CN104159355A - LED drive circuit, and control circuit and control method of LED drive circuit - Google Patents
LED drive circuit, and control circuit and control method of LED drive circuit Download PDFInfo
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- CN104159355A CN104159355A CN201410265245.7A CN201410265245A CN104159355A CN 104159355 A CN104159355 A CN 104159355A CN 201410265245 A CN201410265245 A CN 201410265245A CN 104159355 A CN104159355 A CN 104159355A
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Abstract
Disclosed are an LED drive circuit, and a control circuit and a control method of the LED drive circuit. The control method comprises that during the first time period of each working cycle, an average output current of the LED drive circuit is controlled for being larger than an expected output current according to a current inductive current of the LED drive circuit and a reference signal, wherein the value of the reference signal larger than the value of the expected output current; and that during the second time period of each working cycle, the transient output power of the LED drive circuit is controlled, in order to enable current energy of an input capacitor of the LED drive circuit to meet the requirement of the transient output power. With the application of the technical scheme, ripples of the output current can be reduced, and the method is particularly suitable for an LED drive current adopting a small capacitance value.
Description
Technical field
The present invention relates to electronic applications, relate in particular to a kind of LED drive circuit and control circuit thereof and control method.
Background technology
Along with the extensive use of LED, LED Driving technique is also day by day ripe.LED drive circuit is for normally working with driving LED lamp to LED load output constant current, and it mainly comprises power stage circuit and control circuit.Main switch batch (-type) ground conducting in control circuit power ratio control level circuit, thus make power stage circuit that the input voltage signal receiving is converted to a constant current signal and exports LED load to.Above-mentioned control mode is called LED constant current control.But, day by day ripe along with LED Driving technique, the requirement of the performances such as volume, production cost and the useful life of people to LED drive unit is harsh all the more.
Fig. 1 is the LED constant current control principle block diagram of traditional employing switch type Switching Power Supply (Switched Mode Power Supplies is called for short SMPS) as drive circuit.As seen from Figure 1, in the prior art, in order to obtain higher power factor (power factor is called for short PF) value, adopt little input capacitance at the input of SMPS, make the input current Iin that inputs to SMPS follow input voltage vin variation completely.Adopt the scheme of this little input capacitance, although can improve PF value, but the output current that but makes SMPS has very large ripple, therefore need to access the very large electrochemical capacitor of capacitance as output capacitance at output, the output current of large ripple is exported after excessive electrochemical capacitor again, as the output current Iout for driving LED load.Shown in Figure 2, curve 201 represents to input to the input voltage vin of drive circuit, and curve 202 represents input current Iin, and curve 203 represents the output current (electric current while not passing through output capacitance Cout) of SMPS.At the output of SMPS, electric current flows through after output capacitance Cout filtering is processed and obtains the output current Iout shown in Fig. 3.
But carrying out in research process of the present invention, inventor finds prior art, and at least there are the following problems:
Adopt electrochemical capacitor not only can increase the volume of LED drive unit, also affect the useful life of LED drive unit, and more can increase production cost.In addition, the life-span of LED is far longer than the life-span of electrochemical capacitor, uses electrochemical capacitor also can greatly reduce the life-span of whole LED lamp.
Summary of the invention
One of embodiment of the present invention object is: a kind of LED drive circuit and control circuit thereof and control method are provided.Apply the ripple that this technical scheme is conducive to reduce output current, be specially adapted to adopt the LED drive current of little capacitance.
The first fermentation, a kind of LED drive circuit control method that the embodiment of the present invention provides, described LED drive circuit comprises power stage circuit,
In described power stage circuit, be provided with main switch, described control method comprises:
During the very first time of each work period section, according to the inductive current of current LED drive circuit and a predetermined reference signal, control the average output current of described LED drive circuit during described very first time section and be greater than desired output electric current,
The value of described reference signal is greater than the value of described desired output electric current;
During the second time period of each described work period, control the transient state power output of described LED drive circuit, make the energy in the input capacitance of current described LED drive circuit meet current described transient state power output demand,
The described work period is the cycle that inputs to the input voltage signal of described LED drive circuit;
During described very first time section, be: during described input voltage is more than or equal to the first predetermined magnitude of voltage;
During described the second time period, be: during described input voltage is less than the first predetermined magnitude of voltage.
Alternatively, control the average output current of described LED drive circuit during described very first time section and be greater than desired output electric current, comprising:
According to characterizing the detection signal of current described inductive current and characterizing the signal generated error compensating signal of described reference signal;
In the time that the magnitude of voltage of described detection signal is reduced to predetermined second voltage value, main switch described in conducting, described second voltage value is the magnitude of voltage lower than described compensating signal;
In the time that the magnitude of voltage of described detection signal rises to the magnitude of voltage of described error compensating signal, the main switch in switch-off power level circuit.
Alternatively, control the transient state power output of described LED drive circuit, comprising: control described LED drive circuit and quit work;
Or, comprising:
In the time that described inductive current is reduced to the second predetermined current value, main switch described in conducting,
In the time that described inductive current rises to the peak value of restriction, turn-off described main switch, the peak value of described restriction is less than the peak value of described inductive current during described very first time section, and reduces with described input voltage;
Or, comprising:
In the time that described inductive current is reduced to the second predetermined current value, main switch described in conducting,
When the ON time of described main switch is during to predetermined maximum ON time, turn-off described main switch,
Described maximum ON time is less than or equal to: the ON time of main switch described in the time that described input voltage equals described the first magnitude of voltage.
Alternatively, control the transient state power output of described LED drive circuit, comprising:
Limit the transient state power output of described LED drive circuit, make described transient state power output with the reducing of the current input voltage value that inputs to described LED drive circuit, or to make described transient state power output be zero.
Second aspect, a kind of LED drive circuit control circuit that the embodiment of the present invention provides, described LED drive circuit comprises power stage circuit, in described power stage circuit, is provided with main switch, described control circuit comprises:
First control circuit, be used for according to the inductive current of current LED drive circuit and a predetermined reference signal, output is for the Continuity signal of main switch described in conducting and for turn-offing the first cut-off signals of described main switch, be greater than desired output electric current to control the average output current of described LED drive circuit during the very first time of work period section, the value of described reference signal is greater than the value of described desired output electric current;
Transient state output power limit circuit, for during the second time period of each described work period, produce the power limiting control signal of transient state power output for controlling described LED drive circuit, make the energy in the input capacitance of current described LED drive circuit meet current described transient state power output demand;
Logical circuit, be used for according to described Continuity signal, the first cut-off signals and power limiting control signal, the switch controlling signal that generates conducting and shutoff for controlling described main switch, equals described desired output electric current to control the average output current of described LED drive circuit within the described work period;
During described very first time section, be: during described input voltage is more than or equal to the first predetermined magnitude of voltage;
During described the second time period, be: during described input voltage is less than the first predetermined magnitude of voltage.
Alternatively, described transient state output power limit circuit comprises:
The second cut-off signals circuit for generating, for during described the second time period, before next effective described first cut-off signals output, output is for turn-offing the second cut-off signals of described main switch, using described the second cut-off signals as described power limiting control signal.
Alternatively, described the second cut-off signals circuit for generating, specifically for during described the second time period, in the time that the ON time of described main switch arrives predetermined maximum ON time, output is described the second cut-off signals effectively;
Described maximum ON time is less than or equal to: the ON time of main switch described in the time that described input voltage equals described the first magnitude of voltage.
Alternatively, described the second cut-off signals circuit for generating comprises:
Timing circuit, for during described the second time period, starts timing in the described main switch conducting moment, and in the time that timing duration arrives described maximum ON time, output is described the second cut-off signals effectively.
Alternatively, described the second cut-off signals circuit for generating, specifically for during described the second time period, in the time that described inductive current rises to the peak value of restriction, output is described the second cut-off signals effectively, using described the second cut-off signals as described power limiting control signal.
The peak value of described restriction is less than the peak value of described inductive current during described very first time section, and reduces with described input voltage.
Alternatively, described logical circuit comprises:
The first logical circuit, for when described the first cut-off signals, the second cut-off signals one of them when effective, output is for turn-offing the cut-off signals of described main switch;
The second logical circuit, for according to described Continuity signal, cut-off signals, exports described switch controlling signal.
Alternatively, described transient state output power limit circuit comprises:
Second control circuit, in the time that described input voltage is less than described the first magnitude of voltage, produces one for controlling out-of-work the first control signal of described drive circuit, using described the first control signal as described power limiting control signal.
Alternatively, described first control circuit comprises:
Error compensating signal generative circuit, for according to characterizing the detection signal of described inductive current and characterizing the signal of described reference signal, produces error compensating signal,
The first cut-off signals circuit for generating, in the time that the magnitude of voltage of described detection signal rises to the magnitude of voltage of described error compensating signal, output is described the first cut-off signals effectively;
Continuity signal circuit for generating, in the time that the magnitude of voltage of described detection signal is reduced to described second voltage value, exports effective described Continuity signal.
The third aspect, a kind of LED drive circuit that the embodiment of the present invention provides, comprises power stage circuit and above-mentioned arbitrary described control circuit,
In described power stage circuit, be provided with main switch,
Described control circuit is exported described switch controlling signal to the control end of described main switch, controls the turn-on and turn-off of described main switch, with output one current signal at described LED drive circuit drive circuit.
Therefore, application the present embodiment technical scheme, during the second time period of work period, restriction LED transient state power output, even if LED drive circuit is adopted in the situation of input capacitance of little capacitance, the ripple of output current is very little; During the very first time of work period section, without the transient state power output of restriction LED drive circuit, make during this period average output current be greater than desired output electric current and equal desired output electric current to guarantee the average output current during the whole work period, meet user's expectation demand.Visible, adopt the present embodiment technical scheme can realize the control of LED drive circuit, meet consumers' demand, and the ripple of output current is very little, without at the external electrochemical capacitor of output, the present embodiment technical scheme is specially adapted to adopt the LED drive circuit of little capacitance as input capacitance.
To sum up, application the present embodiment technical scheme can realize input no electrolytic capacitor, exports the also application scheme of no electrolytic capacitor, can effectively reduce the volume of Switching Power Supply, in the useful life of having improved power supply and LED lamp, can also reduce production costs simultaneously.
Brief description of the drawings
Fig. 1 is that prior art adopts the LED constant current control principle block diagram of SMPS as drive circuit;
Fig. 2 is the waveform schematic diagram of input voltage and output signal in circuit shown in prior art Fig. 1;
Fig. 3 is output current wave schematic diagram in circuit shown in prior art Fig. 1;
The control method schematic flow sheet of a kind of LED drive circuit that Fig. 4 provides for the embodiment of the present invention 2;
Fig. 5 is detection signal while limiting the transient state power output of LED drive circuit of the maximum ON time that limits main switch in the embodiment of the present invention 2,3, the waveform schematic diagram of input voltage;
Fig. 6 is the maximum ON time that limits main switch in the embodiment of the present invention 2,3 peak value of output current and the waveform schematic diagram of mean value while limiting the transient state power output of LED drive circuit;
Fig. 7 is the output current wave schematic diagram that adopts the LED constant current of traditional little electric capacity input to drive;
Fig. 8 is the mean value waveform schematic diagram of the output current while adopting the present embodiment 2,3 technical scheme;
The circuit theory schematic diagram of a kind of LED drive circuit control circuit that Fig. 9 provides for the present embodiment 3;
The circuit theory schematic diagram of the buck power stage circuit of the LED drive circuit that Figure 10 provides for the present embodiment 4;
The first logical circuit 502 schematic diagrames that the employing OR circuit that Figure 11 provides for the present embodiment 4 realizes;
The implementing circuit principle schematic of the maximum ON time limiting circuit 5041 that Figure 12 provides for the present embodiment 4;
The circuit theory schematic diagram of a kind of LED drive circuit control circuit that Figure 13 provides for the present embodiment 4.
Embodiment
Describe the present invention in detail below in conjunction with accompanying drawing and specific embodiment, be used for explaining the present invention in this illustrative examples of the present invention and explanation, but not as a limitation of the invention.
Embodiment 1:
The present embodiment provides a kind of LED drive circuit control method.This LED drive circuit comprises power stage circuit, and the topological structure of power stage circuit can be the topological structure of boost type or buck or other type.Rectification circuit inputs to power stage circuit using this half-wave DC voltage signal Vin as the input voltage signal of LED drive circuit after the AC signal of input is converted to half-wave DC voltage signal (its waveform is referring to the waveform of the input voltage vin in Fig. 5).The input voltage signal that inputs to LED drive circuit of various embodiments of the present invention indication is all made this half-wave DC voltage signal Vin.
The work period of the LED drive circuit of indication is the cycle that inputs to the half-wave DC voltage signal Vin of LED drive circuit in the present embodiment.The work period of LED drive circuit is relevant to the AC signal that inputs to rectification circuit.For example, the frequency of the current AC signal that inputs to rectification circuit is 50HZ, and the frequency that inputs to the input voltage signal of LED drive circuit is 100HZ.The AC signal that often inputs in practice rectification circuit is industrial frequency AC signal, and old friends are also called power frequency period by the work period of LED drive circuit.
Within each work period of LED drive circuit, control conducting and the shutoff of main switch SW to main switch (being designated as SW) the input switch control signal (being PMW signal) in power stage circuit, power stage circuit batch (-type) ground receives input voltage vin and converts it into the output current that user expects and exports LED load to, driving LED load is normally worked, and the electric current that flows through LED load is output current.In when application, people wish to control the average current that LED drive circuit exports within the whole work period and equal the desired desired output electric current of user, thereby can meet user's demand.
In LED drive circuit control procedure, in a switch periods (switch periods of the main switch in power stage circuit), the power of LED drive circuit output is the transient state power output of LED drive circuit, and the mean value of transient state power output is the needed power of the normal work of load of the required driving of LED drive circuit.
In the present embodiment, in arbitrary work period, the time period that the input voltage of LED drive circuit is more than or equal to during the first predetermined magnitude of voltage is designated as very first time section, and the time period that the input voltage of LED drive circuit is less than during the first predetermined magnitude of voltage was designated as for the second time period.
In each work period, the LED drive circuit control method of the present embodiment is mainly as follows:
During very first time section, according to the inductive current of current LED drive circuit and a predetermined reference signal, control the average output current of LED drive circuit during very first time section and be greater than desired output electric current; During the second time period, the transient state power output of LED drive circuit is limited and its output current is reduced or is zero,, within this second time period, the average output current of LED drive circuit can be less than desired output electric current.
Wherein, above-mentioned predetermined reference signal is the average output current that LED drive circuit needs during this very first time section, and it is set in the average output current value of the second time period reality according to the desired output current value of LED drive circuit and LED drive circuit.Generally this reference signal is arranged to be greater than a value of desired output electric current, thereby make the average output current of LED drive circuit during very first time section be greater than desired output electric current, just can make up the output current value being reduced due to restriction transient state power output in the second time period, thereby make the output average current of LED drive circuit within the whole work period equal desired output electric current.
As the signal of the present embodiment, concrete the first predetermined magnitude of voltage can recently be determined according to the duty of desired output electric current.For example, if when the duty ratio of desired output electric current is 70%, need to make input voltage to be equal to, or greater than for the first magnitude of voltage duration and account for 70% of the input voltage cycle, general input voltage is steamed bun ripple, this steamed bun wave period is a work period, can be set to the first magnitude of voltage by the input voltage through about 15% work period time.
During the very first time of each work period section, input voltage vin is larger, and the current energy that inputs to LED drive circuit is enough to meet the demand of LED load, therefore, during this very first time section without restriction LED drive circuit transient state power output.Input voltage vin is less, and to show to input to the energy of LED drive circuit less, during input voltage vin is equal to or less than the first magnitude of voltage (i.e. during the second time period), now current input voltage vin approaches the trough value of input voltage signal and in a lower value, the energy that now inputs to LED drive circuit cannot meet the demand of load or can barely meet the demand of load but the energy that needs make main switch SW keep quite long ON time to be just enough to make to input to LED drive circuit meets the demand of load.Therefore during the second time period, need the transient state power output of restriction LED drive circuit, otherwise the output current of LED drive circuit can have larger ripple, and then need to adopt the electrochemical capacitor of large capacitance to carry out filtering ripple at output, but also may make main switch SW in the power stage circuit of LED drive circuit because for a long time in conducting state and easily damaged.Therefore, during the second period section, the transient state power output of the present embodiment control LED drive circuit, so that the energy in the input capacitance of current LED drive circuit can meet the demand of transient state power output, make the energy in the input capacitance at arbitrary moment LED drive circuit during the second period section be enough to meet current transient state power output demand by restriction transient state power output now.
Therefore, adopt the present embodiment technical scheme, owing to making energy in the input capacitance of current LED drive circuit can meet the demand of the transient state power output after being limited by the transient state power output of restriction LED drive circuit during the second time period, the energy that makes current LED drive circuit export load to is less than the energy in the input capacitance of LED drive circuit within the second time period always, thereby can avoid the phenomenon that output current ripple is larger.Although the output average current of LED drive circuit within the second time period is less than the output current of expectation, but by very first time section, make the output average current of LED drive circuit be greater than desired output electric current, thereby make the output average current of LED drive circuit within the whole work cycle still can equal desired output electric current, still meet user's desired output electric current demand.
The present embodiment technical scheme is particularly suitable for adopting the LED drive circuit of little input capacitance.In the LED drive circuit of little input capacitance, during the second less time period of input voltage vin, the energy that inputs to LED drive circuit is less, the energy in input capacitance is also smaller during this period, now, needing main switch to continue conducting just can make the output energy of LED drive circuit meet the demand of load for a long time.And in the present embodiment, during the second time period, limit the transient state power output of LED drive circuit and guarantee that the energy in input capacitance is enough to meet the demand of current transient state power output, and make the output average current of LED drive circuit during very first time section be greater than desired output electric current, thereby make the output average current of LED drive circuit within the whole work period still can equal desired output electric current.Therefore when the technical program is applied in the LED drive circuit of little electric capacity input, under the condition of desired output electric current that meets user, can also make during the second time period that input voltage is less at the ripple of the output current of LED drive circuit also very little, thereby without the electrochemical capacitor that connects large capacitance, can effectively reduce volume, useful life and the manufacturing cost of LED drive unit at the output of drive current.
As the signal of the present embodiment, limit the transient state power output of LED drive circuit during the second time period of work period time, the transient state power output that also makes LED drive circuit during this period reduces and reduces with current input voltage; Or during the second time period of work period, LED drive circuit is quit work, make transient state power output be restricted to zero.
As the signal of the present embodiment, can be greater than desired output electric current by the average output current during the second time period by arbitrary control LED drive circuit of prior art, also can be, but not limited to adopt the technical scheme providing in embodiment 2,3.
Therefore, adopt the present embodiment technical scheme, during the second time period of work period, restriction LED transient state power output, even if LED drive circuit is adopted in the situation of input capacitance of little capacitance, the ripple of output current is very little; During the very first time of work period section, without the transient state power output of restriction LED drive circuit, make during this period average output current be greater than desired output electric current and equal desired output electric current to guarantee the average output current during the whole work period, meet user's expectation demand.Visible, adopt the present embodiment technical scheme can realize the control of LED drive circuit, meet consumers' demand, and the ripple of output current is very little, without at the external electrochemical capacitor of output, the present embodiment technical scheme is specially adapted to adopt the LED drive circuit of little capacitance as input capacitance.
To sum up, application the present embodiment technical scheme can realize input no electrolytic capacitor, exports the also application scheme of no electrolytic capacitor, can effectively reduce the volume of Switching Power Supply, in the useful life of having improved power supply and LED lamp, can also reduce production costs simultaneously.
Embodiment 2:
Shown in Figure 4, the present embodiment, on the basis of embodiment 1, further provides one LED drive circuit control method more specifically, and it mainly comprises following flow process:
Step 401: the detection signal that obtains the inductive current that characterizes the current inductance that flows through LED drive circuit.
The signal of the present embodiment, can cross by sample streams the inductive current of the inductance of LED drive circuit, obtains detection signal Vsense.The detection signal Vsense obtaining is synchronizeed and is changed with inductive current, can characterize current inductive current.
Step 402: produce an error compensating signal according to the signal of detection signal and sign reference signal.
In the present embodiment, to be that a sign is actual wish the average output current of LED drive circuit during very first time section to reference signal, and the value of reference signal is greater than the value of desired output electric current.In the present embodiment, obtain the voltage signal (being designated as reference voltage signal Vref) of this reference signal of sign according to this reference signal.Be that reference voltage signal Vref has characterized: actual average output current of wishing LED drive circuit actual needs during very first time section, actual average output current of wishing LED drive circuit actual needs during very first time section is greater than desired output electric current.
Shown in Figure 9, input respectively detection signal Vsense and two inputs "+" from reference voltage signal Vref to error amplifier EA1, "-", at the output output error compensating signal (being designated as Vcomp) of error amplifier EA1.This error compensating signal Vcomp can characterize the output current of current LED drive circuit and actually wish the error of LED drive circuit between the average output current during very first time section.Therefore during very first time section, adopt error compensating signal Vcomp to control the shutoff of main switch and conducting as the peak value of detection signal Vsense and control the output current of LED drive circuit, can control the average output current of LED drive circuit during first paragraph and be greater than desired output electric current.
Step 403: during very first time section: when the magnitude of voltage of detection signal rises to while being less than error compensating signal Vcomp, turn-off main switch, in the time that the magnitude of voltage of detection signal drops to predetermined second voltage value, conducting main switch; During the second time period: the transient state power output of restriction LED drive circuit.
As the signal of the present embodiment, during the very first time section during the input voltage that inputs to LED drive circuit is equal to, or greater than the first magnitude of voltage, the present embodiment provides following control LED drive circuit constant current output control program:
Specifically, in the time that the magnitude of voltage rising of detection signal Vsense arrives the magnitude of voltage of error compensating signal Vcomp, the main switch in switch-off power level circuit; Conducting main switch in the time that the magnitude of voltage of detection signal Vsense is reduced to predetermined second voltage value, thereby by the control of main switch being realized to the output current control of LED drive circuit.
During the very first time of work period section, the variation of detection signal Vsense is as follows: in the time that the magnitude of voltage of detection signal Vsense slowly increases and arrives the magnitude of voltage of error compensating signal Vcomp during switch conduction, turn-off main switch, the magnitude of voltage of detection signal Vsense is slowly reduced; In the time that the magnitude of voltage of detection signal Vsense is reduced to predetermined second voltage value, conducting main switch, input voltage vin continues as LED drive circuit input energy is provided.
Wherein, second voltage value is less than the magnitude of voltage of error compensating signal Vcomp, and it is generally zero or approach a magnitude of voltage of zero.
During this very first time section, the magnitude of voltage that the time of main switch SW conducting is detection signal Vsense is risen to the magnitude of voltage institute elapsed time section of error compensating signal Vcomp by second voltage value, as the time period of time t1-t2 in Fig. 6.
Because error compensating signal Vcomp has characterized output current and the error of LED drive circuit between the average output current of actual needs during very first time section of current LED drive circuit, thereby, during the very first time of work period section, by the above-mentioned peak value control main switch batch (-type) ground conducting using error compensating signal Vcomp as detection signal Vsense, make LED drive circuit power stage circuit batch (-type) receive input voltage vin, can make the average output current of LED drive circuit during this very first time section be greater than desired output electric current.
As the signal of the present embodiment, during the second time period at the input voltage that inputs to LED drive circuit lower than the first voltage, can limit by the maximum ON time of the main switch of power-limiting level circuit the transient state power output of LED drive circuit, make a concrete analysis of as follows:
In LED drive circuit, input voltage vin is lower, the ON time that obtains the required master power switch pipe of identical transient state power output SW is longer, therefore, during the second time period, a fixed value that is the ON time of main switch in the time that input voltage equals the first magnitude of voltage by the predetermined maximum ON time (being designated as Ttongmax2) of main switch SW.
Reach be scheduled to maximum ON time Ttongmax2 after main switch SW is switched on time, be just turned off, thereby the value of transient state power output that can make LED drive circuit is reducing and reduce with input voltage during the second time period, make energy in the input capacitance of current LED drive circuit can meet the demand of the transient state power output after being limited, even the energy of the energy that current LED drive circuit exports load in the input capacitance that is always less than LED drive circuit during the second time period, thereby can avoid the phenomenon that output current ripple is larger.
As the priority scheme of the present embodiment, can be during the second time period, make main switch be less than or equal to confined maximum ON time Ttongmax2 equal the ON time of main switch in the time that input voltage equals the first magnitude of voltage, thereby can make LED drive circuit obtain higher PF value.
In the present embodiment, the maximum ON time of restriction main switch SW is that Ttongmax2 is while limiting the transient state power output of LED drive circuit, the waveform of detection signal Vsense and input voltage vin as shown in Figure 5, because detection signal Vsense is synchronizeed with inductive current, and the mean value that output current Iout is inductive current, therefore the waveform of output current Iout is similar to the envelope shape of detection signal Vsense, and be trapezoidal (in fact can be equivalent to rectangle) that be more or less the same below, therefore known, the mean value waveform of inductive current and output current as shown in Figure 6, as seen from Figure 6, its inductive current is triangular wave, output current is one trapezoidal, be one to be greater than the steady state value of expecting electric current at the average output current Iout of (during time t1-t2) LED drive circuit during very first time section, at (during time t0-t1 and t2-t3) during the second time period, due to the transient state transient state power output having limited during the maximum ON time of switching tube SW limited for the second time period, the value of the average output current Iout of LED drive circuit is less than desired output electric current during this period, and reduces and reduce with input voltage vin.
As the signal of the present embodiment, during the second time period, can also limit by the peak I out-max of restriction inductive current the transient state power output of LED drive circuit.Specific as follows:
In the present embodiment, during the second time period of work period, according to the peak value of input voltage vin restriction detection signal Vsense, make the peak value of detection signal Vsense be less than the magnitude of voltage of error compensating signal Vcomp, and reducing and reduce with input voltage vin, even during the second time period, the peak value of inductive current is less than the peak value in very first time section, and reducing and reduce with input voltage vin.In the time that inductive current reaches limited peak value, controlling main switch SW turn-offs, thereby transient state power output is reduced with input voltage vin and reduce, limited the transient state power output of LED drive circuit during this second time period, guarantee during the second very little time period of input voltage vin, energy in the input capacitance of current LED drive circuit meets current transient state power output demand, makes to input during this period energy and can meet always the demand of transient state power output.
As the signal of the present embodiment, during the second time period, can also control LED drive circuit quits work, taking restriction LED drive circuit transient state power output as zero, guarantee during the second very little time period of input voltage vin, energy in the input capacitance of current LED drive circuit meets current transient state power output demand, makes to input during this period energy and can meet always the demand of transient state power output.
Therefore, application the present embodiment technical scheme, lower at input voltage, when the current energy that inputs to LED drive circuit cannot meet the demand of load or can barely meet the demand of load (during the second time period), limit the transient state power output of current LED drive circuit, guarantee that the energy in the input capacitance of current LED drive circuit meets current transient state power output demand, and then make the ripple of output current of LED drive circuit very little, thereby without the electrochemical capacitor that adopts large capacitance at output, can effectively reduce the volume of LED drive circuit, useful life and manufacturing cost.Larger in input voltage vin, when current input energy is enough to meet the needed power of load that LED drive circuit drives (during very first time section), without the transient state power output of restriction LED drive circuit, and control LED drive circuit using the error compensation voltage signal Vcomp of the error of the current inductive current of sign and LED drive circuit average output current of actual needs during very first time section as the peak value of the detection signal Vsense of sign inductive current, make the average output current of LED drive circuit during this very first time section be greater than desired output electric current, to make up the output current value being reduced in the second time period that makes LED drive circuit due to restriction transient state output power value, thereby can make the output average current of LED drive circuit within the whole work period equal desired output electric current.
As seen from Figure 6, adopt the present embodiment scheme, the waveform of the output current Iout of LED drive circuit specifically as shown in Figure 8.Shown in Fig. 7 is the output current wave schematic diagram of the LED constant-current drive circuit of the little electric capacity input scheme of available technology adopting, comparison diagram 7,8 can be found out: adopt embodiment of the present invention scheme can obtain the output current that output ripple is less, and have under the condition of identical mean value with the output current shown in Fig. 7, adopt the present embodiment technical scheme, LED drive circuit output current also has less effective value, be conducive to reduce the thermal losses of load, be conducive to improve the useful life of load.
Embodiment 3:
Fig. 9 provides a kind of LED drive circuit control circuit principle schematic.This LED drive circuit comprises power stage circuit, the topological structure of power stage circuit can be the topological structure of boost type or buck or other type, the present embodiment taking buck as example, the circuit theory schematic diagram of the buck power stage circuit that Figure 10 is LED drive circuit.
Shown in Figure 10, power stage circuit mainly comprises main switch SW, one end of main switch SW is connected with input, access input voltage vin, the other end is connected with inductance L, main switch SW is batch (-type) ground conducting and shutoff under the control of the present embodiment control circuit, and LED drive circuit batch (-type) ground receives input voltage vin and converts it into user the output signal needing and exports load LED to, normally works with driving LED load.
Shown in Figure 10, detect the sample inductor current signal of LED drive circuit of resistance R sense in LED load-side series connection one, and the voltage signal that obtains detection resistance R sense two ends characterizes inductive current as detection signal Vsense, detection signal Vsense is synchronizeed and is changed with inductive current, can characterize output current.
Shown in Figure 9, the LED drive circuit control circuit of the present embodiment mainly comprises: first control circuit 500, transient state output power limit circuit 901, logical circuit 902.
Its operation principle is, first control circuit 500 is according to inductive current and a reference signal, output is for the Continuity signal Vtong of conducting main switch, and for turn-offing the first cut-off signals Vduan1 of main switch SW, to control conducting and the shutoff of main switch SW, realize the output current control to LED drive circuit, make the average output current of (during being very first time section) LED drive circuit during the input voltage vin of LED drive circuit is equal to, or greater than the first predetermined magnitude of voltage be greater than desired output electric current, so that LED drive circuit equals desired output electric current at whole duration of work average output current.
Wherein, above-mentioned predetermined reference signal is the average output current that LED drive circuit needs during very first time section.The value of reference signal is set in the average output current value of the second time period reality according to the desired output current value of LED drive circuit and LED drive circuit, generally become to be greater than a value of described desired output electric current with reference to signal setting, thereby can make the average output current of LED drive circuit during very first time section be greater than desired output electric current, just can make up the output current value being reduced in the second time period that makes LED drive circuit due to restriction transient state output power value, thereby make the output average current of LED drive circuit within the whole work cycle still can equal desired output electric current.
During this very first time section, the waveform of LED drive circuit output current is referring in Fig. 6 shown in the t1-t2 time period.
During being less than the first magnitude of voltage, the input voltage of LED drive circuit (was designated as for the second time period), transient state output power limit circuit 901 produces one for controlling the power limiting control signal Vxian of transient state power output of LED drive circuit, makes the energy in the input capacitance of current LED drive circuit meet current transient state power output demand.
Logical circuit 902, according to Continuity signal Vtong, the first cut-off signals Vduan1 and power limiting control signal Vxian, generates the pwm signal of conducting and shutoff for controlling main switch SW.Make the average output current of LED drive circuit during very first time section be greater than desired output electric current, so that equal desired output electric current at the average output current of whole duration of work.During the second time period, limit its transient state power output, make the energy in the input capacitance of current LED drive circuit meet current transient state power output demand.
Analyze in like manner with embodiment 1, application the present embodiment technical scheme can realize input no electrolytic capacitor, exports the also application scheme of no electrolytic capacitor, therefore can effectively reduce the volume of LED drive unit, improve the useful life of LED drive unit and LED lamp, can also reduce production costs simultaneously.
Further operation principle and have an effect to see in detail the corresponding description in embodiment 1,2.
As the signal of the present embodiment, shown in Figure 9, the present embodiment can adopt the second cut-off signals circuit for generating 504 as transient state output power limit circuit 901.Specific as follows:
The second cut-off signals circuit for generating 504 generates the second cut-off signals Vduan2 for turn-offing main switch SW according to input voltage vin, before next effective first cut-off signals Vduan1 output, export the second cut-off signals Vduan2, before the first cut-off signals Vduan1 output of this switch periods, export the second cut-off signals Vduan2, to turn-off in advance the transient state power output of main switch SW restriction LED drive circuit, make transient state power output be less than the current input power that inputs to LED drive circuit, using this second cut-off signals Vduan2 as power limiting control signal Vxian.
As the signal of the present embodiment, the second cut-off signals circuit for generating 504 of the present embodiment can adopt maximum ON time limiting circuit 5041 to realize.During the second time period, in the time that the ON time of main switch SW arrives predetermined maximum ON time Ttongmax2, maximum ON time limiting circuit 5041 is exported effective the second cut-off signals Vduan2, turn-offs to control main switch SW.
Wherein, the setting of maximum ON time Ttongmax2, in detail but be not limited to referring to the corresponding description in embodiment 2.
As the signal of the present embodiment, shown in Figure 12, this maximum ON time limiting circuit 5041 comprises the second comparator C omp2, current source I0, the first capacitor C 0 and the first switch S 0.
Wherein, current source I0 is connected to the second input of the second comparator C omp2, one end of the first capacitor C 0 is connected with the second input, other end ground connection, the first switch S 0 and the first capacitor C 0 are also connected between current source I0 and ground, access the control signal Vs0 of synchronizeing with switch controlling signal pwm signal or with pwm signal at the control end of the first switch S 0.
If effective Continuity signal of main switch SW is high level signal, effectively cut-off signals is low level signal.Therefore in the time that switch controlling signal pwm signal is high level, main switch SW conducting, control signal Vs0 is low level, and the first switch S 0 is in off state, and current source I0 charges to the first capacitor C 0.When charging is through the tertiary voltage value Vth3 of the first input end access of this second comparator C of the voltage rising arrival omp2 in regular hour first capacitor C 0, now, the second comparator C omp2 output low level signal, now export effective the second cut-off signals Vduan2, to turn-off in advance main switch SW before the first cut-off signals Vduan1 output of this switch periods.When main switch SW is during in off state, the control signal Vs0 that inputs to the first switch S 0 is high level, and the first switch S 0 is in conducting state, and the loop that the first capacitor C 0 forms by the first switch S 0 discharges electric charge rapidly until voltage is zero.
In the present embodiment, can determine tertiary voltage value Vth3 according to the size of predetermined maximum ON time Ttongmax2, make to control current source I0 the first 0 charging interval of capacitor C was equaled to this predetermined maximum ON time Ttongmax2.
As the signal of the present embodiment, maximum ON time limiting circuit can also be a timing circuit, during the very first time of work period section, start timing from main switch SW conducting moment timing circuit, in the time that timing reaches predetermined maximum ON time Ttongmax2, timing circuit is exported effective the second cut-off signals Vduan2.Be specifically as follows, the signal of inputting pwm signal or synchronizeing with it to timing circuit, in the time that pwm signal is high level, timing circuit starts timing, in the time that reaching maximum ON time Ttongmax2, timing time produces effective the second cut-off signals Vduan2, control main switch SW and turn-off, be restricted to predetermined maximum ON time Ttongmax2 by the ON time of main switch SW.
As the signal of the present embodiment, the second cut-off signals circuit for generating 504 of the present embodiment can adopt peak limiter circuit (not shown) to realize.During the second time period of work period, peak limiter circuit is the magnitude of voltage that is less than error compensating signal Vcomp by the peak-limitation of detection signal Vsense, and the peak value of restriction reduces and reduces with input voltage, peak limiter circuit is in the time that the magnitude of voltage rising of detection signal Vsense arrives the peak value of current restriction, export effective the second cut-off signals Vduan2, to turn-off in advance main switch SW.
As the signal of the present embodiment, shown in Figure 9, the logical circuit 902 of the present embodiment comprises the first logical circuit 502, the second logical circuit 505.
Wherein, the first logical circuit 502 accesses respectively the first cut-off signals Vduan1, the second cut-off signals Vduan2, when the first cut-off signals Vduan1, the second cut-off signals Vduan2 one of them when effective, the first logical circuit 502 is exported cut-off signals Vduan to the second logical circuit 505, turn-offs main switch SW.As the signal of the present embodiment, this first logical circuit 502 can be, but not limited to as the OR circuit shown in Figure 11.
The second logical circuit 505 is connected with Continuity signal circuit for generating 502, the first cut-off signals circuit for generating 503 and the first logical circuit 502 respectively, for generating according to Continuity signal Vtong and cut-off signals Vduan the pwm signal that is used for conducting and the shutoff of controlling main switch SW.
As the signal of the present embodiment, can adopt rest-set flip-flop to realize the second logical circuit 505.Its circuit structure is specific as follows:
Continuity signal circuit for generating 502 is connected with the set end " S " of rest-set flip-flop, and when to set end " S " input Continuity signal Vtong, the pwm signal of output " Q " output of rest-set flip-flop is the high level signal that makes power switch conducting;
First output of logical circuit 502 and the reset terminal of rest-set flip-flop " R " are connected, and in the time of the effective cut-off signals Vduan of output, the pwm signal of exporting at the output " Q " of rest-set flip-flop is the low level signal that power switch is turn-offed.
As the signal of the present embodiment, shown in Figure 9, the present embodiment provides following first control circuit 500 to realize circuit, and it comprises: error compensating signal generative circuit 501, Continuity signal circuit for generating 502 and the first cut-off signals circuit for generating 503.
Its operation principle is, error compensating signal generative circuit 501 according to characterize current LED drive circuit inductive current detection signal Vsense and characterize the reference voltage signal Vref of actual average output current of wishing LED drive circuit actual needs during very first time section, produce an error compensating signal Vcomp.
As the signal of the present embodiment, error compensating signal generative circuit 501 can be, but not limited to adopt error amplifier EA1 and building-out capacitor Ccomp to realize.To normal phase input end "+" the input reference voltage signal Vref of error amplifier EA1, inverting input "-" input detection signal Vsense, the voltage of the building-out capacitor Ccomp that error amplifier EA1 output connects is: error compensating signal Vcomp.
Continuity signal circuit for generating 502, in the time that inductive current arrives the trough value of inductive current, when the magnitude of voltage of detection signal Vsense is reduced to predetermined second voltage value, is exported effective Continuity signal Vtong, with conducting main switch SW.Wherein this second voltage value is set as lower value, it is generally and equals zero or be slightly larger than zero magnitude of voltage,, near inductive current arrives trough value or trough value time, Continuity signal circuit for generating 502 produces an effective Continuity signal Vtong, to control conducting main switch SW.
The first cut-off signals circuit for generating 503, in the time that the magnitude of voltage of detection signal Vsense rises to the magnitude of voltage of error compensating signal Vcomp, is exported effective the first cut-off signals Vduan1, turn-offs main switch SW for controlling.
As the signal of the present embodiment, shown in Figure 9, can adopt the first comparator C omp1 to realize the first cut-off signals circuit for generating 503, two inputs of the first comparator C omp1 receive respectively detection signal Vsense error compensating signal Vcomp, in the time that the magnitude of voltage of detection signal Vsense rises to the magnitude of voltage of error compensating signal Vcomp, export effective the first cut-off signals Vduan1 at the output of the first comparator C omp1.
Error compensating signal generative circuit 501, Continuity signal circuit for generating 502 and the first cut-off signals circuit for generating 503 are realized the operation principle of the control to LED drive circuit and beneficial effect in detail referring to the description in embodiment 2 according to error compensating signal Vcomp and detection signal Vsense.
Embodiment 4:
A kind of LED drive circuit control circuit shown in Figure 13, the present embodiment provides, itself and 3 differences of embodiment are mainly as follows:
The transient state output power limit circuit 133 of the present embodiment comprises: second control circuit 131.
In the time that input voltage vin is less than the first predetermined magnitude of voltage, second control circuit 131 is exported effective the first control signal, control drive circuit quits work, and using this first control signal as power limiting control signal Vxian, is zero by its transient state output power limit.
In the time that input voltage vin is equal to, or greater than the first magnitude of voltage, second control circuit 132 is exported invalid signals, LED drive circuit is normally worked, LED drive circuit is worked under the control of first control circuit 501 and logical circuit 902, control principle during this very first time section is shown in the corresponding description in embodiment 1,2 in detail, and therefore not to repeat here.
Now, logical circuit 132 can only be realized by rest-set flip-flop, Continuity signal circuit for generating 502 is connected with the set end " S " of rest-set flip-flop, when to set end " S " input Continuity signal Vtong, the pwm signal of output " Q " output of rest-set flip-flop is the high level signal that makes power switch conducting; First output of breaking circuit 503 and the reset terminal of rest-set flip-flop " R " are connected, and in the time of effective the first cut-off signals Vduan1 of output, the pwm signal of exporting at the output " Q " of rest-set flip-flop is the low level signal that power switch is turn-offed.
The further work principle of the present embodiment and beneficial effect are in detail referring to the corresponding description in embodiment 1,2, and therefore not to repeat here.
Above-described execution mode, does not form the restriction to this technical scheme protection range.The amendment done within any spirit at above-mentioned execution mode and principle, be equal to and replace and improvement etc., within all should being included in the protection range of this technical scheme.
Claims (13)
1. a LED drive circuit control method, described LED drive circuit comprises power stage circuit,
In described power stage circuit, be provided with main switch, described control method comprises:
During the very first time of each work period section, according to the inductive current of current LED drive circuit and a predetermined reference signal, control the average output current of described LED drive circuit during described very first time section and be greater than desired output electric current,
The value of described reference signal is greater than the value of described desired output electric current;
During the second time period of each described work period, control the transient state power output of described LED drive circuit, make the energy in the input capacitance of current described LED drive circuit meet current described transient state power output demand,
The described work period is the cycle that inputs to the input voltage signal of described LED drive circuit;
During described very first time section, be: during described input voltage is more than or equal to the first predetermined magnitude of voltage;
During described the second time period, be: during described input voltage is less than the first predetermined magnitude of voltage.
2. LED drive circuit control method according to claim 1, is characterized in that,
Control the average output current of described LED drive circuit during described very first time section and be greater than desired output electric current, comprising:
According to characterizing the detection signal of current described inductive current and characterizing the signal generated error compensating signal of described reference signal;
In the time that the magnitude of voltage of described detection signal is reduced to predetermined second voltage value, main switch described in conducting, described second voltage value is the magnitude of voltage lower than described compensating signal;
In the time that the magnitude of voltage of described detection signal rises to the magnitude of voltage of described error compensating signal, the main switch in switch-off power level circuit.
3. LED drive circuit control method according to claim 1, is characterized in that,
The transient state power output of controlling described LED drive circuit, comprising: control described LED drive circuit and quit work;
Or, comprising:
In the time that described inductive current is reduced to the second predetermined current value, main switch described in conducting,
In the time that described inductive current rises to the peak value of restriction, turn-off described main switch, the peak value of described restriction is less than the peak value of described inductive current during described very first time section, and reduces with described input voltage;
Or, comprising:
In the time that described inductive current is reduced to the second predetermined current value, main switch described in conducting,
When the ON time of described main switch is during to predetermined maximum ON time, turn-off described main switch,
Described maximum ON time is less than or equal to: the ON time of main switch described in the time that described input voltage equals described the first magnitude of voltage.
4. according to the LED drive circuit control method described in claim 1 or 2 or 3, it is characterized in that,
The transient state power output of controlling described LED drive circuit, comprising:
Limit the transient state power output of described LED drive circuit, make described transient state power output with the reducing of the current input voltage value that inputs to described LED drive circuit, or to make described transient state power output be zero.
5. a LED drive circuit control circuit, described LED drive circuit comprises power stage circuit, in described power stage circuit, is provided with main switch, described control circuit comprises:
First control circuit, be used for according to the inductive current of current LED drive circuit and a predetermined reference signal, output is for the Continuity signal of main switch described in conducting and for turn-offing the first cut-off signals of described main switch, be greater than desired output electric current to control the average output current of described LED drive circuit during the very first time of work period section, the value of described reference signal is greater than the value of described desired output electric current;
Transient state output power limit circuit, for during the second time period of each described work period, produce the power limiting control signal of transient state power output for controlling described LED drive circuit, make the energy in the input capacitance of current described LED drive circuit meet current described transient state power output demand;
Logical circuit, be used for according to described Continuity signal, the first cut-off signals and power limiting control signal, the switch controlling signal that generates conducting and shutoff for controlling described main switch, equals described desired output electric current to control the average output current of described LED drive circuit within the described work period;
During described very first time section, be: during described input voltage is more than or equal to the first predetermined magnitude of voltage;
During described the second time period, be: during described input voltage is less than the first predetermined magnitude of voltage.
6. LED drive circuit control circuit according to claim 5, is characterized in that,
Described transient state output power limit circuit comprises:
The second cut-off signals circuit for generating, for during described the second time period, before next effective described first cut-off signals output, output is for turn-offing the second cut-off signals of described main switch, using described the second cut-off signals as described power limiting control signal.
7. LED drive circuit control circuit according to claim 6, is characterized in that,
Described the second cut-off signals circuit for generating, specifically for during described the second time period, in the time that the ON time of described main switch arrives predetermined maximum ON time, output is described the second cut-off signals effectively;
Described maximum ON time is less than or equal to: the ON time of main switch described in the time that described input voltage equals described the first magnitude of voltage.
8. LED drive circuit control circuit according to claim 7, is characterized in that,
Described the second cut-off signals circuit for generating comprises:
Timing circuit, for during described the second time period, starts timing in the described main switch conducting moment, and in the time that timing duration arrives described maximum ON time, output is described the second cut-off signals effectively.
9. LED drive circuit control circuit according to claim 5, is characterized in that,
Described the second cut-off signals circuit for generating, specifically for during described the second time period, in the time that described inductive current rises to the peak value of restriction, output is described the second cut-off signals effectively, using described the second cut-off signals as described power limiting control signal.
The peak value of described restriction is less than the peak value of described inductive current during described very first time section, and reduces with described input voltage.
10. according to arbitrary described LED drive circuit control circuit of claim 6 to 9, it is characterized in that,
Described logical circuit comprises:
The first logical circuit, for when described the first cut-off signals, the second cut-off signals one of them when effective, output is for turn-offing the cut-off signals of described main switch;
The second logical circuit, for according to described Continuity signal, cut-off signals, exports described switch controlling signal.
11. LED drive circuit control circuits according to claim 5, is characterized in that,
Described transient state output power limit circuit comprises:
Second control circuit, in the time that described input voltage is less than described the first magnitude of voltage, produces one for controlling out-of-work the first control signal of described drive circuit, using described the first control signal as described power limiting control signal.
12. according to the arbitrary of claim 5 to 9 or the LED drive circuit control circuit described in 11, it is characterized in that,
Described first control circuit comprises:
Error compensating signal generative circuit, for according to characterizing the detection signal of described inductive current and characterizing the signal of described reference signal, produces error compensating signal,
The first cut-off signals circuit for generating, in the time that the magnitude of voltage of described detection signal rises to the magnitude of voltage of described error compensating signal, output is described the first cut-off signals effectively;
Continuity signal circuit for generating, in the time that the magnitude of voltage of described detection signal is reduced to described second voltage value, exports effective described Continuity signal.
13. 1 kinds of LED drive circuits, is characterized in that, comprise arbitrary described control circuit of power stage circuit and claim 5 to 12,
In described power stage circuit, be provided with main switch,
Described control circuit is exported described switch controlling signal to the control end of described main switch, controls the turn-on and turn-off of described main switch, with output one current signal at described LED drive circuit drive circuit.
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Application publication date: 20141119 |