CN118175691A - Linear LED driving circuit and driving method - Google Patents

Abstract

According to the linear LED driving circuit and the LED driving method provided by the invention, the capacitor structure and the LED load are connected on the same branch, and the capacitor structure comprises a first capacitor and a second capacitor; when the input voltage is larger than a set threshold value, the first capacitor and the second capacitor are connected in parallel, the input voltage supplies power to the LED load, and meanwhile the first capacitor and the second capacitor are charged; when the input voltage is smaller than the LED load voltage, the first capacitor C1 and the second capacitor C2 are connected in series to supply power to the LED load; when the input voltage is between the voltage of the LED load and the set threshold, the LED load is powered by the input voltage, or by the greater of the input voltage and the sum of the first and second capacitor voltages connected in series. By the arrangement, the overall efficiency of the system and the luminous efficiency of the LED load can be improved.

Description

Linear LED driving circuit and driving method

Technical Field

The application relates to the field of LED illumination driving, in particular to a linear LED driving circuit and a driving method.

Background

In the prior art, for a linear LED driving circuit, a linear switching tube is used to provide a current flowing through an LED load, and when an input voltage is higher, a portion of the input voltage higher than the LED load voltage acts on the linear switching tube, so that the loss on the linear switching tube is higher, which is not beneficial to the improvement of the overall efficiency of the system. In addition, when the input voltage is smaller than the voltage on the LED load, the LED does not emit light at this time because the input voltage does not reach the voltage at which the LED load is turned on, which results in lower light emission efficiency of the LED. Accordingly, there is a need for an improved circuit that solves the problems of the prior art.

Disclosure of Invention

In order to solve the defects in the prior art, the application aims to provide a linear LED driving circuit and a driving method thereof so as to solve the problems in the prior art.

The invention provides a linear LED driving circuit, which receives an input voltage obtained after rectification and supplies power to the linear LED driving circuit by the input voltage, and is characterized in that the linear LED driving circuit comprises:

the capacitor structure is connected with the LED load on a branch and comprises a first capacitor and a second capacitor;

When the input voltage is larger than a set threshold value, the capacitor structure is connected with the LED load in series, the first capacitor and the second capacitor are connected in parallel, the input voltage supplies power to the LED load, and meanwhile the first capacitor and the second capacitor are charged; the set threshold is the sum of the voltage of the LED load and the voltage on the first capacitor or the second capacitor at the end of charging;

When the input voltage is smaller than the voltage of the LED load, the first capacitor and the second capacitor are connected in series, and the first capacitor and the second capacitor are connected in series to supply power to the LED load;

when the input voltage is between the voltage of the LED load and the set threshold, the LED load is powered by the input voltage, or by the greater of the input voltage and the sum of the first and second capacitance voltages connected in series.

Optionally, the linear LED driving circuit further includes a first unidirectional conductive element and a second unidirectional conductive element;

The first unidirectional element is connected in series on a branch between the cathode of the LED load and a first end of the capacitor structure, wherein the first end is one end of the capacitor structure close to the cathode of the LED load; the first unidirectional conduction element is unidirectional in conduction from the LED load to the capacitor structure;

The second unidirectional conduction element is arranged on a branch path between the cathode of the first unidirectional conduction element and the anode of the LED load, and the second unidirectional conduction element is unidirectional in conduction from the capacitor structure to the LED load;

when the input voltage is larger than the set threshold value, the first unidirectional conduction element is conducted;

when the input voltage is smaller than the voltage of the LED load, the second unidirectional conduction element is conducted.

Optionally, the linear LED driving circuit further comprises a first current circuit and a second current circuit, wherein the first current circuit is arranged between a cathode of the LED load and a ground terminal; the second current circuit is arranged between a second end of the capacitor structure and a grounding end, and the second end is one end of the capacitor structure close to the grounding end;

Wherein when the input voltage is greater than the set threshold, providing, by the second current circuit, a current of the LED load; when the input voltage is less than the voltage of the LED load or between the voltage of the LED load and the set threshold, a current of the LED load is provided by the first current circuit.

Optionally, the linear LED driving circuit further includes a reference signal generating circuit that generates a reference voltage signal in a proportional relationship with the input voltage, and the first current circuit and the second current circuit generate a current flowing through the LED load based on the reference voltage signal.

Optionally, the first current circuit includes a first switching tube and a first operational amplifier, the first switching tube is connected to a branch between a cathode of the LED load and a ground terminal, a control terminal of the first switching tube is connected to an output terminal of the first operational amplifier, and two input terminals of the first operational amplifier are respectively connected to the reference voltage signal and a signal representing a current flowing through the LED load;

The second current circuit comprises a second switching tube and a second operational amplifier, the second switching tube is connected to a branch between the second end of the capacitor structure and the grounding end, the control end of the second switching tube is connected with the output end of the second operational amplifier, and two input ends of the second operational amplifier are respectively connected with the reference voltage signal and the signal representing the load current flowing through the LED.

Optionally, the linear LED driving circuit further includes a current selection circuit, and when the input voltage is greater than the set threshold, the current selection circuit controls the first switching tube to be turned off;

the current selection circuit controls the second switching tube to be turned off when the input voltage is smaller than the voltage of the LED load or between the voltage of the LED load and the set threshold.

Optionally, the capacitor structure further comprises a first switch, a second switch and a third switch, the first capacitor is connected in series with the first switch to obtain a first series circuit, the second capacitor is connected in series with the second switch to obtain a second series circuit, and the first series circuit and the second series circuit are connected in parallel; a third switch is connected between the first series circuit and the second series circuit, one end of the third switch is connected to a common end of the first capacitor and the second switch, and the other end of the third switch is connected to a common end of the second capacitor and the second switch;

When the input voltage is smaller than the voltage of the LED load, the first switch and the second switch are in an open state, the third switch is in a closed state, and the first capacitor and the second capacitor are connected in series;

When the input voltage is greater than the set threshold, the first switch and the second switch are in a closed state, the third switch is in an open state, and the first capacitor and the second capacitor are connected in parallel.

Optionally, a third unidirectional conducting element is arranged on a branch between the input voltage and the anode of the LED load, the third unidirectional conducting element being unidirectional conducting from the input voltage to the LED load.

Optionally, a fourth unidirectional conducting element is arranged on a branch between the ground terminal and a second terminal of the second capacitor, and the second terminal is one end of the capacitor structure close to the ground terminal; the fourth unidirectional conduction element conducts unidirectionally from the ground terminal to the second terminal.

The invention also provides a linear LED driving method, which receives the rectified input voltage and supplies power to the linear LED driving by the input voltage, and is characterized in that the linear LED driving method comprises the following steps:

the capacitor structure and the LED load are connected on a branch, and the capacitor structure comprises a first capacitor and a second capacitor;

When the input voltage is larger than a set threshold value, the capacitor structure is connected with the LED load in series, the first capacitor and the second capacitor are connected in parallel, the input voltage supplies power to the LED load, and meanwhile the first capacitor and the second capacitor are charged; the set threshold is the sum of the voltage of the LED load and the voltage on the first capacitor or the second capacitor at the end of charging;

When the input voltage is smaller than the voltage of the LED load, the first capacitor and the second capacitor are connected in series, and the first capacitor and the second capacitor are connected in series to supply power to the LED load;

when the input voltage is between the voltage of the LED load and the set threshold, the LED load is powered by the input voltage, or by the greater of the input voltage and the sum of the first and second capacitance voltages connected in series.

Compared with the prior art, the invention has the following advantages:

According to the linear LED driving circuit and the LED driving method, when the input voltage is larger than the set threshold value, the input voltage supplies power to the LED load, meanwhile, the first capacitor C1 and the second capacitor C2 are charged, the first capacitor C1 and the second capacitor C2 are connected in parallel, and the part which is equivalent to the input voltage higher than the voltage of the LED load acts on the first capacitor C1 and the second capacitor C2 which are connected in parallel, so that voltage loss in the prior art is avoided; when the input voltage is smaller than the LED load voltage, the first capacitor C1 and the second capacitor C2 are connected in series to supply power to the LED load, so that the overall efficiency of the system and the luminous efficiency of the LED load can be improved. In addition, compared with the arrangement of a single capacitor, the invention is provided with two capacitors, and when the capacitors are changed from the parallel state to the series state, the voltage on the serially connected capacitors is improved relative to the voltage on the single capacitor, so that the efficiency can be further improved.

Furthermore, the reference voltage signal is set to be in a certain proportion relation with the input voltage, so that the change trend of the input current can follow the change trend of the input voltage, the power factor PF of the whole system is improved, and the THD of the system can be further reduced due to a certain relation between the power factor PF and the THD.

Drawings

FIG. 1 is a schematic diagram of a linear LED driving circuit according to an embodiment of the present application;

FIG. 2 is a schematic diagram of a first current path of a linear LED driver circuit in an embodiment of the present application;

FIG. 3 is a schematic diagram of a second current path of a linear LED driver circuit in an embodiment of the present application;

FIG. 4 is a schematic diagram of a third current path of a linear LED driver circuit in an embodiment of the present application;

FIG. 5 is a specific circuit configuration diagram of a linear LED driving circuit according to an embodiment of the present application;

FIG. 6 is a partial timing diagram of the input voltage versus current through the LED load according to an embodiment of the present application;

Fig. 7 is a simulation diagram of efficiency in the prior art.

FIG. 8 is a simulation diagram of the efficiency of a linear LED driver circuit of the present application;

fig. 9 is a simulation diagram of a power factor PF and total harmonic distortion THD in the prior art;

Fig. 10 is a simulation diagram of the power factor PF and the total harmonic distortion THD of the linear LED driving circuit of the present application.

Detailed Description

In order to make the present application better understood by those skilled in the art, the technical solutions in the specific embodiments of the present application will be clearly and completely described with reference to the accompanying drawings in the embodiments of the present application.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The terms "first," "second," "third," "fourth" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defining "first", "second", "third", and "fourth" may explicitly or implicitly include at least one such feature. As used in this specification and the appended claims, the singular forms "a," "an," and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise.

Fig. 1 shows a linear LED driving circuit according to the present application, which can be applied to a down lamp, a bulb lamp or other lighting devices with integrated circuits, and the linear LED driving circuit is connected to an LED load for driving the LED load.

As one implementation, the linear LED driving circuit includes a rectifying circuit 10, a first current circuit 20, a second current circuit 30, and a capacitive structure 40. The rectifying circuit 10 is connected to an ac input power source, and is configured to rectify the obtained ac voltage and output a dc input voltage V _in, so as to supply power to the linear LED driving circuit. The capacitor structure 40 includes a first capacitor C1 and a second capacitor C2, where the first capacitor C1 and the second capacitor C2 may be one equivalent capacitor composed of a plurality of capacitors, respectively. The first current circuit 20 is disposed between the cathode of the LED load and ground. The second current circuit 30 is disposed between the capacitor structure 40 and ground. As shown in fig. 1, the linear LED driving circuit further includes a first unidirectional conductive element and a second unidirectional conductive element, in fig. 1, a first diode D1 is used as the first unidirectional conductive element, and a second diode D2 is used as the second unidirectional conductive element; the first unidirectional conducting element is arranged between the cathode of the LED load and the capacitor structure 40, that is, the capacitor structure 40 and the second current circuit 30 are connected in series between the cathode of the first unidirectional conducting element and the ground, the second unidirectional conducting element is arranged between the anode of the LED load and the cathode of the first unidirectional conducting element, and the anode of the second unidirectional conducting element is connected with the cathode of the first unidirectional conducting element.

Specifically, in fig. 1, the anode of the first diode D1 is connected to the cathode of the LED load, the cathode of the first diode D1 is connected to one end of the capacitor structure 40, and the other end of the capacitor structure 40 is connected to the second current circuit 30. The anode of the second diode D2 is connected to the common node of the capacitor structure 40 and the first diode D1, and the cathode of the second diode D2 is connected to the anode of the LED load. Further, the capacitor structure 40 further includes a first switch S1, a second switch S2, and a third switch S3, where the first capacitor C1 is connected in series with the first switch S1 to obtain a first series circuit 401, and the second capacitor C2 is connected in series with the second switch S2 to obtain a second series circuit 402, and the first series circuit 401 is connected in parallel with the second series circuit 402; a third switch S3 is connected between the first series circuit 401 and the second series circuit 402, one end of the third switch S3 is connected to the common terminal of the first capacitor C1 and the first switch S1, and the other end of the third switch S3 is connected to the common terminal of the second capacitor C2 and the second switch S2. The switch states of the switch S1, the switch S2 and the switch S3 are controlled according to the magnitude of the input voltage V _in, so that the series-parallel state of the first capacitor C1 and the second capacitor C2 can be changed.

In addition, fig. 1 illustrates that the linear LED driving circuit is further provided with a third unidirectional single-pass element after the input voltage Vin is obtained, and in fig. 1, the diode D0 is taken as an example, so that the unidirectional conduction effect of the input voltage can be achieved, but whether the diode D0 is provided or not can be set according to actual situations. The first unidirectional conduction element, the second unidirectional conduction element and the third unidirectional conduction element can be arranged by adopting other components, so long as the unidirectional conduction effect can be realized. The positional relationship a element of the component according to the present invention is disposed between B and C, for example, as shown in fig. 1, the diode D0 is disposed between the input voltage and the anode of the LED load, and the position of the diode D0 is between the input voltage and the anode of the LED load, and it is not only that one end of the diode D0 is connected to the input voltage, but also that the other end is connected to the anode of the LED load, and when other components are disposed between the input voltage and the anode of the LED load, the diode D0 is disposed between the input voltage and the anode of the LED load together with other components.

For example, when the input voltage V _in is less than the voltage V _F of the LED load, the first switch S1 and the second switch S2 are in an open state, the third switch S3 is in a closed state, the first capacitor C1 and the second capacitor C2 are connected in series to supply the LED load with current, and the first current circuit 20 provides the current flowing through the LED load. The dashed line as shown in fig. 2 represents the current path through the LED load when the input voltage V _in is less than the voltage V _F of the LED load.

For example, when the input voltage V _in is greater than the set threshold, the first switch S1 and the second switch S2 are in the closed state, the third switch S3 is in the open state, the first series circuit 401 and the second series circuit 402 are turned on, that is, the first capacitor C1 and the second capacitor C2 are connected in parallel, the LED load is powered by the input voltage V _in, and the first capacitor C1 and the second capacitor C2 are charged, at this time, the first current circuit 20 is not operated, and the current flowing through the LED load is provided by the second current circuit 30. The dashed line shown in fig. 3 represents the current path through the LED load when the input voltage V _in is greater than the set threshold.

When the input voltage V _in is greater than the set threshold, the set threshold satisfies the following relationship:

V _{Is provided with} ＝V_F+V_C1；

Where V _F is denoted as the voltage of the LED load, V _C1 is denoted as the voltage of the first capacitor C1 in the capacitor structure 40, and here, since the first capacitor C1 and the second capacitor C2 are connected in parallel in a state where the input voltage V _in is greater than the set threshold, the set threshold may also be denoted by the sum of the voltage V _F of the LED load and the voltage V _C2 on the second capacitor C2, where the voltage V _C1 of the first capacitor C1 or the voltage V _C2 of the second capacitor C2 is the voltage value at the end of charging.

Illustratively, the input voltage V _in is between the voltage V _F of the LED load and the set threshold, the current flowing through the LED load is provided by the first current circuit 20, forming a current path from the LED load to the first current circuit 20, when the second current circuit 30 is not operating. The dashed line shown in fig. 4 represents a current path through the LED load for the input voltage V _in to flow between the voltage V _F of the LED load and the set threshold. When the input voltage V _in is between the voltage V _F of the LED load and the set threshold, the input voltage V _in may supply power to the LED load, or may supply power to the LED load based on the larger sum of the input voltage V _in and the voltage V _C1 of the first capacitor C1 and the voltage V _C2 of the second capacitor C2, which may be set according to the requirement in practical application.

As shown in fig. 5, as an implementation manner, the linear LED driving circuit further includes a current selection circuit 50, where an input terminal of the current selection circuit 50 receives the input voltage V _in or a signal representing the input voltage V _in, and an output terminal of the current selection circuit 50 is connected to the first current circuit 20 and the second current circuit 30, respectively. The current selection circuit 50 outputs a corresponding switching signal according to the magnitude of the input voltage V _in or a signal representative of the input voltage V _in to control the first current circuit 20 or the second current circuit 30 to provide a current through the LED load.

Specifically, when the input voltage V _in is less than or equal to the set threshold, the current selection circuit 50 outputs a first switching signal to the first current circuit 20, and the first current circuit 20 provides a current flowing through the LED load in response to the first switching signal. When the input voltage V _in is greater than the set threshold, the current selection circuit 50 outputs a second switching signal to the second current circuit 30, and the second current circuit 30 provides a current flowing through the LED load in response to the second switching signal.

Alternatively, the linear LED driving circuit may also be provided with a switching circuit to achieve the same effect as the current selection circuit 50. Specifically, the input of the first current circuit 20 receives the input voltage V _in or a signal indicative of the input voltage V _in and provides current through the LED load when the input voltage V _in is less than or equal to a set threshold. The input end of the second current circuit 30 receives the input voltage V _in or a signal representing the input voltage V _in, when the input voltage V _in rises to be greater than the set threshold value, the second current circuit 30 outputs a switching signal, and the switching circuit controls the current path from the LED load to the first current circuit 20 to be disconnected according to the switching signal, and the second current circuit 30 provides the current flowing through the LED load. Thereby realizing a switching operation between the first current circuit 20 and the second current circuit 30.

Further, as shown in fig. 5, as an alternative implementation manner, the first current circuit 20 includes a first switching tube M1 and a first operational amplifier U1, where one end of the first switching tube M1 is connected to the cathode of the LED load, the other end of the first switching tube M1 is connected to the ground through a resistor R1, and the output end of the first operational amplifier U1 is connected to the control end of the first switching tube M1. The first operational amplifier U1 receives the reference voltage signal V _REF at a first input terminal and receives a second control signal indicative of the current flowing through the LED load at a second input terminal, here illustrated by the voltage across the resistor R1 as the second control signal, and the first operational amplifier U1 adjusts the magnitude of the current flowing through the LED load by controlling the magnitude of the voltage at the control terminal of the first switching transistor M1. The second current circuit 30 is identical in structure to the first current circuit 20 and will not be described in detail herein. In the prior art, V _REF is generally a constant value, so that the current flowing through the LED load is determined to be a constant value; this way the power factor PF of the system is lower. The trend of the first control signal V _REF provided by the present invention follows the trend of the input voltage V _in. Specifically, the linear LED driving circuit further includes a reference signal generating circuit 60, and output terminals of the reference signal generating circuit 60 are connected to the first current circuit 20 and the second current circuit 30, respectively. The reference signal generating circuit 60 receives the input voltage V _in or a signal representing the input voltage V _in, which receives the voltage obtained by dividing the input voltage V _in (i.e., the signal representing the input voltage V _in) through the resistors RA and RB, and converts the voltage into the reference voltage signal V _REF having the same variation trend as the input voltage V _in, so that the reference voltage signal V _REF can be set to have a proportional relationship with the input voltage V _in, the first current circuit 20 or the second current circuit 30 controls the current flowing through the LED load according to the reference voltage signal V _REF, so that the trend of the current flowing through the LED load approaches the trend of the input voltage V _in. In order to further increase the power factor PF of the system and reduce the total harmonic distortion THD of the system, when the input voltage is between the voltage V _F of the LED load and the set threshold, the LED load may be powered by the input voltage, so as to achieve that the input voltage supplies power to the LED load by the input voltage in a period of time other than the LED load voltage, so that the variation trend of the input current follows the variation trend of the input voltage.

It should be noted that when the input voltage V _in is smaller than the voltage V _F of the LED load, the first switching tube M1 is closed, the second switching tube M2 is opened, the first current circuit 20 provides a current flowing through the LED load, where the current path may be provided by a body diode of the second switching tube M2, and a fourth unidirectional conducting element (e.g., a diode) may be further provided between the ground terminal and an end of the capacitor structure 40 near the ground terminal to provide a conducting path. In practical application, corresponding transformation setting can be performed according to practical situations. In addition, fig. 1 to fig. 5 are only schematic diagrams illustrating a specific embodiment of the present invention, and the connection relation of specific components is not limited to the illustration, and other components may be provided and the corresponding connection position relation may be adjusted, so long as the core concept of the present invention can be implemented, and other modifications are also within the scope of the present invention claimed.

Fig. 6 is a timing chart of the input voltage V _in and the current I _led flowing through the LED load, and fig. 6 (a) is a diagram showing the input voltage V _in divided into a first operating region, a second operating region, a third operating region and a fourth operating region according to the variation trend of the input voltage V _in. The first operating region is the voltage of the input voltage V _in between times T0-T1, when the input voltage V _in is less than the voltage V _F of the LED load. The second operating region is a voltage of the input voltage V _in between times T1-T2, at which time the input voltage V _in is in an ascending trend, and the input voltage V _in is between the voltage V _F of the LED load and the set threshold. The third operating region is the voltage between times T2-T3 of the input voltage V _in, when the input voltage V _in is greater than the set threshold. The fourth operating region is the voltage of the input voltage V _in between times T3-T4, at which time the input voltage V _in is in a decreasing trend, and the input voltage V _in is also between the voltage V _F of the LED load and the set threshold. Fig. 6 (b) is a current curve of the LED load according to the input voltage V _in, fig. 6 (c) is a current curve of the current I _M1 flowing through the first switching tube M1 according to the input voltage V _in, fig. 6 (d) is a current curve of the current I _M2 flowing through the second switching tube M2 according to the input voltage V _in, from which it can be seen that the input voltage V _in is in the first operating region, the second operating region and the fourth operating region, the first switching tube M1 is turned on, i.e. the current flowing through the LED load is provided by the first current circuit, i _led is now equal to I _M1; in the third operating region, the first switching tube M1 is turned off, and the second switching tube M2 is turned on, i.e. the current flowing through the LED load is provided by the second current circuit, where I _led is equal to I _M2.

As shown in fig. 7, the efficiency of the conventional linear LED driving circuit in the prior art is simulated, wherein the efficiency is the ratio of the load power to the input power, and it can be seen from fig. 7 that the efficiency is about 76.6%. Fig. 8 shows the simulation result of the efficiency of the linear LED driving circuit of the present invention, and it can be seen from fig. 8 that the efficiency of the present invention is 81.8%. Therefore, when the input voltage is larger than the set threshold value, the LED load is powered by the input voltage, the first capacitor C1 and the second capacitor C2 are charged, the first capacitor C1 and the second capacitor C2 are connected in parallel, and the part corresponding to the input voltage higher than the voltage of the LED load acts on the first capacitor C1 and the second capacitor C2 which are connected in parallel, so that voltage loss in the prior art is avoided; when the input voltage is smaller than the LED load voltage, the first capacitor C1 and the second capacitor C2 are connected in series to supply power to the LED load, so that the overall efficiency of the system can be improved, and in the prior art, when the input voltage is smaller than the LED load voltage, the LED cannot emit light, and the LED load can be supplied with power through the capacitors connected in series, so that the luminous efficiency of the LED load is improved.

Further, as shown in fig. 9, the simulation results of PF and THD (total harmonic distortion) of the conventional linear LED driving circuit in the prior art are shown, from which it can be seen that the power factor pf=0.922 of the LED driving circuit in the prior art and the total harmonic distortion thd=41.67% of the LED driving circuit in the prior art. Fig. 10 shows simulation results of the linear LED driving circuits PH and THD of the present invention, and it can be seen from the figure that the power factor pf=0.973 of the linear LED driving circuit of the present invention, and the total harmonic distortion thd=23.7% of the linear LED driving circuit. Therefore, the reference voltage signal is set to be in a certain proportion relation with the input voltage, so that the change trend of the input current can follow the change trend of the input voltage, the power factor PF of the whole system is improved, and the THD of the system can be further reduced due to a certain relation between the power factor PF and the THD.

The application also provides a linear LED driving method, which receives the rectified input voltage and supplies power to the linear LED driving by the input voltage, and comprises the following steps: the capacitor structure and the LED load are connected on a branch, and the capacitor structure comprises a first capacitor and a second capacitor; when the input voltage is larger than a set threshold value, the capacitor structure is connected with the LED load in series, the first capacitor is connected with the second capacitor in parallel, the input voltage supplies power to the LED load, and meanwhile the first capacitor and the second capacitor are charged; the threshold value is set to be the sum of the voltage of the LED load and the voltage of the first capacitor or the second capacitor at the end of charging; when the input voltage is smaller than the voltage of the LED load, the first capacitor and the second capacitor are connected in series, and the first capacitor and the second capacitor are connected in series to supply power to the LED load; when the input voltage is between the voltage of the LED load and the set threshold value, the LED load is powered by the input voltage, or by the larger of the input voltage and the sum of the first capacitor and the second capacitor voltage connected in series

In addition, the linear LED driving method further includes other functions of the linear LED driving circuit described above, which are not described in detail herein.

In summary, according to the linear LED driving circuit and the LED driving method provided by the invention, the first capacitor C1 and the second capacitor C2 are provided, when the input voltage is greater than the set threshold value, the input voltage supplies power to the LED load, and the first capacitor C1 and the second capacitor C2 are charged, and at this time, the first capacitor C1 and the second capacitor C2 are connected in parallel, which is equivalent to that the part of the input voltage higher than the LED load voltage acts on the first capacitor C1 and the second capacitor C2 connected in parallel, so that the voltage loss in the prior art is avoided; when the input voltage is smaller than the LED load voltage, the first capacitor C1 and the second capacitor C2 are connected in series to supply power to the LED load, so that the overall efficiency of the system and the luminous efficiency of the LED load can be improved. In addition, compared with the arrangement of a single capacitor, the invention is provided with two capacitors, and when the capacitors are changed from the parallel state to the series state, the voltage on the serially connected capacitors is improved relative to the voltage on the single capacitor, so that the efficiency can be further improved.

Furthermore, the reference voltage signal is set to be in a certain proportion relation with the input voltage, so that the change trend of the input current can follow the change trend of the input voltage, the power factor PF of the whole system is improved, and the THD of the system can be further reduced due to a certain relation between the power factor PF and the THD.

It will be understood that modifications and variations will be apparent to those skilled in the art from the foregoing description, and it is intended that all such modifications and variations be included within the scope of the following claims.

Claims (10)

1. A linear LED driving circuit that receives an input voltage obtained after rectification and that is supplied with power by the input voltage, characterized in that the linear LED driving circuit comprises:

the capacitor structure is connected with the LED load on a branch and comprises a first capacitor and a second capacitor;

When the input voltage is larger than a set threshold value, the capacitor structure is connected with the LED load in series, the first capacitor and the second capacitor are connected in parallel, the input voltage supplies power to the LED load, and meanwhile the first capacitor and the second capacitor are charged; the set threshold is the sum of the voltage of the LED load and the voltage on the first capacitor or the second capacitor at the end of charging;

When the input voltage is smaller than the voltage of the LED load, the first capacitor and the second capacitor are connected in series, and the first capacitor and the second capacitor are connected in series to supply power to the LED load;

when the input voltage is between the voltage of the LED load and the set threshold, the LED load is powered by the input voltage, or by the greater of the input voltage and the sum of the first and second capacitance voltages connected in series.

2. The linear LED driving circuit of claim 1, wherein,

The linear LED driving circuit further comprises a first unidirectional conducting element and a second unidirectional conducting element;

The first unidirectional element is connected in series on a branch between the cathode of the LED load and a first end of the capacitor structure, wherein the first end is one end of the capacitor structure close to the cathode of the LED load; the first unidirectional conduction element is unidirectional in conduction from the LED load to the capacitor structure;

The second unidirectional conduction element is arranged on a branch path between the cathode of the first unidirectional conduction element and the anode of the LED load, and the second unidirectional conduction element is unidirectional in conduction from the capacitor structure to the LED load;

when the input voltage is larger than the set threshold value, the first unidirectional conduction element is conducted;

when the input voltage is smaller than the voltage of the LED load, the second unidirectional conduction element is conducted.

3. The linear LED driving circuit of claim 1, wherein,

The linear LED driving circuit further comprises a first current circuit and a second current circuit, wherein the first current circuit is arranged between the cathode of the LED load and the grounding end; the second current circuit is arranged between a second end of the capacitor structure and a grounding end, and the second end is one end of the capacitor structure close to the grounding end;

Wherein when the input voltage is greater than the set threshold, providing, by the second current circuit, a current of the LED load; when the input voltage is less than the voltage of the LED load or between the voltage of the LED load and the set threshold, a current of the LED load is provided by the first current circuit.

4. A linear LED drive circuit according to claim 3 wherein,

The linear LED driving circuit further includes a reference signal generating circuit that generates a reference voltage signal in a proportional relationship with the input voltage, and the first current circuit and the second current circuit generate a current flowing through the LED load based on the reference voltage signal.

5. The linear LED driving circuit of claim 4, wherein,

The first current circuit comprises a first switching tube and a first operational amplifier, the first switching tube is connected to a branch between a cathode of the LED load and a grounding end, a control end of the first switching tube is connected with an output end of the first operational amplifier, and two input ends of the first operational amplifier are respectively connected with the reference voltage signal and a signal representing current flowing through the LED load;

The second current circuit comprises a second switching tube and a second operational amplifier, the second switching tube is connected to a branch between the second end of the capacitor structure and the grounding end, the control end of the second switching tube is connected with the output end of the second operational amplifier, and two input ends of the second operational amplifier are respectively connected with the reference voltage signal and the signal representing the load current flowing through the LED.

6. The linear LED driving circuit of claim 5, wherein,

The linear LED driving circuit further comprises a current selection circuit, and when the input voltage is larger than the set threshold value, the current selection circuit controls the first switching tube to be turned off;

the current selection circuit controls the second switching tube to be turned off when the input voltage is smaller than the voltage of the LED load or between the voltage of the LED load and the set threshold.

7. The linear LED driving circuit of claim 1, wherein,

The capacitor structure further comprises a first switch, a second switch and a third switch, wherein the first capacitor is connected with the first switch in series to obtain a first series circuit, the second capacitor is connected with the second switch in series to obtain a second series circuit, and the first series circuit and the second series circuit are connected in parallel; a third switch is connected between the first series circuit and the second series circuit, one end of the third switch is connected to a common end of the first capacitor and the second switch, and the other end of the third switch is connected to a common end of the second capacitor and the second switch;

When the input voltage is smaller than the voltage of the LED load, the first switch and the second switch are in an open state, the third switch is in a closed state, and the first capacitor and the second capacitor are connected in series;

When the input voltage is greater than the set threshold, the first switch and the second switch are in a closed state, the third switch is in an open state, and the first capacitor and the second capacitor are connected in parallel.

8. The linear LED driving circuit of claim 1, wherein,

A third unidirectional conducting element is arranged on a branch between the input voltage and the anode of the LED load, and the third unidirectional conducting element conducts unidirectionally from the input voltage to the LED load.

9. The linear LED driving circuit of claim 1, wherein,

A fourth unidirectional conducting element is arranged on a branch between the grounding end and a second end of the second capacitor, and the second end is one end of the capacitor structure close to the grounding end; the fourth unidirectional conduction element conducts unidirectionally from the ground terminal to the second terminal.

10. A linear LED driving method of receiving an input voltage obtained by rectification and supplying power to the linear LED driving by the input voltage, characterized by comprising:

the capacitor structure and the LED load are connected on a branch, and the capacitor structure comprises a first capacitor and a second capacitor;

When the input voltage is larger than a set threshold value, the capacitor structure is connected with the LED load in series, the first capacitor and the second capacitor are connected in parallel, the input voltage supplies power to the LED load, and meanwhile the first capacitor and the second capacitor are charged; the set threshold is the sum of the voltage of the LED load and the voltage on the first capacitor or the second capacitor at the end of charging;

When the input voltage is smaller than the voltage of the LED load, the first capacitor and the second capacitor are connected in series, and the first capacitor and the second capacitor are connected in series to supply power to the LED load;

when the input voltage is between the voltage of the LED load and the set threshold, the LED load is powered by the input voltage, or by the greater of the input voltage and the sum of the first and second capacitance voltages connected in series.