WO2017219648A1 - 一种单段线性恒功率led驱动电路及方法 - Google Patents

一种单段线性恒功率led驱动电路及方法 Download PDF

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Publication number
WO2017219648A1
WO2017219648A1 PCT/CN2016/113736 CN2016113736W WO2017219648A1 WO 2017219648 A1 WO2017219648 A1 WO 2017219648A1 CN 2016113736 W CN2016113736 W CN 2016113736W WO 2017219648 A1 WO2017219648 A1 WO 2017219648A1
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Prior art keywords
voltage
led load
switch tube
power switch
current
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PCT/CN2016/113736
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English (en)
French (fr)
Inventor
刘军
吴泉清
李国成
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华润矽威科技（上海）有限公司
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Priority to US15/755,020 priority Critical patent/US10375778B2/en
Publication of WO2017219648A1 publication Critical patent/WO2017219648A1/zh

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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]
    • H05B45/10—Controlling the intensity of the light
    • H05B45/14—Controlling the intensity of the light using electrical feedback from LEDs or from LED modules
    • 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
    • H05B45/395—Linear regulators
    • 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
    • H05B47/00—Circuit arrangements for operating light sources in general, i.e. where the type of light source is not relevant
    • H05B47/20—Responsive to malfunctions or to light source life; for protection
    • H05B47/24—Circuit arrangements for protecting against overvoltage
    • 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
    • Y02B20/30—Semiconductor lamps, e.g. solid state lamps [SSL] light emitting diodes [LED] or organic LED [OLED]

Definitions

  • the present invention relates to the field of circuit design, and in particular to a single-segment linear constant power LED driving circuit and method.
  • LED is a kind of semiconductor electronic component that can emit light. This kind of electronic component can only emit low-light red light in the early stage. With the continuous advancement of technology, it has now developed to emit visible light, infrared light and ultraviolet light, and the luminosity is also very good. Great improvement. LED has the advantages of high efficiency, long life, not easy to break, high switching speed, high reliability and other traditional light sources, and has been widely used in the field of indicator lights, displays and lighting.
  • the overall efficiency of a single-segment linear LED driver is determined by the LED turn-on voltage and input voltage, which satisfies the following relationship:
  • Figure 1 shows a common structure of a single-segment linear LED drive.
  • the AC voltage is converted into an input voltage V IN through the rectifier bridge and supplies power to the LED segment.
  • the LED segment is formed by connecting n LED lamps in series.
  • the output end of the LED lamp segment is connected to the constant current control chip, and the constant current control is realized by the switch of the constant current control tube in the constant current control chip.
  • the capacitor C and the resistor R are connected in parallel at both ends of the input voltage, and are adjustable devices. Since the number of LEDs in series is fixed, the excess voltage is assumed by the constant current control tube under the LED when the input voltage exceeds the forward voltage drop of the LED.
  • the V IN -V LED is the voltage on the regulator. The higher the input voltage, the lower the efficiency of the system.
  • the output voltage can be increased by increasing the number of LEDs, so that the turn-on voltage of the LED segment is as close as possible to the input voltage, thereby improving efficiency, but the problem is that the input voltage range is narrow and the input voltage is high. The efficiency is still relatively low.
  • high-voltage current reduction technology can be adopted to reduce the loss caused by high voltage, but the constant current effect is not good and the efficiency improvement is limited.
  • an object of the present invention is to provide a single-segment linear constant power LED driving circuit and method for solving the narrow input voltage range and low efficiency in a single-segment linear LED driving in the prior art. problem.
  • the present invention provides a single-segment linear constant power LED driving circuit,
  • the single-segment linear constant power LED driving circuit includes at least:
  • Voltage input module LED load, power switch tube, sampling resistor, current control module, comparison module and overvoltage control module;
  • the voltage input module is configured to provide an input voltage
  • the LED load is connected to an output end of the voltage input module, and is powered by the voltage input module;
  • the drain end of the power switch tube is connected to the output end of the LED load, and the constant current control of the LED load is realized by turning on and off the power switch tube;
  • sampling resistor One end of the sampling resistor is connected to the source end of the power switch tube, and the other end is grounded for sampling a current flowing through the power switch tube and converting it into a sampling voltage;
  • the overvoltage control module is connected to a drain end of the power switch tube, and detects a drain terminal voltage of the power switch tube. When the drain terminal voltage of the power switch tube is greater than a set high voltage, the overvoltage The control module outputs a shutdown signal to control the current flowing through the LED load to turn off;
  • the current control module is connected to a compensation capacitor, the other end of the compensation capacitor is grounded, the current control module receives the sampling voltage, and integrates the compensation capacitor to generate a control signal to limit the flow through the power
  • the peak current of the switch tube thereby achieving a constant current average over different input voltage periods, while receiving the turn-off signal, turning off the current flowing through the LED load when the turn-off signal is active, and thereby reducing Small power consumption;
  • the comparison module is connected to the sampling resistor and the current control module, and compares the sampling voltage with the control signal to generate a switching signal of the power switch tube, thereby implementing constant current control of the LED load .
  • the overvoltage control module includes a first resistor, a second resistor, and an overvoltage detecting unit; one end of the first resistor is connected to the drain end of the power switch tube, and the other end is connected to the second resistor and grounded.
  • the first resistor and the second resistor detect a drain terminal voltage of the power switch tube and output a detection voltage; the overvoltage detecting unit is connected to the first resistor and the second resistor The turn-off signal is generated according to the detected voltage.
  • the overvoltage control module further includes a constant current source, one end of the constant current source being connected between the first resistor and the second resistor, and the other end being grounded, through the first resistor
  • the second resistor and the constant current source regulate a turn-off slope of a current flowing through the LED load.
  • the method further includes an operating voltage generating circuit, wherein the working voltage generating circuit provides an operating voltage for each module; one end of the working voltage generating circuit is connected to the output end of the voltage input module, and the other end is grounded through a storage capacitor. .
  • the present invention also provides a driving method for the above single-segment linear constant power LED driving circuit, and the single-segment linear constant power LED driving method at least includes:
  • the power switch tube is turned on, and when the input voltage is greater than the turn-on voltage of the LED load, the LED load is turned on, and a current flows through the LED load and the power switch tube, and the current control module receives the sampling voltage and integrates the compensation capacitance to obtain a control signal, the control signal controlling the power switch tube to limit a peak current flowing through the LED load To keep the average value of the current in different input voltage cycles constant;
  • the overvoltage control module outputs a turn-off signal to turn off the current flowing through the LED load, thereby reducing Small power consumption;
  • the input voltage is then decreased.
  • the drain terminal voltage of the power switch tube is less than the set high voltage, the turn-off signal fails, current flows through the LED load and the power switch tube, and maintains different input voltages.
  • the average value of the current during the period is constant;
  • the input voltage continues to drop.
  • the input voltage is less than the turn-on voltage of the LED load, the LED load is turned off, and no current flows through the LED load and the power switch.
  • the turn-off slope of the current flowing through the LED load is set by setting a falling point and a turn-off point of the current flowing through the LED load, thereby reducing electromagnetic interference.
  • the drain terminal voltage of the power switch tube is detected, when the detection voltage is greater than zero, the current flowing through the LED load begins to decrease; when the detection voltage is greater than the reference voltage, flowing through the LED load The current is turned off.
  • the drain terminal voltage of the power switch tube is I1*R1, where I1 is a constant current of a constant current source, and R1 is a resistance value of the first resistor.
  • the drain terminal voltage of the power switch tube is (Vref/R2+I1)*(R1+R2), wherein Vref is the reference voltage, and I1 is constant.
  • the single-segment linear constant power LED driving circuit and method of the present invention have the following beneficial effects:
  • the single-segment linear constant power LED driving circuit and method of the invention realizes the control of the average current in the alternating current period by the compensation capacitor, and limits the peak current to realize the constant power output in the wide input voltage range.
  • the single-segment linear constant power LED driving circuit and method of the present invention adjusts the turn-off voltage of the LED through an external resistor, and turns off the LED when the input voltage is high, thereby achieving high efficiency of the system.
  • the single-segment linear constant power LED driving circuit and method of the invention adjusts the turn-off slope of the LED through an external resistor to realize linear shutdown of the LED current and optimize the electromagnetic interference performance of the system.
  • the single-segment linear constant power LED driving circuit and method of the present invention can be highly integrated due to high efficiency, and the peripheral circuit is simplified.
  • FIG. 1 shows a schematic diagram of a single-segment linear LED driving structure in the prior art.
  • FIG. 2 is a schematic diagram showing an embodiment of a single-segment linear constant power LED driving circuit of the present invention.
  • FIG. 3 is a schematic diagram showing another embodiment of a single-segment linear constant power LED driving circuit of the present invention.
  • FIG. 4 is a schematic view showing the operation principle of the single-segment linear constant power LED driving circuit of the present invention.
  • the present invention provides a single-segment linear constant power LED driving circuit 1, and the single-segment linear constant power LED driving circuit 1 includes at least:
  • the voltage input module 11 is used to provide an input voltage V IN _ac.
  • the voltage input module 11 is an external device of the chip, and includes an AC power source AC, a fuse F1, and a rectifying unit.
  • the rectifying unit includes two sets of diode groups connected in parallel, and each diode group includes Two diodes connected in series, the AC power source AC is connected between two diodes of each diode group via the fuse F1, and the voltage input module 11 provides the input voltage V IN _ac, the input voltage V IN _ac is a rectified voltage after continuous or increasing continuous sinusoidal voltage rectification.
  • the LED load 12 is connected to an output end of the voltage input module 11, and is powered by the voltage input module 11.
  • the LED load 12 is a chip external device, and includes a plurality of LED lights connected in series.
  • the LED load 12 may also be a series-parallel structure of a plurality of LED lights, which is not in this embodiment. limit.
  • the voltage input module 11 supplies power to the LED load 12. When the voltage across the LED load 12 reaches its turn-on voltage, the LED in the LED load 12 illuminates to function as an illumination.
  • the drain end of the power switch tube M is connected to the output end of the LED load 12, and the constant current control of the LED load 12 is realized by the on and off of the power switch tube M.
  • the power switch tube M is an N-type MOS tube, and the type of the power switch tube is not limited in actual use.
  • the power switch tube M is an internal device of the chip, and the connection between the drain end of the power switch tube M and the external device of the chip is realized through the S1 port.
  • one end of the sampling resistor Rcs is connected to the source end of the power switch tube M, and the other end is grounded for sampling a current flowing through the power switch tube M and converting it into a sampling voltage Vcs.
  • the sampling resistor Rcs is an external device of the chip, and is connected to the source end of the power switch tube M inside the chip through the CS end.
  • the overvoltage control module 15 is connected to the drain terminal of the power switch tube M, and detects the drain terminal voltage V S1 of the power switch tube M, when the power switch tube M is leaked.
  • the overvoltage control module 15 outputs an off signal to control the current flowing through the LED load 12 to be turned off, thereby reducing power consumption.
  • the input voltage V IN _ac is greater than the operating voltage of the LED load 12.
  • the overvoltage control module 15 includes a first resistor R1, a second resistor R2, and an overvoltage detecting unit 151.
  • the first resistor R1 and the second resistor R2 are external devices of the chip
  • the overvoltage detecting unit 151 is an in-chip device.
  • One end of the first resistor R1 is connected to the drain terminal S1 of the power switch tube M, and the other end is connected to the second resistor R2 and grounded; the voltage division detection by the first resistor R1 and the second resistor R2
  • the drain terminal voltage V S1 of the power switch tube M is obtained by the detection voltage Vov.
  • the overvoltage detecting unit 151 is connected between the first resistor R1 and the second resistor R2, and uses the detection voltage Vov and an internal reference voltage (the reference voltage is the set high voltage through the first The resistor R1 and the second resistor R2 are divided into voltages for comparison, thereby obtaining the turn-off signal and acting on the current control module 13.
  • the turn-off signal output by the overvoltage detecting unit 151 is activated, thereby controlling the current control module 13 to turn off the current flowing through the LED load 12, thereby reducing power consumption and realizing
  • the system is highly efficient.
  • the first resistor R1 and the second resistor R2 are chip external devices, and the current flowing through the LED load 12 can be changed by changing the values of the first resistor R1 and the second resistor R2. Point, the flexibility is greatly improved.
  • the current control module 13 is connected to a compensation capacitor Ccomp, and the other end of the compensation capacitor Ccomp is grounded.
  • the current control module receives the sampling voltage Vcs and integrates the compensation capacitor Ccomp. Generating a control signal to limit the peak current flowing through the power switch tube M, thereby achieving a constant current average value during different input voltages V IN _ac period; while receiving the turn-off signal, when the turn-off signal The current flowing through the LED load is turned off in effect, thereby reducing power consumption.
  • the current control module 13 is an internal device of the chip, and the sampling resistor Rcs and a compensation capacitor Ccomp are connected.
  • the compensation capacitor Ccomp is an external device of the chip, and the compensation capacitor and the capacitor are realized through the COMP port. Referring to the connection of the current control module 13, the current control module 13 generates a control signal for the integration of the compensation capacitor Ccomp, and the voltage on the compensation capacitor Ccomp determines the peak current flowing through the LED load 12. By integrating the compensation capacitor Ccomp, the current average value is constant in different input voltage periods, thereby achieving constant power output in a wide input voltage range.
  • the current control module 13 receives the shutdown signal output by the overvoltage control module 15, and when the shutdown signal fails, does not affect the control signal; when the shutdown signal is activated, Adjusting the control signal to turn off the power switch tube M.
  • the power switch tube M is turned off by reducing the output signal to invert the output signal of the comparison module 14 .
  • the comparison module 14 is connected to the sampling resistor Rcs and the current control module 13, and compares the sampling voltage Vcs with the control signal to generate a switching signal of the power switch tube M. In turn, constant current control of the LED load 12 is achieved.
  • the comparison module 14 is a chip internal device.
  • the comparison module is 14 is a comparator, a non-inverting input terminal of the comparator is connected to the current control module 13, and an inverting input terminal is connected to the sampling resistor Rcs.
  • the comparison is Outputting a low level, driving the power switch tube M to turn off to reduce current flowing through the LED load 12; when the sampling voltage Vcs is less than the control signal, the comparator outputs a high level
  • the power switch tube M is driven to open to increase the current flowing through the LED load 12.
  • the constant current control of the LED load 12 is achieved by the turning on and off of the power switch tube M.
  • the single-segment linear constant power LED driving circuit 1 further includes an operating voltage generating circuit 16 that supplies operating voltages to the modules.
  • the working voltage generating circuit 16 is a chip internal device, and one end thereof is connected to the output end of the voltage input module 11 through an HV port, and the power is input from the voltage input module 11 and the other end is passed.
  • the VCC port is connected to the external storage capacitor Cvcc of the chip and grounded.
  • the operating voltage generating circuit 16 stores the generated voltage VCC on the storage capacitor Cvcc, ensuring that sufficient energy is maintained to maintain the operation of each module even when the input voltage V IN _ac is at the bottom.
  • the present invention provides a single-segment linear constant power LED driving circuit, which has the same structure as that of the first embodiment, except that the overvoltage control module 15 further includes a constant current source I1.
  • the turn-off slope of the current flowing through the LED load 12 is adjusted to reduce electromagnetic interference and optimize circuit performance.
  • the overvoltage control module 15 includes a first resistor R1, a second resistor R2, a constant current source I1, and an overvoltage detecting unit 151.
  • the first resistor R1 and the second resistor R2 are chip external devices
  • the constant current source I1 and the overvoltage detecting unit 151 are intra-chip devices.
  • One end of the first resistor R1 is connected to the drain terminal S1 of the power switch tube M, and the other end is connected to the second resistor R2 and grounded; one end of the constant current source I1 is connected to the first resistor R1 and the The other end of the constant current source I1 is grounded between the second resistor R2; the drain terminal voltage V of the power switch tube M is detected by the first resistor R1, the second resistor R2 and the constant current source I1. S1 and get the detection voltage Vov.
  • two points of the drain terminal voltage V S1 of the power switch tube M are detected by the first resistor R1, the second resistor R2, and the constant current source I1, respectively The drop point and the turn-off point of the current flowing through the LED load 12.
  • the drain terminal voltage V S1 of the power switch tube M when the drain terminal voltage V S1 of the power switch tube M is set to VLED_DEC, a current flows through the overvoltage control module 15, and the detection voltage Vov starts to rise from zero.
  • the break signal begins to take effect, its amplitude is related to the detection voltage Vov, and the current control module 13 is controlled to adjust the control signal to start reducing the current flowing through the LED load 12; setting the power switch
  • the detection voltage Vov reaches the reference voltage Vref inside the overvoltage detecting unit 151, and the off signal controls the current control module 13 to adjust the control signal to completely The current flowing through the LED load 12 is turned off.
  • VLED_DEC is set to I1*R1
  • VLED_OFF is set to (Vref/R2+I1)*(R1+R2)
  • I1 is a constant current of the constant current source I1
  • R1 is the The resistance of the first resistor R1, R2 is the resistance of the second resistor R2, and Vref is the reference voltage inside the overvoltage detecting unit 151, and the first resistor R1 and the second resistor R2 can be changed.
  • the value of the constant current source I1 changes the falling point and the turning point of the current flowing through the LED load 12, and the flexibility is greatly improved, and the specific value can be specifically set according to the system application environment, and the specific values are not one by one. limited.
  • the falling point and the turn-off point determine the turn-off slope of the current flowing through the LED load 12, which can be specifically set according to a specific circuit, and can be effectively reduced by linearly turning off the current flowing through the LED load 12. Loss at small high voltage input, improve system efficiency, and improve immunity to electromagnetic interference.
  • the working principle of the single-stage linear constant power LED driving circuit 1 is as follows:
  • the power switch tube M is turned on.
  • the input voltage V IN _ac is greater than the turn-on voltage of the LED load 12
  • the LED load 12 is turned on, and a current flows through the LED load 12 and the power switch tube M.
  • the control module 13 receives the sampling voltage Vcs and integrates the compensation capacitor Ccomp to obtain a control signal, the control signal controlling the power switch tube M to limit the peak current flowing through the LED load 12 to make the current in different input voltage periods
  • the average value is constant to achieve a constant power output over a wide input voltage range;
  • the input voltage V IN _ac continues to rise.
  • the overvoltage control module 15 outputs a turn-off signal to turn off the flow through the The current of the LED load 12, which in turn reduces power consumption;
  • the input voltage V IN _ac then drops.
  • the drain terminal voltage V S1 of the power switch tube M is less than the set high voltage, the turn-off signal fails, and current flows through the LED load 12 and the power switch tube. M, and the average value of the current during the period of maintaining different input voltages is constant;
  • the input voltage V IN _ac continues to fall.
  • the input voltage V IN _ac is less than the turn-on voltage of the LED load 12
  • the LED load 12 is turned off, no current flows through the LED load 12 and the power Switch tube M.
  • the input voltage V IN _ac is greater than the operating voltage of the LED load 12. It will be understood by those skilled in the art that as the input voltage V IN _ac increases, the LED load 12 is gradually turned on, and the voltages at both ends are stabilized at the operating voltage, and as the input voltage V IN _ac continues to rise, Excessive voltage is borne by the power switch tube M, which inevitably leads to low efficiency. Therefore, those skilled in the art can set the current flowing through the LED load 12 according to different operating current and operating voltage requirements. Set the high pressure, the specific values are not limited.
  • the leakage voltage V S1 of the power switch tube M is detected by the overvoltage control module 15 to reduce loss at a high input voltage and improve system efficiency.
  • the current flowing through the LED load 12 is linearly turned off.
  • the turn-off slope of the current flowing through the LED load 12 is set by setting the falling point and the turn-off point of the current flowing through the LED load 12, thereby reducing electromagnetic interference.
  • I1 is a constant current source.
  • R1 is the resistance of the first resistor; the detection voltage Vov starts to rise from zero, and the current flowing through the LED load 12 begins to drop.
  • the constant current of the constant current source R1 is the resistance of the first resistor, R2 is the resistance of the second resistor, Vref is the reference voltage inside the overvoltage detecting unit 151; the detection voltage Vov reaches the reference voltage Vref, the current flowing through the LED load 12 is completely turned off.
  • the average value of the current flowing through the LED load 12 is the same during different input voltage periods.
  • the specific working process is as follows:
  • V IN _ac ⁇ VLED where VLED is the turn-on voltage of LED load 12, LED load 12 is not conducting, no current flows through LED load 12; start at time t1, V IN _ _ > VLED, LED load 12 Starting to conduct, the peak current flowing through the LED load 12 is determined by the voltage VCOMP on the compensation capacitor Ccomp; before time t2, V IN _ ⁇ VLED + VLED_DEC, so the current flowing through the LED load 12 is maintained constant; IN _ac ⁇ VLED, LED load 12 is turned off again until the end of the cycle at time t3. The average current of the LED load during the period t0-t3 is maintained at a set value.
  • the voltage of the voltage V IN _ac changes and is inversely proportional, that is, the current flowing through the LED load 12 decreases as the input voltage V IN _ac rises; before the time t8, VLED+VLED_DEC>V IN _ac> The VLED, the current flowing through the LED load 12 is clamped by the voltage VCOMP on the compensation capacitor Ccomp. At the end of t9, one cycle ends. The average current of this cycle coincides with the average current of t0-t3 cycle. This process is completed by integrating the compensation capacitor Ccomp.
  • V IN _ac VLED+VLED_OFF
  • V IN _ac VLED+VLED_OFF
  • V IN _ac VLED+VLED_OFF
  • V IN _ac VLED+VLED_OFF
  • VLED+VLED_DEC ⁇ V IN _ac ⁇ VLED+VLED_OFF the current flowing through the LED load 12 rises linearly
  • V IN _ ⁇ VLED+VLED_DEC the current flowing through the LED load 12 is re-compensated by the capacitor Ccomp
  • the voltage on the VCOMP is clamped; after time t16, V IN _ac ⁇ VLED, the LED load 12 is no longer turned on, and the current drops to zero until the end of one cycle at time t17.
  • the average current of the LED at t10-t17 is the same as the previous two cycles.
  • the invention reduces the loss on the power switch tube M by turning off the current flowing through the LED load at a high input voltage, thereby improving the overall efficiency; further, setting the current drop point and turning off to reduce electromagnetic interference Point to adjust the turn-off slope.
  • the average current in the entire period can be kept uniform, thereby achieving constant power output in a wide input voltage range.
  • the output LED load is 250V
  • the output current change rate is ⁇ 1% and the system efficiency is >85% in the input voltage range of 200Vac to 264Vac.
  • the single-segment linear constant power LED driving circuit and method of the present invention have the following beneficial effects:
  • the single-segment linear constant power LED driving circuit and method of the invention realizes the control of the average current in the alternating current period by the compensation capacitor, and limits the peak current to realize the constant power output in the wide input voltage range.
  • the single-segment linear constant power LED driving circuit and method of the present invention adjusts the turn-off voltage of the LED through an external resistor, and turns off the LED when the input voltage is high, thereby achieving high efficiency of the system.
  • the single-segment linear constant power LED driving circuit and method of the invention adjusts the turn-off slope of the LED through an external resistor to realize linear shutdown of the LED current and optimize the electromagnetic interference performance of the system.
  • the single-segment linear constant power LED driving circuit and method of the present invention can be highly integrated due to high efficiency, and the peripheral circuit is simplified.
  • the present invention provides a single-stage linear constant power LED driving circuit and method, including a voltage input module, an LED load, a power switch tube, a sampling resistor, a current control module, a comparison module, and an overvoltage control module;
  • the voltage input module supplies power to the LED load;
  • the power switch tube realizes constant current control of the LED load by turning on and off;
  • the sampling resistor feeds back a sampling voltage;
  • the overvoltage control module pairs the power switch tube
  • the drain terminal voltage is detected, and when the drain terminal voltage of the power switch tube is greater than a set high voltage, the overvoltage control module outputs a turn-off signal to control a current flowing through the LED load to turn off;
  • the module receives the sampling voltage and integrates the compensation capacitor to generate a control signal to limit the peak current flowing through the power switch tube, thereby achieving a constant current average value in different input voltage periods while receiving the Disconnecting a signal that turns off current flowing through the LED load when the shutdown signal is active
  • the power switch tube is turned on, and the LED load is when the input voltage is greater than the turn-on voltage of the LED load Turning on, and having a current flowing through the LED load and the power switch tube, the current control module receiving the sampling voltage and integrating the compensation capacitor to obtain a control signal, the control signal controlling the power switch tube pair to flow through the LED load
  • the peak current is limited to make the average value of the current in different input voltage periods constant; the input voltage continues to rise, and the overvoltage control module outputs when the drain terminal voltage of the power switch tube is greater than a set high voltage a turn-off signal to turn off the current flowing through the LED load, thereby reducing power consumption; then the input voltage is decreased, and when the drain terminal voltage of the power switch tube is less than a set high voltage, the turn-off
  • the signal fails, current flows through the LED load and the power switch tube, and the average value of the current during the period of maintaining different input voltages is constant; the input voltage continues to drop when the input voltage is less than the lead of the LED load When the
  • the single-segment linear constant power LED driving circuit and method of the invention realizes the control of the average current in the alternating current period by the compensation capacitor, and limits the peak current to realize the constant power output in the wide input voltage range; and adjusts the turn-off voltage of the LED through the external resistor
  • the input voltage is high, the LED is turned off to achieve high efficiency of the system; the turn-off slope of the LED is adjusted by an external resistor to realize linear shutdown of the LED current, and the electromagnetic interference performance of the system is optimized; and at the same time, due to high efficiency, the whole
  • the system can be highly integrated to achieve the simplification of peripheral circuits. Therefore, the present invention effectively overcomes various shortcomings in the prior art and has high industrial utilization value.

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Abstract

一种单段线性恒功率LED驱动电路（1）及方法，包括：电压输入模块（11）；LED负载（12）；功率开关管（M）；采样电阻（Rcs）；检测功率开关管漏端电压的过压控制模块（15）；限制LED负载峰值电流的电流控制模块（13）；以及比较模块（14）。当输入电压大于LED负载的导通电压时，电流控制模块对峰值电流进行限制，以使不同输入电压周期内的电流平均值恒定，当输入电压大于设定值时，关断流经LED负载的电流，进而减小功耗；当输入电压小于LED负载的导通电压时，LED负载截止。由补偿电容（Ccomp）实现交流周期内平均电流的控制，并限制峰值电流，实现宽输入电压范围内的恒功率输出；通过外部电阻调整LED的关断电压和关断斜率，实现系统的高效率并优化系统的电磁干扰性能。

Description

一种单段线性恒功率LED驱动电路及方法 技术领域
本发明涉及电路设计领域，特别是涉及一种单段线性恒功率LED驱动电路及方法。
背景技术
LED是一种能发光的半导体电子元件，这种电子元件早期只能发出低光度的红光，随着技术的不断进步，现在已发展到能发出可见光、红外线及紫外线的程度，光度也有了很大的提高。LED具有效率高、寿命长、不易破损、开关速度高、高可靠性等传统光源不及的优点，已被广泛应用于指示灯、显示器及照明领域。
通常情况下，单段线性LED驱动中整体的效率由LED导通电压与输入电压决定，满足如下关系：
Figure PCTCN2016113736-appb-000001
如图1所示为单段线性LED驱动常见的结构，交流电压AC通过整流桥后转化为输入电压VIN，并向LED灯段供电，所述LED灯段由n个LED灯串联形成，所述LED灯段的输出端连接恒流控制芯片，通过恒流控制芯片内的恒流控制管的开关实现恒流控制，电容C和电阻R并联于输入电压的两端，为可调器件。由于串联LED数目是固定的，因此在输入电压超过LED正向压降时多余的电压是由LED下方的恒流控制管承担的，VIN-VLED就是调整管上的电压。输入电压越高，系统的效率就越低。
通常单段线性LED驱动中可以通过提高LED的数目提高输出电压，使得LED灯段的导通电压尽量接近输入电压，从而提高效率，但是带来的问题就是输入电压范围比较窄，同时高输入电压时效率仍然比较低。
另外可以采取高压降电流的技术，减少高压时带来的损耗，但恒流效果不好，效率提升也有限。
因此，如何解决单段线性LED驱动中输入电压范围窄、效率低等问题已成为本领域技术人员亟待解决的问题之一。
发明内容
鉴于以上所述现有技术的缺点，本发明的目的在于提供一种单段线性恒功率LED驱动电路及方法，用于解决现有技术中单段线性LED驱动中输入电压范围窄、效率低等问题。
为实现上述目的及其他相关目的，本发明提供一种单段线性恒功率LED驱动电路，所述 单段线性恒功率LED驱动电路至少包括：
电压输入模块，LED负载，功率开关管，采样电阻，电流控制模块，比较模块及过压控制模块；
所述电压输入模块用于提供输入电压；
所述LED负载连接于所述电压输入模块的输出端，由所述电压输入模块供电；
所述功率开关管的漏端连接于所述LED负载的输出端，通过所述功率开关管的导通和截止实现所述LED负载的恒流控制；
所述采样电阻的一端连接于所述功率开关管的源端，另一端接地，用于对流经所述功率开关管的电流进行采样并转化为采样电压；
所述过压控制模块连接于所述功率开关管的漏端，对所述功率开关管的漏端电压进行检测，当所述功率开关管的漏端电压大于设定高压时，所述过压控制模块输出关断信号以控制流经所述LED负载的电流关断；
所述电流控制模块连接一补偿电容，所述补偿电容的另一端接地，所述电流控制模块接收所述采样电压，并对所述补偿电容进行积分，产生一控制信号以限制流经所述功率开关管的峰值电流，进而实现在不同输入电压周期内的电流平均值恒定，同时接收所述关断信号，当所述关断信号起效时关断流经所述LED负载的电流，进而减小功耗；
所述比较模块连接所述采样电阻及所述电流控制模块，将所述采样电压与所述控制信号进行比较，以产生所述功率开关管的开关信号，进而实现所述LED负载的恒流控制。
优选地，所述过压控制模块包括第一电阻、第二电阻以及过压检测单元；所述第一电阻的一端连接所述功率开关管的漏端、另一端连接所述第二电阻后接地，所述第一电阻及所述第二电阻对所述功率开关管的漏端电压进行检测，并输出检测电压；所述过压检测单元连接于所述第一电阻及所述第二电阻之间，根据所述检测电压产生所述关断信号。
更优选地，所述过压控制模块还包括一恒流源，所述恒流源的一端连接于所述第一电阻及所述第二电阻之间、另一端接地，通过所述第一电阻、所述第二电阻及所述恒流源调节流经所述LED负载的电流的关断斜率。
优选地，还包括一工作电压产生电路，所述工作电压产生电路为各模块提供工作电压；所述工作电压产生电路的一端连接所述电压输入模块的输出端，另一端通过一储能电容接地。
为实现上述目的及其他相关目的，本发明还提供一种上述单段线性恒功率LED驱动电路的驱动方法，所述单段线性恒功率LED驱动方法至少包括：
功率开关管导通，当输入电压大于LED负载的导通电压时，所述LED负载导通，并有 电流流经所述LED负载及所述功率开关管，电流控制模块接收采样电压并对补偿电容积分得到控制信号，所述控制信号控制所述功率开关管对流经所述LED负载的峰值电流进行限制，以使不同输入电压周期内的电流平均值恒定；
所述输入电压继续升高，当所述功率开关管的漏端电压大于设定高压时，所述过压控制模块输出一关断信号，以关断流经所述LED负载的电流，进而减小功耗；
随后所述输入电压下降，当所述功率开关管的漏端电压小于设定高压时，所述关断信号失效，电流流经所述LED负载及所述功率开关管，并在保持不同输入电压周期内的电流平均值恒定；
所述输入电压继续下降，当所述输入电压小于所述LED负载的导通电压时，所述LED负载截止，没有电流流经所述LED负载及所述功率开关管。
优选地，通过设定流经所述LED负载的电流的下降点和关断点，来设置流经所述LED负载的电流的关断斜率，进而减小电磁干扰。
更优选地，对所述功率开关管的漏端电压进行检测，当检测电压大于零时，流经所述LED负载的电流开始下降；当检测电压大于参考电压时，流经所述LED负载的电流关断。
更优选地，当所述检测电压大于零时，所述功率开关管的漏端电压为I1*R1，其中，I1为恒流源的恒定电流，R1为第一电阻的阻值。
更优选地，当所述检测电压大于参考电压时，所述功率开关管的漏端电压为(Vref/R2+I1)*(R1+R2)，其中，Vref为所述参考电压，I1为恒流源的恒定电流，R1为第一电阻的阻值，R2为第二电阻的阻值。
如上所述，本发明的单段线性恒功率LED驱动电路及方法，具有以下有益效果：
1、本发明的单段线性恒功率LED驱动电路及方法由补偿电容实现交流周期内平均电流的控制，并限制峰值电流，实现宽输入电压范围内的恒功率输出。
2、本发明的单段线性恒功率LED驱动电路及方法通过外部电阻调整LED的关断电压，当输入电压较高时关断LED，实现系统的高效率。
3、本发明的单段线性恒功率LED驱动电路及方法通过外部电阻调整LED的关断斜率，实现LED电流的线性关断，优化系统的电磁干扰性能。
4、本发明的单段线性恒功率LED驱动电路及方法由于高效率的实现，整个系统可以高度集成，实现外围电路最简化。
附图说明
图1显示为现有技术中的单段线性LED驱动结构示意图。
图2显示为本发明的单段线性恒功率LED驱动电路的一种实施方式示意图。
图3显示为本发明的单段线性恒功率LED驱动电路的另一种实施方式示意图。
图4显示为本发明的单段线性恒功率LED驱动电路的工作原理示意图。
元件标号说明
1         单段线性恒功率LED驱动电路
11        电压输入模块
12        LED负载
13        电流控制模块
14        比较模块
15        过压控制模块
151       过压检测单元
16        工作电压产生电路
具体实施方式
以下通过特定的具体实例说明本发明的实施方式，本领域技术人员可由本说明书所揭露的内容轻易地了解本发明的其他优点与功效。本发明还可以通过另外不同的具体实施方式加以实施或应用，本说明书中的各项细节也可以基于不同观点与应用，在没有背离本发明的精神下进行各种修饰或改变。
请参阅图2～图4。需要说明的是，本实施例中所提供的图示仅以示意方式说明本发明的基本构想，遂图式中仅显示与本发明中有关的组件而非按照实际实施时的组件数目、形状及尺寸绘制，其实际实施时各组件的型态、数量及比例可为一种随意的改变，且其组件布局型态也可能更为复杂。
实施例一
如图2所示，本发明提供一种单段线性恒功率LED驱动电路1，所述单段线性恒功率LED驱动电路1至少包括：
电压输入模块11，LED负载12，功率开关管M，采样电阻Rcs，电流控制模块13，比较模块14、过压控制模块15以及工作电压产生电路16。
如图2所示，所述电压输入模块11用于提供输入电压VIN_ac。
具体地，如图2所示，所述电压输入模块11为芯片外部器件，包括一交流电源AC、一保险丝F1及一整流单元，所述整流单元包括并联的两组二极管组，各二极管组包括串联的两个二极管，所述交流电源AC经所述保险丝F1后连接于各二极管组的两个二极管之间，所述电压输入模块11提供所述输入电压VIN_ac，所述输入电压VIN_ac为连续增大或连续减小的正弦电压整流后的整流电压。
如图2所示，所述LED负载12连接于所述电压输入模块11的输出端，由所述电压输入模块11供电。
具体地，如图2所示，所述LED负载12为芯片外部器件，包括串联的多个LED灯，所述LED负载12也可以是多个LED灯的串并联结构，不以本实施例为限。所述电压输入模块11为所述LED负载12供电，当所述LED负载12两端的电压达到其导通电压时，所述LED负载12中的LED点亮，起到照明的作用。
如图2所示，所述功率开关管M的漏端连接于所述LED负载12的输出端，通过所述功率开关管M的导通和截止实现所述LED负载12的恒流控制。
具体地，如图2所示，在本实施例中，所述功率开关管M为N型MOS管，在实际使用时，所述功率开关管的类型不限。所述功率开关管M为芯片内部器件，通过S1端口实现所述功率开关管M的漏端与芯片外部器件的连接。
如图2所示，所述采样电阻Rcs的一端连接于所述功率开关管M的源端，另一端接地，用于对流经所述功率开关管M的电流进行采样并转化为采样电压Vcs。
具体地，如图2所示，所述采样电阻Rcs为芯片外部器件，通过CS端与芯片内部的功率开关管M的源端连接。
如图2所示，所述过压控制模块15连接于所述功率开关管M的漏端，对所述功率开关管M的漏端电压VS1进行检测，当所述功率开关管M的漏端电压VS1大于设定高压时，所述过压控制模块15输出关断信号以控制流经所述LED负载12的电流关断，进而减小功耗。在本实施例中，当所述功率开关管M的漏端电压VS1达到设定高压时，所述输入电压VIN_ac大于LED负载12的工作电压。本领域的技术人员可以理解，随着输入电压VIN_ac的增大，所述LED负载12逐渐导通，两端的电压稳定于工作电压，随着所述输入电压VIN_ac的继续升高，多余的电压均由所述功率开关管M承担，势必导致效率的低下，因此，本领域的技术人员可以根据不同的工作电流、工作电压要求设定关断流经所述LED负载12的电流的设定高压，具体数值不一一限定。
具体地，如图2所示，所述过压控制模块15包括第一电阻R1、第二电阻R2以及过压检 测单元151。在本实施例中，所述第一电阻R1、所述第二电阻R2为芯片外部器件，所述过压检测单元151为芯片内器件。所述第一电阻R1的一端连接所述功率开关管M的漏端S1、另一端连接所述第二电阻R2后接地；通过所述第一电阻R1及所述第二电阻R2的分压检测所述功率开关管M的漏端电压VS1，并得到检测电压Vov。所述过压检测单元151连接于所述第一电阻R1及所述第二电阻R2之间，将所述检测电压Vov与内部的参考电压(参考电压为所述设定高压通过所述第一电阻R1及所述第二电阻R2分压得到)作比较，进而得到所述关断信号并作用于所述电流控制模块13。所述检测电压Vov反映所述功率开关管M的漏端电压VS1，当所述功率开关管M的漏端电压VS1大于所述设定高压时，所述检测电压Vov大于所述过压检测单元151内部的参考电压，所述过压检测单元151输出的关断信号起效，进而控制所述电流控制模块13以关断流经所述LED负载12的电流，减小功耗，实现系统的高效率。所述第一电阻R1及所述第二电阻R2为芯片外部器件，可通过改变所述第一电阻R1及所述第二电阻R2的值来改变流经所述LED负载12的电流的关断点，灵活性大大提高。
如图2所示，所述电流控制模块13连接一补偿电容Ccomp，所述补偿电容Ccomp的另一端接地；所述电流控制模块接收所述采样电压Vcs，并对所述补偿电容Ccomp进行积分，产生一控制信号以限制流经所述功率开关管M的峰值电流，进而实现在不同输入电压VIN_ac周期内的电流平均值恒定；同时接收所述关断信号，当所述关断信号起效时关断流经所述LED负载的电流，进而减小功耗。
具体地，如图2所示，所述电流控制模块13为芯片内部器件，连接所述采样电阻Rcs及一补偿电容Ccomp，所述补偿电容Ccomp为芯片外部器件，通过COMP端口实现补偿电容与所述电流控制模块13的连接，所述电流控制模块13对所述补偿电容Ccomp的积分产生一控制信号，所述补偿电容Ccomp上的电压决定了流经所述LED负载12的峰值电流。通过对所述补偿电容Ccomp的积分实现在不同输入电压周期内电流平均值恒定，进而实现宽输入电压范围内的恒功率输出。同时，所述电流控制模块13接收所述过压控制模块15输出的关断信号，当所述关断信号失效时，对所述控制信号不产生影响；当所述关断信号起效时，调整所述控制信号以使所述功率开关管M关断，在本实施例中，通过减小所述控制信号以使所述比较模块14的输出信号翻转，进而关断所述功率开关管M。
如图2所示，所述比较模块14连接所述采样电阻Rcs及所述电流控制模块13，将所述采样电压Vcs与所述控制信号进行比较，以产生所述功率开关管M的开关信号，进而实现所述LED负载12的恒流控制。
具体地，如图2所示，所述比较模块14为芯片内部器件，在本实施例中，所述比较模块 14为一比较器，所述比较器的正相输入端连接所述电流控制模块13，反相输入端连接所述采样电阻Rcs，当所述采样电压Vcs大于所述控制信号时，所述比较器输出低电平，驱动所述功率开关管M关断，以减小流经所述LED负载12的电流；当所述采样电压Vcs小于所述控制信号时，所述比较器输出高电平，驱动所述功率开关管M打开，以增大流经所述LED负载12的电流。通过所述功率开关管M的导通和截止实现所述LED负载12的恒流控制。
如图2所示，所述单段线性恒功率LED驱动电路1还包括一工作电压产生电路16，所述工作电压产生电路16为各模块提供工作电压。
具体地，如图2所示，所述工作电压产生电路16为芯片内部器件，其一端通过HV端口连接所述电压输入模块11的输出端，从所述电压输入模块11获取电能，另一端通过VCC端口与芯片外部储能电容Cvcc连接后接地。所述工作电压产生电路16将产生的电压VCC保存于所述储能电容Cvcc上，保证即使在所述输入电压VIN_ac位于谷底时仍有足够能量维持各模块工作。
实施例二
如图3所示，本发明提供一种单段线性恒功率LED驱动电路，其结构与实施例一基本相同，不同之处在于，所述过压控制模块15还包括一恒流源I1，以调节流经所述LED负载12的电流的关断斜率，进而减小电磁干扰，优化电路性能。
具体地，如图3所示，所述过压控制模块15包括第一电阻R1、第二电阻R2、恒流源I1以及过压检测单元151。在本实施例中，所述第一电阻R1、所述第二电阻R2为芯片外部器件，所述恒流源I1、所述过压检测单元151为芯片内器件。所述第一电阻R1的一端连接所述功率开关管M的漏端S1、另一端连接所述第二电阻R2后接地；所述恒流源I1的一端连接于所述第一电阻R1及所述第二电阻R2之间、恒流源I1的另一端接地；通过所述第一电阻R1、所述第二电阻R2及所述恒流源I1检测所述功率开关管M的漏端电压VS1，并得到检测电压Vov。为了减小电磁干扰，通过所述第一电阻R1、所述第二电阻R2、所述恒流源I1对所述功率开关管M的漏端电压VS1的两个点进行了检测，分别作为流经所述LED负载12的电流的下降点和关断点。在本实施例中，设定所述功率开关管M的漏端电压VS1为VLED_DEC时，开始有电流流过所述过压控制模块15，所述检测电压Vov开始从零上升，所述关断信号开始起效，其幅值与所述检测电压Vov有关，并控制所述电流控制模块13调整所述控制信号以开始减小流经所述LED负载12的电流；设定所述功率开关管M的漏端电压VS1为VLED_OFF时，所述检测电压Vov达到所述过压检测单元151内部的参考电压Vref， 所述关断信号控制所述电流控制模块13调整所述控制信号以完全关断流经所述LED负载12的电流。在本实施例中，VLED_DEC设定为I1*R1，VLED_OFF设定为(Vref/R2+I1)*(R1+R2)，其中，I1为所述恒流源I1的恒定电流，R1为所述第一电阻R1的阻值，R2为所述第二电阻R2的阻值，Vref为所述过压检测单元151内部的参考电压，可通过改变所述第一电阻R1、所述第二电阻R2及所述恒流源I1的值来改变流经所述LED负载12的电流的下降点、关断点，灵活性大大提高，具体数值可根据系统应用环境做具体设定，在此不一一限定。下降点和关断点决定了流经所述LED负载12的电流的关断斜率，该斜率可根据具体电路做具体设定，通过线性关断流经所述LED负载12的电流，可有效减小高电压输入时的损耗，提高系统效率，并提高抗电磁干扰能力。
如图2～图4所示，所述单段线性恒功率LED驱动电路1的工作原理如下：
功率开关管M导通，当输入电压VIN_ac大于LED负载12的导通电压时，所述LED负载12导通，并有电流流经所述LED负载12及所述功率开关管M，电流控制模块13接收采样电压Vcs并对补偿电容Ccomp积分得到控制信号，所述控制信号控制所述功率开关管M对流经所述LED负载12的峰值电流进行限制，以使不同输入电压周期内的电流平均值恒定，以此实现宽输入电压范围内的恒功率输出；
所述输入电压VIN_ac继续升高，当所述功率开关管M的漏端电压VS1大于设定高压时，所述过压控制模块15输出一关断信号，以关断流经所述LED负载12的电流，进而减小功耗；
随后所述输入电压VIN_ac下降，当所述功率开关管M的漏端电压VS1小于设定高压时，所述关断信号失效，电流流经所述LED负载12及所述功率开关管M，并在保持不同输入电压周期内的电流平均值恒定；
所述输入电压VIN_ac继续下降，当所述输入电压VIN_ac小于所述LED负载12的导通电压时，所述LED负载12截止，没有电流流经所述LED负载12及所述功率开关管M。
在本实施例中，当所述功率开关管M的漏端电压VS1达到设定高压时，所述输入电压VIN_ac大于LED负载12的工作电压。本领域的技术人员可以理解，随着输入电压VIN_ac的增大，所述LED负载12逐渐导通，两端的电压稳定于工作电压，随着所述输入电压VIN_ac的继续升高，多余的电压均由所述功率开关管M承担，势必导致效率的低下，因此，本领域的技术人员可以根据不同的工作电流、工作电压要求设定关断流经所述LED负载12的电流的设定高压，具体数值不一一限定。通过所述过压控制模块15检测所述功率开关管M的漏端电压VS1，在高输入电压时减小损耗，提高系统效率。
进一步地，为了优化系统的抗电磁干扰能力，线性关断流经所述LED负载12的电流。
具体地，通过设定流经所述LED负载12的电流的下降点和关断点，来设置流经所述LED负载12的电流的关断斜率，进而减小电磁干扰。
在本实施例中，对应于流经所述LED负载12的电流的下降点，所述功率开关管M的漏端电压VS1设定为VLED_DEC＝I1*R1，其中，I1为恒流源的恒定电流，R1为第一电阻的阻值；所述检测电压Vov开始从零上升，流经所述LED负载12的电流开始下降。对应于流经所述LED负载12的电流的关断点，所述功率开关管M的漏端电压VS1设定为VLED_OFF＝(Vref/R2+I1)*(R1+R2)，其中，I1为恒流源的恒定电流，R1为第一电阻的阻值，R2为所述第二电阻的阻值，Vref为所述过压检测单元151内部的参考电压；所述检测电压Vov达到参考电压Vref，流经所述LED负载12的电流完全关断。
如图4所示，在不同的输入电压周期内，流经所述LED负载12的电流的平均值相同，具体工作过程如下：
在t0时刻，VIN_ac<VLED，其中，VLED为LED负载12的导通电压，LED负载12不导通，没有电流流经LED负载12；t1时刻开始，VIN_ac>VLED，LED负载12开始导通，流经LED负载12的峰值电流由补偿电容Ccomp上的电压VCOMP决定；在t2时刻之前，VIN_ac<VLED+VLED_DEC，因此流经LED负载12的电流维持恒定；t2时刻后VIN_ac<VLED，LED负载12又截止，直到t3时刻周期结束。在t0-t3时刻周期的LED负载的平均电流保持一个设定的值。
t4时刻，另一个输入电压幅值不同的交流周期开始；t5时刻之前VIN_ac<VLED，LED负载12截止；t6时刻之前，VIN_ac<＝VLED+VLED_DEC，此时LED负载12导通，流经LED负载12的峰值电流由补偿电容Ccomp上的电压VCOMP决定，且维持恒定；在t7时刻之前，VLED+VLED_DEC<VIN_ac<VLED+VLED_OFF，此时流经LED负载12的电流随输入电压VIN_ac的电压变化而变化，且成反比关系，即随着所述输入电压VIN_ac的升高流经LED负载12的电流下降；在t8时刻之前，VLED+VLED_DEC>VIN_ac>VLED，流经LED负载12的电流被补偿电容Ccomp上的电压VCOMP钳位。t9时刻一个周期结束，这个周期的平均电流与t0-t3周期的平均电流一致，这个过程通过对补偿电容Ccomp的积分完成。
t10时刻又一个周期开始；在t11时刻VIN_ac＝VLED，之前LED负载12截止，电流为零；t11时刻后LED负载12导通，电流由补偿电容Ccomp上的电压VCOMP决定；在t12时刻VIN_ac＝VLED+VLED_DEC，电流开始线性下降，到t13时刻VIN_ac＝VLED+VLED_OFF，电流降为零；在t14时刻之前，VIN_ac一直大于VLED+VLED_OFF，LED负载12一直被关断； 直到t14时刻开始，VLED+VLED_DEC<VIN_ac<VLED+VLED_OFF，流经LED负载12的电流线性上升；t15时刻之后VIN_ac<VLED+VLED_DEC，流经LED负载12的电流重新被补偿电容Ccomp上的电压VCOMP钳位控制；t16时刻后VIN_ac<VLED，LED负载12不再导通，电流降为零，直到t17时刻一个周期结束。同理t10-t17时刻LED的平均电流同前两个周期一致。
本发明通过在高输入电压时关断流经所述LED负载的电流，来减少功率开关管M上的损耗，提高整体的效率；进一步，为了减小电磁干扰而设定电流下降点和关断点，进而调整关断斜率。同时由于补偿电容Ccomp的积分作用，可以保持整个周期内的平均电流一致，从而实现宽输入电压范围内的恒功率输出。
以一个实际的模拟及仿真案例为例，输出LED负载250V，在200Vac～264Vac输入电压范围内，输出电流变化率<1％，系统效率>85％。
如上所述，本发明的单段线性恒功率LED驱动电路及方法，具有以下有益效果：
1、本发明的单段线性恒功率LED驱动电路及方法由补偿电容实现交流周期内平均电流的控制，并限制峰值电流，实现宽输入电压范围内的恒功率输出。
2、本发明的单段线性恒功率LED驱动电路及方法通过外部电阻调整LED的关断电压，当输入电压较高时关断LED，实现系统的高效率。
3、本发明的单段线性恒功率LED驱动电路及方法通过外部电阻调整LED的关断斜率，实现LED电流的线性关断，优化系统的电磁干扰性能。
4、本发明的单段线性恒功率LED驱动电路及方法由于高效率的实现，整个系统可以高度集成，实现外围电路最简化。
综上所述，本发明提供一种单段线性恒功率LED驱动电路及方法，包括电压输入模块，LED负载，功率开关管，采样电阻，电流控制模块，比较模块及过压控制模块；所述电压输入模块向所述LED负载供电；所述功率开关管通过导通和截止实现所述LED负载的恒流控制；所述采样电阻反馈采样电压；所述过压控制模块对所述功率开关管的漏端电压进行检测，当所述功率开关管的漏端电压大于设定高压时，所述过压控制模块输出关断信号以控制流经所述LED负载的电流关断；所述电流控制模块接收所述采样电压，并对补偿电容进行积分，产生一控制信号以限制流经所述功率开关管的峰值电流，进而实现在不同输入电压周期内的电流平均值恒定，同时接收所述关断信号，当所述关断信号起效时关断流经所述LED负载的电流，进而减小功耗；所述比较模块产生所述功率开关管的开关信号，进而实现所述LED负载的恒流控制。功率开关管导通，当输入电压大于LED负载的导通电压时，所述LED负载 导通，并有电流流经所述LED负载及所述功率开关管，电流控制模块接收采样电压并对补偿电容积分得到控制信号，所述控制信号控制所述功率开关管对流经所述LED负载的峰值电流进行限制，以使不同输入电压周期内的电流平均值恒定；所述输入电压继续升高，当所述功率开关管的漏端电压大于设定高压时，所述过压控制模块输出一关断信号，以关断流经所述LED负载的电流，进而减小功耗；随后所述输入电压下降，当所述功率开关管的漏端电压小于设定高压时，所述关断信号失效，电流流经所述LED负载及所述功率开关管，并在保持不同输入电压周期内的电流平均值恒定；所述输入电压继续下降，当所述输入电压小于所述LED负载的导通电压时，所述LED负载截止，没有电流流经所述LED负载及所述功率开关管。本发明的单段线性恒功率LED驱动电路及方法由补偿电容实现交流周期内平均电流的控制，并限制峰值电流，实现宽输入电压范围内的恒功率输出；通过外部电阻调整LED的关断电压，当输入电压较高时关断LED，实现系统的高效率；通过外部电阻调整LED的关断斜率，实现LED电流的线性关断，优化系统的电磁干扰性能；同时由于高效率的实现，整个系统可以高度集成，实现外围电路最简化。所以，本发明有效克服了现有技术中的种种缺点而具高度产业利用价值。
上述实施例仅例示性说明本发明的原理及其功效，而非用于限制本发明。任何熟悉此技术的人士皆可在不违背本发明的精神及范畴下，对上述实施例进行修饰或改变。因此，举凡所属技术领域中具有通常知识者在未脱离本发明所揭示的精神与技术思想下所完成的一切等效修饰或改变，仍应由本发明的权利要求所涵盖。

Claims (9)

  1. 一种单段线性恒功率LED驱动电路，其特征在于，所述单段线性恒功率LED驱动电路至少包括：
    电压输入模块，LED负载，功率开关管，采样电阻，电流控制模块，比较模块及过压控制模块；
    所述电压输入模块用于提供输入电压；
    所述LED负载连接于所述电压输入模块的输出端，由所述电压输入模块供电；
    所述功率开关管的漏端连接于所述LED负载的输出端，通过所述功率开关管的导通和截止实现所述LED负载的恒流控制；
    所述采样电阻的一端连接于所述功率开关管的源端，另一端接地，用于对流经所述功率开关管的电流进行采样并转化为采样电压；
    所述过压控制模块连接于所述功率开关管的漏端，对所述功率开关管的漏端电压进行检测，当所述功率开关管的漏端电压大于设定高压时，所述过压控制模块输出关断信号以控制流经所述LED负载的电流关断；
    所述电流控制模块连接一补偿电容，所述补偿电容的另一端接地，所述电流控制模块接收所述采样电压，并对所述补偿电容进行积分，产生一控制信号以限制流经所述功率开关管的峰值电流，进而实现在不同输入电压周期内的电流平均值恒定，同时接收所述关断信号，当所述关断信号起效时关断流经所述LED负载的电流，进而减小功耗；
    所述比较模块连接所述采样电阻及所述电流控制模块，将所述采样电压与所述控制信号进行比较，以产生所述功率开关管的开关信号，进而实现所述LED负载的恒流控制。
  2. 根据权利要求1所述的单段线性恒功率LED驱动电路，其特征在于：所述过压控制模块包括第一电阻、第二电阻以及过压检测单元；所述第一电阻的一端连接所述功率开关管的漏端、另一端连接所述第二电阻后接地，所述第一电阻及所述第二电阻对所述功率开关管的漏端电压进行检测，并输出检测电压；所述过压检测单元连接于所述第一电阻及所述第二电阻之间，根据所述检测电压产生所述关断信号。
  3. 根据权利要求2所述的单段线性恒功率LED驱动电路，其特征在于：所述过压控制模块还包括一恒流源，所述恒流源的一端连接于所述第一电阻及所述第二电阻之间、另一端接地，通过所述第一电阻、所述第二电阻及所述恒流源调节流经所述LED负载的电流的关 断斜率。
  4. 根据权利要求1所述的单段线性恒功率LED驱动电路，其特征在于：还包括一工作电压产生电路，所述工作电压产生电路为各模块提供工作电压；所述工作电压产生电路的一端连接所述电压输入模块的输出端，另一端通过一储能电容接地。
  5. 一种如权利要求1～4任意一项所述的单段线性恒功率LED驱动电路的驱动方法，其特征在于，所述单段线性恒功率LED驱动方法至少包括：
    功率开关管导通，当输入电压大于LED负载的导通电压时，所述LED负载导通，并有电流流经所述LED负载及所述功率开关管，电流控制模块接收采样电压并对补偿电容积分得到控制信号，所述控制信号控制所述功率开关管对流经所述LED负载的峰值电流进行限制，以使不同输入电压周期内的电流平均值恒定；
    所述输入电压继续升高，当所述功率开关管的漏端电压大于设定高压时，所述过压控制模块输出一关断信号，以关断流经所述LED负载的电流，进而减小功耗；
    随后所述输入电压下降，当所述功率开关管的漏端电压小于设定高压时，所述关断信号失效，电流流经所述LED负载及所述功率开关管，并在保持不同输入电压周期内的电流平均值恒定；
    所述输入电压继续下降，当所述输入电压小于所述LED负载的导通电压时，所述LED负载截止，没有电流流经所述LED负载及所述功率开关管。
  6. 根据权利要求5所述的单段线性恒功率LED驱动方法，其特征在于：通过设定流经所述LED负载的电流的下降点和关断点，来设置流经所述LED负载的电流的关断斜率，进而减小电磁干扰。
  7. 根据权利要求6所述的单段线性恒功率LED驱动方法，其特征在于：对所述功率开关管的漏端电压进行检测，当检测电压大于零时，流经所述LED负载的电流开始下降；当检测电压大于参考电压时，流经所述LED负载的电流关断。
  8. 根据权利要求7所述的单段线性恒功率LED驱动方法，其特征在于：当所述检测电压大于零时，所述功率开关管的漏端电压为I1*R1，其中，I1为恒流源的恒定电流，R1为第一电阻的阻值。
  9. 根据权利要求7所述的单段线性恒功率LED驱动方法，其特征在于：当所述检测电压大于参考电压时，所述功率开关管的漏端电压为(Vref/R2+I1)*(R1+R2)，其中，Vref为所述参考电压，I1为恒流源的恒定电流，R1为第一电阻的阻值，R2为第二电阻的阻值。
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