High-efficiency and constant-current power conversion circuit and lighting device

Abstract

The utility model relates to the technical field of LED driving, and discloses a high-efficiency and constant-current power conversion circuit and a lighting device, and the power conversion circuit comprises an isolation flyback unit, a constant-current source unit, a voltage sampling unit and a feedback unit. During actual use, the power consumption of the constant current source unit is irrelevant to the voltage drop of the LED load unit, the influence of the voltage drop of the LED load unit on the power consumption of the constant current source unit can be avoided, and when the voltage drop of the LED load unit is reduced or lower than the designed rated voltage drop of the lighting device during actual use of the lighting device, the power consumption of the constant current source unit is reduced. The efficiency reduction amplitude of the LED load unit is reduced, the power utilization rate is higher, and electric energy can be further saved.

Description

TECHNICAL FIELD

[0001] The utility model relates to LED drive technical field, concretely relates to a high efficiency and constant current's power conversion circuit and lighting device. BACKGROUND

[0002] With people's understanding of LED stroboscopic hazards more and more, more and more LED lamps need to be put out without output current ripple LED drive voltage, and the medium and large power power supply meets the high power factor and low harmonic requirement.

[0003] Based on the above consideration, the existing medium and large power isolation power supply solution is divided into the following two schemes according to the applicable power:

[0004] Scheme one: for the product for medium and high power (more than 50W), the isolation power supply includes two-stage circuit, respectively, the front PFC circuit plus the DCDC circuit of the rear stage, and the disadvantage of this scheme is that the cost is too high;

[0005] Scheme two: for the product of small and medium power (between 20-50W), generally adopt the traditional single-stage flyback control type constant voltage circuit cooperates with the linear constant current chip (such as the PM2014 of source micro semiconductor) and the constant current source (the following detection constant current source) composed of the set resistance, that is, the constant current source determines the output current, the LED voltage drop and the voltage drop on the constant current source are equal to the output voltage of the power supply, and the circuit of this scheme is as shown in Figure 1 , Figure 1 The isolation flyback unit, constant current source unit, sampling unit and feedback unit in it compose the power conversion circuit.

[0006] For Figure 1 Circuit, the input AC voltage is output by the traditional isolation flyback unit, the sampling unit samples the output voltage of the isolation flyback unit and outputs the sampling signal, the sampling signal is obtained by the feedback unit and is given to the control chip (such as the PM3203 of source micro semiconductor) of the isolation flyback unit to output control voltage, and the isolation flyback unit obtains the control signal and stabilizes the output voltage, that is, the output voltage between the electrolytic capacitor, this is the typical isolation flyback constant voltage circuit.

[0007] Obviously, the so-called constant voltage circuit, the output voltage is constant, that is, the LED voltage drop of the load LED unit plus the voltage drop of the constant current unit is constant.When the LED lamp bead of the load LED unit works for a period of time, because of heating or if you want to use the constant voltage power supply to drive the LED lamp string with lower design rated value, the voltage drop on the constant current unit will increase.The efficiency of the whole constant current unit η = V LED / Vo*η CV ;Wherein V LED It is the LED voltage drop, Vo is the output voltage of the isolation flyback unit, η CVIt refers to the efficiency of the isolated flyback unit. For a given constant voltage power supply, η CV It is certain, therefore V LED The larger the proportion of Vo, the higher the efficiency; the power in the constant current unit is entirely a loss. When V LED When V decreases LED / Vo's rapid decline leads to a rapid decline in efficiency, but what's worse is V LED The reduced power is entirely converted into the power consumption of the constant current unit, which generates more heat. Because the constant current unit is connected in series with the load LED unit, they are usually arranged together in the layout. This results in a higher local ambient temperature around the LED beads of the load LED unit, further reducing the voltage drop of the LED. Utility Model Content

[0008] In view of the shortcomings of the prior art, the present invention provides a high-efficiency and constant current power conversion circuit and a lighting device. The technical problem to be solved is that the power loss of the constant current unit in the existing power conversion circuit is easily affected by the LED beads of the load LED unit, and the applicable range is small.

[0009] To solve the above technical problems, in the first aspect, this utility model provides a high-efficiency and constant-current power conversion circuit, including an isolated flyback unit, a constant current source unit, a voltage sampling unit, and a feedback unit;

[0010] The isolated flyback unit is used to convert the input AC voltage into the operating voltage;

[0011] The constant current source unit includes a power supply terminal and a load connection terminal. The power supply terminal is electrically connected to the working voltage output terminal of the isolated flyback unit, and the load connection terminal is used to electrically connect to the LED load unit. The constant current source unit generates a constant driving current flowing through the LED load unit based on the working voltage.

[0012] The voltage sampling unit is used to detect the voltage at the load connection terminal and input the sampled voltage to the feedback unit;

[0013] The feedback unit adjusts the control signal at the feedback terminal of the isolation flyback unit based on the magnitude of the sampled voltage, and the isolation flyback unit adjusts the operating voltage based on the control signal.

[0014] In some embodiments of the first aspect, the isolated flyback unit comprises a rectifier bridge BD for converting an input alternating voltage AC into a direct voltage, and a control chip U1 of model PM3203, a direct voltage output end of the rectifier bridge BD is electrically connected with one end of a capacitor C1, one end of a resistor R1, one end of a capacitor C2, one end of a resistor R2, and one end of a primary winding N1 of a transformer T1 respectively, the other end of the capacitor C1 is grounded, the other end of the resistor R1 and an HV pin of the control chip U1 are electrically connected, the other end of the capacitor C2 and the other end of the resistor R2 are electrically connected with a cathode of a diode D1 respectively, an anode of the diode D1 is electrically connected with the other end of the primary winding N1 and a drain of a MOS tube Q1 respectively, a gate of the MOS tube Q1 is electrically connected with a GATE pin of the control chip U1, a source of the MOS tube Q1 is electrically connected with a CS pin of the control chip U1, and is grounded through a resistor R10;

[0015] A FB pin of the control chip U1 is a feedback end of the isolated flyback unit;

[0016] A VDD pin of the control chip U1 is electrically connected with one end of a capacitor C4 and a cathode of a diode D3 respectively, an anode of the diode D3 is electrically connected with one end of a power winding N3 of the transformer T1, the other end of the power winding N3, the other end of the capacitor C4, and a GND pin of the control chip U1 are all grounded;

[0017] One end of a secondary winding N2 of the transformer T1 is electrically connected with an anode of a diode D2, a cathode of the diode D2 is electrically connected with a positive electrode of an electrolytic capacitor C3 for outputting the working voltage, and a negative electrode of the electrolytic capacitor C3 and the other end of the secondary winding N2 are electrically connected for grounding.

[0018] In some embodiments of the first aspect, the MOS tube Q1 is an NMOS tube.

[0019] In some embodiments of the first aspect, the constant current source unit comprises a constant current chip U2 of model PM2014, a VI pin of the constant current chip U2 is the power supply end, a DRN pin of the constant current chip is the load connection end, a GND pin of the constant current chip U2 is grounded, and a CS pin of the constant current chip U2 is grounded through a resistor R11.

[0020] In some embodiments of the first aspect, the voltage sampling unit comprises at least two sampling resistors, all the sampling resistors are connected in series, a first connection end of a first sampling resistor and the load connection end are electrically connected, a second connection end of a last sampling resistor is grounded, and a voltage sampling branch formed by all the series-connected sampling resistors has a voltage sampling node for outputting a sampling voltage.

[0021] In some embodiments of the first aspect, the feedback unit is configured to perform differential amplification on the sampling voltage and a reference voltage, and adjust a size of a control signal at a feedback end of the isolated flyback unit based on a differential amplification value, the control signal being positively correlated with the differential amplification value.

[0022] In some embodiments of the first aspect, the feedback unit comprises an operational amplifier chip U3 of model PM4320 and an optocoupler OPT, a VCC pin of the operational amplifier chip U3 is configured to input the working voltage and is electrically connected to a primary side input end of the optocoupler OPT through a resistor R6, a GND pin of the operational amplifier chip U3 is grounded, an IN- pin of the operational amplifier chip U3 is configured to input the sampling voltage and is electrically connected to one end of a resistor R5, one end of the resistor R5 is electrically connected to one end of a capacitor C5, the other end of the capacitor C5 is electrically connected to a primary side output end of the optocoupler OPT and an OUT pin of the operational amplifier chip U3 respectively, an input end of a secondary side of the optocoupler OPT is electrically connected to the feedback end of the isolated flyback unit, and an output end of the secondary side of the optocoupler OPT is grounded.

[0023] In some embodiments of the first aspect, the feedback unit comprises an operational amplifier and an optocoupler OPT, a positive input end of the operational amplifier is configured to input a reference voltage, the working voltage is input to a primary side input end of the optocoupler OPT through a resistor R6, a negative input end of the operational amplifier is configured to input the sampling voltage and is electrically connected to one end of a resistor R5, one end of the resistor R5 is electrically connected to one end of a capacitor C5, the other end of the capacitor C5 is electrically connected to a primary side output end of the optocoupler OPT and an OUT pin of the operational amplifier chip U3 respectively, an input end of a secondary side of the optocoupler OPT is electrically connected to the feedback end of the isolated flyback unit, and an output end of the secondary side of the optocoupler OPT is grounded.

[0024] In the second aspect, the utility model provides a kind of lighting device, including the power conversion circuit of high efficiency and constant current of above-mentioned, still including LED load unit, the input end of the LED load unit and the working voltage output end of the isolated flyback unit are electrically connected, and the output end of the LED load unit and the load connection end are electrically connected.

[0025] In some embodiments of the second aspect, the LED load unit comprises a plurality of serially connected LED lamp beads, an anode of a first end LED lamp bead is electrically connected to the working voltage output end of the isolated flyback unit, and a cathode of a last end LED lamp bead is electrically connected to the load connection end.

[0026] The advantages of this invention compared to the prior art are as follows: In actual use, the power consumption of the constant current source unit of this invention is independent of the voltage drop of the LED load unit, which can avoid the influence of the voltage drop of the LED load unit on the power consumption of the constant current source unit. Moreover, in actual use, when the voltage drop of the LED load unit becomes smaller or lower than the design rated voltage drop of the lighting device, the efficiency reduction of the LED load unit is smaller, the power utilization rate is higher, and energy can be further saved. Attached Figure Description

[0027] Figure 1 Here is a circuit diagram of an existing lighting system;

[0028] Figure 2 This is a circuit diagram of the lighting device in the embodiment;

[0029] Figure 3 For the present utility model and Figure 1 The relationship between the overall efficiency of the circuit and the voltage drop of the LED load unit is shown in the graph. Detailed Implementation

[0030] The present invention will now be described in further detail with reference to the accompanying drawings. These drawings are simplified schematic diagrams, illustrating only the basic structure of the present invention, and therefore only show the components relevant to the present invention.

[0031] like Figure 2 As shown, this embodiment provides a high-efficiency and constant-current power conversion circuit, including an isolated flyback unit 1, a constant current source unit 2, a voltage sampling unit 3, and a feedback unit 4;

[0032] The isolated flyback unit 1 is used to convert the input AC voltage into the operating voltage;

[0033] The constant current source unit 2 includes a power supply terminal and a load connection terminal. The power supply terminal is electrically connected to the working voltage output terminal of the isolation flyback unit 1, and the load connection terminal is used to electrically connect to the LED load unit 5. The constant current source unit 2 generates a constant driving current flowing through the LED load unit 5 based on the working voltage.

[0034] Voltage sampling unit 3 is used to detect the voltage at the load connection terminal and input the sampled voltage to feedback unit 4;

[0035] Feedback unit 4 adjusts the control signal magnitude at the feedback terminal of isolation flyback unit 1 based on the magnitude of the sampled voltage, and isolation flyback unit 1 adjusts the magnitude of the operating voltage based on the control signal.

[0036] Specifically, in this embodiment, as Figure 2As shown, the isolation flyback unit 1 includes a rectifier bridge BD and a control chip U1 of PM3203, the rectifier bridge BD is used to convert the input alternating voltage AC into direct current voltage, the direct current voltage output end of the rectifier bridge BD is respectively electrically connected with one end of a capacitor C1, one end of a resistor R1, one end of a capacitor C2, one end of a resistor R2 and one end of a primary winding N1 of a transformer T1, the other end of the capacitor C1 is grounded, the other end of the resistor R1 and the HV pin of the control chip U1 are electrically connected, the other end of the capacitor C2 and the other end of the resistor R2 are respectively electrically connected with the cathode of a diode D1, the anode of the diode D1 is respectively electrically connected with the other end of the primary winding N1 and the drain of a MOS tube Q1, the gate of the MOS tube Q1 is electrically connected with the GATE pin of the control chip U1, the source of the MOS tube Q1 is electrically connected with the CS pin of the control chip U1, and is grounded through a resistor R10;

[0037] The FB pin of the control chip U1 is the feedback end of the isolation flyback unit 1;

[0038] The VDD pin of the control chip U1 is respectively electrically connected with one end of a capacitor C4 and the cathode of a diode D3, the anode of the diode D3 is electrically connected with one end of a supply winding N3 of the transformer T1, the other end of the supply winding N3, the other end of the capacitor C4 and the GND pin of the control chip U1 are all grounded;

[0039] One end of a secondary winding N2 of the transformer T1 is electrically connected with the anode of a diode D2, the cathode of the diode D2 is electrically connected with the positive electrode of an electrolytic capacitor C3, for outputting working voltage; the negative electrode of the electrolytic capacitor C3 and the other end of the secondary winding N2 are electrically connected, for grounding.

[0040] Wherein, the MOS tube Q1 is an NMOS tube.

[0041] Specifically, in the embodiment, as shown in the figure, Figure 2 The constant current source unit 2 includes a constant current chip U2 of PM2014, the VI pin of the constant current chip U2 is a power supply end, the DRN pin of the constant current chip is a load connection end, the GND pin of the constant current chip U2 is grounded, and the CS pin of the constant current chip U2 is grounded through a resistor R11.

[0042] Specifically, in the embodiment, as shown in the figure, Figure 2 The voltage sampling unit 3 includes two sampling resistors, namely a resistor R3 and a resistor R4, the first connection end and the load connection end of the resistor R3 are electrically connected, the second connection end of the resistor R3 and the first connection end of the resistor R4 are electrically connected, for outputting sampling voltage, and the second connection end of the resistor R4 is grounded.

[0043] In certain embodiments, the number of sampling resistors in series in the voltage sampling unit 3 can be set to be greater than 2.

[0044] In addition, in the embodiment, the feedback unit 4 is configured to perform differential amplification on the sampling voltage and the reference voltage, and adjust the size of the control signal at the feedback end of the isolated flyback unit 1 based on the differential amplification value, and the control signal is positively correlated with the differential amplification value.

[0045] In the embodiment, the feedback unit 4 has the following two implementation manners, and the first implementation manner is as follows:

[0046] As shown in Figure 2 , the feedback unit includes an operational amplifier chip U3 with a model number of PM4320 and an optocoupler OPT, the operational amplifier chip U3 internally has a low reference voltage, a VCC pin of the operational amplifier chip U3 is configured to input a working voltage, and the working voltage is electrically connected to a primary side input end of the optocoupler OPT through a resistor R6, a GND pin of the operational amplifier chip U3 is grounded, an IN- pin of the operational amplifier chip U3 is configured to input a sampling voltage and is electrically connected to one end of a resistor R5, one end of the resistor R5 is electrically connected to one end of a capacitor C5, the other end of the capacitor C5 is electrically connected to a primary side output end of the optocoupler OPT and an OUT pin of the operational amplifier chip U3 respectively, an input end of a secondary side of the optocoupler OPT is electrically connected to a feedback end of the isolated flyback unit 1, and an output end of the secondary side of the optocoupler OPT is grounded.

[0047] In the implementation manner, the operational amplifier chip U3 internally automatically generates a reference voltage for differential amplification with the sampling voltage.

[0048] The second implementation manner of the feedback unit 4 is as follows:

[0049] The feedback unit 4 includes an operational amplifier and an optocoupler OPT, a positive input end of the operational amplifier is configured to input a reference voltage, a working voltage is input to a primary side input end of the optocoupler OPT through a resistor R6, a negative input end of the operational amplifier is configured to input a sampling voltage and is electrically connected to one end of a resistor R5, one end of the resistor R5 is electrically connected to one end of a capacitor C5, the other end of the capacitor C5 is electrically connected to a primary side output end of the optocoupler OPT and an OUT pin of the operational amplifier chip U3 respectively, an input end of a secondary side of the optocoupler OPT is electrically connected to a feedback end of the isolated flyback unit, and an output end of the secondary side of the optocoupler OPT is grounded.

[0050] In the implementation manner, the positive input end of the operational amplifier needs to be provided with the reference voltage.

[0051] In addition, the embodiment further provides a lighting device, which includes the high-efficiency and constant-current power conversion circuit, and further includes an LED load unit 5, an input end of the LED load unit 5 is electrically connected to a working voltage output end of the isolated flyback unit 1, and an output end of the LED load unit 5 is electrically connected to a load connection end.

[0052] Wherein, the LED load unit 5 comprises a plurality of serially connected LED lamp beads, the anode of the first end LED lamp bead is electrically connected with the working voltage output end of the isolation flyback unit 1, and the cathode of the last end LED lamp bead is electrically connected with the load connection end.

[0053] To Figure 2 The working process of the lighting device shown in the figure is as follows:

[0054] The working voltage output by the isolation flyback unit 1 is denoted as V OUT , and the voltage drop of the LED load unit 5 is denoted as V LED . When V OUT is greater than V LED , the voltage drop of the constant current source unit 2 is V OUT -V LED . Because the constant current chip U2 takes electricity from the anode of the first end LED lamp bead of the LED load unit 4, the constant current chip U2 has started to work, and the current flowing through the constant current source, i.e., the current of the LED, is set as I V REF is the reference voltage generated inside the constant current chip U2, and the voltage sampling unit 3 transmits the sampled voltage V OUT -V LED to the INV- end of the operational amplifier chip U3 after voltage division, and according to the resistance voltage division principle, the voltage of the INV- is V When the voltage of the INV- is greater than the internal reference voltage V REF_EA , according to the negative feedback characteristics of the operational amplifier chip U3, the OUT pin outputs a decrease, the current flowing through the primary side input end of the optocoupler OPT is greater, the current flowing out of the FB pin of the control chip U1 is greater, the FB pin voltage is lower, i.e., the control signal is lower, the FB pin voltage is lower, the on-duty ratio of the MOS tube Q1 is lower, and then the output voltage of the flyback isolation unit 1 is lowered, so as to achieve balance.

[0055] According to the above working process, it can be obtained that the voltage drop V DRN of the constant current source unit 2 is kept at V Obviously, V DRN is greater than V REF_EA , according to the voltage characteristics of the linear working area of the MOS tube, the voltage V DRN of the MOS tube needs only 1-2V to enter the linear working area. Therefore, if V REF_EA is greater than 2V, it will obviously cause excessive MOS loss and low efficiency. In the embodiment, the reference V REF_EA of the operational amplifier chip U2 is set at 0.1V, which ensures that V DRN can make the MOS tube enter the linear working area with the minimum voltage.

[0056] Based on the above description, the calculation of the constant current source voltage results in the loss of the constant current source being... With V LED Irrelevant. The overall efficiency is denoted as η. LED The calculation formula is as follows:

[0057] Where η CV The efficiency of isolated flyback unit 1 is a constant value, V DRN It is the lowest voltage at which constant current source unit 2 operates in the linear region.

[0058] Assuming the rated voltage drop of the LED in LED load unit 5 is 43V, V DRN The voltage requirement is 2V, and the output efficiency of the isolation flyback unit 1 is 90%; this utility model and Figure 1 The circuit efficiency is calculated, and the schematic diagram is shown below. Figure 3 As shown, where η1(V LED The overall efficiency of the existing circuit and V LED The relationship curve, η2(V LED The overall efficiency and V of this utility model are related. LED Relationship curve;

[0059] from Figure 3 It can be obtained if Figure 1 The circuit is set to isolate the constant voltage output of the anti-reverse unit at 45V. Under rated conditions, the overall efficiency is 43 / 45*90%=86%. When the LED load unit 5 causes heat generation or other reasons, the voltage drops to 45V. LED After the voltage drops to 40V, the efficiency falls to 80%. When connected to LED load unit 5 with an operating voltage of 36V, the efficiency drops directly to 72%, a decrease of 14% compared to the rated voltage drop.

[0060] The rated efficiency of the circuit of this utility model is also 86%. When the LED voltage drop drops to 40V, the efficiency is 40 / 42*0.9=85.7%, which is a slight decrease of 0.3%. When the LED load unit 5 with a working voltage of 36V is connected, the efficiency is 36 / 38*0.9=85.2%, which is 0.8% lower than the rated voltage drop.

[0061] In summary, the power consumption of the constant current source unit 3 of this invention is independent of the voltage drop of the LED load unit 5, thus avoiding the influence of the voltage drop of the LED load unit 5 on the power consumption of the constant current source unit 2. Moreover, in actual use, when the voltage drop of the LED load unit 5 decreases or falls below the design rated voltage drop of the lighting device, the efficiency reduction of the LED load unit 5 is smaller, resulting in higher power utilization and further energy saving.

[0062] The above is disclosed by the utility model, through the above description, the relevant staff can make various changes and modifications without deviating from the technical idea of the utility model. The technical scope of the utility model is not limited to the content of the specification, and the technical scope must be determined according to the scope of claims.

Claims

1. A high-efficiency, constant-current power conversion circuit, characterized in that, The isolation flyback unit, the constant current source unit, the voltage sampling unit and the feedback unit are included. The isolation flyback unit is used for converting input alternating voltage into working voltage. The constant current source unit includes a power supply end and a load connection end, the power supply end is electrically connected with the working voltage output end of the isolation flyback unit, and the load connection end is used for being electrically connected with an LED load unit; the constant current source unit generates constant driving current flowing through the LED load unit based on the working voltage. The voltage sampling unit is used for detecting voltage of the load connection end and inputting sampling voltage to the feedback unit. The feedback unit adjusts the size of the control signal of the feedback end of the isolation flyback unit based on the size of the sampling voltage, and the isolation flyback unit adjusts the size of the working voltage based on the control signal.

2. The high efficiency constant current power conversion circuit of claim 1, wherein, The isolation flyback unit includes a rectifier bridge BD and a control chip U1 with a model of PM3203, the rectifier bridge BD is used for converting input alternating voltage AC into direct current voltage, the direct current voltage output end of the rectifier bridge BD is electrically connected with one end of a capacitor C1, one end of a resistor R1, one end of a capacitor C2, one end of a resistor R2 and one end of a primary winding N1 of a transformer T1 respectively, the other end of the capacitor C1 is grounded, the other end of the resistor R1 is electrically connected with an HV pin of the control chip U1, the other end of the capacitor C2 and the other end of the resistor R2 are electrically connected with a cathode of a diode D1 respectively, an anode of the diode D1 is electrically connected with the other end of the primary winding N1 and a drain of a MOS tube Q1 respectively, a gate of the MOS tube Q1 is electrically connected with a GATE pin of the control chip U1, a source of the MOS tube Q1 is electrically connected with a CS pin of the control chip U1, and is grounded through a resistor R10; An FB pin of the control chip U1 is the feedback end of the isolation flyback unit; A VDD pin of the control chip U1 is electrically connected with one end of a capacitor C4 and a cathode of a diode D3 respectively, an anode of the diode D3 is electrically connected with one end of a power supply winding N3 of the transformer T1, the other end of the power supply winding N3, the other end of the capacitor C4 and a GND pin of the control chip U1 are grounded; One end of a secondary winding N2 of the transformer T1 is electrically connected with an anode of a diode D2, a cathode of the diode D2 is electrically connected with a positive electrode of an electrolytic capacitor C3, and is used for outputting the working voltage; a negative electrode of the electrolytic capacitor C3 and the other end of the secondary winding N2 are electrically connected, and are used for grounding.

3. The high efficiency constant current power conversion circuit of claim 2, wherein, The MOS tube Q1 is an NMOS tube.

4. The high efficiency constant current power conversion circuit of claim 1, wherein, The constant current source unit includes a constant current chip U2 with a model of PM2014, a VI pin of the constant current chip U2 is the power supply end, a DRN pin of the constant current chip is the load connection end, a GND pin of the constant current chip U2 is grounded, and a CS pin of the constant current chip U2 is grounded through a resistor R11.

5. The high efficiency constant current power conversion circuit of claim 1, wherein, The voltage sampling unit includes at least two sampling resistors, all the sampling resistors are connected in series, a first connection end of a first sampling resistor and the load connection end are electrically connected, a second connection end of a last sampling resistor is grounded, and a voltage dividing node on a sampling branch formed by all the series-connected sampling resistors is used for outputting the sampling voltage.

6. A high efficiency and constant current power conversion circuit according to any one of claims 1-5, characterized in that, The feedback unit is configured to perform differential operation amplification on the sampling voltage and a reference voltage, and adjust a size of a control signal of a feedback end of the isolated flyback unit based on a differential amplification value, wherein the control signal is positively correlated with the differential amplification value.

7. The high efficiency constant current power conversion circuit of claim 6 wherein, The feedback unit comprises an operational amplifier chip U3 of model PM4320 and an optoelectronic coupler OPT, a VCC pin of the operational amplifier chip U3 is configured to input the working voltage and is electrically connected to a primary side input end of the optoelectronic coupler OPT through a resistor R6, a GND pin of the operational amplifier chip U3 is grounded, an IN- pin of the operational amplifier chip U3 is configured to input the sampling voltage and is electrically connected to one end of a resistor R5, one end of the resistor R5 is electrically connected to one end of a capacitor C5, the other end of the capacitor C5 is electrically connected to a primary side output end of the optoelectronic coupler OPT and an OUT pin of the operational amplifier chip U3 respectively, an input end of a secondary side of the optoelectronic coupler OPT is electrically connected to the feedback end of the isolated flyback unit, and an output end of the secondary side of the optoelectronic coupler OPT is grounded.

8. The high efficiency constant current power conversion circuit of claim 6, wherein, The feedback unit comprises an operational amplifier and an optoelectronic coupler OPT, a positive input end of the operational amplifier is configured to input a reference voltage, the working voltage is input to a primary side input end of the optoelectronic coupler OPT through a resistor R6, a negative input end of the operational amplifier is configured to input the sampling voltage and is electrically connected to one end of a resistor R5, one end of the resistor R5 is electrically connected to one end of a capacitor C5, the other end of the capacitor C5 is electrically connected to a primary side output end of the optoelectronic coupler OPT and an OUT pin of the operational amplifier chip U3 respectively, an input end of a secondary side of the optoelectronic coupler OPT is electrically connected to the feedback end of the isolated flyback unit, and an output end of the secondary side of the optoelectronic coupler OPT is grounded.

9. An illumination device, characterized by The high-efficiency and constant-current power conversion circuit comprises the high-efficiency and constant-current power conversion circuit of any one of claims 1-8, and further comprises an LED load unit, an input end of the LED load unit is electrically connected to a working voltage output end of the isolated flyback unit, and an output end of the LED load unit is electrically connected to the load connection end.

10. A lighting device according to claim 9, characterized in that The LED load unit comprises a plurality of LED lamp beads connected in series, an anode of a first-end LED lamp bead is electrically connected to the working voltage output end of the isolated flyback unit, and a cathode of a last-end LED lamp bead is electrically connected to the load connection end.

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