WO2022142857A1 - 一种led驱动系统及led驱动的闭环控制方法 - Google Patents

一种led驱动系统及led驱动的闭环控制方法 Download PDF

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Publication number
WO2022142857A1
WO2022142857A1 PCT/CN2021/132142 CN2021132142W WO2022142857A1 WO 2022142857 A1 WO2022142857 A1 WO 2022142857A1 CN 2021132142 W CN2021132142 W CN 2021132142W WO 2022142857 A1 WO2022142857 A1 WO 2022142857A1
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Prior art keywords
voltage
electrolytic capacitor
led
unit
module
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PCT/CN2021/132142
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English (en)
French (fr)
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刘军
李国成
吴泉清
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华润微集成电路(无锡)有限公司
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Priority to US18/028,208 priority Critical patent/US11917735B2/en
Priority to EP21913599.3A priority patent/EP4203619A4/en
Publication of WO2022142857A1 publication Critical patent/WO2022142857A1/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]
    • H05B45/50—Circuit arrangements for operating light-emitting diodes [LED] responsive to malfunctions or undesirable behaviour of LEDs; responsive to LED life; Protective circuits
    • H05B45/59—Circuit arrangements for operating light-emitting diodes [LED] responsive to malfunctions or undesirable behaviour of LEDs; responsive to LED life; Protective circuits for reducing or suppressing flicker or glow effects
    • 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
    • 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]
    • 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
    • H05B45/345—Current stabilisation; Maintaining constant current
    • 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]
    • H05B45/40—Details of LED load circuits
    • 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 invention belongs to the field of system design, and relates to an LED driving system and a closed-loop control method for LED driving.
  • the light emitting diode (LED) driver has also increased the requirements for stroboscopic while meeting the requirements of power factor PF, harmonics, efficiency, etc.
  • LED light emitting diode
  • this linear LED driver has also introduced some New solution: one is to add a de-ripple circuit to the traditional linear high-efficiency high PF drive, or to integrate the de-ripple module into the driver chip, as shown in Figure 1.
  • the de-ripple module due to the complexity of the de-ripple module, And the module will lose some additional efficiency, and the cost and performance are not the best solution.
  • the second power switch Q2 part adopts the traditional linear LED constant current drive
  • the first power switch tube Q1 uses measures such as overvoltage drop current to control the charging and discharging of the electrolytic capacitor to achieve high power factor PF, reduce the charging current of the electrolytic capacitor Co when the input voltage peaks, reduce the charging loss of the first power switch Q1 and improve the efficiency.
  • the electrolytic capacitor Co discharges the LED
  • the second power switch Q2 is used to control the constant current of the LED to realize the stroboscopic function.
  • the purpose of the present invention is to provide an LED driving system and a closed-loop control method for LED driving, which are used to solve the problem that the normal operating range of the input voltage of the LED driving system is narrow in the prior art.
  • an LED driving system comprising:
  • the positive pole of the LED load is connected to the bus voltage
  • a constant current control module connected to the negative pole of the LED load, for performing constant current control on the LED load
  • the upper plate of the electrolytic capacitor is connected to the positive electrode of the LED load, and is used for discharging to the LED load when the busbar voltage is lower than the voltage on the electrolytic capacitor;
  • a discharge voltage detection module connected to the negative pole of the LED load, and judges the magnitude of the discharge voltage of the electrolytic capacitor based on the negative pole voltage of the LED load to obtain a control signal;
  • busbar voltage detection module which detects the busbar voltage to obtain a first detection voltage
  • the charging current control module is connected to the discharge voltage detection module, the output terminal of the bus voltage detection module and the lower plate of the electrolytic capacitor, and adjusts the voltage of the electrolytic capacitor based on the control signal and the first detection voltage.
  • charging current wherein the charging current control module includes a compensation unit, the input end of the compensation unit is connected to the discharge voltage detection module, and a corresponding compensation voltage is generated based on the output signal of the discharge voltage module, and the compensation unit includes
  • the addition and subtraction counter reduces the charging current of the electrolytic capacitor by performing a subtraction operation, and increases the charging current of the electrolytic capacitor by performing an addition operation.
  • the constant current control module includes a first power switch tube, a first sampling unit and a first operational amplifying unit; the drain of the first power switch tube is connected to the negative pole of the LED load, and the source is connected to the negative pole of the LED load.
  • the first sampling unit is grounded; the input end of the first operational amplifier unit is respectively connected to the source of the first power switch tube and a reference voltage, and the output end is connected to the gate of the first power switch tube, and the sampling The voltage is compared with the reference voltage to control the amount of current flowing through the LED load.
  • the constant current control module further includes a dimming unit connected to the first operational amplifier unit, the dimming unit receives a dimming control signal, and adjusts the reference voltage based on the dimming control signal. size to set the output current of the LED load.
  • the dimming control signal is an analog signal or a pulse width modulation signal.
  • the discharge voltage detection module includes a detection unit and a comparison unit; the detection unit is connected to the negative electrode of the LED load, and detects the negative electrode voltage of the LED load to obtain a second detection voltage; the comparison unit The output terminal of the detection unit is connected, and the magnitude of the discharge voltage of the electrolytic capacitor is determined based on the second detection voltage.
  • the comparison unit includes a first comparator and a second comparator; the input terminals of the first comparator are respectively connected to the second detection voltage and the first preset voltage. When the voltage is greater than the first preset voltage, a first control signal is output; the input terminals of the second comparator are respectively connected to the second detection voltage and the second preset voltage, when the second detection voltage is smaller than the The second control signal is output at the second preset voltage.
  • the first input terminal of the addition and subtraction counter is connected to the output terminal of the first comparator, and the second input terminal is connected to the output terminal of the second comparator.
  • the charging current control module further includes a second power switch tube, a second sampling unit, a third sampling unit and a second operational amplifier unit, wherein:
  • the drain of the second power switch tube is connected to the lower plate of the electrolytic capacitor, and the source is grounded through the second sampling unit;
  • the first input end of the second operational amplifier unit is connected to the output end of the compensation unit, the second input end is connected to the output end of the bus voltage detection module, and the output end of the second operational amplifier unit is connected to the first
  • the grids of the two power switch tubes are used to adjust the charging current of the electrolytic capacitor
  • One end of the third sampling unit is connected between the bus voltage detection module and the second operational amplifying unit, and the other end is connected between the second power switch tube and the second sampling unit.
  • the compensation unit further includes a compensation voltage generation circuit and a digital-to-analog conversion unit, the output end of the addition and subtraction counter is connected to the input end of the compensation voltage generation circuit via the digital-to-analog conversion unit, and the The output end of the compensation voltage generating circuit is connected to the first input end of the second operational amplifying unit.
  • the compensation unit further includes a third comparator, the first input terminal of the third comparator is connected to the gate of the power switch tube in the constant current control module, and the second input terminal is connected to the third preset voltage, the output terminal is connected to the third input terminal of the addition and subtraction counter, when the gate voltage of the power switch tube in the constant current control module is greater than the third preset voltage, the addition and subtraction counter performs fast addition operation.
  • a third comparator the first input terminal of the third comparator is connected to the gate of the power switch tube in the constant current control module, and the second input terminal is connected to the third preset voltage
  • the output terminal is connected to the third input terminal of the addition and subtraction counter, when the gate voltage of the power switch tube in the constant current control module is greater than the third preset voltage, the addition and subtraction counter performs fast addition operation.
  • the compensation unit further includes a protection module, the protection module is connected to the addition and subtraction counter and the constant current control module, and adjusts the constant current control module based on the overflow signal of the addition and subtraction counter. value of the reference voltage.
  • the LED driving system further includes a fourth sampling unit, the fourth sampling unit is connected between the bus voltage detection module and the ground to adjust the internal control signal of the bus voltage detection module.
  • the LED driving system further includes a working voltage generating module, the working voltage generating module is connected to the bus voltage, and provides the LED driving system with a working voltage based on the bus voltage.
  • the LED driving system further includes a rectifier module, and the rectifier module rectifies the AC power to obtain the bus voltage.
  • the present invention also provides a closed-loop control method for LED driving, comprising the following steps:
  • the electrolytic capacitor discharges the LED load, and performs constant current control on the LED load based on the constant current control module, wherein when the discharge voltage of the electrolytic capacitor is higher than the first setting When the voltage of the electrolytic capacitor is reduced, the subtraction operation is performed by the addition and subtraction counter to reduce the charging current of the electrolytic capacitor, thereby reducing the discharge voltage of the electrolytic capacitor; when the discharge voltage of the electrolytic capacitor is lower than the second set voltage, the The addition and subtraction counter performs addition operation to increase the charging current of the electrolytic capacitor, thereby increasing the discharge voltage of the electrolytic capacitor;
  • the bus voltage When the bus voltage is greater than the on-voltage of the LED, the bus voltage supplies power to the LED load, and the constant current control module performs constant current control on the LED load, and the bus voltage is the same as the LED load.
  • the electrolytic capacitor discharges the LED load, and performs constant current control on the LED load based on the constant current control module.
  • a fast addition operation is performed by an addition and subtraction counter to rapidly increase the charging current of the electrolytic capacitor, thereby rapidly increasing the voltage of the electrolytic capacitor. discharge voltage.
  • the reference voltage of the constant current control module is reduced to reduce the output current of the LED load, thereby reducing the discharge of the electrolytic capacitor;
  • the reference voltage of the constant current control module is increased to increase the output current of the LED load, thereby accelerating the discharge of the electrolytic capacitor.
  • the charging current of the electrolytic capacitor is reduced until zero.
  • the LED driving system and the closed-loop control method for LED driving of the present invention utilize the addition and subtraction counter to realize the digitization of the loop compensation, without using the external compensation large capacitance of the compensation loop, so that the peripheral circuit is simplified and the system cost is low.
  • the present invention can realize some additional functions or protection by using the counting overflow of the addition and subtraction counter, for example, the output current can be reduced without flicker when the low voltage is input.
  • the output of the addition and subtraction counter reflects the working state of the system, and the output digital signal can be provided to the external MCU for intelligent processing, such as intelligent dimming.
  • FIG. 1 is a schematic structural diagram of a linear LED driving system including a de-ripple module.
  • FIG. 2 is a schematic structural diagram of an LED driving system in which the constant current part of the LED and the charging and discharging part of the electrolytic capacitor are separately controlled.
  • FIG. 3 is a schematic structural diagram of an LED constant current driving system that adopts a closed-loop control loop and includes a large external compensation capacitor.
  • FIG. 4 is a schematic structural diagram of the LED driving system of the present invention.
  • FIG. 3 it is an LED constant current drive system using a closed-loop control loop, which controls the charging current of the first power switch Q1 by detecting the drain voltage of the second power switch Q2 for compensation, so that the electrolysis When the capacitor Co is discharging, the drain voltage of the second power switch Q2 is always controlled at a relatively suitable low value to reduce the loss of the second power switch Q2, which solves the stroboscopic and improves the efficiency.
  • the first power switch The control loop of the transistor Q1 and the second power switch transistor Q2 becomes a closed-loop control, which increases the normal working range of the input voltage.
  • the problem with this solution is that in order to establish a closed-loop control loop, a large capacitor Ccomp needs to be added for loop compensation.
  • the present invention realizes the digitization of the loop compensation by using the addition and subtraction counter, can remove the external compensation large capacitance of the compensation loop, simplifies the peripheral circuit and reduces the system cost.
  • this embodiment provides an LED driving system including an LED load 1 , a constant current control module 2 , an electrolytic capacitor Co, a discharge voltage detection module 3 , a bus voltage detection module 4 and a charging current control module 5 .
  • the anode of the LED load 1 is connected to the bus voltage Vin.
  • the bus voltage Vin is provided by the rectifier module 6, and the rectifier module 6 rectifies the alternating current power supply AC to obtain the bus voltage Vin.
  • the rectifier module 6 includes a rectifier bridge structure BD1 and a fuse F1, the rectifier bridge structure BD1 includes two groups of diodes connected in parallel, each diode group includes two diodes connected in series, and the AC power source AC is connected through the fuse F1. between the two diodes of each diode group.
  • the bus voltage Vin is a rectified voltage after sinusoidal voltage rectification.
  • the LED driving system further includes a working voltage generating module 7, the working voltage generating module is connected to the bus voltage Vin, and provides the LED driving system with a working voltage VDD based on the bus voltage Vin.
  • the anode of the LED load 1 is connected to the output end of the rectifier module 6 , the LED load 1 includes a plurality of LED lamps connected in series, and the LED load 1 can also be a series-parallel structure of a plurality of LED lamps , not limited to this embodiment.
  • the LEDs in the LED load 1 are lit to play a role of lighting.
  • the constant current control module 2 is connected to the negative electrode of the LED load 1 for performing constant current control on the LED load 1 .
  • the constant current control module 2 includes a first power switch tube Q1, a first sampling unit and a first operational amplifier unit OP1, and the first sampling unit includes but is not limited to a first sampling resistor Rcs. After the input voltage passes through the load LED, the current is controlled by the first power switch tube Q1, and the first operational amplifying unit OP1 detects the voltage on the first sampling resistor Rcs to perform constant current control on the LED to ensure that the LED current is constant. to eliminate flicker.
  • the drain of the first power switch transistor Q1 is connected to the negative electrode of the LED load, and the source is grounded via the first sampling resistor Rcs; the input terminals of the first operational amplifying unit OP1 are respectively connected to the first sampling resistor Rcs.
  • the source of a power switch Q1 and a reference voltage Ref, the output terminal is connected to the gate of the first power switch Q1, and the sampled voltage is compared with the reference voltage Ref to control the voltage flowing through the LED load 1 Current size, and then realize constant current control.
  • the reference voltage Ref is an internal fixed value or provided externally.
  • the LED load 1 can be adjusted by changing the resistance value of the first sampling resistor Rcs output current.
  • the connection relationship between the input end and the output end of the first operational amplifier unit OP1 can be adjusted, and the same logic relationship can be achieved by adding an inverter, which is not limited to this embodiment.
  • the constant current control module 2 further includes a dimming unit connected to the first operational amplifier unit OP1, the dimming unit receives an external dimming control signal DIM, and adjusts the dimming control signal DIM based on the dimming control signal DIM.
  • the magnitude of the reference voltage Ref is used to set the output current of the LED load 1, thereby realizing dimming control.
  • the dimming control signal DIM includes but is not limited to an analog signal or a pulse width modulation (PWM) signal, which is an extended application.
  • PWM pulse width modulation
  • the upper plate of the electrolytic capacitor Co is connected to the positive electrode of the LED load 1 for discharging to the LED load when the bus voltage Vin is lower than the voltage on the electrolytic capacitor Co.
  • the upper plate of the electrolytic capacitor Co is connected between the rectifier module 6 and the LED load 1, and the lower plate is connected to the charging current control module 5.
  • the bus voltage Vin is greater than the electrolytic When the voltage VCo on the capacitor Co, the bus voltage Vin charges the electrolytic capacitor Co, and at the same time, the bus voltage Vin supplies power to the LED load 1 .
  • the electrolytic capacitor Co supplies power to the LED load 1 .
  • the discharge voltage detection module 3 is connected to the negative electrode of the LED load 1 , and judges the magnitude of the discharge voltage of the electrolytic capacitor Co based on the negative electrode voltage of the LED load 1 to obtain a control signal.
  • the discharge voltage detection module 3 includes a detection unit and a comparison unit; the detection unit is connected to the negative electrode of the LED load, and detects the negative electrode voltage of the LED load to obtain a second detection voltage; the comparison unit The output terminal of the detection unit is connected, and the magnitude of the discharge voltage of the electrolytic capacitor is determined based on the second detection voltage.
  • the detection unit includes a first resistor R1 and a second resistor R2, the first resistor R1 and the second resistor R2 are connected in series between the negative electrode of the LED load and the ground, and the The second detection voltage.
  • the comparison unit includes a first comparator CMP1 and a second comparator CMP2.
  • the forward input terminal of the first comparator CMP1 is connected to the second detection voltage
  • the reverse input terminal is connected to the first preset voltage Ref1
  • the output terminal outputs a first control signal, wherein when the second comparator CMP1 When the detection voltage is greater than the first preset voltage Ref1, the first comparator CMP1 outputs a high level, and the first control signal is valid; when the second detection voltage is less than the first preset voltage Ref1, the The first comparator CMP1 outputs a low level, and the first control signal is invalid.
  • the inverting input terminal of the second comparator CMP2 is connected to the second detection voltage
  • the non-inverting input terminal is connected to the second preset voltage Ref2, and outputs a second control signal.
  • the second detection voltage is greater than the second preset voltage Ref2
  • the second comparator CMP2 outputs a low level, and the second control signal is invalid; when the second detection voltage is lower than the second
  • the preset voltage Ref2 is set, the second comparator CMP2 outputs a high level, and the second control signal is valid.
  • Ref1>Ref2 is usually set.
  • connection relationship between the input terminals and the output terminals of the first comparator CMP1 and the second comparator CMP2 can be adjusted, and the same logical relationship can be achieved by adding an inverter, which is not limited to this embodiment. .
  • the bus voltage detection module 4 is connected to the bus voltage Vin, and detects the bus voltage Vin to obtain a first detection voltage.
  • the bus voltage detection module 4 may include two resistors (not shown), these two resistors are connected in series between the output end of the rectifier module 6 and the ground, and the first detection voltage is obtained through voltage division .
  • the busbar voltage detection module 4 can be integrated inside the chip, or can be arranged outside the chip.
  • the LED driving system may further include a fourth sampling unit (optional), the fourth sampling unit is connected between the bus voltage detection module 4 and the ground to adjust the voltage of the bus voltage detection module 4 Internal control signal.
  • the fourth sampling unit includes but is not limited to a fourth sampling resistor Rpf.
  • the charging current control module 5 is connected to the discharge voltage detection module 3, the output terminal of the bus voltage detection module 4 and the lower plate of the electrolytic capacitor Co, based on the control signal and the first The detection voltage adjusts the charging current of the electrolytic capacitor Co.
  • the charging current control module 5 includes a compensation unit, the input end of the compensation unit is connected to the discharge voltage detection module 3 , and a corresponding compensation voltage is generated based on the output signal of the discharge voltage module 3 .
  • the compensation unit includes an addition-subtraction counter, which reduces the charging current of the electrolytic capacitor by performing a subtraction operation, and increases the charging current of the electrolytic capacitor by performing an addition operation.
  • the up-subtraction counter includes a first input terminal (inverting input terminal -), a second input terminal (forward input terminal +), a third input terminal (forward input terminal +X) and a fourth input terminal (high-speed clock High CLK), the first input terminal is connected to the output terminal of the first comparator CMP1, and the second input terminal is connected to the output terminal of the second comparator CMP2.
  • the charging current control module 5 further includes a second power switch transistor Q2, a second sampling unit, a third sampling unit and a second operational amplifying unit OP2, wherein: the drain of the second power switch transistor Q2 is connected to The bottom plate and source of the electrolytic capacitor Co are grounded through the second sampling unit.
  • the second sampling unit includes, but is not limited to, a second sampling resistor Rs2
  • the third sampling unit includes, but is not limited to, a third sampling resistor Rs1.
  • the first input terminal (forward input terminal+) of the second operational amplifier unit OP2 is connected to the output terminal of the compensation unit, and the second input terminal (reverse input terminal-) is connected to the bus voltage detection module 4, the output end of the second operational amplifying unit OP2 is connected to the gate of the second power switch tube Q2, so as to adjust the charging current of the electrolytic capacitor Co.
  • one end of the third sampling unit is connected between the bus voltage detection module 4 and the second operational amplifier unit OP2, and the other end is connected between the second power switch Q2 and the second sampling unit between units.
  • the compensation unit further includes a compensation voltage generating circuit and a digital-to-analog conversion unit (DAC).
  • the output terminal of the compensation voltage generating circuit is connected to the first input terminal (forward input terminal+) of the second operational amplifying unit OP2.
  • connection relationship between the input end and the output end of the second operational amplifier unit OP2 can be adjusted, and the same logical relationship can be achieved by adding an inverter, which is not limited to this embodiment.
  • the charging current control process of the electrolytic capacitor Co is roughly as follows: the drain voltage of the first power switch tube Q1 in the constant current control module 2 passes through the first resistor R1 and the second resistor The divided voltage of R2 is compared with the internal reference, and then a compensation signal is generated by the addition and subtraction counter.
  • the addition and subtraction counter will eventually reach a balanced state (This equilibrium state will fluctuate to a certain extent, and the fluctuation value can be controlled within the required range by setting the appropriate number of counting digits and counting frequency), after passing through the digital-to-analog conversion unit and the compensation voltage generating circuit, it becomes the compensation signal control
  • the second power switch tube Q2 charges and discharges the electrolytic capacitor Co.
  • the electrolytic capacitor Co can ensure that current can still flow through the LED during the AC valley, and the electrolytic capacitor is controlled by the second power switch Q2, the second operational amplifier unit OP2, and the second sampling unit Rs2. Co charging current, thereby extending the conduction angle of the input current to improve the power factor PF.
  • the bus voltage detection module 4 detects the bus voltage Vin. When the bus voltage Vin is too high, the charging current of the electrolytic capacitor Co is reduced to zero, thereby reducing the loss of controlling the second power switch Q2 and improving the overall efficiency of the system.
  • the size of the internal control signal of the bus voltage detection module 4 can be set and adjusted through an external resistor (the fourth sampling resistor Rpf). When the AC voltage input is high, the current charged by the electrolytic capacitor Co is discharged when the AC input voltage is low, thereby keeping the output LED current constant. In order to ensure the highest system efficiency, the discharge voltage of the electrolytic capacitor Co cannot be too high.
  • the discharge voltage of the electrolytic capacitor Co cannot be too low, which can be judged by the voltage of the OUT pin of the negative terminal of the LED.
  • the OUT pin voltage is detected through the internal voltage divider resistors (the first resistor R1 and the second resistor R2).
  • the comparator CMP1 controls the addition and subtraction counter to perform a subtraction operation (equivalent to discharging the compensation capacitor Ccomp shown in FIG.
  • the compensation capacitor Ccomp is charged), the output voltage of the compensation voltage generating circuit is increased after passing through the digital-to-analog conversion unit, and the charging current of the electrolytic capacitor Co is increased to increase the discharge voltage of the electrolytic capacitor Co.
  • the compensation unit further includes a third comparator CMP3, the non-inverting input terminal of the third comparator CMP3 is connected to the gate of the first power switch Q1, and the inverting input terminal is connected to the third preset voltage Ref3, output a third control signal; when the gate voltage of the first power switch Q1 is greater than the third preset voltage Ref3, output a high level, and the third control signal is valid.
  • the output end of the third comparator CMP3 is connected to the third input end (+X) of the addition and subtraction counter.
  • the discharge voltage of the electrolytic capacitor Co when the discharge voltage of the electrolytic capacitor Co is relatively low, the LED current cannot be maintained and decreases. At this time, the gate voltage of the first power switch Q1 will rise relatively high (especially at the beginning of startup). , the compensation voltage output by the digital-to-analog conversion unit is relatively low), the third comparator CMP3 detects that the gate voltage of the first power switch Q1 exceeds the third internal set value (the third preset voltage Ref3 ), control the addition and subtraction counter to perform fast addition (+X), quickly increase the output voltage of the compensation voltage generating circuit after passing through the digital-to-analog conversion unit, and quickly control the second power switch tube Q2 to increase the electrolysis The charging current of the capacitor Co, thereby rapidly increasing the discharge voltage of the electrolytic capacitor Co. Through the loop adjustment of the addition and subtraction counter module, it is ensured that the minimum level of the OUT voltage (the negative voltage of the LED load) after the LED current is constant current will not be too high to cause loss of system efficiency.
  • connection relationship between the input end and the output end of the third comparator CMP3 can be adjusted, and the same logical relationship can be achieved by adding an inverter, which is not limited to this embodiment.
  • the compensation unit further includes a protection module, the protection module is connected to the addition and subtraction counter and the constant current control module 2, and adjusts the constant current control module based on the overflow signal of the addition and subtraction counter 2 The value of the reference voltage Ref.
  • the addition and subtraction counter when the addition and subtraction counter is added to the highest value during the addition and subtraction operation, an addition overflow signal will be generated, indicating that the OUT voltage is low, the electrolytic capacitor Co is not enough to store energy, and the LED current cannot be constant current.
  • the internal reference can be reduced. (the reference voltage Ref), thereby reducing the LED output current, reducing the discharge of the electrolytic capacitor Co, increasing the OUT voltage, making the loop work normally, and ensuring that the LED output current does not flicker.
  • the reference is lowered by adding the overflow signal, so when the input voltage decreases, the control loop can still maintain constant current operation (less than the rated current) after the output current decreases, so that the output can ensure no stroboscopic, and there will be no unsustainable in the traditional driver.
  • the addition and subtraction counter When the addition and subtraction counter is doing addition and subtraction operations, if the subtraction overflow signal is generated if it is reduced to the minimum, it means that the OUT voltage is high at this time, and the electrolytic capacitor Co stores too much energy. At this time, the loss of the second power switch Q2 will be reduced. Increase, at this time, the internal reference can be raised to increase the LED output current, thereby accelerating the discharge of the electrolytic capacitor Co to reduce the OUT voltage, making the loop work normally, and reducing the loss on the second power switch tube Q2, which can be extended additionally Input voltage operating range.
  • the LED driving system of this embodiment uses an addition and subtraction counter to realize the digitization of the loop compensation, integrates the compensation capacitor compensation function into the chip, and does not need to use the external compensation large capacitor of the compensation loop, so that the peripheral circuit is simplified and the system cost is low.
  • the counting overflow of the addition and subtraction counter can realize some additional functions or protection, for example, the output current can still achieve no flicker when the low voltage input is used.
  • the output of the addition and subtraction counter reflects the working state of the system, and the output digital signal can be provided to an external MCU for intelligent processing, such as intelligent dimming, etc. Its related functions are not repeated here.
  • This embodiment provides a closed-loop control method for LED driving.
  • the closed-loop control method for LED driving can be implemented based on the LED driving system in the first embodiment or other hardware circuits and software codes, and includes the following steps:
  • the electrolytic capacitor discharges the LED load, and performs constant current control on the LED load based on the constant current control module, wherein when the discharge voltage of the electrolytic capacitor is higher than the first setting When the voltage of the electrolytic capacitor is reduced, the subtraction operation is performed by the addition and subtraction counter to reduce the charging current of the electrolytic capacitor, thereby reducing the discharge voltage of the electrolytic capacitor; when the discharge voltage of the electrolytic capacitor is lower than the second set voltage, the The addition and subtraction counter performs addition operation to increase the charging current of the electrolytic capacitor, thereby increasing the discharge voltage of the electrolytic capacitor;
  • the bus voltage When the bus voltage is greater than the on-voltage of the LED, the bus voltage supplies power to the LED load, and the constant current control module performs constant current control on the LED load, and the bus voltage is the same as the LED load.
  • the electrolytic capacitor discharges the LED load, and performs constant current control on the LED load based on the constant current control module.
  • the negative electrode voltage of the LED load is detected to determine the magnitude of the discharge voltage of the electrolytic capacitor.
  • the charging current control process of the electrolytic capacitor Co is roughly as follows: the drain voltage of the first power switch tube Q1 in the constant current control module 2 (also referred to as the The negative voltage of the LED load) is compared with the internal reference after being divided by the first resistor R1 and the second resistor R2, and then a compensation signal is generated through the addition and subtraction counter.
  • the negative voltage of the LED load is a periodic signal, and the addition and subtraction counter will eventually reach a balance state (this balance state will fluctuate to a certain extent, and the fluctuation value can be controlled within the required range by setting the appropriate number of count digits and counting frequency) , after passing through the digital-to-analog conversion unit and the compensation voltage generating circuit, it becomes a compensation signal to control the charging and discharging of the electrolytic capacitor Co by the second power switch tube Q2.
  • the electrolytic capacitor Co can ensure that current can still flow through the LED during the AC valley, and the electrolytic capacitor is controlled by the second power switch Q2, the second operational amplifier unit OP2, and the second sampling unit Rs2. Co charging current, thereby extending the conduction angle of the input current to improve the power factor PF.
  • the discharge voltage of the electrolytic capacitor Co cannot be too high. In order to keep the output LED current constant, the discharge voltage of the electrolytic capacitor Co cannot be too low, which can be judged by the voltage of the OUT pin of the negative terminal of the LED.
  • the electrolysis The discharge voltage of the capacitor Co is relatively high, the comparator CMP1 controls the addition and subtraction counter to perform a subtraction operation (equivalent to discharging the compensation capacitor Ccomp shown in Figure 3), and after the digital-to-analog conversion unit, the output voltage of the compensation voltage generating circuit is reduced, The charging current of the electrolytic capacitor Co is reduced to reduce the discharge voltage of Co.
  • the comparator CMP2 controls the addition and subtraction counter to perform addition operation (equivalent to the comparison of Fig.
  • the compensation capacitor Ccomp shown in 3 is charged), after passing through the digital-to-analog conversion unit, the output voltage of the compensation voltage generating circuit is increased, the charging current of the electrolytic capacitor Co is increased, and the discharge voltage of the electrolytic capacitor Co is increased.
  • the charging current of the electrolytic capacitor is reduced until zero.
  • the busbar voltage detection module 4 detects the busbar voltage Vin, and when the busbar voltage Vin is too high, the charging current of the electrolytic capacitor Co is reduced to zero, thereby reducing the loss of controlling the second power switch tube Q2 and improving the system performance.
  • the size of the internal control signal of the bus voltage detection module 4 can be set and adjusted through an external resistor (the fourth sampling resistor Rpf).
  • the discharge voltage of the electrolytic capacitor Co is relatively low, the LED current cannot be maintained and decreases.
  • the gate voltage of the first power switch Q1 will rise relatively high (especially at the beginning of startup).
  • the compensation voltage output by the digital-to-analog conversion unit is relatively low)
  • the third comparator CMP3 detects that the gate voltage of the first power switch Q1 exceeds the third preset voltage Ref3
  • rapidly increase the output voltage of the compensation voltage generation circuit after passing through the digital-to-analog conversion unit and quickly control the second power switch Q2 to increase the charging current of the electrolytic capacitor Co, thereby quickly
  • the discharge voltage of the electrolytic capacitor Co is increased.
  • the addition and subtraction counter module it is ensured that the minimum level of the OUT voltage will not be too high after the constant current of the LED current, resulting in loss of system efficiency.
  • the reference voltage of the constant current control module is reduced to reduce the output current of the LED load, thereby reducing the discharge of the electrolytic capacitor Co;
  • the reference voltage Ref of the constant current control module is increased to increase the output current of the LED load, thereby accelerating the discharge of the electrolytic capacitor.
  • the addition and subtraction counter when the addition and subtraction counter is added to the highest value during the addition and subtraction operation, an addition overflow signal will be generated, indicating that the OUT voltage is low, the electrolytic capacitor Co is not enough to store energy, and the LED current cannot be constant current.
  • the internal reference can be reduced. (the reference voltage Ref), thereby reducing the LED output current, reducing the discharge of the electrolytic capacitor Co, increasing the OUT voltage, making the loop work normally, and ensuring that the LED output current does not flicker.
  • the internal reference is reduced by the addition overflow signal, so when the input voltage is reduced, the control loop can still maintain constant current operation (less than the rated current) after the output current is reduced, so that the output can ensure no stroboscopic, and there will be no failure in traditional drivers.
  • the power frequency ripple and flicker of the current drop while maintaining the rated current.
  • the addition and subtraction counter When the addition and subtraction counter is doing addition and subtraction operations, if the subtraction overflow signal is generated if it is reduced to the minimum, it means that the OUT voltage is high at this time, and the electrolytic capacitor Co stores too much energy. At this time, the loss of the second power switch Q2 will be reduced. Increase, at this time, the internal reference can be raised to increase the LED output current, thereby accelerating the discharge of the electrolytic capacitor Co to reduce the OUT voltage, making the loop work normally, and reducing the loss on the second power switch tube Q2, which can be extended additionally Input voltage operating range.
  • the closed-loop control method for LED driving in this embodiment uses the addition and subtraction counter to realize the digitization of the loop compensation, and does not need to use the external compensation large capacitor of the compensation loop, which is beneficial to simplify the peripheral circuit and reduce the system cost, and uses the addition and subtraction counter to count
  • the overflow can realize some additional functions or protection, such as the output drop current can still achieve no stroboscopic when the input is low.
  • the output of the addition and subtraction counter reflects the working state of the system, and the output digital signal can be provided to the external MCU for intelligent processing, such as intelligent dimming.
  • the LED driving system and the closed-loop control method for LED driving of the present invention utilize the addition and subtraction counter to realize the digitization of the loop compensation, without using the external compensation large capacitor of the compensation loop, so that the peripheral circuit is simplified and the system cost is low.
  • the present invention can realize some additional functions or protection by using the counting overflow of the addition and subtraction counter, for example, the output current can be reduced without flicker when the low voltage is input.
  • the output of the addition and subtraction counter reflects the working state of the system, and the output digital signal can be provided to the external MCU for intelligent processing, such as intelligent dimming. Therefore, the present invention effectively overcomes various shortcomings in the prior art and has high industrial utilization value.

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Abstract

提供一种LED驱动系统及LED驱动的闭环控制方法，该LED驱动系统包括LED负载（1）、恒流控制模块（2）、电解电容、放电电压检测模块（3）、母线电压检测模块（4）及充电电流控制模块（5），其中，充电电流控制模块（5）连接放电电压检测模块（3）、母线电压检测模块（4）的输出端及电解电容的下极板，基于放电电压检测模块（3）的控制信号及母线电压检测模块（4）的检测电压调整电解电容的充电电流，通过加减法计数器进行加法或减法运算以增大或减小电解电容的充电电流，实现环路补偿数字化，使得外围电路最简化，系统成本低。

Description

一种LED驱动系统及LED驱动的闭环控制方法 技术领域
本发明属于系统设计领域，涉及一种LED驱动系统及LED驱动的闭环控制方法。
背景技术
随着企业资源规划系统(ERP)标准的推行，发光二极管(LED)驱动在满足功率因数PF、谐波、效率等要求下还增加了对频闪的要求，对此线性LED驱动也推出了一些新的方案：一种是在传统的线性高效高PF驱动中外加去纹波电路，或者是将去纹波模块集成到驱动芯片中，如图1所示，但是由于去纹波模块比较复杂，并且该模块会额外损失一些效率，成本和性能都不是最佳的方案。另一种简单的方法，是将LED恒流部分与电解电容充放电部分分开单独控制，如图2所示：第二功率开关管Q2部分采用传统的线性LED恒流驱动，第一功率开关管Q1采用过压降电流等措施对电解电容的充放电进行控制实现高功率因数PF，在输入电压高峰时减少电解电容Co的充电电流，降低第一功率开关管Q1的充电损耗提高效率，在输入电压波谷时电解电容Co对LED放电，通过第二功率开关管Q2进行LED恒流控制实现去频闪功能。在图2所示的方案中，第一功率开关管Q1和第二功率开关管Q2是两个独立的控制回路，无法相互配合达到最佳状态，因此在输入高压时，第一功率开关管Q1充电时间会增加导致电解电容Co充电电压上升，从而第二功率开关管Q2漏极上承担的电压(VQ2＝VCo-VLED)升高从而增加损耗降低效率，输入低压时第一功率开关管Q1充电时间会减少导致电解电容Co充电电压下降，从而第二功率开关管Q2的工作电压不足使LED出现掉电流的工频纹波。
以上两种方法都不是闭环控制系统，输出受输入电压变化的影响比较大，因此输入电压的正常工作范围都比较窄。
因此，如何提供一种满足ERP标准的LED驱动闭环控制方案，并简化外围电路、降低系统成本、减小器件面积，成为本领域技术人员亟待解决的一个重要技术问题。
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LED驱动系统及LED驱动的闭环控制方法，用于解决现有技术中LED驱动系统的输入电压正常工作范围较窄的问题。
为实现上述目的及其他相关目的，本发明提供一种LED驱动系统，包括：
LED负载，所述LED负载的正极连接母线电压；
恒流控制模块，连接所述LED负载的负极，用于对所述LED负载进行恒流控制；
电解电容，所述电解电容的上极板连接所述LED负载的正极，用于在所述母线电压小于所述电解电容上的电压时向所述LED负载放电；
放电电压检测模块，连接所述LED负载的负极，基于所述LED负载的负极电压判断所述电解电容的放电电压大小，得到控制信号；
母线电压检测模块，对所述母线电压进行检测得到第一检测电压；
充电电流控制模块，连接所述放电电压检测模块、所述母线电压检测模块的输出端及所述电解电容的下极板，基于所述控制信号及所述第一检测电压调整所述电解电容的充电电流，其中，所述充电电流控制模块包括补偿单元，所述补偿单元的输入端连接所述放电电压检测模块，基于所述放电电压模块的输出信号产生相应的补偿电压，所述补偿单元包括加减法计数器，通过进行减法运算以减小所述电解电容的充电电流，通过进行加法运算以增大所述电解电容的充电电流。
可选的，所述恒流控制模块包括第一功率开关管、第一采样单元及第一运算放大单元；所述第一功率开关管的漏极连接所述LED负载的负极，源极经由所述第一采样单元接地；所述第一运算放大单元的输入端分别连接所述第一功率开关管的源极及一参考电压，输出端连接所述第一功率开关管的栅极，将采样电压与所述参考电压进行比较以控制流经所述LED负载的电流大小。
更可选地，所述恒流控制模块还包括连接所述第一运算放大单元的调光单元，所述调光单元接收调光控制信号，基于所述调光控制信号调整所述参考电压的大小以设置所述LED负载的输出电流。
更可选地，所述调光控制信号为模拟信号或脉冲宽度调制信号。
可选的，所述放电电压检测模块包括检测单元及比较单元；所述检测单元连接所述LED负载的负极，对所述LED负载的负极电压进行检测以得到第二检测电压；所述比较单元连接所述检测单元的输出端，基于所述第二检测电压判断所述电解电容的放电电压大小。
更可选地，所述比较单元包括第一比较器及第二比较器；所述第一比较器的输入端分别连接所述第二检测电压及第一预设电压，当所述第二检测电压大于所述第一预设电压时输出第一控制信号；所述第二比较器的输入端分别连接所述第二检测电压及第二预设电压，当所述第二检测电压小于所述第二预设电压时输出第二控制信号。
更可选地，所述加减法计数器的第一输入端连接所述第一比较器的输出端，第二输入端连接所述第二比较器的输出端。
可选的，所述充电电流控制模块还包括第二功率开关管、第二采样单元、第三采样单元及第二运算放大单元，其中：
所述第二功率开关管的漏极连接所述电解电容的下极板，源极经由所述第二采样单元接地；
所述第二运算放大单元的第一输入端连接所述补偿单元的输出端，第二输入端连接所述母线电压检测模块的输出端，所述第二运算放大单元的输出端连接所述第二功率开关管的栅极，以实现对所述电解电容的充电电流的调整；
所述第三采样单元的一端连接于所述母线电压检测模块与所述第二运算放大单元之间，另一端连接于所述第二功率开关管与所述第二采样单元之间。
更可选地，所述补偿单元还包括补偿电压产生电路及数模转换单元，所述加减法计数器的输出端经由所述数模转换单元连接所述补偿电压产生电路的输入端，所述补偿电压产生电路的输出端连接所述第二运算放大单元的所述第一输入端。
可选的，所述补偿单元还包括第三比较器，所述第三比较器的第一输入端连接所述恒流控制模块中功率开关管的栅极，第二输入端连接第三预设电压，输出端连接所述加减法计数器的第三输入端，当所述恒流控制模块中功率开关管的栅极电压大于所述第三预设电压时，所述加减法计数器进行快速加法运算。
可选的，所述补偿单元还包括保护模块，所述保护模块连接所述加减法计数器及所述恒流控制模块，并基于所述加减法计数器的溢出信号调整所述恒流控制模块的参考电压的值。
可选的，所述LED驱动系统还包括第四采样单元，所述第四采样单元连接于所述母线电压检测模块与地之间以调整所述母线电压检测模块的内部控制信号。
可选的，所述LED驱动系统还包括工作电压产生模块，所述工作电压产生模块连接所述母线电压，基于所述母线电压为所述LED驱动系统提供工作电压。
可选的，所述LED驱动系统还包括整流模块，所述整流模块对交流电源进行整流以得到所述母线电压。
本发明还提供一种LED驱动的闭环控制方法，包括以下步骤：
当母线电压小于LED的导通电压时，电解电容对LED负载放电，并基于恒流控制模块对所述LED负载进行恒流控制，其中，当所述电解电容的放电电压高于第一设定电压时，通过加减法计数器进行减法运算以减小所述电解电容的充电电流，进而降低所述电解电容 的放电电压；当所述电解电容的放电电压低于第二设定电压时，通过加减法计数器进行加法运算以增大所述电解电容的充电电流，进而提高所述电解电容的放电电压；
当所述母线电压大于LED的导通电压时，所述母线电压为所述LED负载供电，并基于所述恒流控制模块对所述LED负载进行恒流控制，同时所述母线电压为所述电解电容充电；
当所述母线电压小于所述电解电容的电压时，所述电解电容对所述LED负载放电，并基于所述恒流控制模块对所述LED负载进行恒流控制。
可选的，当所述电解电容的放电电压低于第三设定电压时，通过加减法计数器进行快速加法运算以快速增大所述电解电容的充电电流，进而快速提高所述电解电容的放电电压。
可选的，当所述加减法计数器产生加法溢出信号时，降低所述恒流控制模块的参考电压以降低所述LED负载的输出电流，进而减少所述电解电容的放电；当所述加减法计数器产生减法溢出信号时，升高所述恒流控制模块的参考电压以提高所述LED负载的输出电流，进而加快所述电解电容的放电。
可选的，当所述母线电压大于LED的导通电压并大于第四设定电压时，降低所述电解电容的充电电流直至为零。
如上所述，本发明的LED驱动系统及LED驱动的闭环控制方法利用加减法计数器实现环路补偿数字化，无需采用补偿环路的外部补偿大电容，使得外围电路最简化，系统成本低。本发明利用加减法计数器的计数溢出可以实现一些额外功能或保护，例如低压输入时输出降电流仍能实现无频闪。此外，加减法计数器的输出反映了系统的工作状态，其输出的数字信号可以提供给外部MCU进行智能化处理，如智能调光等。
附图说明
图1显示为一种包含去纹波模块的线性LED驱动系统的结构示意图。
图2显示为一种将LED恒流部分与电解电容充放电部分分开单独控制的LED驱动系统的结构示意图。
图3显示为一种采用闭环控制回路且包含外部补偿大电容的LED恒流驱动系统的结构示意图。
图4显示为本发明的LED驱动系统的结构示意图。
元件标号说明
1                      LED负载
2                      恒流控制模块
3                      放电电压检测模块
4                      母线电压检测模块
5                      充电电流控制模块
6                      整流模块
7                      工作电压产生模块
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3至图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。
如图3所示，显示为一种采用闭环控制回路的LED恒流驱动系统，其通过检测第二功率开关管Q2的漏极电压进行补偿来控制第一功率开关管Q1的充电电流，使得电解电容Co在放电时将第二功率开关管Q2漏极电压始终控制在一个比较合适的低值来减少第二功率开关管Q2的损耗，解决了频闪的同时也提高了效率，第一功率开关管Q1与第二功率开关管Q2的控制环路成为一个闭环控制，使得输入电压正常工作范围增加。该方案的问题在于其为了建立闭环控制回路，需要外加一个大电容Ccomp进行环路补偿，这个外置电容无法集成到芯片内部，因此增加了系统成本并占用了PCB板的可利用空间。本发明通过新的系统设计，利用加减法计数器实现环路补偿数字化，可以去掉补偿环路的外部补偿大电容，使得外围电路最简化，并降低系统成本。下面通过具体的实施例来详述本发明的技术方案。
实施例一
请参阅图4，本实施例提供一种LED驱动系统，包括LED负载1、恒流控制模块2、电解电容Co、放电电压检测模块3、母线电压检测模块4及充电电流控制模块5。
具体的，所述LED负载1的正极连接母线电压Vin。本实施例中，所述母线电压Vin由整流模块6提供，所述整流模块6对交流电源AC进行整流以得到所述母线电压Vin。所述整流模块6包括整流桥结构BD1及保险丝F1，所述整流桥结构BD1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。所述母线电压Vin为正弦电压整流后的整流电压。本实施例中，所述LED驱动系统还包括工作电压产生模块7，所述工作电压产生模块连接所述母线电压Vin，基于所述母线电压Vin为所述LED驱动系统提供工作电压VDD。
作为示例，所述LED负载1的正极连接于所述整流模块6的输出端，所述LED负载1包括串联的多个LED灯，所述LED负载1也可以是多个LED灯的串并联结构，不以本实施例为限。当所述LED负载1两端的电压达到其导通电压时，所述LED负载1中的LED点亮，起到照明的作用。
具体的，所述恒流控制模块2连接所述LED负载1的负极，用于对所述LED负载1进行恒流控制。本实施例中，所述恒流控制模块2包括第一功率开关管Q1、第一采样单元及第一运算放大单元OP1，所述第一采样单元包括但不限于第一采样电阻Rcs。输入电压经过负载LED后由所述第一功率开关管Q1控制电流，所述第一运算放大单元OP1检测所述第一采样电阻Rcs上的电压对LED进行恒流控制，确保LED电流恒定不变以消除频闪。
作为示例，所述第一功率开关管Q1的漏极连接所述LED负载的负极，源极经由所述第一采样电阻Rcs接地；所述第一运算放大单元OP1的输入端分别连接所述第一功率开关管Q1的源极及一参考电压Ref，输出端连接所述第一功率开关管Q1的栅极，将采样电压与所述参考电压Ref进行比较以控制流经所述LED负载1的电流大小，进而实现恒流控制。
需要说明的是，所述参考电压Ref为内部固定值或外部提供，当所述参考电压Ref为内部固定值时，可通过改变所述第一采样电阻Rcs的阻值来调整所述LED负载1的输出电流。所述第一运算放大单元OP1的输入端、输出端的连接关系可调整，通过增加反相器即可实现相同的逻辑关系，不以本实施例为限。
作为示例，所述恒流控制模块2还包括连接所述第一运算放大单元OP1的调光单元，所述调光单元接收外部调光控制信号DIM，基于所述调光控制信号DIM调整所述参考电压Ref的大小以设置所述LED负载1的输出电流，进而实现调光控制。
作为示例，所述调光控制信号DIM包括但不限于模拟信号或脉冲宽度调制(PWM)信号，是一种扩展应用。
具体的，所述电解电容Co的上极板连接所述LED负载1的正极，用于在所述母线电压Vin小于所述电解电容Co上的电压时向所述LED负载放电。
作为示例，所述电解电容Co的上极板连接于所述整流模块6及所述LED负载1之间，下极板连接所述充电电流控制模块5，当所述母线电压Vin大于所述电解电容Co上的电压VCo时，所述母线电压Vin给所述电解电容Co充电，同时所述母线电压Vin为所述LED负载1供电。当所述母线电压Vin小于所述电解电容Co上的电压VCo时，所述电解电容Co为所述LED负载1供电。
具体的，所述放电电压检测模块3连接所述LED负载1的负极，基于所述LED负载1的负极电压判断所述电解电容Co的放电电压大小，得到控制信号。
作为示例，所述放电电压检测模块3包括检测单元及比较单元；所述检测单元连接所述LED负载的负极，对所述LED负载的负极电压进行检测以得到第二检测电压；所述比较单元连接所述检测单元的输出端，基于所述第二检测电压判断所述电解电容的放电电压大小。
作为示例，所述检测单元包括第一电阻R1及第二电阻R2，所述第一电阻R1及所述第二电阻R2串联于所述LED负载的负极与地之间，通过分压获得所述第二检测电压。
作为示例，所述比较单元包括第一比较器CMP1及第二比较器CMP2。
作为示例，所述第一比较器CMP1的正向输入端连接所述第二检测电压，反向输入端连接第一预设电压Ref1，输出端输出第一控制信号，其中，当所述第二检测电压大于所述第一预设电压Ref1时，第一比较器CMP1输出高电平，所述第一控制信号有效；当所述第二检测电压小于所述第一预设电压Ref1时，所述第一比较器CMP1输出低电平，所述第一控制信号无效。
作为示例，所述第二比较器CMP2的反相输入端连接所述第二检测电压，正相输入端连接第二预设电压Ref2，输出第二控制信号。当所述第二检测电压大于所述第二预设电压Ref2时，所述第二比较器CMP2输出低电平，所述第二控制信号无效；当所述第二检测电压小于所述第二预设电压Ref2时，所述第二比较器CMP2输出高电平，所述第二控制信号有效。
作为示例，为了优化系统性能，通常设置Ref1>Ref2。
需要说明的是，所述第一比较器CMP1及所述第二比较器CMP2输入端、输出端的连接关系可调整，通过增加反相器即可实现相同的逻辑关系，不以本实施例为限。
具体的，母线电压检测模块4连接所述母线电压Vin，对所述母线电压Vin进行检测得到第一检测电压。
作为示例，所述母线电压检测模块4可包括两个电阻(未图示)，这两个电阻串联于所述整流模块6的输出端与地之间，通过分压获得所述第一检测电压。所述母线电压检测 模块4可以集成在芯片内部，也可以设置在芯片外部。
作为示例，所述LED驱动系统还可进一步包括第四采样单元(非必需)，所述第四采样单元连接于所述母线电压检测模块4与地之间以调整所述母线电压检测模块4的内部控制信号。所述第四采样单元包括但不限于第四采样电阻Rpf。
具体的，所述充电电流控制模块5连接所述放电电压检测模块3、所述母线电压检测模块4的输出端及所述电解电容Co的下极板，基于所述控制信号及所述第一检测电压调整所述电解电容Co的充电电流。
作为示例，所述充电电流控制模块5包括补偿单元，所述补偿单元的输入端连接所述放电电压检测模块3，基于所述放电电压模块3的输出信号产生相应的补偿电压。
作为示例，所述补偿单元包括加减法计数器，通过进行减法运算以减小所述电解电容的充电电流，通过进行加法运算以增大所述电解电容的充电电流。
作为示例，所述加减法计数器包括第一输入端(反向输入端-)、第二输入端(正向输入端+)、第三输入端(正向输入端+X)及第四输入端(高速时钟High CLK)，所述第一输入端连接所述第一比较器CMP1的输出端，所述第二输入端连接所述第二比较器CMP2的输出端。
作为示例，所述充电电流控制模块5还包括第二功率开关管Q2、第二采样单元、第三采样单元及第二运算放大单元OP2，其中：所述第二功率开关管Q2的漏极连接所述电解电容Co的下极板，源极经由所述第二采样单元接地。所述第二采样单元包括但不限于第二采样电阻Rs2，所述第三采样单元包括但不限于第三采样电阻Rs1。
作为示例，所述第二运算放大单元OP2的第一输入端(正向输入端+)连接所述补偿单元的输出端，第二输入端(反向输入端-)连接所述母线电压检测模块4的输出端，所述第二运算放大单元OP2的输出端连接所述第二功率开关管Q2的栅极，以实现对所述电解电容Co的充电电流的调整。
作为示例，所述第三采样单元的一端连接于所述母线电压检测模块4与所述第二运算放大单元OP2之间，另一端连接于所述第二功率开关管Q2与所述第二采样单元之间。
作为示例，所述补偿单元还包括补偿电压产生电路及数模转换单元(DAC)，所述加减法计数器的输出端经由所述数模转换单元连接所述补偿电压产生电路的输入端，所述补偿电压产生电路的输出端连接所述第二运算放大单元OP2的所述第一输入端(正向输入端+)。
需要说明的是，所述第二运算放大单元OP2的输入端、输出端的连接关系可调整，通过增加反相器即可实现相同的逻辑关系，不以本实施例为限。
具体的，所述电解电容Co的充电电流控制过程大致如下：所述恒流控制模块2中的所述第一功率开关管Q1的漏极电压经过所述第一电阻R1与所述第二电阻R2的分压后与内部基准进行比较，然后经过所述加减法计数器产生一个补偿信号，由于OUT电压(所述LED负载的负极电压)是个周期信号，加减法计数器最终会达到一个平衡态(这个平衡态会有一定波动，可以通过设置合适的计数位数及计数频率将波动值控制在需要的范围内)，经过所述数模转换单元及所述补偿电压产生电路后成为补偿信号控制第二功率开关管Q2对所述电解电容Co的充放电。所述电解电容Co能够保证在交流谷底期间LED仍能有电流流过，通过所述第二功率开关管Q2、所述第二运算放大单元OP2、所述第二采样单元Rs2控制所述电解电容Co的充电电流，从而扩展输入电流的导通角来提高功率因数PF。所述母线电压检测模块4检测母线电压Vin，母线电压Vin过高时降低电解电容Co的充电电流直至为零，从而减小控制所述第二功率开关管Q2的损耗，提高系统的整体效率，所述母线电压检测模块4内部控制信号大小可以通过外接电阻(所述第四采样电阻Rpf)来设置调整。交流电压输入高时电解电容Co充进的电流在交流输入电压低时放电，从而保持输出LED电流恒定不变。为了保证系统效率的最高，所述电解电容Co的放电电压不能太高，为了输出LED电流保持恒定，因此所述电解电容Co的放电电压也不能太低，可以通过LED负端OUT脚电压来判断电解电容Co的放电电压(VOUT＝VCo-VLED)。通过内部分压电阻(所述第一电阻R1及所述第二电阻R2)检测OUT脚电压，当OUT电压高于第一内部设定值(所述第一预设电压Ref1)时，说明所述电解电容Co放电电压比较高，比较器CMP1控制加减法计数器进行减法运算(相当于对图3所示补偿电容Ccomp进行放电)，经过数模转换单元后降低所述补偿电压产生电路的输出电压，减小所述电解电容Co的充电电流从而降低Co的放电电压。当OUT电压低于第二内部设定值(第二预设电压Ref2)时，说明所述电解电容Co放电电压比较低，比较器CMP2控制加减法计数器进行加法运算(相当于对图3所示补偿电容Ccomp进行充电)，经过数模转换单元后提高所述补偿电压产生电路的输出电压，增大所述电解电容Co的充电电流从而提高所述电解电容Co的放电电压。
作为示例，所述补偿单元还包括第三比较器CMP3，所述第三比较器CMP3的正相输入端连接所述第一功率开关管Q1的栅极，反相输入端连接第三预设电压Ref3，输出第三控制信号；当所述第一功率开关管Q1的栅极电压大于所述第三预设电压Ref3时输出高电平，所述第三控制信号有效。所述第三比较器CMP3的输出端连接所述加减法计数器的第三输入端(+X)，当所述恒流控制模块2中所述第一功率开关管Q1的栅极电压大于所述第三预设电压Ref3时，所述加减法计数器进行快速加法运算。
具体的，当所述电解电容Co的放电电压偏低较多时，LED电流会无法维持并下降，此时所述第一功率开关管Q1的栅极电压会升得比较高(尤其在刚启动时，所述数模转换单元输出的补偿电压比较低)，所述第三比较器CMP3检测到所述第一功率开关管Q1的栅极电压超过第三内部设定值(第三预设电压Ref3)时，控制加减法计数器进行快速加法(+X)，经过所述数模转换单元后快速提高所述补偿电压产生电路的输出电压，快速控制所述第二功率开关管Q2增加所述电解电容Co的充电电流，从而快速提高所述电解电容Co的放电电压。经过所述加减法计数器模块的环路调整，确保LED电流恒流后OUT电压(所述LED负载的负极电压)最低电平不会太高而导致系统效率的损失。
需要说明的是，所述第三比较器CMP3输入端、输出端的连接关系可调整，通过增加反相器即可实现相同的逻辑关系，不以本实施例为限。
作为示例，所述补偿单元还包括保护模块，所述保护模块连接所述加减法计数器及所述恒流控制模块2，并基于所述加减法计数器的溢出信号调整所述恒流控制模块2的参考电压Ref的值。
具体的，当加减法计数器在做加减运算时加到最高会产生加法溢出信号时，说明OUT电压偏低，电解电容Co存储能量不够，LED电流会无法恒流，此时可以降低内部基准(所述参考电压Ref)的值，从而降低LED输出电流，减少电解电容Co放电，提高OUT电压，使环路进入正常工作，保证LED输出电流无频闪。通过加法溢出信号降低基准，因此当输入电压降低时输出电流减小后，控制环路仍能保持恒流工作(小于额定电流)，从而输出能保证无频闪，不会出现传统驱动器中无法维持额定电流而出现的掉电流的工频纹波及闪烁。
而当加减法计数器在做加减运算时如果减到最低会产生减法溢出信号，说明此时OUT电压偏高，电解电容Co存储能量过多，此时所述第二功率开关管Q2损耗会增加，此时可以升高内部基准来提高LED输出电流，从而加快电解电容Co放电来降低OUT电压，使环路进入正常工作，并降低所述第二功率开关管Q2上的损耗，可以额外扩展输入电压的工作范围。
本实施例的LED驱动系统利用加减法计数器实现环路补偿数字化，将补偿电容补偿功能集成到芯片内部，无需采用补偿环路的外部补偿大电容，使得外围电路最简化，系统成本低。加减法计数器的计数溢出可以实现一些额外功能或保护，例如低压输入时输出降电流仍能实现无频闪。此外，加减法计数器的输出反映了系统的工作状态，其输出的数字信号可以提供给外部MCU进行智能化处理，如智能调光等，其相关功能在此不再一一赘述。
实施例二
本实施例提供一种LED驱动的闭环控制方法，该LED驱动的闭环控制方法可基于实施例一中的LED驱动系统实现或其他硬件电路、软件代码实现，包括以下步骤：
当母线电压小于LED的导通电压时，电解电容对LED负载放电，并基于恒流控制模块对所述LED负载进行恒流控制，其中，当所述电解电容的放电电压高于第一设定电压时，通过加减法计数器进行减法运算以减小所述电解电容的充电电流，进而降低所述电解电容的放电电压；当所述电解电容的放电电压低于第二设定电压时，通过加减法计数器进行加法运算以增大所述电解电容的充电电流，进而提高所述电解电容的放电电压；
当所述母线电压大于LED的导通电压时，所述母线电压为所述LED负载供电，并基于所述恒流控制模块对所述LED负载进行恒流控制，同时所述母线电压为所述电解电容充电；
当所述母线电压小于所述电解电容的电压时，所述电解电容对所述LED负载放电，并基于所述恒流控制模块对所述LED负载进行恒流控制。
作为示例，对所述LED负载的负极电压进行检测以判断所述电解电容的放电电压大小。
具体的，以图4所示系统为例，所述电解电容Co的充电电流控制过程大致如下：所述恒流控制模块2中的所述第一功率开关管Q1的漏极电压(亦为所述LED负载的负极电压)经过所述第一电阻R1与所述第二电阻R2的分压后与内部基准进行比较，然后经过所述加减法计数器产生一个补偿信号，由于OUT电压(所述LED负载的负极电压)是个周期信号，加减法计数器最终会达到一个平衡态(这个平衡态会有一定波动，可以通过设置合适的计数位数及计数频率将波动值控制在需要的范围内)，经过所述数模转换单元及所述补偿电压产生电路后成为补偿信号控制第二功率开关管Q2对所述电解电容Co的充放电。所述电解电容Co能够保证在交流谷底期间LED仍能有电流流过，通过所述第二功率开关管Q2、所述第二运算放大单元OP2、所述第二采样单元Rs2控制所述电解电容Co的充电电流，从而扩展输入电流的导通角来提高功率因数PF。交流电压输入高时电解电容Co充进的电流在交流输入电压低时放电，从而保持输出LED电流恒定不变。为了保证系统效率的最高，所述电解电容Co的放电电压不能太高，为了输出LED电流保持恒定，因此所述电解电容Co的放电电压也不能太低，可以通过LED负端OUT脚电压来判断电解电容Co的放电电压(VOUT＝VCo-VLED)。通过内部分压电阻(所述第一电阻R1与第二电阻R2)检测OUT脚电压，当OUT电压高于第一预设电压Ref1(对应所述第一设定电压)时，说明所述电解电容Co放电电压比较高，比较器CMP1控制加减法计数器进行 减法运算(相当于对图3所示补偿电容Ccomp进行放电)，经过数模转换单元后降低所述补偿电压产生电路的输出电压，减小所述电解电容Co的充电电流从而降低Co的放电电压。当OUT电压低于第二预设电压Ref2(对应所述第二设定电压)时，说明所述电解电容Co放电电压比较低，比较器CMP2控制加减法计数器进行加法运算(相当于对图3所示补偿电容Ccomp进行充电)，经过数模转换单元后提高所述补偿电压产生电路的输出电压，增大所述电解电容Co的充电电流从而提高所述电解电容Co的放电电压。
作为示例，当所述母线电压大于LED的导通电压并大于第四设定电压时，降低所述电解电容的充电电流直至为零。
具体的，所述母线电压检测模块4检测母线电压Vin，母线电压Vin过高时降低电解电容Co的充电电流直至为零，从而减小控制所述第二功率开关管Q2的损耗，提高系统的整体效率，所述母线电压检测模块4内部控制信号大小可以通过外接电阻(所述第四采样电阻Rpf)来设置调整。
作为示例，当所述电解电容Co的放电电压低于第三设定电压时，通过加减法计数器进行快速加法运算以快速增大所述电解电容的充电电流，进而快速提高所述电解电容的放电电压。
具体的，当所述电解电容Co的放电电压偏低较多时，LED电流会无法维持并下降，此时所述第一功率开关管Q1的栅极电压会升得比较高(尤其在刚启动时，所述数模转换单元输出的补偿电压比较低)，所述第三比较器CMP3检测到所述第一功率开关管Q1的栅极电压超过第三预设电压Ref3时，控制加减法计数器进行快速加法(+X)，经过所述数模转换单元后快速提高所述补偿电压产生电路的输出电压，快速控制所述第二功率开关管Q2增加所述电解电容Co的充电电流，从而快速提高所述电解电容Co的放电电压。经过所述加减法计数器模块的环路调整，确保LED电流恒流后OUT电压最低电平不会太高而导致系统效率的损失。
作为示例，当所述加减法计数器产生加法溢出信号时，降低所述恒流控制模块的参考电压以降低所述LED负载的输出电流，进而减少所述电解电容Co的放电；当所述加减法计数器产生减法溢出信号时，升高所述恒流控制模块的参考电压Ref以提高所述LED负载的输出电流，进而加快所述电解电容的放电。
具体的，当加减法计数器在做加减运算时加到最高会产生加法溢出信号时，说明OUT电压偏低，电解电容Co存储能量不够，LED电流会无法恒流，此时可以降低内部基准(所述参考电压Ref)的值，从而降低LED输出电流，减少电解电容Co放电，提高OUT电压，使环路进入正常工作，保证LED输出电流无频闪。通过加法溢出信号降低内部基准，因此 当输入电压降低时输出电流减小后，控制环路仍能保持恒流工作(小于额定电流)，从而输出能保证无频闪，不会出现传统驱动器中无法维持额定电流而出现的掉电流的工频纹波及闪烁。
而当加减法计数器在做加减运算时如果减到最低会产生减法溢出信号，说明此时OUT电压偏高，电解电容Co存储能量过多，此时所述第二功率开关管Q2损耗会增加，此时可以升高内部基准来提高LED输出电流，从而加快电解电容Co放电来降低OUT电压，使环路进入正常工作，并降低所述第二功率开关管Q2上的损耗，可以额外扩展输入电压的工作范围。
本实施例的LED驱动的闭环控制方法利用加减法计数器实现环路补偿数字化，无需采用补偿环路的外部补偿大电容，有利于简化外围电路，降低系统成本，并且利用加减法计数器的计数溢出可以实现一些额外功能或保护，例如低压输入时输出降电流仍能实现无频闪。此外，加减法计数器的输出反映了系统的工作状态，其输出的数字信号可以提供给外部MCU进行智能化处理，如智能调光等。
综上所述，本发明的LED驱动系统及LED驱动的闭环控制方法利用加减法计数器实现环路补偿数字化，无需采用补偿环路的外部补偿大电容，使得外围电路最简化，系统成本低。本发明利用加减法计数器的计数溢出可以实现一些额外功能或保护，例如低压输入时输出降电流仍能实现无频闪。此外，加减法计数器的输出反映了系统的工作状态，其输出的数字信号可以提供给外部MCU进行智能化处理，如智能调光等。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 (18)

  1. 一种LED驱动系统，其特征在于，包括：
    LED负载，所述LED负载的正极连接母线电压；
    恒流控制模块，连接所述LED负载的负极，用于对所述LED负载进行恒流控制；
    电解电容，所述电解电容的上极板连接所述LED负载的正极，用于在所述母线电压小于所述电解电容上的电压时向所述LED负载放电；
    放电电压检测模块，连接所述LED负载的负极，基于所述LED负载的负极电压判断所述电解电容的放电电压大小，得到控制信号；
    母线电压检测模块，对所述母线电压进行检测得到第一检测电压；
    充电电流控制模块，连接所述放电电压检测模块、所述母线电压检测模块的输出端及所述电解电容的下极板，基于所述控制信号及所述第一检测电压调整所述电解电容的充电电流，其中，所述充电电流控制模块包括补偿单元，所述补偿单元的输入端连接所述放电电压检测模块，基于所述放电电压模块的输出信号产生相应的补偿电压，所述补偿单元包括加减法计数器，通过进行减法运算以减小所述电解电容的充电电流，通过进行加法运算以增大所述电解电容的充电电流。
  2. 根据权利要求1所述的LED驱动系统，其特征在于：所述恒流控制模块包括第一功率开关管、第一采样单元及第一运算放大单元；所述第一功率开关管的漏极连接所述LED负载的负极，源极经由所述第一采样单元接地；所述第一运算放大单元的输入端分别连接所述第一功率开关管的源极及一参考电压，输出端连接所述第一功率开关管的栅极，将采样电压与所述参考电压进行比较以控制流经所述LED负载的电流大小。
  3. 根据权利要求2所述的LED驱动系统，其特征在于：所述恒流控制模块还包括连接所述第一运算放大单元的调光单元，所述调光单元接收调光控制信号，基于所述调光控制信号调整所述参考电压的大小以设置所述LED负载的输出电流。
  4. 根据权利要求3所述的LED驱动系统，其特征在于：所述调光控制信号为模拟信号或脉冲宽度调制信号。
  5. 根据权利要求1所述的LED驱动系统，其特征在于：所述放电电压检测模块包括检测单元及比较单元；所述检测单元连接所述LED负载的负极，对所述LED负载的负极电压 进行检测以得到第二检测电压；所述比较单元连接所述检测单元的输出端，基于所述第二检测电压判断所述电解电容的放电电压大小。
  6. 根据权利要求5所述的LED驱动系统，其特征在于：所述比较单元包括第一比较器及第二比较器；所述第一比较器的输入端分别连接所述第二检测电压及第一预设电压，当所述第二检测电压大于所述第一预设电压时输出第一控制信号；所述第二比较器的输入端分别连接所述第二检测电压及第二预设电压，当所述第二检测电压小于所述第二预设电压时输出第二控制信号。
  7. 根据权利要求6所述的LED驱动系统，其特征在于：所述加减法计数器的第一输入端连接所述第一比较器的输出端，第二输入端连接所述第二比较器的输出端。
  8. 根据权利要求1所述的LED驱动系统，其特征在于：所述充电电流控制模块还包括第二功率开关管、第二采样单元、第三采样单元及第二运算放大单元，其中：
    所述第二功率开关管的漏极连接所述电解电容的下极板，源极经由所述第二采样单元接地；
    所述第二运算放大单元的第一输入端连接所述补偿单元的输出端，第二输入端连接所述母线电压检测模块的输出端，所述第二运算放大单元的输出端连接所述第二功率开关管的栅极，以实现对所述电解电容的充电电流的调整；
    所述第三采样单元的一端连接于所述母线电压检测模块与所述第二运算放大单元之间，另一端连接于所述第二功率开关管与所述第二采样单元之间。
  9. 根据权利要求8所述的LED驱动系统，其特征在于：所述补偿单元还包括补偿电压产生电路及数模转换单元，所述加减法计数器的输出端经由所述数模转换单元连接所述补偿电压产生电路的输入端，所述补偿电压产生电路的输出端连接所述第二运算放大单元的所述第一输入端。
  10. 根据权利要求1所述的LED驱动系统，其特征在于：所述补偿单元还包括第三比较器，所述第三比较器的第一输入端连接所述恒流控制模块中功率开关管的栅极，第二输入端连接第三预设电压，输出端连接所述加减法计数器的第三输入端，当所述恒流控制模块中功率开关管的栅极电压大于所述第三预设电压时，所述加减法计数器进行快速加法运算。
  11. 根据权利要求1所述的LED驱动系统，其特征在于：所述补偿单元还包括保护模块，所述保护模块连接所述加减法计数器及所述恒流控制模块，并基于所述加减法计数器的溢出信号调整所述恒流控制模块的参考电压的值。
  12. 根据权利要求1所述的LED驱动系统，其特征在于：所述LED驱动系统还包括第四采样单元，所述第四采样单元连接于所述母线电压检测模块与地之间以调整所述母线电压检测模块的内部控制信号。
  13. 根据权利要求1所述的LED驱动系统，其特征在于：所述LED驱动系统还包括工作电压产生模块，所述工作电压产生模块连接所述母线电压，基于所述母线电压为所述LED驱动系统提供工作电压。
  14. 根据权利要求1所述的LED驱动系统，其特征在于：所述LED驱动系统还包括整流模块，所述整流模块对交流电源进行整流以得到所述母线电压。
  15. 一种LED驱动的闭环控制方法，其特征在于，包括以下步骤：
    当母线电压小于LED的导通电压时，电解电容对LED负载放电，并基于恒流控制模块对所述LED负载进行恒流控制，其中，当所述电解电容的放电电压高于第一设定电压时，通过加减法计数器进行减法运算以减小所述电解电容的充电电流，进而降低所述电解电容的放电电压；当所述电解电容的放电电压低于第二设定电压时，通过加减法计数器进行加法运算以增大所述电解电容的充电电流，进而提高所述电解电容的放电电压；
    当所述母线电压大于LED的导通电压时，所述母线电压为所述LED负载供电，并基于所述恒流控制模块对所述LED负载进行恒流控制，同时所述母线电压为所述电解电容充电；
    当所述母线电压小于所述电解电容的电压时，所述电解电容对所述LED负载放电，并基于所述恒流控制模块对所述LED负载进行恒流控制。
  16. 根据权利要求15所述的LED驱动的闭环控制方法，其特征在于：当所述电解电容的放电电压低于第三设定电压时，通过加减法计数器进行快速加法运算以快速增大所述电解电容的充电电流，进而快速提高所述电解电容的放电电压。
  17. 根据权利要求15所述的LED驱动的闭环控制方法，其特征在于：当所述加减法计数 器产生加法溢出信号时，降低所述恒流控制模块的参考电压以降低所述LED负载的输出电流，进而减少所述电解电容的放电；当所述加减法计数器产生减法溢出信号时，升高所述恒流控制模块的参考电压以提高所述LED负载的输出电流，进而加快所述电解电容的放电。
  18. 根据权利要求15所述的LED驱动的闭环控制方法，其特征在于：当所述母线电压大于LED的导通电压并大于第四设定电压时，降低所述电解电容的充电电流直至为零。
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