generate the plurality of channel setting currents. The constant current control circuit of claim 2, wherein each bipolar junction transistor current mirror in the plurality of bipolar junction transistor current mirrors includes a negative feedback resistance of the emitter. The constant current control circuit according to any one of claims 1 to 3, wherein the plurality of Each of the channel voltage generators includes a channel voltage generating resistor, and a corresponding one of the plurality of channel setting currents generates a corresponding one channel voltage through the channel voltage generating resistor. A constant current control circuit for an LED backlight system, comprising: A channel setting current generator, operable to generate a channel setting current according to the reference voltage and the size of the external resistance; a channel voltage converter operable to convert the channel set current to a plurality of channel voltages for each of the plurality of LED channels; and a plurality of LED channel drivers operable to generate a plurality of LED drive currents for the plurality of LED channels, respectively, based on the plurality of channel voltages, wherein Each LED channel driver in the plurality of LED channel drivers includes an operational amplifier and a driving current generating resistor, and the operational amplifier generates a corresponding one of the plurality of channel voltages and the size of the driving current generating resistor according to a corresponding one of the plurality of channel voltages. LED drive current for a corresponding one of the plurality of LED channels, The operational amplifier includes an op amp input pair tube, an offset voltage storage pair tube, and an offset voltage storage capacitor. The offset voltage storage pair tube connects the op amp input pair tube to the op amp input pair tube before the operational amplifier generates the LED drive current. The offset voltage is stored on the offset voltage storage capacitor, and when the operational amplifier generates the LED drive current, the offset voltage of the op amp input pair tube stored on the offset voltage storage capacitor is superimposed on the The op amp input to the tube can eliminate the influence of the offset voltage of the op amp input to the tube on the LED driving current. A constant current control method for a multi-channel LED backlight system, comprising: The channel setting current generator generates multiple channel setting currents for multiple LED channels respectively according to the reference voltage and the size of the external resistance; generating, by a plurality of channel voltage generators, a plurality of channel voltages for the plurality of LED channels, respectively, according to the plurality of channel setting currents; and A plurality of LED drive currents for the plurality of LED channels, respectively, are generated by the plurality of LED channel drivers according to the plurality of channel voltages, wherein Each LED channel driver in the plurality of LED channel drivers includes an operational amplifier and a driving current generating resistor, the operational amplifier generates an LED for a corresponding one of the plurality of LED channels according to the corresponding one of the plurality of channel voltages and the size of the driving current generating resistor drive current, The operational amplifier includes an op amp input pair tube, an offset voltage storage pair tube, and an offset voltage storage capacitor. The offset voltage storage pair tube connects the op amp input pair tube to the op amp input pair tube before the operational amplifier generates the LED drive current. The offset voltage is stored on the offset voltage storage capacitor, and when the operational amplifier generates the LED drive current, the offset voltage of the op amp input pair tube stored on the offset voltage storage capacitor is superimposed on the The input of the op amp to the tube is used to eliminate the influence of the offset voltage of the input of the op amp to the tube on the driving current of the LED. A constant current control method for a multi-channel LED backlight system, comprising: The channel setting current generator generates the channel setting current according to the reference voltage and the size of the external resistance; converting the channel setting current into a plurality of channel voltages respectively for a plurality of LED channels by a channel voltage converter; A plurality of LED drive currents for the plurality of LED channels, respectively, are generated by the plurality of LED channel drivers according to the plurality of channel voltages, wherein Each LED channel driver in the plurality of LED channel drivers includes an operational amplifier and a driving current generating resistor, and the operational amplifier generates a corresponding one of the plurality of channel voltages according to the size of the driving current generating resistor and the corresponding one of the channel voltages. LED drive current for a corresponding one of the plurality of LED channels, The operational amplifier includes an op amp input pair tube, an offset voltage storage pair tube, and an offset voltage storage capacitor. The offset voltage storage pair tube connects the op amp input pair tube to the op amp input pair tube before the operational amplifier generates the LED drive current. The offset voltage is stored on the offset voltage storage capacitor, and when the operational amplifier generates the LED drive current, the offset voltage of the op amp input pair tube stored on the offset voltage storage capacitor is superimposed on the The input of the op amp to the tube is used to eliminate the influence of the offset voltage of the input of the op amp to the tube on the driving current of the LED. A multi-channel LED backlight system, comprising the constant current control circuit according to any one of claim 1 to 5.

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