CN109089350B - Control circuit for constant current drive circuit, control method for obtaining constant current and step-down constant current drive system - Google Patents
Control circuit for constant current drive circuit, control method for obtaining constant current and step-down constant current drive system Download PDFInfo
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Abstract
The invention discloses a control circuit for a constant current drive circuit, a control method for obtaining constant current and a step-down constant current drive system, wherein the constant current drive circuit comprises an inductor and a transistor coupled with the inductor, and the control circuit comprises: an inductor current processing circuit and a driving signal generating circuit; the input end of the inductor current processing circuit receives a detection signal representing the current flowing through the transistor, and the output end of the inductor current processing circuit outputs an inductor current processing signal, wherein the inductor current processing signal is controlled by the detection signal continuously for at least a period of time in one period; the driving signal generating circuit receives the inductance current processing signal and outputs a control signal to control the transistor. The control circuit for the constant current driving circuit, the control method for obtaining the constant current and the step-down constant current driving system can feed the charging current of the inductor back to the control loop in real time, and even if the circuit has nonlinear characteristics in the process of charging the inductor, the constant current output precision of the system can be ensured.
Description
Technical Field
The invention belongs to the technical field of power electronics, relates to a constant current drive circuit, and particularly relates to a control circuit for the constant current drive circuit, a control method for obtaining constant current and a step-down constant current drive system.
Background
The LED lighting lamp has the advantages of low energy consumption, high luminous efficiency, long service life and the like, and is widely applied to various lighting occasions at present. However, LEDs generally require high-precision constant current power supply driving, fig. 1 is a schematic diagram of constant current driving of a step-down LED, and in a conventional step-down LED constant current driving method using a low-side architecture, constant current integration operation is performed by sampling peak values of inductor current, the peak values of the inductor current cannot reflect average inductor current in an inductor charging time in real time, and particularly under low voltage input, since voltages at two ends of the inductor are lower, the charging current of the inductor can exhibit branching characteristics, and the average inductor current calculated by using peak inductor current is smaller than actual inductor current, so that the output constant current value of the system is increased, and the service life of an LED lighting device is affected.
Fig. 2 depicts inductor current versus time in a buck LED constant current drive system. As can be seen from fig. 2, when the current varies linearly during the charging and discharging process of the inductor current, the average value Ilavg =0.5×ilpk× (ton+ tdem)/T of the inductor current, and a buck LED constant current driving algorithm of the prior art uses this principle to realize the constant current output function of the system.
Fig. 3 illustrates a buck LED constant current driving algorithm of the prior art, in ton time, the peak sample/hold circuit samples the CS peak voltage, the peak sample/hold circuit output signal Vcspk performs Vcspk x (ton+ tdem)/T operation and then inputs the result to the inverting input terminal of the error amplifier EA, the EA output signal COMP sets the on time ton of Q1, and the whole loop is a negative feedback loop. Under the action of the negative feedback loop, the positive input of the error amplifier is equal to the negative input of the error amplifier, i.e. Vcspk (ton+ tdem)/t=vref. In the step-down constant current driving system, the system constant current output average value Iout is equal to the inductance current average value Ilpk, the inductance current peak value Ilpk = Vcspk/Rcs, and the inductance current average value is equal to Ilavg =0.5×ilpk (ton+ tdem)/T, so that the step-down constant current system output current average value iout= Ilavg =0.5×vref/Rcs is obtained, the Iout is determined by the reference voltage Vref and the sampling resistance ratio, and the constant current output function is realized independent of other parameters of the system.
The precondition for realizing constant current by the existing constant current driving algorithm is that the inductance current linearly changes in the inductance charging time ton and the inductance discharging time tdem. When the input voltage is higher, the differential pressure between two ends of the inductor is larger, the inductor current linearly rises in the charging time (ton), and linearly drops in the discharging time (tdem), and the traditional constant-current algorithm can realize a better constant-current effect; however, since the inductor is not an ideal device, the input voltage decreases, and when the voltage difference across the inductor is small, the current in the inductor charging time (ton) will exhibit a nonlinear characteristic. Referring to fig. 4, fig. 4 is a schematic diagram showing branching of current in an inductance charging process; as shown in fig. 4, at this time, the actual value of the average current in the inductor charging time (ton) is greater than half of the peak current of the inductor, and a larger error occurs in calculating the average value of the current in the inductor charging time (ton) through the peak current of the inductor, so that the constant current value actually output by the system is higher than the design value, and the constant current effect of the system in the full-voltage input range (85 Vac-277 Vac) is poor. Referring to fig. 5, fig. 5 is a schematic diagram of a constant current curve of the conventional algorithm within a full voltage input range (85 Vac-277 Vac); as shown in fig. 5, as the input voltage of the system decreases, the output current of the system increases, and the service life of the LED lamp beads is shortened due to the increase of the output current of the system, thereby shortening the service life of the whole LED lamp.
Therefore, the constant current characteristic price of the system in the full voltage input range is poor, the output current value of the system is larger than a typical design value when the input voltage is lower, and the service life of the LED lamp beads can be shortened after the actual working current of the LED lamp beads is larger than the rated working current of the LED lamp beads, so that the service life of the whole LED lamp is shortened.
In view of this, there is an urgent need to design a control manner of the constant current driving circuit so as to overcome the above-mentioned drawbacks of the existing control manner.
Disclosure of Invention
The technical problems to be solved by the invention are as follows: the control circuit for the constant current drive circuit, the control method for obtaining constant current and the step-down constant current drive system are provided, and the constant current output precision of the constant current drive circuit can be ensured.
In order to solve the technical problems, the invention adopts the following technical scheme:
A control circuit for a constant current drive circuit including an inductor and a transistor, the control circuit comprising:
An inductor current processing circuit, the input end of which is coupled with the transistor and used for receiving a detection signal representing the current flowing through the transistor, and the output end of which outputs an inductor current processing signal, wherein the inductor current processing signal is controlled by the detection signal which is continuous for at least a period of time in one period;
and the driving signal generating circuit receives the inductance current processing signal and outputs a control signal to control the transistor.
As one embodiment of the present invention, an inductor current processing circuit includes:
A first current signal acquisition circuit for acquiring a first current signal for when the transistor is turned on;
And a second current signal acquisition circuit including a peak sampling circuit for acquiring a peak signal of the detection signal, the second current signal acquisition circuit acquiring the second current signal when the transistor is turned off based on the peak signal.
As one embodiment of the present invention, the first current signal acquisition circuit includes an integrator for integrating the detection signal during a full period or a transistor on period;
The second current signal acquisition circuit is used for calculating a current signal of the inductive discharge process according to the peak value signal;
The inductive current processing circuit further comprises an adder, wherein a first end of the adder is coupled with the output end of the first current signal acquisition circuit, and a second end of the adder is coupled with the output end of the second current signal acquisition circuit.
As an embodiment of the present invention, the current signal of the inductive discharge process is vint2= Vcspk ×tdem/2, where Vcspk is the peak signal and Tdem is the inductive discharge duration.
As one embodiment of the present invention, the first current signal acquisition circuit includes a first switch, a first end of the first switch is used for receiving the detection signal, and a second end of the first switch is coupled to the driving signal generation circuit;
The second current signal acquisition circuit further comprises a second switch, the second switch is connected with the peak value sampling circuit in series, and the second end of the second switch is coupled with the driving signal generation circuit;
the inductive current processing circuit further comprises a third switch, a first end of the third switch is coupled with the driving signal generating circuit, and a second end of the third switch is grounded.
As one embodiment of the present invention, when the transistor is turned on, the first switch is turned on, and the second switch and the third switch are turned off; when the inductor discharges, the first switch and the second switch are turned off, and the second switch is turned on; during the rest of the time, the first switch and the second switch are turned off, and the third switch is turned on.
As one embodiment of the present invention, a drive signal generation circuit includes:
The first input end of the error amplifier is coupled with the output end of the inductive current processing circuit, and the second input end of the error amplifier is coupled with the reference voltage;
the first input end of the comparator is coupled with the output end of the error amplifier, and the second input end of the comparator is coupled with a sawtooth wave signal;
the inductance current zero-crossing detection circuit outputs an inductance current zero-crossing signal when inductance current passes zero;
The first input end of the trigger is coupled with the output end of the comparator, and the second input end of the trigger is coupled with the output end of the inductance current zero-crossing detection circuit;
The input end of the driving circuit is coupled with the output end of the trigger, and the output end of the driving circuit is coupled with the control end of the transistor.
As one embodiment of the invention, the constant current driving circuit comprises a resistor connected in series with a transistor, the detection signal is a voltage drop signal on the resistor, and the constant current output value is determined by a reference voltage and the resistance value of the resistor.
A buck constant current drive system comprising:
The rectification circuit is used for rectifying the alternating current input power supply;
the load, the inductance and the transistor are connected in series and are coupled between the output end of the rectifying circuit and the ground;
A diode coupled to the inductor and the load for freewheeling when the transistor is turned off; and
The control circuit of any of the above embodiments.
A control method for obtaining a constant current in a step-down constant current driving circuit, comprising:
coupling a load, an inductance and a transistor in series between the bus bar and ground;
acquiring a detection signal representative of the current flowing through the transistor;
Obtaining an inductor current processing signal, wherein the inductor current processing signal is controlled by a continuous detection signal for at least a period of time in one period;
the inductor current processing signal is controlled to follow a reference voltage.
As an embodiment of the present invention, the inductor current processing signal is a sum of a first current signal and a second current signal, the first current signal is a detection signal and is integrated with respect to time in a full period, the second signal is vint2= Vcspk ×tdem/2, wherein Vcspk is a peak signal, and Tdem is an inductor discharge duration.
A control circuit for a constant current drive circuit including an inductor and a transistor coupled to the inductor, the control circuit comprising:
the inductance current processing circuit is used for respectively acquiring current information of the inductance during charging and discharging and transmitting the acquired current information to the driving signal generating circuit;
the driving signal generating circuit is used for receiving the inductive current processing signal transmitted by the inductive current processing circuit and outputting a control signal to control the transistor.
As one embodiment of the present invention, the inductor current processing circuit includes:
The first inductance current processing circuit is used for acquiring current information of the inductance during charging and transmitting the acquired current information to the driving signal generating circuit;
And the second inductor current processing circuit is used for acquiring current information of the inductor during discharging and transmitting the acquired current information to the driving signal generating circuit.
As one embodiment of the present invention, the current information of the inductance charging process obtained by the first inductance current processing circuit is fed back to the driving signal generating circuit in real time; the current information of the inductance discharging process obtained by the second inductance current processing circuit is equivalent to half of the inductance peak current, and the current information is indirectly fed back to the driving signal generating circuit.
The invention has the beneficial effects that: the control circuit for the constant current driving circuit, the control method for obtaining the constant current and the step-down constant current driving system can feed the charging current of the inductor back to the control loop in real time, and even if the circuit has nonlinear characteristics in the process of charging the inductor, the constant current output precision of the system can be ensured, and the service life of the LED lamp beads is not influenced due to the current increase. The LED lamp bead service life can be prolonged, so that the service life of the whole LED lamp is prolonged.
Drawings
Fig. 1 is a schematic diagram of a buck LED constant current drive.
Fig. 2 is a diagram of the inductor current timing relationship of the buck LED constant current drive system.
Fig. 3 is a buck LED constant current driving algorithm of the prior art architecture.
Fig. 4 is a schematic diagram showing non-linearity of the inductor charging process current.
FIG. 5 is a schematic diagram of a constant current curve of the prior algorithm within the full voltage input range (85 Vac-277 Vac).
Fig. 6 is a circuit diagram of a constant current driving system including a control circuit according to an embodiment of the invention.
FIG. 7 is a diagram of an IL_ton waveform in a control circuit according to an embodiment of the present invention.
FIG. 8 is a waveform diagram of IL_ tdem in the control circuit according to an embodiment of the present invention.
Fig. 9 is a circuit diagram of another constant current driving system including a control circuit according to an embodiment of the invention.
FIG. 10 is a graph of inductor current, vcs and VINV in accordance with one embodiment of the present invention.
FIG. 11 is a graph showing IL, vcs and VINV relationships when inductor current is divided into linearities in an embodiment of the invention.
Detailed Description
Preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings.
For a further understanding of the present invention, preferred embodiments of the invention are described below in conjunction with the examples, but it should be understood that these descriptions are merely intended to illustrate further features and advantages of the invention, and are not limiting of the claims of the invention.
The description of this section is intended to be illustrative of only a few exemplary embodiments and the invention is not to be limited in scope by the description of the embodiments. It is also within the scope of the description and claims of the invention to interchange some of the technical features of the embodiments with other technical features of the same or similar prior art.
The term "coupled" or "connected" in the specification includes both direct and indirect connections, such as through some active, passive, or electrically conductive medium. "plurality" means two or more.
Referring to fig. 6, fig. 6 shows a constant current driving system according to an embodiment of the invention. The constant current drive circuit includes an inductance L and a transistor Q1. Preferably, the constant current driving system is a step-down constant current driving system. In the illustrated embodiment, specifically, the step-down type constant current driving system includes: a rectifying circuit for rectifying an alternating current input power source AC at a bus to a bus voltage Vbus; the load, the inductor L, the low-order transistor Q1 and the resistor Rcs which are connected in series are coupled between the bus and the ground; a diode D1 coupled to the inductor L and the load for freewheeling when the transistor Q1 is turned off; and a control circuit for the constant current drive system. In one embodiment, the constant current driving system may omit the resistor Rcs, and other methods are employed to detect the current flowing through the transistor Q1 to obtain the detection signal Vcs. In one embodiment, transistor Q1 may be located between the rectifying circuit and the load. Wherein the load is an LED in the illustrated embodiment, it can also be regarded as a parallel LED and a capacitor Cout.
The control circuit includes: an inductor current processing circuit 1 and a driving signal generating circuit 2.
The inductor current processing circuit 1 has an input coupled to the resistor Rcs for obtaining a detection signal Vcs indicative of the current flowing through the resistor Rcs, and an output for outputting an inductor current processing signal VINV, wherein the inductor current processing signal is controlled by a continuous detection signal for at least a period of time during one cycle. The drive signal generating circuit 2 receives the inductor current processing signal and outputs a control signal to control the transistor Q1.
The inductor current processing signal is controlled by a continuous detection signal for at least a period of time in one period, wherein the period of time can be the whole period, or can be one period of time in one period, such as the period that the transistor is on. The inductor current processing signal is controlled by the continuous detection signal for at least a period of time in one period, so that even if the peak signal of the detection signal is unchanged, the value of the inductor current processing signal can still change because the detection signal presents different waveforms for a period of time.
The method that the inductor current processing signal is controlled by the continuous detection signal at least in a period of time and then the transistor is controlled is abandoned, and the mode that the current flowing through the transistor is only controlled by the peak signal of the detection signal and is not controlled by the continuous detection signal is adopted. In one embodiment, the inductor current processing signal is generated based on the voltage drop signal and the peak signal of the voltage drop signal, respectively, i.e. the current detection signal and the peak signal of the detection signal are not necessary for generating the inductor current processing signal. This and the inductor current processing signal may only depend on the generation of the peak signal of the detection signal, although the acquisition of the peak signal depends on the detection signal is a different concept.
In some embodiments of the present invention, the inductor current processing circuit 1 includes: a first current signal acquisition circuit 101, a second current signal acquisition circuit 103. The first current signal acquisition circuit 101 is configured to acquire a first current signal Vint1 for when the transistor Q1 is turned on; the second current signal acquisition circuit 103 includes a peak sampling circuit for acquiring a peak signal Vcspk of the detection signal, and the second current signal acquisition circuit acquires a second current signal Vint2 when the transistor is turned off based on the peak signal Vcspk.
In some embodiments of the present invention, the first current signal acquisition circuit 101 may include a first integrator for integrating the detection signal Vcs during a full period or during the transistor Q1 is turned on; the second current signal acquisition circuit 103 is configured to calculate a current signal Vint2 of the inductive discharge process according to the peak signal Vcspk. The second current signal acquiring circuit 103 may also include a second integrator.
The inductor current processing circuit 1 further comprises an adder 105, a first end of the adder 105 is coupled to the output end of the first current signal acquisition circuit, and a second end of the adder 105 is coupled to the output end of the second current signal acquisition circuit. Of course, it should be appreciated that the term "device" is not intended to refer specifically to a device or apparatus, but rather may represent "circuitry" or a portion of "circuitry".
The current signal in the inductive discharge process is vint2= Vcspk ×tdem/2, wherein Vcspk is the peak signal and Tdem is the inductive discharge duration.
With continued reference to fig. 6, in one embodiment of the present invention, the driving signal generating circuit 2 includes: error amplifier 201, comparator 203, turn-on control circuit 204, flip-flop 205, and drive circuit 207.
A first input terminal of the error amplifier 201 is coupled to the output terminal of the inductor current processing circuit 1, and a second input terminal of the error amplifier 201 is coupled to the reference voltage. The constant current output value of the constant current driving circuit can be determined by the reference voltage and the resistance value of the resistor Rcs. A first input terminal of the comparator 203 is coupled to the output terminal of the error amplifier 201, and a second input terminal of the comparator 203 is coupled to a sawtooth signal. In one embodiment, the turn-on control circuit 204 is an inductor current zero crossing detection circuit. When the inductance current passes through zero, the inductance current zero-crossing detection circuit outputs an inductance current zero-crossing signal to trigger the conduction of the transistor Q1. A first input of the flip-flop 205 is coupled to the output of the comparator 203, and a second input of the flip-flop 205 is coupled to the output of the inductor current zero crossing detection circuit 204. An input terminal of the driving circuit 207 is coupled to an output terminal of the touch generator 205, and an output terminal of the driving circuit 207 is coupled to a control terminal of the transistor.
In some embodiments of the invention, the flip-flop 205 is an RS flip-flop.
In some embodiments of the present invention, the sawtooth signal is generated by a sawtooth signal generating circuit, which includes a current source Iref, a third capacitor C3, a fourth capacitor C4, and a switch pwm_b. The output terminal of the current source Iref is coupled to the first terminal of the fourth capacitor C4, the second input terminal (may be a positive input terminal) of the comparator 203, and the first terminal of the switch pwm_b, respectively; a first terminal of the third capacitor C3 is connected to the output terminal of the error amplifier 201 and a first input terminal (which may be an inverting input terminal) of the comparator 203, respectively. The second end of the third capacitor C3, the second end of the fourth capacitor C4, and the second end of the switch pwm_b are grounded, respectively.
With continued reference to fig. 6, in the buck-type constant current control system, the LED and the inductor are connected in series in a loop, and the average LED current, i.e., the system output current Iout, is equal to the average inductor current Ilavg. According to the method, through the action of a negative feedback system, the inductance current average value Ilavg =Vref/Rcs is controlled, and the constant current output of the system is realized irrespective of other parameters of the system.
Fig. 2 depicts a timing diagram of inductor current in a typical buck-type constant current control system. As can be seen from fig. 2, there are three states of inductor current: the first state, the inductive charging process in ton time; the second state, the inductive discharge process within tdem time; the third state, the process of inductor current 0 in time T- (ton + tdem).
The invention divides the inductance current into three parts for calculation:
A first part: referring to fig. 7, fig. 7 is a schematic diagram of an il_ton waveform in a control circuit according to an embodiment of the invention. Referring to the il_ton section of fig. 7, the inductor current of the ton section is taken alone. Although the il_ton waveform is shown as linear for ton time in the figure for simplicity of description, it should be understood that IL waveform is not generally strictly linear for ton time in practice. During ton time, Q1 is on, inductor current flows through Q1 and Rcs, and is converted into voltage signal Vcs in real time on Rcs. During other times T-ton, Q1 is off, vcs=0, and il_ton is also 0, so Vcs (T)/rcs=il_ton (T). Vcs is subjected to real-time full integration by an integrator 1, and the average value Vint1 of Vcs is obtained, wherein Vint1/Rcs is equal to the average value of il_ton.
A second part: referring to fig. 8, fig. 8 is a waveform diagram of il_ tdem in a control circuit according to an embodiment of the present invention. Referring to section IL tdem of fig. 8, the inductor current at section tdem is taken. The inductor current is linearly reduced from the peak value to 0 during the inductor discharge process, so that the average value of the inductor current in tdem time is equal to half of the peak value of the inductor current, and thus the average value of il_ tdem is equal to 0.5 x ilpk x tdem/T. Since Vcspk/rcs= Ilpk, integrator 2 performs a 0.5×vcspk×tdem/T integration operation by sampling and holding Vcspk values, and outputs signals Vint2, vint 2/rcs=0.5×vcspk×tdem/T/rcs=0.5×ilpk×tdem/T, vint2/Rcs is equal to the average value of il_ tdem.
As described above, vint1/Rcs is equal to the average value of IL_ton, vint2/Rcs is equal to the average value of IL_ tdem, and Vin3 is equal to zero. Inductor current IL is comprised of il_ton and il_ tdem. The inductor current average il_avg=vint 1/rcs+vint2/Rcs.
As shown in fig. 6, vint1 and Vint2 are output through the adder, vinv=vint1+vint2, and VINV is input to the inverting input terminal of the error amplifier EA, and the control circuit forms a negative feedback system in which vref=vinv is satisfied, so that vint1+vint2=vref, that is, the average value il_avg=vint1/rcs+vint2/rcs=vref/Rcs, is the average value il_avg=vint2+vint2=rvs.
In the buck type constant current system, the output constant current value Iout of the system is equal to the average value of the inductance current, so that the output constant current value iout=Vref/Rcs of the system is irrelevant to other parameters of the system, and constant current control in the buck type system is realized.
Because the inductor is not an ideal device, when the input voltage is reduced, the inductor charging current can show nonlinear characteristics (as shown in fig. 4), and the current in the inductor charging process is fed back to the reverse input end of the error amplifier EA in real time through Vcs, so that the inductor current value can be truly reflected, and high-precision constant current output can be realized when the inductor charging current can show nonlinear characteristics.
Referring to fig. 9, fig. 9 is a circuit diagram of a constant current driving system including a control circuit according to another embodiment of the invention.
The control circuit includes an inductor current processing circuit 1 and a drive signal generating circuit 2. The inductor current processing circuit 1 includes a first current signal acquisition circuit for acquiring a first current signal for when the transistor Q1 is turned on, and a second current signal acquisition circuit for acquiring a second current signal when the transistor is turned off based on a peak signal of the detection signal. In some embodiments of the present invention, the first current signal acquiring circuit includes a first switch K1, a first terminal of the first switch K1 is configured to receive a detection signal indicating a current flowing through the resistor, and a second terminal of the first switch K1 is coupled to the driving signal generating circuit 2. The circuit comprises a peak sampling circuit 111 for acquiring a peak signal of the detection signal Vcs, and further comprises a second switch K2, the second switch K2 is connected in series with the peak sampling circuit 111, and a second end of the second switch K2 is coupled to the driving signal generating circuit 2. A divider 113 may be connected in series between the peak sampling circuit 111 and the second switch K2 for dividing the peak signal by 2.
The inductor current processing circuit further comprises a third switch K3, a first end of the third switch K3 is coupled with the driving signal generating circuit 2, and a second end of the third switch K3 is grounded. When the transistor is turned on, the first switch K1 is turned on, and the second switch K2 and the third switch K3 are turned off; when the inductor discharges, the first switch K1 and the second switch K2 are turned off, and the second switch K2 is turned on; during the rest of the time, the first switch K1 and the second switch K2 are turned off, and the third switch K3 is turned on.
Specifically, in ton time, the first switch K1 is closed, the second switch K2 and the third switch K3 are opened, and the signal vinv=vcs is input to the inverting input terminal of the error amplifier EA.
In Tdem time, the first switch K1 and the third switch K3 are opened, the second switch K2 is closed, and the signal vinv=0.5×vcspk is input to the inverting input terminal of the error amplifier EA, where vcspk is the peak voltage of Vcs.
In the time T- (ton+ tdem), the first switch K1 and the second switch K2 are opened, the third switch K3 is closed, and the signal vinv=0 is input to the inverting input terminal of the error amplifier EA.
Referring to FIG. 10, FIG. 10 is a graph showing inductor current, vcs and VINV in accordance with one embodiment of the present invention.
Referring to FIG. 11, FIG. 11 is a graph showing IL, vcs and VINV relationships when inductor current is divided into linearities according to an embodiment of the invention. As shown in fig. 11, il=vcs/rcs=vinv/Rcs during ton time; for tdem times, inductor average current il_avg=0.5 x vcspk/rcs=vinv/Rcs; il=vinv=0 for T- (ton+ tdem) time.
The average VINV_avg of VINV/Rcs is therefore equal to the average IL_avg of IL. The average value vinv_avg=vref of VINV is input to the inverting input of the error amplifier, and by control loop negative feedback, il_avg=vinv_avg/rcs=vref/Rcs. In the buck constant current system, the constant current output value iout=il_avg of the system is completely determined by the reference voltages Vref and Rcs, is irrelevant to other parameters of the system, and the current IL flowing through the inductor during ton tracks Vref/Rcs in real time, preferably Vref and Rcs as two fixed parameters, so that the constant current output function of the system is realized.
Because the inductor is not an ideal device, when the input voltage is reduced, the inductor charging current can show nonlinear characteristics (as shown in fig. 11), and the current in the inductor charging process is fed back to the reverse input end of the error amplifier EA in real time through the VCS, so that the inductor current value can be truly reflected, and high-precision constant current output can be realized when the inductor charging current can show nonlinear characteristics.
In an embodiment of the present invention, the constant current driving circuit includes an inductor, and the control circuit includes: an inductor current processing circuit and a driving signal generating circuit. The inductance current processing circuit is used for respectively acquiring current information of the inductance during charging and discharging and transmitting the acquired current information to a driving signal generating circuit; the driving signal generating circuit is used for receiving the inductive current processing signal transmitted by the inductive current processing circuit and outputting a control signal to control the transistor.
In one embodiment of the present invention, the inductor current processing circuit includes: the first inductor current processing circuit and the second inductor current processing circuit. The first inductance current processing circuit is used for acquiring current information of the inductance in real time during charging and transmitting the acquired current information to the driving signal generating circuit; the second inductor current processing circuit is used for acquiring current information of the inductor during discharging and transmitting the acquired current information to the driving signal generating circuit. The driving signal generating circuit is used for receiving the inductive current processing signals transmitted by the first inductive current processing circuit and the second inductive current processing circuit and outputting control signals to control the transistor.
In an embodiment of the present invention, the first inductor current processing circuit may include the first integrator 101 in fig. 6, and the second inductor current processing circuit may include the second integrator 103 in fig. 6; the control circuit may further include an adder 105, where the adder 105 is used as a part of the first inductor current processing circuit and the second inductor current processing circuit, and the adder 105, together with the first inductor current processing circuit and the second inductor current processing circuit, feeds back current data of the inductor during charging and discharging to the driving signal generating circuit. Of course, the adder may be regarded as not belonging to the first inductor current processing circuit and the second inductor current processing circuit, but as being independent of the first inductor current processing circuit and the second inductor current processing circuit.
In an embodiment of the present invention, the first inductor current processing circuit may include the first switch K1 in fig. 9, and the second inductor current processing circuit may include the second switch K2 and the peak sampling circuit 111 in fig. 9.
The current information of the inductance charging process acquired by the first inductance current processing circuit is fed back to the driving signal generating circuit in real time; the current information of the inductance discharging process obtained by the second inductance current processing circuit is equivalent to half of the inductance peak current, and the current information is indirectly fed back to the driving signal generating circuit. Details of the specific processes are described above, and are not described here.
The invention also discloses a control method for obtaining constant current in the step-down constant current driving circuit, which comprises the following steps:
coupling a load, an inductance and a transistor in series between the bus bar and ground;
acquiring a detection signal representative of the current flowing through the transistor;
obtaining an inductor current processing signal, wherein the inductor current processing signal is controlled by a continuous detection signal for at least a period of time in one period; ;
the inductor current processing signal is controlled to follow a reference voltage.
In one embodiment, the inductor current processing signal is generated in one period based on the detection signal and the peak signal of the detection signal, respectively. That is, the current detection signal and the peak signal of the detection signal are indispensable for generating the inductor current processing signal. The current sense signal here includes a real-time current sense signal over a period of time. This is quite different from the fact that the inductor current processing signal may only rely on the generation of the peak signal of the detection signal, although the generation of the peak signal depends on the detection signal.
In one embodiment, the transistor is a low-order transistor.
In one embodiment, the method further comprises connecting a resistor in series with the transistor and obtaining a current sense signal through the transistor by sensing a voltage drop signal across the resistor.
In an embodiment of the present invention, the inductor current processing signal is a sum of a first current signal and a second current signal, the first current signal is a detection signal and integrates the detection signal with respect to time in a full period, the second signal is vint2= Vcspk ×tdem/2, wherein Vcspk is a peak signal, and Tdem is an inductor discharge duration.
The specific control process of the control method of the present invention can be referred to the above description of the control circuit, and will not be described herein.
The invention discloses a step-down constant current driving system, which comprises: the rectifying circuit, load, inductance, low-order transistor and resistance, diode, control circuit of series connection. The rectification circuit is used for rectifying the alternating current input power supply; the load, the inductor, the low-order transistor and the resistor which are connected in series are coupled between the output end of the rectifying circuit, namely the bus and the ground; the diode couples the inductor and the load for freewheeling when the transistor is off. The control circuit may be the control circuit of the present invention described above.
In summary, the control circuit for the constant current driving circuit, the control method for obtaining the constant current and the step-down constant current driving system provided by the invention can feed back the inductance charging current to the control loop in real time, and even if the circuit has nonlinear characteristics in the inductance charging process, the constant current output precision of the system can be ensured, and the service life of the LED lamp beads is not influenced due to the current increase. The LED lamp bead service life can be prolonged, so that the service life of the whole LED lamp is prolonged.
The description and applications of the present invention herein are illustrative and are not intended to limit the scope of the invention to the embodiments described above. Variations and modifications of the embodiments disclosed herein are possible, and alternatives and equivalents of the various components of the embodiments are known to those of ordinary skill in the art. It will be clear to those skilled in the art that the present invention may be embodied in other forms, structures, arrangements, proportions, and with other assemblies, materials, and components, without departing from the spirit or essential characteristics thereof. Other variations and modifications of the embodiments disclosed herein may be made without departing from the scope and spirit of the invention.
Claims (12)
1. A control circuit for a constant current drive circuit, the constant current drive circuit comprising an inductor and a transistor coupled to the inductor, the control circuit comprising:
an inductor current processing circuit, the input end of which is coupled with the transistor and used for receiving a detection signal representing the current flowing through the transistor, and the output end of which outputs an inductor current processing signal, wherein the inductor current processing signal is controlled by the detection signal which is continuous for at least a period of time in one period;
A drive signal generating circuit for receiving the inductor current processing signal and outputting a control signal to control the transistor;
The inductor current processing circuit includes:
A first current signal acquisition circuit for acquiring a first current signal for when the transistor is turned on;
A second current signal acquisition circuit including a peak sampling circuit for acquiring a peak signal of the detection signal, the second current signal acquisition circuit acquiring a second current signal when the transistor is turned off based on the peak signal;
The first current signal acquisition circuit comprises an integrator, which is used for integrating the detection signal in a full period or a transistor on period;
The second current signal acquisition circuit is used for calculating a current signal of the inductive discharge process according to the peak value signal;
The inductive current processing circuit further comprises an adder, wherein a first end of the adder is coupled with the output end of the first current signal acquisition circuit, and a second end of the adder is coupled with the output end of the second current signal acquisition circuit.
2. The control circuit of claim 1, wherein the current signal of the inductive discharge process is vint2= Vcspk Tdem/2, wherein Vcspk is a peak signal and Tdem is an inductive discharge duration.
3. The control circuit of claim 1, wherein:
The first current signal acquisition circuit comprises a first switch, a first end of the first switch is used for receiving the detection signal, and a second end of the first switch is coupled with the driving signal generation circuit;
The second current signal acquisition circuit further comprises a second switch, the second switch is connected with the peak value sampling circuit in series, and the second end of the second switch is coupled with the driving signal generation circuit;
the inductive current processing circuit further comprises a third switch, a first end of the third switch is coupled with the driving signal generating circuit, and a second end of the third switch is grounded.
4. The control circuit of claim 3, wherein the first switch is on, and the second switch and the third switch are off when the transistor is on; when the inductor discharges, the first switch and the second switch are turned off, and the second switch is turned on; during the rest of the time, the first switch and the second switch are turned off, and the third switch is turned on.
5. The control circuit according to claim 1, wherein the drive signal generation circuit includes:
The first input end of the error amplifier is coupled with the output end of the inductive current processing circuit, and the second input end of the error amplifier is coupled with the reference voltage;
the first input end of the comparator is coupled with the output end of the error amplifier, and the second input end of the comparator is coupled with a sawtooth wave signal;
the inductance current zero-crossing detection circuit outputs an inductance current zero-crossing signal when inductance current passes zero;
The first input end of the trigger is coupled with the output end of the comparator, and the second input end of the trigger is coupled with the output end of the inductance current zero-crossing detection circuit;
The input end of the driving circuit is coupled with the output end of the trigger, and the output end of the driving circuit is coupled with the control end of the transistor.
6. The control circuit of claim 5 wherein the constant current drive circuit comprises a resistor in series with the transistor, the sense signal is a voltage drop signal across the resistor, and the constant current output value is determined by the reference voltage and the resistance of the resistor.
7. A step-down constant current drive system, characterized by comprising:
The rectification circuit is used for rectifying the alternating current input power supply;
the load, the inductance and the transistor are connected in series and are coupled between the output end of the rectifying circuit and the ground;
A diode coupled to the inductor and the load for freewheeling when the transistor is turned off; and
A control circuit as claimed in any one of claims 1 to 6.
8. A control method for obtaining a constant current in a step-down constant current driving circuit, comprising:
coupling a load, an inductance and a transistor in series between the bus bar and ground;
acquiring a detection signal representative of the current flowing through the transistor;
Obtaining an inductor current processing signal through an inductor current processing circuit, wherein the inductor current processing signal is controlled by a continuous detection signal in at least one period of time;
Controlling the inductor current processing signal to follow a reference voltage;
The inductor current processing circuit includes:
A first current signal acquisition circuit for acquiring a first current signal for when the transistor is turned on; the first current signal acquisition circuit comprises an integrator, which is used for integrating the detection signal in a full period or a transistor on period;
A second current signal acquisition circuit including a peak sampling circuit for acquiring a peak signal of the detection signal, the second current signal acquisition circuit acquiring a second current signal when the transistor is turned off based on the peak signal; the second current signal acquisition circuit is used for calculating a current signal of the inductive discharge process according to the peak value signal;
The inductive current processing circuit further comprises an adder, wherein a first end of the adder is coupled with the output end of the first current signal acquisition circuit, and a second end of the adder is coupled with the output end of the second current signal acquisition circuit.
9. The control method of claim 8, wherein the inductor current processing signal is a sum of a first current signal and a second current signal, the first current signal being a detection signal integrated over time during a full period, the second signal being vint2= Vcspk Tdem/2, wherein Vcspk is a peak signal and Tdem is an inductor discharge duration.
10. A control circuit for a constant current drive circuit, the constant current drive circuit comprising an inductor and a transistor coupled to the inductor, the control circuit comprising:
the inductance current processing circuit is used for respectively acquiring current information of the inductance during charging and discharging and transmitting the acquired current information to the driving signal generating circuit;
The driving signal generating circuit is used for receiving the inductive current processing signal transmitted by the inductive current processing circuit and outputting a control signal to control the transistor;
The inductor current processing circuit includes:
A first current signal acquisition circuit for acquiring a first current signal for when the transistor is turned on;
A second current signal acquisition circuit including a peak sampling circuit for acquiring a peak signal of the detection signal, the second current signal acquisition circuit acquiring a second current signal when the transistor is turned off based on the peak signal;
The first current signal acquisition circuit comprises an integrator, which is used for integrating the detection signal in a full period or a transistor on period;
The second current signal acquisition circuit is used for calculating a current signal of the inductive discharge process according to the peak value signal;
The inductive current processing circuit further comprises an adder, wherein a first end of the adder is coupled with the output end of the first current signal acquisition circuit, and a second end of the adder is coupled with the output end of the second current signal acquisition circuit.
11. The control circuit of claim 10, wherein the inductor current processing circuit comprises:
The first inductance current processing circuit is used for acquiring current information of the inductance during charging and transmitting the acquired current information to the driving signal generating circuit;
And the second inductor current processing circuit is used for acquiring current information of the inductor during discharging and transmitting the acquired current information to the driving signal generating circuit.
12. The control circuit according to claim 11, wherein the current information of the inductive charging process obtained by the first inductive current processing circuit is fed back to the driving signal generating circuit in real time; the current information of the inductance discharging process obtained by the second inductance current processing circuit is equivalent to half of the inductance peak current, and the current information is indirectly fed back to the driving signal generating circuit.
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