CN104519618A - LED driving circuit - Google Patents
LED driving circuit Download PDFInfo
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- CN104519618A CN104519618A CN201310460978.1A CN201310460978A CN104519618A CN 104519618 A CN104519618 A CN 104519618A CN 201310460978 A CN201310460978 A CN 201310460978A CN 104519618 A CN104519618 A CN 104519618A
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Abstract
The invention discloses an LED driving circuit which comprises a direct-current conversion unit, a control driving unit and a signal processing unit. The direct-current conversion unit is controlled by the control driving unit, the signal processing unit is connected with the control driving unit and comprises a first signal sampling unit, a second signal sampling unit, a division operational unit and a comparator, signals sampled by the first signal sampling unit are first signals, signals sampled by the second signal sampling unit are second signals, reference signals can be formed after the first signals and the second signals are subjected to division operation by the aid of the division operational unit, and the reference signals and inductive currents of the direct-current conversion unit are compared to one another by the aid of the comparator, so that control signals can be outputted and are inputted to the control driving unit, and the direct-current conversion unit can output constant currents under the control of the control signals.
Description
[technical field]
The present invention relates to a kind of LED drive circuit, especially a kind of constant current driver circuit for LED.
[background technology]
LED light source needs constant current to drive, to guarantee the consistency of light output under different input voltage and output voltage (being equivalent to different loads) situation, also can ensure that LED light source will drive the overheated light output that makes caused to decay because of overcurrent simultaneously, shorten lamp life.In prior art, the topology of constant-current drive circuit has isolated topology structure and non-isolated topology structure.Not in isolated topology, such as reduction voltage circuit and step-up/step-down circuit, due to LED load and switch drive not altogether, make output current sample very difficult; Although LED load and switch drive are common ground structures in booster circuit, conveniently can carry out the current feedback of LED load, but, the sampling of LED load electric current needs, at constant-current drive circuit output loop series connection sampling resistor, to increase the loss that sampling resistor can increase circuit, simultaneously, also need to increase electric current outer shroud to control, comprise a reference source and operational amplifier, set peak current with outputting inductance current peak reference signal, constant-current drive circuit is controlled very complicated.And in isolated topology, sampled output current needs to increase secondary current sampling A/D chip and respective chip power supply circuits, output current signal is by opto-coupled feedback to former limit control chip, and circuit structure is also very complicated and cost is high, is unfavorable for reducing driving power volume.Do not have a general signal processing circuit can be applicable to different topological realization output constant currents in prior art to control yet.
Therefore, in order to overcome above-mentioned defect, be necessary the constant current driver circuit for LED that a kind of improvement is provided.
[summary of the invention]
The object of the present invention is to provide a kind of constant current driver circuit for LED.
To achieve these goals, the present invention adopts following technical scheme: a kind of LED drive circuit, comprise DC converting unit, control the control driver element of described DC converting unit and connect the signal processing unit of described control driver element, the load of described DC converting unit output current driving LED, described DC converting unit has inductance, described signal processing unit comprises the first signal sampling unit, secondary signal sampling unit, divider and comparator, described first signal sampling unit sampling to signal be the first signal, the signal that described secondary signal sampling unit samples is secondary signal, described first signal and secondary signal form reference signal after divider, described reference signal is passed through comparing of comparator to export control signal with the inductive current of DC converting unit, described control signal inputs described control driver element thus controls described DC converting unit constant current output.
Preferably, described DC converting unit comprises reduction voltage circuit, and described first signal and described secondary signal are direct current signal.
Preferably, described first signal sampling unit comprises divider resistance, has divider resistance between described first signal sampling unit and described secondary signal sampling unit.
Preferably, described secondary signal sampling unit is sampled the input voltage signal of described LED drive circuit.
Preferably, described DC converting unit comprises booster circuit, and described first signal sampling unit gathers the output voltage of described LED drive circuit.
Preferably, described first signal sampling unit comprises divider resistance.
Preferably, described DC converting unit comprises step-up/step-down circuit, and described first signal sampling unit gathers the input and output voltage sum of described LED drive circuit.
Preferably, described first signal sampling unit comprises divider resistance.
Preferably, described LED drive circuit also comprises switch element, and described signal processing unit exports cut-off signals, and described cut-off signals controls the shutoff of described switch element.
Preferably, described switch element connects a sampling resistor, described sampling resistor one end connects described switch element, other end ground connection, the first input end of described comparator connects the output of divider, and the second input of described comparator connects between described sampling resistor and described switch element.
Compared to prior art, LED drive circuit of the present invention has following advantage: can realize constant current output by simple circuit, and can reduce the loss of circuit.
[accompanying drawing explanation]
Fig. 1 is the schematic diagram of LED drive circuit of the present invention.
Fig. 2 is the circuit diagram of the first preferred embodiment of LED drive circuit of the present invention.
Fig. 3 is the circuit diagram of the second preferred embodiment of LED drive circuit of the present invention.
Fig. 4 is the circuit diagram of the 3rd preferred embodiment of LED drive circuit of the present invention.
[embodiment]
Please refer to shown in Fig. 1, a kind of LED drive circuit of the present invention, comprise DC converting unit, control the control driver element of DC converting unit and the signal processing unit of connection control driver element, the load of DC converting unit output current driving LED, DC converting unit has inductance, signal processing unit comprises the first signal sampling unit, secondary signal sampling unit, divider and comparator, first signal sampling unit sampling to signal be the first signal, the signal that secondary signal sampling unit samples is secondary signal, first signal and secondary signal form reference signal after divider, reference signal is passed through comparing of comparator to export control signal with the inductive current of DC converting unit, control signal input control driver element thus control DC converting unit constant current output.The present invention carries out division arithmetic to the first signal and secondary signal, and obtain the ratio of the first signal and secondary signal as reference signal, this reference signal is connected to comparator as the reference value of inductive current peak.Another input of comparator is then inductive current peak sampling, the comparator upset when inductive current peak exceedes reference value, thus outputs control signals to control driver element, to control the shutoff of DC converting unit.In the present embodiment, division arithmetic is realized by logarithm operational amplifier, and division is converted into subtraction, in other embodiments, also in built-in chip type digital core, can pass through algorithm realization.Signal processing unit of the present invention, to the mode of signal transacting, makes the sample circuit of the first signal and secondary signal can be simpler.
Particularly, when DC converting unit is reduction voltage circuit, first signal and secondary signal are all direct current signal, when DC converting unit is booster circuit, voltage raising and reducing circuit etc. circuit, the input voltage signal of secondary signal sampling unit sampling LED drive circuit, first signal sampling unit to be sampled different signals according to different topologys, and secondary signal sampling unit comprises divider resistance.
Please refer to shown in Fig. 2, the LED drive circuit 1 of first embodiment of the invention comprises DC converting unit 10, controls the control driver element (non-label) of DC converting unit 10 and the signal processing unit 11 of connection control driver element, the load of DC converting unit 10 output current driving LED, DC converting unit 10 has inductance L.DC converting unit 10 comprises diode D, inductance L and output capacitance C.Signal processing unit 11 comprises the first signal sampling unit (non-label), secondary signal sampling unit (non-label), divider 110 and comparator 112.First signal sampling unit sampling to signal be the first signal A, the signal that secondary signal sampling unit samples is secondary signal B, first signal A and secondary signal B forms reference signal after divider 110, and reference signal is passed through comparing of comparator 112 to export control signal with the inductor current signal of DC converting unit 10.Control signal input control driver element, controls the shutoff of DC converting unit 10, thus controls DC converting unit 10 constant current output.
In first embodiment, DC converting unit 10 comprises reduction voltage circuit, and the first signal A and secondary signal B is direct current signal.Direct current signal can, from chip internal, as VCC or band gap reference, also can be the input voltage vin of DC converting unit 10, or output capacitance C negative terminal voltage.In the present embodiment, the first signal sampling unit comprises divider resistance R1, R2.Secondary signal B sampling unit comprises divider resistance R2.Between first signal A sampling unit and secondary signal B sampling unit, there is divider resistance R1.In the present embodiment, the first signal sampling unit also comprises divider resistance R0, and the input of the first signal A of divider 110 is connected between divider resistance R0 and divider resistance R1.Between first signal A and secondary signal B, there is voltage difference, and the first signal A divided by secondary signal be greater than 1 value.DC converting unit is in other embodiments of reduction voltage circuit, first signal A and secondary signal B can be identical direct current signal, namely divider resistance is not had between the first signal A and secondary signal B, also can the first signal A and secondary signal B transposition, namely secondary signal B is divided by the first signal A, obtains the value that is less than 1.
LED drive circuit 1 also comprises the switch element Q controlling the shutoff of DC converting unit 10 and conducting, and signal processing unit 11 also comprises sampling resistor Rs, in the present embodiment, and sampling resistor Rs one end connecting valve element Q, other end ground connection.The first input end (non-label) of comparator 112 connects reference signal, second input (non-label) is connected between sampling resistor Rs and switch element Q, make inductor current signal input the second input, thus control the inductive current peak of DC converting unit 10.In the present embodiment, the first input end of comparator 112 is the negative pole of comparator 112, and the second input is the positive pole of comparator 112, and the first signal A and secondary signal B is through divider, and the first signal A is divided by secondary signal B.In other embodiments, also the first input end of comparator 112 can be set to positive pole, the second input is set to negative pole, i.e. the positive pole of reference signal input comparator 112, the negative pole of inductor current signal input comparator 112.
In the present embodiment, input direct-current signal carries out dividing potential drop by resistance R0, R1 and R2, voltage signal between resistance R0 and R1 inputs divider 110 as the first signal A, voltage signal between resistance R1 and R2 inputs as secondary signal B, direct current signal can from chip internal, as VCC or band gap reference, also can be the input voltage vin of DC converting unit 10, or output capacitance C negative terminal voltage.The ratio value expression of the first signal A and secondary signal B is A/B=(R1+R2)/R2.Have nothing to do from the ratio of the known first signal A and secondary signal B of this expression formula and direct current biasing, also have nothing to do with resistance R0, when resistance R1 is not equal to zero, this ratio can be greater than one, if the input of the first signal A and secondary signal B is exchanged, then can obtain the ratio being less than one.The ratio of the first signal A and secondary signal B is reference signal, and this reference signal is as the reference of inductive current peak.Inductive current peak feedback is then obtained by sampling resistor Rs, and when inductive circuit peak value exceedes the value of reference signal, comparator 112 overturns, and switch element Q disconnects.Visible, inductive current peak is controlled in a fixed value, this fixed value and input voltage vin, output voltage Vo do not have functional relation, to the reduction voltage circuit be operated under critical current pattern, fixing inductive current peak means fixing output current, and output current is the half of inductive current peak.The expression formula of output current Io is Io=(R1+R2)/(2*R2*Rs).The LED drive circuit 1 of the present embodiment, it doesn't matter for the size of output current Io and input voltage vin and output voltage Vo, and only relevant with the ratio of resistance R1, R2, Rs, therefore, as long as arrange the first signal A, secondary signal B and sampling resistor Rs as required, constant current output can be realized.The sample circuit of the present invention first signal A and secondary signal B is very simple, and the process through signal processing unit 11 can be good at controlling DC converting unit 10 constant current output.
Please refer to shown in Fig. 3, the LED drive circuit 2 of second embodiment of the invention comprises DC converting unit 20, controls the control driver element (non-label) of DC converting unit 20 and the signal processing unit 21 of connection control driver element, the load of DC converting unit 20 output current driving LED, DC converting unit 20 has inductance L.DC converting unit 20 comprises diode D, inductance L and output capacitance C.Signal processing unit 21 comprises the first signal sampling unit (non-label), secondary signal sampling unit (non-label), divider 210 and comparator 212.First signal sampling unit sampling to signal be the first signal A, the signal that secondary signal sampling unit samples is secondary signal B, first signal A and secondary signal B forms reference signal after divider 210, and reference signal is passed through comparing of comparator 212 to export control signal with the inductor current signal of DC converting unit 20.Control signal input control driver element, controls the shutoff of DC converting unit 20, thus controls DC converting unit 20 constant current output.
DC converting unit 20 is booster circuit, and the first signal sampling unit gathers the output voltage signal of LED drive circuit 2.Secondary signal sampling unit gathers the input voltage signal of LED drive circuit 2.One end of first signal sampling unit is in parallel with output capacitance C, and the other end connects the first signal input part of divider 210.First signal sampling unit comprises divider resistance R3 and divider resistance R4.First signal input part of divider 210 is connected between divider resistance R3 and divider resistance R4.Secondary signal sampling unit one end connects the input of LED drive circuit 2 with sampled input voltage Vin, and the other end connects the secondary signal input of divider 210.Namely the first signal A is the output voltage signal of DC converting unit 20, and secondary signal B is the input voltage signal of LED drive circuit 2.
LED drive circuit 2 also comprises the switch element Q controlling the shutoff of DC converting unit 20 and conducting, and signal processing unit 21 also comprises sampling resistor Rs, in the present embodiment, and sampling resistor Rs one end connecting valve element Q, other end ground connection.The first input end (non-label) of comparator 212 connects reference signal, second input (non-label) is connected between sampling resistor Rs and switch element Q, make inductor current signal input the second input, thus control the inductive current peak of DC converting unit 20.In the present embodiment, the first input end of comparator 212 is the negative pole of comparator 212, and the second input is the positive pole of comparator 212, and the first signal A and secondary signal B is through divider, and the first signal A is divided by secondary signal B.In other embodiments, also the first input end of comparator 212 can be set to positive pole, the second input is set to negative pole, i.e. the positive pole of reference signal input comparator 212, the negative pole of inductor current signal input comparator 212.
In the present embodiment, input voltage vin feeds back to secondary signal B input through resistance R1 and R2 dividing potential drop, output voltage Vo feeds back to the first signal A input through resistance R3 and R4, and the ratio value expression of such first signal A and secondary signal B is A/B=Vo* [R3/ (R3+R4)]/Vin* [R2/ (R1+R2)]=K* (Vo/Vin).Wherein K is design parameter.The ratio of the first signal A and secondary signal B and input voltage vin and output voltage Vo have relation, and when input voltage vin becomes large or output voltage Vo diminishes, this ratio can diminish, corresponding minimizing inductive current peak, otherwise, then increase inductive current peak.Output current Io expression formula is then Io=current peak/2* (Vin/Vo)=K/ (2*Rs).Can find out, the control signal through signal processing unit 21 controls DC converting unit 20, makes output current Io be a steady state value, only relevant with design parameter K and sampling resistor Rs, not by the impact that input voltage vin and output voltage Vo change.And the sampling of the first signal A and secondary signal B is very simple and convenient.
Please refer to shown in Fig. 4, the LED drive circuit 3 of third embodiment of the invention comprises DC converting unit 30, controls the control driver element (non-label) of DC converting unit 30 and the signal processing unit 31 of connection control driver element, the load of DC converting unit 30 output current driving LED, DC converting unit 30 has inductance L.DC converting unit 30 comprises diode D, inductance L and output capacitance C.Signal processing unit 31 comprises the first signal sampling unit (non-label), secondary signal sampling unit (non-label), divider 310 and comparator 312.First signal sampling unit sampling to signal be the first signal A, the signal that secondary signal sampling unit samples is secondary signal B, first signal A and secondary signal B forms reference signal after divider 310, and reference signal is passed through comparing of comparator 312 to export control signal with the inductor current signal of DC converting unit 30.Control signal input control driver element, controls the shutoff of DC converting unit 30, thus controls DC converting unit 30 constant current output.
DC converting unit 30 is step-up/step-down circuit, and the first signal sampling unit gathers input voltage vin and the output voltage Vo sum of LED drive circuit 3.Secondary signal sampling unit gathers the input voltage signal of LED drive circuit 3.
LED drive circuit 3 comprises the switch element Q controlling the disconnected and conducting of DC converting unit 30, and signal processing unit 31 also comprises sampling resistor Rs, in the present embodiment, and sampling resistor Rs one end connecting valve element Q, one end ground connection.The DC converting unit 30 of step-up/step-down circuit, its inductance L and output capacitance C are connected in parallel, and connect diode D between inductance L and output capacitance C.Diode D one end connects output capacitance C, other end connecting valve element Q.Inductance L one end connects output capacitance C, other end connecting valve element Q.
First signal sampling unit gathers input voltage vin and the output voltage Vo sum of LED drive circuit 3, and therefore first signal sampling unit one end is connected between diode D and output capacitance C, and the other end connects the first signal input part of divider 310.First signal sampling unit comprises divider resistance R3 and divider resistance R4.First signal input part of divider 310 is connected between divider resistance R3 and divider resistance R4.Secondary signal sampling unit one end connects the input of LED drive circuit 2 with sampled input voltage Vin, and the other end connects the secondary signal input of divider 310.Namely the first signal A is input and output voltage and the signal of LED drive circuit 3, and secondary signal B is the input voltage signal of LED drive circuit 3.
The first input end (non-label) of comparator 312 connects reference signal, second input (non-label) is connected between sampling resistor Rs and switch element Q, make inductor current signal input the second input, thus control the inductive current peak of DC converting unit 30.In the present embodiment, the first input end of comparator 312 is the negative pole of comparator 312, and the second input is the positive pole of comparator 312, and the first signal A and secondary signal B is through divider, and the first signal A is divided by secondary signal B.In other embodiments, also the first input end of comparator 312 can be set to positive pole, the second input is set to negative pole, i.e. the positive pole of reference signal input comparator 312, the negative pole of inductor current signal input comparator 312.
In the present embodiment, input voltage vin carries out dividing potential drop by resistance R1 and R2, and as secondary signal B input, the first signal A is then from the positive terminal voltage of output capacitance C, and this voltage equals input voltage vin and output voltage Vo sum (Vin+Vo).Input voltage vin and output voltage Vo sum are connected to the first signal input part by resistance R3 and R4 dividing potential drop, thus input divider 310.Now the ratio value expression of the first signal A and secondary signal B is A/B=[(Vin+Vo) * R3/ (R3+R4)]/[Vin*R2/ (R1+R2)]=K* [(Vin+Vo)/Vin].Wherein K is design parameter, K=[R3* (R1+R2)]/[R2* (R3+R4)].The ratio of the first signal A and secondary signal B is not fixed value, but has relation with input voltage vin and output voltage Vo, and inductive current peak is then followed this ratio and adjusted.Under the control, output current Io expression formula is Io=[current peak/2] * [Vin/ (Vin+Vo)]=K/ (2*Rs).Can find out, output current Io is also a steady state value, only relevant with design parameter K and sampling resistor Rs, not by the impact that input voltage vin and output voltage Vo change.And the sampling of the first signal A and secondary signal B is very simple and convenient.
Claims (10)
1. a LED drive circuit, comprise DC converting unit, control the control driver element of described DC converting unit and connect the signal processing unit of described control driver element, the load of described DC converting unit output current driving LED, described DC converting unit has inductance, described signal processing unit comprises the first signal sampling unit, secondary signal sampling unit, divider and comparator, described first signal sampling unit sampling to signal be the first signal, the signal that described secondary signal sampling unit samples is secondary signal, described first signal and secondary signal form reference signal after divider, described reference signal is passed through comparing of comparator to export control signal with the inductive current of DC converting unit, described control signal inputs described control driver element thus controls described DC converting unit constant current output.
2. LED drive circuit as claimed in claim 1, it is characterized in that, described DC converting unit comprises reduction voltage circuit, and described first signal and described secondary signal are direct current signal.
3. LED drive circuit as claimed in claim 2, it is characterized in that, described first signal sampling unit comprises divider resistance, has divider resistance between described first signal sampling unit and described secondary signal sampling unit.
4. LED drive circuit as claimed in claim 1, is characterized in that, described secondary signal sampling unit is sampled the input voltage signal of described LED drive circuit.
5. LED drive circuit as claimed in claim 4, it is characterized in that, described DC converting unit comprises booster circuit, and described first signal sampling unit gathers the output voltage of described LED drive circuit.
6. LED drive circuit as claimed in claim 5, it is characterized in that, described first signal sampling unit comprises divider resistance.
7. LED drive circuit as claimed in claim 4, it is characterized in that, described DC converting unit comprises step-up/step-down circuit, and described first signal sampling unit gathers the input and output voltage sum of described LED drive circuit.
8. LED drive circuit as claimed in claim 7, it is characterized in that, described first signal sampling unit comprises divider resistance.
9. LED drive circuit as claimed in claim 1, it is characterized in that, described LED drive circuit also comprises switch element, and described signal processing unit exports cut-off signals, and described cut-off signals controls the shutoff of described switch element.
10. LED drive circuit as claimed in claim 1, it is characterized in that, described switch element connects a sampling resistor, described sampling resistor one end connects described switch element, other end ground connection, the first input end of described comparator connects the output of divider, and the second input of described comparator connects between described sampling resistor and described switch element.
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| CN201310460978.1A CN104519618B (en) | 2013-09-29 | 2013-09-29 | A kind of LED drive circuit |
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| CN201310460978.1A CN104519618B (en) | 2013-09-29 | 2013-09-29 | A kind of LED drive circuit |
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| CN104519618A true CN104519618A (en) | 2015-04-15 |
| CN104519618B CN104519618B (en) | 2017-11-07 |
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN106612579A (en) * | 2015-10-21 | 2017-05-03 | 晶豪科技股份有限公司 | A light emitting diode driving module and a light emitting diode module |
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