CN102740540A - Light emitting diode driving system - Google Patents

Abstract

Disclosed is a light emitting diode (LED) driving system which is used for converting a voltage provided by an input power into a voltage which is suitable for driving an LED array to work, wherein the LED array comprises a plurality of LED strings connected in parallel. The LED driving system comprises a converter, a pulse width modulation controller, a plurality of switch elements, a plurality of sensing resistors, and a current balance controller, wherein the converter is connected to a power supply and positive electrodes of the LED strings, the pulse width modulation controller is connected to the converter, first electrodes of the plurality of the switch elements are correspondingly connected to negative electrodes of the LED strings in a one-to-one manner and third electrodes of the plurality of the switch elements are all connected to the pulse width modulation controller, one ends of the plurality of the sensing resistors are correspondingly connected to the third electrodes of the plurality of the switch elements in a one-to-one manner and the other ends are all grounded, and the current balance controller is used for respectively controlling the size of breakover periods of the plurality of the switch elements according to voltages of the sensing resistors so as to enable current on the plurality of the LED strings in parallel to flow uniformly. The LED driving system of the invention enables the current on each LED string to flow uniformly, and power loss of each LED string is small.

Description

LED drive system

Technical field

The present invention relates to a kind of LED drive system, relate in particular to a kind of LED drive system that comprises current balance controller.

Background technology

(light emitting diode LED) is applied to because of the power and energy saving is increasing in the illumination light-emitting diode.To the application of LED, need uniform light source, therefore need in the LED drive system, add current balance controller, with improve because of the LED different characteristic cause under identical direct voltage drive, the different situation of each string LED electric current.Usually, current balance controller adopts current-limiting resistance or linear adjustment circuit to control the electric current of LED, but current balance controller self can produce bigger power consumption like this.

Summary of the invention

In view of this, a kind of LED drive system need be provided, it can make the electric current current-sharing on every string LED, and the power loss of every string LED is little.

A kind of LED drive system; The voltage transitions that being used for importing power supply provides is the voltage that is fit to the work of driven for emitting lights diode array; Said light emitting diode matrix comprises the light emitting diode string of a plurality of parallel connections, and said LED drive system comprises transducer, Pwm controller, a plurality of switch element, a plurality of detecting resistance and current balance controller.Said transducer connects the anode of said input power supply and said light emitting diode string, is used for voltage transitions that said input power supply is provided, and is luminous to drive said light emitting diode string.Said Pwm controller links to each other with said transducer, is used to control said transducer.Said a plurality of switch element comprises first electrode, second electrode and third electrode respectively, and said first electrode is corresponding one by one continuous with the negative electrode of said light emitting diode string, and third electrode all links to each other with said Pwm controller.One end of said a plurality of detecting resistance links to each other the equal ground connection of the other end with the third electrode of said a plurality of switch elements is corresponding one by one.Said current balance controller all links to each other with second electrode, the third electrode of said a plurality of switch elements; And link to each other with reference voltage source; Be used for controlling respectively the turn-on cycle size of said a plurality of switch elements, thereby make the electric current current-sharing of the light emitting diode string of said a plurality of parallel connections according to the voltage of said detecting resistance.Said current balance controller comprises sampler, a plurality of divider and a plurality of comparator.The input of said sampler all links to each other with the third electrode of said a plurality of switch elements, and the minimum voltage value that said sampler is used for taking out the third electrode of said a plurality of switch elements is worth as a reference.One input of said a plurality of dividers links to each other with the third electrode of said a plurality of switch elements is corresponding one by one; Another input all receives said reference value; The voltage that is respectively applied for the third electrode that makes said reference value and said a plurality of switch elements is divided by one by one, and output ratio.The positive input of a plurality of comparators links to each other with the output of said divider is corresponding one by one; Negative input links to each other with reference voltage source respectively; The output of said a plurality of comparators is corresponding one by one continuous with second electrode of said a plurality of switch elements; More said respectively ratio of said comparator and said reference voltage source, output high level signal or low level signal, the turn-on cycle of controlling said a plurality of switch elements is big or small.

Preferably, said current balance controller also comprises a plurality of multipliers.Said a plurality of multiplier connects one to one between the positive input of the output of said divider and said comparator; And all link to each other with said external dimmer signal, input to the positive input of said comparator after being used for the ratio of said a plurality of dividers output and said external dimmer signal multiplied each other respectively.

Preferably, said reference voltage source is a sawtooth waveforms.

Preferably; Said a plurality of switch element is N type metal oxide semiconductor FET; Said first electrode is the drain electrode of N type metal oxide semiconductor FET; Said second electrode is the grid of N type metal oxide semiconductor FET, and said third electrode is the source electrode of N type metal oxide semiconductor FET.

Above-mentioned LED drive system is according to the size of the said a plurality of switch element duty ratios of voltage control of an end of said detecting resistance, thereby makes the electric current current-sharing on the LED string of said a plurality of parallel connections, and the power loss of every string LED is little.

Description of drawings

Fig. 1 is the module map of LED drive system in an embodiment of the present invention.

Fig. 2 is the circuit diagram of the current balance controller of LED drive system in the first embodiment of the invention.

Fig. 3 is the circuit diagram of the current balance controller of LED drive system in the second embodiment of the invention.

The main element symbol description

LED drive system 10

Input power supply Vin

Ledarray 20

Transducer 110

Current balance controller 111a, 111b

Pwm controller 112

Switch element Q1, Q2

Detecting resistance R 1, R2

Reference voltage source Va

Comparator U1, U2

Reference value Vs

Multiplier S1, S2

Divider M1, M2

Dividing potential drop V1, the V2 of detecting resistance

External dimmer signal PDIM

A plurality of switch element Q

A plurality of detecting resistance R

Sampler P

Following embodiment will combine above-mentioned accompanying drawing to further specify the present invention.

Embodiment

Fig. 1 is that (Light Emitting Diode, the voltage transitions that the LED) module map ofdrive system 10,LED drive system 10 are used for input power supply Vin is provided is for being fit to the voltage that drivingLED array 20 is done for light-emitting diode in an embodiment of the presentinvention.Led array 20 comprises the LED string of a plurality of parallel connections in this execution mode, and each LED string forward is composed in series by a plurality of LED, and the anode of LED string is meant the anode of first LED of LED string, and the negative electrode of led array is meant the negative electrode of last LED of LED string.LED drive system 10 comprisestransducer 110,Pwm controller 112, a plurality of switch element Q, a plurality of detecting resistance R and current balance controller 111.In this execution mode, the quantity of switch element and detecting resistance is corresponding with the quantity of the LED string of parallel connection.For example the quantity of the LED shown in Fig. 1 string is two, so corresponding switch element is two, i.e. and switch element Q1 and Q2, what detect resistance also is two, i.e. resistance R 1 and R2.Transducer 110 connects input power supply Vin, is used for importing the voltage transitions that power supply Vin provides, and is luminous with driving LED array 20.Pwm controller 112 links to each other withtransducer 110, is used to produce pulse width modulating signalcontrol transformation device 110.

Switch element Q1 and Q2 comprise first electrode, second electrode and third electrode respectively; First electrode of switch element Q1 and Q2 is corresponding one by one continuous with the negative electrode of corresponding LED string; Be the negative electrode that switch element Q1 connects first LED string, switch element Q2 connects the negative electrode of second LED string.The third electrode of switch element Q1 and Q2 all links to each other with Pwm controller 112.Switch element Q1 and Q2 are equivalent to switch, and are not used for regulating the electric current of corresponding LED string.The end of detecting resistance R 1 and R2 links to each other with the third electrode of switch element Q1 and Q2 is corresponding one by one, and the equal ground connection of the other end is used to detect the electric current of corresponding LED string and converts current signal into voltagesignal.Pwm controller 112 connects detecting resistance R 1 and R2, also is used for the electric current according to the LED string of the correspondence of detecting resistance R 1 and R2 detecting, the duty ratio of adjustment pulse width modulating signal, thereby the voltage thatadjustment transducer 110 is exported.Current balance controller 111 all links to each other with second electrode, the third electrode of switch element Q1 and Q2; And Va links to each other with reference voltage source; Be used for turn-on cycle size, thereby make the electric current current-sharing on the LED string of said a plurality of parallel connections according to said switch element Q1 of branch pressure-controlled and the Q2 of detecting resistance R 1 and R2.

In this execution mode; The voltage of the end of detecting resistance R 1 and R2 is through adjusting back and reference voltage source Va relatively;Current balance controller 111 can be exported high level or low level; The turn-on cycle of control corresponding switch element Q1 and Q2 is big or small, and then controls the size of every string LED electric current, realizes the electric current current-sharing of the LED string of said a plurality of parallel connections.It is wide that switch element Q1 and Q2 only are used for ending through conducting the ripple of the electric current of adjusting LED string, thereby the power loss of LED string is little.

Fig. 2 circuit diagram of a kind ofexecution mode 111a of current balance controller in theLED drive system 10 of having explained in detail in the first embodiment of the invention.In this execution mode,current balance controller 111a comprises sampler P, a plurality of divider M1, M2...... and a plurality of comparator U1, U2.......In this execution mode, the quantity of divider and comparator is also corresponding with the quantity that the LED of parallel connection goes here and there.Because of the quantity of LED string among Fig. 1 is two, so two divider M1 and M2 and two comparator U1 and U2 only are shown in Fig. 2.The input of sampler P all links to each other with the third electrode of switch element Q1 and Q2, and sampler P is used to take out the minimum voltage value of the third electrode of switch element Q1 and Q2, and output minimum voltage value is worth Vs as a reference.The input of divider M1 and M2 links to each other with the third electrode of switch element Q1 and Q2 is corresponding one by one; Another input all receives reference value Vs; Be used to make the voltage of the third electrode of reference value Vs and switch element Q1 and Q2 to be divided by one by one, and export the value after said being divided by.The positive input of comparator U1 and U2 is corresponding one by one continuous with the output of divider M1 and M2, and negative input links to each other with reference voltage source Va respectively, and the output of comparator U1 and U2 is corresponding one by one continuous with second electrode of switch element Q1 and Q2.Comparator U1 and U2 compare value and the reference voltage source Va that said divider M1 and M2 are exported respectively, and with definite output high level or low level signal, thereby the turn-on cycle of control switch element Q1 and Q2 is big or small.

In this execution mode, reference voltage source Va is a sawtooth waveforms.Switch element Q1 and Q2 are N type metal oxide semiconductor FET; Said first electrode is the drain electrode of N type metal oxide semiconductor FET; Said second electrode is the grid of N type metal oxide semiconductor FET, and said third electrode is the source electrode of N type metal oxide semiconductor FET.

In this execution mode; Reference value Vs is the minimum value among dividing potential drop V1 that detects resistance R 1 and the dividing potential drop V2 that detectsresistance R 2; And the maximum of the voltage of reference voltage source Va is greater than reference value Vs, and the minimum value of the voltage of reference voltage source Va is less than reference value Vs.When the detecting resistance R 1 dividing potential drop V1 greater than the detectingresistance R 2 dividing potential drop V2 the time; During electric current that the electric current of the LED that promptly links to each other with switch element Q1 string is gone here and there greater than the LED that links to each other with switch element Q2, then the voltage of the output of divider M1 is less than the voltage of divider M2 output.Again because at the voltage of reference voltage source Va during less than the voltage of divider M1 and M2 output; Comparator U1 and U2 just can export high level; Switch element Q1 and Q2 just understand conducting; So the duty ratio of the signal that the grid of switch element Q1 receives is less than the duty ratio of the signal of switch element Q2 grid reception, promptly the turn-on cycle of switch element Q1 is less than the turn-on cycle of switch element Q2.Thereby the ripple of the wide electric current less than the LED string that links to each other with switch element Q2 of the ripple of the electric current of the LED that links to each other with switch element Q1 string is wide, thereby makes the electric current current-sharing on the LED string of switch element Q1 and switch element Q2 correspondence.

For example, when the dividing potential drop V1 of detecting resistance R 1 equals 0.8V, the dividing potential drop V2 of detectingresistance R 2 is when equaling 0.4V, and reference value Vs is the smaller value among the dividing potential drop V2 of the dividing potential drop V1 of detecting resistance R 1 and detectingresistance R 2, and promptly reference value Vs equals 0.4V.Like this, the value of divider M1 output is that 0.4V/0.8V is 0.5, and the value of divider M2 output is that 0.4V/0.4V is 1.Because when the value that the voltage of reference voltage source Va is exported less than divider M1 and M2, comparator U1 and U2 just can export high level, switch element Q1 and Q2 just understand conducting again.So when the voltage of reference voltage source Va during less than 0.5V, comparator U1 and U2 all can export high level, the equal conducting of switch element Q1 and Q2; When the voltage of reference voltage source Va during greater than 0.5V and less than 1V, comparator U1 output low level and comparator U2 output high level, switch element Q1 by and switch element Q2 conducting.Like this; The turn-on cycle of switch element Q1 is less than the turn-on cycle of switch element Q2; The ripple of the wide electric current less than the LED string that links to each other with switch element Q2 of the ripple of the electric current of the LED that links to each other with switch element Q1 string is wide, thereby realizes the electric current current-sharing on the LED string of switch element Q1 and switch element Q2 correspondence.

Fig. 3 circuit diagram ofcurrent balance controller 111b in theLED drive system 10 of having explained in detail in the second embodiment of the invention.Current balance controller 111b in this execution mode and the circuit ofcurrent balance controller 111a shown in Figure 2 are basic identical, and difference is thatcurrent balance controller 111b also comprises a plurality of multiplier S1 and S2.Multiplier S1 and S2 connect one to one between the positive input of the output of divider M1 and M2 and comparator U1 and U2, and all link to each other with external dimmer signal PDIM.After being used for the ratio of the output of divider M1 and M2 and external dimmer signal PDIM multiplied each other respectively, said multiplier S1 and S2 input to the positive input of comparator U1 and U2.

Electric current current-sharing on the wide LED of the making string of ripple of the electric current that the circuit working principle of this execution mode and the difference of first execution mode are to utilize external dimmer signal PDIM to combine said LED string has increased the wide adjustability of ripple of the electric current that said LED goes here and there.Outside dim signal PDIM is a square wave in this execution mode.

Above-mentionedLED drive system 10 is according to the turn-on cycle size of voltage (V1 and V2 only are shown in the drawings) a plurality of switch element Q of control (Q1 and Q2 only are shown in the drawings) of a plurality of detecting resistance R (R1 and R2 only are shown in the drawings); Thereby make the electric current current-sharing on the LED string of a plurality of parallel connections, and the power loss of every string LED is little.

Claims (4)

1. LED drive system; The voltage transitions that being used for importing power supply provides is the voltage that is fit to the work of driven for emitting lights diode array; Said light emitting diode matrix comprises the light emitting diode string of a plurality of parallel connections, it is characterized in that, said LED drive system comprises:

Transducer connects the anode of said input power supply and said light emitting diode string, is used for voltage transitions that said input power supply is provided, and is luminous to drive said light emitting diode string;

Pwm controller links to each other with said transducer, is used to control said transducer;

A plurality of switch elements comprise first electrode, second electrode and third electrode respectively, and said first electrode is corresponding one by one continuous with the negative electrode of said light emitting diode string, and third electrode all links to each other with said Pwm controller;

A plurality of detecting resistance, an end is corresponding one by one continuous with the third electrode of said a plurality of switch elements, the equal ground connection of the other end; And

Current balance controller; All link to each other with second electrode, the third electrode of said a plurality of switch elements; And link to each other with reference voltage source; Be used for controlling respectively according to the voltage of said detecting resistance the turn-on cycle size of said a plurality of switch elements, thereby make the electric current current-sharing of the light emitting diode string of said a plurality of parallel connections, said current balance controller comprises:

Sampler, the input of said sampler all links to each other with the third electrode of said a plurality of switch elements, and the minimum voltage value that said sampler is used for taking out the third electrode of said a plurality of switch elements is worth as a reference;

A plurality of dividers; One input of said a plurality of dividers links to each other with the third electrode of said a plurality of switch elements is corresponding one by one; Another input all receives said reference value; Said a plurality of divider is used to make the voltage of the third electrode of said reference value and said a plurality of switch elements to be divided by one by one, and output ratio; And

A plurality of comparators; Positive input is corresponding one by one continuous with the output of said divider; Negative input links to each other with reference voltage source respectively, and the output of said a plurality of comparators is corresponding one by one continuous with second electrode of said a plurality of switch elements, more said respectively ratio of said comparator and said reference voltage source; Output high level signal or low level signal, the turn-on cycle of controlling said a plurality of switch elements is big or small.

2. LED drive system as claimed in claim 1 is characterized in that, said current balance controller also comprises:

A plurality of multipliers; Connect one to one between the positive input of the output of said divider and said comparator; And all link to each other with said external dimmer signal, input to the positive input of said comparator after being used for the ratio of said a plurality of dividers output and said external dimmer signal multiplied each other respectively.

3. according to claim 1 or claim 2 LED drive system is characterized in that said reference voltage source is a sawtooth waveforms.

4. according to claim 1 or claim 2 LED drive system; It is characterized in that; Said a plurality of switch element is N type metal oxide semiconductor FET; Said first electrode is the drain electrode of N type metal oxide semiconductor FET, and said second electrode is the grid of N type metal oxide semiconductor FET, and said third electrode is the source electrode of N type metal oxide semiconductor FET.

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