CN101489335A - LED driving circuit and secondary side controller thereof - Google Patents
LED driving circuit and secondary side controller thereof Download PDFInfo
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- CN101489335A CN101489335A CNA2008100011778A CN200810001177A CN101489335A CN 101489335 A CN101489335 A CN 101489335A CN A2008100011778 A CNA2008100011778 A CN A2008100011778A CN 200810001177 A CN200810001177 A CN 200810001177A CN 101489335 A CN101489335 A CN 101489335A
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Abstract
A light emitting diode driving circuit of the invention and a secondary side controller control the output voltage to a first driving voltage or a second driving voltage. When the output voltage is in the first driving voltage, the light emitting diode module can be in a stable light emitting state. When the output voltage is in the second driving voltage, the output voltage is approximately in the threshold voltage (larger than zero voltage) of light emitting diode module so that the light emitting diode module hardly radiates. Thus the variation of voltage applied to the light emitting diode module is less than the present voltage variation in light modulation process, thereby avoiding the problem of overlarge voltage stress or inaccurate light modulation control of light emitting diode in prior art.
Description
Technical field
The present invention relates to a kind of LED driving circuit and secondary side controller thereof of tool dimming function, especially finger is a kind of in the light modulation process, light emitting diode driving voltage can be controlled in the LED driving circuit and the secondary side controller thereof of one first driving voltage and one second driving voltage.
Background technology
As shown in Figure 1, be existing buck (Buck) LED driving circuit.When transistor switch Q2 conducting (TURN ON), power supply V4 provides electric current to flow through transistor switch Q2 to inductance L 1, capacitor C 4 charging energy storage and provide energy to make it luminous to light-emitting diode D2, D5 simultaneously.Being released energy by inductance L 1, capacitor C 4 when transistor switch Q2 closes (TURN OFF) makes light-emitting diode D2, D5 lasting luminous again.The electric current of light-emitting diode D2, D5 of flowing through can produce voltage drop and produce a current detection signal at resistance R 7 two ends.The negative input end of error amplifier U4 receives this current detection signal, and positive input terminal receives a voltage reference signal Vref, exports an error amplification signal in output in view of the above.Pulse-width modulation (Pulse Width Modulated, PWM) comparator U5 receives this error amplification signal and a triangular signal, relatively export a pwm signal behind this two signal, with the ON time of decision transistor switch Q2, and reach control power supply V4 provides energy to the buck LED driving circuit number in each cycle.Basically transistor switch Q2 ON time can allow circuit export enough voltage and electric current by feedback voltage control, make resistance R 7 current sensors equal default value, if output current too much or very little, the voltage at resistance R 7 two ends will change, and then the ON time of change transistor switch Q2, so can reach the electric current current stabilization the voltage at resistance R 7 two ends for being held in definite value.
Refer again to Fig. 1, utilize a NAND gate (NAND gate) U7A to receive a dim signal and this pwm signal simultaneously and reach the function of light modulation.When input dim signal when being low level (LOW LEVEL), make the output of NAND gate U7A transfer high level to and stop power transistor switch Q2 conducting.Though inductance L 1 and capacitor C 4 can release energy by diode D8 and keep light-emitting diode D2, D5 after transistor switch Q2 ended, yet because the cycle of dim signal is longer, inductance L 1 and capacitor C 4 can release energy, and when being lower than the critical voltage of light-emitting diode D2, D5, light-emitting diode D2, D5 are no longer luminous to output voltage (the contact voltage of inductance L 1 and capacitor C 4).Yet because the existence of some leakage paths, till the energy storage that output voltage still can continue to drop to inductance L 1 and capacitor C 4 discharges fully.When input dim signal when transferring high level to (HIGH LEVEL), the output of NAND gate U7A transfers to and controlled by pwm signal, will recover as the aforementioned FEEDBACK CONTROL and reaches stabilized illumination.So change and then control LED lights and obtains a mean flow rate with the shut-in time ratio and meet the requirements of dimming mode by the control signal pulse bandwidth.
This existing dimming mode is because be operated in conducting with extreme by both, excessive instantaneous voltage will be produced, its voltage and current waveform as shown in Figure 2, its change in voltage is that zero volt is to N*VF, wherein N is the light-emitting diode quantity of series connection, VF is the cross-pressure of light-emitting diode when flowing through scheduled current, and if any the dozens of series LED, then the change in voltage at its two ends will reach hundreds of volts.And the cross-pressure that N*VFmin wherein is meant when light-emitting diode is in critical voltage to be caused, when output voltage drops to N*VFmin by N*VF, light-emitting diode almost stops luminous, and the rate of release of the energy storage of electric capacity will slow down slowly until discharging fully at this moment as shown in Figure 2.Because the conducting once more of light-emitting diode needs ON time, when the voltage that moment provides excessive, to have in the light-emitting diodes will bear many series connection and make light-emitting diode burn danger situation greater than a lot of voltage stress of specification to take place, therefore must provide voltage the slow control circuit that rises because of conducting is different.Though voltage is slow to be risen control circuit and can solve the above problems by adding, so this measure has not only increased the cost of LED driving circuit, and the instantaneous time of the voltage up-down of light modulation process also can increase and influences the accuracy of brightness adjustment control.
Summary of the invention
In view of this, for solving the problems of the technologies described above, the object of the present invention is to provide a kind of have to close at light-emitting diode (LED) module still keep a fundamental voltage at the light-emitting diode (LED) module two ends when dark, make it can guarantee that input has small voltage just to change at the light-emitting diode (LED) module two ends, make the design of LED driving circuit increase extra output current-limiting circuit in addition and to ensure that light-emitting diode component does not have the danger of damage and takes place, therefore can reduce LED driving circuit cost and the layout of simplifying the PCB circuit board because of considering the output voltage rise time.
For reaching above-mentioned purpose, the invention provides a kind of LED driving circuit, comprise a change-over circuit, a light-emitting diode (LED) module, a current detector and a control module.Above-mentioned change-over circuit is to convert an input voltage to an output voltage according to a control signal.Above-mentioned light-emitting diode (LED) module couples this change-over circuit, and according to this output voltage and luminous.Above-mentioned current detector couples this light-emitting diode (LED) module, produces a current detection signal according to an electric current of this light-emitting diode (LED) module of flowing through.Above-mentioned control module produces this control signal according to this current detection signal and a dim signal, makes this output voltage be controlled in one first driving voltage or one second driving voltage.Wherein, when this output voltage was positioned at this first driving voltage, this light-emitting diode (LED) module is in decided the current drives state and stable luminous; And when output voltage was positioned at this second driving voltage, this output voltage made this light-emitting diode (LED) module luminous hardly approximately near a critical voltage of this light-emitting diode (LED) module.
The present invention also provides another kind of LED driving circuit, and it comprises a change-over circuit, a light-emitting diode (LED) module, a current detector, a voltage detector and a control module.Above-mentioned change-over circuit is to convert an input voltage to an output voltage according to a control signal.Above-mentioned light-emitting diode (LED) module couples this change-over circuit, and according to this output voltage and luminous.Above-mentioned current detector couples this light-emitting diode (LED) module, produces a current detection signal according to an electric current of this light-emitting diode (LED) module of flowing through.Above-mentioned voltage detector couples this light-emitting diode (LED) module, to produce a voltage detection signal according to putting on one of this light-emitting diode (LED) module voltage.Above-mentioned control module produces this control signal according to this current detection signal, this voltage detection signal and a dim signal, makes this output voltage be controlled in one first driving voltage or one second driving voltage.Wherein, when this output voltage was positioned at this first driving voltage, this light-emitting diode (LED) module is in decided the current drives state and stable luminous; And when output voltage was positioned at this second driving voltage, this output voltage made this light-emitting diode (LED) module luminous hardly approximately near a critical voltage of this light-emitting diode (LED) module.
The present invention also provides a kind of secondary side control circuit, it is applied to a LED driving circuit, wherein this LED driving circuit comprises at least one detector that a primary side control circuit, a change-over circuit and are coupled to this change-over circuit, and this secondary side control circuit couples this at least one detector.Above-mentioned secondary side control circuit can comprise a signal processor and a signal selecting circuit.Wherein, above-mentioned signal processor couples this at least one detector, and produces corresponding at least one processing signals according at least one detection signal that this at least one detector produced; Above-mentioned signal selecting circuit couples this signal processor and selects one of this at least one processing signals of output according to a dim signal.In addition, above-mentioned secondary side control circuit also can comprise a signal selecting circuit and a signal processor.Wherein, above-mentioned signal selecting circuit couples this at least one detector and selects one of output received signal according to a dim signal; Above-mentioned signal processor couples this signal selecting circuit, and selects the signal that circuit produced to export a processing signals according to this number.
In sum, in the light modulation process, LED driving circuit of the present invention and secondary side controller thereof put on the change in voltage of light-emitting diode (LED) module less than existing change in voltage, light-emitting diode is subjected to excessive voltage stress or the coarse problem of brightness adjustment control in the skill so can avoid having now, thereby can reduce electromagnetic interference, LED driving circuit cost and the layout of simplifying the PCB circuit board.
Description of drawings
Fig. 1 is existing buck (Buck) LED driving circuit;
Fig. 2 is the driving voltage and the drive current waveform schematic diagram of existing LED driving circuit;
Fig. 3 A to Fig. 3 D is the circuit diagram according to LED driving circuit of the present invention;
Fig. 4 is according to the driving voltage of the light-emitting diode (LED) module of those embodiment of the present invention and drive current waveform schematic diagram.
The primary clustering symbol description:
10... change-over circuit 12,12c... primary side control unit
242a, U4... error amplifier 241a signal selector
29c... minimum working period signal generator
20a, 20b... secondary side control unit
24a, 24b, 24c, 26a... signal processor
28a, 28b, 28c... signal selecting circuit
30... light-emitting diode (LED) module 32... current detector
34... first fen splenium of voltage detector 34a...
34b... second fen splenium 36... isolated location
VIN... input voltage Vref... reference voltage
Vref1... the first reference voltage Vref 2..., second reference voltage
Vref3... the 3rd reference voltage Q2... works as transistor switch
V4... power supply L1... inductance
C4... electric capacity D2, D5... light-emitting diode
D8... diode R7... resistance
U... comparator U7A... NAND gate
Embodiment
The invention is characterized in that in the brightness adjustment control process output voltage of LED driving circuit is controlled in one first driving voltage or one second driving voltage.When output voltage was positioned at first driving voltage, light-emitting diode (LED) module was a Current Feedback Control, so be in stable luminance; And when output voltage is positioned at second driving voltage, be Voltage Feedback control, so rough critical voltage (but greater than zero volt) that equals light-emitting diode (LED) module of this output voltage, make light-emitting diode (LED) module luminous hardly, be preferably the critical voltage that is slightly less than light-emitting diode (LED) module, not luminous to guarantee light-emitting diode (LED) module.So, in the light modulation process, the change in voltage that puts on light-emitting diode (LED) module is less than existing change in voltage, light-emitting diode bears too high voltages or the coarse problem of brightness adjustment control and reduction because of crossing the electromagnetic interference (EMI, Electromagnetic Interference) that large amplitude produces in the skill so can avoid having now.
Decide electric current in order to reach above-mentioned control, can to use, decide that voltage switches or the mode of decide electric current and minimum work period switching is implemented.Below will illustrate with preferred embodiments more of the present invention.
Fig. 3 A is a circuit diagram of deciding the LED driving circuit embodiment that electric current/decide voltage switches according to the present invention.As shown in Figure 3A, LED driving circuit comprises a change-over circuit 10, a control module, a light-emitting diode (LED) module 30, a current detector 32 and a voltage detector 34.Control module comprises a primary side control unit 12, a secondary side control unit 20a and an isolated location 36.Change-over circuit 10 converts an input voltage VIN to an output voltage V 0, for the usefulness of driven for emitting lights diode (led) module 30 according to a control signal of primary side control unit 12.Voltage detector 34 detects the voltage of light-emitting diode (LED) module 30, to export a voltage detection signal; Current detector 32 is connected with light-emitting diode (LED) module 30, and the electric current that detects the light-emitting diode (LED) module 30 of flowing through is to produce a current detection signal.Secondary side control unit 20a receives this voltage detection signal, this current detection signal and a dim signal, and produce a secondary side control signal in view of the above, and be sent to primary side control unit 12 by isolated location 36, isolated location 36 is optical coupler in the present embodiment, can be transformer or other barrier assembly when practical application.Primary side control unit 12 can be the prior PWM controller, and it produces above-mentioned control signal according to this selection control signal, converts input voltage to output voltage V 0 with control transformation circuit 10.In the present embodiment, change-over circuit 10 is to be example explanation with the flyback DC-to-DC switching circuit, and can be change-over circuit such as forward type, semibridge system, full-bridge type in the practical application and not limited.
Secondary side control unit 20a has comprised voltage detection signal processor 24a, current detection signal processor 26a and signal selecting circuit 28a.Voltage detection signal processor 24a receives voltage detection signal and dim signal, and produces a voltage processing signals in view of the above; And current detection signal processor 26a received current detection signal, to produce a current processing signal.Signal selecting circuit 28a receives voltage processing signals and current processing signal, and selects to export one of them according to varying in size of both signals.In the present embodiment, dim signal is pulse signal and inputs to voltage detection signal processor 24a, to adjust the voltage processing signals size of voltage detection signal processor 24a output.
Voltage detection signal processor 24a comprises signal selector 241a and error amplifier 242a.Signal selector 241a selects first higher reference voltage Vref 1 of output or the second lower reference voltage Vref 2 according to dim signal.First reference voltage Vref 1 or second reference voltage Vref 2 that the in-phase input end received signal selector 241a of error amplifier 242a is exported, inverting input receive the voltage detection signal of voltage detector 34, and output voltage processing signals in view of the above.Current detection signal processor 26a is an error amplifier, receives the 3rd reference voltage Vref 3 in in-phase input end, the current detection signal of inverting input received current detector 32, and output current processing signals in view of the above.Signal selecting circuit 28a comprises two diodes, the negative terminal of these diodes couples voltage detection signal processor 24a and current detection signal processor 26a respectively, anode then all is coupled to isolated location 36, and select output voltage processing signals and current processing signal in than low level person.In the present embodiment, when the dimming control signal level is that representative is when " closing " first level signal of " OFF ", second reference voltage Vref 2 that signal selector 241a output is lower makes voltage detection signal processor 24a reduce the level of the voltage processing signals of being exported.At this moment, the level of voltage processing signals is lower than the level of current processing signal, and signal selecting circuit 28a selects the output voltage processing signals.Therefore, LED driving circuit operates in constant voltage mode, and output voltage is reduced near the critical voltage of light-emitting diode (LED) module, and this moment, light-emitting diode (LED) module was luminous hardly.When the dimming control signal level was second level signal of representative " ON ", first reference voltage Vref 1 that signal selector 241a output is higher made voltage detection signal processor 24a improve the level of the voltage processing signals of being exported.At this moment, signal selecting circuit 28a selects the output current processing signals.Therefore, LED driving circuit operates in constant current mode, output voltage rise and the current stabilization that makes light-emitting diode (LED) module in a predetermined current value, this moment the light-emitting diode (LED) module stabilized illumination.So, the output voltage of LED driving circuit is the first driving voltage (constant current mode, current stabilization is in predetermined current value) or the second driving voltage (constant voltage mode, voltage is stable at a scheduled voltage), avoid aforementioned the problems of the prior art thereby the difference of two driving voltages is less.In addition; if circuit is opened a way; make the current detection signal level of current detector 32 feedbacks very low; the voltage detection signal that this moment, output voltage V 0 can constantly rise to voltage detector 34 arrives till first reference voltage Vref 1; this moment, voltage detection signal processor 24a obtained the FEEDBACK CONTROL ownership once again, the maximum of restriction output voltage V 0 and reach over-voltage protecting function.
Certainly, dim signal except that as the input signal of above-mentioned in-phase input end with control voltage detection signal processor 24a reach the control output signal level, also the level of the input signal of the inverting input of may command voltage detection signal processor 24a or the means such as output output signal level of directly controlling voltage detection signal processor 24a reach above-mentioned functions, even also arbitrary input signal or the output signal of controllable current detection signal processor 26a reach above-mentioned functions.With reference to figure 3B, be the LED driving circuit schematic diagram of the incoming signal level of the inverting input of control voltage detection signal processor 24a.In the present embodiment, voltage detector 34 comprises first fen splenium 34a and second fen splenium 34b, utilize the dividing potential drop ratio of signal selector 241a switched voltage detector 34, switch LED driving circuit in the function of constant current mode or constant voltage mode and reach.
In addition, in the practical application, dim signal can be direct current light modulation (as the direct current dim signal DCDIM among Fig. 3 C), pulse signal or clock light modulation (promptly calculate the quantity of clock signal in a scheduled time length, and be converted into the work period of light modulation) etc. and not limited.Below, another preferred embodiment illustrates with the direct current light modulation.
Fig. 3 C is the LED driving circuit schematic diagram according to a direct current light modulation of the present invention (promptly just representing the amplitude of light modulation with the level of dim signal) embodiment.Wherein, secondary side control unit 20b has comprised signal processor 24b and signal selecting circuit 28b.Signal selecting circuit 28b receives direct current dim signal, voltage detection signal and current detection signal, and select one of voltage sense signal and current detection signal to signal processor 24b based on the direct current dim signal, signal processor 24b outputs signal to primary side control unit 12 according to voltage detection signal that is received or current detection signal, makes primary side control unit 12 control transformation circuit 10 in view of the above.Present embodiment is compared to the 3rd A figure illustrated embodiment, and is except that dim signal is direct current signal, also that signal selecting circuit is preposition and can save the quantity of signal processor.
In the present embodiment, the pulse signal level that changes pulse converter 281b output when direct current is representative when " closing " first level signal of " OFF ", signal selector 283b voltage sense signal.Therefore, LED driving circuit operates in constant voltage mode, and output voltage is reduced near the critical voltage of light-emitting diode (LED) module, and this moment, light-emitting diode (LED) module was luminous hardly.When direct current changes pulse signal level that pulse converter 281b selects output is representative when " opening " second level signal of " ON ", and signal selector 283b selects the output current detection signal.At this moment, LED driving circuit operates in constant current mode, output voltage rise and the current stabilization that makes light-emitting diode (LED) module in a predetermined current value, this moment the light-emitting diode (LED) module stabilized illumination.
As previously mentioned, the present invention can also decide the mode that electric current and minimum work period switch and implements.Please refer to Fig. 3 D, for decide the circuit diagram of the preferred embodiment that electric current and minimum work period switch according to the present invention.Secondary side control unit 20c comprises a signal processor 24c, a minimum working period signal generator 29c and signal news selector 28c.Signal processor 24c is an error amplifier, exports a current processing signal according to a current detection signal and a reference voltage that current detector 32 is produced.Minimum working period signal generator 29c can be set the size of minimum work period by the outside, adjusts to cooperate the different application environment, as: the resistance shown in the embodiment by the outside, perhaps set by electric capacity or alternate manner.The minimum working period signal that signal selector 28c received current processing signals and minimum working period signal generator 29c are produced, and according to the output of dim signal DIM selection one.Primary side control unit 12c receives the signal of the secondary side control unit 20c output that is transmitted by isolated location 36, and control transformation circuit 10 in view of the above.
In the present embodiment, when the level of dim signal DIM was first level signal of representative " OFF ", signal selector 28c selected the minimum working period signal of output.The minimum work period through suitably setting, primary side control unit 12c is minimum according to the work period of the control signal that minimum working period signal is exported, and makes the rough basic loss of keeping light-emitting diode (LED) module 30 circuit unit in addition of energy that reaches secondary side through change-over circuit 10.That is to say that after driving voltage is reduced near the critical voltage of light-emitting diode (LED) module 30 stop to descend and maintain about a magnitude of voltage, this moment, light-emitting diode (LED) module was luminous hardly.When the level of dim signal DIM was second level signal of representative " ON ", signal selector 28c selected the output current detection signal.Therefore, LED driving circuit operates in constant current mode, output voltage rise and the current stabilization that makes light-emitting diode (LED) module in a predetermined current value, this moment the light-emitting diode (LED) module stabilized illumination.
See also Fig. 4, be driving voltage and drive current waveform schematic diagram according to the light-emitting diode (LED) module of those embodiment of the present invention.When dim signal DIM was the level of representative " ON ", the driving voltage of light-emitting diode (LED) module was for maintaining near the first driving voltage N*VF, and the light-emitting diode (LED) module drive current of this moment also stably is controlled at I; When dim signal DIM was the level of representative " OFF ", the driving voltage of light-emitting diode (LED) module maintained near the second driving voltage N*VFmin, and this moment, the light-emitting diode (LED) module drive current was zero (or near zero).So, under the driving voltage variation of the light-emitting diode situation little, still can reach dimming function than the driving voltage variation of prior art.
In sum, though the present invention discloses above content with preferred embodiment, but be not in order to limit scope of the invention process, any those skilled in the art, without departing from the spirit and scope of the present invention, when doing a little change and retouching, promptly all according to equalization variation and modification that the present invention did, should be claim of the present invention and contain.
Claims (16)
1, a kind of LED driving circuit is characterized in that, it comprises:
Change-over circuit converts input voltage to output voltage according to control signal;
Light-emitting diode (LED) module is coupled to this change-over circuit output, and according to this output voltage and luminous;
Current detector couples this light-emitting diode (LED) module, and the electric current that detects this light-emitting diode (LED) module of flowing through produces current detection signal; And
Control module according to this current detection signal and dim signal, produces this control signal, makes this output voltage be controlled in first driving voltage or second driving voltage;
Wherein, when this output voltage was positioned at this first driving voltage, this light-emitting diode (LED) module was in stable luminance; And when output voltage was positioned at this second driving voltage, this light-emitting diode (LED) module was not luminous, and the difference of this first driving voltage and this second driving voltage poor less than this first driving voltage and earthing potential.
2, LED driving circuit according to claim 1 is characterized in that: described control module comprises:
The secondary side control unit couples this current detector, and this secondary side control unit receives this current detection signal and produces the current processing signal in view of the above, and exports this current processing signal or minimum working period signal according to this dim signal;
Isolated location is coupled to this secondary side control unit, and this isolated location receives the signal that this secondary side control unit is exported, and produces a secondary side signal in view of the above; And
The primary side control unit couples this isolated location, to produce this control signal according to this secondary side signal.
3, LED driving circuit according to claim 2 is characterized in that: described secondary side control unit comprises:
Signal processor receives this current detection signal, and produces the current processing signal in view of the above;
Minimum working period signal generator is in order to produce a minimum working period signal; And
Signal news selector couples this signal processor and this minimum working period signal generator, and selects this current processing signal of output or one of should the minimum working period signal according to this dim signal.
4, a kind of LED driving circuit is characterized in that, comprises:
Change-over circuit, this change-over circuit converts input voltage to output voltage according to control signal;
Light-emitting diode (LED) module is coupled to this change-over circuit output, and according to this output voltage and luminous;
Current detector couples this light-emitting diode (LED) module, according to current detection signal of electric current generation of this light-emitting diode (LED) module of flowing through;
Voltage detector couples this light-emitting diode (LED) module, produces a voltage detection signal according to the voltage that puts on this light-emitting diode (LED) module; And
Control module according to this current detection signal, this voltage detection signal and dim signal, produces this control signal, makes this output voltage be controlled in first driving voltage or second driving voltage;
Wherein, when this output voltage was positioned at this first driving voltage, this light-emitting diode (LED) module was in stable luminance; And when output voltage was positioned at this second driving voltage, this light-emitting diode (LED) module was not luminous, and the difference of this first driving voltage and this second driving voltage poor less than this first driving voltage and earthing potential.
5, LED driving circuit according to claim 4 is characterized in that, described control module comprises:
The secondary side control unit, couple this current detector and this this voltage detector, this secondary side control unit receives this current detection signal and this voltage detection signal, and produce a current processing signal and a voltage processing signals in view of the above respectively, and export this current processing signal or this voltage processing signals according to this dim signal;
Isolated location is coupled to this secondary side control unit, and this isolated location receives the signal that this secondary side control unit is exported, and produces a secondary side signal in view of the above; And
The primary side control unit couples this isolated location, to produce this control signal according to this secondary side signal.
6, LED driving circuit according to claim 5 is characterized in that, described secondary side control unit comprises:
The current signal processor receives this current detection signal, and produces the current processing signal in view of the above;
Processor voltage signal receives this voltage detection signal and this dim signal, and produces a voltage processing signals in view of the above; And
Signal news selector couples this current signal processor and this processor voltage signal, and accept this current processing signal and this voltage processing signals and select to export its one of.
7, LED driving circuit according to claim 6, it is characterized in that, described current signal processor comprises first error amplifier, and this first error amplifier receives this current detection signal and first reference voltage, to produce this current processing signal.
8, LED driving circuit according to claim 6, it is characterized in that, described processor voltage signal comprises second error amplifier, and this second error amplifier receives this voltage detection signal and second reference voltage, to produce this voltage processing signals.
9, LED driving circuit according to claim 8 is characterized in that, the level of one of described second reference voltage and this voltage detection signal is adjusted according to this dim signal.
10, a kind of secondary side control circuit that is applied to a LED driving circuit, this LED driving circuit comprises primary side control circuit, change-over circuit and is coupled at least one detector of this change-over circuit, this secondary side control circuit couples this at least one detector, it is characterized in that this secondary side control circuit comprises:
Signal processor couples this at least one detector, and produces at least one corresponding processing signals according at least one detection signal that described at least one detector produced; And
Signal selecting circuit couples this signal processor and selects a signal among described at least one processing signals of output according to dim signal.
11, secondary side control circuit according to claim 10 is characterized in that: also comprise level adjuster, couple one of described at least one detector in order to adjust the level of this corresponding detection signal.
12, secondary side control circuit according to claim 10, it is characterized in that: described signal processor comprises at least one error amplifier, and each error amplifier produces this processing signals according to this detection signal and the reference voltage of correspondence.
13, secondary side control circuit according to claim 10, it is characterized in that: described signal selecting circuit comprises at least one diode, the anode of each diode couples this signal processor to receive this corresponding processing signals, and the negative terminal of described diode couples mutually.
14, a kind of secondary side control circuit that is applied to LED driving circuit, this LED driving circuit comprises primary side control circuit, change-over circuit and is coupled at least one detector of this change-over circuit, this secondary side control circuit couples this at least one detector, it is characterized in that this secondary side control circuit comprises:
Signal selecting circuit couples described detector and selects one of output received signal according to dim signal; And
Signal processor couples this signal selecting circuit, and selects processing signals of signal output that circuit produced according to this number.
15, secondary side control circuit according to claim 14 is characterized in that: also include minimum working period signal generator, this signal generator produces a minimum working period signal to this signal selecting circuit.
16, secondary side control circuit according to claim 14, it is characterized in that: described signal processor comprises error amplifier, and this error amplifier produces this processing signals according to signal and the reference voltage that this signal selecting circuit produced.
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