CN107846745A - LED drive circuit and its control method - Google Patents
LED drive circuit and its control method Download PDFInfo
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- CN107846745A CN107846745A CN201710943558.7A CN201710943558A CN107846745A CN 107846745 A CN107846745 A CN 107846745A CN 201710943558 A CN201710943558 A CN 201710943558A CN 107846745 A CN107846745 A CN 107846745A
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- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
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- H05B45/40—Details of LED load circuits
Abstract
This application discloses LED drive circuit and its control method.The LED drive circuit is used to drive the first LED and the second LED, including：First linear constant current circuit, including be connected to the first end of feeder ear, be connected to the first LED anode the second end and be connected to the second LED negative electrode the 3rd end；And second linear constant current circuit, first end including the negative electrode that is connected to the second LED and the second end being connected to the ground, wherein, first linear constant current circuit selects one of the first current path and the 3rd current path, first current path is located between first end and the second end of the first linear constant current circuit, 3rd current path is located between the 3rd end and the second end of the first linear constant current circuit, second linear constant current circuit selectively turns on or disconnected the second current path, and the second current path is located between first end and the second end of the second linear constant current circuit.The LED drive circuit reduces the parameter request of input capacitance using the switching of the connected mode of LED load.
Description
Technical field
The present invention relates to LED illumination technology, more particularly, to LED drive circuit and its control method.
Background technology
LED (light emitting diode) has the excellent of small volume, energy-conservation, long lifespan, high brightness and environmental protection relative to conventional light source
Point, therefore it is widely used for indoor and outdoors illumination.
The brightness of LED is related to driving current, and corresponding drive scheme is Linear Driving scheme and switch drive scheme.
The mode of linear regulation transistor is respectively adopted in the two and the mode of switch controlling transistor adjusts driving current.
Fig. 1 shows the schematic circuit of the LED drive circuit according to prior art.As illustrated, LED drive circuit
100 include ac current source 101, rectifier bridge 102, input capacitance Cin, current sampling resistor Rs, linear constant current circuit 110.It is whole
Bridge 102 is flowed to be used for AC rectification into direct current.Input capacitance Cin carries out smothing filtering.Two output ends of rectifier bridge 102
Between input voltage vin is provided.LED 103 is connected in series in rectifier bridge with linear constant current circuit 110 and current sampling resistor Rs
Between 102 two output ends.
Linear constant current circuit 110 includes power tube M10 and amplifier 111.Amplifier 111 obtains current sampling resistor Rs
Current sampling signal compared with reference voltage Vref, drive signal, control power tube M10 are produced according to the difference of the two
In the driving current that flows through.After circuit stability, the value for the driving current that linear constant current circuit 100 controls is Vref/Rs.
In above-mentioned LED drive circuit, the signal of input is the signal for exchanging 50Hz/60Hz, it is necessary to there is big input
Electric capacity Cin, cause the increase of circuit volume.Input capacitance short life is additionally, since, therefore shortens integral LED drive circuit
Life-span.
The content of the invention
In view of the above problems, it is an object of the invention to provide LED drive circuit and its control method, wherein, by cutting
Changing the connected mode of LED load reduces the parameter request of input capacitance, so as to reduce circuit volume and improve reliability and use
Life-span.
According to an aspect of the present invention, there is provided a kind of LED drive circuit, for driving the first LED and the second LED,
Including：First linear constant current circuit, including be connected to the first end of feeder ear, be connected to the first LED anode the second end,
And it is connected to the 3rd end of the negative electrode of the second LED；And second linear constant current circuit, including it is connected to the second LED
The first end of negative electrode and the second end being connected to the ground, wherein, first linear constant current circuit select the first current path and
One of 3rd current path, first current path be located at first linear constant current circuit first end and the second end it
Between, the 3rd current path is located between the 3rd end and the second end of first linear constant current circuit, and described second is linear
Constant-current circuit selectively turns on or disconnected the second current path, and second current path is located at second linear constant current electricity
Between the first end on road and the second end.
Preferably, first linear constant current circuit and second linear constant current circuit are respectively according to the feeder ear
Input voltage selects current path so that first LED and second LED switch in parallel connect according to input voltage
One of connect and be connected in series.
Preferably, in addition to：Diode, its anode are connected to the negative electrode of second LED, and its negative electrode is connected to described
3rd end of the first linear constant current circuit.
Preferably, first linear constant current circuit includes：First linear constant-current control module, is connected to the First Line
Between the first end of property constant-current circuit and the second end, for providing the first current path；Third linear constant-current control module, connection
Between the 3rd end of first linear constant current circuit and the second end, for providing the 3rd current path；And first path
Selecting module, it is connected with the described first linear constant-current control module and the 3rd constant-current control module, for selecting electric current
Path, wherein, when the input voltage of the feeder ear is less than or equal to predetermined value, described in the first path selecting module disconnection
3rd current path, and conducting first current path, it is described when the input voltage of the feeder ear is more than predetermined value
First path selecting module disconnects first current path, and conducting the 3rd current path.
Preferably, second linear constant current circuit includes：Second linear constant current control module, it is connected to second line
Between the first end of property constant-current circuit and the second end, for providing the second current path；Alternate path selecting module, with described
Bilinear constant-current control module is connected, for selecting current path, wherein, it is less than or equal in the input voltage of the feeder ear
During predetermined value, the alternate path selecting module turns on second current path, is more than in the input voltage of the feeder ear
During predetermined value, the alternate path selecting module disconnects second current path.
Preferably, the described first linear constant-current control module, the second linear constant current control module and the 3rd line
Property constant-current control module includes respectively：Power tube, for controlling the current value of corresponding current path；And amplifier, it is used for
Reference voltage is compared to produce the drive signal of the power tube with current sampling signal.
Preferably, first linear constant current circuit also includes：Current sampling resistor, positioned at first current path and
On the common path of 3rd current path, the first path selecting module is the current sampling resistor.
Preferably, the reference voltage of amplifier is less than the third linear constant current in the described first linear constant-current control module
The reference voltage of amplifier in control module.
Preferably, first linear constant current circuit also includes：First current sampling resistor, with first linear constant current
Power tube in control module is connected in series, and first node between provides the first current sampling signal；And the 3rd
Power tube in current sampling resistor, with the third linear constant-current control module is connected in series, between Section three
Point provides the 3rd current sampling signal, wherein, the first path selecting module is by the amplification of the 3rd current sampling signal
Signal averaging is on the current sampling signal or reference voltage of the described first linear constant-current control module amplifier.
Preferably, the first path selecting module includes：It is connected in series in the first node and the 3rd node
Between the first feedback resistance and amplification module, wherein, the current sample of first linear constant-current control module amplifier letter
The fourth node number being derived between first feedback resistance and the amplification module.
Preferably, when the 3rd current path turns on, the amplification module is by the 3rd current sampling signal
Amplified signal is applied in the fourth node as control signal, and the control signal is more than the described first linear current constant control
The reference voltage of amplifier in module, so as to disconnect first current path.
Preferably, second linear constant current circuit also includes：Second current sampling resistor, with second linear constant current
Power tube in control module is connected in series, and section point between provides the second current sampling signal, wherein, it is described
Alternate path selecting module produces control signal according to the voltage sampling signal of the input voltage, and by the control signal
It is superimposed upon on the current sampling signal or reference voltage of the second linear constant current control module amplifier.
Preferably, the alternate path selecting module includes：First divider resistance and the second divider resistance, are connected in series in
Between the first end of second linear constant current circuit and the second end, and first divider resistance and second partial pressure electricity
The 5th node between resistance provides the voltage feedback signal for characterizing the input voltage；It is connected in series section point and the 5th
Voltage comparator and the second feedback resistance between node, wherein, the electricity of amplifier in the second linear constant current control module
Stream sampled signal is derived from the 6th node between second feedback resistance and the voltage comparator, and the voltage comparator will
The voltage feedback signal is compared with reference voltage to obtain control signal so that believes in the voltage sample of the input voltage
When number being less than the reference voltage, the alternate path selecting module turns on second current path, in the input voltage
Voltage sampling signal when being more than or equal to the reference voltage, the alternate path selecting module disconnects the second electric current road
Footpath.
Preferably, the alternate path selecting module includes：3rd divider resistance and the 4th divider resistance, are connected in series in
Between second end of the negative electrode of the diode and second linear constant current circuit, wherein, the 3rd divider resistance and
The 7th node between four divider resistances provides the voltage feedback signal of the cathode voltage for characterizing the diode, as institute
State reference voltage.
According to another aspect of the present invention, there is provided a kind of control method for LED drive circuit, for driving first
LED and the second LED, including：When the input voltage of feeder ear is less than or equal to predetermined value, the first current path is used as institute
State the first LED and the first electric current is provided, and the second current path provides the second electric current for second LED so that be described
First LED and the second LED parallel operation；And when the input voltage of feeder ear is more than predetermined value, using the 3rd
Current path provides the 3rd electric current for first LED and second LED so that the first LED and described second
LED is connected in series.
Preferably, first is set respectively on the first to the 3rd current path to third linear constant-current control module, to divide
Not Kong Zhi the first to the 3rd electric current current value, wherein, first current path is successively via the first linear constant current control
Molding block and first LED, second current path is successively via second LED and second linear constant current
Control module, the 3rd current path are passed through by second LED, the third linear constant-current control module and institute successively
State the first LED.
Preferably, the described first to the 3rd constant-current control module respectively by the current sampling signal of the first to the 3rd electric current with
Reference voltage compares, to control the current value of the first to the 3rd electric current.
Preferably, it is respective to third linear flow control module according to described first according to the input voltage of the feeder ear
Conducting and off-state, so as to realize first LED and second LED be connected in series and be connected in parallel cut
Change.
Preferably, the described first linear constant-current control module and third linear constant-current control module common current sampling
Resistance, and the reference voltage of amplifier is less than the third linear current constant control mould in the first linear constant-current control module
The reference voltage of amplifier in block so that when the 3rd current path turns on, first current path disconnects.
Preferably, the described first linear constant-current control module and the third linear constant-current control module obtain first respectively
Current sampling signal and the 3rd current sampling signal, the amplified signal of the 3rd current sampling signal are superimposed upon first electricity
Flow on sampled signal or reference voltage.
Preferably, when the 3rd current path turns on, using the amplified signal of the 3rd current sampling signal as
Control signal is superimposed upon on first current sampling signal, and the control signal is more than the described first linear constant-current control module
Reference voltage so that when the 3rd current path turns on, first current path disconnects.
Preferably, the second linear constant current control module obtains the second current sampling signal, according to the input voltage
Voltage sampling signal produce control signal, and the control signal is superimposed upon the second linear constant current control module and put
On second current sampling signal of big device, when the voltage sampling signal of the input voltage is less than the reference voltage, conducting
Second current path, when the voltage sampling signal of the input voltage is more than or equal to the reference voltage, described in disconnection
Second current path.
Preferably, in addition to：Diode, be connected to second LED and the third linear constant-current control module it
Between, and when the 3rd current path turns on, the diode current flow, wherein, the voltage sample letter of the input voltage
The anode of the diode number is derived from, the reference voltage is derived from the negative electrode of the diode.
LED drive circuit according to embodiments of the present invention and its control method, the first current path is used as the first LED
First electric current is provided, uses the second current path to provide the second electric current for the 2nd LED, and uses the 3rd current path as first
LED and the second LED provide the 3rd electric current, so as to realize first LED and the second LED parallel operation and
First LED and the second LED series-fed.Under parallel operation state, the first linear constant-current control module with
First LED is connected in turn on the first current path, and the second LED and the second linear constant current control module are connected to the in turn
On two current paths.Under series-fed state, the second LED, third linear constant-current control module and the first LED connect successively
It is connected on the 3rd current path.This method can realize the first LED and the second LED connection side using simple circuit structure
The flexible configuration of formula.
In a preferred embodiment, according to the input voltage of feeder ear automatic switchover first LED and described second
The connected mode of LED.When the input voltage of feeder ear is less than or equal to predetermined value, the first LED and the 2nd LED are switched to
Parallel operation.When the input voltage of feeder ear is more than predetermined value, the first LED and the 2nd LED are switched into series-fed.The
One LED and the second LED are automatically switched to according to input voltage and one of are connected in parallel and are connected in series as load, can be with
The parameter of input capacitance is reduced, so as to reduce circuit volume and improve reliability and service life, and improves lamp bead
Utilization rate, complete machine cost is reduced, improve efficiency.
Brief description of the drawings
By the description to the embodiment of the present invention referring to the drawings, above-mentioned and other purposes of the invention, feature and
Advantage will be apparent from.
Fig. 1 shows the schematic circuit of the LED drive circuit according to prior art；
Fig. 2 shows the schematic circuit of LED drive circuit according to a first embodiment of the present invention；
Fig. 3 shows the schematic circuit of linear constant current circuit in LED drive circuit according to a second embodiment of the present invention；
Fig. 4 shows the schematic circuit of linear constant current circuit in LED drive circuit according to a third embodiment of the present invention；
Fig. 5 shows the schematic circuit of linear constant current circuit in LED drive circuit according to a fourth embodiment of the present invention；
And
Fig. 6 shows the schematic circuit of linear constant current circuit in LED drive circuit according to a fifth embodiment of the present invention.
Embodiment
Various embodiments of the present invention are more fully described hereinafter with reference to accompanying drawing.In various figures, identical element
Represented using same or similar reference.For the sake of clarity, the various pieces in accompanying drawing are not necessarily to scale.
In this application, term " LED " is, for example, the LED string that multiple LED strip connection connections are formed.If multiple LED
LED string is formed, then previous LED negative electrode is connected to next LED anode in LED string.The anode of LED refers to
The anode of first LED in LED string, the negative electrode of LED refer to the negative electrode of last LED in LED string.
The present invention can be presented in a variety of manners, some of examples explained below.
Fig. 2 shows the schematic circuit of LED drive circuit according to a first embodiment of the present invention.As illustrated, LED drives
Dynamic circuit 200 includes ac current source 101, rectifier bridge 102, input capacitance Cin, diode D1, the and of linear constant current circuit 210
220.Rectifier bridge 102 is used for AC rectification into direct current.Input voltage is provided between two output ends of rectifier bridge 102
Vin.Input capacitance Cin carries out smothing filtering to input voltage vin.
LED 103 and linear constant current circuit 210 are connected in series between two output ends of rectifier bridge 102.Linear constant current
The first end of circuit 210 is connected with the hot end of rectifier bridge 102, and the second end is connected to the anode of LED 103.LED
103 minus earth.
LED 104 and linear constant current circuit 220 are connected in series between two output ends of rectifier bridge 102.LED 104
Anode be connected with the hot end of rectifier bridge 102, the first end of the negative electrode of LED 104 connection linear constant current circuit 220.
The second end ground connection of linear constant current circuit 220.
Different from the LED drive circuit of prior art, linear constant current circuit 210 also includes the 3rd end, via diode D1
It is connected with the negative electrode of LED 104.Linear constant current circuit 210 provides the first current path between first end and the second end and the
The 3rd current path between three ends and the second end.Linear constant current circuit 220 provides the second electricity between first end and the second end
Flow path.Diode D1 anode is connected to the negative electrode of LED 104, and negative electrode is connected to the 3rd end of linear constant current circuit 210,
So as to ensure the one-way flow of the 3rd current path.Below in conjunction with the embodiment described in Fig. 6, diode D1 anode voltage
V1 and cathode voltage V2 will lead on and off for path selecting module the 3rd current path of progress in linear constant current circuit 220
Open control.
When alternating voltage is relatively low, the input current difference two-way after rectification.The electric current that rectifier bridge 102 provides flows separately through
First current path and the second current path, the 3rd current path disconnect, LED 103 and the parallel operation of LED 104.First electricity
Stream is since the first output end of rectifier bridge 102, linear constant-current circuit 210, LED 103, returns again to the of rectifier bridge 102
Two output ends.Linear constant current circuit 210 controls the current value of the first electric current.First output end of second electric current from rectifier bridge 102
Start, through LED 104, linear constant current circuit 220, return again to the second output end of rectifier bridge 102.Linear constant current circuit 220 is controlled
Make the current value of the second electric current.Now diode disconnects, and does not have electric current to flow through in the 3rd current path.
When alternating voltage is higher, the input current after rectification is single channel.The electric current that rectifier bridge 102 provides flows through the 3rd electricity
Flow path, the first current path and the second current path disconnect, LED 103 and the tandem working of LED 104.3rd electric current is from whole
First output end of stream bridge 102 starts, and through LED 104, linear constant current circuit 210, LED 103, returns again to rectifier bridge 102
Second output end.Linear constant current circuit 210 controls the current value of the 3rd electric current.Now diode current flow, in the 3rd current path
Electric current flows through.
Linear constant current circuit 210 includes linear constant current module 110 and 120 and path selecting module 111.Linear constant current
Module 110 is located on the first current path, for controlling the current value of the first electric current.Linear constant current module 120 is positioned at the 3rd electricity
On flow path, for controlling the current value of the 3rd electric current.Linear constant current circuit 220 includes linear constant current module 130 and path
Selecting module 112.Linear constant current module 130 is located on the second current path, for controlling the current value of the second electric current.
Linear constant current module 110,120 and 130 is respectively used to realize the current constant control of the first to the 3rd current path.Path
Selecting module 111 and 112 is respectively used to enabled or disabled linear constant current module 120 and 130, so as to realize the first current path,
The selection of second current path and the 3rd current path, to change the connected mode of LED load.
Fig. 3 shows the schematic circuit of linear constant current circuit in LED drive circuit according to a second embodiment of the present invention.
Linear constant current circuit 210 is used for the selectivity conducting for providing one of the first current path and the 3rd current path.First electric current road
Footpath for linear constant current circuit 210 first end to the current path between the second end, the 3rd current path is linear constant current circuit
210 the 3rd end is to the current path between the second end.
Linear constant current circuit 210 includes power tube M1 and M3, amplifier 301 and 303 and current sampling resistor Rs1.Work(
Between rate pipe M1 and current sampling resistor Rs1 is connected in series between the first end and a second end, the first node of the two provides electric current and adopted
Sample signal.Power tube M3 is connected between the 3rd end and first node.Amplifier 301 is by current sampling signal and reference voltage
Vref1 is compared to produce drive signal, is the first electric current I1 so as to control the electric current flowed through in power tube M1, for example, the
One electric current I1 constant current value is Vref1/Rs1.Amplifier 303 by current sampling signal compared with reference voltage Vref 3 with
Drive signal is produced, is the 3rd electric current I3 so as to control the electric current flowed through in power tube M3, for example, the 3rd electric current I3 constant current value
For Vref3/Rs1.
In this embodiment, the electric current that the first current path in linear constant current circuit 210 and the 3rd current path share
Sampling resistor Rs1 is also used as path selecting module, for controlling power tube M1 to turn off so that linear constant current circuit 210 is used to carry
Turned on for the selectivity of one of the first current path and the 3rd current path.
When alternating voltage is relatively low, diode D1 disconnects, and power tube M3 does not have electric current to flow through.Now, power tube M1 is flowed through
Current value be limited to Vref1/Rs1.Therefore, the first current path turns on, and the 3rd current path disconnects.
When alternating voltage gradually rises, diode D1 conductings, power tube M3 has electric current to flow through.The electric current that power tube M1 flows through
The electric current that power tube M3 flows through is subtracted for Vref1/Rs1.Power tube M3 electric currents gradually increase, it is constant after current value be Vref3/
Rs1.Power tube M1 electric currents are gradually reduced, it is constant after current value be Vref1/Rs1-Vref3/Rs1.As long as ensure herein
Vref3 is more than Vref1, it is possible to and to ensure when power tube M3 electric currents is Vref3/Rs1, the electric current that power tube M1 flows through is 0,
So as to realize automatically shutting down for power tube M1.Therefore, the first current path disconnects, the conducting of the 3rd current path.
Fig. 4 shows the schematic circuit of linear constant current circuit in LED drive circuit according to a third embodiment of the present invention.
Linear constant current circuit 310 is used for the selectivity conducting for providing one of the first current path and the 3rd current path.First electric current road
Footpath for linear constant current circuit 310 first end to the current path between the second end, the 3rd current path is linear constant current circuit
310 the 3rd end is to the current path between the second end.
Linear constant current circuit 310 includes power tube M1 and M3, amplifier 301 and 303, feedback resistance R11, current sample electricity
Hinder Rs1 and Rs3 and amplification module 401.Power tube M1 and current sampling resistor Rs1 are connected in series in first end and the second end
Between, the first node of the two provides the first current sampling signal.Power tube M3 and current sampling resistor Rs3 is connected in series in
Between three ends and the second end, the 3rd node of the two provides the 3rd current sampling signal.
The inverting input of amplifier 301 receives control signal, and in-phase input end receives reference voltage Vref 1.Amplifier
301 by control signal compared with reference voltage Vref 1 to produce drive signal, so as to control the electricity flowed through in power tube M1
Flow for the first electric current I1, for example, the first electric current I1 constant current value is Vref1/Rs1.
The inverting input of amplifier 303 receives the 3rd current sampling signal, and in-phase input end receives reference voltage
Vref3.Amplifier 301 by the 3rd current sampling signal compared with reference voltage Vref 3 to produce drive signal, so as to control
The electric current flowed through in power tube M3 processed is the 3rd electric current I3, for example, the first electric current I3 constant current value is Vref3/Rs3.
The path selecting module of linear constant current circuit 310 includes amplification module 401 and feedback resistance R11.Feedback resistance R11
And amplification module 401 is connected in series between first node and the 3rd node.Between feedback resistance R11 and amplification module 401
Node provide control signal.The inverting input of amplifier 301 receives control signal.Therefore, amplification module 401 is electric by the 3rd
Sampled signal amplification is flowed, so as to obtain control signal K*Vref3/Rs3, wherein K is the amplification coefficient of amplification module 401.
When alternating voltage is relatively low, diode D1 disconnects, and power tube M3 does not have electric current to flow through.Now, power tube M1 is flowed through
Current value be limited to Vref1/Rs1.Therefore, the first current path turns on, and the 3rd current path disconnects.
When alternating voltage gradually rises, diode D1 conductings, power tube M3 has electric current to flow through.In this embodiment, amplify
The inverting input of device 301 receives control signal K*Vref3/Rs3, because control signal K*Vref3/Rs3 is not only greater than the
One current sampling signal, and it is more than reference voltage Vref 1, therefore drive signal controlling transistor M1 caused by amplifier 301
Disconnect.In alternate embodiments, control signal K*Vref3/Rs3 subtracts each other with reference voltage Vref 1, so as to reduce amplifier
The numerical value of the reference voltage of 301 in-phase input end, therefore drive signal controlling transistor M1 caused by amplifier 301 disconnects.
Fig. 5 shows the schematic circuit of linear constant current circuit in LED drive circuit according to a fourth embodiment of the present invention.
Linear constant current circuit 220 is used for the selectivity conducting for providing the second current path.Second current path is linear constant current circuit 220
First end to the second current path between the second end.
Linear constant current circuit 220 include power tube M2, amplifier 302, voltage comparator 321, divider resistance R31 and R32,
Feedback resistance 322 and current sampling resistor Rs2.Power tube M2 and current sampling resistor Rs2 is connected in series in first end and
Between two ends, the section point of the two provides current sampling signal.Power tube M2 is connected between first end and section point.Put
Big device 302 by current sampling signal compared with reference voltage Vref 2 to produce drive signal, so as to control in power tube M2
The electric current flowed through is the second electric current I2, for example, the second electric current I2 constant current value is Vref2/Rs2.Amplifier 302 is by current sample
Signal, to produce drive signal, is second so as to control the electric current flowed through in power tube M2 compared with reference voltage Vref 2
Electric current I2, for example, the second electric current I2 constant current value is Vref2/Rs2.
In this embodiment, the path selecting module in linear constant current circuit 220 includes voltage comparator 321, partial pressure electricity
Hinder R31 and R32, feedback resistance 322.Divider resistance R31 and R32 be connected in series in first end in linear constant current circuit 220 and
Between second end, the voltage (i.e. power tube M2 drain terminal voltage) of the negative electrode for obtaining LED 104.Due to transistor M2 works
Make in linear condition, the voltage of the negative electrode of LED 104 is corresponding with input voltage vin, and what divider resistance R31 and R32 were obtained adopts
Sample voltage is the voltage sampling signal of input voltage vin.
The first input end of voltage comparator 321 is connected to divider resistance R31 and R32 intermediate node, for being somebody's turn to do
Voltage sampling signal, the second input receive reference voltage Vref 4.The output end of voltage comparator 321 is connected to amplifier 302
Inverting input.Feedback resistance 322 is connected between the inverting input of section point and amplifier 302.Voltage comparator
321 output voltage is superimposed to the inverting input of amplifier 302 as control signal.When input voltage vin is more than or equal to ginseng
When examining the scheduled voltage of voltage Vref4 signs, the control signal reduces the electric current for flowing through power tube M2, until power tube M2 is closed
It is disconnected.When input voltage vin is less than the scheduled voltage that reference voltage Vref 4 characterizes, the control signal is 0, amplifier 302
Inverting input receives the second electric current I2 current feedback signal, realizes current constant control.
When alternating voltage is relatively low, power tube M2 electric currents are flowed through, and the current value for now flowing through power tube M1 is limited to
Vref2/Rs2。
When alternating voltage gradually rises, power tube M2 does not have electric current to flow through.Path selecting module realizes oneself of power tube M2
Dynamic shut-off.
Fig. 6 shows the schematic circuit of linear constant current circuit in LED drive circuit according to a fifth embodiment of the present invention.
Linear constant current circuit 320 is used for the selectivity conducting for providing the second current path.Second current path is linear constant current circuit 320
First end to the current path between the second end.
Linear constant current circuit 320 include power tube M2, amplifier 302, voltage comparator 321, divider resistance R31 and R32,
Divider resistance R33 and R34, feedback resistance 322 and current sampling resistor Rs2.Power tube M2 and current sampling resistor Rs2 strings
Between connection connection between the first end and a second end, the section point of the two provides current sampling signal.Power tube M2 is connected to first
Between end and section point.Amplifier 302 believes current sampling signal compared with reference voltage Vref 2 to produce driving
Number, it is the second electric current I2 so as to control the electric current flowed through in power tube M2, for example, the second electric current I2 constant current value is Vref2/
Rs2.Amplifier 302 by current sampling signal compared with reference voltage Vref 2 to produce drive signal, so as to control power
The electric current flowed through in pipe M2 is the second electric current I2, for example, the second electric current I2 constant current value is Vref2/Rs2.
In this embodiment, the path selecting module in linear constant current circuit 320 includes voltage comparator 321, partial pressure electricity
Hinder R31 and R32, divider resistance R33 and R34, feedback resistance 322.Diode D1 anode voltage V1 and cathode voltage V2 is used for
Path selecting module in linear constant current circuit 320 carries out the conducting of current path and disconnects control.Divider resistance R31 and R32
Between the first end being connected in series in linear constant current circuit 320 and the second end, for obtaining diode D1 anode voltage V1
(i.e. power tube M2 drain terminal voltage).Divider resistance R33 and R34 are connected in series in diode D1 negative electrode and linear constant current circuit
Between the second end in 320, for obtaining reference voltage Vref 4.Because transistor works in linear condition, power tube M2 is being led
The drain terminal voltage of logical state is corresponding with input voltage vin, and the sampled voltage that divider resistance R31 and R32 are obtained is input voltage
Vin voltage sampling signal.
The first input end of voltage comparator 321 is connected to divider resistance R31 and R32 node, for obtaining the voltage
Sampled signal, the second input receive reference voltage Vref 4.The output end of voltage comparator 321 is connected to the anti-of amplifier 302
Phase input.Feedback resistance 322 is connected between the inverting input of section point and amplifier 302.When input voltage vin is big
When the scheduled voltage characterized equal to reference voltage Vref 4, the output voltage of voltage comparator 321 is superimposed to amplifier 302
Inverting input, so as to reduce the electric current for flowing through power tube M2, until power tube M2 turn off.When input voltage vin is less than ginseng
When examining the scheduled voltage of voltage Vref4 signs, the output voltage of voltage comparator 321 is 0, the anti-phase input of amplifier 302
End receives the second electric current I2 current feedback signal, realizes current constant control.
When alternating voltage is relatively low, power tube M2 electric currents are flowed through, and the current value for now flowing through power tube M1 is limited to
Vref2/Rs2。
When alternating voltage gradually rises, power tube M2 does not have electric current to flow through.Path selecting module realizes oneself of power tube M2
Dynamic shut-off.
In this embodiment, linear constant current circuit 320 controls according to diode D1 anode voltage V1 and cathode voltage V2
The conducting and disconnection of current path.Switch the conducting with diode D1 due to the current path of linear constant current circuit 210 and 320
State is related, it is thereby achieved that the synchronism switching of linear constant current circuit 210 and 320, further improves LED drive circuit
Job stability.
LED drive circuit according to embodiments of the present invention, for driving the first LED and the second LED, including First Line
Property constant-current circuit and the second linear constant current circuit, wherein the first linear constant current circuit selects the first current path and the 3rd electric current road
One of footpath, the second linear constant current circuit selectively turn on the second current path so that first LED and described second
LED switches to according to input voltage one of to be connected in parallel and is connected in series, so as to reduce the parameter of input capacitance, so as to reduce
Circuit volume and raising reliability and service life.
For example above according to embodiments of the invention, these embodiments do not have all details of detailed descriptionthe, do not limit yet
The specific embodiment that the invention is only.Obviously, as described above, can make many modifications and variations.This specification is chosen simultaneously
These embodiments are specifically described, are in order to preferably explain the principle and practical application of the present invention, so that art
Technical staff can be used using modification of the invention and on the basis of the present invention well.Protection scope of the present invention should be with
The scope that the claims in the present invention are defined is defined.
Claims (23)
1. a kind of LED drive circuit, for driving the first LED and the second LED, including：
First linear constant current circuit, including be connected to the first end of feeder ear, be connected to the first LED anode the second end,
And it is connected to the 3rd end of the negative electrode of the second LED；And
Second linear constant current circuit, including the second end for being connected to the first end of the negative electrode of the second LED and being connected to the ground,
Wherein, the selection of the first linear constant current circuit one of first current path and the 3rd current path, first electric current
Path is located between first end and the second end of first linear constant current circuit, and the 3rd current path is located at described first
Between 3rd end of linear constant current circuit and the second end,
Second linear constant current circuit selectively turns on or disconnected the second current path, and second current path is located at institute
State between the first end of the second linear constant current circuit and the second end.
2. LED drive circuit according to claim 1, wherein, first linear constant current circuit and described second linear
Constant-current circuit selects current path according to the input voltage of the feeder ear respectively so that first LED and described second
LED switches to according to input voltage one of to be connected in parallel and is connected in series.
3. LED drive circuit according to claim 1, in addition to：Diode, its anode are connected to second LED
Negative electrode, its negative electrode is connected to the 3rd end of first linear constant current circuit.
4. LED drive circuit according to claim 3, wherein, first linear constant current circuit includes：
First linear constant-current control module, it is connected between first end and the second end of first linear constant current circuit, is used for
First current path is provided；
Third linear constant-current control module, it is connected between the 3rd end and the second end of first linear constant current circuit, is used for
3rd current path is provided；And
First path selecting module, it is connected with the described first linear constant-current control module and the 3rd constant-current control module,
For selecting current path,
Wherein, when the input voltage of the feeder ear is less than or equal to predetermined value, described in the first path selecting module disconnection
3rd current path, and conducting first current path,
When the input voltage of the feeder ear is more than predetermined value, the first path selecting module disconnects the first electric current road
Footpath, and conducting the 3rd current path.
5. LED drive circuit according to claim 4, wherein, second linear constant current circuit includes：
Second linear constant current control module, it is connected between first end and the second end of second linear constant current circuit, is used for
Second current path is provided；
Alternate path selecting module, it is connected with the second linear constant current control module, for selecting current path,
Wherein, when the input voltage of the feeder ear is less than or equal to predetermined value, described in the alternate path selecting module conducting
Second current path,
When the input voltage of the feeder ear is more than predetermined value, the alternate path selecting module disconnects the second electric current road
Footpath.
6. LED drive circuit according to claim 5, wherein, the first linear constant-current control module, second line
Property constant-current control module and the third linear constant-current control module include respectively：
Power tube, for controlling the current value of corresponding current path；And
Amplifier, for reference voltage to be compared to produce the drive signal of the power tube with current sampling signal.
7. LED drive circuit according to claim 6, wherein, first linear constant current circuit also includes：Current sample
Resistance, on the common path of first current path and the 3rd current path, the first path selecting module
For the current sampling resistor.
8. LED drive circuit according to claim 7, wherein, amplifier in the first linear constant-current control module
Reference voltage is less than the reference voltage of amplifier in the third linear constant-current control module.
9. LED drive circuit according to claim 6, wherein, first linear constant current circuit also includes：
Power tube in first current sampling resistor, with the described first linear constant-current control module is connected in series, between
First node provide the first current sampling signal；And
Power tube in 3rd current sampling resistor, with the third linear constant-current control module is connected in series, between
The 3rd node provide the 3rd current sampling signal,
Wherein, the amplified signal of the 3rd current sampling signal is superimposed upon the First Line by the first path selecting module
On the current sampling signal or reference voltage of property constant-current control module amplifier.
10. LED drive circuit according to claim 9, wherein, the first path selecting module includes：
The first feedback resistance and amplification module being connected in series between the first node and the 3rd node,
Wherein, the current sampling signal of the described first linear constant-current control module amplifier is derived from first feedback resistance and institute
State the fourth node between amplification module.
11. LED drive circuit according to claim 10, wherein when the 3rd current path turns on, the amplification
The amplified signal of 3rd current sampling signal is applied in the fourth node by module as control signal, the control
Signal is more than the reference voltage of amplifier in the described first linear constant-current control module, so as to disconnect first current path.
12. LED drive circuit according to claim 6, wherein, second linear constant current circuit also includes：
Power tube in second current sampling resistor, with the second linear constant current control module is connected in series, between
Section point provide the second current sampling signal,
Wherein, the alternate path selecting module produces control signal according to the voltage sampling signal of the input voltage, and
The control signal is superimposed upon on the current sampling signal or reference voltage of the second linear constant current control module amplifier.
13. LED drive circuit according to claim 12, wherein, the alternate path selecting module includes：
First divider resistance and the second divider resistance, it is connected in series in first end and the second end of second linear constant current circuit
Between, and the 5th node between first divider resistance and second divider resistance is provided for characterizing the input
The voltage feedback signal of voltage；
The voltage comparator and the second feedback resistance being connected in series between section point and the 5th node,
Wherein, in the second linear constant current control module the current sampling signal of amplifier be derived from second feedback resistance and
The 6th node between the voltage comparator,
The voltage comparator compares the voltage feedback signal to obtain control signal with reference voltage so that described
When the voltage sampling signal of input voltage is less than the reference voltage, the alternate path selecting module turns on second electric current
Path, when the voltage sampling signal of the input voltage is more than or equal to the reference voltage, the alternate path selecting module
Disconnect second current path.
14. LED drive circuit according to claim 13, wherein, the alternate path selecting module includes：
3rd divider resistance and the 4th divider resistance, it is connected in series in the negative electrode and second linear constant current electricity of the diode
Between second end on road,
Wherein, the 7th node between the 3rd divider resistance and the 4th divider resistance is provided for characterizing the diode
The voltage feedback signal of cathode voltage, as the reference voltage.
15. a kind of control method for LED drive circuit, for driving the first LED and the second LED, including：
When the input voltage of feeder ear is less than or equal to predetermined value, the first current path is used to provide for first LED
One electric current, and the second current path provide the second electric current for second LED so that first LED and described
Two LED parallel operations；And
When the input voltage of feeder ear is more than predetermined value, the 3rd current path is used as first LED and described second
LED provides the 3rd electric current so that the first LED and second LED are connected in series.
16. control method according to claim 15, wherein, set respectively on the first to the 3rd current path first to
Third linear constant-current control module, to control the current value of the first to the 3rd electric current respectively,
Wherein, first current path is described successively via the described first linear constant-current control module and first LED
Second current path is successively via second LED and the second linear constant current control module, the 3rd current path
Pass through successively due to second LED, the third linear constant-current control module and first LED.
17. control method according to claim 16, wherein, the described first to the 3rd constant-current control module is respectively by first
To the 3rd electric current current sampling signal compared with reference voltage, with control the first to the 3rd electric current current value.
18. control method according to claim 16, wherein, according to the input voltage of the feeder ear according to described first
To the respective conducting of third linear flow control module and off-state, so as to realize first LED and second LED
The switching for being connected in series and being connected in parallel.
19. control method according to claim 16, wherein, the first linear constant-current control module and the 3rd line
Property constant-current control module common current sampling resistor, and in the first linear constant-current control module amplifier reference voltage
Less than the reference voltage of amplifier in the third linear constant-current control module so that when the 3rd current path turns on,
First current path disconnects.
20. control method according to claim 16, wherein, the first linear constant-current control module and the 3rd line
Property constant-current control module obtains the first current sampling signal and the 3rd current sampling signal, the 3rd current sampling signal respectively
Amplified signal be superimposed upon on first current sampling signal or reference voltage.
21. control method according to claim 20, wherein, when the 3rd current path turns on, by the described 3rd
The amplified signal of current sampling signal is superimposed upon on first current sampling signal as control signal, and the control signal is big
In the reference voltage of the described first linear constant-current control module so that when the 3rd current path turns on, first electricity
Flow path disconnects.
22. control method according to claim 16, wherein, the second linear constant current control module obtains the second electric current
Sampled signal, control signal is produced according to the voltage sampling signal of the input voltage, and the control signal is superimposed upon
On second current sampling signal of the second linear constant current control module amplifier,
When the voltage sampling signal of the input voltage is less than the reference voltage, second current path is turned on, in institute
When stating the voltage sampling signal of input voltage and being more than or equal to the reference voltage, second current path is disconnected.
23. control method according to claim 22, in addition to：Diode, it is connected to second LED and described
Between three linear constant current control modules, and when the 3rd current path turns on, the diode current flow,
Wherein, the voltage sampling signal of the input voltage is derived from the anode of the diode, and the reference voltage is derived from described
The negative electrode of diode.
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Application publication date: 20180327 |