CN202310233U - Circuit capable of reducing mismatch among multiple channel LED constant current controllers - Google Patents

Abstract

The utility model relates to a circuit capable of reducing mismatch among multiple channel LED constant current controllers. An operational amplifier of each channel includes an amplifier module and a switch control module which carry out the mismatch control to an LED constant current module of the channel. The amplifier module is provided with input paired PMOS pipes (P1 and P2), current mirror load NMOS pipes (N1 and N2), a second stage amplifier input NMOS pipe (N3), two constant current sources (I1 and I2), and eight switches (S1 to S8). The switch control module outputs a switching signal CP having a 50% duty ratio. The switching signal changes the positive and negative input terminals of the P1 and P2 continuously, and at the same time, N1 and N2 continuously change the output terminal of an amplifier, so the error between the two differential paired pipes (P1 and P2) and the error between the current mirror loads (N1 and N2) can be offset and eliminated in the continuous P1 and P2 and N1 and N2 working state changing process along with the changes of the CP signal.

Description

A kind of circuit that reduces a plurality of channel LED constant-current controller mismatches

Technical field

The utility model relates to a kind of circuit that reduces a plurality of channel LED constant-current controller mismatches, is mainly used in the brightness uniformity and the glow color uniformity that improve LCD or LCD TV backlight.

Background technology

LED (light-emitting diode) is used widely in illumination and field of backlights at present.Because LED than traditional incandescent lamp, fluorescent lamp energy-conservation, the light quality, the life-span, reliability, response speed, environmental protection all has superiority on the aspect.Therefore, LED in, replaced other light sources gradually on the backlight application of the LCD of big molded dimension or LCD TV.

LED belongs to current device, and the brightness of LED and color are very responsive to change in current.In order to keep using a plurality of LED lamps is brightness and solid colour, and LED is together in series usually can the holding current unanimity.Yet in, need tens in the backlight application of large-scale LCD TV; Hundreds of is individual; Even thousands of LED lamps, and therefore the normal working voltage of LED lamp drives the voltage that so many LED lamps just need the hundreds of volt even go up kilovolt between 3 to 3.5V.This is to be difficult to realize.Therefore just need tens LED of a kind of every road series connection as a passage, the structure that a plurality of passages are together in parallel realizes the application of more number LED-backlit.

Each LED channels in series all needs a constant-current controller and makes current stabilization.LED constant-current controller electric current between the different paths must be consistent.Just the matching precision between each passage wants high.Yet because the error of actual process is added the structural reason of galvanostat own.All be that certain matching error (being also referred to as mismatch) is arranged between each passage.So will produce luminance difference and color distortion between each passage.Current mismatch between each passage is big more, and this differentiation also can be big more.Therefore, has only the matching error that reduces as much as possible between each passage.Could realize that the whole screen of LCD TV has higher brightness consistency and colour consistency.Since the different LED passage all connect same reference voltage Vref, all use same precision resister R, but the offset voltage of the operational amplifier between the different passages is different, so offset voltage Vos becomes the main cause that influences the LED current mismatch.

Summary of the invention

The purpose of the utility model provides a kind of circuit that reduces a plurality of channel LED constant-current controller mismatches, each Channel Design a kind of operational amplifier of eliminating inefficacy voltage, and this operational amplifier is applied in the multi-channel LED constant-current control circuit.Thereby reach the purpose of the currents match error that reduces each LED passage.

For realizing above-mentioned purpose; The technical scheme that the utility model adopts is: a kind of circuit that reduces a plurality of channel LED constant-current controller mismatches; Each passage is equipped with operational amplifier and LED constant-current controller; It is characterized in that: the operational amplifier of each passage comprises that an identical amplifier module and switch control module carry out mismatch control to this LED channels constant flow module, wherein:

The LED constant-current controller comprises LED pipe, NMOS pipe N4 and the resistance of a plurality of series connection, and the positive pole of first LED pipe meets power supply VCC, and the negative electrode of an end LED pipe connects the leakage level of NMOS pipe N4, source class connecting resistance one end of NMOS pipe N4, resistance other end ground connection;

Amplifier module comprises that two PMOS pipe P1 and P2, three NMOS manage N1, N2 and N3, two constant-current source I1 and I2,8 switch S 1-S8; The end of switch S 1 and S2 links together and connects reference voltage V ref; The end of switch S 3 and S4 links together and connects the source class of the pipe of NMOS in constant-current controller N4; The other end of switch S 1 and S4 links together and connects the grid that PMOS manages P2; The other end of switch S 2 and S3 links together and connects the grid that PMOS manages P1, the source class interconnection of PMOS pipe P1 and PMOS pipe P2 and the negative pole of connection constant-current source I1, and the positive pole of constant-current source I1 meets power vd D; The leakage level of PMOS pipe P1 connects leakage level, an end of switch S 5 and the end of switch S 8 of NMOS pipe N1 respectively; The leakage level of PMOS pipe P2 connects leakage level, an end of switch S 7 and the end of switch S 6 of NMOS pipe N2 respectively, and NMOS manages source class interconnection and the ground connection of N1 and NMOS pipe N2, and NMOS pipe N1 and NMOS manage the gate interconnection of N2 and link together with the other end of switch S 6 and the other end of switch S 5; The other end of switch S 7 and switch S 8 all connects the grid of NMOS pipe N3; The source ground of NMOS pipe N3, the leakage level of NMOS pipe N3 connect constant-current source I2 negative pole and NMOS pipe N4 source class and as the output end vo of amplifier module, constant-current source I2 positive pole meets power vd D;

Switch control module comprises an inverter, and the input of inverter connects switching signal CP and as the control signal of switch S 1, S3, S5 and S7, the output of inverter is as the control signal of switch S 2, S4, S6 and S8.

The advantage of the utility model and showing effect: the utility model is used into a kind of novel operational amplifier that can eliminate offset voltage instead to the operational amplifier of traditional LED constant-current control circuit.Thereby can reduce the matching error between the different LED passage greatly.Make very high brightness uniformity and the colour consistency of maintenance between each channel LED lamp.

Description of drawings

The theory diagram of Fig. 1 the utility model;

Fig. 2 the utility model physical circuit figure;

Fig. 3 switch S 1, S3, S5, the equivalent circuit diagram of amplifier when S7 is operated in closure state;

Fig. 4 switch S 2, S4, S6, the equivalent circuit diagram of amplifier when S8 is operated in closure state.

Embodiment

Referring to Fig. 1,2; The utility model proposes a kind of circuit that reduces a plurality of channel LED constant-current controller mismatches; Each passage is equipped with operational amplifier and LED constant-current controller, and the operational amplifier of each passage comprises that an identical amplifier module and switch control module carry out mismatch control to this LED channels constant flow module.

The LED constant-current controller comprises LED pipe, NMOS pipe N4 and the resistance of a plurality of series connection, and the positive pole of first LED pipe meets power supply VCC, and the negative electrode of an end LED pipe connects the leakage level of NMOS pipe N4, source class connecting resistance one end of NMOS pipe N4, resistance other end ground connection.

Amplifier module comprises that input arrives S8 to pipe PMOS pipe P1 and P2, current mirror load NMOS pipe N1 and N2, second level amplifier input pipe NMOS pipe N3, two constant-current source I1 and I2 and 8 switch S 1.The end of switch S 1 and S2 links together and connects reference voltage V ref; The end of switch S 3 and S4 links together and connects the source class voltage Vn (being the offset voltage Vos into operational amplifier between reference voltage V ref and the Vn) of the pipe of NMOS in constant-current controller N4; The other end of switch S 1 and S4 links together and connects the grid that PMOS manages P2; The other end of switch S 2 and S3 links together and connects the grid that PMOS manages P1; The negative pole of the source class interconnection of PMOS pipe P1 and PMOS pipe P2 and connection constant-current source I1; The positive pole of constant-current source I1 meets power vd D, and the leakage level of PMOS pipe P1 connects leakage level, an end of switch S 5 and the end of switch S 8 of NMOS pipe N1 respectively, and the leakage level of PMOS pipe P2 connects leakage level, an end of switch S 7 and the end of switch S 6 of NMOS pipe N2 respectively; Source class interconnection and the ground connection of NMOS pipe N1 and NMOS pipe N2; NMOS pipe N1 and NMOS manage the gate interconnection of N2 and link together with the other end of switch S 6 and the other end of switch S 5, and the other end of switch S 7 and switch S 8 all connects the grid of NMOS pipe N3, the source ground of NMOS pipe N3; The leakage level of NMOS pipe N3 connect constant-current source I2 negative pole and NMOS pipe N4 source class and as the output end vo of amplifier module, constant-current source I2 positive pole meets power vd D; Switch control module comprises an inverter, and the input of inverter connects switching signal CP and directly as the control signal of switch S 1, S3, S5 and S7, the output of inverter is as the control signal of switch S 2, S4, S6 and S8; Switch S 2, S4, S6; S8 is and S1; S3, S5, the signal that the S7 phase place is opposite.Because size and the threshold voltage of two differential pair tube P1 and P2 are not equal fully, have certain error; Size and the threshold voltage of two current mirror NMOS pipe N1 and N2 are not equal fully, have certain error; So amplifier can produce certain offset voltage.

When CP (duty ratio is 50% switching signal) is high level, switch S 1, S3, S5, S7 are opening, switch S 2, S4, S6, S8 are closed condition.This moment, Vref termination PMOS managed the grid of P2, the grid of Vn termination PMOS pipe P1, and the grid of NMOS pipe N1 and N2 is connected the drain electrode of P1 and N1.The drain electrode of P2 and N2 connects the grid of NMOS pipe N3.Vref is the positive input terminal of amplifier like this, and Vn is the negative input end of amplifier.The leakage level that is output as NMOS pipe N2 and PMOS pipe P2 of primary amplifier, they receive secondary amplifier input terminal---the grid of NMOS pipe N3.Its equivalent electric circuit is as shown in Figure 3.

When CP is low level, switch S 1, S3, S5, S7 are closed condition, switch S 2, S4, S6, S8 is for closing opening.This moment, Vref termination PMOS managed the grid of P1, the grid of Vn termination PMOS pipe P2, and the grid of NMOS pipe N1 and N2 is connected the drain electrode of P2 and N2.The drain electrode of P1 and N1 connects the grid of NMOS pipe N3.Vref still is the positive input terminal of amplifier equally like this, and Vn also still is the negative input end of amplifier.The leakage level that is output as NMOS pipe N1 and PMOS pipe P1 of primary amplifier, receive secondary amplifier input terminal---the grid of NMOS pipe N3.Its equivalent electric circuit is as shown in Figure 4.

Can reach a conclusion according to above-mentioned two kinds of operating states; No matter CP is high level or low level; The positive-negative input end of amplifier does not all have to change; What change is the inner annexation of primary amplifier, i.e. PMOS pipe P1 and the continuous conversion positive-negative input end of P2, and NMOS pipe N1 and N2 are also at the output of continuous conversion primary amplifier simultaneously.Promptly along with the CP signal becomes low level by high level, the drain terminal of former cause P1 and N1 becomes by the drain terminal of P2 and the N2 output as primary amplifier as the output of primary amplifier.The operating state that is to say P1 and N1 and P2 and N2 is along with the height variation of CP signal and mutual the conversion.Like this by between two differential pair tube P1 and the P2 and the error that produces between current mirror load N1 and the N2 can be along with the continuous variation of CP signal, at P1 and P2, be cancelled in the continuous conversion operating state of N1 and N2 and eliminate.Suppose that the input offset voltage of amplifier when CP is high level is Vos, the input offset voltage of amplifier when CP is low level is exactly-Vos so.So along with the continuous variation of CP signal, total offset voltage of amplifier be Vos+ (Vos)=0.

Below further specify the operation principle of the utility model:

As shown in Figure 2, the LED constant-current control circuit is a kind of current/charge-voltage convertor.Amplifier and power NMOS pipe N4 and resistance R constitute a negative feedback structure.This structure is the LED electric current I that the reference voltage V ref of fixed voltage value is converted to the fixed current value _LED, promptly Wherein Vref is the reference voltage in the system, and Vos is the offset voltage of operational amplifier.

In fact, in the multi-channel LED constant-current system, every passage is all just like a galvanostat of this structure of Fig. 2.Give an example with first passage and second channel, the electric current of two passes is respectively:

$I_{\mathrm{<figure-callout\; id="1"\; label="LED"\; filenames="111107202332.png"\; state="\{\{state\}\}">LED</figure-callout>}1}=\frac{\mathrm{Vref}-\mathrm{Vos}1}{R1}---\left(1\right)$

$I_{\mathrm{<figure-callout\; id="2"\; label="LED"\; filenames="111107202326.png"\; state="\{\{state\}\}">LED</figure-callout>}2}=\frac{\mathrm{Vref}-\mathrm{Vos}2}{R2}---\left(2\right)$

Mismatch (being matching error) between two paths is defined as:

$\mathrm{\&epsiv;}=\&PlusMinus;\frac{I_{\mathrm{LED}1}-I_{\mathrm{LED}2}}{I_{\mathrm{<figure-callout\; id="1"\; label="LED"\; filenames="111107202332.png"\; state="\{\{state\}\}">LED</figure-callout>}1}+I_{\mathrm{LED}2}}---\left(3\right)$

Draw after bringing formula (1) and formula (2) into formula (3):

$\mathrm{\&epsiv;}=\&PlusMinus;\frac{I_{\mathrm{LED}1}-I_{\mathrm{LED}2}}{I_{\mathrm{<figure-callout\; id="1"\; label="LED"\; filenames="111107202332.png"\; state="\{\{state\}\}">LED</figure-callout>}1}+I_{\mathrm{<figure-callout\; id="2"\; label="LED"\; filenames="111107202326.png"\; state="\{\{state\}\}">LED</figure-callout>}2}}=\frac{\mathrm{Vref}(R2-R1)-\mathrm{<figure-callout\; id="2"\; label="R"\; filenames="111107202326.png"\; state="\{\{state\}\}">R</figure-callout>}2\&CenterDot;\mathrm{Vos}1+\mathrm{<figure-callout\; id="1"\; label="R"\; filenames="111107202332.png"\; state="\{\{state\}\}">R</figure-callout>}1\&CenterDot;\mathrm{Vos}2}{\mathrm{Vref}(\mathrm{<figure-callout\; id="2"\; label="R"\; filenames="111107202326.png"\; state="\{\{state\}\}">R</figure-callout>}2+R1)-\mathrm{<figure-callout\; id="2"\; label="R"\; filenames="111107202326.png"\; state="\{\{state\}\}">R</figure-callout>}2\&CenterDot;\mathrm{Vos}1-\mathrm{<figure-callout\; id="1"\; label="R"\; filenames="111107202332.png"\; state="\{\{state\}\}">R</figure-callout>}1\&CenterDot;\mathrm{Vos}2}---\left(4\right)$

Because the resistance between leading to is all made the form of mutual coupling in the plate-making of reality, especially high-precision POLY resistance or injection resistance, precision can reach 0.4% under situation about matching each other, and the error that this error ratio Vos produces is little a lot.Therefore, after the negligible resistance matching error.Mismatch between passage 1 and the passage 2 is:

$\mathrm{\&epsiv;}=\&PlusMinus;\frac{\mathrm{Vos}2-\mathrm{Vos}1}{2\mathrm{Vref}-\mathrm{Vos}2-\mathrm{Vos}1}---\left(5\right)$

Can find out that by formula (5) offset voltage that reduces operational amplifier in the galvanostat can effectively reduce the mismatch between the different passages of LED.For example, in order to improve circuit efficiency, in the galvanostat resistance general smaller be 5 Ω.The resistors match error is 0.4%.Reference voltage is 1V, and the offset voltage of amplifier is 2mV generally speaking, and the LED electric current is 50mA.The mismatch ε of system=1.6% in this case; If after the offset voltage elimination, mismatch ε=0.4%.This mismatch can satisfy the requirement of high accuracy LED-backlit.Therefore, the offset voltage of elimination operational amplifier has important function to improving multi-channel LED currents match degree.

Claims (1)

1. circuit that reduces a plurality of channel LED constant-current controller mismatches; Each passage is equipped with operational amplifier and LED constant-current controller; It is characterized in that: the operational amplifier of each passage comprises that amplifier module and switch control module carry out mismatch control to this LED channels constant flow module, wherein:

The LED constant-current controller comprises LED pipe, NMOS pipe N4 and the resistance of a plurality of series connection, and the positive pole of first LED pipe meets power supply VCC, and the negative electrode of an end LED pipe connects the leakage level of NMOS pipe N4, source class connecting resistance one end of NMOS pipe N4, resistance other end ground connection;

Amplifier module comprises that two PMOS pipe P1 and P2, three NMOS manage N1, N2 and N3, two constant-current source I1 and I2,8 switch S 1-S8; The end of switch S 1 and S2 links together and connects reference voltage V ref; The end of switch S 3 and S4 links together and connects the source class of the pipe of NMOS in constant-current controller N4; The other end of switch S 1 and S4 links together and connects the grid that PMOS manages P2; The other end of switch S 2 and S3 links together and connects the grid that PMOS manages P1, the source class interconnection of PMOS pipe P1 and PMOS pipe P2 and the negative pole of connection constant-current source I1, and the positive pole of constant-current source I1 meets power vd D; The leakage level of PMOS pipe P1 connects leakage level, an end of switch S 5 and the end of switch S 8 of NMOS pipe N1 respectively; The leakage level of PMOS pipe P2 connects leakage level, an end of switch S 7 and the end of switch S 6 of NMOS pipe N2 respectively, and NMOS manages source class interconnection and the ground connection of N1 and NMOS pipe N2, and NMOS pipe N1 and NMOS manage the gate interconnection of N2 and link together with the other end of switch S 6 and the other end of switch S 5; The other end of switch S 7 and switch S 8 all connects the grid of NMOS pipe N3; The source ground of NMOS pipe N3, the leakage level of NMOS pipe N3 connect constant-current source I2 negative pole and NMOS pipe N4 source class and as the output end vo of amplifier module, constant-current source I2 positive pole meets power vd D;

Switch control module comprises an inverter, and the input of inverter connects switching signal CP and is connected with the control signal end of switch S 1, S3, S5 and S7, and the output of inverter is connected with the control signal end of switch S 2, S4, S6 and S8.

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