CN102542979A - Constant current light emitting diode (LED) driving circuit - Google Patents

Abstract

The invention discloses a constant current light emitting diode (LED) driving circuit, which is characterized by comprising a constant current generating circuit, an accurate current mirror circuit and an LED output driving circuit, wherein input reference voltage is converted into current through the constant current generating circuit to produce a bias voltage, the bias voltage produced by the constant current generating circuit is converted through the accurate current mirror circuit to obtain another one bias voltage, the current in the accurate current mirror circuit is copied by the LED output driving circuit to produce steady LED driving current.

Description

A kind of constant current LED drive circuit

Technical field

The present invention relates to led drive circuit, especially a kind of constant current LED drive circuit belongs to LED display technique field.

Background technology

LED is born in the sixties in 20th century the earliest.Early stage LED is main to send faint red-light spectrum, and luminosity orange green blueness etc. just occurred afterwards in 0.001 lumens/watt.Because technology at that time and process conditions show that what the early stage light emitting diode of producing adopted is liquid phase place epitaxy technology, the LED lightness of this kind explained hereafter does not surpass 0.1 lumens/watt all the time.After the 1980s, Japanese enterprises takes the lead in realizing technological breakthrough, and luminosity reaches the 5-10 lumens/watt.After nineteen nineties; Along with the new material the reach of science; Take more advanced low pressure metal organics gaseous phase extended (LPMOVPE) and low pressure metal organic-matter chemical vapor deposition and epitaxial method (LPMOCVD) to develop the more LED of high brightness; Make that the application of LED is more wide, LED shows that using is exactly a kind of important application wherein.

In recent years, along with the develop rapidly of national economy, every profession and trade also becomes to the demand of LED display and sharply enlarges.It has been widely used in industry-by-industry and government work departments such as telecommunications, postal service, finance, traffic, stadiums.In addition; Development along with computer networking technology; The operating position of LED display under network environment is more and more, and in the information display system that multimedia, multiple display device are formed, intelligent network control and internet control multi-screen technology also are applied in reality.And the special LED drive controlling chip of the application need of LED, it can make LED obtain good, even and stable electric current, thus it is more even that LED is shown, can prolong the serviceable life of LED simultaneously, satisfies the application requirements of various occasions.

See from driving principle, can be divided into three kinds of charge-pump type, type switching power and linear adjusting types.Linear adjusting type high-brightness LED chip for driving mainly is to be applied to battery-driven occasion; Adopt the type of drive (the visual input voltage of serial number and decide) of a plurality of LED series connection constant currents; This driving can not bring EMI interference problem, ripple rejection ratio good, and circuit structure is simple relatively.What Fig. 1 showed is a kind of traditional linear adjusting type led drive circuit; The high voltage end of resistance R 1 followed reference voltage V ref1 to by the voltage follower that is made up of operational amplifier A MPa and NMOS pipe M3; Because reference voltage V ref1 is stable, the variation with working temperature and working power does not change, so the current constant of resistance R 1; Current mirror through PMOS pipe M1 and M2 constitute provides more constant electric current to LED.But current mirror for PMOS pipe M1 and M2 formation; Because drain voltage is unequal, when current replication, can have certain error, causes the current replication out of true; When multichannel output constantly even can influence the brightness of LED lamp, cause the LED lamp brightness disunities of different strings.

Summary of the invention

The invention provides a kind of constant current LED drive circuit; Its purpose is to overcome the defective of conventional linear adjusting type led drive circuit; Design a kind of high stability led drive circuit very little to the mains voltage variations sensitivity; Utilize in the circuit existing reference voltage V ref1 to form stable reference current, the drain electrode of duplicating pipe through current limit equates, obtains accurate LED drive current.

The objective of the invention is to realize like this: a kind of constant current LED drive circuit; It is characterized in that: be provided with constant-current generating circuit, accurate current mirroring circuit and LED output driving circuit; Constant-current generating circuit becomes electric current with the input reference voltage transitions; Produce a bias voltage, accurately current mirroring circuit is changed the bias voltage that constant-current generating circuit produces through accurate current mirroring circuit, obtains another bias voltage; The LED output driving circuit copies the electric current in the accurate current mirroring circuit, produces stable LED drive current; Wherein:

Constant-current generating circuit is provided with 1 operational amplifier A MPa, 1 NMOS pipe M3 and two resistance R 1 and R2 with opposite temperature coefficients; The positive input termination reference voltage V ref1 of operational amplifier A MPa; The negative input end of operational amplifier A MPa links to each other with the source electrode of NMOS pipe M3; The grid of the output termination NMOS pipe M3 of operational amplifier A MPa is connected between NMOS pipe M3 source electrode and the common after resistance R 1 and the R2 series connection, the drain electrode output offset voltage Vb1 of NMOS pipe M3;

Accurately current mirroring circuit is provided with 2 operational amplifier A MPb and AMPc, 3 PMOS pipe M1, M2 and M4 and 1 NMOS pipe M5; The source electrode of PMOS pipe M1 and M2 is connected to supply voltage Vdd1 jointly; The drain electrode of the drain electrode of the grid of PMOS pipe M1 and M2, PMOS pipe M1, the pipe of the NMOS in constant-current generating circuit M3 and the positive input terminal of operational amplifier A MPb link together; The drain electrode of the negative input end of operational amplifier A MPb and PMOS pipe M2 and PMOS pipe M4 source electrode link together; The output terminal of operational amplifier A MPb connects the grid of PMOS pipe M4; The drain electrode of the drain electrode of PMOS pipe M4 and NMOS pipe M5 and the positive input terminal of operational amplifier A MPc link together; The negative input end of AMPc connects reference voltage V ref2, and the output terminal of operational amplifier A MPc is connected with the grid of NMOS pipe M5 and as the output terminal of bias voltage Vb2, NMOS manages the source electrode connection common of M5;

The LED output driving circuit is provided with i operational amplifier A MP1～AMPi, i NMOS pipe N11～Ni1, i NMOS pipe N12～Ni2 and i*j LED lamp, and i and j are positive integers; Each positive input terminal of i operational amplifier A MP1～AMPi all connects reference voltage V ref2; Corresponding respectively each drain electrode that connects each source electrode and the NMOS pipe N12～Ni2 of i NMOS pipe N11～Ni1 of each negative input end of i operational amplifier A MP1～AMPi; Corresponding respectively each grid that connects i NMOS pipe N11～Ni1 of each output terminal of i operational amplifier A MP1～AMPi; Each grid of i NMOS pipe N12～Ni2 all connects the grid of NMOS pipe M5 in the accurate current mirroring circuit; Each source electrode of i NMOS pipe N12～Ni2 all connects common; I*j LED lamp comprises the i string, every string j, is respectively LED11～LED1j, LED21～LED2j ... LEDi1～LEDij; Each is gone here and there the positive pole of its first LED lamp of LED lamp series connection back and all connects supply voltage Vdd2, and each is gone here and there, and the negative pole of its end LED lamp of LED lamp series connection back is corresponding respectively to connect each drain electrode that i NMOS manages N11～Ni1.

Advantage of the present invention and remarkable result: compared with prior art, the present invention is superior to linear led drive circuit commonly used at present aspect a lot.

(1) the reference voltage V ref1 that exists in the directly employing system of led drive circuit of the present invention utilizes the high precision of Vref1 and the characteristics of low temperature drift, obtains the LED drive current of same high precision and low temperature drift;

(2) led drive circuit of the present invention has overcome the long mudulation effect of ditch that the MOS device exists, and forms precise current output, and the output error of having avoided the small size metal-oxide-semiconductor to bring is applicable to submicrometer processing, has reduced chip cost;

(3) led drive circuit of the present invention parallel connection simultaneously drives i string LED lamp (i is a positive integer), j LED lamp of every string (j is a positive integer), and driving force is strong, and is applied widely;

(4) led drive circuit of the present invention has characteristics simple in structure, low in energy consumption, helps promoting in all kinds of LED application scenario.

Description of drawings

Fig. 1 is existing led drive circuit

Fig. 2 is a led drive circuit structured flowchart of the present invention

Fig. 3 is the physical circuit figure of led drive circuit of the present invention

Embodiment

Referring to Fig. 2; A kind of constant current LED drive circuit of the present invention is provided with constant-current generating circuit 1, accurate current mirroring circuit 2 and LED output driving circuit 3; Constant-current generating circuit 1 converts input reference voltage Vref1 to electric current; Produce a bias voltage Vb1, accurately current mirroring circuit 21 bias voltage Vb1 that constant-current generating circuit is produced is through accurate current mirroring circuit conversion, obtains another bias voltage Vb2 (Vb1＞Vb2) usually; The LED output driving circuit copies the electric current in the accurate current mirroring circuit, produces stable LED drive current.

Fig. 3 is the physical circuit of Fig. 2.Constant-current generating circuit 1 is followed the first reference voltage V ref1 to the source electrode of NMOS pipe M3 through operational amplifier A MPa; Form electric current I 1 by resistance R 1 with R2 again; R1 and R2 adopt the resistance of opposite temperature coefficients respectively, and ((R1 and R2 position can exchange; R1 is designed to positive temperature coefficient resistor, and then R2 is designed to negative temperature coefficient resister; On the contrary, R1 negative temperature coefficient, then R2 positive temperature coefficient (PTC)),, obtain the steady current I1 of low temperature drift through the temperature compensation of resistance R 1 and R2.Accurately the operational amplifier A MPb of current mirroring circuit 2 makes PMOS pipe M1 have identical drain voltage with M2, so the current mirror of M1 and M2 formation can overcome enough long mudulation effects, carries out accurate current copy; Operational amplifier A MPc makes the drain voltage of NMOS pipe M5 equate with the second reference voltage V ref2; The drain voltage that operational amplifier A MP1～AMPi makes i string constant-current LED drive NMOS pipe N12～Ni2 in the branch road in the LED output driving circuit 3 also equals the second reference voltage V ref2; Therefore manage N12～Ni2 for NMOS in NMOS pipe M5 in the accurate current mirroring circuit 2 and the LED output driving circuit 3 and have identical grid voltage and identical drain voltage; Can form precise current copy branch road, LED11～LED1j, LED21～LED2j ... This i string (every string j) constant current LED drive circuit of LEDi1～LEDij has steady current output Io1～Ion.

(Vdd1 is 3-5V usually, and Vdd2 selects suitable size according to the number of series LED lamp, and number Vdd2 after a little while can be selected low voltage as energized Vdd1 and Vdd2; Number is more to be to select high voltage) after, with the source electrode that the first reference voltage V ref1 follows NMOS pipe M3, form electric current I 1 by resistance R 1 with R2 through operational amplifier A MPa again; PMOS pipe M1 and M2 constitute current mirror; By the electric current of M2 copy M1, in order to ensure the precision of current copy, operational amplifier A MPb makes the drain electrode of PMOS pipe M1 and M2 equate; Therefore well overcome enough long mudulation effects, promptly drain-source voltage is to the influence of current copy precision.Accurately the operational amplifier A MPc in the current mirroring circuit 2 makes the drain voltage of NMOS pipe M5 equal the second reference voltage V ref2 (0.3V≤Vref2≤1V); Operational amplifier A MP1～AMPi in the LED output driving circuit 3 (i is a positive integer) makes that the drain voltage of NMOS pipe N12～Ni2 also equals the second reference voltage V ref2 in the LED output driving circuit 3; Therefore manage N12～Ni2 for NMOS in the pipe of the NMOS in the accurate current mirroring circuit 2 M5 and the LED output driving circuit 3 and have identical grid voltage, drain voltage, source voltage; Therefore form i to accurate current mirror; These electric current I o1 that duplicates～Ion offer i string LED lamp respectively; Form constant-current driving,, make each road drive current of LED lamp reach designing requirement through the design of device parameters.

Vref1 is an input reference voltage, has characteristics little with the mains voltage variations fluctuation, low temperature drift, and therefore, for the electric current at resistance two ends in the constant-current generating circuit 1, in the promptly accurate current mirroring circuit 2 there be the electric current I 1 of PMOS pipe M1:

$\mathrm{<figure-callout\; id="1"\; label="I"\; filenames="111107204812.png"\; state="\{\{state\}\}">I</figure-callout>}1=\frac{\mathrm{Vref}1}{R1+R2}---\left(1\right)$

In design, to get the resistance that R1 and R2 are opposite temperature coefficients, thereby obtain the all-in resistance R1+R2 of low temperature drift, electric current I 1 is just temperature independent.

Accurately PMOS pipe M1 and M2 constitute current mirroring circuit in the current mirroring circuit 2, suppose that the breadth length ratio of PMOS pipe M1 is k1, and the breadth length ratio of M2 is k2, considers the long mudulation effect of ditch, so have:

$\frac{I2}{\mathrm{<figure-callout\; id="1"\; label="I"\; filenames="111107204812.png"\; state="\{\{state\}\}">I</figure-callout>}1}=\frac{k2(1+\mathrm{\&lambda;Vsd}2)}{k1(1+\mathrm{\&lambda;Vsd}1)}---\left(2\right)$

Wherein I2 is the electric current of M2 pipe, and λ is the long index of modulation of metal-oxide-semiconductor ditch.

The accurately introducing of operational amplifier A MPb in the current mirroring circuit 2 makes the drain voltage of M1 and M2 equate, so Vsd2=Vsd1, and Vsd1 and Vsd2 are respectively the source-drain voltages of PMOS pipe M1 and M2.So formula (2) abbreviation is:

$\frac{I2}{\mathrm{<figure-callout\; id="1"\; label="I"\; filenames="111107204812.png"\; state="\{\{state\}\}">I</figure-callout>}1}=\frac{k2}{k1}---\left(3\right)$

Accurately NMOS pipe N12～Ni2 has identical grid voltage, source voltage and drain voltage in NMOS pipe M5 in the current mirroring circuit 2 and the LED output driving circuit 3; The breadth length ratio of supposing NMOS pipe M5 in the accurate current mirroring circuit 2 is k5; The breadth length ratio of NMOS pipe N12～Ni2 is respectively k12～ki2 in the LED output driving circuit 3, therefore has:

$\frac{\mathrm{Io}1}{\mathrm{<figure-callout\; id="2"\; label="I"\; filenames="111107204812.png"\; state="\{\{state\}\}">I</figure-callout>}2}=\frac{k12}{k5},\frac{\mathrm{Io}2}{\mathrm{<figure-callout\; id="2"\; label="I"\; filenames="111107204812.png"\; state="\{\{state\}\}">I</figure-callout>}2}=\frac{k22}{k5},\&CenterDot;\&CenterDot;\&CenterDot;\&CenterDot;\&CenterDot;\&CenterDot;,\frac{\mathrm{Ioi}}{\mathrm{<figure-callout\; id="2"\; label="I"\; filenames="111107204812.png"\; state="\{\{state\}\}">I</figure-callout>}2}=\frac{\mathrm{ki}2}{k5}---\left(4\right)$

Bring formula (1) and formula (3) in the formula (4) each expression formula, can obtain:

$\mathrm{Io}1=\frac{\mathrm{<figure-callout\; id="11"\; label="k"\; filenames="111107204812.png"\; state="\{\{state\}\}">k</figure-callout>}11\&CenterDot;k2}{k5\&CenterDot;\mathrm{<figure-callout\; id="1"\; label="k"\; filenames="111107204812.png"\; state="\{\{state\}\}">k</figure-callout>}1}\frac{\mathrm{Vref}1}{\mathrm{<figure-callout\; id="1"\; label="R"\; filenames="111107204812.png"\; state="\{\{state\}\}">R</figure-callout>}1+\mathrm{<figure-callout\; id="2"\; label="R"\; filenames="111107204812.png"\; state="\{\{state\}\}">R</figure-callout>}2},\mathrm{Io}2=\frac{\mathrm{<figure-callout\; id="12"\; label="k"\; filenames="111107204805.png,111107204812.png"\; state="\{\{state\}\}">k</figure-callout>}12\&CenterDot;k2}{k5\&CenterDot;\mathrm{<figure-callout\; id="1"\; label="k"\; filenames="111107204812.png"\; state="\{\{state\}\}">k</figure-callout>}1}\frac{\mathrm{Vref}1}{\mathrm{<figure-callout\; id="1"\; label="R"\; filenames="111107204812.png"\; state="\{\{state\}\}">R</figure-callout>}1+\mathrm{<figure-callout\; id="2"\; label="R"\; filenames="111107204812.png"\; state="\{\{state\}\}">R</figure-callout>}2},\&CenterDot;\&CenterDot;\&CenterDot;\&CenterDot;\&CenterDot;\&CenterDot;,\mathrm{Ioi}=\frac{\mathrm{ki}2\&CenterDot;k2}{k5\&CenterDot;\mathrm{<figure-callout\; id="1"\; label="k"\; filenames="111107204812.png"\; state="\{\{state\}\}">k</figure-callout>}1}\frac{\mathrm{Vref}1}{\mathrm{<figure-callout\; id="1"\; label="R"\; filenames="111107204812.png"\; state="\{\{state\}\}">R</figure-callout>}1+R2}---\left(5\right)$

Visible by formula (5), through the concrete parameter of design k11, k5, k2, k1, R1 and R2, and, can obtain the output constant current value of needed led drive circuit according to the value of reference voltage V ref1.For example, need obtain Io1 is 10mA, so just

In selected concrete k11, k5, k2, k1, R1 and R2, let $\frac{\mathrm{<figure-callout\; id="11"\; label="k"\; filenames="111107204812.png"\; state="\{\{state\}\}">k</figure-callout>}11\&CenterDot;k2}{k5\&CenterDot;\mathrm{<figure-callout\; id="1"\; label="k"\; filenames="111107204812.png"\; state="\{\{state\}\}">k</figure-callout>}1}=\frac{\mathrm{Vref}1}{R1+R2}=10\mathrm{MA}$ Get final product.

Claims (1)

1. constant current LED drive circuit; It is characterized in that: be provided with constant-current generating circuit, accurate current mirroring circuit and LED output driving circuit, constant-current generating circuit becomes electric current with the input reference voltage transitions, produces a bias voltage; Accurately current mirroring circuit is changed the bias voltage that constant-current generating circuit produces through accurate current mirroring circuit; Obtain another bias voltage, the LED output driving circuit copies the electric current in the accurate current mirroring circuit, produces stable LED drive current; Wherein:

Constant-current generating circuit is provided with 1 operational amplifier A MPa, 1 NMOS pipe M3 and two resistance R 1 and R2 with opposite temperature coefficients; The positive input termination reference voltage V ref1 of operational amplifier A MPa; The negative input end of operational amplifier A MPa links to each other with the source electrode of NMOS pipe M3; The grid of the output termination NMOS pipe M3 of operational amplifier A MPa is connected between NMOS pipe M3 source electrode and the common after resistance R 1 and the R2 series connection, the drain electrode output offset voltage Vb1 of NMOS pipe M3;

Accurately current mirroring circuit is provided with 2 operational amplifier A MPb and AMPc, 3 PMOS pipe M1, M2 and M4 and 1 NMOS pipe M5; The source electrode of PMOS pipe M1 and M2 is connected to supply voltage Vdd1 jointly; The drain electrode of the drain electrode of the grid of PMOS pipe M1 and M2, PMOS pipe M1, the pipe of the NMOS in constant-current generating circuit M3 and the positive input terminal of operational amplifier A MPb link together; The drain electrode of the negative input end of operational amplifier A MPb and PMOS pipe M2 and PMOS pipe M4 source electrode link together; The output terminal of operational amplifier A MPb connects the grid of PMOS pipe M4; The drain electrode of the drain electrode of PMOS pipe M4 and NMOS pipe M5 and the positive input terminal of operational amplifier A MPc link together; The negative input end of AMPc connects reference voltage V ref2, and the output terminal of operational amplifier A MPc is connected with the grid of NMOS pipe M5 and as the output terminal of bias voltage Vb2, NMOS manages the source electrode connection common of M5;

The LED output driving circuit is provided with i operational amplifier A MP1 ~ AMPi, i NMOS pipe N11 ~ Ni1, i NMOS pipe N12 ~ Ni2 and i*j LED lamp, and i and j are positive integers; Each positive input terminal of i operational amplifier A MP1 ~ AMPi all connects reference voltage V ref2; Corresponding respectively each drain electrode that connects each source electrode and the NMOS pipe N12 ~ Ni2 of i NMOS pipe N11 ~ Ni1 of each negative input end of i operational amplifier A MP1 ~ AMPi; Corresponding respectively each grid that connects i NMOS pipe N11 ~ Ni1 of each output terminal of i operational amplifier A MP1 ~ AMPi; Each grid of i NMOS pipe N12 ~ Ni2 all connects the grid of NMOS pipe M5 in the accurate current mirroring circuit; Each source electrode of i NMOS pipe N12 ~ Ni2 all connects common; I*j LED lamp comprises the i string, every string j, is respectively LED11 ~ LED1j, LED21 ~ LED2j ... LEDi1 ~ LEDij; Each is gone here and there the positive pole of its first LED lamp of LED lamp series connection back and all connects supply voltage Vdd2, and each is gone here and there, and the negative pole of its end LED lamp of LED lamp series connection back is corresponding respectively to connect each drain electrode that i NMOS manages N11 ~ Ni1.

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