WO2018133263A1 - 一种led驱动电路及其驱动方法 - Google Patents

一种led驱动电路及其驱动方法 Download PDF

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Publication number
WO2018133263A1
WO2018133263A1 PCT/CN2017/084305 CN2017084305W WO2018133263A1 WO 2018133263 A1 WO2018133263 A1 WO 2018133263A1 CN 2017084305 W CN2017084305 W CN 2017084305W WO 2018133263 A1 WO2018133263 A1 WO 2018133263A1
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Prior art keywords
circuit
current
voltage
detection
output
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PCT/CN2017/084305
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English (en)
French (fr)
Inventor
杨世红
王虎
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陕西亚成微电子股份有限公司
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Publication of WO2018133263A1 publication Critical patent/WO2018133263A1/zh
Priority to US16/259,637 priority Critical patent/US10772168B2/en

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    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
    • H05B45/00—Circuit arrangements for operating light-emitting diodes [LED]
    • H05B45/30—Driver circuits
    • H05B45/345—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]
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F21—LIGHTING
    • F21S—NON-PORTABLE LIGHTING DEVICES; SYSTEMS THEREOF; VEHICLE LIGHTING DEVICES SPECIALLY ADAPTED FOR VEHICLE EXTERIORS
    • F21S4/00—Lighting devices or systems using a string or strip of light sources
    • F21S4/10—Lighting devices or systems using a string or strip of light sources with light sources attached to loose electric cables, e.g. Christmas tree lights
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F21—LIGHTING
    • F21V—FUNCTIONAL FEATURES OR DETAILS OF LIGHTING DEVICES OR SYSTEMS THEREOF; STRUCTURAL COMBINATIONS OF LIGHTING DEVICES WITH OTHER ARTICLES, NOT OTHERWISE PROVIDED FOR
    • F21V23/00—Arrangement of electric circuit elements in or on lighting devices
    • F21V23/06—Arrangement of electric circuit elements in or on lighting devices the elements being coupling devices, e.g. connectors
    • 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
    • H05B45/36—Circuits for reducing or suppressing harmonics, ripples or electromagnetic interferences [EMI]
    • 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
    • H05B47/28—Circuit arrangements for protecting against abnormal temperature

Definitions

  • the present invention relates to the field of LED driving, and in particular to an LED driving circuit and a driving method thereof.
  • the control circuit controls the current flowing through the LED string to be a constant value, and the constant value does not change with the change of the input voltage of the external circuit, and the control circuit diagram is as shown in FIG.
  • the excess voltage drop is applied to the current control circuit IC, which causes the IC temperature to rise, increases power consumption, and burns out the IC;
  • the input voltage is less than the set voltage, The charging voltage on the capacitor is lowered. Under the same conditions, the discharge time of the capacitor becomes shorter, and the strobe of the LED string is severe.
  • V1 represents the voltage waveform after rectification and filtering
  • I3 represents the current waveform of the LED string, because the voltage drop on the LED string is a constant value.
  • the voltage waveform V3 at the input of the current control circuit 50 coincides with the waveform of V1, as shown by V3 in the figure.
  • the filter circuit 20 includes an electrolytic capacitor C, and thus the magnitude of the voltage V1 is related to the following factors: the magnitude of the power supply input voltage, the size of the electrolytic capacitor C, and the magnitude of the charge and discharge current of the circuit.
  • the LED lamp string positive voltage V1 exceeds the voltage required for the LED string to be turned on, the LED string is turned on, and the charging current in the filter circuit 20 is the largest. As the voltage increases, the charging current decreases, and the current is controlled.
  • the circuit 50 controls the current I3 flowing through the LED string to be a constant value, and the voltage drop across the LED string is equal to V11; at time t2, the power input voltage reaches a maximum value, and the voltage on the filter circuit 20 also reaches a maximum value.
  • the capacitor in the filter circuit 20 stops charging, and the voltage V3 at the input terminal of the current control circuit 50 also reaches a maximum value; then the input voltage gradually decreases, the capacitance in the filter circuit 20 begins to discharge, and the sum of the discharge current and the current flowing from the power source is equal to
  • the current in the LED string maintains the LED string on, and the voltage V3 at the input of the current control circuit 50 also decreases; at time t3, the power supply voltage is lower than the voltage of the filter circuit 20, the power supply stops the input current, and the filter circuit 20 discharges.
  • the voltage of the filter circuit 20 is decreased; at time t31, the voltage V1 of the filter circuit 20 is equal to the turn-on voltage V11 of the LED string, and the voltage is decreased in the LED string.
  • the flow decreases; at time t5, the voltage V1 drops to a minimum, the current in the LED string is minimized, and then the voltage V1 increases as the input voltage increases, and the current in the LED string increases; At time t51, the voltage V1 again reaches the turn-on voltage of the LED string, and the above process is repeated.
  • V1 changes according to the sine law; at time t3 to t5, V1 decreases exponentially, when discharging The inter-constant is related to the size of the capacitor, the magnitude of the discharge current, etc.; at time t3 to t5, the capacitance in the filter circuit 20 is discharged, and the magnitude of the discharge current is controlled by the current control circuit 50, and the voltage V1 falls.
  • the voltage V1 of the filter circuit 20 and the positive terminal of the LED light string increases.
  • the next charge is started again when the previous discharge has not been discharged.
  • the voltage on the filter circuit increases, the voltage V1 moves up as a whole, and is greater than the conduction voltage of the LED string during the whole cycle.
  • the current in the LED string is a constant value.
  • the LED string has no stroboscopic light, as shown in the figure.
  • the waveform V12 of 3 the voltage V3 of the negative pole of the LED string is also increased, as shown by the waveform V32, that is, the voltage drop on the current control circuit 50 is increased, the power consumption is increased, and the heat generation is increased.
  • V11 is a waveform diagram of the positive voltage of the LED string when the input voltage is equal to the rated voltage
  • V31 is a waveform diagram of the anode voltage of the LED string.
  • the present invention provides an LED driving circuit, including: a rectifier circuit, a filter circuit, a current limiting circuit, a detection control circuit, and an LED light string; the rectifier circuit is connected to an AC power source.
  • the second end of the rectifier circuit is connected to the second end of the filter circuit and the second end of the detection control circuit; the input end of the current limiting circuit is connected to the positive terminal of the rectifier circuit, and the first output end of the current limiting circuit and the LED light string
  • the positive pole is connected to the input end of the filter circuit, and the second output end of the current limiting circuit is connected to the third end of the detection control circuit; the negative pole of the LED light string is connected to the input end of the detection control circuit.
  • the detection control circuit comprises a control circuit and a voltage dividing circuit
  • the voltage dividing circuit comprises voltage dividing resistors R1 and R2 connected in series.
  • the second output end of the current limiting circuit is connected to the third end of the control circuit, and the negative pole of the LED string is connected to the input end of the control circuit and the input end of the resistor R1; the resistor R1 and the resistor R2 are connected in series
  • the fourth end of the control circuit is connected to the output end of the resistor R1 and the input end of the resistor R2; the cathode of the rectifier circuit is connected to the second end of the control circuit and the output end of the resistor R2.
  • a filter capacitor C1 is added at a position of the fourth end of the control circuit, and the capacitor C1 is connected in parallel with the resistor R2.
  • the current limiting circuit is configured to control a charging current of the filter circuit and a current I3 in the LED string.
  • the detection control circuit is configured to detect a current in the LED string and control the current limiting circuit and the filter circuit according to the detection result.
  • the detection control circuit detects the voltage V3 of the negative pole of the LED string, and the voltage V3 is referred to as a first detection voltage;
  • the first output flowing from the first output end of the current limiting circuit The current I2 is the first constant current I21, the first constant current I21 provides the charging current of the filter circuit and the current I3 of the LED string, and the current I3 flowing through the LED string is controlled by the detection control circuit, and the second output of the current limiting circuit No current output, the second output current I5 is zero;
  • the first output current I2 of the current limiting circuit decreases as the first detection voltage V3 increases, and at the same time, the limit The second output current I5 flowing to the detection control circuit of the flow circuit increases as the first detection voltage V3 increases;
  • the first output current I2 of the current limiting circuit is maintained at the second constant current I22, and the second output current I5 of the current limiting circuit is maintained at the third constant current I51.
  • the second constant current I22 is the current minimum flowing from the current limiting circuit to the LED lamp string and the filter circuit
  • the third constant current I51 is the current maximum flowing from the current limiting circuit to the detection control circuit.
  • the invention also provides a driving method of the LED driving circuit, the detecting control circuit detects the first detecting voltage V3 of the negative pole of the LED string and controls the magnitude of the current flowing through the LED string current I3 according to the magnitude of the first detecting voltage V3:
  • the first detection voltage V3 When the first detection voltage V3 is less than the first set voltage value V31, no current flows in the LED string, and the first output current I2 of the current limiting circuit is the first constant current I21, all used for the capacitance in the filter circuit. Charging, at this time, the charging current I4 of the filter circuit is the largest, and the second output current I5 of the current limiting circuit is zero;
  • the first detection voltage V3 When the first detection voltage V3 is equal to the first set voltage V31, a current flows through the LED string, and at this time, the first output current I2 flowing out of the current limiting circuit is maintained as a first constant current I21, the first constant
  • the current I21 is divided into two parts, one part is used for charging the filter circuit, a part is flowing through the LED light string for lighting the LED light string, and the second output current I5 of the current limiting circuit continues to be zero;
  • the first output current I2 flowing out of the current limiting circuit continues to be maintained at the first constant current I21, along with the first detection voltage V3.
  • Increasing the current I3 flowing through the LED string also increases, the charging current I4 of the filter circuit decreases, and the second output current I5 of the current limiting circuit continues to be zero;
  • the first output current I2 flowing out of the current limiting circuit is the first constant current I21, and the detection control circuit controls the flow of the LED light.
  • the current I3 of the string is the fourth constant current I32.
  • the first detection voltage V3 When the first detection voltage V3 is greater than or equal to the third set voltage V33 and less than the fourth set voltage V34, the first output current I2 flowing out of the current limiting circuit decreases as the first detection voltage V3 increases, and The detection control circuit draws the second output current I5 from the current limiting circuit, and the second output current I5 flowing from the current limiting circuit to the detection control circuit follows the first detection
  • the voltage V3 increases and the detection control circuit controls the current I3 flowing through the LED string to be maintained as the fourth constant current I32, and the second output current I5 is much smaller than the first output current I2;
  • the first output current I2 flowing out of the current limiting circuit is maintained as the second constant current I22, and the second output current I5 flowing out of the current limiting circuit maintains the third constant current. I51.
  • the second constant current I22 is a current minimum flowing from the current limiting circuit to the LED lamp string and the filter circuit
  • the third constant current I51 is a current maximum flowing from the current limiting circuit to the detection control circuit
  • the third The constant current I51 is much smaller than the second constant current I22.
  • the first detection voltage V3 is divided to obtain a second detection voltage V4, and the second detection voltage V4 correspondingly reduces the voltage fluctuation, so that the first output current I2 of the current limiting circuit is correspondingly reduced in fluctuation, so that the LED lamp
  • the current I3 on the string and the voltage drop on the detection control circuit are relatively stable; and different voltage division ratios can be adapted to different input voltages.
  • the second detection voltage V4 is filtered to obtain a constant second detection voltage V4, so that the first output current I2 of the current limiting circuit is also a constant value, ensuring that the current I3 on the LED string is constant and the detection control circuit The voltage drop is stable.
  • the current limiting circuit includes a second power supply circuit, a control driving circuit, a second driving circuit, a second current sampling circuit, and a power tube Q2.
  • the second driving circuit is connected to the second power supply circuit, the control driving circuit, and the second The current sampling circuit and the control terminal of the power tube Q2 are connected to the control driving circuit.
  • the control circuit includes a first power supply circuit, a reference circuit, a first driving circuit, a first current sampling circuit, a voltage sampling circuit, a pull-down current circuit, and a power tube Q1, and the reference circuit is connected to the first power supply circuit and the first a driving circuit, the first driving circuit is connected to the control end of the power tube Q1 and the first current sampling circuit, and the voltage sampling circuit is connected to the pull-down current circuit and the first current sampling circuit.
  • the current limiting circuit is provided with a second over temperature protection circuit connected to the second driving circuit.
  • the control circuit is provided with a first over-temperature protection circuit connected to the first driving circuit.
  • the invention can solve the problem that the power consumption increases when the power supply voltage increases and the current control circuit burns out, and the strobe of the LED light string is increased when the power supply voltage is reduced.
  • FIG. 1 is a schematic diagram of an LED control circuit in the prior art
  • FIG. 2 is a diagram showing a relationship between voltage and current at an output end of a rectifier circuit in an LED control circuit in the prior art
  • FIG. 3 is a diagram showing relationship between voltage and current of a rectifier circuit in different input voltages in the LED control circuit of the prior art
  • FIG. 4 is a schematic diagram of an LED driving circuit of the present invention.
  • FIG. 5 is a schematic diagram showing the operation of a current limiting circuit of an LED control circuit according to the present invention.
  • FIG. 6 is a control diagram of a detection control circuit and a current limiting circuit of an LED control circuit according to the present invention
  • Figure 9 is a schematic diagram showing waveform diagrams when different input voltages are drawn together.
  • Figure 10 is a preferred embodiment of an LED driving circuit of the present invention.
  • FIG. 11 is a waveform diagram of the circuit of FIG. 10 when the power input voltage is greater than a second threshold less than a fourth threshold;
  • Figure 12 is a preferred embodiment of another LED driving circuit of the present invention.
  • Figure 13 is a waveform diagram of voltage V2/V3 and current I2/I3 across the LED string in the circuit of Figure 12;
  • Figure 14 is a schematic structural view of a current limiting circuit of the present invention.
  • 15 is a schematic structural view of an over-current protection circuit in a current limiting circuit according to the present invention.
  • Figure 16 is a schematic structural view of a control circuit in the present invention.
  • Figure 17 is a schematic view showing the structure of an over-temperature protection circuit provided in the control circuit of the present invention.
  • a schematic diagram of an LED driving circuit of the present invention includes a rectifying circuit 40, a filter circuit 20, a current limiting circuit 10, a detection control circuit 30, and an LED light string.
  • the rectifier circuit 40 is connected to an alternating current power source for converting the alternating current voltage into a direct current voltage; the negative terminal of the rectifier circuit 40 is connected to the second end of the filter circuit 20 and the second end of the detection control circuit 30.
  • the input end of the current limiting circuit 10 is connected to the positive pole of the rectifier circuit 40, and the first output end of the current limiting circuit 10 is connected to the anode of the LED light string and the input end of the filter circuit 20, and the current limiting circuit 10
  • the second output is coupled to the third end of the detection control circuit 30.
  • the current limiting circuit 10 is configured to control how much the electrolytic capacitor in the filter circuit 20 is charged, that is, to control the charging current of the filter circuit 20 and the current I3 in the LED string;
  • the detection control circuit 30 is configured to detect the voltage of the negative pole of the LED string. The size is simultaneously fed back to the control current limiting circuit 10 and controls the magnitude of the current I3 flowing through the LED string.
  • the input end of the filter circuit 20 is connected to the first output end of the current limiting circuit 10, and the filter circuit 20 is for reducing ripple in the DC voltage.
  • the cathode of the LED string is connected to the input of the detection control circuit 30. Because the voltage drop across the LED string is solid Therefore, the voltage at the input end of the detection control circuit 30 changes according to the voltage V2 of the filter circuit 20 and the positive pole of the LED string, and the waveform of the voltage V3 at the input end of the detection control circuit 30 is consistent with the waveform of the voltage V2 of the filter circuit 20 and the positive pole of the LED string. .
  • the third end of the detection control circuit 30 is connected to the second output of the current limiting circuit 10.
  • the detection control circuit 30 is for detecting a current in the LED string and controlling the current limiting circuit 10 and the filter circuit 20 according to the detection result.
  • the working principle of the current limiting circuit 10 of an LED driving circuit of the present invention is as follows:
  • the voltage V3 of the negative pole of the LED string is the same as the waveform of the positive voltage V2, and the detection control circuit 30 detects the voltage V3 of the negative pole of the LED string.
  • the voltage V3 is referred to as the first detection voltage, and the current limiting circuit 10 is divided into the following cases:
  • the first output current I2 flowing out from the first output end of the current limiting circuit 10 is the first constant current I21, and the first constant current I21 provides the filter circuit 20.
  • the charging current and the current I3 of the LED string, the current I3 flowing through the LED string are controlled by the detection control circuit 30, the second output of the current limiting circuit 10 has no current output, and the second output current I5 is zero;
  • the first output current I2 of the current limiting circuit 10 decreases as the first detection voltage V3 increases, and simultaneously The second output current I5 flowing from the current limiting circuit 10 to the detection control circuit 30 increases as the first detection voltage V3 increases.
  • the first detection voltage V3 is greater than or equal to the fourth set voltage V34
  • the first output current I2 of the current limiting circuit 10 is maintained at the second constant current I22
  • the second output current I5 of the current limiting circuit 10 is maintained at the third state.
  • the constant current I51 at this time, the second constant current I22 is the current minimum flowing from the current limiting circuit 10 to the LED lamp string and the filter circuit 20, and the third constant current I51 is the maximum current flowing from the current limiting circuit to the detection control circuit 30. value.
  • the magnitude of the second output current I5 is much smaller than the magnitude of the first output current I2.
  • control of the detection control circuit 30 of an LED driving circuit of the present invention is as follows:
  • the detection control circuit 30 detects the first detection voltage V3 of the negative pole of the LED string and controls the magnitude of the current flowing through the LED string current I3 according to the magnitude of the first detection voltage V3:
  • the first detection voltage V3 is less than the first set voltage value V31, no current flows in the LED string, and the first output current I2 of the current limiting circuit 10 is the first constant current I21, all used for the filter circuit.
  • the capacitor in 20 is charged, at this time, the charging current I4 of the filter circuit 20 is the largest, and the second output current I5 of the current limiting circuit 10 is zero;
  • the first constant current I21 is divided into two parts, one part is used for charging the filter circuit 20, a part is flowing through the LED light string for lighting the LED light string, and the second output current I5 of the current limiting circuit 10 continues to be zero;
  • the first detection voltage V3 is greater than the first set voltage V31 and less than the second set voltage V32, the first output current I2 flowing out of the current limiting circuit 10 continues to be maintained at the first constant current I21, with the first The detection voltage V3 increases the current I3 flowing through the LED string, and the charging current I4 of the filter circuit 20 decreases, and the second output current I5 of the current limiting circuit 10 continues to be zero;
  • the first output current I2 flowing out of the current limiting circuit 10 is the first constant current I21, and the detection control circuit 30 controls The current I3 flowing through the LED string is the fourth constant current I32, at which time the fluctuation of the first detection voltage V3 does not cause the fluctuation of the current I3, and the second output current I5 of the current limiting circuit 10 continues to be zero.
  • the detection control circuit 30 draws the second output current I5 from the current limiting circuit 10, and the second output current I5 flowing from the current limiting circuit 10 to the detection control circuit 30 increases as the first detection voltage V3 increases, and the detection control The circuit 30 controls the current I3 flowing through the LED string to be held at a fourth constant current I32, which is much smaller than the first output current I2.
  • the first output current I2 flowing out of the current limiting circuit 10 is maintained as the second constant current I22, and the second output current I5 flowing out of the current limiting circuit remains
  • the third constant current I51 at this time, the second constant current I22 is the current minimum flowing from the current limiting circuit to the LED lamp string and the filter circuit 20, and the third constant current I51 is the maximum current flowing from the current limiting circuit to the detection control circuit 30.
  • the value, and the third constant current I51 is much smaller than the second constant current I22.
  • the output current fluctuation of the current limiting circuit 10 is also reduced.
  • the first detection voltage V3 is a constant value
  • the first output current I2 of the current limiting circuit 10 is correspondingly A constant value ensures that the current I3 on the LED string is constant and the voltage drop across the detection control circuit 30 is stable.
  • the first to fourth set voltages V31 to V34 of the first detection voltage V3 correspond to the first threshold voltage V101 to the fourth threshold voltage V104 of the output voltage V1 of the rectifier circuit 40, respectively.
  • the output voltage V2 of the current limiting circuit 10 of the LED driving circuit of the present invention and the waveform of the first output current I2 are as shown in FIGS. 7 and 8:
  • V1 is the current limiting circuit 10 in the figure.
  • the voltage at the input terminal V2 is the voltage at the output of the current limiting circuit 10
  • I2 is the first output current of the current limiting circuit 10
  • V3 is the first detection voltage at the input of the detection control circuit 30
  • I3 is the current at the input of the detection control circuit 30
  • I5 Is the second output current of the current limiting circuit 10, because the second output current I5 is much smaller than the first output current I2, so the figure is not the same ratio, drawn in The same figure is just for easy understanding.
  • the voltage across the LED string is greater than the conduction voltage of the LED string, and the LED string is turned on.
  • the first detection voltage V3 is the smallest, less than the second set voltage value V32, and flows into the LED string.
  • the current I3 value is also the smallest, and the first output current I2 of the current limiting circuit 10 has the largest value;
  • the current I3 As the first detection voltage V3 increases, the current I3 also increases accordingly, and the first output current I2 remains constant. At time t11, the first detection voltage V3 is equal to the second set voltage value V32, and the current I3 is equal to the fourth constant current. I32, the first output current I2 is equal to the first constant current I21, at this stage, the current limiting circuit 10 does not flow out of the detection control circuit 30 the second output current I5;
  • the first detection voltage V3 is equal to the third set voltage V33, then the first detection voltage V3 continues to increase, the first output current I2 begins to decrease, and the second output is output from the current limiting circuit 10 to the detection control circuit 30.
  • the current I5 increases as the first detection voltage V3 increases;
  • the voltage V2 at the output of the current limiting circuit 10 is equal to the rectified power supply input voltage V21, the capacitance in the filter circuit 20 begins to discharge, the first output current I2 of the current limiting circuit 10 is zero, and the current of the capacitor discharge is detected.
  • the control circuit 30 controls, for a constant value, the voltage V2 decreases linearly, the first detection voltage V3 also decreases linearly, and the second output current I5 decreases correspondingly.
  • the first detection voltage V3 falls to be equal to the third setting. Voltage V33, at this time, the second output current I5 is zero.
  • the voltage V2 on the filter circuit 20 drops to near minimum, the first detection voltage V3 is smaller than the second set voltage value V32, and the current I3 is from a constant value.
  • the first detection voltage V3 is the smallest, the current I3 is also the smallest, and the current I2 is the largest from the first output of the current limiting circuit 10.
  • V1 is the voltage at the input end of the current limiting circuit 10
  • V2 is the voltage at the output end of the current limiting circuit 10
  • I2 is the current limiting circuit 10.
  • the first output current V3 is the first detection voltage at the input of the detection control circuit 30, I3 is the current at the input of the detection control circuit 30, and I5 is the second output current of the current limiting circuit 10, because the second output current I5 is much smaller than the second
  • An output current I2 is not the same ratio in the figure, and it is only easy to understand in the same figure.
  • the voltage across the LED string is greater than the conduction voltage of the LED string, and the LED string is turned on.
  • the first detection voltage V3 is the smallest, and the first detection voltage V3 is greater than the third set voltage V33.
  • the fourth set voltage V34 the current I3 flowing into the LED string is the fourth constant value I32, the first output current I2 of the current limiting circuit 10 is the maximum, and the second output current I5 of the current limiting circuit 10 is the smallest;
  • the first detection voltage V3 is increased, the current I3 is kept constant, the current I2 is gradually decreased, and the second output current I5 of the current limiting circuit 10 is correspondingly increased;
  • the first detection voltage V3 is equal to the fourth set voltage value V34, and the current I3 is kept constant, the first output The current I2 is the second constant current value I22, and the second output current I5 is the third constant current value I51. Thereafter, the voltage V3 is increased and the current I3, the first output current I2, and the second output current I5 are kept constant;
  • the first detection voltage V3 is the same as the voltage after the rectification circuit, the first output current I2 of the current limiting circuit 10 is zero, the filter circuit 20 stops charging and supplies the current I3 to the LED string, because the discharge current is The constant value, the voltage on the filter circuit 20 decreases linearly, and the voltage V3 also decreases linearly.
  • the first detection voltage V3 is smaller than the fourth set voltage value V34, the current I3 remains constant, and the second output current I5 follows the first detection. The voltage V3 decreases while decreasing; until T5, the voltage V3 and the second output current I5 are minimized.
  • the current limiting circuit 10 provides the first output when the power supply input voltage is low (the highest voltage is V11) when the current limiting circuit 10 provides the first output current I2 for a time T11 that is less than the power supply input voltage (the highest voltage is V12).
  • the time T1 of the current I2 (when the input voltage is high, the charging process starts again when the previous discharge is not completed), that is, when the charging time of the filter circuit 20 is lower than when the power input voltage is low, the charging circuit 20 is charged.
  • the discharge time T21 of the filter circuit 20 is greater than the discharge time T2 of the filter circuit 20 when the power supply input voltage is high, in order to maintain the voltage on the filter circuit substantially unchanged when the power supply input voltage changes, the LED light is maintained.
  • the current on the string is constant, it is necessary to reduce the input current when the input voltage of the power supply increases, so that the energy storage on the electrolytic capacitor in the filter circuit is the same in each cycle when the input voltage is different, and the current limiting circuit 10 is based on the input voltage of the power supply. Differently, the first output current is controlled in stages to improve the power efficiency.
  • the power stored in the filter capacitor of the filter circuit 20 can ensure that the current on the LED string is uninterrupted during discharge, that is, the LED string is not strobed, and the detection control circuit 30 controls during discharge.
  • the current on the LED string is reduced, extending the discharge time of the filter capacitor.
  • the first output current I2 of the current limiting circuit 10 is a constant value, does not fluctuate with fluctuations of the input voltage, but increases with the input voltage of the power supply.
  • the first, output current I2 of the current limiting circuit 10 decreases as the power supply input voltage increases.
  • the first output current I2 is as shown by the waveform I24, and when the power input voltage is as shown in 210 (the maximum value is V12), the first output Current I2, as shown by waveform I25, can be seen that as the power supply input voltage increases, the first output current I2 decreases correspondingly; while the current I3 in the LED string remains at a constant value.
  • FIG. 10 is a preferred embodiment of an LED driving circuit of the present invention.
  • the detecting control circuit 30 includes a control circuit 70 and a voltage dividing circuit 60.
  • the voltage dividing circuit 60 It includes series voltage dividing resistors R1 and R2.
  • the second output end of the current limiting circuit 10 is connected to the third end of the control circuit 70, and the negative pole of the LED light string is connected to the input end of the control circuit 70 and the input end of the resistor R1; the resistor R1 and the resistor R2 In series, the fourth end of the control circuit 70 is connected to the output end of the resistor R1 and the input end of the resistor R2; the cathode of the rectifier circuit 40 is connected to the second end of the control circuit 70 and the output end of the resistor R2.
  • the magnitude of the second detecting voltage V4 can be changed, thereby changing the range of the detectable input voltage, so that the circuit is suitable for different power supply input voltage ranges.
  • the voltage value of the divided voltage V4 (second detection voltage) is detected, and by adjusting the resistance of R1/R2, the value range of the voltage value of the second detection voltage can be changed, thereby Make the circuit suitable for different input voltage changes.
  • FIG. 11 is a waveform diagram of the circuit of FIG. 10 when the power input voltage is greater than a second threshold less than a fourth threshold.
  • V1 is the input voltage rectified voltage
  • V2 is the voltage of the output terminal of the current limiting circuit 10 (that is, the positive pole of the LED string)
  • V3 is the first detection voltage
  • the waveforms of V3 and V2 are the same.
  • the fluctuation of the second detection voltage V4 is smaller than the fluctuation of the first detection voltage V3
  • the signal fluctuation of the detection control circuit 30 fed back to the current limiting circuit 10 is correspondingly reduced
  • the fluctuation of the output current I2 of the current limiting circuit 10 is correspondingly reduced.
  • the voltage drop across control circuit 30 remains stable.
  • the current I3 in the LED string remains at a constant value.
  • the first detection voltage V3 is divided to obtain a second detection voltage V4, and the second detection voltage V4 correspondingly reduces the voltage fluctuation, so that the first output current I2 of the current limiting circuit 10 is correspondingly reduced in fluctuation, so that the LED light string
  • the current I3 and the voltage drop on the detection control circuit 30 are relatively stable; and different voltage division ratios can be adapted to different input voltages.
  • FIG. 12 is a schematic illustration of a preferred embodiment of an LED driver circuit of the present invention.
  • the filter capacitor C1 is added at the sampling point of the voltage dividing circuit, and the capacitor C1 is connected in parallel with the resistor R2.
  • the filter capacitor C1 is sufficient to filter out the voltage fluctuation on the second detection voltage V4, the voltage V4 ripple can be ignored, and the input voltage is different.
  • the current waveform of the first output current I2 is as shown in FIG.
  • Figure 13 is a waveform diagram of voltage V2/V3 and current I2/I3 across the LED string in the circuit of Figure 12.
  • V1 is the voltage after the power input voltage is rectified
  • V2 is the voltage at the output of the current limiting circuit
  • V3 is the first detection voltage of the negative pole of the LED string
  • V4 is the second detection voltage after being filtered again
  • I2 is limited.
  • the first output current of the stream circuit 10, I3, is the current on the LED string.
  • the current limiting circuit 10 is a constant value according to the second detection voltage V4, and the first output current I2 and the second output voltage I5 are also constant values, thereby making the output of the current limiting circuit 10
  • the voltage V2 increases linearly or decreases, and the current I3 in the LED string is also a constant value.
  • the second detection voltage V4 is a fifth constant value
  • the second output current I5 flowing out of the current limiting circuit 10 is also a constant value, which is a sixth constant value.
  • the first output current of the current limiting circuit 10 is obtained.
  • I2 is also a constant value, that is, a seventh constant value
  • the current I3 in the LED string is the eighth constant value.
  • the first detection voltage V3 changes within all the set ranges
  • the second detection voltage V4 is a constant value and increases or decreases with the power supply input voltage to increase the parallel up or parallel shift.
  • the constant value of the first output current I2 of the current limiting circuit 10 is also shifted up or down correspondingly to the constant value of the current I3 in the LED string.
  • a current limiting circuit is disposed at an output end of the rectifier circuit and an anode of the LED light string and an input end of the filter circuit, and the detection control circuit detects the current of the LED light string while detecting the current of the LED light string negative electrode.
  • the current limiting circuit controls the charging current of the filter circuit and the current in the LED light string according to the change of the detected voltage, namely:
  • the current limiting circuit When the power input voltage is less than the third threshold V103, the current limiting circuit is in an open state, the input voltage is applied to the filter circuit, the LED light string and the detection control circuit, and the input current flows into the filter circuit and the LED light string;
  • the three threshold value V103 is less than the fourth threshold value V104, the output current of the current limiting circuit is reduced, that is, the charging current I4 of the filter circuit and the conduction current I3 of the LED string are reduced, and the voltage drop on the detection control circuit is lowered.
  • the power input current I1 decreases correspondingly as the power supply voltage increases, because the output current I2 of the current limiting circuit 10 is approximately equal to the power supply input current I1, and thus the output current I2 of the current limiting circuit 10 increases with the input voltage of the current limiting circuit 10 correspondingly.
  • the current limiting circuit 10 maintains the charging current I4 of the filter circuit and the conduction current I2 of the LED light string to a constant value, at which time the power supply input current I1 is minimum.
  • first threshold, the second threshold, the third threshold, and the fourth threshold in the present invention are all preset.
  • the current limiting circuit 10 includes a second power supply circuit 170, a control driving circuit 180, a second driving circuit 190, a second current sampling circuit 300, and a power tube Q2.
  • the second driving circuit 190 is connected to the second power supply circuit 170.
  • Control the driving circuit 180, the second current sampling circuit 300 and the control terminal of the power tube Q2, and the second power supply circuit 170 is connected and controlled.
  • the drive circuit 180 is formed.
  • the current limiting circuit 10 is provided with a second over-temperature protection circuit 320 connected to the second driving circuit 190 for over-temperature protection of the power tube Q2.
  • the control circuit 70 includes a first power supply circuit 110, a reference circuit 120, a first drive circuit 130, a first current sampling circuit 140, a voltage sampling circuit 150, a pull-down current circuit 160, and a power transistor Q1.
  • the reference circuit 120 The first power supply circuit 110 and the first current driving circuit 130 are connected.
  • the first driving circuit 130 is connected to the control terminal of the power tube Q1 and the first current sampling circuit 140.
  • the voltage sampling circuit 150 is connected to the pull-down current circuit 160 and the first current sampling circuit 140.
  • control circuit 70 is provided with a first over-temperature protection circuit 310 connected to the first driving circuit 130 for over-temperature protection of the power tube Q1.
  • the voltage sampling circuit 150 sends a V11 signal to the first current sampling circuit 140, and the first driving circuit 130 controls the power according to the sampling result of the V11 signal and the first current sampling circuit 140.
  • the voltage sampling circuit 150 sends a V12 signal to the pull-down current circuit 160.
  • the pull-down current circuit 160 outputs an ICS signal to the control driving circuit 180 according to the V12 signal, and the second driving circuit 190 is controlled according to the control.
  • the output signal of the drive circuit 180 controls the conduction of the power transistor Q2, thereby controlling the input current of the power supply.
  • the value of the first setting range is smaller than the value of the second setting range, or the value of the first setting range partially overlaps with the value of the second setting range.
  • the first setting range is 0 ⁇ Vdim ⁇ 1.2V
  • the second setting range is 1.2V ⁇ Vdim ⁇ 2.4V.

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Abstract

一种LED驱动电路及其驱动方法，包括：整流电路（40）、滤波电路（20）、限流电路（10）、检测控制电路（30）和LED灯串；整流电路与交流电源连接，整流电路的负极连接滤波电路的第二端和检测控制电路的第二端；限流电路的输入端与整流电路的正极连接，限流电路的第一输出端与LED灯串的正极和滤波电路的输入端连接，限流电路的第二输出端连接检测控制电路的第三端；LED灯串的负极与检测控制电路的输入端连接。这种电路和方法可以解决现有技术中电源电压增大时功耗增大及可能引起电流控制电路烧坏的问题，以及电源电压减小时LED灯串频闪加重的问题。

Description

一种LED驱动电路及其驱动方法 技术领域
本发明涉及一种LED驱动领域，尤其涉及一种LED驱动电路及其驱动方法。
背景技术
目前市场上的高压线性IC普遍存在两个问题：1、LED负载灯珠电压严重受限于输入电压，灯珠总压降不能低于输入电压过多；2、输入电压波动时LED光照频闪严重。
现有技术中，在LED电源控制中，控制电路控制流过LED灯串的电流为一恒定值，且此恒定值并不随外电路输入电压的变化而变化，其控制电路图如图1所示，当输入电压大于设定电压时，多余的电压降会施加在电流控制电路IC上，从而使IC温度升高，增大了功耗，且会烧坏IC；当输入电压小于设定电压时，电容上的充电电压降低，在同样的条件下，电容放电时间变短，LED灯串的频闪严重。
整流电路输出端的电压电流关系图如图2所示，图中V1表示整流滤波后的电压波形图，I3表示LED灯串的电流波形图，因LED灯串上的电压降为一恒定值，因而电流控制电路50输入端的电压波形V3与V1波形一致，如图中V3所示。
一般情况下，滤波电路20包括一个电解电容C，因而电压V1的大小与以下因素有关：电源输入电压的大小、电解电容C的大小及电路的充放电电流大小。
在t11时刻，LED灯串正极电压V1超过了LED灯串导通所需要的电压，LED灯串导通，滤波电路20中的充电电流最大，随着电压增大，充电电流减小，电流控制电路50控制流过LED灯串的电流I3为一恒定值，其LED灯串两端的的电压降等于V11；在t2时刻，电源输入电压达到最大值，滤波电路20上的电压也达到最大值，滤波电路20中的电容停止充电，电流控制电路50输入端的电压V3也达到最大值；随后输入电压逐渐减小，滤波电路20中的电容开始放电，其放电电流与从电源流入的电流之和等于LED灯串中的电流，维持LED灯串导通，电流控制电路50输入端的电压V3也随着下降；在t3时刻，电源电压低于滤波电路20的电压，电源停止输入电流，滤波电路20放电维持LED灯串导通，滤波电路20电压下降；在t31时刻，滤波电路20电压V1等于LED灯串导通电压V11，随着电压V1下降，LED灯串中的电流随着减小；在t5时刻，电压V1下降到最小值，LED灯串中的电流最小，随后电压V1随输入电压的增大而增大，LED灯串中的电流随着增大；在t51时刻，电压V1再次达到LED灯串的导通电压，重复上述过程。
在t1到t3时刻，V1按正弦规律变化；在t3到t5时刻，V1按指数曲线下降，放电时 间常数与电容的大小、放电电流大小等有关；在t3到t5时刻，滤波电路20中的电容放电，放电电流的大小由电流控制电路50控制，电压V1下降。
当电源输入电压小于额定电压时，滤波电路20上的储能不足以维持放电到输入电压再次达到导通时所需的电能，就会加重LED灯串的频闪。
当输入电压大于额定电压时，滤波电路20与LED灯串正端的电压V1增大，在滤波电路20充电与放电的过程中，前一次的放电还未放完时下一次的充电又开始了，因而滤波电路上的电压增大，电压V1整体上移，在全周期过程中都大于LED灯串的导通电压，LED灯串中的电流为恒定值，此时LED灯串无频闪，如图3中波形V12所示，但相应地，LED灯串负极的电压V3也增大，如波形V32所示，也就是说电流控制电路50上的电压降增大，功耗增大，发热增加导致温度急剧上升，可靠性下降。图中V11是输入电压等于额定电压时，LED灯串正极电压的波形图，V31为LED灯串负极电压的波形图。
发明内容
为克服现有技术中所存在的缺陷，本发明提出一种LED驱动电路，包括：整流电路、滤波电路、限流电路、检测控制电路和LED灯串；所述整流电路与交流电源连接，所述整流电路的负极连接滤波电路的第二端和检测控制电路的第二端；所述限流电路的输入端与整流电路的正极连接，所述限流电路的第一输出端与LED灯串的正极和滤波电路的输入端连接，所述限流电路的第二输出端连接检测控制电路的第三端；所述LED灯串的负极与检测控制电路的输入端连接。
其中，所述检测控制电路包括控制电路与分压电路，所述分压电路包括串联的分压电阻R1和R2。
其中，所述限流电路的第二输出端与控制电路的第三端连接，所述LED灯串的负极与控制电路的输入端及电阻R1的输入端连接；所述电阻R1和电阻R2串联，所述控制电路的第四端与电阻R1的输出端和电阻R2的输入端连接；所述整流电路的负极与控制电路的第二端及电阻R2的输出端连接。
其中，在所述控制电路的第四端位置增加滤波电容C1，所述电容C1与电阻R2并联。
其中，所述限流电路用于控制滤波电路的充电电流和LED灯串中的电流I3。
其中，所述检测控制电路用于检测LED灯串中的电流并根据检测结果控制限流电路和滤波电路。
其中，所述检测控制电路检测LED灯串负极的电压V3，电压V3称为第一检测电压；
当第一检测电压V3小于第三设定电压V33时，从限流电路第一输出端流出的第一输出 电流I2为第一恒定电流I21，第一恒定电流I21提供滤波电路的充电电流与LED灯串的电流I3，流过LED灯串的电流I3由检测控制电路控制，限流电路的第二输出端无电流输出，第二输出电流I5为零；
当第一检测电压V3大于等于第三设定电压V33且小于第四设定电压V34时，限流电路的第一输出电流I2随第一检测电压V3的增大而减小，同时，从限流电路流向检测控制电路的第二输出电流I5随第一检测电压V3的增大而增大；
当第一检测电压V3大于等于第四设定电压V34时，限流电路的第一输出电流I2保持为第二恒定电流I22，限流电路的第二输出电流I5保持为第三恒定电流I51，此时，第二恒定电流I22是从限流电路流向LED灯串与滤波电路的电流最小值，而第三恒定电流I51是从限流电路流向检测控制电路的电流最大值。
本发明还提供了一种LED驱动电路的驱动方法，检测控制电路检测LED灯串负极的第一检测电压V3并根据第一检测电压V3的大小控制流过LED灯串电流I3的大小：
当第一检测电压V3小于第一设定电压值V31时，LED灯串中没有电流流过，限流电路的第一输出电流I2为第一恒定电流I21，全部用于对滤波电路中的电容充电，此时滤波电路的充电电流I4最大，限流电路的第二输出电流I5为零；
当第一检测电压V3等于第一设定电压V31时，LED灯串导通有电流流过，此时，限流电路流出的第一输出电流I2保持为第一恒定电流I21，该第一恒定电流I21分成两部分，一部分用于对滤波电路充电，一部分流过LED灯串用于点亮LED灯串，限流电路的第二输出电流I5继续为零；
当第一检测电压V3大于第一设定电压V31而小于第二设定电压V32时，从限流电路流出的第一输出电流I2继续保持为第一恒定电流I21，随着第一检测电压V3增大流过LED灯串的电流I3也增大，滤波电路的充电电流I4减小，限流电路的第二输出电流I5继续为零；
当第一检测电压V3大于等于第二设定电压V32而小于第三设定电压V33时，从限流电路流出的第一输出电流I2为第一恒定电流I21，检测控制电路控制流过LED灯串的电流I3为第四恒定电流I32，此时第一检测电压V3的波动不会引起电流I3的波动，限流电路的第二输出电流I5继续为零；
当第一检测电压V3大于等于第三设定电压V33且小于第四设定电压V34时，从限流电路流出的第一输出电流I2随第一检测电压V3的增大而减小，同时，检测控制电路从限流电路汲取第二输出电流I5，从限流电路流向检测控制电路的第二输出电流I5随第一检测 电压V3的增大而增大，检测控制电路控制流过LED灯串的电流I3保持为第四恒定电流I32，第二输出电流I5远小于第一输出电流I2；
当第一检测电压V3大于等于第四设定电压V34时，限流电路流出的第一输出电流I2保持为第二恒定电流I22，从限流电路流出的第二输出电流I5保持第三恒定电流I51，此时，第二恒定电流I22是从限流电路流向LED灯串与滤波电路的电流最小值，而第三恒定电流I51是从限流电路流向检测控制电路的电流最大值，且第三恒定电流I51远小于第二恒定电流I22。
其中，对第一检测电压V3进行分压得到第二检测电压V4，第二检测电压V4相应的减小了电压波动，从而使得限流电路的第一输出电流I2相应减小波动，使LED灯串上的电流I3及检测控制电路上电压降相对稳定；且不同的分压比例，可相应的适应不同的输入电压。
其中，对第二检测电压V4进行滤波，得到恒定的第二检测电压V4，使得限流电路的第一输出电流I2相应也为一恒定值，保证LED灯串上的电流I3恒定及检测控制电路上电压降稳定。
其中，所述限流电路包括第二供电电路、控制驱动电路、第二驱动电路、第二电流采样电路和功率管Q2，所述第二驱动电路连接第二供电电路、控制驱动电路、第二电流采样电路和功率管Q2的控制端，所述第二供电电路连接控制驱动电路。
其中，所述控制电路包括第一供电电路、基准电路、第一驱动电路、第一电流采样电路、电压采样电路、下拉电流电路和功率管Q1，所述基准电路连接第一供电电路和第一驱动电路，第一驱动电路连接功率管Q1的控制端和第一电流采样电路，电压采样电路连接下拉电流电路和第一电流采样电路。
其中，所述限流电路设置有第二过温保护电路，与第二驱动电路连接。
其中，所述控制电路设置有第一过温保护电路，与第一驱动电路连接。
通过本发明，可以解决现有技术中电源电压增大时功耗增大及可能引起电流控制电路烧坏的问题，以及电源电压减小时LED灯串频闪加重的问题。
附图说明
图1为现有技术中的LED控制电路示意图；
图2为现有技术中的LED控制电路中整流电路输出端的电压电流关系图；
图3为现有技术中的LED控制电路中整流电路在不同输入电压时的电压电流关系图；
图4为本发明的一种LED驱动电路的示意图；
图5为本发明的一种LED控制电路的限流电路的工作原理图；
图6为本发明的一种LED控制电路的检测控制电路与限流电路的控制情况图；
图7为在较低输入电压范围时，限流电路的输出电压V2与第一输出电流I2的一种波形图；
图8为在较高输入电压范围时，限流电路的输出电压V2与第一输出电流I2的一种波形图；
图9为将不同输入电压时的波形图绘制在一起的示意图；
图10为本发明的一种LED驱动电路的优选实施例；
图11是图10电路在电源输入电压大于第二阈值小于第四阈值时的波形图；
图12为本发明的另一种LED驱动电路的优选实施例；
图13是图12电路中LED灯串两端的电压V2/V3与电流I2/I3波形图；
图14为本发明中限流电路的结构示意图；
图15为本发明中限流电路设置过温保护电路的结构示意图；
图16为本发明中控制电路的结构示意图；
图17为本发明中控制电路设置过温保护电路的结构示意图。
具体实施方式
下面，结合附图1-17对本发明作进一步详细描述。
如图4所示，本发明的一种LED驱动电路的示意图，包括整流电路40、滤波电路20、限流电路10、检测控制电路30和LED灯串。
所述整流电路40与交流电源连接，用于将交流电压变成直流电压；所述整流电路40的负极连接滤波电路20的第二端和检测控制电路30的第二端。
所述限流电路10的输入端与整流电路40的正极连接，所述限流电路10的第一输出端与LED灯串的正极和滤波电路20的输入端连接，所述限流电路10的第二输出端连接检测控制电路30的第三端。所述限流电路10用于控制滤波电路20中的电解电容充能多少，即控制滤波电路20的充电电流和LED灯串中的电流I3；检测控制电路30用于检测LED灯串负极的电压大小同时反馈给控制限流电路10，并控制流过LED灯串的电流I3大小。
所述滤波电路20的输入端与限流电路10的第一输出端连接，所述滤波电路20用于减小直流电压中的纹波。
所述LED灯串的负极与检测控制电路30的输入端连接。因为LED灯串上的电压降是固 定的，所以检测控制电路30输入端的电压随滤波电路20和LED灯串正极的电压V2变化而变化，检测控制电路30输入端的电压V3波形与滤波电路20和LED灯串正极的电压V2波形一致。
所述检测控制电路30的第三端与限流电路10的第二输出端连接。所述检测控制电路30用于检测LED灯串中的电流并根据检测结果控制限流电路10和滤波电路20。
如图5所示，本发明的一种LED驱动电路的限流电路10的工作原理如下：
LED灯串负极的电压V3与其正极电压V2波形相同，检测控制电路30检测LED灯串负极的电压V3，电压V3称为第一检测电压，限流电路10工作分为以下几种情况：
1.当第一检测电压V3小于第三设定电压V33时，从限流电路10第一输出端流出的第一输出电流I2为第一恒定电流I21，第一恒定电流I21提供滤波电路20的充电电流与LED灯串的电流I3，流过LED灯串的电流I3由检测控制电路30控制，限流电路10的第二输出端无电流输出，第二输出电流I5为零；
2.当第一检测电压V3大于等于第三设定电压V33且小于第四设定电压V34时，限流电路10的第一输出电流I2随第一检测电压V3的增大而减小，同时，从限流电路10流向检测控制电路30的第二输出电流I5随第一检测电压V3的增大而增大。
3.当第一检测电压V3大于等于第四设定电压V34时，限流电路10的第一输出电流I2保持为第二恒定电流I22，限流电路10的第二输出电流I5保持为第三恒定电流I51，此时，第二恒定电流I22是从限流电路10流向LED灯串与滤波电路20的电流最小值，而第三恒定电流I51是从限流电路流向检测控制电路30的电流最大值。
第二输出电流I5的大小远远小于第一输出电流I2的大小。
如图6所示，本发明的一种LED驱动电路的检测控制电路30的控制情况如下：
检测控制电路30检测LED灯串负极的第一检测电压V3并根据第一检测电压V3的大小控制流过LED灯串电流I3的大小：
1.当第一检测电压V3小于第一设定电压值V31时，LED灯串中没有电流流过，限流电路10的第一输出电流I2为第一恒定电流I21，全部用于对滤波电路20中的电容充电，此时滤波电路20的充电电流I4最大，限流电路10的第二输出电流I5为零；
2.当第一检测电压V3等于第一设定电压V31时，LED灯串导通有电流流过，此时，限流电路10流出的第一输出电流I2保持为第一恒定电流I21，该第一恒定电流I21分成两部分，一部分用于对滤波电路20充电，一部分流过LED灯串用于点亮LED灯串，限流电路10的第二输出电流I5继续为零；
3.当第一检测电压V3大于第一设定电压V31而小于第二设定电压V32时，从限流电路10流出的第一输出电流I2继续保持为第一恒定电流I21，随着第一检测电压V3增大流过LED灯串的电流I3也增大，滤波电路20的充电电流I4减小，限流电路10的第二输出电流I5继续为零；
4.当第一检测电压V3大于等于第二设定电压V32而小于第三设定电压V33时，从限流电路10流出的第一输出电流I2为第一恒定电流I21，检测控制电路30控制流过LED灯串的电流I3为第四恒定电流I32，此时第一检测电压V3的波动不会引起电流I3的波动，限流电路10的第二输出电流I5继续为零。
5.当第一检测电压V3大于等于第三设定电压V33且小于第四设定电压V34时，从限流电路10流出的第一输出电流I2随第一检测电压V3的增大而减小，同时，检测控制电路30从限流电路10汲取第二输出电流I5，从限流电路10流向检测控制电路30的第二输出电流I5随第一检测电压V3的增大而增大，检测控制电路30控制流过LED灯串的电流I3保持为第四恒定电流I32，第二输出电流I5远小于第一输出电流I2。
6.当第一检测电压V3大于等于第四设定电压V34时，限流电路10流出的第一输出电流I2保持为第二恒定电流I22，从限流电路流出的第二输出电流I5保持第三恒定电流I51，此时，第二恒定电流I22是从限流电路流向LED灯串与滤波电路20的电流最小值，而第三恒定电流I51是从限流电路流向检测控制电路30的电流最大值，且第三恒定电流I51远小于第二恒定电流I22。
7.当第一检测电压V3的波动小时，限流电路10的输出电流波动也就减小，当第一检测电压V3为一恒定值时，限流电路10的第一输出电流I2相应也为一恒定值，保证LED灯串上的电流I3恒定及检测控制电路30上电压降稳定。
8.第一检测电压V3的第一设定电压V31至第四设定电压V34分别对应整流电路40输出电压V1的第一阈值电压V101至第四阈值电压V104。
在不同输入电压时，本发明的一种LED驱动电路的限流电路10的输出电压V2与第一输出电流I2波形图，如图7、图8所示：
一、输入电压范围属于第一阈值V101与第三阈值V103之间时，如图7所示，此时输入电压的最大值为V11，经过整流电路40后，图中，V1为限流电路10输入端的电压，V2为限流电路10输出端的电压，I2为限流电路10的第一输出电流，V3为检测控制电路30输入端的第一检测电压，I3为检测控制电路30输入端的电流，I5为限流电路10的第二输出电流，因第二输出电流I5远小于第一输出电流I2，因而图中并不是相同比例，画在 同一图中只是便于理解。
在t1时刻，LED灯串两端的电压大于LED灯串的导通电压，LED灯串导通，此时，第一检测电压V3值最小，小于第二设定电压值V32，流入LED灯串的电流I3值也是最小，而限流电路10的第一输出电流I2值最大；
随着第一检测电压V3增大，电流I3也相应增大，第一输出电流I2保持恒定，在t11时刻，第一检测电压V3等于第二设定电压值V32，电流I3等于第四恒定电流I32，第一输出电流I2等于第一恒定电流I21，在这一阶段，从限流电路10不向检测控制电路30流出第二输出电流I5；
在t12时刻，第一检测电压V3等于第三设定电压V33，随后第一检测电压V3继续增大，第一输出电流I2开始减小，从限流电路10向检测控制电路30流出第二输出电流I5，并随第一检测电压V3的增大而增大；
在t3时刻，限流电路10输出端的电压V2等于整流后的电源输入电压V21，滤波电路20中的电容开始放电，限流电路10的第一输出电流I2为零，电容放电的电流大小由检测控制电路30控制，为一恒定值，电压V2线性下降，第一检测电压V3也线性下降，第二输出电流I5相应的减小，在t31时刻，第一检测电压V3下降到等于第三设定电压V33，此时，第二输出电流I5为零，在接近t5时刻，滤波电路20上的电压V2下降到接近最小，第一检测电压V3小于第二设定电压值V32，电流I3从恒定值开始减小，在t5时刻，第一检测电压V3值最小，电流I3值也是最小，而从限流电路10的第一输出端电流I2最大。
随着时间增加，重复上述过程。
二、电源输入电压范围大于第三阈值V103时，如图8所示，经过整流电路后，V1为限流电路10输入端的电压，V2为限流电路10输出端的电压，I2为限流电路10的第一输出电流，V3为检测控制电路30输入端的第一检测电压，I3为检测控制电路30输入端的电流，I5为限流电路10的第二输出电流，因第二输出电流I5远小于第一输出电流I2，因而图中并不是相同比例，画在同一图中只是便于理解。
在t1时刻，LED灯串两端的电压大于LED灯串的导通电压，LED灯串导通，此时，第一检测电压V3值最小，第一检测电压V3值大于第三设定电压值V33而小于第四设定电压V34，流入LED灯串的电流I3为第四恒定值I32，限流电路10的第一输出电流I2为最大，限流电路10的第二输出电流I5最小；随着第一检测电压V3增大，电流I3保持恒定，电流I2逐渐减小，限流电路10的第二输出电流I5相应增大；
在t2时刻，第一检测电压V3等于第四设定电压值V34，电流I3保持恒定，第一输出 电流I2为第二恒定电流值I22，第二输出电流I5为第三恒定电流值I51，此后，电压V3增大而电流I3、第一输出电流I2、第二输出电流I5均保持恒定；
在t3时刻，第一检测电压V3与经整流电路后的电压相同，限流电路10的第一输出电流I2为零，滤波电路20停止充电转而为LED灯串提供电流I3，因放电电流为恒定值，滤波电路20上的电压线性下降，电压V3也线性下降，在t31时刻，第一检测电压V3小于第四设定电压值V34，电流I3保持恒定，第二输出电流I5随第一检测电压V3的减小而减小；直至T5时刻，电压V3与第二输出电流I5达到最小。
然后重复上述过程。
三、将不同输入电压时的波形图绘制在同一个图中，如图9所示，设此时检测电压V3处于V33与V34之间。
从图9可以看出，在电源输入电压低(最高电压为V11)时限流电路10提供第一输出电流I2的时间T11小于电源输入电压高(最高电压为V12)时限流电路10提供第一输出电流I2的时间T1(在输入电压高时，上次放电未完时又开始了充电过程)，也就是说在电源输入电压低时滤波电路20的充电时间小于电源输入电压高时滤波电路20的充电时间，而电源输入电压低时滤波电路20的放电时间T21大于电源输入电压高时滤波电路20的放电时间T2，为了保持在电源输入电压变化时滤波电路上的电压基本保持不变，维持LED灯串上的电流恒定，就需要在电源输入电压增大时减小输入电流，使不同输入电压时在每个周期内滤波电路中电解电容上的储能相同，限流电路10根据电源输入电压的不同，分段控制第一输出电流，提高电源效率。
同时，在电源输入电压低时滤波电路20中滤波电容上储存的电能要能够保证在放电时LED灯串上的电流不间断，也就是LED灯串无频闪，在放电时检测控制电路30控制LED灯串上的电流减小，延长滤波电容的放电时间。
因限流电路10的存在，电源输入电压高时滤波电路20上的电压V22与电流输入电压低时滤波电路20上的电压V21相比变化不大。
当电源输入电压范围在第三阈值V103与第四阈值V104之间时，限流电路10的第一输出电流I2为恒定值，并不随输入电压的波动而波动，但随着电源输入电压的增大，限流电路10的第一输出电流I2随电源输入电压的增大而减小。当电源输入电压如图中110所示(最大值为V11)时，第一输出电流I2如波形I24所示，当电源输入电压如图中210所示(最大值为V12)时，第一输出电流I2如波形I25所示，可以看出，当电源输入电压增大，第一输出电流I2相应的减小；而LED灯串中的电流I3保持为恒定值。
四、具体的，图10为本发明的一种LED驱动电路的一优选实施例，如图10所示，所述检测控制电路30包括控制电路70与分压电路60，所述分压电路60包括串联的分压电阻R1和R2。所述限流电路10的第二输出端与控制电路70的第三端连接，所述LED灯串的负极与控制电路70的输入端及电阻R1的输入端连接；所述电阻R1和电阻R2串联，所述控制电路70的第四端与电阻R1的输出端和电阻R2的输入端连接；所述整流电路40的负极与控制电路70的第二端及电阻R2的输出端连接。
通过设置分压电路中分压电阻的数值，可改变第二检测电压V4的数值大小，从而改变可检测输入电压的范围，使本电路适用于不同的电源输入电压范围。经过对第一检测电压V3进行分压，检测分压电压V4(第二检测电压)的电压值，通过调节R1/R2的阻值，可以改变第二检测电压的电压值的取值范围，从而使电路适用于不同的输入电压变化。
图11是图10电路在电源输入电压大于第二阈值小于第四阈值时的波形图，
图中V1是输入电压整流后电压，V2是限流电路10输出端(也就是LED灯串正极)的电压，V3是第一检测电压，V3与V2的波形相同，经过电阻分压后，第二检测电压V4其波动比第一检测电压V3的波动小，检测控制电路30反馈给限流电路10的信号波动相应减小，限流电路10的输出电流I2波动相应的也减小，在检测控制电路30上的电压降保持平稳。LED灯串中的电流I3保持恒定值。
对第一检测电压V3进行分压得到第二检测电压V4，第二检测电压V4相应的减小了电压波动，从而使得限流电路10的第一输出电流I2相应减小波动，使LED灯串上的电流I3及检测控制电路30上电压降相对稳定；且不同的分压比例，可相应的适应不同的输入电压。
五、从以上可知，第一检测电压V3波动越小，限流电路10输出的电流也就越稳定，为了减小第二检测电压V4上的电压波动，在控制电路70的第四端位置增加滤波电容C1，第二检测电压V4的平稳反馈过来影响限流电路10的第一输出电流I2和第二输出电流I5的平稳。
对第二检测电压V4进行滤波，得到恒定的第二检测电压V4，使得限流电路10的第一输出电流I2相应也为一恒定值，保证LED灯串上的电流I3恒定及检测控制电路30上电压降稳定。
图12所示的为本发明的一种LED驱动电路的优选实施例的示意图。从图12可以看出，在分压电路的采样点位置增加滤波电容C1，所述电容C1与电阻R2并联。当滤波电容C1足够滤掉第二检测电压V4上的电压波动，电压V4纹波可以忽略不计，则在不同的输入电 压时，第一输出电流I2的电流波形如图13所示。
图13是图12电路中LED灯串两端的电压V2/V3与电流I2/I3波形图。
图中，V1为电源输入电压整流后的电压，V2为限流电路10输出端的电压，V3为LED灯串负极的第一检测电压，V4为经过再次滤波后的第二检测电压，I2为限流电路10的第一输出电流，I3为LED灯串上的电流。
因第二检测电压V4的纹波可忽略，限流电路10根据第二检测电压V4为恒定值，第一输出电流I2和第二输出电压I5也为恒定值，从而使限流电路10输出端的电压V2线性增大或减小，LED灯串中的电流I3也为恒定值。
第二检测电压V4为第五恒定值，限流电路10流出的第二输出电流I5也是恒定值，为第六恒定值，根据限流电路10的原理，则限流电路10的第一输出电流I2也是恒定值即第七恒定值，LED灯串中的电流I3为第八恒定值。
当输入电压增大或减小时，第一检测电压V3在所有设定范围内变化，第二检测电压V4为恒定值并随电源输入电压增大或减小相应的平行上移或平行下移，限流电路10的第一输出电流I2恒定值与LED灯串中的电流I3恒定值也相应的上移或下移。
在本发明的方案中，在整流电路的输出端与LED灯串的正极和滤波电路的输入端设置限流电路，检测控制电路在控制LED灯串的电流的同时还检测LED灯串负极的电压变化，并根据LED灯串负极的电压变化控制限流电路，限流电路根据检测电压的变化控制滤波电路的充电电流大小和LED灯串中的电流大小，即：
在电源输入电压小于第三阈值V103时，限流电路处于打开状态，输入电压施加在滤波电路、LED灯串和检测控制电路上，输入电流流入滤波电路和LED灯串；在电源输入电压大于第三阈值V103且小于第四阈值V104时，限流电路输出电流减小，也就是减小滤波电路的充电电流I4和LED灯串的导通电流I3，降低检测控制电路上的电压降，此时电源输入电流I1随电源电压增大相应地减小，因为限流电路10的输出电流I2约等于电源输入电流I1，因而限流电路10的输出电流I2随限流电路10的输入电压增大相应地减小；在电源电压大于第四阈值V104时，限流电路10保持滤波电路的充电电流I4和LED灯串的导通电流I2为一恒定值，此时电源输入电流I1最小。
需要说明的是，本发明中的第一阈值、第二阈值、第三阈值、第四阈值都是预设的。
如图14所示，限流电路10包括第二供电电路170、控制驱动电路180、第二驱动电路190、第二电流采样电路300和功率管Q2，第二驱动电路190连接第二供电电路170、控制驱动电路180、第二电流采样电路300和功率管Q2的控制端，第二供电电路170连接控 制驱动电路180。
如图15所示，限流电路10设置有第二过温保护电路320，与第二驱动电路190连接，用于对功率管Q2进行过温保护。
如图16所示，控制电路70包括第一供电电路110、基准电路120、第一驱动电路130、第一电流采样电路140、电压采样电路150、下拉电流电路160和功率管Q1，基准电路120连接第一供电电路110和第一驱动电路130，第一驱动电路130连接功率管Q1的控制端和第一电流采样电路140，电压采样电路150连接下拉电流电路160和第一电流采样电路140。
如图17所示，控制电路70设置有第一过温保护电路310，与第一驱动电路130连接，用于对功率管Q1进行过温保护。
当第二检测电压V4属于第一设定范围时，电压采样电路150发出V11信号给第一电流采样电路140，第一驱动电路130根据V11信号和第一电流采样电路140的采样结果，控制功率管Q1的导通，从而控制流过LED灯串的电流大小；
当第二检测电压V4属于第二设定范围时，电压采样电路150发出V12信号给下拉电流电路160，下拉电流电路160根据V12信号输出ICS信号给控制驱动电路180，第二驱动电路190根据控制驱动电路180的输出信号控制功率管Q2的导通，从而控制电源的输入电流。
其中，第一设定范围的数值小于第二设定范围的数值，或第一设定范围的数值与第二设定范围的数值部分重叠。
优选的，第一设定范围为0≤Vdim≤1.2V，第二设定范围为1.2V≤Vdim≤2.4V。
当Vdim超出第二设定范围时，下拉电流电路160的输出保持为最大值。
虽然通过实施例描述了本发明，本领域普通技术人员知道，本发明有许多变形和变化而不脱离本发明的精神，希望所附的权利要求包括这些变形和变化而不脱离本发明的精神。

Claims (14)

  1. 一种LED驱动电路，其特征在于，所述驱动电路包括：整流电路(40)、滤波电路(20)、限流电路(10)、检测控制电路(30)和LED灯串；
    所述整流电路(40)与交流电源连接，所述整流电路(40)的负极连接滤波电路(20)的第二端和检测控制电路(30)的第二端；
    所述限流电路(10)的输入端与整流电路(40)的正极连接，所述限流电路(10)的第一输出端与LED灯串的正极和滤波电路(20)的输入端连接，所述限流电路(10)的第二输出端连接检测控制电路(30)的第三端；
    所述LED灯串的负极与检测控制电路(30)的输入端连接。
  2. 根据权利要求1所述的LED驱动电路，其特征在于，所述检测控制电路(30)包括控制电路(70)与分压电路(60)，所述分压电路(60)包括串联的分压电阻R1和R2。
  3. 根据权利要求2所述的LED驱动电路，其特征在于：所述限流电路(10)的第二输出端与控制电路(70)的第三端连接，所述LED灯串的负极与控制电路(70)的输入端及电阻R1的输入端连接；所述电阻R1和电阻R2串联，所述控制电路(70)的第四端与电阻R1的输出端和电阻R2的输入端连接；所述整流电路(40)的负极与控制电路(70)的第二端及电阻R2的输出端连接。
  4. 根据权利要求3所述的LED驱动电路，其特征在于：
    在所述控制电路(70)的第四端位置增加滤波电容C1，所述电容C1与电阻R2并联。
  5. 根据权利要求1所述的LED驱动电路，其特征在于：所述限流电路(10)用于控制滤波电路(20)的充电电流和LED灯串中的电流I3。
  6. 根据权利要求1所述的LED驱动电路，其特征在于：所述检测控制电路(30)用于检测LED灯串中的电流并根据检测结果控制限流电路(10)和滤波电路(20)。
  7. 根据权利要求1所述的LED驱动电路，其特征在于：
    所述检测控制电路(30)检测LED灯串负极的电压V3，电压V3称为第一检测电压；
    当第一检测电压V3小于第三设定电压V33时，从限流电路(10)第一输出端流出的第一输出电流I2为第一恒定电流I21，第一恒定电流I21提供滤波电路(20)的充电电流与LED灯串的电流I3，流过LED灯串的电流I3由检测控制电路(30)控制，限流电路(10)的第二输出端无电流输出，第二输出电流I5为零；
    当第一检测电压V3大于等于第三设定电压V33且小于第四设定电压V34时，限流电路(10)的第一输出电流I2随第一检测电压V3的增大而减小，同时，从限流电路(10)流向检测控制电路(30)的第二输出电流I5随第一检测电压V3的增大而增大；
    当第一检测电压V3大于等于第四设定电压V34时，限流电路(10)的第一输出电流I2保持为第二恒定电流I22，限流电路(10)的第二输出电流I5保持为第三恒定电流I51，此时，第二恒定电流I22是从限流电路(10)流向LED灯串与滤波电路(20)的电流最小值，而第三恒定电流I51是从限流电路流向检测控制电路(30)的电流最大值。
  8. 一种根据权利要求1-7任一项所述的LED驱动电路的驱动方法，其特征在于：检测控制电路(30)检测LED灯串负极的第一检测电压V3并根据第一检测电压V3的大小控制流过LED灯串电流I3的大小：
    当第一检测电压V3小于第一设定电压值V31时，LED灯串中没有电流流过，限流电路(10)的第一输出电流I2为第一恒定电流I21，全部用于对滤波电路(20)中的电容充电，此时滤波电路(20)的充电电流I4最大，限流电路(10)的第二输出电流I5为零；
    当第一检测电压V3等于第一设定电压V31时，LED灯串导通有电流流过，此时，限流电路(10)流出的第一输出电流I2保持为第一恒定电流I21，该第一恒定电流I21分成两部分，一部分用于对滤波电路(20)充电，一部分流过LED灯串用于点亮LED灯串，限流电路(10)的第二输出电流I5继续为零；
    当第一检测电压V3大于第一设定电压V31而小于第二设定电压V32时，从限流电路(10)流出的第一输出电流I2继续保持为第一恒定电流I21，随着第一检测电压V3增大流过LED灯串的电流I3也增大，滤波电路(20)的充电电流I4减小，限流电路(10)的第二输出电流I5继续为零；
    当第一检测电压V3大于等于第二设定电压V32而小于第三设定电压V33时，从限流电路(10)流出的第一输出电流I2为第一恒定电流I21，检测控制电路(30)控制流过LED灯串的电流I3为第四恒定电流I32，此时第一检测电压V3的波动不会引起电流I3的波动，限流电路(10)的第二输出电流I5继续为零；
    当第一检测电压V3大于等于第三设定电压V33且小于第四设定电压V34时，从限流电路(10)流出的第一输出电流I2随第一检测电压V3的增大而减小，同时，检测控制电路(30)从限流电路(10)汲取第二输出电流I5，从限流电路(10)流向检测控制电路(30)的第二输出电流I5随第一检测电压V3的增大而增大，检测控制电路(30)控制流过LED灯串的电流I3保持为第四恒定电流I32，第二输出电流I5远小于第一输出电流I2；
    当第一检测电压V3大于等于第四设定电压V34时，限流电路(10)流出的第一输出电流I2保持为第二恒定电流I22，从限流电路流出的第二输出电流I5保持第三恒定电流I51，此时，第二恒定电流I22是从限流电路流向LED灯串与滤波电路(20)的电流最小值，而 第三恒定电流I51是从限流电路流向检测控制电路(30)的电流最大值，且第三恒定电流I51远小于第二恒定电流I22。
  9. 根据权利要求8所述的驱动方法，其特征在于：
    对第一检测电压V3进行分压得到第二检测电压V4，第二检测电压V4相应的减小了电压波动，从而使得限流电路(10)的第一输出电流I2相应减小波动，使LED灯串上的电流I3及检测控制电路(30)上电压降相对稳定；且不同的分压比例，可相应的适应不同的输入电压。
  10. 根据权利要求9所述的驱动方法，其特征在于：
    对第二检测电压V4进行滤波，得到恒定的第二检测电压V4，使得限流电路(10)的第一输出电流I2相应也为一恒定值，保证LED灯串上的电流I3恒定及检测控制电路(30)上电压降稳定。
  11. 根据权利要求1所述的LED驱动电路，其特征在于：所述限流电路(10)包括第二供电电路(170)、控制驱动电路(180)、第二驱动电路(190)、第二电流采样电路(300)和功率管Q2，所述第二驱动电路(190)连接第二供电电路(170)、控制驱动电路(180)、第二电流采样电路(300)和功率管Q2的控制端，所述第二供电电路(170)连接控制驱动电路(180)。
  12. 根据权利要求2所述的LED驱动电路，其特征在于：所述控制电路(70)包括第一供电电路(110)、基准电路(120)、第一驱动电路(130)、第一电流采样电路(140)、电压采样电路(150)、下拉电流电路(160)和功率管Q1，所述基准电路(120)连接第一供电电路(110)和第一驱动电路(130)，第一驱动电路(130)连接功率管Q1的控制端和第一电流采样电路(140)，电压采样电路(150)连接下拉电流电路(160)和第一电流采样电路(140)。
  13. 根据权利要求11所述的LED驱动电路，其特征在于：所述限流电路(10)设置有第二过温保护电路(320)，与第二驱动电路(190)连接。
  14. 根据权利要求12所述的LED驱动电路，其特征在于：所述控制电路(70)设置有第一过温保护电路(310)，与第一驱动电路(130)连接。
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