CN103442489A - Average pattern constant-current controlling circuit and controlling method for LED driving circuit - Google Patents
Average pattern constant-current controlling circuit and controlling method for LED driving circuit Download PDFInfo
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- CN103442489A CN103442489A CN2013103881162A CN201310388116A CN103442489A CN 103442489 A CN103442489 A CN 103442489A CN 2013103881162 A CN2013103881162 A CN 2013103881162A CN 201310388116 A CN201310388116 A CN 201310388116A CN 103442489 A CN103442489 A CN 103442489A
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Abstract
The invention discloses an LED driving circuit. The LED driving circuit comprises an input voltage source, an energy transmission unit, a switch circuit and a freewheel diode, wherein the input voltage source provides input voltages, the energy transmission unit is coupled with the input voltage source and provides currents for a load circuit, the switch circuit is coupled with the energy transmission unit and the input voltage source, and the freewheel diode supplies follow currents to the energy transmission unit. An average pattern constant-current controlling circuit and a controlling method for the LED driving circuit are characterized in that the LED driving circuit further comprises a control circuit which is used for controlling the switch circuit coupled with the energy transmission unit and the input voltage source, and therefore the current flowing through a load circuit can be controlled.
Description
Technical field
The present invention relates to LED and drive field, relate in particular to a kind of average mode constant-current control circuit and control method of LED drive circuit.
Background technology
The current-voltage relation of LED and conventional diode are all the exponential type relations, when the forward voltage that applies with less dV/dt rate of change, can cause having the forward current of larger di/dt rate of change.Therefore, keeping the LED current constant is the best approach of driving LED.Fig. 1 is a kind of voltage-dropping type LED drive circuit schematic diagram commonly used.The control method that this circuit adopts peak current to control, control the peak current and the valley point current that flow through inductance.Because inductance 107 is cascaded with load LED 109, so the average current of load LED and inductance average current equate.
Inductive current during sampling resistor 104 sampled power metal-oxide-semiconductor conducting obtains a sampled voltage signal, control chip 103 according to this signal sets the current peak of inductance 107, make the current peak reference voltage Vref fixing and chip of inductance 107 proportional.Go up the turn-off time Toff of the sensibility reciprocal design power metal-oxide-semiconductor of voltage drop and inductance according to load LED109, make the electric current valley of inductance 107 remain a fixed value.The inductance average current that fixing inductive current peak and fixing inductive current valley are fixed, load LED average current is fixed, and the current formula of load LED is:
The reference voltage that wherein Vref is control chip 103 internal control inductive current peaks, voltage drop when Vled is load LED109 forward conduction, the power tube that Toff is 105 settings of frequency setting resistance is the turn-off time fixedly, the inductance value that L is inductance.
From top formula, can find out, the load LED average current of existing voltage-dropping type LED drive circuit is easy to be subject to the impact of various parameters, such as, different input voltage VIN, and inductance value L, and voltage degradation during load LED109 forward conduction.The impact of these parameters has brought adverse effect to large-scale production and the application of LED lighting apparatus, and the variation of the LED of load simultaneously electric current also can be given the useful life of load LED and be brought adverse effect.To LED, illumination proposes in the situation of high request more and more in current market, and existing LED drive circuit can not meet the demands.In view of this, the present invention will provide a kind of more high-performance, and irrelevant LED drive circuit and the control methods thereof all of the voltage drop during with input voltage, inductance value and load LED forward conduction.
The shortcoming of summing up prior art is: one, the impact that the average electrical of load LED fails to be convened for lack of a quorum and changed by inductance value; Its two, the fail to be convened for lack of a quorum impact of the voltage drop while being subject to load LED forward conduction of the average electrical of load LED; Its three, the average electrical of load LED fails to be convened for lack of a quorum and is subject to the impact that input voltage changes.
Summary of the invention
In order to solve the shortcoming of existing LED drive circuit, the present invention proposes a kind of average mode constant-current control circuit of LED drive circuit, adopts the load current of the LED drive circuit of this scheme can obtain controlling comparatively accurately.A kind of LED drive circuit according to one embodiment of the invention, comprise the input voltage source that input voltage is provided; The Energy Transfer unit coupled with input voltage source, for described load circuit provides electric current; The switching circuit coupled with Energy Transfer unit and input voltage source; And be the fly-wheel diode of Energy Transfer unit afterflow, it is characterized in that, described LED drive circuit also comprises a control circuit, for controlling the switching circuit coupled with Energy Transfer unit and input voltage source, thereby controls the electric current of the load circuit of flowing through.
Preferably, the control circuit of described LED drive circuit comprises:
Current detection circuit, for when described switching circuit switches on and off, the electric current that all provides indication to flow through described Energy Transfer unit, and output electric current measure signal;
The current peak control circuit, couple with described current detection signal and the first reference voltage, and generation current peak value control signal;
Electric current valley control circuit, couple with described current detection signal and the second reference voltage, and generation current valley control signal;
Pulse width modulating signal produces circuit, with described current peak control signal and electric current valley control signal, couples, and produces a pulse width modulating signal control switch circuit and switches on and off, and take the constant desired value for setting of average current that maintains load circuit;
Wherein, the reference ground of the reference of LED drive circuit ground and control circuit is not same with reference to ground.
Preferably, the input voltage that described input voltage source provides comprises: the direct voltage of the direct voltage of AC-DC converter output, DC-to-DC converter output or alternating voltage be the direct voltage after rectifier bridge directly.
Preferably, be the reference of described control circuit the common node of Energy Transfer unit and current detection circuit, or the common node of current detection circuit and switching circuit.
Preferably, the switching circuit of described LED drive circuit is comprised of field-effect transistor (FET), bipolar transistor (BJT) or other switching mode devices.
Preferably, the Energy Transfer unit of described LED drive circuit is an inductance or transformer.
Preferably, described LED drive circuit is based on buck-boost type topological structure or booster type topological structure.
Preferably, the current detection circuit of described control circuit is coupled in series on the current path between switching circuit and inductance, and one end and inductance couple, and the common port of the other end and load circuit and switching circuit couples, comprise,
One current sense resistor, inductive current flows through this resistance, and produces the current detection signal of indication inductive current transient current on current sense resistor.
Preferably, the current peak control circuit of described control circuit comprises,
Sample circuit, the pulse width modulating signal and its logical inverse signal that produce circuit output with current detection signal, pulse width modulating signal couple, and export a current detecting sampled signal;
The first averaging circuit, couple with the first reference voltage and current detecting sampled signal, and export the first average value signal;
The current peak testing circuit, couple output current peak value control signal with described the first average value signal and current detection signal.
Preferably, described sample circuit comprises the first sampling switch and the second sampling switch, first end and the current detection signal of the first sampling switch couple, and the second end and current detecting sampled signal couple, and the logical inverse signal of the 3rd end and pulse width modulating signal couples; The first end of the second sampling switch and current detecting sampled signal couple, and the second end and control circuit couple with reference to ground, and the 3rd end and pulse width modulating signal couple.When pulse width modulating signal is logic low, the first sampling switch is connected, and the second sampling switch disconnects, current detecting sampled signal and current detection signal same-phase; When pulse width modulating signal is logic high, the first sampling switch disconnects, and the second sampling switch is connected, and the current detecting sampled signal remains zero level.
Preferably, described the first averaging circuit comprises the first error amplifier, and the first error intergal electric capacity of its output, and the in-phase input end of described error amplifier and the first reference voltage couple, inverting input and current detecting sampled signal couple, and it is output as the first average value signal; The output of the first error intergal electric capacity one end and the first error amplifier couples, and couples to the reference of an end and control circuit.
Preferably, described current peak testing circuit comprises the first comparator, and its in-phase input end and current detection signal couple, and inverting input and described the first average value signal couple, and it is output as the current peak control signal.
Preferably, the electric current valley control circuit of described control circuit comprises,
The second comparator, its in-phase input end and the second reference voltage couple, and inverting input and current detection signal couple, and its output is electric current valley control signal.
Preferably, the second reference voltage of described electric current valley control circuit can be set to no-voltage, and take that this controls and realizes that the electric current valley is as zero current.
Preferably, the pulse width modulating signal of described control circuit produces circuit and comprises a rest-set flip-flop, its reset terminal and current peak control signal couple, set end and electric current valley control signal couple, the Q output is pulse width modulating signal, the pulse width modulating signal of output switches on and off for the switching circuit of controlling and inductance couples, and take and maintains the desired value of load LED current constant as setting.
According to the LED drive circuit of another preferred embodiment of the present invention, wherein, described LED drive circuit is only variant with the first embodiment on control circuit.
Preferably, the current peak control circuit of described control circuit comprises,
The 3rd comparator, its in-phase input end and current detection signal couple, and inverting input and the first reference voltage couple, and its output is the current peak control signal.
Preferably, the electric current valley control circuit of described control circuit comprises,
Sample circuit, pulse width modulating signal and its logical inverse signal of producing circuit output with current detection signal and pulse width modulating signal couple, and export a current detecting sampled signal;
The second averaging circuit, couple with the second reference voltage and current detecting sampled signal, and export the second average value signal;
The electric current valley value detection circuit, couple output current valley control signal with described the second average value signal and current detection signal.
Preferably, described sample circuit comprises the first sampling switch and the second sampling switch, first end and the current detection signal of the first sampling switch couple, and the second end and current detecting sampled signal couple, and the logical inverse signal of the 3rd end and pulse width modulating signal couples; The first end of the second sampling switch and current detecting sampled signal couple, and the second end and control circuit couple with reference to ground, and the 3rd end and pulse width modulating signal couple.When pulse width modulating signal is logic low, the first sampling switch is connected, and the second sampling switch disconnects, current detecting sampled signal and current detection signal same-phase; When pulse width modulating signal is logic high, the first sampling switch disconnects, and the second sampling switch is connected, and the current detecting sampled signal remains zero level.
Preferably, described the second averaging circuit comprises the second error amplifier, and the second error intergal electric capacity of its output.The second error amplifier in-phase input end and the second reference voltage couple, and inverting input and current detecting sampled signal couple, and it is output as the second average value signal; The output of the second error intergal electric capacity one end and the second error amplifier couples, and couples to the reference of an end and control circuit.
Preferably, described electric current valley value detection circuit comprises the 4th comparator, and its in-phase input end and described the second average value signal couple, and inverting input and current detection signal couple, and its output is inductive current valley control signal.
According to the LED drive circuit of another preferred embodiment of the present invention, described LED drive circuit is only variant with the first embodiment on control circuit.
Preferably, the electric current valley control circuit of described control circuit comprises,
One zero current detecting circuit, the common port of its input and inductance and current detection circuit couples, output is electric current valley control signal, zero current detecting circuit utilizes inductive current to drop to after zero, the principle of LC vibration appears in the common port of inductance and current detection circuit, and can detect inductive current is zero moment point.
According to embodiments of the invention, a kind of average mode constant current control method of LED drive circuit has also been proposed, adopt the LED drive circuit of described control method at least to comprise switching circuit and the inductance or the transformer that are coupled to described switching circuit, along with switching on and off of switching circuit, described inductance or transformer storage and output energy, described average mode constant current control method comprises the following steps:
A. current detecting step: during switching circuit is connected, detect the electric current that flows through described switching circuit, obtain a current detection signal;
B. current sample step: the sample rate current detection signal obtains a current detecting sampled signal relevant to load current;
C. mean value calculation step: by current detecting sampled signal and the first reference voltage value of averaging computing, obtain the first average value signal;
D. current peak is controlled step: compare with the first average value signal and current detection signal, when current detection signal is more than or equal to the first average value signal, switching circuit is disconnected, obtained the peak value of inductive current;
E. the electric current valley is controlled step, with the second reference voltage and current detection signal, compares, and when current detection signal is less than the second reference voltage, switching circuit is connected, and has obtained the valley of inductive current;
F. steps A-E forms the cycle of operation, and at described LED drive circuit duration of work, steps A-E repetitive cycling operation, realize average mode constant current control.
Preferably, the electric current valley of described average mode constant current control method is controlled step the second reference voltage can be set is that the valley that no-voltage arranges inductive current is zero current.
Preferably, the electric current valley of described average mode constant current control method is controlled step and also can be adopted zero current detecting circuit to detect the moment point that inductive current is zero, it detects principle: when inductive current drops to zero, the node that inductance and switching circuit couple there will be the LC vibration.
According to embodiments of the invention, a kind of average mode constant current control method of driving LED has also been proposed, adopt the LED drive circuit of described control method at least to comprise switching circuit and the inductance or the transformer that are coupled to described switching circuit, along with switching on and off of switching circuit, described inductance or transformer storage and output energy, described average mode constant current control method comprises the following steps:
A. current detecting step: during switching circuit is connected, detect the electric current that flows through described switching circuit, obtain a current detection signal;
B. current sample step: the sample rate current detection signal obtains a current detecting sampled signal relevant to load current;
C. mean value calculation step: by current detecting sampled signal and the second reference voltage value of averaging computing, obtain the second average value signal;
D. the electric current valley is controlled step: compare with the second average value signal and current detection signal, when current detection signal is less than the second average value signal, switching circuit is connected, obtained the valley of inductive current;
E. current peak is controlled step, with the first reference voltage and current detection signal, compares, and when current detection signal is more than or equal to the first reference voltage, switching circuit is disconnected, and has obtained the peak value of inductive current;
F. steps A-E forms the cycle of operation, and at described LED drive circuit duration of work, steps A-E repetitive cycling operation, realize average mode constant current control.
Compared with prior art, the helpfulness effect of technology provided by the present invention is: the average current of LED will be more accurate, and can not be subject to input voltage, the impact of inductance value and LED forward drop.
The accompanying drawing explanation
Figure 1 shows that the theory diagram of a kind of LED drive circuit that adopts prior art.
Figure 2 shows that the theory diagram according to the first embodiment of the present invention.
Fig. 3 A is depicted as the part schematic diagram according to the control circuit of one embodiment of the invention.
Fig. 3 B is depicted as the schematic diagram according to sample circuit of the present invention.
Fig. 3 C is depicted as the oscillogram according to the first implementing circuit of the present invention.
Fig. 4 A is depicted as the part schematic diagram according to the control circuit of another embodiment of the present invention.
Fig. 4 B is depicted as the oscillogram according to the second implementing circuit of the present invention.
Fig. 5 A is depicted as the theory diagram according to the third embodiment of the present invention.
Fig. 5 B is depicted as the electric current valley control circuit schematic diagram according to the third embodiment of the present invention.
Drawing reference numeral
100 start dropping resistor; 101 input filter capacitors; 103 control chips; 104 sampling resistors; 105 frequency setting resistance; 106 power MOS pipes; 107 inductance; 108 diodes; 109 load LED; 110 output filter capacitors; 200LED drive circuit the first embodiment; 201 first control circuit embodiment; 210 input voltage sources; 220 switching circuits; 221 power switchs; 230 load circuits; 231 fly-wheel diodes; 240 Energy Transfer unit; 241 inductance; 250 current detection circuits; 251 current sense resistors; 260 electric current valley control circuits; 270 current peak control circuits; 280 pulse width modulating signals produce circuit; 300 second control circuit embodiment; 310 sample circuits; 311 first sampling switchs; 312 second sampling switchs; 320 first averaging circuits; 321 first error intergal electric capacity; 322 first error amplifiers; 330 current peak testing circuits; 331 first comparators; 340 second comparators; 350 first rest-set flip-flops; 400 the 3rd control circuit embodiment; 420 second averaging circuits; 421 second error intergal electric capacity; 422 second error amplifiers; 430 electric current valley value detection circuits; 431 the 3rd comparators; 440 the 4th comparators; 500 LED drive circuit the second embodiment; 560 second embodiment electric current valley control circuits; 510 zero current detecting circuits.
Embodiment
Below will describe specific embodiments of the invention in detail, it should be noted that the embodiments described herein, only for illustrating, is not limited to the present invention.In the following description, in order to provide thorough understanding of the present invention, a large amount of specific detail have been set forth.Yet, for those of ordinary skills, it is evident that: needn't adopt these specific detail to carry out the present invention.In other embodiments, for fear of obscuring the present invention, do not specifically describe known circuit, material or method.
In whole specification, " embodiment ", " embodiment ", " example " or mentioning of " example " are meaned: special characteristic, structure or characteristic in conjunction with this embodiment or example description are comprised at least one embodiment of the present invention.Therefore, phrase " in one embodiment ", " in an embodiment ", " example " or " example " occurred in each place of whole specification differs to establish a capital and refers to same embodiment or example.In addition, can, with any suitable combination and/or sub-portfolio by specific feature, structure or characteristic, be combined in one or more embodiment or example.In addition, it should be understood by one skilled in the art that the accompanying drawing provided at this is all for illustrative purposes, and accompanying drawing is not necessarily drawn in proportion.Should be appreciated that it can be directly connected or coupled to another element or can have intermediary element when claiming element " connection ", " being connected to " or " coupling ", " being couple to " another element.On the contrary, when claiming element " to be directly connected to " or during " being directly coupled to " another element, not having intermediary element.Identical Reference numeral is indicated identical element.Term used herein " and/or " comprise any and all combinations of one or more relevant projects of listing.
With reference to figure 2, be depicted as the theory diagram according to an embodiment of LED drive circuit of the present invention, comprise the input voltage source 210 that input voltage VIN is provided, the Energy Transfer unit 240 coupled with input voltage source 210, for described load circuit 230 provides electric current; The switching circuit 220 coupled with Energy Transfer unit 240 and input voltage source 210; And be the fly-wheel diode 231 of Energy Transfer unit 240 afterflows, described LED drive circuit 200 also comprises a control circuit 201, for controlling the switching circuit 220 coupled with Energy Transfer unit 240 and input voltage source 210, thereby control the electric current of the load circuit 230 of flowing through.Control circuit 201 further comprises: current detection circuit 250, with switching circuit 220, Energy Transfer unit 240 and load circuit 230, couple, for when described switching circuit 220 switches on and off, the electric current that all provides indication to flow through described Energy Transfer unit 240, and output electric current measure signal Vcs.Current peak control circuit 270, couple with described current detection signal Vcs and the first reference voltage VR1, and generation current peak value control signal Vpk, and its peak value that has meaned inductive current is directly relevant with the first reference voltage.Electric current valley control circuit 260, with described current detection signal Vcs and the second reference voltage VR2, couple, and generation current valley control signal Vva, if can guarantee that whole LED drive circuit 200 is operated in continuous current mode pattern (CCM pattern), or critical current mode pattern (CRM pattern), the valley of inductive current is just directly relevant with the second reference voltage so.Pulse width modulating signal produces circuit 280, with described current peak control signal Vpk and electric current valley control signal Vva, couple, produce a pulse width modulating signal PWM1 control switch circuit 220 and switch on and off, take and maintain the desired value of load circuit 230 current constants as setting.
In one embodiment, the input voltage VIN that input voltage source 210 provides comprises: the direct voltage of the direct voltage of AC-DC converter output, DC-to-DC converter output or alternating voltage be the direct voltage after rectifier bridge directly.The reference ground of LED drive circuit 200 and the reference ground of control circuit 201 are not same with reference to ground, in one embodiment, are the reference of described control circuit 201 common node of Energy Transfer unit 240 and current detection circuit 250.In one embodiment, be the reference of described control circuit 201 common node of current detection circuit 250 and switching circuit 220.In one embodiment, the switch 221 in the switching circuit 220 of described LED drive circuit 200 is comprised of field-effect transistor (FET), bipolar transistor (BJT) or other switching mode devices.In one embodiment, the Energy Transfer unit 240 of described LED drive circuit 200 is inductance 241 or a transformer, inductance 241 and 240 equivalences of Energy Transfer unit in following description.In one embodiment, switching circuit 220, inductance 241 and the fly-wheel diode 231 in described LED drive circuit 200 formed the buck-boost type topological structure.In one embodiment, switching circuit 220, inductance 241 and the fly-wheel diode 231 in described LED drive circuit 200 also can form the booster type topological structure.In one embodiment, described current detection circuit 250 comprises a current sense resistor 251, and inductive current flows through this resistance, and produces the current detection signal Vcs of indication inductive current transient current on current sense resistor 251.
Fig. 3 A is the part schematic diagram 300 according to the control circuit of one embodiment of the invention, in order further to understand operation principle of the present invention, need to together with Fig. 3 C, set forth in conjunction with Fig. 3 A, Fig. 3 B.The current peak control circuit 370 of described control circuit 300 comprises, sample circuit 310, the pulse width modulating signal PWM1 and its logical inverse signal PWM1B that produce circuit 280 outputs with current detection signal Vcs and pulse width modulating signal couple, and export a current detecting sampled signal Vcssp; In one embodiment, described sample circuit 310 comprises the first sampling switch 311 and the second sampling switch 312, the first end of the first sampling switch 311 and current detection signal Vcs couple, the second end and current detecting sampled signal Vcssp couple, and the logical inverse signal PWM1B of the 3rd end and pulse width modulating signal PWM1 couples; The first end of the second sampling switch 312 and current detecting sampled signal Vcssp couple, and the second end and control circuit couple with reference to ground, and the 3rd end and pulse width modulating signal PWM1 couple.When pulse width modulating signal PWM1 is logic low, the first sampling switch 311 is connected, and the second sampling switch 312 disconnects, current detecting sampled signal Vcssp and current detection signal Vcs same-phase; When pulse width modulating signal PWM1 is logic high, the first sampling switch 311 disconnects, and the second sampling switch 312 is connected, and current detecting sampled signal Vcssp remains zero level.In one embodiment, LED drive circuit 200 works in the buck topological structure, when pulse width modulating signal PWM1 is logic high, switching circuit 220 is connected, input voltage VIN is charged to inductance 241, now load circuit 230 does not have electric current, and the current detection signal Vcs on current sense resistor 251 has reacted the charging current of input voltage VIN to inductance 241; When pulse width modulating signal PWM1 is logic low, switching circuit 220 disconnects, inductance 241 is discharged by 231 pairs of load circuits 230 of fly-wheel diode, now load circuit 230 has electric current to flow through, and the current detection signal Vcs on current sense resistor 251 has reacted the size of current that load circuit 230 flows through.So the current detecting sampled signal Vcssp obtained by sample circuit 310 has directly reacted the load current information that flows through load circuit 230.The first averaging circuit 320, couple with the first reference voltage VR1 and current detecting sampled signal Vcssp, and export the first average value signal ILpk; In one embodiment, described the first averaging circuit 320 comprises the first error amplifier 322, the first error intergal electric capacity 321 with its output, the in-phase input end of described error amplifier and the first reference voltage VR1 couple, inverting input and current detecting sampled signal Vcssp couple, and it is output as the first average value signal ILpk; The output of the first error intergal electric capacity 321 1 ends and the first error amplifier 322 couples, and couples to the reference of an end and control circuit.The first averaging circuit 320 by the error accumulation of the current detecting sampled signal Vcssp of the first reference voltage VR1 and reaction load electric current in the first error intergal electric capacity 321, for controlling the peak value of inductive current.
Current peak testing circuit 330, couple output current peak value control signal Vpk with described the first average value signal ILpk and current detection signal Vcs; In one embodiment, described current peak testing circuit comprises the first comparator 331, and its in-phase input end and current detection signal Vcs couple, and inverting input and described the first average value signal ILpk couple, and it is output as current peak control signal Vpk.When current detection signal Vcs is more than or equal to the first average value signal ILpk, current peak control signal Vpk is logic high, and when current detection signal Vcs is less than the first average value signal ILpk, current peak control signal Vpk is logic low.
In one embodiment, the electric current valley control circuit 360 of described control circuit 300 comprises, the second comparator 340, and its in-phase input end and the second reference voltage VR2 couple, inverting input and current detection signal Vcs couple, and its output is electric current valley control signal Vva.When current detection signal Vcs is less than the second reference voltage VR2, electric current valley control signal Vva is logic high, and when current detection signal Vcs is more than or equal to the second reference voltage VR2, electric current valley control signal Vva is logic low.
In one embodiment, the second reference voltage VR2 of described electric current valley control circuit 360 can be set to no-voltage, and take that this controls and realizes that the electric current valley is as zero current.
In one embodiment, the pulse width modulating signal of described control circuit 300 produces circuit 280 and comprises a rest-set flip-flop 350, its reset terminal and current peak control signal Vpk couple, set end and electric current valley control signal Vva couple, the Q output is pulse width modulating signal PWM1, the pulse width modulating signal PWM1 of output switches on and off for the switching circuit 220 of controlling and inductance 241 couples, and take and maintains the desired value of load circuit current constant as setting.When current peak control signal Vpk is logic high, pulse width modulating signal PWM1 is logic low; When electric current valley control signal Vva is logic high, pulse width modulating signal PWM1 is logic high.
The level of the first average value signal ILpk has meaned the mean value of current detecting sampled signal Vcssp and the accumulated error between the first reference voltage VR1, for controlling the peak value of inductive current.When the mean value of current detecting sampled signal Vcssp is less than the first reference voltage VR1, the level of the first average value signal ILpk will raise, the inductive current peak that current peak testing circuit 330 is controlled simultaneously also can synchronously raise motor current to detect the mean value of sampled signal Vcssp, make the mean value of current detecting sampled signal Vcssp equal the first reference voltage VR1, vice versa.Current peak control signal Vpk has determined that by the first reference voltage VR1 the peak value of inductive current is ILpk/Rcs, electric current valley control signal Vva has determined that by the second reference voltage VR2 the valley of inductive current is VR2/Rcs, and the first reference voltage VR1 has also determined that the load current mean value of load circuit 230 is VR1/Rcs simultaneously.
Fig. 4 A is the part schematic diagram 400 according to the control circuit of another embodiment of the present invention, with control circuit 300, compares, and the two only has any different on current peak control circuit and electric current valley control circuit.In order further to understand operation principle of the present invention, need to together with Fig. 4 B, set forth in conjunction with Fig. 4 A, Fig. 3 B.The electric current valley control circuit 460 of described control circuit 400 comprises, sample circuit 310, the pulse width modulating signal PWM1 and its logical inverse signal PWM1B that produce circuit 280 outputs with current detection signal Vcs and pulse width modulating signal couple, and exporting a current detecting sampled signal Vcssp, described current detecting sampled signal Vcssp has directly reacted the load current information that flows through load circuit 230.The second averaging circuit 420, couple with the second reference voltage VR2 and current detecting sampled signal Vcssp, and export the second average value signal ILva; In one embodiment, described the second averaging circuit 420 comprises the second error amplifier 422, the second error intergal electric capacity 421 with its output, the in-phase input end of described error amplifier and the second reference voltage VR2 couple, inverting input and current detecting sampled signal Vcssp couple, and it is output as the second average value signal ILva; The output of the second error intergal electric capacity 421 1 ends and the second error amplifier 422 couples, and couples to the reference of an end and control circuit.The second averaging circuit 420 by the error accumulation of the current detecting sampled signal Vcssp of the second reference voltage VR2 and reaction load electric current in the second error intergal electric capacity 421, for controlling the valley of inductive current.
Electric current valley value detection circuit 430, couple output current valley control signal Vva with described the second average value signal ILva and current detection signal Vcs; In one embodiment, described electric current valley value detection circuit comprises the 3rd comparator 431, and its inverting input and current detection signal Vcs couple, and in-phase input end and described the second average value signal ILva couple, and it is output as electric current valley control signal Vva.When current detection signal Vcs is more than or equal to the second average value signal ILva, electric current valley control signal Vva is logic low, and when current detection signal Vcs is less than the second average value signal ILva, electric current valley control signal Vva is logic high.
In one embodiment, the current peak control circuit 470 of described control circuit 400 comprises, the 4th comparator 440, and its inverting input and the first reference voltage VR1 couple, in-phase input end and current detection signal Vcs couple, and its output is current peak control signal Vpk.When current detection signal Vcs is less than the first reference voltage VR1, current peak control signal Vpk is logic low, and when current detection signal Vcs is more than or equal to the first reference voltage VR1, current peak control signal Vpk is logic high.
The level of the second average value signal ILva has meaned the mean value of current detecting sampled signal Vcssp and the accumulated error between the second reference voltage VR2, for controlling the valley of inductive current.When the mean value of current detecting sampled signal Vcssp is less than the second reference voltage VR2, the level of the second average value signal ILva will raise, the inductive current valley that electric current valley value detection circuit 430 is controlled simultaneously also can synchronously raise motor current to detect the mean value of sampled signal Vcssp, make the mean value of current detecting sampled signal Vcssp equal the second reference voltage VR2, vice versa.Electric current valley control signal Vva has determined that by the second reference voltage VR2 the valley of inductive current is ILva/Rcs, current peak control signal Vpk has determined that by the first reference voltage VR1 the peak value of inductive current is VR1/Rcs, and the second reference voltage VR2 has also determined that the load current mean value of load circuit 230 is VR2/Rcs simultaneously.
Described the second embodiment 500 according to LED drive circuit of the present invention with reference to figure 5A, described LED drive circuit is only variant with the first embodiment 200 on control circuit 501.The electric current valley control circuit 560 of the control circuit 501 of the LED drive circuit 500 of the present embodiment comprises, a zero current detecting circuit 510 as shown in Figure 5 B, the common port that its input is inductance 241 and current detection circuit 250, output is electric current valley control signal Vva, zero current detecting circuit 560 utilizes inductive current to drop to after zero, the principle of LC vibration appears in the common port of inductance 241 and current detection circuit 205, and can detect inductive current is zero moment point.
According to embodiments of the invention, a kind of average mode constant current control method of LED drive circuit has also been proposed, adopt the LED drive circuit of described control method at least to comprise switching circuit and the inductance or the transformer that are coupled to described switching circuit, along with switching on and off of switching circuit, described inductance or transformer storage and output energy, described average mode constant current control method comprises the following steps:
A. current detecting step: during switching circuit is connected, detect the electric current that flows through described switching circuit, obtain a current detection signal;
B. current sample step: the sample rate current detection signal obtains a current detecting sampled signal relevant to load current;
C. mean value calculation step: by current detecting sampled signal and the first reference voltage value of averaging computing, obtain the first average value signal;
D. current peak is controlled step: compare with the first average value signal and current detection signal, when current detection signal is more than or equal to the first average value signal, switching circuit is disconnected, obtained the peak value of inductive current;
E. the electric current valley is controlled step, with the second reference voltage and current detection signal, compares, and when current detection signal is less than the second reference voltage, switching circuit is connected, and has obtained the valley of inductive current;
F. steps A-E forms the cycle of operation, and at described LED drive circuit duration of work, steps A-E repetitive cycling operation, realize average mode constant current control.
In one embodiment, the electric current valley of described average mode constant current control method is controlled step the second reference voltage can be set is that the valley that no-voltage arranges inductive current is zero current.
In one embodiment, the electric current valley of described average mode constant current control method is controlled step and also can be adopted zero current detecting circuit to detect the moment point that inductive current is zero, it detects principle: when inductive current drops to zero, the node that inductance and switching circuit couple there will be the LC vibration.
According to embodiments of the invention, a kind of average mode constant current control method of driving LED has also been proposed, adopt the LED drive circuit of described control method at least to comprise switching circuit and the inductance or the transformer that are coupled to described switching circuit, along with switching on and off of switching circuit, described inductance or transformer storage and output energy, described average mode constant current control method comprises the following steps:
A. current detecting step: during switching circuit is connected, detect the electric current that flows through described switching circuit, obtain a current detection signal;
B. current sample step: the sample rate current detection signal obtains a current detecting sampled signal relevant to load current;
C. mean value calculation step: by current detecting sampled signal and the second reference voltage value of averaging computing, obtain the second average value signal;
D. the electric current valley is controlled step: compare with the second average value signal and current detection signal, when current detection signal is less than the second average value signal, switching circuit is connected, obtained the valley of inductive current;
E. current peak is controlled step, with the first reference voltage and current detection signal, compares, and when current detection signal is more than or equal to the first reference voltage, switching circuit is disconnected, and has obtained the peak value of inductive current;
F. steps A-E forms the cycle of operation, and at described LED drive circuit duration of work, steps A-E repetitive cycling operation, realize average mode constant current control.
Although with reference to several exemplary embodiments, described the present invention, should be appreciated that term used is explanation and exemplary, nonrestrictive term.The spirit or the essence that do not break away from invention because the present invention can specifically implement in a variety of forms, so be to be understood that, above-described embodiment is not limited to any aforesaid details, and explain widely in the spirit and scope that should limit in the claim of enclosing, therefore fall into whole variations in claim or its equivalent scope and remodeling and all should be the claim of enclosing and cover.
Claims (10)
1. a LED drive circuit, comprise the input voltage source that input voltage is provided; The Energy Transfer unit coupled with input voltage source, for described load circuit provides electric current; The switching circuit coupled with Energy Transfer unit and input voltage source; And be the fly-wheel diode of Energy Transfer unit afterflow, it is characterized in that, described LED drive circuit also comprises a control circuit, for controlling the switching circuit coupled with Energy Transfer unit and input voltage source, thereby controls the electric current of the load circuit of flowing through.
2. LED drive circuit according to claim 1, is characterized in that, described control circuit comprises:
Current detection circuit, for when described switching circuit switches on and off, the electric current that all provides indication to flow through described Energy Transfer unit, and output electric current measure signal;
The current peak control circuit, couple with described current detection signal and the first reference voltage, and generation current peak value control signal;
Electric current valley control circuit, couple with described current detection signal and the second reference voltage, and generation current valley control signal;
Pulse width modulating signal produces circuit, with described current peak control signal and electric current valley control signal, couples, and produces a pulse width modulating signal control switch circuit and switches on and off, and take the constant desired value for setting of average current that maintains load circuit;
Wherein, the reference ground of the reference of LED drive circuit ground and control circuit is not same with reference to ground.
3. LED drive circuit according to claim 1, it is characterized in that, the input voltage that described input voltage source provides comprises: the direct voltage of the direct voltage of AC-DC converter output, DC-to-DC converter output or alternating voltage be the direct voltage after rectifier bridge directly.
4. LED drive circuit according to claim 1, is characterized in that, the reference ground of described control circuit is the common node of Energy Transfer unit and current detection circuit, or the common node of current detection circuit and switching circuit.
5. LED drive circuit according to claim 1, is characterized in that, described switching circuit is comprised of field-effect transistor (FET), bipolar transistor (BJT) or other switching mode devices.
6. LED drive circuit according to claim 1, is characterized in that, described Energy Transfer unit is an inductance or transformer.
7. LED drive circuit according to claim 1, is characterized in that, described LED drive circuit is based on buck-boost type topological structure or booster type topological structure.
8. LED drive circuit according to claim 2, it is characterized in that, the current detection circuit of described control circuit is coupled in series on the current path between switching circuit and inductance, one end and inductance couple, the common port of the other end and load circuit and switching circuit couples, comprise a current sense resistor, inductive current flows through this resistance, and produces the current detection signal of indication inductive current transient current on current sense resistor.
9. LED drive circuit according to claim 2, is characterized in that, the current peak control circuit of described control circuit comprises,
Sample circuit, the pulse width modulating signal and its logical inverse signal that produce circuit output with current detection signal, pulse width modulating signal couple, and export a current detecting sampled signal;
The first averaging circuit, couple with the first reference voltage and current detecting sampled signal, and export the first average value signal;
The current peak testing circuit, couple output current peak value control signal with described the first average value signal and current detection signal.
10. LED drive circuit according to claim 9, it is characterized in that, described sample circuit comprises the first sampling switch and the second sampling switch, first end and the current detection signal of the first sampling switch couple, the second end and current detecting sampled signal couple, and the logical inverse signal of the 3rd end and pulse width modulating signal couples; The first end of the second sampling switch and current detecting sampled signal couple, and the second end and control circuit couple with reference to ground, and the 3rd end and pulse width modulating signal couple; When pulse width modulating signal is logic low, the first sampling switch is connected, and the second sampling switch disconnects, current detecting sampled signal and current detection signal same-phase; When pulse width modulating signal is logic high, the first sampling switch disconnects, and the second sampling switch is connected, and the current detecting sampled signal remains zero level.
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Application publication date: 20131211 |