CN220823319U

CN220823319U - Lighting circuit

Info

Publication number: CN220823319U
Application number: CN202322171525.9U
Authority: CN
Inventors: 吴明浩
Original assignee: Joulwatt Technology Co Ltd
Current assignee: Joulwatt Technology Co Ltd
Priority date: 2023-08-11
Filing date: 2023-08-11
Publication date: 2024-04-19
Anticipated expiration: 2033-08-11

Abstract

The utility model provides a lighting circuit, which comprises a rectifying circuit, wherein an alternating current input voltage is rectified to obtain a rectified voltage; the output end of the rectifying circuit is sequentially connected with a first string of LEDs to an N string of LEDs in series, wherein N is an integer greater than or equal to 2; the first switching tube is connected to the cathodes of the first string of LEDs to the N-th string of LEDs in sequence; the control circuit is used for taking power from any node between the rectifying circuit and the cathode of the first string of LEDs to generate a power supply voltage, generating N bias voltages according to the power supply voltage, and controlling the switching states of the Ns switching tubes according to the reference voltage, the N bias voltages and sampling voltages representing the LED current; the utility model can meet the wide-range input and realize high-efficiency output.

Description

Lighting circuit

Technical Field

The utility model relates to the field of lighting circuits, in particular to a lighting circuit.

Background

Because the European new ERP certification has the energy efficiency requirement, the A-level energy efficiency has very high requirement on the driving efficiency, and the standard requirements such as harmonic PF and the like can not be met within 5W, the driving efficiency can be more than 96% within 5W, the requirement on the A-level energy efficiency is met, and the system cost is low. Conventional low PF LED control circuits such as BUCK, boost, or single-segment linear circuits as shown in fig. 1 have difficulty achieving drive efficiency >96% within 5W of input power, and operating voltage ranges meeting the requirements of the 198-264VAC narrow voltage range.

The current low-PF switching circuit realizes the drive efficiency of LED drive of about 95% (under 4W input condition), and has more peripheral devices, the magnetic field strength Bmax is required to be small, the magnetic size required to be introduced is larger, and the system cost is high; the scheme of driving the LEDs by a single-segment linear circuit is difficult to meet the working range of 198-264V.

Disclosure of utility model

The utility model aims to provide a high-efficiency lighting circuit, which solves the problems that the output efficiency in the prior art cannot meet the requirement and the working voltage range is difficult to meet the requirement.

The present utility model also provides an illumination circuit comprising:

the rectification circuit rectifies the alternating current input voltage to obtain rectified voltage;

N strings of LEDs, namely a first string of LEDs to an N string of LEDs are sequentially connected in series at the output end of the rectifying circuit, wherein N is an integer greater than or equal to 2;

The first ends of the N switching tubes are respectively connected to the cathodes of the first string of LEDs to the N string of LEDs, and the second ends of the N switching tubes are connected together and connected to low potential;

And the control circuit is used for taking power from any node between the rectifying circuit and the cathode of the first string of LEDs to generate a supply voltage, generating N bias voltages according to the supply voltage, and controlling the switching states of the N switching tubes according to the reference voltage, the sampling voltage representing the LED current and the N bias voltages.

Optionally, the N bias voltages include first to nth bias voltages that decrease in sequence.

Optionally, the sampling voltages are sequentially overlapped on the first bias voltage to the Nth bias voltage to obtain the first voltage to the Nth voltage;

The control circuit respectively amplifies errors of the reference voltage and the first voltage to the Nth voltage so as to respectively control the switching states of the first switching tube to the Nth switching tube.

Optionally, the control circuit further includes a first current source and N resistors, the first current source is configured to generate the first current source according to the supply voltage, and the first current source outputs a first current, which flows through the first resistor to the nth resistor sequentially connected in series, to generate the first bias voltage to the nth bias voltage respectively.

Optionally, the control circuit further includes N current sources and N resistors, and resistance values of a first resistor to an nth resistor in the N resistors are sequentially reduced;

And generating the N current sources according to the power supply voltage, wherein the N current sources output N currents which respectively flow through the first resistor to the N resistor, and respectively generate the first bias voltage to the N bias voltage.

Optionally, when the rectified voltage is greater than the sum of the conduction voltage drops of the first string of LEDs to the kth string of LEDs and is less than the sum of the conduction voltage drops of the first string of LEDs to the kth+1th string of LEDs, the kth operational amplifier performs operational amplification on the reference voltage and the kth voltage to control the kth switching tube to be conducted, wherein K is greater than or equal to 1 and less than N.

Optionally, when the N is 2, the ac input power voltage is between 198V and 264V, the on-voltage drop of the first string of LEDs is configured to be 240V to 270V, the on-voltage drop of the second string of LEDs is configured to be 70V to 40V, and the total on-voltage drop of the first string of LEDs and the second string of LEDs is greater than 290V and less than 320V.

Optionally, two bias voltages are generated according to the supply voltage, and the switching states of the first switching tube and the second switching tube are controlled according to the reference voltage, the sampling voltage and the two bias voltages.

Optionally, a first bias voltage and a second bias voltage in the two bias voltages are respectively overlapped with the sampling voltage to obtain a first voltage and a second voltage, and the reference voltage and the first voltage and the second voltage are respectively subjected to error amplification to respectively control the switching states of the first switching tube and the second switching tube.

Optionally, when the ac input power voltage is greater than or equal to 220V and less than 264V, the first switching tube is in an off state, and the second switching tube is in an on state;

When the alternating current input power supply voltage is greater than or equal to 198V and smaller than 220V, the first switching tube is in an on state, and the second switching tube is in an off state.

Optionally, the power supply circuit includes thyristor, first adjusting tube and error amplifier, the first serial LED negative pole of thyristor first end connection, the first adjusting tube first end of thyristor second end connection, thyristor control end ground connection, two series connection's bleeder resistors are connected to first adjusting tube second end, error amplifier carries out error amplification with band gap benchmark and two the voltage of bleeder resistor link, error amplifier output connection first adjusting tube control end, first adjusting tube second end output supply voltage.

Optionally, the device further comprises a first sampling resistor connected between the second ends of the N switching tubes and the reference ground, and the voltage on the first sampling resistor is obtained to obtain the sampling voltage, and the node potential corresponding to the sampling voltage is the low potential.

Compared with the prior art, the utility model has the following advantages: the utility model is used for controlling N strings of LEDs (N is more than or equal to 2), each string of LEDs corresponds to a switching tube, power is taken from any node between a rectifying circuit and the cathode of a first string of LEDs to generate power supply voltage, N bias voltages are generated according to the power supply voltage, and the switching states of the N switching tubes are controlled according to reference voltage, the N bias voltages and sampling voltages representing LED currents; the power supply method is various in power supply mode, power supply loss can be reduced by taking power from the negative electrode of the first string of LEDs, and the power supply capacity can drive all the switching tubes to work normally, so that the situation that the power supply voltage is too low and enough driving voltage cannot be generated to drive all the switching tubes to work normally is avoided; when two strings of LEDs exist, the output efficiency can be more than 96% when the input power is within 5W, meanwhile, the power variation of the alternating current input voltage between 198 and 264VAC is small, the constant power effect is excellent, and the requirements of a new national standard and no stroboscopic effect can be met; when multiple strings of LEDs are connected in series, a wider AC input range than the 198-264VAC range, such as 180-280VAC wide input, can be satisfied, and an efficient output is achieved.

Drawings

FIG. 1 is a schematic diagram of a conventional single-segment linear LED control circuit;

FIG. 2 is a schematic diagram of an embodiment of an illumination circuit according to the present utility model;

FIG. 3 is a schematic diagram of a lighting circuit according to a second embodiment of the present utility model;

FIG. 4 is a schematic diagram of a lighting circuit according to a third embodiment of the present utility model;

fig. 5 is a schematic diagram of a power supply circuit according to the present utility model.

Detailed Description

The preferred embodiments of the present utility model will be described in detail below with reference to the accompanying drawings, but the present utility model is not limited to these embodiments only. The utility model is intended to cover any alternatives, modifications, equivalents, and variations that fall within the spirit and scope of the utility model.

In the following description of preferred embodiments of the utility model, specific details are set forth in order to provide a thorough understanding of the utility model, and the utility model will be fully understood to those skilled in the art without such details.

The utility model is more particularly described by way of example in the following paragraphs with reference to the drawings. It should be noted that the drawings are in a simplified form and are not to scale in order to facilitate a clear and concise description of embodiments of the present utility models.

In the lighting circuit, in order to realize high-efficiency output in a wider alternating current input range, a plurality of strings of LED loads are sequentially connected in series, and N (N is more than or equal to 2) strings of LEDs are taken as an example, and optionally, each string of LEDs comprises a plurality of lamp beads connected in series; a switching tube is connected between the negative electrode of each string of LED load and a sampling resistor, the sampling resistor is connected with a plurality of strings of LEDs in series and is used for sampling the current flowing through the LEDs, and the voltage on the sampling resistor represents the current flowing through the LEDs; and taking power from any node between the rectifying circuit and the cathode of the first string of LEDs to generate a power supply voltage VDD so as to supply power to the control circuit of the switching tube, generating N bias voltages according to the power supply voltage VDD, and controlling the switching states of the switching tubes according to the reference voltage, the N bias voltages and the sampling voltage.

Referring to fig. 2, a schematic diagram of an embodiment of a lighting circuit according to the present utility model is illustrated, where a lighting circuit load uses 2 series LEDs as an example, and further includes a rectifying circuit, two switching tubes, and a control circuit, where the rectifying circuit converts an AC input power AC into a rectified voltage VBUS to supply power to two LEDs connected in series sequentially, and the lighting circuit further includes an input filter circuit connected between the rectifying circuit and the LED lamp string, where an LED on a side close to the rectifying circuit is a first LED (LED 1 in the drawing) and another LED is a second LED (LED 2 in the drawing), specifically, an anode of the first LED is connected to a rectified current output end, a cathode of the first LED is connected to an anode of the second LED, and a cathode of the second LED is connected to a sampling resistor Rcs, where the sampling resistor Rcs is used to sample a current flowing through the LED string, and a voltage on the sampling resistor Rcs is a sampled voltage Vcs, which characterizes a magnitude of the current flowing through the LED. The two strings of LEDs correspond to two switching tubes, the first string of LEDs and the second string of LEDs correspond to a first switching tube M2 and a second switching tube M1 respectively, the first switching tube M1 is connected between the cathode of the first string of LEDs and a sampling resistor Rcs, the second switching tube M2 is connected between the cathode of the second string of LEDs and the sampling resistor Rcs, and the control circuit controls the switching states of the switching tubes M1 and M2; the control circuit comprises a power supply circuit and a control circuit, wherein the power supply circuit is used for generating a power supply voltage VDD from any node power taking between the rectifier circuit and the first string of LED cathodes to supply power to the control circuit, the LED strings comprise a plurality of lamp beads, and the power taking from the rectifier circuit to the first string of LED cathodes can be the power taking from any node of the lamp beads or the power taking from the bus voltage; the first bias voltage is generated according to the supply voltage VDD, the first voltage V1 is generated according to the sum of the first bias voltage and the sampling voltage Vcs, the first switching tube M1 is controlled according to the reference voltage Vref and the first voltage V1, and the second switching tube M2 is controlled according to the reference voltage Vref and the sampling voltage Vcs. The control circuit further comprises a first operational amplifier U1 and a second operational amplifier U2, wherein a first input end of the first operational amplifier U1 receives the reference voltage Vref, a second input end of the first operational amplifier U1 receives the first voltage V1, and an output end of the first operational amplifier U1 is connected with a control end of the first switching tube M1; the first input end of the second operational amplifier U2 receives the reference voltage Vref, the second input end of the second operational amplifier U2 receives the sampling voltage Vcs, and the output end of the second operational amplifier U2 is connected with the control end of the second switching tube M2; the method comprises the steps that sampling voltage Vcs is superimposed on first bias voltage to obtain first voltage V1, specifically, a first current source is generated according to power supply voltage VDD to output first current I1, the first current I1 flows through a first resistor R1 to generate first bias voltage, the first end of the first resistor R1 is connected with a common connection end of the sampling resistor Rcs and an adjusting tube, and the second end of the first resistor R1 generates the first voltage V1; the utility model can also generate or directly give a first bias voltage larger than zero in other modes, then add the first bias voltage with the sampling voltage Vcs to obtain the first voltage V1, and the generation mode of the first bias voltage is not limited; the sampling voltage Vcs received by the second input end of the second operational amplifier U2 of the present utility model corresponds to the second voltage V2 corresponding to the first voltage V1, and is equivalent to that the second voltage V2 is obtained by superposing a bias voltage with a magnitude of zero on the sampling voltage Vcs. The working principle of the two-string LED control circuit is as follows:

because the conduction voltage drop of the first string of LEDs is VF1, and the conduction voltage drop of the second string of LEDs is VF2, when the rectification voltage VBUS obtained after the alternating current input power source AC passes through the rectification circuit is greater than VF1+VF2, the second operational amplifier U2 carries out error amplification on the reference voltage Vref and the sampling voltage Vcs to drive and control the second switching tube M2 to be conducted, so that the conduction of the first string of LEDs and the second string of LEDs is controlled; according to the operation characteristics of the operational amplifier, when the operation of the second operational amplifier U2 is stable, the voltage of the first input end of the second operational amplifier U2 is equal to the voltage of the second input end thereof, namely the sampling voltage Vcs is equal to the reference voltage Vref, and V1> Vref is provided because v1=i1×r1+vcs, namely the voltage of the non-inverting input end of the first operational amplifier U2 is greater than the voltage of the inverting input end thereof, the first operational amplifier U1 outputs negative pressure, the first switching tube M1 with the NMOS tube cannot be driven to be turned on, namely the first operational amplifier U1 outputs negative pressure to control the first switching tube M1 to be turned off. Because the second switching tube M2 is conducted, the first switching tube M1 is not conducted, the current flowing through the first string of LEDs is consistent with the current flowing through the second string of LEDs, the current flowing through the LEDs is Vref/Rcs, and the reference voltage Vref controls the magnitude of the current flowing through the LED strings;

When the rectified voltage VBUS obtained after the alternating current input power source AC passes through the rectifying circuit is larger than VF1 and smaller than VF1+VF2, the size of the rectified voltage VBUS is insufficient to drive the second string of LEDs to be conducted, and then the second switching tube M2 connected with the cathodes of the second string of LEDs is also not conducted; the first operational amplifier U1 amplifies the error between the reference voltage Vref and the first voltage V1 and drives the first switching tube M1 to turn on, after the first operational amplifier U1 works stably, the first voltage V1 is equal to the reference voltage Vref due to the virtual short characteristic thereof, and v1=vcs+i1×r1, then vcs=vref-i1×r1, and the current flowing through the first string of LEDs is (Vref-I1×r1)/Rcs; when the first current I1 and the first resistor R1 are set to be small, the current flowing through the first string of LEDs is approximately equal to the current flowing through the first string of LEEDs and the second string of LEDs when the first switching tube M2 is turned on and the second switching tube M2 is turned on, so that the LED current can be kept substantially unchanged and maintained in a constant current state even when the ac input power source is changed from large to small.

In one embodiment, the range of the alternating current input power source AC is 198VAC-264VAC, the range of the rectified voltage VBUS after rectification is about 280V-370V, the conduction voltage drop of the first string of LEDs is about 240V-270V, the voltage drop of the second string of LEDs is about 70V-40V, and the sum of the conduction voltage drops of the first string of LEDs and the second string of LEDs is more than 290V and less than 320V; when the alternating current input power supply reaches high input voltage 264VAC, the peak value of the rectified voltage VBUS reaches 320V, the first switching tube M1 is turned off, the second switching tube M2 is turned on, the LEDs 1 and 2 are both turned on, the voltage drop of the LED2 is the lowest, and the efficiency is high; when the alternating current input power supply reaches 230VAC, the rectification voltage VBUS is continuously larger than 320V, the first switching tube M1 is turned off, the second switching tube M2 is turned on, the first string of LEDs and the second string of LEDs are continuously turned on, the rectification voltage VBUS is close to the total voltage drop of the LED strings, the input is close to the output, the system works at the highest efficiency point, the valley voltage of the bus input voltage is larger than the sum of the total voltage drops of the LED strings, current can be always provided, the condition of insufficient working current can not occur, and the output efficiency of the system can reach 97% -98% under the condition of output within 5W; when the alternating current input voltage is greater than 230VAC, the valley voltage of the busbar voltage VBUS is greater than the sum of the voltage drops of the LEDs of the total lamp string, so that voltage and current can be always provided, the condition of insufficient current can not occur, and stroboscopic can not occur; when the alternating current input power supply is lower than 220VAC, the rectified voltage VBUS is close to the conduction voltage drop of the first string of LEDs and the second string of LEDs but insufficient to drive the first string of LEDs and the second string of LEDs to conduct simultaneously, so that the first string of LEDs is conducted and the second string of LEDs is not conducted; when the alternating current input power supply is continuously reduced to 198VAC, the first string of LEDs is continuously conducted, the second string of LEDs is continuously not conducted, the input voltage is close to the voltage drop of the first string of LEDs when the voltage is at a low voltage of 198V, the extra output loss is not very large, the consumption is not very large, the driving efficiency of the first string of LEDs is highest, the minimum variation of the input power can be ensured, and the condition that an adjusting tube is directly closed and then the input power drops instantly when the traditional single-section linear control scheme under 220V input is not caused. In addition, in the case of low-power applications, for example 4W, the electrolytic capacitance value after the rectifying circuit can ensure that the ripple of the rectified voltage VBUS is sufficiently small. The application of the embodiment can meet the energy efficiency requirements of European new ERP authentication. The two-string LED control circuit of the present application is not limited to the description of the above embodiments, but the first string LED and the second string LED in the above embodiments are selected to achieve unexpectedly efficient output.

The two-string LED control circuit has the advantages of simple structure, no requirement on magnetic field intensity, low cost and high-efficiency (the output efficiency can reach 96% or more) output even in a narrow-voltage conventional alternating current input range (198 VAC-264 VAC); in addition, in the occasion that the power is little, circuit power supply loss is very outstanding, gets electricity from rectifier circuit to the arbitrary node of first cluster LED negative pole, and it is various to get the electricity mode, gets electricity from first cluster LED negative pole and can be compared directly from input VBUS and get electricity and give control circuit power supply, can reduce the loss of high-voltage power supply, and efficiency improvement is showing under low-power application scenario.

As shown in fig. 3, a second schematic diagram of an embodiment of the lighting circuit of the present utility model is illustrated, in which, in the lighting circuit load, three series-connected LEDs are taken as an example, a third series of LEDs (LED 3) is further connected in series on the basis of the two series of LEDs illustrated in fig. 2, and a third switching tube M3 is correspondingly added, that is, a first series of LEDs, a second series of LEDs and a third series of LEDs are sequentially connected in series from one side of the rectifying circuit, and the lighting circuit load has a corresponding first switching tube M1, a second switching tube M2 and a third switching tube M3, and the first switching tube M1, the second switching tube M2 and the third switching tube M3 are respectively connected between the cathodes of the first series of LEDs, the second series of LEDs and the third series of LEDs and the sampling resistor Rcs; the control circuit further comprises a third operational amplifier U3, a second resistor R2 and a third resistor R3 on the basis of FIG. 2. The first input end of the first operational amplifier U1 receives the reference voltage Vref, the second input end of the first operational amplifier U1 receives the first voltage V1, and the output end of the first operational amplifier U1 is connected with the control end of the first switching tube M1; the first input end of the second operational amplifier U2 receives the reference voltage Vref, the second input end of the second operational amplifier U2 receives the second voltage V2, and the output end of the second operational amplifier U2 is connected with the control end of the second switching tube M2; the first input end of the third operational amplifier U3 receives the reference voltage Vref, the second input end of the third operational amplifier U3 receives the third voltage V3, and the control end of the third operational amplifier U3 is connected with the control end of the third switching tube M3; the first current I1 output by the first current source flows through a first resistor R1, a second resistor R2 and a third resistor which are connected in series, the first end of the third resistor R3 is connected with the common connecting end of the sampling resistor Rcs and the switching tube, the second end of the third resistor R3 is connected with the first end of the second resistor R2, the second end of the second resistor R2 is connected with the first end of the first resistor R1, the second end of the first resistor R1 is connected with the common connecting end of the sampling resistor Rcs and the LED string, the sum of voltage drops generated by the first current I1 on the three resistors is a first bias voltage, the sum of voltage drops generated by the first current I1 on the second resistor R2 and the third resistor R3 is a second bias voltage, the voltage drop generated by the first current I1 on the first resistor R1 is a third bias voltage, the second end of the first resistor R1 generates a first voltage V1 which is the sum of the first bias voltage and the sampling voltage Vcs, the second voltage V2 generated by the second end of the second resistor R1 is the sum of the second bias voltage Vcs and the third bias voltage Vcs, and the third voltage Vcs generated by the third resistor R3 and the third bias voltage Vcs; optionally, the resistance of the third resistor R3 may be zero, that is, the third bias voltage is zero, the third voltage V3 is the sampling voltage Vcs, which is equivalent to not setting the third resistor R1, and referring to fig. 2, the second input end of the third op-amp directly receives the sampling voltage Vcs; the working principle of the three-string LED control circuit refers to the working principle of the two-string LED control circuit, and is briefly described below:

The conduction voltage drops of the first string of LEDs, the second string of LEDs and the third string of LEDs are VF1, VF2 and VF3 respectively, and when the rectification voltage VBUS is greater than VF1+VF2+VF3, the third switching tube M3 is controlled to be conducted; when the rectified voltage VBUS is larger than VF1+VF2 and smaller than VF1+VF2+VF3, the second switching tube is controlled to be conducted; when the rectified voltage VBUS is larger than VF1 and smaller than VF1+VF2, the first switching tube is controlled to be conducted;

When the rectification voltage VBUS is greater than VF1+VF2+VF3, the third operational amplifier U3 carries out error amplification on the reference voltage Vref and the third voltage V3 to drive the third switching tube M3 to be conducted, the third voltage V3 is pulled to be equal to the reference voltage Vref in size, the first voltage V1 and the second voltage V2 are greater than the third voltage V3, namely, the first voltage V1 and the second voltage V2 are greater than the reference voltage Vref, therefore, the first operational amplifier U1 and the second operational amplifier U2 both output negative pressure, the first switching tube M1 and the second switching tube M2 are respectively controlled to be turned off, and the LED1, the LED2 and the LED3 are connected in series; when vf1+vf2< VBUS < vf1+vf2+vf3, the rectified voltage VBUS is insufficient to drive the LED3 to be turned on, the second operational amplifier U2 amplifies the error between the reference voltage Vref and the second voltage V2 to drive the second switching tube M2 to be turned on, the second voltage V2 is pulled to the Vref value, the first voltage V1 is greater than v2=vref, the first operational amplifier U1 amplifies the error between the reference voltage Vref and the first voltage V1 to output negative voltage to control the first switching tube M1 to be turned off, and therefore the LED1 and the LED2 are turned on in series; when VF1< VBUS < vf1+vf2, the rectified voltage is insufficient to drive LED2 and LED3 to be turned on, and the first op-amp U3 amplifies the error between the reference voltage Vref and the first voltage V1 to drive the first switching tube M1 to be turned on. The three-string LED control can further increase the input range of the rectified voltage VBUS, support wider range input, realize high-efficiency output at the same time, and avoid the problem of narrow single-segment linear control input range.

As shown in fig. 4, a third principle diagram of an embodiment of the lighting circuit of the present utility model is illustrated, which is a further expansion based on the schematic diagrams of fig. 2 and 3, and supports the embodiment illustrated in fig. 2 and 3, where the lighting circuit load takes N strings of LEDs as an example, N is an integer greater than or equal to 2, and includes a first string of LEDs to an nth string of LEDs, each string of LEDs corresponds to a switching tube, that is, the first string of LEDs to the nth string of LEDs corresponds to the first switching tube to the nth switching tube, each switching tube is connected between a corresponding LED negative electrode and a low potential, and in general, each switching tube is connected between a corresponding LED negative electrode and a sampling resistor Rcs, where a voltage corresponding node potential on the sampling resistor Rcs is the low potential; preferably, the low potential may also be a reference ground potential, and a sampling resistor Rcs is connected between the positive electrode of each LED string and the output terminal of the rectifying circuit. The control circuit comprises a power supply circuit and N resistors, the power supply circuit takes power from any node from the rectifying circuit to the cathode of the first string of LEDs to generate a power supply voltage VDD, N bias voltages are generated according to the power supply voltage VDD, the N bias voltages comprise first bias voltages to N bias voltages, the first bias voltages to N bias voltages are sequentially increased, the first bias voltages to the N bias voltages are respectively overlapped with a sampling voltage Vcs to obtain first voltages V1 to N voltages VN, the N bias voltages can be set to be zero, namely the N voltages VN are the sampling voltages Vcs; specifically, as shown in fig. 4, the power supply voltage VDD generates a first current to flow through the first resistor R1 to the first resistor RN, the voltages generated on all the resistors are the first bias voltage, the sum of the voltage drops generated on the second resistor R2 to the nth resistor is the second bias voltage, and so on, the voltage drop generated on the nth resistor RN is the first voltage, the resistance value of the nth resistor RN may be zero, that is, the first bias voltage is zero, the first voltage V1 is the sampling voltage Vcs, which is equivalent to not setting the nth resistor RN, and the nth-1 resistor RN-1 is directly connected to the common connection end of the switching tube and the sampling resistor Rcs; in another embodiment, N first currents I1 with equal magnitudes are generated according to the supply voltage VDD, the N first currents respectively flow through N resistors with sequentially decreasing resistance values, the voltage drop generated by the first current I1 at the first resistor R1 is a first bias voltage, and the voltage drop generated by the first current I1 at the nth resistor RN is an nth bias voltage. As shown in the figure, the control circuit further comprises N operational amplifiers, which sequentially correspond to the N switching tubes, and the first operational amplifier U1 to the N operational amplifier UN respectively carry out operational amplification on the reference voltage Vref and the first voltage V1 to the N voltage to control the first switching tube M1 to the N switching tube MN. The LED string can comprise a plurality of lamp beads, and the power taking from any node between the output end of the rectifying circuit and the negative electrode of the first string of LEDs can be the power taking from the bus voltage or the power taking from any lamp bead node; in addition, the power consumption from the first string of LED cathodes is lower than the power consumption generated by the power consumption from the output end of the rectifying circuit, the high-voltage power consumption is reduced, and the efficiency improvement is remarkable particularly in a low-power scene. In addition, the output loss can be reduced by generating a plurality of bias voltages according to the power supply voltage VDD to generate a plurality of operational amplifier negative phase input voltages, compared with the case that a plurality of operational amplifier negative phase input voltages are generated through a plurality of sampling resistors through which LED current flows; particularly, when a plurality of LED strings are adopted, the more the LED strings are, the more sampling resistors are needed, and as the sampling resistors are gradually increased and increased, the larger the loss generated by the LED current flowing through the sampling resistors is, the larger the output loss is, and the lower the output efficiency is; compared with the single-string LED sampling, the utility model does not increase extra output loss, and the utility model generates smaller first current according to the power supply voltage VDD and generates a plurality of bias voltages to flow through a plurality of resistors, thereby having smaller influence on the power supply loss.

In the schematic diagram, when N is 2, two strings of LED control circuits illustrated in fig. 2 are used, and when N is 3, three strings of LED control circuits illustrated in fig. 3 are used, and the working principles illustrated in fig. 2 and 3 are referred to further briefly explain the multi-string LED control: taking N >2 as an example, when the rectification voltage VBUS is larger than the conduction voltage drop of all LEDs, controlling the N switch tube MN to be conducted; when the rectification voltage VBUS is larger than the first string of LED conduction voltage drops and smaller than the sum of the first string of LED conduction voltage drops and the second string of LED conduction voltage drops, controlling the first switching tube to conduct; when the rectification voltage VBUS is larger than the sum of the conduction voltage drops of the first string of LEDs to the K (1 < K < N) th string of LEDs and smaller than the sum of the conduction voltage drops of the first string of LEDs to the K+1th string of LEDs, the K-th switching tube is controlled to be conducted;

When the rectification voltage VBUS is larger than the conduction voltage drop of all LEDs, the Nth operational amplifier UN carries out error amplification on the reference voltage Vref and the Nth voltage VN to drive the Nth switching tube MN to be conducted, and the Nth voltage VN is pulled to be equal to the reference voltage Vref in size, so that other operational amplifiers except the Nth operational amplifier UN output negative voltages to respectively control the corresponding switching tubes to be turned off, all LED strings are conducted in series, and the conduction current is (Vref-I1 x RN)/Rcs; when the rectified voltage VBUS is greater than the sum of the conduction voltage drops of the first string of LEDs to the K (1 < K < n)), and is smaller than the sum of the conduction voltage drops of the first string of LEDs to the k+1th string of LEDs, the K operational amplifier performs error amplification on the reference voltage Vref and the K voltage to control the conduction of the K switch tube, the first string of LEDs to the K string of LEDs are conducted in series, the K voltage VK is pulled to Vref, and if vref=vk=i1 (rk+,..+rn) +vcs, vcs=vref-I1 (rk+,..+rn), the current flowing through the LED string is (Vref-I1+,..+rn))/Rcs, and the first current and the resistors with smaller values can make the LED currents approximately equal to be close to constant current output, and the additional loss generated by the first current is smaller, so that the influence on the output efficiency is not great; according to the utility model, only one sampling resistor Rcs is arranged, the resistance values of the arranged first to nth resistors are far smaller than those of the sampling resistor Rcs, the loss generated by the LED current flowing through one sampling resistor Rcs is not very large, compared with the arrangement of a plurality of sampling resistors, the LED current flowing through a plurality of sampling resistors to generate a plurality of sampling voltages to control a plurality of switching tubes, so that the output loss can be further saved, and the output efficiency is increased. The lighting circuit load of the utility model is provided with a plurality of strings of LEDs connected in series, so that a wide input range can be further supported, and the condition that the LEDs are not conducted and the input power is low under the condition of narrow range input can not occur; and a plurality of strings of LEDs are selected for control, and high-efficiency output, high driving efficiency and constant power output effect can be realized.

As shown in fig. 5, a schematic diagram of a power supply circuit of the present utility model is illustrated, including a thyristor J01, an adjusting tube M01, an error amplifier U01, a bandgap reference generating circuit U02, and voltage dividing resistors R01 and R02, wherein a first end of the thyristor is connected to a first LED negative pole, a control end thereof is grounded, a second end thereof is connected to the bandgap reference generating circuit U02, and the bandgap reference generating circuit U02 generates a bandgap reference Vref' according to a voltage of a second end of the thyristor J01; the first end of the adjusting tube M01 is connected with the second end of the thyristor J01, and the second end of the adjusting tube M01 is connected with the divider resistors R01 and R02 which are connected in series; the error amplifier U01 carries out error amplification on the voltage of the connection ends of the band gap reference and the divider resistors R01 and R02 to drive the adjusting tube M01, and the second end of the adjusting tube M01 outputs the power supply voltage VDD to supply power to the control circuit. The LED lamp string comprises a plurality of lamp beads, and the power taking from the rectifying circuit to any node between the first string of LED cathodes can be the power taking from any node of the lamp beads or the power taking from the bus voltage. The power supply method is various in power supply mode, and the power supply capacity of the first series of LED cathodes can be guaranteed to be enough to drive all the switching tubes to normally turn on and off, and the power supply voltage is lower than the power supply voltage generated by directly taking power from the bus, so that the power supply loss can be effectively reduced.

Although the embodiments have been described and illustrated separately above, and with respect to a partially common technique, it will be apparent to those skilled in the art that alternate and integration may be made between embodiments, with reference to one embodiment not explicitly described, and reference may be made to another embodiment described.

The above-described embodiments do not limit the scope of the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the above embodiments should be included in the scope of the present invention.

Claims

1. A lighting circuit, comprising:

2. A lighting circuit as recited in claim 1, wherein: the N bias voltages comprise first bias voltages to Nth bias voltages which are reduced in sequence.

3. A lighting circuit as recited in claim 2, wherein: sequentially superposing the sampling voltages on the first bias voltage to the Nth bias voltage to obtain first voltage to the Nth voltage;

4. A lighting circuit as recited in claim 2, wherein: the control circuit further comprises a first current source and N resistors, the first current source is generated according to the power supply voltage, the first current source outputs a first current, the first current flows through the first resistor to the N resistor which are sequentially connected in series, and the first bias voltage to the N bias voltage are respectively generated.

5. A lighting circuit as recited in claim 2, wherein: the control circuit further comprises N current sources and N resistors, and the resistance values of the first resistor to the N resistor in the N resistors are sequentially reduced;

6. A lighting circuit as recited in claim 3, wherein: when the rectification voltage is larger than the sum of the conduction voltage drops of the first string of LEDs to the K string of LEDs and smaller than the sum of the conduction voltage drops of the first string of LEDs to the K+1th string of LEDs, the K operational amplifier carries out operational amplification on the reference voltage and the K voltage to control the conduction of the K switching tube, wherein K is more than or equal to 1 and less than N.

7. A lighting circuit as recited in claim 1, wherein: when the N is 2, the alternating current input voltage is between 198V and 264V, the conducting voltage drop of the first string of LEDs is configured to be 240V to 270V, the conducting voltage drop of the second string of LEDs is configured to be 70V to 40V, and the total conducting voltage drop of the first string of LEDs and the second string of LEDs is more than 290V and less than 320V.

8. A lighting circuit as recited in claim 7, wherein: and generating two bias voltages according to the power supply voltage, and controlling the switching states of the first switching tube and the second switching tube according to the reference voltage, the sampling voltage and the two bias voltages.

9. A lighting circuit as recited in claim 8, wherein: and a first bias voltage and a second bias voltage in the two bias voltages are respectively overlapped with the sampling voltage to obtain a first voltage and a second voltage, and the reference voltage, the first voltage and the second voltage are respectively subjected to error amplification to respectively control the switching states of the first switching tube and the second switching tube.

10. A lighting circuit as recited in claim 9, wherein: when the alternating current input voltage is greater than or equal to 220V and smaller than 264V, the first switching tube is in an off state, and the second switching tube is in an on state;

When the alternating current input voltage is greater than or equal to 198V and smaller than 220V, the first switching tube is in an on state, and the second switching tube is in an off state.

11. A lighting circuit as recited in claim 1, wherein: the control circuit comprises a power supply circuit, the power supply circuit comprises a thyristor, a first adjusting tube and an error amplifier, the first end of the thyristor is connected with the negative electrode of the first string of LEDs, the second end of the thyristor is connected with the first end of the first adjusting tube, the control end of the thyristor is grounded, the second end of the first adjusting tube is connected with two voltage dividing resistors connected in series, the error amplifier carries out error amplification on the voltage of the band gap reference and the voltage of the connecting ends of the voltage dividing resistors, the output end of the error amplifier is connected with the control end of the first adjusting tube, and the second end of the first adjusting tube outputs the power supply voltage.

12. A lighting circuit as recited in claim 1, wherein: the sampling circuit further comprises a first sampling resistor which is connected between the second ends of the N switching tubes and the reference ground, the voltage on the first sampling resistor is obtained to obtain the sampling voltage, and the node potential corresponding to the sampling voltage is the low potential.