CN203387742U - Constant current drive device - Google Patents
Constant current drive device Download PDFInfo
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- CN203387742U CN203387742U CN201320482188.9U CN201320482188U CN203387742U CN 203387742 U CN203387742 U CN 203387742U CN 201320482188 U CN201320482188 U CN 201320482188U CN 203387742 U CN203387742 U CN 203387742U
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Abstract
The utility model belongs to the constant current driving field and provides a constant current drive device. The current preopening technology is utilized in the constant current drive device. The moment a circuit is turned on, a stray capacitance is provided and through an electric energy discharge closed circuit of a power switch tube Q2, so that a voltage at the current output port of the constant current drive device is dropped rapidly to a voltage at the current output port when a load is fully on, the load rapidly goes into a fully on state, the different between effective turning-on time of the load and active level time of an enable control signal is greatly reduced. When the load is an LED, difference between the actual brightness of the load and brightness corresponding to the set value output by an LED screen controller is reduced, display effect is optimized, and user experience is improved.
Description
Technical field
The utility model belongs to constant current and drives field, relates in particular to a kind of driving LED that is mainly used in luminous and can realize the constant current driving device of the pre-open function of electric current.
Background technology
Known ground, show field at LED, and the fluency for low gray scale display color authenticity and the picture of enhancing LED display are play, except needing high refresh rate, also need to possess the ability of high output levels, expresses the abundanter demonstration image of color.For this reason, require the luminosity of LED in LED display can not produce deviation when display frame, luminosity due to LED is to be determined by the average current by LED again, therefore, require the current average of the luminous constant-current driven chip output of driving LED identical with the settings of LED display controller output.
Usually, the deviation between the settings that the current average that the output current precision of constant-current driven chip has reflected constant-current driven chip output and LED display controller are exported.For the different display brightness of LED display, the average current by LED varies in size, and the LED display controller recently realizes that to the duty of the pulse width modulating signal of LED output the picture of LED display plays by constant-current driven chip is set.That is to say, in each LED display display cycle T, the LED display controller arranges the current lead-through time t1 difference of LED, and the ratio of current lead-through time t1 and display cycle T is called electric current duty ratio D, and has:
if 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, make the electric current of constant-current driven chip output have electric current opening time and electric current shut-in time.For the deviation between the intrinsic brilliance that the reduces LED brightness corresponding with the settings of LED display controller output as far as possible, require this electric current opening time and electric current shut-in time as far as possible little, and the refresh rate of LED display is higher, require electric current opening time and electric current shut-in time less, be generally tens of ns ranks.
Yet in the prior art, there is parasitic capacitance in the output current port of constant-current driven chip, and the parasitic capacitance value difference of the output current port of different constant-current driven chips.Fig. 1 shows a kind of typical structure of the constant-current driven chip that prior art provides, and wherein D1 means load LED, and CL wherein means 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 by LED display controller output, in order to the unlatching of controlling output current port OUT whether.
The operation principle of the constant-current driven chip shown in Fig. 1 is: within the opening time of output current port OUT, the electric current by 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, 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, have:
V
OUT2＝VDD-V
LED2
Conduction voltage drop due to load D1 is V again
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
sbe the PN junction reverse saturation current, be constant under constant temperature; N is emission ratio, relevant to size and the material of PN junction, and it is worth 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
tmean the current lead-through LED two ends pressure drop of 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 the time, the On current of load D1 is very little, and is reduced to V when the magnitude of voltage of output current port OUT
oUT1the time electric conduction flow valuve increase very soon.
Existence due to the parasitic capacitance CL of output current port in existing constant-current driven chip, when the output current port OUT that enables control signal EN and arrange constant-current driven chip opens, the magnitude of voltage of output current port OUT descends, load D1 starts conducting, parasitic capacitance CL starts the electric 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 appearance value of parasitic capacitance CL is larger, and the magnitude of voltage of output current port OUT descends 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, and the discharge time of output current port OUT parasitic capacitance CL in opening process is longer, electric current opening time t
risealso longer.So just the electric current opening time t that easily causes load D1
risebe greater than the electric current shut-in time t of load D1
fall, making effective pulsewidth time of the electric current by load D1 less than normal than the settings that enable control signal EN, and then make the brightness more corresponding than the settings of LED display controller output of the intrinsic brilliance of LED partially dark, display effect is not good, and user experience is poor.
The utility model content
The purpose of the utility model embodiment is to provide a kind of constant current driving device, be intended to solve the existing constant-current driven chip luminous for driving LED, existence due to the parasitic capacitance of output current port, make the brightness more corresponding than settings of the intrinsic brilliance of LED partially dark, the problem that display effect is not good.
The utility model embodiment realizes like this, a kind of constant current driving device, described constant current driving device comprises power switch pipe Q1 and power switch pipe Q2, the high-end connection direct current of described power switch pipe Q1, the drive end of described power switch pipe Q1 connects the low side of described power switch pipe Q1, the low side ground connection of described power switch pipe Q2, described constant current driving device also comprises:
Input connects the described control signal that enables, output is as the output current port of described constant current driving device and connect the drive end of load, described output connects the high-end of described power switch pipe Q2 simultaneously, described, enable the control signal valid period and drives the constant current driving unit of described load conducting;
Output connects the low side of described power switch pipe Q1, and the low side that described power switch pipe Q1 is set flows into the electric current setting unit of the variable reference current of described electric current setting unit;
First input end connects the drive end of described power switch pipe Q1, the second input connects the described control signal that enables, output connects the drive end of described power switch pipe Q2, described, enables the current detecting unit that the control signal valid period detects described reference current and control described power switch pipe Q2 conducting according to testing result;
First input end connects the described control signal that enables, the second input connects the output of described constant current driving unit, output connects the drive end of described power switch pipe Q2, described, enable that the control signal valid period is detected the magnitude of voltage of described output current port and control the voltage detection unit that described power switch pipe Q2 ends during the voltage of described output current port when the magnitude of voltage of described output current port is reduced to the complete conducting of described load.
Wherein, described power switch pipe Q1 can be the metal-oxide-semiconductor of P type, the source electrode of described metal-oxide-semiconductor Q1 is high-end as described power switch pipe Q1's, and 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.
Wherein, described power switch pipe Q2 can be 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, and the drain electrode of described metal-oxide-semiconductor Q2 is high-end as described power switch pipe Q2's, and the grid of described metal-oxide-semiconductor Q2 is as the drive end of described power switch pipe Q2.
In above-mentioned constant current driving device, described load can be light-emitting diode.
Above-mentioned constant current driving device also can comprise:
Input connects the described control signal that enables, output connects the second input of described current detecting unit, in the described time-delay closing unit that enables the control signal valid period and control described current detecting unit time-delay closing after the voltage of described output current port when the magnitude of voltage of described output current port is reduced to the complete conducting of described load, the second input of described current detecting unit connects the described control signal that enables by described time-delay closing unit.
Now, described time-delay closing unit can comprise: the metal-oxide-semiconductor Q3 of bias current sources A1, inverter U1, NAND gate U3, Schmidt trigger U2, N-type and capacitor C 1;
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 is as the input of described time-delay closing unit and connect the described control signal that enables, described capacitor C 1 is connected in parallel between the source electrode and drain electrode of described metal-oxide-semiconductor Q3, 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 the second input of described NAND gate U3, the output of described NAND gate U3 is as the output of described time-delay closing unit and connect described current detecting unit.
Now, described current detecting unit can comprise: the metal-oxide-semiconductor Q4 of the metal-oxide-semiconductor Q3 of P type, the metal-oxide-semiconductor Q7 of P type, N-type, the metal-oxide-semiconductor Q5 of N-type, metal-oxide-semiconductor Q6, the bias current sources A2 of N-type;
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 drain electrode of grid and the described metal-oxide-semiconductor Q4 of described metal-oxide-semiconductor Q5, 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 is as the output of described current detecting unit 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 is as the first input end of described current detecting unit 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 is as the second input of described current detecting unit and connect described time-delay closing unit.
Now, described voltage detection unit can comprise: for reference voltage generation module, comparator U5, inverter U4, the metal-oxide-semiconductor Q8 of N-type, the metal-oxide-semiconductor Q9 of N-type and the metal-oxide-semiconductor Q10 of N-type that generates and export the first reference voltage and the second reference voltage;
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 the first reference voltage, the drain electrode of described metal-oxide-semiconductor Q10 connects described the second reference voltage, and described the first reference voltage is less than described the 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 is as the second input of described voltage detection unit and connect described constant current driving unit, the earth terminal of described comparator U5 is as the first input end of described voltage detection unit and connect the described control signal that enables, the source ground of described metal-oxide-semiconductor Q8, the drain electrode of described metal-oxide-semiconductor Q8 is as the output of described voltage detection unit and connect the drive end of described power switch pipe Q2.
The constant current driving device the utility model proposes adopts the pre-opening technology of electric current, the moment of opening at circuit provides parasitic capacitance via the electric energy of the power switch pipe Q2 path of releasing, so that the voltage of the voltage of the output current port of constant current driving device output current port while being dropped rapidly to the complete conducting of load, and then make load enter rapidly complete conducting state, thereby greatly shortened the effective ON time of load and enabled the difference between the control signal significant level time, when load is LED, dwindled the deviation of the load intrinsic brilliance brightness corresponding with the settings of LED display controller output, optimized display effect, improved user experience.
The accompanying drawing explanation
Fig. 1 is a kind of exemplary block diagram of the constant-current driven chip that provides of prior art;
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 driving device that provides of the utility model embodiment mono-;
Fig. 4 is the circuit theory diagrams of the constant current driving device that provides of the utility model embodiment bis-;
Fig. 5 is the circuit diagram of Fig. 4.
Embodiment
In order to make the purpose of this utility model, technical scheme and advantage clearer, below in conjunction with drawings and Examples, the utility model is further elaborated.Should be appreciated that specific embodiment described herein is only in order to explain the utility model, and be not used in restriction the utility model.
The problem existed for prior art, the constant current driving device the utility model proposes adopts the pre-opening technology of electric current, the moment of opening at circuit provides the electric energy of the parasitic capacitance path of releasing, so that the voltage V of the voltage of the output current port of constant current driving device output current port while being dropped rapidly to the complete conducting of load
oUT1, and then make load enter rapidly complete conducting state.Describe the utility model implementation in detail below in conjunction with embodiment:
embodiment mono-
The utility model embodiment mono-has proposed a kind of constant current driving device, as shown in Figure 2, for convenience of explanation, only shows the part relevant to the utility model embodiment mono-.
Specifically, the constant current driving device that the utility model embodiment mono-proposes comprises power switch pipe Q1 and power switch pipe Q2, the high-end connection direct current VDD of power switch pipe Q1, the drive end 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 driving device also comprises: constant current driving unit 14, the input connection of constant current driving unit 14 enables control signal EN, the output OUT of constant current driving unit 14 is as the output current port of constant current driving device 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 the load conducting enabling the control signal EN valid period, and stop driving load between dynamic stage enabling control signal EN; Electric current setting unit 11, the output of electric current setting unit 11 connects the low side of power switch pipe Q1, for the variable reference current I of low side inflow current setting unit 11 that power switch pipe Q1 is set
rEF1; Current detecting unit 12, the first input end of current detecting unit 12 connects the drive end of power switch pipe Q1, the second input connection of current detecting unit 12 enables control signal EN, the output of current detecting unit 12 connects the drive end of power switch pipe Q2, for detecting reference current enabling the control signal EN valid period, and according to testing result power ratio control switching tube Q2 conducting; Voltage detection unit 13, the first input end connection of voltage detection unit 13 enables control signal EN, the 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 enabling the control signal EN valid period and detect the magnitude of voltage of output current port, and when the magnitude of voltage of output current port is reduced to the complete conducting of load the voltage V of output current port
oUT1the time, power ratio control switching tube Q2 cut-off.
Preferably, in the utility model embodiment mono-, power switch pipe Q1 is the metal-oxide-semiconductor Q1 of P type, and the source electrode of metal-oxide-semiconductor Q1 is high-end as power switch pipe Q1's, 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 metal-oxide-semiconductor Q2 of N-type, and the source electrode of metal-oxide-semiconductor Q2 is as the low side of power switch pipe Q2, and the drain electrode of metal-oxide-semiconductor Q2 is high-end as power switch pipe Q2's, and the grid of metal-oxide-semiconductor Q2 is as the drive end of power switch pipe Q2.
In the utility model embodiment mono-, electric current setting unit 11 also can be further according to the reference current size detected, the On current size of power ratio control switching tube Q2, to realize the release control of time of 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 driving device that the utility model embodiment mono-proposes is: for example, during enabling control signal EN invalid (EN=1), voltage detection unit 13 is not worked, the level of the output of voltage detection unit 13 is 0, constant current driving unit 14 no-outputs, the magnitude of voltage of output current port is V
oUT2.Afterwards, for example, when enabling control signal EN effective (EN=0), constant current driving unit 14 is progressively opened, its output current Iout increases gradually by zero: instantaneous what open, the output output zero level of voltage detection unit 13, electric current setting unit 11 detects reference currents, and according to testing result to the grid output high level of power switch pipe Q2 so that power switch pipe Q2 conducting, because the magnitude of voltage of output current port now still equals V
oUT2, load is still in closed condition, and parasitic capacitance CL discharges 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; An end is in the time afterwards, along with continuing that parasitic capacitance CL discharges over the ground, the voltage of output current port starts to descend, and the electric current I out of output current port increases gradually, but the voltage V of the magnitude of voltage of output current port output current port while still being greater than the complete conducting of load
oUT1; The voltage V of output current port when the magnitude of voltage of output current port is reduced to the complete conducting of load
oUT1the time, the output of voltage detection unit 13 is exported high level and power ratio control switching tube Q2 cut-off, thereby does not affect the On current of load, 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 to descend, 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 driving device proposed due to the utility model embodiment mono-adopts the pre-opening technology of electric current, the moment of opening at circuit provides parasitic capacitance CL via the electric energy of the power switch pipe Q2 path of releasing, so that the voltage V of the voltage of the output current port of constant current driving device output current port while being dropped rapidly to the complete conducting of load
oUT1and then make load enter rapidly complete conducting state, thereby greatly shortened the effective ON time of load and enabled the difference of control signal EN significant level between the time, when load is LED, dwindled the deviation of the load intrinsic brilliance brightness corresponding with the settings of LED display controller output, optimize display effect, improved user experience.
embodiment bis-
The utility model embodiment bis-has proposed a kind of constant current driving device, as shown in Figure 4, for convenience of explanation, only shows the part relevant to the utility model embodiment bis-.
In order to reduce the power consumption of this constant current driving device, after being desirably in the complete conducting of load, current detecting unit 12 is closed, for this reason, different from embodiment mono-, the constant current driving device that embodiment bis-provides also can comprise: time-delay closing unit 15, the second input of current detecting unit 12 connects and enables control signal EN by time-delay closing unit 15, the input connection of time-delay closing unit 15 enables control signal EN, the output of time-delay closing unit 15 connects the second input of current detecting unit 12, for enabling the control signal EN valid period, the voltage V of output current port when the magnitude of voltage of output current port is reduced to the complete conducting of load
oUT1after, control current detecting unit 12 time-delay closings.
With respect to embodiment mono-, the constant current driving device that the utility model embodiment bis-proposes can, after the complete conducting of load, reduce the power consumption of this constant current driving device by time-delay closing current detecting unit 12.Although closing, the pass of current detecting unit 12 make power switch pipe Q2 close, due to the voltage V that is output current port when the magnitude of voltage of output current port is reduced to the complete conducting of load
oUT1rear time-delay closing, thus the ON time that has guaranteed power switch pipe Q2 only by the magnitude of voltage of output current port by V
oUT2be reduced to V
oUT1time dependent, guaranteed the reliability that power switch pipe Q2 releases to the electric energy of parasitic capacitance CL.
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 capacitor C 1.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 connects and enables control signal EN as the input of time-delay closing unit 15, and capacitor C 1 is connected in parallel between the source electrode and drain electrode of metal-oxide-semiconductor Q3; 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 the second input of NAND gate U3, and the output of NAND gate U3 connects the second input of current detecting unit 12 as the output of time-delay closing unit 15.
Particularly, current detecting unit 12 can comprise: the metal-oxide-semiconductor Q4 of the metal-oxide-semiconductor Q3 of P type, the metal-oxide-semiconductor Q7 of P type, N-type, the metal-oxide-semiconductor Q5 of N-type, metal-oxide-semiconductor Q6, the bias current sources A2 of N-type.Wherein, the source grounding of the source electrode of the source electrode of metal-oxide-semiconductor Q4, metal-oxide-semiconductor Q5, metal-oxide-semiconductor Q6; 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, and the grid of metal-oxide-semiconductor Q6 connects the drive end of power switch pipe Q2 as the output of current detecting unit 12; 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, and the grid of metal-oxide-semiconductor Q3 connects the drive end of power switch pipe Q1 as the first input end of current detecting unit 12; 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, and the grid of metal-oxide-semiconductor Q7 connects the output of time-delay closing unit 15 as the second input of current detecting unit 12.
Particularly, voltage detection unit 13 can comprise: for generating and export 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 the metal-oxide-semiconductor Q10 of N-type.Wherein, the in-phase end of comparator U5+source electrode of connection metal-oxide-semiconductor Q9 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 the second input of voltage detection unit 13 and connect the output OUT of constant current driving unit 14, the earth terminal of comparator U5 is as the first input end of voltage detection unit 13 and connect and enable control signal EN; The source ground of metal-oxide-semiconductor Q8, the drain electrode of metal-oxide-semiconductor Q8 is as the output of voltage detection unit 13 and connect the drive end of power switch pipe Q2.
Below will describe the operation principle of circuit shown in Fig. 5 in detail:
Enabling control signal EN=1, enabling control signal EN between 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, the in-phase end of comparator U5+selection input the first reference voltage V
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, capacitor C 1 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 of the drop-down metal-oxide-semiconductor Q6 of metal-oxide-semiconductor Q5 is to zero, and the grid voltage that makes metal-oxide-semiconductor Q2 is zero closing, 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, so V
oUT2>V
rEF1.
Afterwards, when enabling control signal EN=0, enable control signal EN significant level and come temporarily, 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, so comparator U5 output low level, metal-oxide-semiconductor Q8 closes; In time-delay closing unit 15, metal-oxide-semiconductor Q3 cut-off, bias current I
bias1start capacitor C 1 charging, in the trailing edge moment that enables control signal EN, capacitor C 1 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 be I
bIAS2, the On current of metal-oxide-semiconductor Q6 is I
mN6the time, meet: I
mN6=I
bIAS2-I
rEF2; Simultaneously, metal-oxide-semiconductor Q2 conducting, equal V due to the voltage of output current port constantly enabling control signal EN trailing edge
oUT2load is still in closed condition, and the parasitic capacitance CL of output current port OUT discharges 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, and parasitic capacitance CL flows into the electric current I of 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 descend, and the electric current I out of output current port OUT progressively increases, in this process, and Iout<I
cL, parasitic capacitance CL is still by metal-oxide-semiconductor Q2 electric discharge, the On current I of metal-oxide-semiconductor Q2
mN2descend 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
rEF2the reference current I less, that electric current setting unit 11 arranges
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 the complete conducting of load
oUT1(be V
rEF1) time, in voltage detection unit 13, the output of comparator U5 is inverted to high level, and causes the output voltage vibration of comparator U5 for the voltage disturbance that prevents the output current port, now the in-phase end of comparator U5+switch to and select the second reference voltage V
rEF2; Simultaneously, metal-oxide-semiconductor Q8 opens, and then the grid voltage of metal-oxide-semiconductor Q2 is pulled down to zero, makes metal-oxide-semiconductor Q2 close, and the electric current of the metal-oxide-semiconductor Q2 that flows through is zero.Afterwards, at power switch pipe Q2, end moment, 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 to descend, the rapid conducting of load, load current equals the electric current I out of output current port.
The voltage variety of supposing parasitic capacitance CL two ends is Δ U, and the appearance value of parasitic capacitance CL is C, and the charging and discharging currents of parasitic capacitance CL is I, according to capacitor charge and discharge Time Calculation formula, can obtain parasitic capacitance CL by the time that the discharges and recharges t of metal-oxide-semiconductor Q2
fmeet:
can be found out by this formula, arrive moment in the low level that enables control signal EN, the On current I of metal-oxide-semiconductor Q2
mN2determined t discharge time of parasitic capacitance CL
f, and discharge time t
fshorter, mean that the load opening time enables the time delay of trailing edge of control signal EN relatively shorter, and the rise time of the On current of load is shorter, the effective ON time of load and to enable the difference of control signal EN significant level between the time less, make the deviation of the load intrinsic brilliance brightness corresponding with the settings of LED display controller output less.
Afterwards, in time-delay closing unit 15, after the voltage of capacitor C 1 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, thereby makes metal-oxide-semiconductor Q7 time-delay closing.The time of supposing metal-oxide-semiconductor Q7 time-delay closing is t_delay1, can be by the pull-down bias electric current I is set
bias1value and/or the appearance value of capacitor C 1, adjust t_delay1, to meet t_delay1>t
fthereby, when reducing chip power-consumption, the ON time that has also guaranteed 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 driving device the utility model proposes adopts the pre-opening technology of electric current, the moment of opening at circuit provides parasitic capacitance CL via the electric energy of the power switch pipe Q2 path of releasing, so that the voltage V of the voltage of the output current port of constant current driving device output current port while being dropped rapidly to the complete conducting of load
oUT1and then make load enter rapidly complete conducting state, thereby greatly shortened the effective ON time of load and enabled the difference of control signal EN significant level between the time, when load is LED, dwindled the deviation of the load intrinsic brilliance brightness corresponding with the settings of LED display controller output, optimize display effect, improved user experience.In addition, also can and enable at current detecting unit 12 increases time-delay closing unit 15 between control signal EN input, time-delay closing unit 15 can be after the complete conducting of load, reduce the power consumption of this constant current driving device 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, guaranteed the reliability that power switch pipe Q2 releases to the electric energy of parasitic capacitance CL.
The foregoing is only preferred embodiment of the present utility model; not in order to limit the utility model; all any modifications of doing within spirit of the present utility model and principle, be equal to and replace and improvement etc., within all should being included in protection range of the present utility model.
Claims (8)
1. a constant current driving device, it is characterized in that, described constant current driving device comprises power switch pipe Q1 and power switch pipe Q2, the high-end connection direct current of described power switch pipe Q1, the drive end of described power switch pipe Q1 connects the low side of described power switch pipe Q1, the low side ground connection of described power switch pipe Q2, described constant current driving device also comprises:
Input connects the described control signal that enables, output is as the output current port of described constant current driving device and connect the drive end of load, described output connects the high-end of described power switch pipe Q2 simultaneously, described, enable the control signal valid period and drives the constant current driving unit of described load conducting;
Output connects the low side of described power switch pipe Q1, and the low side that described power switch pipe Q1 is set flows into the electric current setting unit of the variable reference current of described electric current setting unit;
First input end connects the drive end of described power switch pipe Q1, the second input connects the described control signal that enables, output connects the drive end of described power switch pipe Q2, described, enables the current detecting unit that the control signal valid period detects described reference current and control described power switch pipe Q2 conducting according to testing result;
First input end connects the described control signal that enables, the second input connects the output of described constant current driving unit, output connects the drive end of described power switch pipe Q2, described, enable that the control signal valid period is detected the magnitude of voltage of described output current port and control the voltage detection unit that described power switch pipe Q2 ends during the voltage of described output current port when the magnitude of voltage of described output current port is reduced to the complete conducting of described load.
2. constant current driving device as claimed in claim 1, it is characterized in that, described power switch pipe Q1 is the metal-oxide-semiconductor of P type, the source electrode of described metal-oxide-semiconductor Q1 is high-end as described power switch pipe Q1's, 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.
3. constant current driving device as claimed in claim 1, 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, the drain electrode of described metal-oxide-semiconductor Q2 is high-end as described power switch pipe Q2's, and the grid of described metal-oxide-semiconductor Q2 is as the drive end of described power switch pipe Q2.
4. constant current driving device as described as the claims 1 to 3 any one, is characterized in that, described load is light-emitting diode.
5. constant current driving device as described as the claims 1 to 3 any one, is characterized in that, described constant current driving device also comprises:
Input connects the described control signal that enables, output connects the second input of described current detecting unit, in the described time-delay closing unit that enables the control signal valid period and control described current detecting unit time-delay closing after the voltage of described output current port when the magnitude of voltage of described output current port is reduced to the complete conducting of described load, the second input of described current detecting unit connects the described control signal that enables by described time-delay closing unit.
6. constant current driving device as claimed in claim 5, 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 capacitor C 1;
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 is as the input of described time-delay closing unit and connect the described control signal that enables, described capacitor C 1 is connected in parallel between the source electrode and drain electrode of described metal-oxide-semiconductor Q3, 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 the second input of described NAND gate U3, the output of described NAND gate U3 is as the output of described time-delay closing unit and connect described current detecting unit.
7. constant current driving device as claimed in claim 5, is characterized in that, described current detecting unit comprises: the metal-oxide-semiconductor Q4 of the metal-oxide-semiconductor Q3 of P type, the metal-oxide-semiconductor Q7 of P type, N-type, the metal-oxide-semiconductor Q5 of N-type, metal-oxide-semiconductor Q6, the bias current sources A2 of N-type;
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 drain electrode of grid and the described metal-oxide-semiconductor Q4 of described metal-oxide-semiconductor Q5, 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 is as the output of described current detecting unit 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 is as the first input end of described current detecting unit 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 is as the second input of described current detecting unit and connect described time-delay closing unit.
8. constant current driving device as claimed in claim 5, it is characterized in that, described voltage detection unit comprises: for reference voltage generation module, comparator U5, inverter U4, the metal-oxide-semiconductor Q8 of N-type, the metal-oxide-semiconductor Q9 of N-type and the metal-oxide-semiconductor Q10 of N-type that generates and export the first reference voltage and the second reference voltage;
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 the first reference voltage, the drain electrode of described metal-oxide-semiconductor Q10 connects described the second reference voltage, and described the first reference voltage is less than described the 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 is as the second input of described voltage detection unit and connect described constant current driving unit, the earth terminal of described comparator U5 is as the first input end of described voltage detection unit and connect the described control signal that enables, the source ground of described metal-oxide-semiconductor Q8, the drain electrode of described metal-oxide-semiconductor Q8 is as the output of described voltage detection unit and connect the drive end of described power switch pipe Q2.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN201320482188.9U CN203387742U (en) | 2013-08-07 | 2013-08-07 | Constant current drive device |
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN201320482188.9U CN203387742U (en) | 2013-08-07 | 2013-08-07 | Constant current drive device |
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| CN203387742U true CN203387742U (en) | 2014-01-08 |
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ID=49876187
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| Application Number | Title | Priority Date | Filing Date |
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| CN201320482188.9U Expired - Lifetime CN203387742U (en) | 2013-08-07 | 2013-08-07 | Constant current drive device |
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Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN104349539A (en) * | 2013-08-07 | 2015-02-11 | 深圳市明微电子股份有限公司 | Constant-current driving circuit |
| CN110599945A (en) * | 2019-08-06 | 2019-12-20 | 北京集创北方科技股份有限公司 | LED display device and driving method thereof |
| CN114489215A (en) * | 2022-04-06 | 2022-05-13 | 江苏长晶科技股份有限公司 | Low-noise reference circuit and low-dropout linear voltage stabilizing circuit thereof |
| CN117544149A (en) * | 2023-12-27 | 2024-02-09 | 西安航天民芯科技有限公司 | Load switch circuit |
-
2013
- 2013-08-07 CN CN201320482188.9U patent/CN203387742U/en not_active Expired - Lifetime
Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN104349539A (en) * | 2013-08-07 | 2015-02-11 | 深圳市明微电子股份有限公司 | Constant-current driving circuit |
| CN104349539B (en) * | 2013-08-07 | 2018-12-28 | 深圳市明微电子股份有限公司 | A kind of constant-current drive circuit |
| CN110599945A (en) * | 2019-08-06 | 2019-12-20 | 北京集创北方科技股份有限公司 | LED display device and driving method thereof |
| CN114489215A (en) * | 2022-04-06 | 2022-05-13 | 江苏长晶科技股份有限公司 | Low-noise reference circuit and low-dropout linear voltage stabilizing circuit thereof |
| CN117544149A (en) * | 2023-12-27 | 2024-02-09 | 西安航天民芯科技有限公司 | Load switch circuit |
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