CN111511074B - LED driving circuit and control method - Google Patents

LED driving circuit and control method Download PDF

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Publication number
CN111511074B
CN111511074B CN202010369151.XA CN202010369151A CN111511074B CN 111511074 B CN111511074 B CN 111511074B CN 202010369151 A CN202010369151 A CN 202010369151A CN 111511074 B CN111511074 B CN 111511074B
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voltage
resistor
control unit
current
unit
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CN111511074A (en
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夏勤
安文杰
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Shaanxi Reactor Microelectronics Co ltd
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Shaanxi Reactor Microelectronics Co ltd
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    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
    • H05B45/00—Circuit arrangements for operating light-emitting diodes [LED]
    • H05B45/30—Driver circuits
    • H05B45/32—Pulse-control circuits
    • H05B45/325—Pulse-width modulation [PWM]
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02B—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS
    • Y02B20/00—Energy efficient lighting technologies, e.g. halogen lamps or gas discharge lamps
    • Y02B20/40—Control techniques providing energy savings, e.g. smart controller or presence detection

Abstract

The invention discloses an LED driving circuit and a control method, wherein the circuit comprises a rectifying unit, a current control unit, a constant current control unit and an LED load, wherein the rectifying unit is used for providing input voltage; the current control unit is used for controlling the input current of the LED load according to the input voltage; the constant current control unit is used for keeping the output current of the LED load constant; the first end and the third end of the rectifying unit are connected with an alternating current power supply, the second end of the rectifying unit is connected with the first end of the current control unit, the second end of the current control unit is connected with the first end of the LED load, the second end of the LED load is connected with the first end of the constant current control unit, the fourth end of the rectifying unit, the third end of the current control unit and the second end of the constant current control unit are all grounded, and power factors and efficiency are compensated within different time through effective control over input current of the LED load.

Description

LED driving circuit and control method
Technical Field
The application relates to the technical field of LED constant current control, in particular to an LED driving circuit and a control method.
Background
The LED is a semiconductor electronic component capable of emitting light, has advantages of high efficiency, long service life, energy saving, environmental protection, etc. compared with the conventional light source, and has been widely used in various illumination fields such as displays, indicator lamps, indoor life illumination, outdoor landscape illumination, etc.
Efficiency (Efficiency) is the ratio of the average power of the LEDs to the average power input to the power supply during a cycle, and low Efficiency increases the power supply losses.
The Power factor (Power factor) is a cosine value of a phase difference between an input voltage and an input current, and low Power factor increases loss of a Power grid.
In the LED linear driving circuit, in a normal use range, the power factor PF value of the system increases with an increase in the input voltage, but the efficiency decreases, and both cannot be satisfied.
As shown in FIG. 1, a conventional single-segment linear LED driving circuit is configured such that an AC voltage is converted into an input voltage V after passing through a rectifier bridgeINAnd supplies power to the LED lamp string which is composed of n single LEDs connected in series, and the total voltage is VLED＝n*VLEDiIn which V isLEDiIs the voltage drop of a single LED, the value of which is determined by the application scheme. The input end of the LED lamp string is connected with the output end of the rectifier bridge, the output end of the LED lamp string is connected with the constant current control chip, and the constant current control chip controls the constant currentThe circuit module realizes constant current output.
FIG. 2 is a waveform diagram of the single-stage linear LED driving circuit, which is shown in FIG. 2, and is applied at different input voltages VINIn the period when the input voltage V isINGreater than the set voltage V of the lamp beadLEDIn time, the excessive voltage drop is applied to the control circuit IC, so that the temperature of the IC is increased, the power consumption is increased, and the IC is burnt out; when the input voltage VINLess than the set voltage V of the lamp beadLEDThen the LED string is not conducting and the LED is conducting for time t 1. The input voltage VINThe larger the amplitude of (c), the larger the power factor of the system, but conversely the input voltage VINThe larger the amplitude of (c), the lower the efficiency of the system.
In the LED driving circuit structure, one control circuit method for improving efficiency is to control the input current I, the control circuit diagram of which is shown in fig. 3, sample the voltage at the upper end of the resistor R, then input the voltage and the reference voltage Vref to the comparator, and the output is fed back to the voltage control circuit. The waveform of the input current I can be changed by the voltage control circuit when the input voltage V isINWhen the voltage is increased to be higher than the set voltage VLED of the lamp beads, the larger the voltage is, the smaller the current flowing through the LED lamp string is, so that the input power is maintained to be basically unchanged, and the efficiency of the system is improved. The operating waveform of the above-described drive circuit is shown in FIG. 4, and is applied to an input voltage VINWhen being higher than the total pressure drop of the LED lamp beads, the LED is conducted, otherwise, the LED is not conducted. However, this method has the disadvantage that the phase relationship between the input voltage and the input current is changed, so that the power factor is deteriorated and the power factor requirement cannot be met.
Therefore, it is one of the problems to be solved by those skilled in the art to provide an LED driving circuit with balanced efficiency and power factor and improved performance.
Disclosure of Invention
The invention provides an LED driving circuit, which is used for solving the technical problem that efficiency and power factor cannot be balanced in the LED driving circuit due to the fact that the efficiency and the power factor have a trade-off relation in the prior art.
In some embodiments of the present application, the circuit includes a rectifying unit, a current control unit, a constant current control unit, and an LED load,
the rectifying unit is used for providing input voltage;
the current control unit is used for controlling the input current of the LED load according to the input voltage;
the constant current control unit is used for keeping the output current of the LED load constant;
the first end and the third end of the rectifying unit are connected with an alternating current power supply, the second end of the rectifying unit is connected with the first end of the current control unit, the second end of the current control unit is connected with the first end of the LED load, the second end of the LED load is connected with the first end of the constant current control unit, and the fourth end of the rectifying unit, the third end of the current control unit and the second end of the constant current control unit are all grounded.
In some embodiments of the present application, the current control unit further includes a voltage detection unit, an on-time control unit, and a current adjustment unit,
the voltage detection unit is used for outputting a voltage detection result corresponding to the input voltage as a time control pulse signal and a detection voltage value and inputting the time control pulse signal and the detection voltage value into the conduction time control unit;
the on-time control unit is used for generating a control signal according to the time control pulse signal and the detection voltage value and controlling the output of the current adjusting unit based on the control signal;
the current adjusting unit is used for controlling the input current according to the control signal;
the first end of the voltage detection unit and the first end of the current adjustment unit are connected with the first end of the current control unit, the second end of the voltage detection unit is connected with the first end of the conduction time control unit, the second end of the conduction time control unit is connected with the second end of the current adjustment unit, the third end of the conduction time control unit is the third end of the current control unit, and the third end of the current adjustment unit is the second end of the current control unit.
In some embodiments of the present application, the voltage detection unit further includes a first resistor, a second resistor, a third resistor, a fourth resistor, a fifth resistor, a sixth resistor, a seventh resistor, an eighth resistor, a comparator, an inverter, a first voltage regulator and a second voltage regulator,
the first resistor, the second resistor, the third resistor, the fourth resistor and the fifth resistor are sequentially connected in series between the first end of the voltage detection unit and the ground, the connecting point of the first resistor and the second resistor is connected with the first end of the sixth resistor, the second end of the sixth resistor and the first end of the seventh resistor are connected to the positive input end of the comparator in common, the negative input end of the comparator is connected with a fixed reference voltage, the output end of the comparator is connected with the first end of the eighth resistor, the second end of the seventh resistor, the second end of the eighth resistor and the anode of the first voltage regulator tube are connected to the input end of the inverter in common, the output end of the phase inverter is the second end of the voltage detection unit, the cathode of the first voltage-stabilizing tube is connected with the cathode of the second voltage-stabilizing tube, and the anode of the second voltage-stabilizing tube is grounded.
In some embodiments of the present application, the constant current control unit further includes an error amplifier, a power transistor, and a ninth resistor,
the positive input end of the error amplifier is connected with a fixed reference voltage, the negative input end of the error amplifier and the source electrode of the power tube are connected with the first end of the ninth resistor in common, the output end of the error amplifier is connected with the grid electrode of the power tube, the drain electrode of the power tube is the first end of the constant current control unit, and the second end of the ninth resistor is the second end of the constant current control unit.
In some embodiments of the present application, the circuit further comprises:
the current comparison unit is used for keeping the average value of the drain voltage of the power tube constant;
the first end of the current comparison unit and the first end of the constant current control unit are connected to the second end of the LED load in a shared mode, and the second end of the current comparison unit is connected with the fourth end of the current control unit.
In some embodiments of the present application, the current comparing unit further includes a tenth resistor, an eleventh resistor, a twelfth resistor, a thirteenth resistor, a fourteenth resistor, a first transistor, a second transistor, a third transistor, an operational amplifier, a constant current source, and a capacitor,
the tenth resistor, the eleventh resistor, the twelfth resistor, and the thirteenth resistor are sequentially connected in series between a first end of the current comparing unit and ground, a connection point of the eleventh resistor and the twelfth resistor is connected to a positive input end of the operational amplifier, a negative input end of the operational amplifier and a first end of the fourteenth resistor are connected to a source of the first transistor in common, an output end of the operational amplifier is connected to a gate of the first transistor, a drain of the second transistor, a gate of the second transistor, and a gate of the third transistor are connected to a drain of the first transistor in common, a source of the second transistor and a source of the third transistor are connected to a dc power supply, and a drain of the third transistor and a first end of the capacitor are connected to an input end of the constant current source in common, the second end of the fourteenth resistor, the output end of the constant current source and the second end of the capacitor are all grounded, and the first end of the capacitor is the second end of the current comparison unit.
In some embodiments of the present application, the circuit further includes a filtering unit connected to the second terminal of the current control unit, and the filtering unit is configured to provide a current to the LED load according to a control signal of the current control unit.
Corresponding to the LED drive circuit in the embodiment of the application, the application also provides a control method of the LED drive circuit, which is applied to the LED drive circuit comprising a rectifying unit, a current control unit, a constant current control unit and an LED load,
in some embodiments of the present application, the method comprises:
receiving an input voltage provided by the rectifying unit;
generating a current control signal of the current control unit according to the variation trend of the input voltage and the voltage value of the input voltage;
and controlling the input current of the LED load according to the current control signal, and keeping the output current of the LED load constant based on the constant current control unit.
In some embodiments of the present application, the generating the current control signal of the current control unit according to the variation trend of the input voltage and the voltage value of the input voltage specifically includes:
if the input voltage is in a rising trend and the voltage value is between a first preset threshold value and a second preset threshold value, determining a first change trend of the input current according to a change trend of first detection voltage corresponding to the input voltage, and generating the current control signal according to the first change trend;
if the voltage value is larger than a second preset threshold value, determining a second variation trend of the input current according to a variation trend of second detection voltage corresponding to the input voltage, and generating the current control signal according to the second variation trend;
if the input voltage is in a descending trend and the voltage value is between the first preset threshold and the second preset threshold, determining a third change trend of the input current according to a change trend of a third detection voltage corresponding to the input voltage, and generating the current control signal according to the third change trend.
In some embodiments of the present application, the circuit further comprises a filtering unit connected to the current control unit, and the method further comprises:
when the voltage value is larger than the first preset threshold value, charging the filtering unit;
when the LED load is in a working state and the voltage value is smaller than the first preset threshold value, the input current is generated based on the filtering unit.
Compared with the prior art, the invention has the following beneficial effects:
the invention discloses an LED driving circuit and a control method, the circuit comprises a rectifying unit, a current control unit, a constant current control unit and an LED load, wherein the first end and the third end of the rectifying unit are connected with an alternating current power supply, the second end of the rectifying unit is connected with the first end of the current control unit, the second end of the current control unit is connected with the first end of the LED load, the second end of the LED load is connected with the first end of the constant current control unit, the fourth end of the rectifying unit, the third end of the current control unit and the second end of the constant current control unit are all grounded, and when the LED is kept not stroboflash, the power factor and efficiency can be compensated in different time through effective control of input current of the LED load, so that the power factor and the efficiency of the LED driving circuit are improved.
The invention discloses an LED driving circuit and a control method, which can realize balanced compromise of efficiency and power factor by adjusting the compensation voltage value of the efficiency and the power factor through a resistor.
Drawings
In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings needed to be used in the description of the embodiments are briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present application, and it is obvious for those skilled in the art to obtain other drawings based on these drawings without creative efforts.
FIG. 1 is a schematic diagram of a single-segment linear LED driving circuit in the prior art;
FIG. 2 is a schematic diagram showing the structural operation waveforms of a single-segment linear LED driving circuit in the prior art;
FIG. 3 is a schematic diagram of another prior art single-segment linear LED driving circuit;
FIG. 4 is a schematic diagram showing the structural operation waveforms of another single-segment linear LED driving circuit in the prior art;
FIG. 5 is a schematic diagram of an LED driving circuit according to an embodiment of the present invention;
FIG. 6 is a schematic diagram of an LED driving circuit according to another embodiment of the present invention;
FIG. 7 is a schematic structural diagram of a voltage detection unit according to an embodiment of the present invention;
FIG. 8 is a schematic diagram showing a structure of a current comparing unit according to an embodiment of the present invention;
fig. 9 shows a flow chart of a control method of an LED driving circuit in an embodiment of the present invention:
fig. 10 is a schematic waveform diagram illustrating a control method of an LED driving circuit according to an embodiment of the present invention.
Detailed Description
The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application, and it is obvious that the described embodiments are only a part of the embodiments of the present application, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present application.
As described in the background, in the prior art, since the efficiency and the power factor have a trade-off relationship, the efficiency and the power factor cannot be equalized in the LED driving circuit.
An embodiment of the present invention provides an LED driving circuit, as shown in fig. 5, the circuit includes a rectifying unit 101, a current control unit 102, a constant current control unit 104 and an LED load 103,
the rectifying unit 101 is used for providing an input voltage;
the current control unit 102 is configured to control an input current of the LED load 104 according to the input voltage;
the constant current control unit 103 is configured to keep an output current of the LED load 104 constant;
the first end and the second end of the rectifying unit 101 are connected with an alternating current power supply AC, the second end of the rectifying unit 101 is connected with the first end of the current control unit 102, the second end of the current control unit 102 is connected with the first end of the LED load 104, the second end of the LED load 104 is connected with the first end of the constant current control unit 103, and the fourth end of the rectifying unit 101, the third end of the current control unit 102 and the second end of the constant current control unit 103 are all grounded.
In order to make the current control unit output a qualified input current, in the preferred embodiment of the present application, as shown in fig. 6, the current control unit further includes a voltage detection unit 10, an on-time control unit 20 and a current adjustment unit 30,
the voltage detection unit 10 is configured to output a voltage detection result corresponding to the input voltage as a time control pulse signal and a detection voltage value, and input the time control pulse signal and the detection voltage value to the on-time control unit 20;
the on-time control unit 20 is configured to generate a control signal according to the time control pulse signal and the detection voltage value, and control the output of the current adjustment unit 30 based on the control signal;
the current adjusting unit 30 is configured to control the input current according to the control signal;
the first end of the voltage detection unit 10 and the first end of the current adjustment unit 30 are commonly connected to the first end of the current control unit 102, the second end of the voltage detection unit 10 is connected to the first end of the on-time control unit 20, the second end of the on-time control unit 20 is connected to the second end of the current adjustment unit 30, the third end of the on-time control unit 20 is the third end of the current control unit 102, and the third end of the current adjustment unit 30 is the second end of the current control unit 102.
In order to enable the voltage detection unit 10 to output a qualified voltage detection result, in a preferred embodiment of the present application, as shown in fig. 7, the voltage detection unit 10 further includes a first resistor R1, a second resistor R2, a third resistor R3, a fourth resistor R4, a fifth resistor R5, a sixth resistor R6, a seventh resistor R7, an eighth resistor R8, a comparator comp, an inverter INV, a first voltage regulator D1, and a second voltage regulator D2,
the first resistor R1, the second resistor R2, the third resistor R3, the fourth resistor R4 and the fifth resistor R5 are sequentially connected in series between the first end of the voltage detection unit 10 and the ground, a connection point of the first resistor R1 and the second resistor R2 is connected with the first end of the sixth resistor R6, the second end of the sixth resistor R6 and the first end of the seventh resistor R7 are commonly connected to the positive input end of the comparator comp, the negative input end of the comparator comp is connected with a fixed reference voltage, the output end of the comparator comp is connected with the first end of the eighth resistor R8, the second end of the seventh resistor R7, the second end of the eighth resistor R8 and the anode of the first diode D1 are commonly connected to the input end of the inverter INV, the output end of the inverter INV is the second end of the voltage detection unit 10, the cathode of the first diode D1 is connected with the cathode of the second diode D2, the anode of the second regulator tube D2 is grounded.
Specifically, the first resistor R1, the second resistor R2, the third resistor R3, the fourth resistor R4 and the fifth resistor R5 form an adjustable resistor, and the voltage V is detected by different resistor ratiosINGenerating a voltage pulse through a comparator comp according to the detected voltage value and the set level; the inverter is used for realizing a voltage detection result which is logically opposite to the voltage pulse.
In order to ensure that the output current of the LED load 104 is stable, in the preferred embodiment of the present application, as shown in fig. 6, the constant current control unit 103 further includes an error amplifier amp, a power transistor Mn and a ninth resistor R9,
the positive input end of the error amplifier amp is connected with a fixed reference voltage, the negative input end of the error amplifier amp and the source electrode of the power tube Mn are commonly connected with the first end of the ninth resistor R9, the output end of the error amplifier amp is connected with the gate electrode of the power tube Mn, the drain electrode of the power tube Mn is the first end of the constant current control unit 103, and the second end of the ninth resistor R9 is the second end of the constant current control unit 103.
Specifically, the value of the fixed reference voltage VREF and the resistance value of the resistor R9 determine the constant current operating current of the LED load, and if the constant current operating current is Iled, we will say that Iled is VREF/R9.
In order to keep the average value of the output voltage of the LED load 104 stable, in the preferred embodiment of the present application, as shown in fig. 6, the circuit further includes:
a current comparison unit 50 for keeping the average value of the drain voltage of the power transistor Mn constant;
a first end of the current comparing unit 50 and a first end of the constant current control unit 103 are commonly connected to a second end of the LED load 104, and a second end of the current comparing unit 50 is connected to a fourth end of the current control unit 102.
Specifically, the purpose of the current comparison unit is to detect the change of the drain voltage Mn of the power transistor in the constant current control unit 103, i.e., V2, and then maintain the average value of the drain voltage constant through the adjustment of other modules of the circuit. Mn drain voltage and input voltage V of power tubeINIn-phase variation, system input voltage VINWill cause the drain voltage to rise, the system input voltage VINThe decrease in voltage causes a decrease in the drain voltage. When the drain voltage is increased, excessive voltage falls on the power switch tube, the power consumption of the power switch tube is increased, the system efficiency is reduced, and the chip is even damaged by high voltage; when the drain voltage is reduced, the constant current control unit enters a non-constant current working state, so that the current flowing through the LED load is changed, and the optical stroboflash of the LED is caused. Therefore, the average value of the drain voltage is kept at a stable value by the current comparison unit, so that the average value is not influenced by the line voltage fluctuation, the optical stroboflash of the LED is reduced, and the stability of the system is improved.
To further ensure the stability of the average value of the output voltage of the LED load 104, in the preferred embodiment of the present application, as shown in fig. 8, the current comparing unit 50 further includes a tenth resistor R10, an eleventh resistor R11, a twelfth resistor R12, a thirteenth resistor R13, a fourteenth resistor R14, a first transistor M1, a second transistor M2, a third transistor M3, an operational amplifier OP, a constant current source u, and a capacitor C,
the tenth resistor R10, the eleventh resistor R11, the twelfth resistor R12 and the thirteenth resistor R13 are sequentially connected in series between the first end of the current comparing unit 50 and the ground, a connection point of the eleventh resistor R11 and the twelfth resistor R12 is connected to a positive input terminal of the operational amplifier OP, a negative input terminal of the operational amplifier OP and the first end of the fourteenth resistor R14 are commonly connected to a source of the first transistor M1, an output terminal of the operational amplifier OP is connected to a gate of the first transistor M1, a drain of the second transistor M2, a gate of the second transistor M2 and a gate of the third transistor M3 are commonly connected to a drain of the first transistor M1, a source of the second transistor M2 and a source of the third transistor M3 are all connected to a power supply Vdd, a drain of the third transistor M3 and a first end of the capacitor C are commonly connected to an input terminal of the constant current source, a second end of the fourteenth resistor R14, an output end of the constant current source u, and a second end of the capacitor C are all grounded, and a first end of the capacitor C is a second end of the current comparing unit 50.
Specifically, as shown in fig. 8, the current comparing unit is mainly composed of a resistor, a transistor, a capacitor, and an operational amplifier. The voltage of V2 is the sampling voltage of drain terminal, and resistance R10-R13 are divider resistance, and electric capacity C is external paster electric capacity. M2 and M3 are a pair of current mirrors, and Ibias1 is the bias current. The working principle of the current comparison unit is as follows: the drain voltage V2 is sampled and then divided by a certain proportion of resistors and input to the non-inverting input terminal of the operational amplifier OP. A current of I14 is then generated at R14 and mirrored to the output by a current mirror. When I14 is greater than Ibias1, the capacitor C starts to charge, the voltage across the capacitor C rises, and the drain voltage V2 is reduced by the current adjusting unit 30; when I14 is smaller than Ibias1, the capacitor C starts to discharge, the voltage across the capacitor C decreases, and the drain voltage V2 is increased by the current adjusting unit 30, so that the average voltage of the holding voltage V2 remains stable throughout the cycle.
In order to ensure the continuity of the current input to the LED load 104 when the input voltage of the LED load 104 is lower than the turn-on threshold, in the preferred embodiment of the present application, as shown in fig. 6, the circuit further includes a filtering unit 40 connected to the second terminal of the current control unit 102, and the filtering unit 40 is configured to provide the current to the LED load 104 according to the control signal of the current control unit 102.
Specifically, the filtering unit 40 may include an electrolytic capacitor, and the current control unit 102 may control the magnitude of the charging current in the filtering unit 40, so as to ensure the continuity of the current input to the LED load 104 when the input voltage of the LED load 104 is lower than the turn-on threshold.
By applying the technical scheme, the first end and the third end of the rectifying unit are connected with an alternating current power supply, the second end of the rectifying unit is connected with the first end of the current control unit, the second end of the current control unit is connected with the first end of the LED load, the second end of the LED load is connected with the first end of the constant current control unit, the fourth end of the rectifying unit, the third end of the current control unit and the second end of the constant current control unit are all grounded, the circuit can effectively realize constant current control through the current comparison unit corresponding to the feedback link, and compensation of power factors and efficiency in different time is realized through effective control of input current of the LED load under the condition that the stroboscopic characteristic of an LED is not damaged.
In order to further illustrate the technical idea of the present invention, the technical solution of the present invention will now be described with reference to specific application scenarios.
The embodiment of the invention provides a driving circuit, which samples input voltage output by a rectifying circuit through a voltage detection unit and outputs a voltage detection result, wherein the voltage detection result is input into a conduction time control unit, an output signal of the conduction time control unit is adjusted according to the change of voltage corresponding to the voltage detection result, and the output signal is input into a current adjustment unit; the current comparison unit detects the voltage of the output end of the LED load, then the output result is input to the current adjustment unit, the current adjustment unit supplies power to the LED load through the adjusted input current, and the constant current control unit realizes constant current control on the LED load.
The following explains the operating principle of the LED driving circuit in the embodiment of the present application:
the power tube Mn is conducted, and the power voltage Vac passes through the rectifier unitAfter 101, a rectified voltage V is obtainedINWhen the input voltage V isINWhen the voltage is larger than the on-state voltage of the LED load 104, the LED load 104 is turned on, and the constant current control unit 103 performs constant current control on the current flowing through the LED load 104; when the input voltage VINWhen the conduction voltage of the LED load 104 is less than the conduction voltage of the LED load 104, the LED load 104 is powered by the filtering unit 40 to realize constant current conduction.
With said input voltage VINRise when the input voltage V isINWhen the voltage rises between the first preset threshold and the second preset threshold, the LED load 104 is turned on and follows the input voltage VINThe on-time control unit 20 outputs a signal so that the input current I is appliedINWith a first tendency to change, in particular with the input voltage VINIncreases and correspondingly decreases, with LED load 104 operating for time t 1;
the input voltage VINContinues to rise when the input voltage VINWhen the input current is greater than the second predetermined threshold, the on-time control unit 20 outputs a signal to make the input current IINWith a second tendency to change, in particular to start following the input voltage VINDecreasing after increasing, and the LED load 104 is operated at time t 2;
then, with the input voltage VINWhen the input voltage V is reducedINWhen the current level falls between the first preset threshold and the second preset threshold, the on-time control unit 20 outputs a signal to make the input current IINWith a third tendency to change, in particular to start following the input voltage VINDecreasing and increasing, the LED load 104 is operated at time t 3;
when the input voltage V isINWhen the voltage of the LED load continues to drop below a first preset threshold corresponding to the LED load turn-on voltage, the LED load 104 is powered by a filtering unit connected to the input end of the LED load to realize constant current turn-on.
The operation process of the LED driving circuit in one period is carried out. By controlling the input current, the input power and the power factor are selectively and respectively compensated in different conduction time stages, thereby meeting the requirements on the system efficiency and the power factorAnd (6) obtaining. FIG. 10 is a schematic waveform diagram showing a control method of an LED driving circuit according to an embodiment of the present invention, wherein VINFor an input voltage, IINFor input current, V2 is the drain voltage, and I2 is the LED current.
Charging a filter unit connected to an input end of an LED load in a time period when the input current is not zero when the input voltage V isINAnd when the voltage continuously drops to be lower than a first preset threshold corresponding to the LED load conduction voltage, the power is supplied to the LED load through the filtering unit.
Since the voltage drop across the LED load 104 is fixed, the voltage drop across the current adjusting unit 30 varies with the voltage V1 at the input terminals of the filtering unit 40 and the LED load 104, and the waveform of the voltage V2 at the input terminal of the current comparing unit 50 is consistent with the waveform variation rule of the voltage V1 at the input terminals of the filtering unit 40 and the LED load 104.
The control principle of the on-time control unit 20 is as follows:
the on-time control unit 20 collects the detection voltage Vbi of the voltage detection unit 10, adjusts the output voltage of the on-time control unit 20 according to the magnitude of the detection voltage Vbi, and controls the magnitude of the current I2 flowing through the LED load 104. Here, a first preset threshold and a second preset threshold are preset, and the second preset threshold is larger than the first preset threshold. Vbi represents the different sampling voltages of the voltage detection unit, in particular:
when the input voltage VINWhen the total voltage drop is less than the total voltage drop of the LED load, the constant current control unit 103 and the current adjusting unit 30, the input loop is not conducted, and the input current I isINIs zero;
with input voltage VINWhen the detected voltage Vb rises to be greater than the first preset threshold, the output time control signal S1 is at a low level of zero, the input end of the on-time control unit 20 collects the first detected voltage Vb1 of the voltage detection unit 10, and the first output current I of the current adjustment unit 30INDecreases as the first detected voltage Vb1 increases;
when the detected voltage Vb is greater than the second preset threshold, the output time control signal S1 is at a high level, and the input end of the on-time control unit 20 collects the voltage detection unit 10The second detected voltage Vb2, the first output current I of the current adjusting unit 30INDecreases as the second detected voltage Vb2 increases;
with input voltage VINWhen the detected voltage Vb is smaller than the second preset threshold, the output time control signal S1 is low level zero, the input end of the on-time control unit 20 collects the third detected voltage Vb3 of the voltage detection unit 10, and the first output current I of the current adjustment unit 30INIncreases as the waveform of the third detection voltage Vb3 decreases;
with input voltage VINWhen the input voltage V continues to decreaseINWhen the voltage drop is less than the total voltage drop of the LED load, the constant current control unit 103 and the current regulation unit 30, the input loop is not conducted, and the first input current IINAt this time, the electric energy stored in the filter capacitor of the filter circuit 20 should ensure that the current on the LED load is continuous during discharging, that is, the LED load has no stroboflash, and the magnitude of the current I2 flowing through the LED load is controlled by the constant current control unit 103.
The above is a working process of the driving circuit for one period, and the above process is repeated as time increases.
Corresponding to the LED driving circuit in the embodiment of the present application, the embodiment of the present application further provides a control method of an LED driving circuit, which is applied to an LED driving circuit including a rectifying unit, a current control unit, a constant current control unit, and an LED load, as shown in fig. 9, the method includes:
step S901, receiving an input voltage provided by the rectifying unit;
step S902, generating a current control signal of the current control unit according to the variation trend of the input voltage and the voltage value of the input voltage;
in order to ensure that a reliable current control signal is output, in a preferred embodiment of the present application, the current control signal of the current control unit is generated according to a variation trend of the input voltage and a voltage value of the input voltage, and specifically, the current control signal of the current control unit is generated by:
if the input voltage is in a rising trend and the voltage value is between a first preset threshold value and a second preset threshold value, determining a first change trend of the input current according to a change trend of first detection voltage corresponding to the input voltage, and generating the current control signal according to the first change trend;
if the voltage value is larger than a second preset threshold value, determining a second variation trend of the input current according to a variation trend of second detection voltage corresponding to the input voltage, and generating the current control signal according to the second variation trend;
if the input voltage is in a descending trend and the voltage value is between the first preset threshold and the second preset threshold, determining a third change trend of the input current according to a change trend of a third detection voltage corresponding to the input voltage, and generating the current control signal according to the third change trend.
And step S903, controlling the input current of the LED load according to the current control signal, and keeping the output current of the LED load constant based on the constant current control unit.
In order to maintain the continuity of the current of the LED load when the input voltage is less than the first preset threshold, in a preferred embodiment of the present application, the circuit further includes a filtering unit connected to the current control unit, and the method further includes:
when the voltage value is larger than the first preset threshold value, charging the filtering unit;
when the LED load is in a working state and the voltage value is smaller than the first preset threshold value, the input current is generated based on the filtering unit.
By applying the technical scheme, the LED driving circuit comprises a rectifying unit, a current control unit, a constant current control unit and an LED load, and receives input voltage provided by the rectifying unit; generating a current control signal of the current control unit according to the variation trend of the input voltage and the voltage value of the input voltage; and controlling the input current of the LED load according to the current control signal, keeping the output current of the LED load constant based on the constant current control unit, and realizing compensation of power factors and efficiency in different time by effectively controlling the input current of the LED load.
Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present application, and not to limit the same; although the present application has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; such modifications and substitutions do not necessarily depart from the spirit and scope of the corresponding technical solutions in the embodiments of the present application.

Claims (7)

1. An LED drive circuit is characterized in that the circuit comprises a rectifying unit, a current control unit, a constant current control unit and an LED load,
the rectifying unit is used for providing input voltage;
the current control unit is used for controlling the input current of the LED load according to the input voltage;
the constant current control unit is used for keeping the output current of the LED load constant;
the first end and the third end of the rectifying unit are connected with an alternating current power supply, the second end of the rectifying unit is connected with the first end of the current control unit, the second end of the current control unit is connected with the first end of the LED load, the second end of the LED load is connected with the first end of the constant current control unit, and the fourth end of the rectifying unit, the third end of the current control unit and the second end of the constant current control unit are all grounded;
the current control unit also comprises a voltage detection unit, a conduction time control unit and a current adjustment unit,
the voltage detection unit is used for outputting a voltage detection result corresponding to the input voltage as a time control pulse signal and a detection voltage value and inputting the time control pulse signal and the detection voltage value into the conduction time control unit;
the on-time control unit is used for generating a control signal according to the time control pulse signal and the detection voltage value and controlling the output of the current adjusting unit based on the control signal;
the current adjusting unit is used for controlling the input current according to the control signal;
the first end of the voltage detection unit and the first end of the current adjustment unit are connected with the first end of the current control unit, the second end of the voltage detection unit is connected with the first end of the conduction time control unit, the second end of the conduction time control unit is connected with the second end of the current adjustment unit, the third end of the conduction time control unit is the third end of the current control unit, and the third end of the current adjustment unit is the second end of the current control unit;
the voltage detection unit further comprises a first resistor, a second resistor, a third resistor, a fourth resistor, a fifth resistor, a sixth resistor, a seventh resistor, an eighth resistor, a comparator, a phase inverter, a first voltage regulator tube and a second voltage regulator tube;
the first resistor, the second resistor, the third resistor, the fourth resistor and the fifth resistor are sequentially connected in series between the first end of the voltage detection unit and the ground, the connecting point of the first resistor and the second resistor is connected with the first end of the sixth resistor, the second end of the sixth resistor and the first end of the seventh resistor are connected to the positive input end of the comparator in common, the negative input end of the comparator is connected with a fixed reference voltage, the output end of the comparator is connected with the first end of the eighth resistor, the second end of the seventh resistor, the second end of the eighth resistor and the anode of the first voltage regulator tube are connected to the input end of the inverter in common, the output end of the phase inverter is the second end of the voltage detection unit, the cathode of the first voltage-stabilizing tube is connected with the cathode of the second voltage-stabilizing tube, and the anode of the second voltage-stabilizing tube is grounded.
2. The circuit of claim 1, wherein the constant current control unit further comprises an error amplifier, a power tube, and a ninth resistor,
the positive input end of the error amplifier is connected with a fixed reference voltage, the negative input end of the error amplifier and the source electrode of the power tube are connected with the first end of the ninth resistor in common, the output end of the error amplifier is connected with the grid electrode of the power tube, the drain electrode of the power tube is the first end of the constant current control unit, and the second end of the ninth resistor is the second end of the constant current control unit.
3. The circuit of claim 2, wherein the circuit further comprises:
the current comparison unit is used for keeping the average value of the drain voltage of the power tube constant;
the first end of the current comparison unit and the first end of the constant current control unit are connected to the second end of the LED load in a shared mode, and the second end of the current comparison unit is connected with the fourth end of the current control unit.
4. The circuit of claim 3, wherein the current comparing unit further comprises a tenth resistor, an eleventh resistor, a twelfth resistor, a thirteenth resistor, a fourteenth resistor, a first transistor, a second transistor, a third transistor, an operational amplifier, a constant current source, and a capacitor,
the tenth resistor, the eleventh resistor, the twelfth resistor, and the thirteenth resistor are sequentially connected in series between a first end of the current comparing unit and ground, a connection point of the eleventh resistor and the twelfth resistor is connected to a positive input end of the operational amplifier, a negative input end of the operational amplifier and a first end of the fourteenth resistor are connected to a source of the first transistor in common, an output end of the operational amplifier is connected to a gate of the first transistor, a drain of the second transistor, a gate of the second transistor, and a gate of the third transistor are connected to a drain of the first transistor in common, a source of the second transistor and a source of the third transistor are connected to a dc power supply, and a drain of the third transistor and a first end of the capacitor are connected to an input end of the constant current source in common, the second end of the fourteenth resistor, the output end of the constant current source and the second end of the capacitor are all grounded, and the first end of the capacitor is the second end of the current comparison unit.
5. The circuit of claim 1, further comprising a filtering unit connected to a second terminal of the current control unit, the filtering unit configured to provide current to the LED load according to a control signal of the current control unit.
6. A control method of an LED drive circuit is applied to the LED drive circuit comprising a rectifying unit, a current control unit, a constant current control unit and an LED load, and comprises the following steps:
receiving an input voltage provided by the rectifying unit;
generating a current control signal of the current control unit according to the variation trend of the input voltage and the voltage value of the input voltage;
controlling the input current of the LED load according to the current control signal, and keeping the output current of the LED load constant based on the constant current control unit;
generating a current control signal of the current control unit according to the variation trend of the input voltage and the voltage value of the input voltage, specifically:
if the input voltage is in a rising trend and the voltage value is between a first preset threshold value and a second preset threshold value, determining a first change trend of the input current according to a change trend of first detection voltage corresponding to the input voltage, and generating the current control signal according to the first change trend;
if the voltage value is larger than a second preset threshold value, determining a second variation trend of the input current according to a variation trend of second detection voltage corresponding to the input voltage, and generating the current control signal according to the second variation trend;
if the input voltage is in a descending trend and the voltage value is between the first preset threshold and the second preset threshold, determining a third change trend of the input current according to a change trend of a third detection voltage corresponding to the input voltage, and generating the current control signal according to the third change trend.
7. The method of claim 6, wherein the circuit further comprises a filtering unit connected to the current control unit, the method further comprising:
when the voltage value is larger than the first preset threshold value, charging the filtering unit;
when the LED load is in a working state and the voltage value is smaller than the first preset threshold value, the input current is generated based on the filtering unit.
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