CN112365853A - Multi-path LED backlight system and constant current control circuit and method thereof - Google Patents
Multi-path LED backlight system and constant current control circuit and method thereof Download PDFInfo
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- G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
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- G09G3/00—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes
- G09G3/20—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters
- G09G3/34—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters by control of light from an independent source
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Abstract
A multi-path LED backlight system and a constant current control circuit and method thereof are provided. The constant current control circuit includes: the channel setting current generator generates a plurality of channel setting currents according to the reference voltage and the external resistor; a plurality of channel voltage generators that generate a plurality of channel voltages from the plurality of channel setting currents; a plurality of LED channel drivers to generate a plurality of LED drive currents for the plurality of LED channels according to the plurality of channel voltages. Each LED channel driver includes an operational amplifier. The operational amplifier comprises an operational amplifier input pair tube, an offset voltage storage pair tube and an offset voltage storage capacitor, wherein the offset voltage storage pair tube stores the offset voltage of the operational amplifier input pair tube on the offset voltage storage capacitor before the operational amplifier generates the LED driving current, and the offset voltage of the operational amplifier input pair tube is superposed on the operational amplifier input pair tube when the operational amplifier generates the LED driving current, so that the influence of the offset voltage of the operational amplifier input pair tube on the LED driving current is eliminated, and the matching between channel currents is improved.
Description
Technical Field
The invention relates to the field of circuits, in particular to a multi-path LED backlight system and a constant current control circuit and method thereof.
Background
In a multi-channel Light Emitting Diode (LED) backlight system, in order to ensure uniform brightness across the screen, it is required that the LED drive currents for the individual LED channels must be precisely matched.
In an LED backlight system employing a low frequency (e.g., 100Hz to 1000Hz) Pulse Width Modulation (PWM) dimming scheme, after a maximum LED driving current for each LED channel is set, the brightness of the LEDs is adjusted by adjusting the duty ratio of the LED driving current for each LED channel. The current matching is done for the maximum LED drive current for each LED channel. When the brightness of the LED is small, increasing the brightness of the LED by increasing the duty ratio of the LED driving current for each LED channel does not affect the matching of the maximum LED driving current for each LED channel, but the screen may have a flickering phenomenon, which has a certain influence on the health of eyes.
In an LED backlight system adopting an analog dimming mode, the brightness of LEDs is adjusted by adjusting the magnitude of LED driving current for each LED channel. When the brightness of the LED is small, increasing the brightness of the LED by increasing the LED driving current for each LED channel does not cause flickering of the screen, but it is necessary to ensure matching between the LED driving currents for each LED channel, thereby ensuring uniform brightness of the entire screen.
Disclosure of Invention
In view of one or more of the above-mentioned problems, the present invention provides a novel multi-LED backlight system and a constant current control circuit and method thereof.
The constant current control circuit for the multi-path LED backlight system comprises: the channel setting current generator is operable to generate a plurality of channel setting currents for the plurality of LED channels respectively according to the reference voltage and the magnitude of the external resistor; a plurality of channel voltage generators operable to generate a plurality of channel voltages respectively for the plurality of LED channels according to the plurality of channel setting currents; and a plurality of LED channel drivers operable to generate a plurality of LED driving currents for the plurality of LED channels, respectively, according to a plurality of channel voltages, wherein each of the plurality of LED channel drivers includes an operational amplifier and a driving current generating resistor, the operational amplifier generating an LED driving current for a corresponding one of the plurality of LED channels according to a corresponding one of the plurality of channel voltages and a magnitude of the driving current generating resistor, the operational amplifier including an operational amplifier input pair transistor, an offset voltage storage pair transistor, and an offset voltage storage capacitor, the offset voltage storage pair transistor storing an offset voltage of the operational amplifier input pair transistor on the offset voltage storage capacitor before the operational amplifier generates the LED driving current, and superimposing the offset voltage of the operational amplifier input pair transistor stored on the offset voltage storage capacitor to the operational amplifier input pair transistor when the operational amplifier generates the LED driving current, the influence of the offset voltage of the operational amplifier input pair tube on the LED driving current is eliminated.
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 the reference voltage and the magnitude of the external resistor; a channel voltage converter operable to convert the channel setting current into a plurality of channel voltages for the plurality of LED channels, respectively; and a plurality of LED channel drivers operable to generate a plurality of LED driving currents for the plurality of LED channels, respectively, according to a plurality of channel voltages, wherein each of the plurality of LED channel drivers includes an operational amplifier and a driving current generating resistor, the operational amplifier generating an LED driving current for a corresponding one of the plurality of LED channels according to a corresponding one of the plurality of channel voltages and a magnitude of the driving current generating resistor, the operational amplifier including an operational amplifier input pair transistor, an offset voltage storage pair transistor, and an offset voltage storage capacitor, the offset voltage storage pair transistor storing an offset voltage of the operational amplifier input pair transistor on the offset voltage storage capacitor before the operational amplifier generates the LED driving current, and superimposing the offset voltage of the operational amplifier input pair transistor stored on the offset voltage storage capacitor to the operational amplifier input pair transistor when the operational amplifier generates the LED driving current, the influence of the offset voltage of the operational amplifier input pair tube on the LED driving current is eliminated.
The constant current control method for the multi-path LED backlight system comprises the following steps: generating a plurality of channel setting currents for a plurality of LED channels respectively by a channel setting current generator according to the reference voltage and the external resistor; 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 generating a plurality of LED driving currents respectively used for the plurality of LED channels 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 comprises an operational amplifier and a driving current generating resistor, the operational amplifier generates the LED driving current used for the corresponding one of the plurality of LED channels according to the corresponding one of the plurality of channel voltages and the magnitude of the driving current generating resistor, the operational amplifier comprises an operational amplifier input pair transistor, an offset voltage storage pair transistor and an offset voltage storage capacitor, the offset voltage storage pair transistor stores the offset voltage of the operational amplifier input pair transistor on the offset voltage storage capacitor before the operational amplifier generates the LED driving current, and superposes the offset voltage of the operational amplifier input pair transistor stored on the offset voltage storage capacitor to the operational amplifier input pair transistor when the operational amplifier generates the LED driving current, the influence of the offset voltage of the operational amplifier input pair tube on the LED driving current is eliminated.
The constant current control method for the multi-path LED backlight system comprises the following steps: generating a channel setting current by a channel setting current generator according to the reference voltage and the external resistor; converting, by a channel voltage converter, a channel setting current into a plurality of channel voltages for a plurality of LED channels, respectively; generating a plurality of LED driving currents respectively used for a plurality of LED channels by a plurality of LED channel drivers according to a plurality of channel voltages, wherein each LED channel driver in the plurality of LED channel drivers comprises an operational amplifier and a driving current generating resistor, the operational amplifier generates the LED driving current used for a corresponding one of the plurality of LED channels according to a corresponding one of the plurality of channel voltages and the magnitude of the driving current generating resistor, the operational amplifier comprises an operational amplifier input pair transistor, an offset voltage storage pair transistor and an offset voltage storage capacitor, the offset voltage storage pair transistor stores the offset voltage of the operational amplifier input pair transistor on the offset voltage storage capacitor before the operational amplifier generates the LED driving current, and superposes the offset voltage of the operational amplifier input pair transistor stored on the offset voltage storage capacitor to the operational amplifier input pair transistor when the operational amplifier generates the LED driving current, the influence of the offset voltage of the operational amplifier input pair tube on the LED driving current is eliminated.
The multi-path LED backlight system comprises the constant current control circuit.
According to the constant current control system and the method for the multi-path LED backlight system, disclosed by the embodiment of the invention, the current matching precision among all LED channels in the multi-path LED backlight system can be improved.
Drawings
The invention may be better understood from the following description of specific embodiments thereof taken in conjunction with the accompanying drawings, in which:
FIG. 1 illustrates an example system block diagram of a multi-channel LED backlight system according to an embodiment of this disclosure;
FIG. 2 illustrates an example system block diagram of a constant current control circuit for a multi-LED backlight system in accordance with 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 illustrates an example system block diagram of a constant current control circuit for a multi-LED backlight system in accordance with 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.
Detailed Description
Features and exemplary embodiments of various aspects of the present invention will be 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. It will be apparent, however, 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 merely intended to provide a better understanding of the present invention by illustrating examples of the present invention. The present invention is in no way limited to any specific configuration and algorithm set forth below, but rather covers any modification, replacement or improvement of elements, components or algorithms without departing from the spirit of the 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. 1 illustrates an example system block diagram of a multi-way LED backlight system 100 in accordance with an embodiment of this disclosure. In the multi-LED backlight system 100 shown in fig. 1, current begins to flow through the LEDs when the output voltage Vout of the switch-mode power supply system 102 rises above the turn-on voltage of the LEDs; 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 is operable to set a magnitude of an LED driving current for each LED channel, the LED channel drivers 1044-1 to 1044-n are operable to generate n LED driving currents for the n LED channels, respectively; the dynamic margin control module 106 is operable to detect the voltages at the LED pins LED1 to LEDn respectively connecting each LED channel and feed back the detected lowest voltage VLED to the switch mode power supply system 102 for controlling the output voltage Vout to optimize the system efficiency.
Fig. 2 shows an exemplary system block diagram of the constant current control circuit 104 for the multi-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 a channel setting current I1 according to the reference voltage Vref and the magnitude of the external resistance of the pin ISET; the channel voltage converter 1042-2 is operable to convert the channel setting current I1 into n channel voltages V1 to Vn for a plurality of LED channels, respectively; the 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 part of the channel current control module 1042, i.e., the channel current control module 1042 includes the channel setting current generator 1042-1 and the 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 implement the function of the channel setting current generator 1042-1, i.e. to generate the channel setting current I1 according to the reference voltage Vref and the external resistor R3C of the ISET pin; the PMOS current mirrors PM31 and PM32 and the resistor R30 are used to realize the function of the channel voltage converter 1042-2, that is, the mirror currents generated by mirroring the channel setting current I1 by the PMOS current mirrors PM31 and PM32 are 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 functions of the LED channel drivers 1044-1 to 1044-n, i.e., to generate n LED channel currents for n LED channels respectively according to n channel voltages V1 to Vn.
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 generation resistor R3m, wherein the operational amplifier OP3m generates an LED driving current for a corresponding one of the n LED channels (i.e., the LED channel to which the LED pin LED is connected) according to a corresponding one of the channel voltages V1 to Vn and the magnitude of the driving current generation resistor R3 m. Here, m is an integer, and 1. ltoreq. m.ltoreq.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 OP3 n. Since the matching between the resistor R30 and the resistors R31 to R3n is difficult to be balanced, and the voltages across the resistors R31 to R3n are too low when the channel setting current I1 is small, the offset voltages of the operational amplifiers OP31 to OP3n have a great influence on the LED driving currents output to the respective LED channels, whereas the conventional field effect transistor (MOS) operational amplifier is difficult to be very low in offset voltage (within 1 mV), which may cause the matching consistency of the LED driving currents between the LED channels to be poor.
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-LED backlight system to improve the matching accuracy of LED driving currents between respective LED channels.
Fig. 4 shows an exemplary system block diagram of the constant current control circuit 104' for the multi-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 setting currents Ich1 to Ichn for the n LED channels, respectively, according to the reference voltage Vref and the magnitude of the external resistance of the ISET pin; the channel voltage generators 1042-21 to 1042-2n are operable to generate n channel voltages V1 'to Vn' according to the n channel setting currents Ich1 to Ichn; the 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'. Similarly, it should be appreciated that the channel setting current generator 1042-1 'and the channel voltage generators 1042-21 through 1042-2n are part of the channel current control module 1042', i.e., the channel current control module 1042 'includes the channel setting current generator 1042-1' and the channel voltage generators 1042-21 through 1042-2 n.
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, the operational amplifier OPC51 and n triode current mirrors including PMOS transistors PM51 and PM1 to PMn, triodes Q51 and Q1 to Qn of emitters of the PMOS transistors, and degeneration resistors R51 and R53-1 to R53-n of emitters of the PMOS transistors are used to implement the function of the channel setting current generator 1042-1', i.e., the operational amplifier OPC51 generates the channel setting source current Ic according to the reference voltage Vref and the size of the external resistor R5c of the ISET pin, the channel setting source current Ic generates the channel setting currents Ich1 to Ichn via the mirrors of the n triode current mirrors; the channel voltage generation resistors Rc1 to Rcn are used to realize the functions of the channel voltage generators 1042-21 to 1042-2n, i.e., the channel voltage generation resistors Rc1 to Rcn generate 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 generation resistors R1 to Rm are used to realize the functions of the LED channel drivers 1044-1 'to 1044-n', i.e., to generate n LED driving currents for n LED channels, respectively, according to the channel voltages V1 'to Vn'.
Specifically, as shown in fig. 5, a triode current mirror m including a PMOS transistor PM51, any one of PMOS transistors PM1 to PMn, triodes Q51 and Qm of the emitters of PMOS transistors PM51 and PMm, and degeneration resistors R51 and R53-m of the emitters of PMOS transistors PM51 and PMm generates a channel setting current Ichm by mirroring a channel setting source current Ic; generating a channel voltage Vm' by any one channel voltage generating resistor Rcm of channel voltage generating resistors Rc1 to Rcn according to a channel setting current Ichm; any one of the LED channel drivers 1044-1 ' to 1044-n ' includes an operational amplifier OPm that generates an LED driving current for the LED channel to which the LED pin LEDm is connected according to the channel voltage Vm ' and the magnitude of the driving current generation resistance Rm, and a driving current generation resistance Rm.
Compared with the constant current control circuit 104, the constant current control circuit 104' has the following technical advantages: 1) a triode current mirror is adopted, so that accurate current mirror matching can be achieved; 2) the negative feedback resistance of the emitter is added in the triode current mirror, so that the matching precision of the current mirror can be further improved; 3) for any one of the LED channels 1 to n, only accurate resistance electrical distribution between the channel voltage generating resistance Rcm and the driving current generating resistance Rm needs to be realized.
It should be appreciated that not all of the above three technical advantages of the constant current control circuit 104' need necessarily be achieved to improve the matching accuracy of the LED drive currents between the various LED channels. In contrast, in some embodiments, the matching accuracy of the LED driving currents between the respective LED channels may be improved to some extent by achieving one or more of the above three technical advantages of the constant current control circuit 104', as desired.
In some embodiments, the matching accuracy of the LED driving current between the individual LED channels can also be improved by making improvements to the LED channel drivers. 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 to the constant current control circuit 104 shown in fig. 2 and the constant current control circuit 104' shown in fig. 4, the matching accuracy of the LED driving currents between the respective LED channels can also be improved to some extent. That is, each of the LED channel drivers 1044-1 to 1044-n (e.g., LED channel driver 1044-m) and each of the LED channel drivers 1044-1 ' to 1044-n ' (e.g., LED channel driver 1044-m ') may be implemented in the form of an LED channel driver as illustrated in fig. 6 to improve the matching accuracy of the LED driving current 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 the operational amplifier input pair transistors PM65 and PM66 and the offset voltage storage pair transistors PM62 and PM 63; the OP-amp input connects the channel voltage Vm or Vm 'to the VR terminals of the pair of transistors PM65 and PM66 (i.e., the positive input of the OP-amp OP3m or OPm in the LED channel driver 1044-m or 1044-m'). Normally, the operational amplifier OP3m or OPm has the following two operating phases: a first phase, namely before generating the LED driving current, the switch SW1 is closed to connect the VN terminals (i.e. the inverting input terminals of the operational amplifiers OP3m or OPm in the LED channel drivers 1044-m or 1044-m') and the VR terminals of the operational amplifier input pair transistors PM65 and PM66 together, meanwhile, the switches SW2 and SW5 are turned off to open the resistor feedback loop, and the switches SW3 and SW4 are closed to make the offset voltage storage capacitor C1 store the offset voltage of the operational amplifier input pair transistors; in the second stage, when the LED driving current is generated, the switch SW1 is turned off, the switches SW2 and SW5 are turned on, so as to form a resistance feedback loop to perform constant current control on the LED driving current, and simultaneously the switches SW3 and SW4 are turned off to convert the offset voltage stored in the offset voltage storage capacitor C1 in the first stage into current through the offset voltage storage tubes PM62 and PM63 and superimpose the current onto the Drain ends of the operational amplifier input pair transistors PM65 and PM66, so as to eliminate the influence of the offset voltage of the operational amplifier OP3m or OPm on the LED driving current output to the LED channel m.
That is, the operational amplifier OP3m or OPm includes an operational amplifier input pair transistor, an offset voltage storage pair transistor, and an offset voltage storage capacitor, the offset voltage storage pair transistor stores the offset voltage of the operational amplifier input pair transistor on the offset voltage storage capacitor before the operational amplifier generates the LED driving current, and superimposes the offset voltage of the operational amplifier input pair transistor stored on the offset voltage storage capacitor on the operational amplifier input pair transistor when the operational amplifier generates the LED driving current, so as to eliminate the influence of the offset voltage of the operational amplifier input pair transistor on the LED driving current.
In achieving 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 fig. 6, the matching of the LED drive currents between all channels can be optimized for a wide range of currents. For example, the matching can be made less than 3% for LED drive currents around 5 mA.
In summary, the constant current control circuit 104' according to the embodiment of the present invention can implement a constant current control method, including: generating a plurality of channel setting currents for a plurality of LED channels respectively by a channel setting current generator according to the reference voltage and the external resistor; 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 generating a plurality of LED driving currents respectively used for the plurality of LED channels 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 comprises an operational amplifier and a driving current generating resistor, the operational amplifier generates the LED driving current used for the corresponding one of the plurality of LED channels according to the corresponding one of the plurality of channel voltages and the magnitude of the driving current generating resistor, the operational amplifier comprises an operational amplifier input pair transistor, an offset voltage storage pair transistor and an offset voltage storage capacitor, the offset voltage storage pair transistor stores the offset voltage of the operational amplifier input pair transistor on the offset voltage storage capacitor before the operational amplifier generates the LED driving current, and superposes the offset voltage of the operational amplifier input pair transistor stored on the offset voltage storage capacitor to the operational amplifier input pair transistor when the operational amplifier generates the LED driving current, the influence of the offset voltage of the operational amplifier input pair tube on the LED driving current is eliminated.
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 external resistor; converting, by a channel voltage converter, a channel setting current into a plurality of channel voltages for a plurality of LED channels, respectively; generating a plurality of LED driving currents respectively used for a plurality of LED channels by a plurality of LED channel drivers according to a plurality of channel voltages, wherein each LED channel driver in the plurality of LED channel drivers comprises an operational amplifier and a driving current generating resistor, the operational amplifier generates the LED driving current used for a corresponding one of the plurality of LED channels according to a corresponding one of the plurality of channel voltages and the magnitude of the driving current generating resistor, the operational amplifier comprises an operational amplifier input pair transistor, an offset voltage storage pair transistor and an offset voltage storage capacitor, the offset voltage storage pair transistor stores the offset voltage of the operational amplifier input pair transistor on the offset voltage storage capacitor before the operational amplifier generates the LED driving current, and superposes the offset voltage of the operational amplifier input pair transistor stored on the offset voltage storage capacitor to the operational amplifier input pair transistor when the operational amplifier generates the LED driving current, the influence of the offset voltage of the operational amplifier input pair tube on the LED driving current is eliminated.
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 fig. 2 to 6, and therefore, detailed description thereof is omitted 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 the specific embodiments may be modified without departing from the basic spirit of the invention. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.
Claims (8)
1. A constant current control circuit for a multi-path LED backlight system comprises:
the channel setting current generator is operable to generate a plurality of channel setting currents for the plurality of LED channels respectively according to the reference voltage and the magnitude of the external resistor;
a plurality of channel voltage generators operable to generate 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 channel drivers operable to generate a plurality of LED drive currents for the plurality of LED channels, respectively, according to the plurality of channel voltages, wherein
Each of the plurality of LED channel drivers comprising an operational amplifier and a drive current generating resistance, the operational amplifier generating an LED drive current for a respective one of the plurality of LED channels based on a respective one of the plurality of channel voltages and a magnitude of the drive current generating resistance,
the operational amplifier comprises an operational amplifier input pair transistor, an offset voltage storage pair transistor and an offset voltage storage capacitor, wherein the offset voltage storage pair transistor stores the offset voltage of the operational amplifier input pair transistor on the offset voltage storage capacitor before the operational amplifier generates the LED driving current, and the offset voltage of the operational amplifier input pair transistor stored on the offset voltage storage capacitor is superposed on the operational amplifier input pair transistor when the operational amplifier generates the LED driving current, so that the influence of the offset voltage of the operational amplifier input pair transistor on the LED driving current is eliminated.
2. 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 external resistor; and
and mirroring the channel setting source current by using a plurality of triode current mirrors to generate the plurality of channel setting currents.
3. The constant current control circuit of claim 2, wherein each of the plurality of triode current mirrors comprises a degeneration resistance of an emitter.
4. The constant current control circuit according to any one of claims 1 to 3, wherein each of the plurality of channel voltage generators includes a channel voltage generating resistance through which a corresponding one of the plurality of channel setting currents generates a corresponding one of the channel voltages.
5. 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 magnitude of the external resistor;
a channel voltage converter operable to convert the channel setting current into a plurality of channel voltages for a plurality of LED channels, respectively; and
a plurality of LED channel drivers operable to generate a plurality of LED drive currents for the plurality of LED channels, respectively, according to the plurality of channel voltages, wherein
Each of the plurality of LED channel drivers comprising an operational amplifier and a drive current generating resistance, the operational amplifier generating an LED drive current for a respective one of the plurality of LED channels based on a respective one of the plurality of channel voltages and a magnitude of the drive current generating resistance,
the operational amplifier comprises an operational amplifier input pair transistor, an offset voltage storage pair transistor and an offset voltage storage capacitor, wherein the offset voltage storage pair transistor stores the offset voltage of the operational amplifier input pair transistor on the offset voltage storage capacitor before the operational amplifier generates the LED driving current, and the offset voltage of the operational amplifier input pair transistor stored on the offset voltage storage capacitor is superposed on the operational amplifier input pair transistor when the operational amplifier generates the LED driving current, so that the influence of the offset voltage of the operational amplifier input pair transistor on the LED driving current is eliminated.
6. A constant current control method for a multi-path LED backlight system comprises the following steps:
generating a plurality of channel setting currents for a plurality of LED channels respectively by a channel setting current generator according to the reference voltage and the external resistor;
generating, by a plurality of channel voltage generators, a plurality of channel voltages respectively for the plurality of LED channels according to the plurality of channel setting currents; and
generating, by a plurality of LED channel drivers, a plurality of LED drive currents for the plurality of LED channels, respectively, according to the plurality of channel voltages, wherein
Each of the plurality of LED channel drivers comprising an operational amplifier and a drive current generating resistance, the operational amplifier generating an LED drive current for a respective one of the plurality of LED channels based on a respective one of the plurality of channel voltages and a magnitude of the drive current generating resistance,
the operational amplifier comprises an operational amplifier input pair transistor, an offset voltage storage pair transistor and an offset voltage storage capacitor, wherein the offset voltage storage pair transistor stores the offset voltage of the operational amplifier input pair transistor on the offset voltage storage capacitor before the operational amplifier generates the LED driving current, and the offset voltage of the operational amplifier input pair transistor stored on the offset voltage storage capacitor is superposed on the operational amplifier input pair transistor when the operational amplifier generates the LED driving current, so that the influence of the offset voltage of the operational amplifier input pair transistor on the LED driving current is eliminated.
7. A constant current control method for a multi-path LED backlight system comprises the following steps:
generating a channel setting current by a channel setting current generator according to the reference voltage and the external resistor;
converting, by a channel voltage converter, the channel setting current into a plurality of channel voltages for a plurality of LED channels, respectively;
generating, by a plurality of LED channel drivers, a plurality of LED drive currents for the plurality of LED channels, respectively, according to the plurality of channel voltages, wherein
Each of the plurality of LED channel drivers comprising an operational amplifier and a drive current generating resistance, the operational amplifier generating an LED drive current for a respective one of the plurality of LED channels based on a respective one of the plurality of channel voltages and a magnitude of the drive current generating resistance,
the operational amplifier comprises an operational amplifier input pair transistor, an offset voltage storage pair transistor and an offset voltage storage capacitor, wherein the offset voltage storage pair transistor stores the offset voltage of the operational amplifier input pair transistor on the offset voltage storage capacitor before the operational amplifier generates the LED driving current, and the offset voltage of the operational amplifier input pair transistor stored on the offset voltage storage capacitor is superposed on the operational amplifier input pair transistor when the operational amplifier generates the LED driving current, so that the influence of the offset voltage of the operational amplifier input pair transistor on the LED driving current is eliminated.
8. A multi-channel LED backlight system comprising the constant current control circuit of any one of claims 1 to 5.
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| CN202311514697.XA CN117475938A (en) | 2020-11-13 | 2020-11-13 | Multi-channel LED backlight system and constant current control circuit and method thereof |
| CN202011268020.9A CN112365853A (en) | 2020-11-13 | 2020-11-13 | Multi-path LED backlight system and constant current control circuit and method thereof |
| TW110101160A TWI761028B (en) | 2020-11-13 | 2021-01-12 | Multi-channel LED backlight system and its constant current control circuit and method |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN114333713A (en) * | 2021-12-30 | 2022-04-12 | 北京奕斯伟计算技术有限公司 | LED drive circuit, backlight module and display device |
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| Publication number | Publication date |
|---|---|
| CN117475938A (en) | 2024-01-30 |
| TWI761028B (en) | 2022-04-11 |
| TW202220497A (en) | 2022-05-16 |
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