Lighting circuit

Abstract

The utility model provides a lighting circuit, comprising a rectification circuit used for rectifying an AC input to obtain an input voltage; the LED load is connected with the output end of the rectifying circuit; a first capacitor connected in series with the LED load; the first end of the first switch tube is connected with an LED load, and the second end is connected with a low potential; the first end of the second switch tube is connected with the first capacitor, and the second end is connected with low potential; the anode of the discharge diode is connected with the anode of the first capacitor, and the cathode is connected with the anode of the LED load. According to the lighting circuit provided by the utility model, the LED load and the first capacitor are connected in series, so that the conduction voltage drop of the LED load is reduced to half of the peak value of the input voltage, the moment when the input current is generated in each period of the input voltage is advanced, the effective range of the input current is widened, and the requirements of high PF and low THDi are further met; and the scheme also meets the stroboscopic requirement.

Description

Technical Field

[0001] The utility model belongs to the field of lighting, and particularly relates to a lighting circuit. Background Art

[0002] In the field of lighting, linear LED solutions are widely used in the prior art due to advantages such as fewer components, no EMI problems, and easier integrated design. Currently, multi-segment linear LED solutions can often achieve high PF (PF>9.5) and low THDi (THDi<25%@120Vac). However, each segment of LED beads in the multi-segment linear LED solution requires stroboscopic elimination, so the cost of stroboscopic elimination processing for the multi-segment linear LED solution is relatively high. The traditional single-segment linear LED solution has a lower cost of stroboscopic elimination, but it is difficult to meet the requirements of high PF and low THDi.

[0003] As Figure 1 shown, the traditional single-segment linear LED solution includes: a rectifier circuit, an LED load, a load switch, a first capacitor connected in parallel across the LED load, and a load current control circuit for driving the load switch. The rectifier circuit is connected to the AC input terminal. The AC input is rectified to obtain an input voltage. The load current will only be reflected from the input terminal when the input voltage is greater than or equal to the conduction voltage drop of the load (i.e., the input current is greater than zero), and the conduction voltage drop of its LED load is close to the peak value of the input voltage. When the input voltage is less than the conduction voltage drop of the LED load, the first capacitor supplies power to the LED load. As Figure 2 shown, the effective range of the input current in the traditional single-segment linear LED solution is small (the input current is only generated during the T2 period in each cycle of the input voltage), and it is impossible to meet the requirements of high PF and low THDi.

[0004] Therefore, if a single-segment linear LED solution with high PF, low THDi, and meeting the stroboscopic requirements can be designed, the cost can be effectively reduced and the design can be simplified. Summary of the Utility Model

[0005] In order to solve the technical problem in the prior art that there is a lack of a single-segment linear LED solution with high PF, low THDi, and meeting the stroboscopic requirements, the utility model provides a lighting circuit, including:

[0006] A rectifier circuit for rectifying the AC input to obtain an input voltage;

[0007] An LED load connected to the output terminal of the rectifier circuit;

[0008] A first capacitor connected in series with the LED load;

[0009] A first switching tube, with the first end connected to the LED load and the second end connected to a low potential, and the input voltage supplies power to the LED load through the first switching tube;

[0010] A second switching transistor, having a first end connected to the first capacitor and a second end connected to a low potential, wherein the input voltage supplies power to both the LED load and the first capacitor through the second switching transistor;

[0011] A discharge diode, having a positive electrode connected to the positive electrode of the first capacitor and a negative electrode connected to the positive electrode of the LED load, wherein the first capacitor supplies power to the LED load through the discharge diode;

[0012] Wherein, the conduction voltage drop of the LED load is close to half of the peak value of the input voltage, so that the moment of generating the input current is advanced in each cycle of the input voltage.

[0013] Further, a driving circuit is further included. The driving circuit takes a point from any node between the rectifying circuit and the negative electrode of the LED load to generate a supply voltage, and generates a bias voltage according to the supply voltage.

[0014] The driving circuit controls the on / off of the first switching transistor and the second switching transistor according to a reference voltage, a sampling voltage representing the LED load current, and the bias voltage.

[0015] Further, the reference voltage is a preset threshold value, or the reference voltage is generated according to the input voltage, and the reference voltage changes following the input voltage.

[0016] Further, the driving circuit, the first switching transistor, and the second switching transistor are integrally arranged on a single chip.

[0017] Further, a sampling resistor is further included. The second ends of the first switching transistor and the second switching transistor are connected to the sampling resistor, the other end of the sampling resistor is connected to a reference ground, and the voltage of the sampling resistor is the sampling voltage.

[0018] Further, a second diode and a third diode are further included. The positive electrode of the second diode is connected to the negative electrode of the first capacitor and the positive electrode is connected to the first end of the second switching transistor, and the positive electrode of the third diode is connected to the second end of the first switching transistor and the negative electrode is connected to the negative electrode of the first capacitor.

[0019] Further, the driving circuit includes a first operational amplifier and a second operational amplifier. The first operational amplifier amplifies the error between a first voltage and the reference voltage to control the on / off of the first switching transistor, and the second operational amplifier amplifies the error between the reference voltage and the sampling voltage to control the on / off of the second switching transistor.

[0020] Wherein, the first voltage is obtained by superimposing the sampling voltage and the bias voltage.

[0021] Further, the driving circuit further includes a first current source and a first resistor. The first current source outputs a first current according to the supply voltage, and the first current flows through the first resistor to generate the bias voltage.

[0022] Further, a voltage dividing unit connected to the input voltage is further included, and the voltage dividing unit outputs the reference signal proportional to the input voltage.

[0023] Further, a fourth diode is further included. The fourth diode is connected in series between the LED load and the first capacitor, and the negative electrode of the fourth diode is connected to the positive electrode of the first capacitor.

[0024] The lighting circuit proposed by the present utility model, by designing the LED load and the first capacitor in series, can reduce the conduction voltage drop of the LED load in the lighting circuit to half of the peak value of the input voltage, so that the generation time of the input current in each cycle of the input voltage is advanced and the effective range of the input current is broadened. Furthermore, the lighting circuit meets the requirements of high PF and low THDi. At the same time, the lighting circuit controls the input voltage to supply power to the LED load, the input voltage to supply power to the LED load and the first capacitor, and the first capacitor to supply power to the LED load in stages in each cycle of the input voltage, so that the stroboscopic effect of the lighting circuit meets the requirements. Description of the Drawings

[0025] Figure 1 is a single-stage linear LED solution in the prior art;

[0026] Figure 2 is Figure 1 the waveform diagram of the input current in;

[0027] Figure 3 is the structural diagram of the lighting circuit proposed by the present utility model;

[0028] Figure 4 is the first circuit structure of the lighting circuit;

[0029] Figure 5 is Figure 4 the waveform diagram of the input current in;

[0030] Figure 6 is the second circuit structure of the lighting circuit;

[0031] Figure 7 is Figure 6 the waveform diagram of the input current in. Detailed Embodiments

[0032] To facilitate the understanding of the present utility model, the present utility model will be described more comprehensively below with reference to the relevant drawings. The preferred embodiments of the present utility model are shown in the drawings. However, the present utility model can be implemented in different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the understanding of the disclosure of the present utility model more thorough and comprehensive.

[0033] In order to solve the problem that the existing single-stage linear LED lighting solution cannot meet the requirements of high PF and low THDi, the present utility model proposes a lighting circuit, as Figure 3 shown, comprising:

[0034] A rectifier circuit that rectifies the AC input to obtain an input voltage;

[0035] An LED load connected to the output terminal of the rectifier circuit;

[0036] A first capacitor connected in series with the LED load;

[0037] A first switching tube, with the first end connected to the LED load and the second end connected to a low potential, and the input voltage supplies power to the LED load through the first switching tube;

[0038] A second switching tube, with the first end connected to the first capacitor and the second end connected to a low potential, and the input voltage supplies power to the LED load and the first capacitor simultaneously through the second switching tube;

[0039] A discharge diode, with the positive pole connected to the positive pole of the first capacitor and the negative pole connected to the positive pole of the LED load, and the first capacitor supplies power to the LED load through the discharge diode;

[0040] Wherein, the conduction voltage drop of the LED load is close to half of the peak value of the input voltage, advancing the moment when the input current is generated in each cycle of the input voltage.

[0041] In summary, the lighting circuit proposed by the present utility model, by designing the series connection of the LED load and the first capacitor, can reduce the conduction voltage drop of the LED load in the lighting circuit to half of the peak value of the input voltage, thereby advancing the moment when the input current is generated in each cycle of the input voltage, broadening the effective range of the input current, and further enabling the lighting circuit to meet the requirements of high PF and low THDi. At the same time, the lighting circuit controls the input voltage to supply power to the LED load, the input voltage to supply power to the LED load and the first capacitor, and the first capacitor to supply power to the LED load in stages in each cycle of the input voltage, thereby making the stroboscopic effect of the lighting circuit meet the requirements.

[0042] Furthermore, in combination with Figure 4 a further explanatory description is made for the lighting circuit proposed by the present utility model.

[0043] In the first embodiment, asFigure 4 As shown in Figure 4 , the lighting circuit proposed by the present utility model includes:

[0044] A rectifying circuit that rectifies the AC input to obtain an input voltage;

[0045] An LED load connected to the output terminal of the rectifying circuit;

[0046] A first capacitor C1 connected in series with the LED load;

[0047] A first switching transistor M1, the drain of the first switching transistor M1 is connected to the negative electrode of the LED load, the source of the first switching transistor M1 is connected to the sampling resistor Rcs and then grounded, and the gate of the first switching transistor M1 is connected to the driving circuit;

[0048] A second switching transistor M2, the drain of the second switching transistor M2 is connected to the negative electrode of the first capacitor C1, the source of the second switching transistor M2 is connected to the sampling resistor Rcs and then grounded, and the gate of the second switching transistor M2 is connected to the driving circuit;

[0049] A discharge diode D1, the positive electrode of the discharge diode D1 is connected to the positive electrode of the first capacitor C1, and the negative electrode of the discharge diode D1 is connected to the positive electrode of the LED load;

[0050] A fourth diode D4 is connected in series between the LED load and the first capacitor C1, and the negative electrode of the fourth diode D4 is connected to the positive electrode of the first capacitor C1 to prevent the first capacitor C1 from discharging when the input voltage supplies power to the LED load through the first switching transistor M1;

[0051] The driving circuit takes power from any node between the rectifying circuit and the negative electrode of the LED load to generate a supply voltage, and generates a bias voltage according to the supply voltage. The driving circuit controls the on and off of the first switching transistor M1 and the second switching transistor M2 according to the reference voltage, the sampling voltage representing the input voltage, and the bias voltage.

[0052] Wherein, the conduction voltage drop VF of the LED load is close to half of the peak value of the input voltage Vin, the sum of the conduction voltage drop VF of the LED load and the rated voltage VC1 of the first capacitor C1 is close to the peak value of the input voltage Vin, and the rated voltage VC1 of the first capacitor C1 is greater than the conduction voltage drop VF of the LED load.

[0053] The working principle of the above lighting circuit is as follows: when the input voltage is less than the conduction voltage drop VF of the LED load, the discharge diode D1 conducts, and the drive circuit controls the first switching transistor M1 to conduct. A current path is formed by the first capacitor C1, the discharge diode D1, the LED load, the first switching transistor M1, and the sampling resistor Rcs, and the first capacitor C1 discharges to supply power to the LED load. When the input voltage rises to be greater than or equal to the conduction voltage drop VF of the LED load, the discharge diode D1 cuts off, and the drive circuit controls the first switching transistor M1 to conduct. A current path is formed by the input voltage Vin, the LED load, the first switching transistor M1, and the sampling resistor Rcs, and the input voltage Vin supplies power to the LED load. When the input voltage Vin continues to rise to be greater than or equal to the sum of the conduction voltage drop VF of the LED load and the voltage of the first capacitor C1, the drive circuit controls the first switching transistor M1 to turn off and the second switching transistor M2 to conduct. A current path is formed by the input voltage Vin, the LED load, the first capacitor C1, the second switching transistor M2, and the sampling resistor Rcs, and the input voltage Vin supplies power to the LED load and the first capacitor C1 simultaneously.

[0054] Specifically, as Figure 5 shown, taking one cycle of the input voltage as an example, during T1: the input voltage is less than the conduction voltage drop VF of the LED load, the first capacitor C1 discharges to supply power to the LED load, and the input current is 0. During T2: the input voltage is greater than or equal to the conduction voltage drop VF of the LED load, the input voltage Vin supplies power to the LED load, and the input current is I1. During T3: the input voltage Vin is greater than or equal to the sum of the conduction voltage drop VF of the LED load and the voltage of the first capacitor C1, the input voltage Vin supplies power to the LED load and the first capacitor C1 simultaneously, and the input current is I2. The T4 stage is the same as the T2 stage, and the T5 stage is the same as the T1 stage.

[0055] It can be seen from this that compared with Figure 5 and Figure 2 , compared with the prior art, in the utility model, the conduction voltage drop of the LED load is reduced to half of the peak value of the input voltage Vin, so that the generation moment of the input current is significantly advanced in each cycle of the input voltage Vin. Furthermore, the lighting circuit proposed by the utility model can achieve high PF and low THDi. Specifically, as Figure 2 shown, in the prior art, the effective range of the input current corresponds to the stage where the input voltage Vin is greater than or equal to the LED load (i.e., the T2 stage), and the conduction voltage drop of its LED load is close to the peak value of the input voltage Vin. As Figure 5 shown, in the utility model, the effective range of the input current corresponds to the stage where the input voltage Vin is greater than or equal to the LED load (the T2 stage, the T3 stage, and the T4 stage). However, in this lighting circuit, the conduction voltage drop of the LED load is reduced to half of the peak value of the input voltage Vin, the generation moment of the input current is significantly advanced, and the effective range of the input current is significantly broadened.

[0056] Further, in the first embodiment, the driving circuit includes a first operational amplifier U1, a second operational amplifier U2, a first current source, and a first resistor R1. The first current source generates a first current according to the supply voltage, and the first current flows through the first resistor R1 to generate a bias voltage. The non-inverting input terminal of the first operational amplifier U1 receives a reference voltage Vref, the inverting input terminal of the first operational amplifier U1 receives a first voltage V1, and the output terminal of the first operational amplifier U1 is connected to the gate of the first switching transistor M1. The first voltage is the sum of the bias voltage and the sampling voltage Vcs. The non-inverting input terminal of the second operational amplifier U2 receives the reference voltage Vref, and the inverting input terminal of the second operational amplifier U2 receives the sampling voltage Vcs. The voltage of the sampling resistor Rcs is the sampling voltage Vcs, and the reference voltage Vref is a preset threshold with a fixed value.

[0057] When the input voltage Vin is greater than or equal to the conduction voltage drop of the LED load, there is a voltage drop between the drain and source of the first switching transistor M1. At this time, the first voltage V1 is less than the reference voltage Vref, the first operational amplifier U1 outputs a positive voltage, and the first switching transistor M1 conducts. At this time, the voltage drop between the drain and source of the second switching transistor M2 is zero, and the second switching transistor M2 turns off. When the input voltage Vin is greater than the sum of the conduction voltage drop VF of the LED load and the voltage of the first capacitor C1, there is a voltage drop between the drain and source of the second switching transistor M2, and the second switching transistor M2 conducts. At this time, according to the working characteristic of the virtual short of the operational amplifier, when the second operational amplifier U2 is stable, the voltage of the non-inverting input terminal is equal to the voltage of the inverting input terminal, that is, the sampling voltage Vcs is equal to the reference voltage Vref. Then, the first voltage V1 (sampling voltage Vcs + bias voltage) is greater than the reference voltage Vref, and the first operational amplifier U1 outputs a negative voltage, and the first switching transistor M1 turns off. When the input voltage Vin is less than the conduction voltage drop of the LED load, the discharge diode D1 conducts, there is a voltage drop between the drain and source of the first switching transistor M1. At this time, the first voltage V1 is less than the reference voltage Vref, the first operational amplifier U1 outputs a positive voltage, and the first switching transistor M1 conducts. At this time, the voltage drop between the drain and source of the second switching transistor M2 is zero, and the second switching transistor M2 turns off.

[0058] In the second embodiment, in order to further improve the PF of the lighting circuit and reduce the THDi of the lighting circuit, as Figure 6 shown, the voltage dividing unit composed of series voltage dividing resistors outputs a reference signal Vref proportional to the input voltage. Thus, as Figure 7 shown, the input current changes sinusoidally, which is different from the segmented change in the first embodiment. The change of the input current is smoother, so that the PF of the lighting circuit is higher and the THDi is lower. The other structures of the lighting circuit are the same as those in the first embodiment and will not be elaborated here.

[0059] Further, when the first switching transistor M1, the second switching transistor M2 and the driving circuit are integrated on a single chip, due to the presence of the body diode of the second switching transistor M2, a negative current will be generated inside the chip when the first capacitor supplies power to the LED load (the current path will flow from the body diode of the second switching transistor M2 to the negative electrode of the first capacitor). To avoid this situation, the lighting circuit further includes a second diode D2 and a third diode D3. The positive electrode of the second diode D2 is connected to the negative electrode of the first capacitor C1, and the negative electrode is connected to the drain of the second switching transistor M2. The positive electrode of the third diode D3 is grounded, and the negative electrode is connected to the negative electrode of the first capacitor.

[0060] It should be noted that the conduction voltage drop of the LED load is close to half of the peak value of the input voltage. Specifically, it can be quantified that the conduction voltage drop of the LED load fluctuates around a certain percentage of half of the peak value of the input voltage. For example, the value range of the conduction voltage drop of the LED load is: half of the peak value of the input voltage * (1 - X%) to half of the peak value of the input voltage * (1 + X%). The specific value of X can be set according to the specific parameters of each device in the actual lighting circuit. For example, X can take values such as 10, 15, 20, etc. For example, taking the AC input of 230V as an example, the value range of the conduction voltage drop of the LED load is: half of the peak value of the input voltage * 80% to half of the peak value of the input voltage * 85%.

[0061] It should be added that the specific embodiments and the corresponding legends given are only a way to describe the implementation method of the present invention, and do not limit the specific structure of the embodiments of the present invention. Without departing from the principle and essence of the present invention, various changes or modifications can be made to these embodiments, but these changes and modifications all fall within the protection scope of the present invention.

[0062] Although the above embodiments are described and explained separately, for the common technologies involved, in the view of those of ordinary skill in the art, substitutions and integrations can be made between the embodiments. For the content not clearly recorded in one of the embodiments, reference can be made to the other embodiment with records.

[0063] The above-described embodiments do not constitute a limitation on the protection scope of the technical solution. Any modifications, equivalent substitutions, and improvements made within the spirit and principle of the above embodiments shall be included in the protection scope of the technical solution.

Claims

1. An illumination circuit, characterized in that, Comprising: A rectifier circuit that rectifies an AC input to obtain an input voltage; An LED load connected to the output terminal of the rectifier circuit; A first capacitor connected in series with the LED load; A first switching transistor, with its first terminal connected to the LED load and its second terminal connected to a low potential, and the input voltage supplies power to the LED load through the first switching transistor; A second switching transistor, with its first terminal connected to the first capacitor and its second terminal connected to a low potential, and the input voltage supplies power to the LED load and the first capacitor simultaneously through the second switching transistor; A discharge diode, with its positive electrode connected to the positive electrode of the first capacitor and its negative electrode connected to the positive electrode of the LED load, and the first capacitor supplies power to the LED load through the discharge diode; Wherein, the conduction voltage drop of the LED load is close to half of the peak value of the input voltage, advancing the moment when the input current is generated in each cycle of the input voltage.

2. The lighting circuit according to claim 1, wherein Further comprising a drive circuit that takes a point from any node between the rectifier circuit and the negative electrode of the LED load to generate a supply voltage, and generates a bias voltage based on the supply voltage, The drive circuit controls the on / off of the first switching transistor and the second switching transistor according to a reference voltage, a sampling voltage representing the LED load current, and the bias voltage.

3. The lighting circuit according to claim 2, wherein The reference voltage is a preset threshold value, or the reference voltage is generated according to the input voltage, and the reference voltage changes following the input voltage.

4. The lighting circuit according to claim 2, characterized in that, The drive circuit, the first switching transistor, and the second switching transistor are integrally provided on a single chip.

5. The lighting circuit according to claim 2, wherein, Further comprising a sampling resistor, with the second terminals of the first switching transistor and the second switching transistor connected to the sampling resistor, and the other end of the sampling resistor connected to a reference ground, and the voltage of the sampling resistor is the sampling voltage.

6. The lighting circuit according to claim 4, wherein Further comprising a second diode and a third diode, with the positive electrode of the second diode connected to the negative electrode of the first capacitor and its positive electrode connected to the first terminal of the second switching transistor, and the positive electrode of the third diode connected to the second terminal of the first switching transistor and its negative electrode connected to the negative electrode of the first capacitor.

7. The lighting circuit according to claim 2, wherein, The drive circuit includes a first operational amplifier and a second operational amplifier. The first operational amplifier performs error amplification on a first voltage and the reference voltage to control the on / off of the first switching transistor, and the second operational amplifier performs error amplification on the reference voltage and the sampling voltage to control the on / off of the second switching transistor, Wherein, the first voltage is obtained by superimposing the sampling voltage and the bias voltage.

8. The lighting circuit according to claim 7, characterized in that, The drive circuit further includes a first current source and a first resistor. The first current source outputs a first current according to the supply voltage, and the first current flows through the first resistor to generate the bias voltage.

9. The lighting circuit according to claim 3, wherein Further comprising a voltage dividing unit connected to the input voltage, and the voltage dividing unit outputs the reference voltage proportional to the input voltage.

10. The lighting circuit according to claim 1, wherein Further comprising a fourth diode, with the fourth diode connected in series between the LED load and the first capacitor, and the negative electrode of the fourth diode connected to the positive electrode of the first capacitor.

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