CN101262729A - A LED constant current driving circuit - Google Patents

Abstract

The invention relates to an LED constant current drive circuit which comprises a first shift register (3), a flip-latch (2), a constant current output pole (1), a second shift register (4) connected with the constant current output pole (1), a reader controller (5) used for controlling the flow direction of the data and for controlling the multiplexing capabilities of the first shift register (3) and the second shift register (4), and a read only memory (6) that solidifies the data therein through the reader controller (5). Based on the structure of the original 16-way LED constant current drive circuit, the LED constant current drive circuit of the invention is improved and realizes the current program-control fine tuning on the precondition that no other input port is added and realizes the final solidification; besides, the LED constant current drive circuit of the invention completes white balance adjustment and read-in of other data by utilizing a date latch control terminal LAT and a clock signal input terminal DCK, and completes the pin multiplexing capabilities of a serial date input terminal DAI and a serial date output terminal DAO under different models.

Description

A kind of LED constant current driving circuit

Technical field

The present invention relates to the light-emitting diode constant-current driving, more particularly, relate to a kind of LED constant current driving circuit with the white balance adjusting function.

Background technology

LED is exactly light emitting diode, and the english abbreviation of light-emitting diode is called for short LED.And light emitting diode (LED) display screen (LED panel) is a kind of display mode by the control semiconductor light-emitting-diode, is used for the display screen of various information such as display text, figure, image, animation, market, video, video signal.Nowadays live in the bustling city, the light-emitting diode advertisement screen that is seen everywhere dazzling, picture displayed is also done to such an extent that become better and better, and this just improves the conforming requirement of each pixel of forming picture thereupon.

When the output of LED constant current driving circuit is subjected to enough voltage, the output characteristic of constant-current drive circuit be configured to stablize constant.That is to say that the electric current of output can not change along with variation, supply voltage or the ambient temperature of light-emitting diode electrical characteristic.Because predetermined current is to set via built-in feedback control circuit institute is special, and in electric current quite on a large scale, the accuracy of electric current can guarantee.Therefore, constant-current drive circuit can be sent to light-emitting diode to predetermined current, makes light-emitting diode reach the brightness of expection.The output consistency of LED constant current driving circuit is the same with constancy important.LED constant current driving circuit can drive row's light-emitting diode, and the inconsistency between constant-current drive circuit can reduce the quality of show image.For the constant-current drive circuit of 8 channels and 16 channels, the consistency between the output channel need be considered.And for volume production, how the stability of semiconducter engineering also challenging the output consistency between the design chips.Currently marketed LED constant current driving circuit generally includes following a few class, promptly has the LED constant current driving circuit of light-emitting diode error detection function, the LED constant current driving circuit of tool current gain function, the LED constant current driving circuit of tool PWM function, a LED constant current driving circuit of tool signal transmission technology.

Our said white balance just is meant the balance of white, i.e. the balance of 3: 6: 1 ratios of brightness of R, G, three kinds of colors of B; The brightness ratio of R, G, three kinds of colors of B and the adjusting of white coordinate are called white balance adjusting.The LED constant current driving circuit of the band white balance adjusting function that exists on the current market normally adopts the form of 28 pins, what adopted its inside is 16 bit shift register, 16 latchs and 16 constant current output stages, and the LED constant current driving circuit of 24 pin does not generally have the white balance adjusting function.Therefore, how to design a kind of LED constant current driving circuit that under the situation that does not increase pin number, has the white balance adjusting function and promptly become emphasis of the present invention.

Summary of the invention

The technical problem to be solved in the present invention provides a kind of LED constant current driving circuit with the white balance adjusting function, defective at needs 28 pins of band white balance adjusting function on the prior art, it improves on the architecture basics of original 16 road LED constant current driving circuit, under the prerequisite of not adding other input port, 28 pins are changed 24 pins, utilize data latching control end LAT and clock signal input part DCK to finish writing of white balance adjusting data, finished serial data input DAI and the pin multiplexing function of serial data output DAO under different mode simultaneously.

The technical solution adopted for the present invention to solve the technical problems is: construct a kind of LED constant current driving circuit, comprise first shift register, latch and constant current output stage, it also comprises second shift register that is connected with described constant current output stage, is used for the flow direction of control data and controls first shift register and the read-write controller of the multiplexing function of second shift register and data are solidificated in wherein read-only memory by described read-write controller.

In LED constant current driving circuit of the present invention, described first shift register is 16 bit shift register, described second shift register is 80 bit shift register, and described latch is 16 latchs, and described constant current output stage is 16 constant current output stages.

In LED constant current driving circuit of the present invention, adopt the packing forms of PDIP24, SOP24 or SSOP24, comprise following 24 pins: serial data input DAI, serial data output DAO, data latching control end LAT, output enable control end EN, clock signal input terminal DCK, outer meeting resistance input REXT, chip power VDD, control logic and drive current earth terminal GND, constant-current source output OUT0-OUT15.

In LED constant current driving circuit of the present invention, described serial data input DAI and serial data output DAO are first shift register and the second shift register data shared input/output terminal.

In LED constant current driving circuit of the present invention, also comprise the first diverter switch S1 and the second diverter switch S2 that are subjected to described read-write controller control, be used to switch the multiplexing function of first shift register and second shift register.

In LED constant current driving circuit of the present invention, described read-write controller comprises the digit counter LAT-Count that links to each other with data latching control end LAT, and the output of described digit counter LAT-Count is respectively the signal that the displacement output control of second shift register, read-only memory write control and switch S 1, S2 switching controls.

In LED constant current driving circuit of the present invention, the output of described clock signal input terminal DCK, data latching control end LAT and digit counter LAT-Count with and produce the clock signal of second shift register.

In LED constant current driving circuit of the present invention, described constant current output stage also comprises transistor MP3, MP4, MP5, MP6 and the MP7 that is used for electric current fine setting and is used for the Current Regulation branch road and by transistor MPS1, MPS2, MPS3, MPS4 and the MPS5 of the switching signal SN_1-SN_5 control of reading from second shift register.

In LED constant current driving circuit of the present invention, described clock signal input terminal DCK keeps high level, digit counter LAT-Count output is overflowed, and again data latching control end LAT will be imported data as clock signal and move into second shift register from serial data input DAI.

In LED constant current driving circuit of the present invention, described second shift register is under the control of described read-write controller, to described constant current output stage, described constant current output stage can will be examined wrong information data transmission to described first shift register with the white balance adjusting transfer of data.

Implement LED constant current driving circuit of the present invention, has following beneficial effect: change existing 28 pins into 24 pins, on the architecture basics of original 16 road LED constant current driving circuits, improve, the current-programmed fine setting that realizes the constant current delivery outlet under the prerequisite of not adding other input port also can finally be solidified, utilize data latching control end LAT and clock signal input part DCK to finish writing of white balance adjusting data, serial data input DAI and the pin multiplexing function of serial data output DAO under different mode have been finished simultaneously, so the output current of its each output port can be write inside and writes the mode of ROM finely tune 20% on the basis of reference current, degree of regulation with 64 rank, and the chip of a large amount of circulations on its pin and the market is compatible fully.

Description of drawings

The invention will be further described below in conjunction with drawings and Examples, in the accompanying drawing:

Fig. 1 is the schematic diagram of the pin of LED constant current driving circuit of the present invention;

Fig. 2 is the structural representation of the chip internal of LED constant current driving circuit of the present invention;

Fig. 3 is the schematic diagram of the read-write controller of LED constant current driving circuit of the present invention;

Fig. 4 is the logic timing figure of the pin of LED constant current driving circuit of the present invention;

Fig. 5 be LED constant current driving circuit of the present invention increase the circuit theory diagrams of constant current output stage of white balance adjusting structure;

Fig. 6 is the system block diagram of the practical application of LED constant current driving circuit of the present invention.

Embodiment

The present invention is directed to existing LED constant current driving circuit and adopt the form of 28 pins and 16 bit shift register, designed a kind of LED constant current driving circuit that under the situation that does not increase pin number, has the white balance adjusting function.The present invention changes existing 28 pins into 24 pins, on the architecture basics of original 16 road LED constant current driving circuits, improve, under the prerequisite of not adding other input port, utilize data latching control end LAT and clock signal input part DCK to finish writing of white balance adjusting and other data, finished serial data input DAI and the pin multiplexing function of serial data output DAO under different mode simultaneously.

As shown in Figure 1, LED constant current driving circuit of the present invention adopts the packing forms of PDIP24, SOP24 or SSOP24, comprises following 24 pins: serial data input DAI, serial data output DAO, data latching control end LAT, output enable control end EN, clock signal input terminal DCK, outer meeting resistance input REXT, chip power VDD, control logic and drive current earth terminal GND, constant-current source output OUT0-OUT15.Wherein, REXT is the input that connects external resistance, and this external resistance can be set the output current of all output channels.EN is the output enable control end, when EN is low level, will start constant-current source output OUT0-OUT15, and when EN was high level, OUT0-OUT15 then can be closed.LAT is the data latching control end, and when LAT was high level, the input data can be sent to latch 2, and when LAT was low level, data will be latched.DCK is the input of clock signal, will be shifted to data when high level.DAI and DAO are respectively input, the outputs of data, and the DAI end can connect the DAO end of another chip.

As shown in Figure 2, LED constant current driving circuit of the present invention comprises interconnective first shift register 3, latch 2, constant current output stage 1, and it also comprises interconnective second shift register 4, read-write controller 5, read-only memory (ROM) 6.The first shown shift register 3 is 16 bit shift register, and second shift register 4 is 80 bit shift register, and latch 2 is 16 latchs, and constant current output stage 1 is 16 constant current output stages.Second shift register 4 also is connected with constant current output stage 1 as random asccess memory (RAM), is used to store the control data of constant current output stage 1.The switching that read-write controller 5 is used to control the flow direction of input data and controls first shift register 3, second shift register, 4 multiplexing functions.Read-only memory 6 is used for confirmed data are solidificated in wherein, and these data comprise white balance adjusting data, video data or the like.Constituted chip input control unit for data by second shift register 4, read-write controller 5 and read-only memory 6 among the figure.It can also be seen that from figure serial data input DAI and serial data output DAO are the shared data input/output terminal of first shift register 3 and second shift register 4.Shown LED constant current driving circuit also comprises the first diverter switch S1 and the second diverter switch S2 that is subjected to read-write controller 5 controls, is used to switch the multiplexing function of first shift register 3 and second shift register 4.The first diverter switch S1 is connected between serial data input DAI and first, second shift register 3,4, the second diverter switch S2 is connected between serial data output DAO and first, second shift register 3,4, so that can finish the multiplexing functions of first and second shift registers 3,4 under the control of read-write controller 5.Second shift register 4 arrives constant current output stage 1 with white balance adjusting and other transfer of data under the control of read-write controller 5, constant current output stage then 1 can will be examined wrong information data transmission to first shift register 3.Shown structure is improved on the architecture basics of original 16 road LED constant current driving circuits, under the prerequisite of not adding other input port, utilize LAT pin and DCK pin to finish writing of white balance adjusting data, finished DAI and the DAO pin multiplexing function under different mode simultaneously.

As shown in Figure 3, there is shown the schematic diagram of the read-write controller 5 of LED constant current driving circuit of the present invention.Read-write controller 5 comprises the digit counter LAT-Count that links to each other with data latching control end LAT, and the output of digit counter LAT-Count is respectively the signal that second shift register 4 displacement output control, read-only memory 6 write control and switch S 1, S2 switching controls.The displacement input of RAM (i.e. second shift register 4) and the displacement input of 16 bit shift register (i.e. first shift register 3) also link to each other with external pin DAI together, and promptly DAI makes the shared data input pin of RAM and 16 bit shift register.The clock signal of second shift register 4 be by the output of clock signal input terminal DCK, data latching control end LAT and digit counter LAT-Count with and produce.

With reference to Fig. 3 and Fig. 4, now the logic timing figure to the pin of LED constant current driving circuit of the present invention describes.If the input data are moved into second shift register 4, must make clock signal DCK keep high level so.Data latching control end LAT produces 1+2 earlier continuously ⁿAfter individual (n is the figure place of counter LAT-Count) pulse, the output of digit counter LAT-Count is overflowed, and again data latching control end LAT is moved into second shift register 4 to data from serial data input DAI as clock signal.Simultaneously the displacement output of second shift register 4 is linked on the serial data output DAO pin, this moment, serial data output DAO was output as the data that shift out in second shift register 4.Digit counter LAT-Count removes at rising edge or the trailing edge of clock signal DCK, to guarantee the normal read-write to first shift register (3).After digit counter LAT-Count resetted, the output of 16 bit shift register was linked on the DAO pin.This has just realized that DAO and DAI functions of pins are multiplexing.When normal, in the program process,, thereby can make digit counter LAT-Count can't produce spill over, also just can't produce ROM program enable signal and RAM data and move into clock signal owing to the rising edge of clock signal DCK and the continuous appearance of trailing edge.Yet the present invention has realized the multiplexing functions of data latching control end LAT and clock signal input terminal DCK, has solved the problem on the present invention and the existing product compatibility.

Fig. 5 be LED constant current driving circuit of the present invention increase the circuit theory diagrams of constant current output stage 1 of white balance adjusting structure.Constant current output stage 1 of the present invention has increased transistor MP3, MP4, MP5, MP6 and MP7 as electric current fine setting pipe on original circuit base, increased transistor MPS1, MPS2, MPS3, MPS4 and the MPS5 switch control valve as the Current Regulation branch road simultaneously.Wherein, switching signal SN_1-SN_5 will read from the ROM the inside, and they are control signals of transistor MPS1, MPS2, MPS3, MPS4 and MPS5.When switching signal SN_1-SN_5 is low level, represents that this branch road opens, otherwise represent this branch road to turn-off.MN4 among Fig. 5 is an injectron, combine with amplifier OP2 simultaneously and form active grid common source configuration altogether to increase the output impedance of output, CHARGE CONTROL unit is used to control the unlatching and the shutoff of single passage, OP1, MN1, MP1 and REXT have formed electric current the unit have been set, formed current mirror structure by MP1 and MP2-MP7, the ratio of MP1 and MP2-MP7 was made as 1: 1, formed the current mirror structure for amplifying by MN2 and MN3, and the multiplication factor of MN3 and MN2 is made as M.When SN_1-SN_5 was low level entirely, the lowest high-current value of each passage was set by external resistance R EXT, and lowest high-current value is as follows:

$I_{\mathrm{OUTN}\_\mathrm{MAX}}=\frac{\mathrm{<figure-callout\; id="1"\; label="VREF"\; filenames="A20081006680500131.png,A20081006680500151.png"\; state="\{\{state\}\}">VREF</figure-callout>}1}{\mathrm{REXT}}\&times;M---\left(1\right)$

Wherein, the current ratio between MP3, MP4, MP5, MP6, the MP7 was made as 1: 2: 4: 8: 16, and the electric current sum of MP3-MP7 accounts for 20% of MP1 electric current, therefore always has 32 grades fine setting effect, so the adjustable precision of single channel electric current is 0.625%.

As shown in Figure 6, there is shown a kind of practical application of LED constant current driving circuit of the present invention.The intelligent digital camera is used to gather the monochrome information of the three-color light-emitting diode on each pixel on the light emitting diode (LED) display screen, then these monochrome informations is converted to quantitative information.Computer is used to analyze the quantitative information that the intelligent digital camera produces, and the result is converted into the binary coded data that brightness is exported in fine setting, and then these numbers are sent to LED constant current driving circuit.LED constant current driving circuit has solidified the program timing sequence of constant-current drive circuit able to programme, and the output current of its each output port can finely tune 20% by the mode of writing ROM on the basis of reference current, and has the degree of regulation on 64 rank.

LED constant current driving circuit of the present invention has the white balance adjusting function, it changes existing 28 pins into 24 pins, on the architecture basics of original 16 road LED constant current driving circuits, improve, under the prerequisite of not adding other input port, utilize data latching control end LAT and clock signal input part DCK to finish writing of white balance adjusting data, serial data input DAI and the pin multiplexing function of serial data output DAO under different mode have been finished simultaneously, the output current of its each output port can be write inside and writes the mode of ROM finely tune 20% on the basis of reference current like this, degree of regulation with 64 rank, and the chip of a large amount of circulations on its pin and the market is compatible fully.

The present invention is described by some embodiment, and those skilled in the art know, under the situation that does not break away from the spirit and scope of the present invention, can carry out various changes or equivalence replacement to these features and embodiment.In addition, under instruction of the present invention, can make amendment to these features and embodiment can not break away from the spirit and scope of the present invention to adapt to concrete situation and material.Therefore, the present invention is not subjected to the restriction of specific embodiment disclosed herein, and all interior embodiment of claim scope that fall into the application belong to protection scope of the present invention.

Claims (10)

1, a kind of LED constant current driving circuit, comprise first shift register (3), latch (2) and constant current output stage (1), it is characterized in that, also comprise second shift register (4) that is connected with described constant current output stage (1), be used for the flow direction of control data and control first shift register (3) and the read-write controller (5) of the multiplexing function of second shift register (4) and data are solidificated in wherein read-only memory (6) by described read-write controller (5).

2, LED constant current driving circuit according to claim 1, it is characterized in that, described first shift register (3) is 16 bit shift register, described second shift register (4) is 80 bit shift register, described latch (2) is 16 latchs, and described constant current output stage (1) is 16 constant current output stages.

3, LED constant current driving circuit according to claim 2, it is characterized in that, adopt the packing forms of PDIP24, SOP24 or SSOP24, comprise following 24 pins: serial data input DAI, serial data output DAO, data latching control end LAT, output enable control end EN, clock signal input terminal DCK, outer meeting resistance input REXT, chip power VDD, control logic and drive current earth terminal GND, constant-current source output OUT0-OUT15.

4, LED constant current driving circuit according to claim 3 is characterized in that, described serial data input DAI and serial data output DAO are first shift register (3) and second shift register (4) data shared input/output terminal.

5, LED constant current driving circuit according to claim 4, it is characterized in that, also comprise the first diverter switch S1 and the second diverter switch S2 that are subjected to described read-write controller (5) control, be used to switch the multiplexing function of first shift register (3) and second shift register (4).

6, LED constant current driving circuit according to claim 5, it is characterized in that, described read-write controller (5) comprises the digit counter LAT-Count that links to each other with data latching control end LAT, and the output of described digit counter LAT-Count is respectively the signal that second shift register (4) displacement output control, read-only memory (6) write control and switch S 1, S2 switching controls.

7, LED constant current driving circuit according to claim 6, it is characterized in that, the output of described clock signal input terminal DCK, data latching control end LAT and digit counter LAT-Count with and produce the clock signal of second shift register (4).

8, LED constant current driving circuit according to claim 7, it is characterized in that described constant current output stage (1) also comprises transistor MP3, MP4, MP5, MP6 and the MP7 that is used for electric current fine setting and is used for the Current Regulation branch road and by transistor MPS1, MPS2, MPS3, MPS4 and the MPS5 of the switching signal SN_1-SN_5 control of reading from second shift register (4).

9, LED constant current driving circuit according to claim 8, it is characterized in that, described clock signal input terminal DCK keeps high level, digit counter LAT-Count output is overflowed, and again data latching control end LAT will be imported data as clock signal and move into second shift register (4) from serial data input DAI.

10, LED constant current driving circuit according to claim 9, it is characterized in that, described second shift register (4) is under the control of described read-write controller (5), to described constant current output stage (1), described constant current output stage (1) can will be examined wrong information data transmission to described first shift register (3) with the white balance adjusting transfer of data.

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