CN104349539A - Constant-current driving circuit - Google Patents
Constant-current driving circuit Download PDFInfo
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- CN104349539A CN104349539A CN201310342763.XA CN201310342763A CN104349539A CN 104349539 A CN104349539 A CN 104349539A CN 201310342763 A CN201310342763 A CN 201310342763A CN 104349539 A CN104349539 A CN 104349539A
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Abstract
The invention belongs to the field of constant-current driving and provides a constant-current driving circuit. A current pre-opening technology is adopted in the constant-current driving circuit; parasitic capacitance is provided instantaneously when the circuit is opened, and flows through an electric energy discharging channel of a power switch pipe Q2, so that the voltage of an output current port of the constant-current driving circuit is quickly reduced to be output when load is completely conducted, the load quickly enters a complete conduction state, and the difference value between the effective conduction time of the load and the effective level time of an enable control signal is greatly shortened; when the load is an LED (light-emitting diode), the corresponding brightness deflection between the practical brightness of the load and set value output by an LED display screen controller is reduced, the displaying effect is optimized, and the user experience is improved.
Description
Technical field
The invention belongs to constant current and drive field, particularly relate to a kind of driving LED that is mainly used in luminous and the constant-current drive circuit of the pre-open function of electric current can be realized.
Background technology
Well known, show field at LED, be the fluency that the low gray scale display color authenticity and picture that strengthen LED display are play, except needing high refresh rate, also need the ability possessing high output levels, expressing the display image that color is abundanter.For this reason, require that the luminosity of LED in LED display can not produce deviation when display frame, again because the luminosity of LED is determined by the average current by LED, therefore, the current average requiring the constant-current driven chip of driving LED luminescence to export is identical with the settings that LED display controller exports.
Usually, the output current precision of constant-current driven chip reflects the deviation between current average and the settings that export of LED display controller that constant-current driven chip exports.For the different display brightness of LED display, varied in size by the average current of LED, the picture that LED display controller realizes LED display by the duty ratio of the pulse width modulating signal arranging constant-current driven chip and export to LED is play.That is to say, in each LED display display cycle T, the current lead-through time t1 that LED display controller arranges LED is different, and the ratio of current lead-through time t1 and display cycle T is called current duty cycle D, and has:
if then the settings of the output current of constant-current driven chip are i
d, by the average current i of LED
avemeet: i
ave=i
d* D.
Due to the existence of duty ratio D, there is electric current opening time and electric current shut-in time in the electric current that constant-current driven chip is exported.In order to the deviation between the brightness that the intrinsic brilliance reducing LED is corresponding with the settings that LED display controller exports as far as possible, require this electric current opening time and the electric current shut-in time as far as possible little, and the refresh rate of LED display is higher, require the electric current opening time and the electric current shut-in time less, be generally tens of ns rank.
But in the prior art, the output current port of constant-current driven chip exists parasitic capacitance, and the parasitic capacitance value of the output current port of different constant-current driven chip is different.Fig. 1 shows a kind of typical structure of the constant-current driven chip that prior art provides, and wherein D1 represents load LED, and CL wherein represents the parasitic capacitance of output current port.This constant-current driven chip comprises enable port EN and output current port OUT, and the constant current driving unit of constant-current driven chip inside connects enable port EN and output current port OUT.Wherein, enable control signal EN is exported by LED display controller, in order to whether to control the unlatching of output current port OUT.
The operation principle of the constant-current driven chip shown in Fig. 1 is: within the opening time of output current port OUT, by the electric current of load D1 via constant current driving unit to ground, if now the voltage of output current port OUT is V
oUT1, the conduction voltage drop of load D1 is V
lED1, then have:
V
OUT1＝VDD-V
LED1
Within the shut-in time of output current port OUT, the voltage of output current port OUT is increased to V gradually
oUT2, load D1 closes gradually, if the cut-off pressure drop of load D1 is V
lED2, then have:
V
OUT2＝VDD-V
LED2
Again because the conduction voltage drop of load D1 is V
lED1be greater than cut-off pressure drop V
lED2, therefore have: V
oUT1< V
oUT2.For the load LED of PN junction structure, its On current I
lEDwith two ends pressure drop V
lEDbetween meet:
Wherein, I
sbeing PN junction reverse saturation current, is constant at a constant temperature; N is emission ratio, relevant with material to the size of PN junction, and its value is between 1 ~ 2; V
t=k*T/q, wherein k is Boltzmann constant, and T is thermodynamic temperature, and q is electronic charge; I-V relation curve corresponding to this formula as shown in Figure 2, V wherein
trepresent the LED two ends pressure drop of current lead-through moment.
With reference to known shown in above-mentioned formula and Fig. 2, the magnitude of voltage of the output current port OUT of constant-current driven chip is at V
oUT1to V
oUT2between time, the On current of load D1 is very little, and when the magnitude of voltage of output current port OUT is reduced to V
oUT1time turn on current value increase very soon.
Due to the existence of the parasitic capacitance CL of output current port in existing constant-current driven chip, when the output current port OUT that enable control signal EN arranges constant-current driven chip opens, the magnitude of voltage of output current port OUT declines, load D1 starts conducting, parasitic capacitance CL starts to discharge to output current port OUT, until the magnitude of voltage of output current port OUT drops to V
oUT1, the complete conducting of load D1.The capacitance of parasitic capacitance CL is larger, and the magnitude of voltage of output current port OUT declines slower, and the On current of load D1 increases slower, i.e. the electric current opening time t of load D1
riselonger, and the settings of LED display controller are less, output current port OUT is longer for the discharge time of parasitic capacitance CL in opening process, electric current opening time t
risealso longer.So just the electric current opening time t of load D1 is easily caused
risebe greater than the electric current shut-in time t of load D1
fall, make effective pulse width time of the electric current by load D1 less than normal than the settings of enable control signal EN, and then brightness corresponding to the settings that the intrinsic brilliance of LED is exported than LED display controller is partially dark, display effect is not good, and user experience is poor.
Summary of the invention
The object of the embodiment of the present invention is to provide a kind of constant-current drive circuit, be intended to solve in the existing constant-current driven chip for driving LED luminescence, due to the existence of the parasitic capacitance of output current port, the brightness making the intrinsic brilliance of LED more corresponding than settings is partially dark, the problem that display effect is not good.
The embodiment of the present invention is achieved in that a kind of constant-current drive circuit, and described constant-current drive circuit comprises power switch pipe Q1 and power switch pipe Q2, and described constant-current drive circuit also comprises:
Constant current driving unit, the output of described constant current driving unit as described constant-current drive circuit output current port and connect the drive end of load, the output of described constant current driving unit connects the high-end of described power switch pipe Q2, for driving described load conduction in the enable control signal valid period;
Current setting unit, the low side for arranging described power switch pipe Q1 flows into the variable reference current of described current setting unit;
Current detecting unit, for detecting described reference current in the described enable control signal valid period, and controls described power switch pipe Q2 conducting according to testing result;
Voltage detection unit, for detecting the magnitude of voltage of output current port in the described enable control signal valid period, and when the magnitude of voltage of described output current port is reduced to described load complete conducting during the voltage of described output current port, controls described power switch pipe Q2 and end.
The constant-current drive circuit that the present invention proposes adopts the pre-opening technology of electric current, parasitic capacitance is provided to release path via the electric energy of power switch pipe Q2 in the moment that circuit is opened, the voltage of output current port when being dropped rapidly to the complete conducting of load with the voltage of the output current port making constant-current drive circuit, and then make load enter rapidly complete conducting state, thus the difference greatly shortened between the effective ON time of load and enable control signal significant level time, when load is LED, reduce the deviation of the load intrinsic brilliance brightness corresponding with the settings that LED display controller exports, optimize display effect, improve user experience.
Accompanying drawing explanation
Fig. 1 is a kind of exemplary block diagram of the constant-current driven chip that prior art provides;
Fig. 2 is in prior art, the I-V graph of relation of LED;
Fig. 3 is the circuit theory diagrams of the constant-current drive circuit that the embodiment of the present invention one provides;
Fig. 4 is the circuit theory diagrams of the constant-current drive circuit that the embodiment of the present invention two provides;
Fig. 5 is the circuit diagram of Fig. 4.
Embodiment
In order to make object of the present invention, technical scheme and advantage clearly understand, below in conjunction with drawings and Examples, the present invention is further elaborated.Should be appreciated that specific embodiment described herein only in order to explain the present invention, be not intended to limit the present invention.
For prior art Problems existing, the constant-current drive circuit that the present invention proposes adopts the pre-opening technology of electric current, the electric energy of parasitic capacitance is provided to release path in the moment that circuit is opened, the voltage V of output current port when being dropped rapidly to the complete conducting of load with the voltage of the output current port making constant-current drive circuit
oUT1, and then make load enter rapidly complete conducting state.Implementation of the present invention is described in detail below in conjunction with embodiment:
embodiment one
The embodiment of the present invention one proposes a kind of constant-current drive circuit, as shown in Figure 2, for convenience of explanation, illustrate only the part relevant to the embodiment of the present invention one.
Specifically, the constant-current drive circuit that the embodiment of the present invention one proposes comprises power switch pipe Q1 and power switch pipe Q2, the drive end of high-end connection direct current VDD, the power switch pipe Q1 of power switch pipe Q1 connects the low side of power switch pipe Q1, the low side ground connection of power switch pipe Q2; This constant-current drive circuit also comprises: constant current driving unit 14, the input of constant current driving unit 14 connects enable control signal EN, the output OUT of constant current driving unit 14 as constant-current drive circuit output current port and connect the drive end of load, the output OUT of constant current driving unit 14 connects the high-end of power switch pipe Q2 simultaneously, for driving load conduction in the enable control signal EN valid period, and stop driving load between enable control signal EN dynamic stage; Current setting unit 11, the output of current setting unit 11 connects the low side of power switch pipe Q1, for arranging the variable reference current I of the low side inflow current setting unit 11 of power switch pipe Q1
rEF1; Current detecting unit 12, the first input end of current detecting unit 12 connects the drive end of power switch pipe Q1, second input of current detecting unit 12 connects enable control signal EN, the output of current detecting unit 12 connects the drive end of power switch pipe Q2, for detecting reference current in the enable control signal EN valid period, and control power switch pipe Q2 conducting according to testing result; Voltage detection unit 13, the first input end of voltage detection unit 13 connects enable control signal EN, second input of voltage detection unit 13 connects the output OUT of constant current driving unit 14, the output of voltage detection unit 13 connects the drive end of power switch pipe Q2, for detecting the magnitude of voltage of output current port in the enable control signal EN valid period, and when the magnitude of voltage of output current port is reduced to load complete conducting the voltage V of output current port
oUT1time, control power switch pipe Q2 cut-off.
Preferably, in the embodiment of the present invention one, power switch pipe Q1 is high-end as power switch pipe Q1 of the source electrode of the metal-oxide-semiconductor Q1 of P type, metal-oxide-semiconductor Q1, the drain electrode of metal-oxide-semiconductor Q1 is as the low side of power switch pipe Q1, and the grid of metal-oxide-semiconductor Q1 is as the drive end of power switch pipe Q1; Power switch pipe Q2 is the low side of source electrode as power switch pipe Q2 of the metal-oxide-semiconductor Q2 of N-type, metal-oxide-semiconductor Q2, high-end as power switch pipe Q2 of the drain electrode of metal-oxide-semiconductor Q2, and the grid of metal-oxide-semiconductor Q2 is as the drive end of power switch pipe Q2.
In the embodiment of the present invention one, current setting unit 11 also further according to the reference current size detected, can control the On current size of power switch pipe Q2, to realize the control of time of releasing to the electric energy of output current port parasitic capacitance CL.
Take load as LED be example, the course of work of the above-mentioned constant-current drive circuit that the embodiment of the present invention one proposes is: in enable control signal EN invalid (such as EN=1) period, voltage detection unit 13 does not work, the level of the output of voltage detection unit 13 is 0, constant current driving unit 14 no-output, the magnitude of voltage of output current port is V
oUT2.Afterwards, when enable control signal EN effective (such as EN=0), constant current driving unit 14 is progressively opened, its output current Iout increases gradually by zero: instantaneous what open, the output of voltage detection unit 13 exports zero level, current setting unit 11 detects reference current, and exports high level to make power switch pipe Q2 conducting, because the magnitude of voltage of now output current port still equals V according to testing result to the grid of power switch pipe Q2
oUT2, load is still in closed condition, and parasitic capacitance CL is discharged over the ground by power switch pipe Q2, and constant current driving unit 14 is in opening, and the electric current I out of output current port is zero; In one end time afterwards, that discharges over the ground along with parasitic capacitance CL continues, the voltage of output current port starts to decline, and the electric current I out of output current port increases gradually, but the voltage V of output current port when the magnitude of voltage of output current port is still greater than load complete conducting
oUT1; The voltage V of output current port when the magnitude of voltage of output current port is reduced to load complete conducting
oUT1time, the output of voltage detection unit 13 exports high level and controls power switch pipe Q2 and end, thus does not affect the On current of load, moment is ended at power switch pipe Q2, load is in critical conduction mode, and the electric current I out of output current port continues to increase, the voltage V of output current port
oUT1after continuing decline, the rapid conducting of load, load current equals the electric current I out of output current port.
As can be seen here, the constant-current drive circuit proposed due to the embodiment of the present invention one adopts the pre-opening technology of electric current, parasitic capacitance CL is provided to release path via the electric energy of power switch pipe Q2 in the moment that circuit is opened, the voltage V of output current port when being dropped rapidly to the complete conducting of load with the voltage of the output current port making constant-current drive circuit
oUT1and then make load enter rapidly complete conducting state, thus the difference greatly shortened between the effective ON time of load and enable control signal EN significant level time, when load is LED, reduce the deviation of the load intrinsic brilliance brightness corresponding with the settings that LED display controller exports, optimize display effect, improve user experience.
embodiment two
The embodiment of the present invention two proposes a kind of constant-current drive circuit, as shown in Figure 4, for convenience of explanation, illustrate only the part relevant to the embodiment of the present invention two.
In order to reduce the power consumption of this constant-current drive circuit, after being desirably in the complete conducting of load, current detecting unit 12 is closed, for this reason, different from embodiment one, the constant-current drive circuit that embodiment two provides also can comprise: time-delay closing unit 15, second input of current detecting unit 12 connects enable control signal EN by time-delay closing unit 15, the input of time-delay closing unit 15 connects enable control signal EN, the output of time-delay closing unit 15 connects the second input of current detecting unit 12, for in the enable control signal EN valid period, the voltage V of output current port when the magnitude of voltage of output current port is reduced to load complete conducting
oUT1after, control current detecting unit 12 time-delay closing.
Relative to embodiment one, the constant-current drive circuit that the embodiment of the present invention two proposes after the complete conducting of load, can reduce the power consumption of this constant-current drive circuit by time-delay closing current detecting unit 12.Although close in the pass of current detecting unit 12, power switch pipe Q2 is closed, owing to being the voltage V of the output current port when the magnitude of voltage of output current port is reduced to load complete conducting
oUT1rear time-delay closing, thus the ON time that ensure that power switch pipe Q2 only by the magnitude of voltage of output current port by V
oUT2be reduced to V
oUT1time dependent, ensure that the reliability that the electric energy of power switch pipe Q2 to parasitic capacitance CL is released.
Fig. 5 shows the circuit of Fig. 4.
Particularly, time-delay closing unit 15 can comprise: the metal-oxide-semiconductor Q3 of bias current sources A1, inverter U1, NAND gate U3, Schmidt trigger U2, N-type and electric capacity C1.Wherein, the drain electrode of metal-oxide-semiconductor Q3 connects direct current VDD by bias current sources A1, the source ground of metal-oxide-semiconductor Q3, the grid of metal-oxide-semiconductor Q3 as time-delay closing unit 15 input and connect enable control signal EN, electric capacity C1 is connected in parallel between the source electrode of metal-oxide-semiconductor Q3 and drain electrode; The drain electrode of metal-oxide-semiconductor Q3 connects the input of Schmidt trigger U2 simultaneously, the grid of metal-oxide-semiconductor Q3 connects the input of inverter U1 simultaneously, the output of Schmidt trigger U2 connects the first input end of NAND gate U3, the output of inverter U1 connects second input of NAND gate U3, the output of NAND gate U3 as time-delay closing unit 15 output and connect the second input of current detecting unit 12.
Particularly, current detecting unit 12 can comprise: the metal-oxide-semiconductor Q7 of metal-oxide-semiconductor Q3, P type of P type, the metal-oxide-semiconductor Q4 of N-type, the metal-oxide-semiconductor Q5 of N-type, the metal-oxide-semiconductor Q6 of N-type, bias current sources A2.Wherein, source electrode, the source electrode of metal-oxide-semiconductor Q5, the source grounding of metal-oxide-semiconductor Q6 of metal-oxide-semiconductor Q4; The grid of metal-oxide-semiconductor Q4 connects the grid of metal-oxide-semiconductor Q5 and the drain electrode of metal-oxide-semiconductor Q4, and the drain electrode of metal-oxide-semiconductor Q6 connects the drain electrode of metal-oxide-semiconductor Q5 and the grid of metal-oxide-semiconductor Q6, the grid of metal-oxide-semiconductor Q6 as current detecting unit 12 output and connect the drive end of power switch pipe Q2; The drain electrode of metal-oxide-semiconductor Q4 connects the drain electrode of metal-oxide-semiconductor Q3 simultaneously, and the source electrode of metal-oxide-semiconductor Q3 connects direct current VDD, the grid of metal-oxide-semiconductor Q3 as current detecting unit 12 first input end and connect the drive end of power switch pipe Q1; The drain electrode of metal-oxide-semiconductor Q6 connects the drain electrode of metal-oxide-semiconductor Q7, and the source electrode of metal-oxide-semiconductor Q7 connects direct current VDD by bias current sources A2, the grid of metal-oxide-semiconductor Q7 as current detecting unit 12 the second input and connect the output of time-delay closing unit 15.
Particularly, voltage detection unit 13 can comprise: for generating and exporting the first reference voltage V
rEF1with the second reference voltage V
rEF2reference voltage generation module 131, comparator U5, inverter U4, the metal-oxide-semiconductor Q8 of N-type, the metal-oxide-semiconductor Q9 of N-type and N-type metal-oxide-semiconductor Q10.Wherein, the in-phase end+source electrode of connection metal-oxide-semiconductor Q9 of comparator U5 and the source electrode of metal-oxide-semiconductor Q10, the drain electrode of metal-oxide-semiconductor Q9 connects the first reference voltage V
rEF1, the drain electrode of metal-oxide-semiconductor Q10 connects the second reference voltage V
rEF2, and the first reference voltage V
rEF1be less than the second reference voltage V
rEF2; The output of comparator U5 connects the input of inverter U4, and the output of inverter U4 connects the grid of metal-oxide-semiconductor Q9, and the output of comparator U5 connects the grid of metal-oxide-semiconductor Q8 and the grid of metal-oxide-semiconductor Q10 simultaneously; The end of oppisite phase of comparator U5-as voltage detection unit 13 the second input and connect the output OUT of constant current driving unit 14, the earth terminal of comparator U5 as voltage detection unit 13 first input end and connect enable control signal EN; The source ground of metal-oxide-semiconductor Q8, the drain electrode of metal-oxide-semiconductor Q8 as voltage detection unit 13 output and connect the drive end of power switch pipe Q2.
To the operation principle of circuit shown in Fig. 5 be described in detail below:
At enable control signal EN=1, namely between enable control signal EN dynamic stage, constant current driving unit 14 is closed, and the electric current I out of output current port equals zero; Comparator U5 in voltage detection unit 13 does not work, comparator U5 output low level, in-phase end+selection input first reference voltage V of comparator U5
rEF1, and V
rEF1=VDD-V
lED1; In time-delay closing unit 15, metal-oxide-semiconductor Q3 conducting, pull-down bias electric current I
bias1, electric capacity C1 two ends pressure drop is zero, inverter U1 output low level, and NAND gate U3 exports high level; In current detecting unit 12, metal-oxide-semiconductor Q7 closes, the drain current I of metal-oxide-semiconductor Q5
rEF2be zero, the grid voltage to zero of the drop-down metal-oxide-semiconductor Q6 of metal-oxide-semiconductor Q5, makes the grid voltage of metal-oxide-semiconductor Q2 be zero to close, and now, power vd D is by load to parasitic capacitance CL charging, and the voltage of output current port OUT meets: V
oUT2=VDD-V
lED2, due to conduction voltage drop V
lED1be greater than cut-off pressure drop V
lED2, therefore V
oUT2> V
rEF1.
Afterwards, as enable control signal EN=0, namely enable control signal EN significant level comes interim, and constant current driving unit 14 is progressively opened, and the electric current of output current port progressively increases by zero, in voltage detection unit 13, due to V
oUT2> V
rEF1, therefore comparator U5 output low level, metal-oxide-semiconductor Q8 closes; In time-delay closing unit 15, metal-oxide-semiconductor Q3 ends, bias current I
bias1start to charge to electric capacity C1, in the trailing edge moment of enable control signal EN, electric capacity C1 both end voltage is zero, and Schmidt trigger U2 exports high level, and inverter U1 exports high level, NAND gate U3 output low level; In current detecting unit 12, metal-oxide-semiconductor Q7 conducting, the drain current I of metal-oxide-semiconductor Q5
rEF2non-vanishing, metal-oxide-semiconductor Q5 conducting, and when the bias current of bias current sources A2 is I
bIAS2, the On current of metal-oxide-semiconductor Q6 is I
mN6time, meet: I
mN6=I
bIAS2-I
rEF2; Meanwhile, metal-oxide-semiconductor Q2 conducting, because the voltage of output current port equals V in the enable control signal EN trailing edge moment
oUT2load is still in closed condition, and the parasitic capacitance CL of output current port OUT is discharged over the ground by metal-oxide-semiconductor Q2, and constant current driving unit 14 is in opening, the electric current I out of output current port OUT is zero, the parasitic capacitance CL electric current I flowing into output current port OUT
cLbe the On current of metal-oxide-semiconductor Q2; Afterwards, along with the carrying out of parasitic capacitance CL electric discharge, the voltage of output current port OUT starts to decline, and the electric current I out of output current port OUT progressively increases, in the process, and Iout < I
cL, parasitic capacitance CL is still discharged by metal-oxide-semiconductor Q2, the On current I of metal-oxide-semiconductor Q2
mN2decline gradually, and meet: I
mN2=I
cL-Iout; By above-mentioned formula I
mN6=I
bIAS2-I
rEF2visible, the drain current I of metal-oxide-semiconductor Q5
rEF2less, i.e. the reference current I of current setting unit 11 setting
rEF1more hour, the On current I of metal-oxide-semiconductor Q6
mN6larger, the On current I of metal-oxide-semiconductor Q2
mN2larger.
Afterwards, the voltage V of output current port when the magnitude of voltage of output current port is reduced to load complete conducting
oUT1(i.e. V
rEF1) time, in voltage detection unit 13, the output of comparator U5 is inverted to high level, and in order to prevent the voltage disturbance of output current port from causing the output voltage of comparator U5 to vibrate, now the in-phase end+switch to selection second reference voltage V of comparator U5
rEF2; Meanwhile, metal-oxide-semiconductor Q8 opens, and then the grid voltage of metal-oxide-semiconductor Q2 is pulled down to zero, and metal-oxide-semiconductor Q2 is closed, and the electric current flowing through metal-oxide-semiconductor Q2 is zero.Afterwards, end moment at power switch pipe Q2, load is in critical conduction mode, and the electric current I out of output current port continues to increase, the voltage V of output current port
oUT1after continuing decline, the rapid conducting of load, load current equals the electric current I out of output current port.
The charging and discharging currents supposing the voltage variety at parasitic capacitance CL two ends to be the capacitance of Δ U, parasitic capacitance CL be C, parasitic capacitance CL is I, then can obtain the discharge and recharge time t of parasitic capacitance CL by metal-oxide-semiconductor Q2 according to capacitor charge and discharge Time Calculation formula
fmeet:
as can be seen from this formula, arrive moment in the low level of enable control signal EN, the On current I of metal-oxide-semiconductor Q2
mN2determine t discharge time of parasitic capacitance CL
f, and discharge time t
fshorter, represent that the time delay of the trailing edge of load opening time relatively enable control signal EN is shorter, and the rise time of the On current of load is shorter, difference between the effective ON time of load and enable control signal EN significant level time is less, and the deviation of the brightness making load intrinsic brilliance corresponding with the settings that LED display controller exports is less.
Afterwards, when in time-delay closing unit 15, after the voltage of electric capacity C1 is increased to the trigging signal of Schmidt trigger U2, Schmidt trigger U2 output low level, the output redirect of NAND gate U3 is high level, thus makes metal-oxide-semiconductor Q7 time-delay closing.Suppose that the time of metal-oxide-semiconductor Q7 time-delay closing is t_delay1, by arranging pull-down bias electric current I
bias1value and/or the capacitance of electric capacity C1, adjustment t_delay1, to meet t_delay1 > t
f, thus while reduction chip power-consumption, the ON time that also assures that power switch pipe Q2 only by the magnitude of voltage of output current port by V
oUT2be reduced to V
oUT1time dependent.
In sum, the constant-current drive circuit that the present invention proposes adopts the pre-opening technology of electric current, parasitic capacitance CL is provided to release path via the electric energy of power switch pipe Q2 in the moment that circuit is opened, the voltage V of output current port when being dropped rapidly to the complete conducting of load with the voltage of the output current port making constant-current drive circuit
oUT1and then make load enter rapidly complete conducting state, thus the difference greatly shortened between the effective ON time of load and enable control signal EN significant level time, when load is LED, reduce the deviation of the load intrinsic brilliance brightness corresponding with the settings that LED display controller exports, optimize display effect, improve user experience.In addition, also can increase time-delay closing unit 15 between current detecting unit 12 and enable control signal EN input, time-delay closing unit 15 can after the complete conducting of load, reduced the power consumption of this constant-current drive circuit by time-delay closing current detecting unit 12, and the ON time of guaranteed output switching tube Q2 only by the magnitude of voltage of output current port by V
oUT2be reduced to V
oUT1time dependent, ensure that the reliability that the electric energy of power switch pipe Q2 to parasitic capacitance CL is released.
The foregoing is only preferred embodiment of the present invention, not in order to limit the present invention, all any amendments done within the spirit and principles in the present invention, equivalent replacement and improvement etc., all should be included within protection scope of the present invention.
Claims (9)
1. a constant-current drive circuit, is characterized in that, described constant-current drive circuit comprises power switch pipe Q1 and power switch pipe Q2, and described constant-current drive circuit also comprises:
Constant current driving unit, the output of described constant current driving unit as described constant-current drive circuit output current port and connect the drive end of load, the output of described constant current driving unit connects the high-end of described power switch pipe Q2, for driving described load conduction in the enable control signal valid period;
Current setting unit, the low side for arranging described power switch pipe Q1 flows into the variable reference current of described current setting unit;
Current detecting unit, for detecting described reference current in the described enable control signal valid period, and controls described power switch pipe Q2 conducting according to testing result;
Voltage detection unit, for detecting the magnitude of voltage of output current port in the described enable control signal valid period, and when the magnitude of voltage of described output current port is reduced to described load complete conducting during the voltage of described output current port, controls described power switch pipe Q2 and end.
2. constant-current drive circuit as claimed in claim 1, it is characterized in that, the high-end connection direct current of described power switch pipe Q1, the low side of described power switch pipe Q1 connects the output of described current setting unit, the grid of described power switch pipe Q1 connects the low side of described power switch pipe Q1, and the drive end of described power switch pipe Q1 connects the first input end of described current detecting unit;
The low side ground connection of described power switch pipe Q2, the drive end of described power switch pipe Q2 connects the output of described current detecting unit, and the drive end of described power switch pipe Q2 connects the output of described voltage detection unit;
The input of described constant current driving unit connects described enable control signal, second input of described current detecting unit connects described enable control signal, the first input end of described voltage detection unit connects described enable control signal, and the second input of described voltage detection unit connects the output of described constant current driving unit.
3. constant-current drive circuit as claimed in claim 2, it is characterized in that, described power switch pipe Q1 is the metal-oxide-semiconductor of P type, high-end as described power switch pipe Q1 of the source electrode of described metal-oxide-semiconductor Q1, the drain electrode of described metal-oxide-semiconductor Q1 is as the low side of described power switch pipe Q1, and the grid of described metal-oxide-semiconductor Q1 is as the drive end of described power switch pipe Q1.
4. constant-current drive circuit as claimed in claim 2, it is characterized in that, described power switch pipe Q2 is the metal-oxide-semiconductor of N-type, the source electrode of described metal-oxide-semiconductor Q2 is as the low side of described power switch pipe Q2, high-end as described power switch pipe Q2 of the drain electrode of described metal-oxide-semiconductor Q2, the grid of described metal-oxide-semiconductor Q2 is as the drive end of described power switch pipe Q2.
5. the constant-current drive circuit as described in any one of Claims 1-4, is characterized in that, described load is light-emitting diode.
6. the constant-current drive circuit as described in any one of Claims 1-4, is characterized in that, described constant-current drive circuit also comprises:
Time-delay closing unit, in the described enable control signal valid period, when the magnitude of voltage of described output current port is reduced to the complete conducting of described load described output current port voltage after, control described current detecting unit time-delay closing.
7. constant-current drive circuit as claimed in claim 6, it is characterized in that, described time-delay closing unit comprises: the metal-oxide-semiconductor Q3 of bias current sources A1, inverter U1, NAND gate U3, Schmidt trigger U2, N-type and electric capacity C1;
The drain electrode of described metal-oxide-semiconductor Q3 connects direct current by described bias current sources, the source ground of described metal-oxide-semiconductor Q3, the grid of described metal-oxide-semiconductor Q3 as described time-delay closing unit input and connect described enable control signal, described electric capacity C1 is connected in parallel between the source electrode of described metal-oxide-semiconductor Q3 and drain electrode, the drain electrode of described metal-oxide-semiconductor Q3 connects the input of described Schmidt trigger U2 simultaneously, the grid of described metal-oxide-semiconductor Q3 connects the input of described inverter U1 simultaneously, the output of described Schmidt trigger U2 connects the first input end of described NAND gate U3, the output of described inverter U1 connects second input of described NAND gate U3, the output of described NAND gate U3 as described time-delay closing unit output and connect described current detecting unit.
8. constant-current drive circuit as claimed in claim 6, it is characterized in that, described current detecting unit comprises: the metal-oxide-semiconductor Q7 of metal-oxide-semiconductor Q3, P type of P type, the metal-oxide-semiconductor Q4 of N-type, the metal-oxide-semiconductor Q5 of N-type, the metal-oxide-semiconductor Q6 of N-type, bias current sources A2;
The source electrode of described metal-oxide-semiconductor Q4, the source electrode of described metal-oxide-semiconductor Q5, the source grounding of described metal-oxide-semiconductor Q6, the grid of described metal-oxide-semiconductor Q4 connects the grid of described metal-oxide-semiconductor Q5 and the drain electrode of described metal-oxide-semiconductor Q4, the drain electrode of described metal-oxide-semiconductor Q6 connects the drain electrode of described metal-oxide-semiconductor Q5 and the grid of described metal-oxide-semiconductor Q6, the grid of described metal-oxide-semiconductor Q6 as described current detecting unit output and connect the drive end of described power switch pipe Q2, the drain electrode of described metal-oxide-semiconductor Q4 connects the drain electrode of described metal-oxide-semiconductor Q3 simultaneously, the source electrode of described metal-oxide-semiconductor Q3 connects direct current, the grid of described metal-oxide-semiconductor Q3 as described current detecting unit first input end and connect the drive end of described power switch pipe Q1, the drain electrode of described metal-oxide-semiconductor Q6 connects the drain electrode of described metal-oxide-semiconductor Q7, the source electrode of described metal-oxide-semiconductor Q7 connects direct current by described bias current sources, the grid of described metal-oxide-semiconductor Q7 as described current detecting unit the second input and connect described time-delay closing unit.
9. constant-current drive circuit as claimed in claim 6, it is characterized in that, described voltage detection unit comprises: for generating and exporting the metal-oxide-semiconductor Q10 of the reference voltage generation module of the first reference voltage and the second reference voltage, comparator U5, inverter U4, the metal-oxide-semiconductor Q8 of N-type, the metal-oxide-semiconductor Q9 of N-type and N-type;
The in-phase end of described comparator U5 connects the source electrode of described metal-oxide-semiconductor Q9 and the source electrode of described metal-oxide-semiconductor Q10, the drain electrode of described metal-oxide-semiconductor Q9 connects described first reference voltage, the drain electrode of described metal-oxide-semiconductor Q10 connects described second reference voltage, and described first reference voltage is less than described second reference voltage, the output of described comparator U5 connects the input of described inverter U4, the output of described inverter U4 connects the grid of described metal-oxide-semiconductor Q9, the output of described comparator U5 connects the grid of described metal-oxide-semiconductor Q8 and the grid of described metal-oxide-semiconductor Q10 simultaneously, the end of oppisite phase of described comparator U5 as described voltage detection unit the second input and connect described constant current driving unit, the earth terminal of described comparator U5 as described voltage detection unit first input end and connect described enable control signal, the source ground of described metal-oxide-semiconductor Q8, the drain electrode of described metal-oxide-semiconductor Q8 as described voltage detection unit output and connect the drive end of described power switch pipe Q2.
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