LED drive circuit and lighting circuit

Abstract

The invention provides an LED drive circuit and a lighting circuit, AC input voltage passes through a rectification circuit to obtain bus voltage, the LED drive circuit comprises a first capacitor, a unidirectional conduction element, a switch connection circuit and a second capacitor, the first end of the first capacitor is connected with the output end of the rectification circuit through the unidirectional conduction element and is connected with the anode of an LED load, and the second end of the first capacitor is connected with the output end of the rectification circuit through the unidirectional conduction element. The second end of the first capacitor is connected with the output end of the rectifying circuit through the switch connecting circuit; the second capacitor is connected in parallel to the two ends of the LED load; wherein the on-off of the switch connection circuit and the one-way conduction element is controlled according to the magnitude of the bus voltage. The power factor of the system can be improved, THD is reduced, and the purposes of reducing loss and improving efficiency are achieved.

Description

Technical Field

[0001] The present invention relates to the field of power electronics, and in particular to an LED drive circuit and a lighting circuit. Background Art

[0002] In the field of lighting, many customers now hope to adopt the DOB solution, that is, the driving power supply and LED lamp beads are placed on the aluminum substrate for heat dissipation. Therefore, the LED driving circuit adopts a linear driving solution, which is more suitable for the DOB solution. It has EMI problems, fewer power devices, and it is easier to integrate the LED driving circuit with the lamp beads on the PCB board. If the LED driving circuit adopts a switch driving solution, not only more power devices are required, but also when the driving circuit is placed on the aluminum substrate, it is difficult to pass the relevant regulations in terms of electromagnetic compatibility and conducted radiation.

[0003] Generally, there are no devices such as inductors or capacitors that affect the phase at the front end of the linear LED drive circuit, so it can be considered that the phase shift φ of the input voltage and input current is close to 0, that is, cosφ≈1, and λ represents the PF size, so when the THD of the designed system is less than 0.25, the PF of the system can be close to greater than 0.97. In the linear drive solution, many customers hope that the single-stage lamp bead can achieve high PF (PF>0.95) and THDi<25%@120Vac, but the traditional single-stage lamp bead solution is difficult to meet the requirements.

[0004] Now, most of them are controlled by multi-segment LED lamp beads, including 2-segment lamp beads, 3-segment lamp beads, 4-segment lamp beads, etc. The application of multi-segment lamp beads has a higher cost for stroboscopic processing. For filament lamp applications, only two output lines (LED+, LED-) are needed, and usually only single-segment lamp beads can be used. Multi-segment lamp beads are rare in filament lamp applications. In dimming applications, due to the limitations of optical design, the drive of single-segment lamp beads is easier to design. Summary of the invention

[0005] The purpose of the present invention is to provide a simple and efficient LED driving circuit and lighting circuit, which are used to solve the problems of low power factor and complex structure of LED driving circuit in the prior art.

[0006] The present invention provides an LED driving circuit, which is used to drive an LED load. An AC input voltage is passed through a rectifier circuit to obtain a bus voltage. The circuit includes a first capacitor, a unidirectional conductive element, a switch connection circuit, and a second capacitor. A first end of the first capacitor is connected to an output end of the rectifier circuit through the unidirectional conductive element and connected to an anode of the LED load. A second end of the first capacitor is connected to the output end of the rectifier circuit through the switch connection circuit.

[0007] The second capacitor is connected in parallel across the LED load;

[0008] Wherein, the on / off state of the switch connection circuit and the unidirectional conducting element is controlled according to the magnitude of the bus voltage.

[0009] Optionally, when the bus voltage is less than the first capacitor voltage, and the sum of the bus voltage and the first capacitor voltage is less than the turn-on voltage of the LED load, the switch connection circuit and the unidirectional conduction element are turned off, and the first capacitor is neither charged nor discharged.

[0010] Optionally, when the bus voltage is less than the first capacitor voltage, and the sum of the bus voltage and the first capacitor voltage is greater than the turn-on voltage of the LED load, the switch connection circuit is turned on, the unidirectional conduction element is turned off, and the first capacitor discharges to the LED load.

[0011] Optionally, when the bus voltage is greater than the voltage of the first capacitor and less than the conduction voltage of the LED load, the switch connection circuit is turned off, the unidirectional conduction element is turned on, and the bus voltage charges the first capacitor.

[0012] Optionally, when the bus voltage is greater than the conduction voltage of the LED load, the switch connection circuit is turned off, the unidirectional conducting element is turned on, and the bus voltage supplies power to the LED load.

[0013] Optionally, when the LED load is turned on, an LED load current is greater than a charging current of the first capacitor, and the charging current of the first capacitor is greater than a discharging current of the first capacitor.

[0014] Optionally, it further includes a first switch tube, wherein the first switch tube is connected between the second end of the first capacitor and the first sampling resistor;

[0015] When the bus voltage is greater than the voltage of the first capacitor and the bus voltage is less than the conduction voltage of the LED load, the first switch tube is turned on.

[0016] Optionally, it further includes a first operational amplifier, which performs operational amplification on the first reference voltage and the voltage of the first sampling resistor, and the output end of the first operational amplifier is connected to the control end of the first switch tube.

[0017] Optionally, it further includes a second switch tube, wherein the second switch tube is connected between the cathode of the LED load and the first sampling resistor;

[0018] When the bus voltage is less than the first capacitor voltage and the sum of the bus voltage and the first capacitor voltage is greater than the turn-on voltage of the LED load, or when the bus voltage is greater than the turn-on voltage of the LED load, the second switch tube is turned on.

[0019] Optionally, it also includes a second operational amplifier, which performs operational amplification on the second reference voltage and the voltage of the first sampling resistor, and the output end of the second operational amplifier is connected to the control end of the second switch tube.

[0020] Optionally, the unidirectional conducting element includes a first diode, an anode of the first diode is connected to an output end of the rectifier circuit, and a cathode of the first diode is connected to a first end of the first capacitor.

[0021] Optionally, the switch connection circuit includes a second diode and a third switch tube, the second diode and the third switch tube are connected in series, an anode of the second diode is connected to an output end of a rectifier circuit, and a cathode of the second diode is connected to a second end of the first capacitor;

[0022] When the bus voltage is less than the voltage of the first capacitor, and the sum of the bus voltage and the voltage of the first capacitor is greater than the turn-on voltage of the LED load, the third switch tube is turned on.

[0023] Optionally, the switch connection circuit further includes a first resistor, a first voltage regulator tube and a first switch, wherein a first end of the first resistor is connected to an output end of a rectifier circuit, and a second end of the first resistor is connected to a control end of the third switch tube; a cathode of the first voltage regulator tube is connected to the control end of the third switch tube, and an anode of the first voltage regulator tube is connected to a second end of the first capacitor;

[0024] The control end of the third switch tube is grounded through the first switch.

[0025] Optionally, the switch connection circuit further includes a third operational amplifier and a first switch, the third operational amplifier performs operational amplification on a third reference voltage and a fourth sampling signal representing the fourth switch current, and an output end of the third operational amplifier is connected to a control end of the fourth switch tube;

[0026] The control end of the fourth switch tube is also grounded through the first switch.

[0027] The present invention further provides a lighting circuit, comprising an LED load, and also comprising any one of the above-mentioned LED driving circuits for driving the LED load.

[0028] Compared with the prior art, the present invention has the following advantages: the charge and discharge state of the first capacitor is controlled according to the bus voltage, so as to select the first capacitor, the second capacitor or the bus voltage to supply power to the LED load. The present invention only needs to control the charge and discharge of two capacitors to realize single-stage LED linear drive, and has the advantages of high PF and low THDi, and can also meet the requirements of low LED flicker. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is a schematic diagram of an LED driving circuit embodiment 1 of the present invention;

[0030] Figure 2 This is a schematic diagram of a second embodiment of an LED driving circuit of the present invention;

[0031] Figure 3 This is a working timing diagram of the LED driving circuit of the present invention. DETAILED DESCRIPTION

[0032] The preferred embodiments of the present invention are described in detail below in conjunction with the accompanying drawings, but the present invention is not limited to these embodiments. The present invention covers any substitution, modification, equivalent method and scheme made on the spirit and range of the present invention.

[0033] In order to make the public have a thorough understanding of the present invention, specific details are described in detail in the following preferred embodiments of the present invention, but those skilled in the art can fully understand the present invention without the description of these details.

[0034] The present invention is described in more detail in the following paragraphs by way of example with reference to the accompanying drawings. It should be noted that the accompanying drawings are all simplified and not in exact proportions, in order to facilitate and clearly assist in explaining the purpose of the embodiments of the present invention.

[0035] Reference Figure 1 , illustrates the principle diagram of embodiment 1 of the LED driving circuit of the present invention, the AC input voltage AC is passed through the rectifier circuit (the rectifier bridge in the figure) to obtain the bus voltage Vbus. The LED driving circuit of the present invention includes a first capacitor C1, a second capacitor C2, a unidirectional conduction element and a switch connection circuit 01, the first end of the first capacitor C1 is connected to the output end of the rectifier circuit through the unidirectional conduction element, the first end of the first capacitor C1 is also connected to the anode of the LED load, the second end of the first capacitor C1 is connected to the output end of the rectifier circuit through the switch connection circuit 01, and the second capacitor C2 is connected in parallel to the two ends of the LED load; the unidirectional conduction element is preferably a diode D1, the anode of the diode D1 is connected to the output end of the rectifier circuit, and the cathode of the diode D1 is connected to the anode of the LED load and the first end of the first capacitor C1. According to the size of the bus voltage Vbus, the on-off state of the unidirectional conduction element and the switch connection circuit 01 is controlled to control the charging and discharging state of the first capacitor C1, and the first capacitor C1, the second capacitor C2 or the bus voltage Vbus are selected to supply power to the LED load.

[0036] Further, when the bus voltage Vbus is less than the first capacitor voltage VC1, and the sum of the bus voltage Vbus and the first capacitor voltage VC1 is less than the conduction voltage VF of the LED load, the switch connection circuit 01 and the unidirectional conduction element are both turned off, the first capacitor C1 is neither charged nor discharged, and the second capacitor C2 is discharged to the LED load; when the bus voltage Vbus is less than the first capacitor voltage VC1, and the sum of the bus voltage Vbus and the first capacitor voltage VC1 is greater than the conduction voltage VF of the LED load, the switch connection circuit 01 is turned on, the unidirectional conduction element is turned off, the first capacitor C1 is discharged to the LED load and charges the second capacitor C2 through the switch connection circuit 01, and the switch The connection circuit 01, the first capacitor C1, the LED load / the second capacitor C2, and the diode of the rectifier circuit form a discharge loop; when the bus voltage Vbus is greater than the first capacitor voltage VC1, and the bus voltage Vbus is less than the conduction voltage VF of the LED load, the switch connection circuit 01 is turned off, the unidirectional conduction element is turned on, the bus voltage Vbus charges the first capacitor C1 through the unidirectional conduction element, and the second capacitor C2 discharges to the LED load; when the bus voltage Vbus is greater than the conduction voltage VF of the LED load, the switch connection circuit 01 is turned off, the unidirectional conduction element is turned on, and the bus voltage supplies power to the LED load and charges the second capacitor C2 through the unidirectional conduction element. Preferably, when the LED load is turned on, the LED load current is greater than the charging current of the first capacitor C1, and the charging current of the first capacitor C1 is greater than the discharge current of the first capacitor C1, so that the input current Iin on the bus is closer to a sine wave, thereby reducing the THD of the input signal.

[0037] Furthermore, the LED driving circuit of the present invention also includes a first switch tube Q1, a second switch tube Q2, a first operational amplifier U1, and a second operational amplifier U2. The first end of the first switch tube Q1 is connected to the second end of the first capacitor C1, and the second end of the first switch tube Q1 is grounded through a first sampling resistor Rcs1. The first operational amplifier U1 performs operational amplification on the first reference voltage Vref1 and the voltage Vcs1 of the first sampling resistor Rcs1 to drive the first switch tube Q1. When the first capacitor C1 is charged, it is used to control the charging current of the first capacitor C1 according to the first reference voltage Vref1. The control end of the first switch tube Q1 is also connected to the first switch S1. The first switch S1 is turned on when the first capacitor C1 is not charged to turn off the first switch tube Q1. The first end of the second switch tube Q2 is connected to the cathode of the LED load, and the second end of the second switch tube Q2 is connected to the second end of the first switch tube Q1. The second operational amplifier U2 performs operational amplification on the second reference voltage Vref2 and the first sampling voltage Vcs1 to drive the second switch tube Q2. When the first capacitor C1 or the bus voltage Vbus supplies power to the LED load, it is used to control the LED load current according to the second reference voltage Vref1. By adjusting the first reference voltage Vref1 and the second reference voltage Vref2, the charging current of the first capacitor C1 and the LED load current can be adjusted.

[0038] Furthermore, in this embodiment of the present invention, the switch connection circuit 01 includes a diode D2 and a switch tube Q3 connected in series, the anode of the diode D2 is connected to the output end of the rectifier circuit, and the cathode of the diode D2 is connected to the second end of the first capacitor C2. When the bus voltage Vbus is less than the voltage VC1 of the first capacitor, and the sum of the bus voltage Vbus and the voltage VC1 of the first capacitor is greater than the turn-on voltage VF of the LED load, the third switch tube Q3 is controlled to be turned on, so that the first capacitor C1 supplies power to the LED load and charges the second capacitor C2 through the switch connection circuit 01; further, the switch connection circuit 01 also includes a resistor R1 and a voltage regulator tube Dz, the resistor R1 is connected between the output end of the rectifier circuit and the control end of the switch tube Q3, and the voltage regulator tube Dz is connected between the control end of the switch tube Q3 and the second end of the first capacitor C1. When the bus voltage Vbus is less than the first capacitor voltage VC1 and the sum of the bus voltage Vbus and the first capacitor voltage VC1 is greater than the conduction voltage VF of the LED load, the gate-source voltage Vgs of the switch tube Q3 reaches the starting threshold, so that the switch tube Q3 is self-conducting. The resistor R1 is selected to have a larger value, which can be set to be greater than a certain threshold, to prevent the discharge current generated when the first capacitor C1 is discharged from flowing into the gate of the switch tube Q3 in large quantities, causing large losses and affecting the LED power supply; the switch connection circuit 01 also includes a switch S2, which is turned on when the first capacitor C1 is not discharged, and is used to pull the gate of the second switch tube Q2 to the ground to turn off the second switch tube Q2. When the bus voltage Vbus reaches a certain value, the switch connection circuit 01 can achieve self-conduction, simplifying the circuit structure.

[0039] The LED driving circuit of the present invention only includes two capacitors and two switch tubes, and adopts fewer electronic devices; the present invention controls the charging and discharging of the first capacitor C1 and the second capacitor C2 according to the size of the bus voltage Vbus, and selects the first capacitor C1, the second capacitor C2 or the bus voltage Vbus to power the LED load, and the circuit structure is simple; the present invention can achieve the control effect of low THDi and high PF, the THDi can reach less than 25%, and the PF can reach more than 0.95; the LED load of the present invention adopts a single-stage lamp bead, and the requirement of low flicker can also be achieved.

[0040] Reference Figure 2 , which illustrates the schematic diagram of Embodiment 2 of the LED driving circuit of the present invention. Figure 2 and Figure 1 The difference lies in the different implementation methods of the switch connection circuit 01. Figure 2 and Figure 1The same parts will not be repeated. The switch connection circuit 01 in this embodiment also includes a switch tube Q3, a diode D2 and a switch S2, and also includes an operational amplifier U3 and a sampling resistor Rcs2. The switch tube Q3 and the diode D2 are connected in series, the anode of the diode D2 is connected to the output end of the rectifier circuit, and the cathode of the diode D2 is connected to the second end of the first capacitor C1. The switch S2 is turned on when the first capacitor C1 is not discharged, and the gate of the second switch tube Q2 is pulled to the ground to turn off the second switch tube Q2. The sampling resistor Rcs2 is connected in series with the switch tube Q3 to sample the current flowing through the switch tube Q3. The sampling resistor Rcs2 is selected to have a smaller value, which can be set to be less than a certain threshold to avoid causing large losses. The operational amplifier U3 performs operational amplification on the third reference voltage Vref3 and the sampling voltage Vcs2 at the connection end of the resistor Rcs2 and the switch tube Q3. The output end of the operational amplifier U3 is connected to the gate of the switch tube Q3 to drive the switch tube Q3 to control the current flowing through the switch tube Q3. Compared to Figure 1 , Figure 2 Optimized Figure 1 The loss caused by the middle resistor R1 further improves the efficiency.

[0041] Reference Figure 3 , illustrates the working timing diagram of the LED driving circuit of the present invention, combined with Figure 1The working timing of the LED driving circuit is described. In the figure, Iin is the input current on the bus, Vcs1 is the voltage across the sampling resistor Rcs1, VC1 is the voltage of the first capacitor C1, VF is the conduction voltage of the LED load, and Vbus is the bus voltage. At the initial moment, the bus voltage Vbus starts to rise from the bottom. Before time t0, Vbus < VC1 and VC1 + Vbus < VF, both the switch connecting circuit 01 and the diode D1 are turned off, the first capacitor C1 neither charges nor discharges, and both the input current Iin and the voltage Vcs1 are 0; in the time period from t0 to t1, Vbus < VC1 and VC1 + Vbus > VF, the first capacitor C1 discharges to the LED load, the input current Iin is equal to the discharge current of the first capacitor C1 and is equal to the LED load current. In this stage, the voltage Vcs1 represents the LED load current, and both the input current Iin and the voltage Vcs1 are greater than zero and have the same waveform; in the time period from t1 to t2, Vbus > VC1 and Vbus < VF, the first capacitor C1 charges, the input current Iin is equal to the charging current of the first capacitor C1. In this stage, the voltage Vcs1 represents the charging current of the first capacitor C1, and both the input current Iin and the voltage Vcs1 are greater than zero and have the same waveform; in the time period from t1 to t2, Vbus > VF, the bus voltage Vbus supplies power to the LED load, the input current Iin is equal to the current of the LED load. In this stage, the voltage Vcs1 represents the LED load current, and both the input current Iin and the voltage Vcs1 are greater than zero and have the same waveform. The working states are the same at the symmetric positions on both sides of the peak value of the bus voltage Vbus. The signal waveform in the time period from t3 to t4 is the same as that in the time period from t1 to t2, and the signal waveform in the time period from t4 to t5 is the same as that in the time period from t0 to t1, and no further description will be given. The present invention can adjust the magnitude of the input current Iin by adjusting the magnitudes of the first reference voltage Vref1 and the second reference voltage Vref2, making the waveform of the input current Iin closer to a sine wave, thereby optimizing the system THDi.

[0042] The present invention improves the PF of the system, reduces the THDi. At the same time, when the bus voltage Vbus is relatively low, it can also discharge through the capacitor C1 to supply power to the LED, improving the driving efficiency. Moreover, the present invention has fewer power switch tubes and a simple structure.

[0043] Furthermore, the present invention also provides an illumination circuit, including the above-described LED driving circuit for driving the LED load, so as to improve the illumination efficiency of the illumination circuit, optimize the THDi of the illumination circuit, reduce the stroboscopic effect of the lamp beads, and make the illumination circuit meet the relevant standards.

[0044] Although the embodiments are described and illustrated separately above, some common technologies are involved. It is the opinion of ordinary technicians in this field that the embodiments can be replaced and integrated. If the content is not clearly recorded in one of the embodiments, reference can be made to another recorded embodiment.

[0045] The above-described implementation methods do not constitute a limitation on the protection scope of the technical solution. Any modification, equivalent replacement and improvement made within the spirit and principle of the above-described implementation methods shall be included in the protection scope of the technical solution.

Claims

1. An LED driving circuit, used to drive an LED load, wherein an AC input voltage is converted into a bus voltage through a rectifier circuit, and is characterized in that: The device comprises a first capacitor, a unidirectional conductive element, a switch connection circuit and a second capacitor, wherein a first end of the first capacitor is connected to an output end of the rectifier circuit through the unidirectional conductive element and is connected to an anode of an LED load, and a second end of the first capacitor is connected to the output end of the rectifier circuit through the switch connection circuit; The second capacitor is connected in parallel across the LED load; Wherein, the on / off state of the switch connection circuit and the unidirectional conducting element is controlled according to the magnitude of the bus voltage.

2. The LED driving circuit according to claim 1, characterized in that: When the bus voltage is less than the first capacitor voltage, and the sum of the bus voltage and the first capacitor voltage is less than the conduction voltage of the LED load, the switch connection circuit and the unidirectional conduction element are turned off, and the first capacitor is neither charged nor discharged.

3. The LED driving circuit according to claim 1, characterized in that: When the bus voltage is less than the first capacitor voltage, and the sum of the bus voltage and the first capacitor voltage is greater than the conduction voltage of the LED load, the switch connection circuit is turned on, the unidirectional conduction element is turned off, and the first capacitor discharges to the LED load.

4. The LED driving circuit according to claim 1, characterized in that: When the bus voltage is greater than the voltage of the first capacitor and less than the conduction voltage of the LED load, the switch connection circuit is turned off, the unidirectional conduction element is turned on, and the bus voltage charges the first capacitor.

5. The LED driving circuit according to claim 1, characterized in that: When the bus voltage is greater than the conduction voltage of the LED load, the switch connection circuit is turned off, the unidirectional conducting element is turned on, and the bus voltage supplies power to the LED load.

6. The LED driving circuit according to claim 1, characterized in that: When the LED load is turned on, the LED load current is greater than the charging current of the first capacitor, and the charging current of the first capacitor is greater than the discharging current of the first capacitor.

7. The LED driving circuit according to claim 1, characterized in that: It also includes a first switch tube, which is connected between the second end of the first capacitor and the first sampling resistor; When the bus voltage is greater than the voltage of the first capacitor and the bus voltage is less than the turn-on voltage of the LED load, the first switch tube is turned on.

8. The LED driving circuit according to claim 7, characterized in that: It also includes a first operational amplifier, which performs operational amplification on the first reference voltage and the voltage of the first sampling resistor, and the output end of the first operational amplifier is connected to the control end of the first switch tube.

9. The LED driving circuit according to claim 1, characterized in that: It also includes a second switch tube, wherein the second switch tube is connected between the cathode of the LED load and the first sampling resistor; When the bus voltage is less than the first capacitor voltage and the sum of the bus voltage and the first capacitor voltage is greater than the turn-on voltage of the LED load, or when the bus voltage is greater than the turn-on voltage of the LED load, the second switch tube is turned on.

10. The LED driving circuit according to claim 9, characterized in that: It also includes a second operational amplifier, which performs operational amplification on the second reference voltage and the voltage of the first sampling resistor, and the output end of the second operational amplifier is connected to the control end of the second switch tube.

11. The LED driving circuit according to claim 1, characterized in that: The unidirectional conducting element includes a first diode, an anode of the first diode is connected to the output end of the rectifier circuit, and a cathode of the first diode is connected to the first end of the first capacitor.

12. The LED driving circuit according to claim 1, characterized in that: The switch connection circuit includes a second diode and a third switch tube, the second diode and the third switch tube are connected in series, the anode of the second diode is connected to the output end of the rectifier circuit, and the cathode of the second diode is connected to the second end of the first capacitor; When the bus voltage is less than the voltage of the first capacitor, and the sum of the bus voltage and the voltage of the first capacitor is greater than the turn-on voltage of the LED load, the third switch tube is turned on.

13. The LED driving circuit according to claim 12, characterized in that: The switch connection circuit also includes a first resistor, a first voltage regulator tube and a first switch, wherein the first end of the first resistor is connected to the output end of the rectifier circuit, and the second end of the first resistor is connected to the control end of the third switch tube; the cathode of the first voltage regulator tube is connected to the control end of the third switch tube, and the anode of the first voltage regulator tube is connected to the second end of the first capacitor; The control end of the third switch tube is grounded through the first switch.

14. The LED driving circuit according to claim 12, characterized in that: The switch connection circuit further includes a third operational amplifier and a first switch, wherein the third operational amplifier performs operational amplification on a third reference voltage and a fourth sampling signal representing the fourth switch current, and an output end of the third operational amplifier is connected to a control end of the fourth switch tube; The control end of the fourth switch tube is also grounded through the first switch.

15. A lighting circuit, comprising an LED load, characterized in that: It also includes the LED driving circuit according to any one of claims 1 to 14, used for driving an LED load.

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