CN108925005B

CN108925005B - Linear LED drive circuit

Info

Publication number: CN108925005B
Application number: CN201810918204.1A
Authority: CN
Inventors: 王建新; 郑清良
Original assignee: Hangzhou Silergy Semiconductor Technology Ltd
Current assignee: Hangzhou Silergy Semiconductor Technology Ltd
Priority date: 2018-08-13
Filing date: 2018-08-13
Publication date: 2020-11-06
Anticipated expiration: 2038-08-13
Also published as: CN108925005A

Abstract

The first branch and the second branch in the linear LED driving circuit are connected between output ports of a rectifying circuit in parallel, so that when the linear LED driving circuit works in a first state, the first branch and the second branch both receive output energy of the rectifying circuit, and therefore the efficiency and the linear adjustment rate of the linear LED driving circuit can be improved.

Description

Linear LED drive circuit

Technical Field

The invention relates to power electronic technology, in particular to a linear LED driving circuit.

Background

Fig. 1 shows a linear LED driving circuit in the prior art, and the linear LED driving circuit 1 is a half-line linear circuit. The linear LED driving circuit 1 includes a rectifying circuit 11, a capacitor C1, diodes D1 and D2, switching tubes Q1 and Q2, and an LED load LED. When the output voltage VBUS of the rectifying circuit 11 is smaller than the voltage of the load LED, the switching tube Q1 is controlled to be turned on, the switching tube Q2 is controlled to be turned off, and the capacitor C1 supplies energy to the load LED load. That is, the current path at this time is C1-Q1-LED-D2-C1. When the output voltage VBUS of the rectifying circuit 11 is greater than the load LED, the switching tube Q1 is controlled to be turned off, the switching tube Q2 is controlled to be turned on, and the voltage VBUS charges the capacitor C1 and simultaneously provides energy to the LED. The current path at this time is AC-C1-D1-Q2-LED-AC. As shown in fig. 1, the linear LED driving circuit 1 of the prior art can only be applied to the high-voltage input and half-voltage output, but cannot be applied to the full-voltage input application.

Disclosure of Invention

In view of the above, the present invention provides a linear LED driving circuit to improve the efficiency and linear adjustment rate of the linear LED driving circuit.

In a first aspect, a linear LED driving circuit is provided, including:

the first branch circuit and the second branch circuit are connected between two output ports of the rectifying circuit in parallel;

the first branch circuit comprises an energy storage element, and the second branch circuit comprises an LED load and a controllable current source which are connected in series, so that when the linear LED driving circuit is in a first state, the first branch circuit and the second branch circuit both receive output energy of the rectifying circuit.

Further, the linear LED driving circuit further includes:

and the third branch circuit is connected between the first branch circuit and the second branch circuit in a predetermined mode, so that when the linear LED driving circuit is in a second state, only the second branch circuit receives the output energy of the rectifying circuit, when the linear LED driving circuit is in a third state, the energy storage element and the LED load receive the output energy of the rectifying circuit through the third branch circuit, and when the linear LED driving circuit is in a fourth state, the LED load receives the output energy of the energy storage element.

Further, the first branch further comprises a first transistor connected in series with the energy storage element.

Further, the third branch comprises a unidirectional conducting element.

Further, the second branch further comprises a second transistor connected in series with the LED load and the controllable current source.

Further, the first branch further comprises a third transistor connected in series with the energy storage element.

Further, the third branch further comprises a fourth transistor connected in series with the unidirectional conducting element, wherein the fourth transistor is configured to switch between a constant current state and an off state.

Further, the linear LED driving circuit is configured to be in the first state when a peak value of the ac input voltage is below a preset value.

Further, the linear LED driving circuit is configured to switch between the second state, the third state and the fourth state when a peak value of the ac input voltage is higher than a preset value.

Further, the linear LED driving circuit is configured to be in the second state when a voltage sampling signal representing an output voltage instantaneous value of the rectifying circuit is smaller than a first voltage threshold, in the third state when the voltage sampling signal is larger than the first voltage threshold, and in the fourth state when the output voltage of the rectifying circuit is zero or approximately zero.

Further, the linear LED driving circuit further includes:

a controller configured to obtain a peak state of an alternating current input voltage by sampling a voltage of an alternating current input port, a voltage of a first end of the third branch, or a voltage of a first end of a rectification output port, and control the linear LED driving circuit to switch between the first state, the second state, the third state, and the fourth state according to the peak state of the alternating current input voltage.

Further, the energy storage element is connected between the first end of the rectification output port and the first end of the third branch; the LED load and the controllable current source are connected in series between the second end of the third branch and the second end of the rectification output port.

Further, the first transistor is connected between the first end of the third branch and the second end of the rectification output port; the second transistor is connected between the first end of the rectified output port and the second end of the third branch.

Further, the LED load and the controllable current source are connected in series between a first end of a rectified output port and a first end of the third branch; the energy storage element is connected between the second end of the third branch and the second end of the rectification output port.

Further, the second transistor is connected between the first end of the third branch and the second end of the rectification output port; the first transistor is connected between a first end of the rectified output port and a second end of the third branch.

Further, the LED load is connected between the first end of the third branch and the first end of the rectification output port; the energy storage element and the third transistor are connected in series between the second end of the third branch and the second end of the rectification output port;

wherein the third transistor is configured to switch between a constant current state, an on state, and an off state.

Further, the controllable current source is connected between the first end of the third branch and the second end of the rectified output port; the first transistor is connected between a first end of the rectified output port and a second end of the third branch.

Further, the energy storage element is connected between the first end of the rectification output port and the first end of the third branch; the LED load is connected between the second end of the third branch and the second end of the rectified output port.

Further, the first transistor is connected between the first end of the third branch and the second end of the rectification output port; the controllable current source is connected between the first end of the rectified output port and the second end of the third branch.

Further, in the first state, the first transistor and the second transistor are controlled to be turned on; in the second state, the first transistor is controlled to be turned off, and the second transistor is controlled to be turned on; in the third state, the first transistor and the second transistor are controlled to be turned off; in the fourth state, the first transistor is turned on through a parasitic diode, and the second transistor is controlled to be turned on.

Further, in the first state, the first transistor and the third transistor are controlled to be turned on; in the second state, the first transistor and the third transistor are controlled to be turned off; in the third state, the transistor in the controllable current source and the first transistor are controlled to be turned off, and the third transistor is controlled to work in a constant current state; in the fourth state, the third transistor is controlled to be turned on, and the first transistor is turned on through a parasitic diode.

Further, in the first state, the first transistor is controlled to be turned on, and the fourth transistor is controlled to be turned off; in the second state, the first transistor and the fourth transistor are controlled to be turned off; in the third state, the first transistor is controlled to be turned off, the fourth transistor is controlled to work in a constant current state, and the transistor in the controllable current source is controlled to be turned off; in the fourth state, the first transistor is turned on through a parasitic diode, and the fourth transistor is controlled to be turned off.

In a second aspect, a linear LED driving circuit is provided, comprising:

a first branch and a second branch connected in parallel between output ports of the rectifying circuit; the first branch circuit comprises an energy storage element, and the second branch circuit comprises an LED load and a controllable current source which are connected in series; and

a third branch connected between the first branch and the second branch;

the first branch, the second branch and the third branch are configured such that when the linear LED driving circuit is in a first state, only the second branch receives output energy of a rectifying circuit, when the linear LED driving circuit is in a second state, the energy storage element and the LED load receive output energy of the rectifying circuit through the third branch, and when the linear LED driving circuit is in a third state, the LED load receives output energy of the energy storage element.

Further, when the linear LED driving circuit is in a fourth state, the first branch and the second branch are connected in parallel between output ports of the rectifying circuit, so that both the first branch and the second branch receive output energy of the rectifying circuit.

Further, the first branch circuit further comprises a switching tube connected in series with the energy storage element.

Further, the third branch comprises a unidirectional conducting element.

Further, the second branch further comprises a first transistor connected in series with the LED load and the controllable current source.

Further, the first branch further comprises a second transistor connected in series with the energy storage element.

Further, the switch tube is a transistor or a diode.

According to the technical scheme of the embodiment of the invention, the first branch circuit and the second branch circuit in the linear LED drive circuit are connected in parallel between the output ports of the rectification circuit, so that when the linear LED drive circuit works in a first state, the first branch circuit and the second branch circuit both receive the output energy of the rectification circuit, and the efficiency and the linear adjustment rate of the linear LED drive circuit are improved.

Drawings

The above and other objects, features and advantages of the present invention will become more apparent from the following description of the embodiments of the present invention with reference to the accompanying drawings, in which:

FIG. 1 is a circuit diagram of a prior art linear LED drive circuit;

fig. 2 is a circuit diagram of a linear LED driving circuit according to a first embodiment of the present invention;

FIG. 3 is a circuit diagram of a controller of an embodiment of the present invention;

FIG. 4 is a waveform diagram illustrating the operation of the linear LED driving circuit according to the embodiment of the present invention when the AC input voltage is low;

FIG. 5 is a waveform diagram illustrating the operation of the linear LED driving circuit according to the embodiment of the present invention when the AC input voltage is high;

FIG. 6 is a circuit diagram of a linear LED driver circuit according to a second embodiment of the present invention;

fig. 7 is a circuit diagram of a linear LED driving circuit according to a third embodiment of the present invention;

FIG. 8 is a circuit diagram illustrating a linear LED driving circuit according to a third embodiment of the present invention in a first state;

FIG. 9 is a circuit diagram illustrating a third embodiment of a linear LED driving circuit according to the present invention in a second state;

FIG. 10 is a circuit diagram illustrating a third exemplary embodiment of a linear LED driving circuit according to the present invention;

FIG. 11 is a circuit diagram illustrating a linear LED driving circuit according to a third embodiment of the present invention in a fourth state;

fig. 12 is a circuit diagram of a linear LED driving circuit according to a fourth embodiment of the present invention.

Detailed Description

The present application is described below based on examples, but the present application is not limited to only these examples. In the following detailed description of the present application, certain specific details are set forth in detail. It will be apparent to one skilled in the art that the present application may be practiced without these specific details. Well-known methods, procedures, components and circuits have not been described in detail so as not to obscure the present application.

Further, those of ordinary skill in the art will appreciate that the drawings provided herein are for illustrative purposes and are not necessarily drawn to scale.

Meanwhile, it should be understood that, in the following description, a "circuit" refers to a conductive loop constituted by at least one element or sub-circuit through electrical or electromagnetic connection. When an element or circuit is referred to as being "connected to" another element or element/circuit is referred to as being "connected between" two nodes, it may be directly coupled or connected to the other element or intervening elements may be present, and the connection between the elements may be physical, logical, or a combination thereof. In contrast, when an element is referred to as being "directly coupled" or "directly connected" to another element, it is intended that there are no intervening elements present.

Unless the context clearly requires otherwise, throughout the description and the claims, the words "comprise", "comprising", and the like are to be construed in an inclusive sense as opposed to an exclusive or exhaustive sense; that is, what is meant is "including, but not limited to".

In the description of the present application, it is to be understood that the terms "first," "second," and the like are used for descriptive purposes only and are not to be construed as indicating or implying relative importance. In addition, in the description of the present application, "a plurality" means two or more unless otherwise specified.

Fig. 2 is a circuit diagram of a linear LED driving circuit according to a first embodiment of the present invention. Fig. 3 is a circuit diagram of a controller of an embodiment of the present invention. Fig. 4 is a waveform diagram of the linear LED driving circuit according to the embodiment of the present invention when the ac input voltage is low. Fig. 5 is a waveform diagram of the linear LED driving circuit according to the embodiment of the present invention when the ac input voltage is high.

As shown in fig. 2, the linear LED driving circuit 2 of the present embodiment includes a first branch 21, a second branch 22, a third branch 23, a rectifying circuit 24 and a controller 25. The rectifier circuit 24 is configured to convert an ac input voltage Vin into a dc voltage and output the dc voltage to the dc BUS. The first branch 21 and the second branch 22 are both connected between the rectified output ports (i.e., the output ports of the rectification circuit 24).

The first branch 21 comprises an energy storage element C21 and a transistor Q21. Wherein the energy storage element C21 is connected between the first end i1 of the rectified output port and the first intermediate end CN (i.e., the first end of the third branch 23). The transistor Q21 is connected between the first intermediate terminal CN and the second terminal i2 of the rectified output port. The second terminal i2 of the rectified output port is a ground terminal. The transistor Q21 is controlled by the switch control signal S2 to turn on or off.

The second branch 22 comprises a LED load LED1, a controllable current source 221 and a transistor Q22. The transistor Q22 is connected between the first end i1 of the rectified output port and the second intermediate end LP (i.e., the second end of the third branch 23). The controllable current source 221 and the LED load LED1 are connected in series between the second intermediate terminal LP and the second terminal i2 of the rectified output port. The transistor Q22 is controlled by the switch control signal S1 to be turned on or off. The controllable current source 221 is configured to keep the current through the LED load LED1 at a set value. The controllable current source 221 includes a transistor Q23, an error amplifier gm1, and a resistor R1.

The third leg 23 is connected between the first intermediate terminal CN and the second intermediate terminal LP. The third branch includes a unidirectional pass element D21. Wherein the anode of the one-way conduction element D21 is connected to the first intermediate terminal CN, and the cathode is connected to the second intermediate terminal LP.

The controller 25 is configured to generate switch control signals S1 and S2 to control the transistors Q22 and Q21, respectively, based on the voltage sampling signal. The voltage sampling signal is used to characterize the output voltage of the rectifier circuit 24. As shown in fig. 3, the controller 25 includes a sampling circuit 251, a comparator cmp1, a filter 252, and a comparator cmp 2.

The sampling circuit 251 is configured to sample and obtain a voltage sampling signal Vs representing the output voltage of the rectifying circuit 24 at the dc BUS or at the first intermediate terminal CN.

The comparator cmp1 has an input terminal receiving the voltage sampling signal Vs and a first voltage threshold Vref1, and an output terminal outputting a switch control signal S1 to control the transistor Q22 to be turned on or off. When the voltage sampling signal Vs is smaller than the first voltage threshold Vref1, the comparator cmp1 outputs an active switch control signal S1 to control the transistor Q22 to be turned on.

The filter 252 is configured to filter the voltage sample signal Vs to output a filtered voltage sample signal Vs _ a. The comparator cmp2 has an input terminal receiving the filtered voltage sampling signal Vs _ a and a second voltage threshold Vref2, and an output terminal outputting a switch control signal S2 to control the transistor Q21 to be turned on or off. When the filtered voltage sampling signal Vs _ a is smaller than the second voltage threshold Vref2, the comparator cmp2 outputs an active switch control signal S2 to control the transistor Q21 to be turned on.

In the present embodiment, the linear LED driving circuit 2 operates in four different states according to the peak state of the ac input voltage Vin.

When the peak value of the ac input voltage Vin is lower than the preset value, the linear LED driving circuit 2 operates in the first state. When the peak value of the ac input voltage Vin is higher than the preset value, the linear LED driving circuit 2 switches in the second state, the third state, and the fourth state. The peak state of the ac input voltage Vin can be obtained through the voltage sampling signal Vs to determine whether the linear LED driving circuit 2 operates in a low-voltage state or a high-voltage state. In another alternative implementation, the peak state of the ac input voltage Vin may be obtained by sampling the voltage of the ac input port to determine whether the linear LED driving circuit 2 operates in the low voltage state or the high voltage state.

It will be appreciated that the above preset values may be set according to the actual requirements of the circuit and the performance of the components in the linear LED driving circuit 2. Wherein the second voltage threshold Vref2 corresponds to the preset value.

The linear LED driving circuit 2 operates in the first state when the ac input voltage Vin is a low voltage (i.e. the peak value of the ac input voltage Vin is lower than the preset value), and the operating waveform diagram is shown in fig. 4. When the peak value of the ac input voltage Vin is lower than the preset value, the voltage sampling signal Vs is always smaller than the first voltage threshold Vref 1. Therefore, the comparator cmp1 always outputs the active switch control signal S1, and the control transistor Q22 is continuously turned on. The filtered voltage sampling signal Vs _ a is always smaller than the second voltage threshold Vref2 when the ac input voltage Vin is low. Therefore, the comparator cmp2 always outputs the active switch control signal S2, and the control transistor Q21 is continuously turned on. That is, when the ac input voltage Vin is low, the controller 25 controls the transistors Q21 and Q22 to be turned on in the linear LED driving circuit 2. As shown in fig. 2, when both the transistors Q21 and Q22 are turned on, the voltage of the first intermediate terminal CN is less than that of the second intermediate terminal LP, so the unidirectional conductive element D21 is not turned on at this time. That is, when the peak value of the ac input voltage Vin is lower than the preset value, the first branch 21 and the second branch 22 are connected in parallel to the output port of the rectifier circuit 24, and both can receive the output energy of the rectifier circuit 24. In fig. 4, when the bus voltage Vbus is greater than Vled (i.e., the LED load on-state voltage), the current Iled flowing through the LED load is substantially maintained at I1 due to the regulation of the controllable current source 221. When the BUS voltage BUS is less than Vled, the current Iled flowing through the LED load gradually decreases to 0.

That is, when the ac input voltage Vin of the linear LED driving circuit 2 is low, the energy storage element C21 is connected in parallel in the circuit to improve the linear adjustment rate of the linear LED driving circuit 2 in a low voltage state, so as to improve the stability of the output voltage.

The linear LED driving circuit 2 switches between the second state, the third state and the fourth state when the ac input voltage Vin is at a high voltage (that is, the peak value of the ac input voltage Vin is higher than a preset value), and the working waveform diagram is shown in fig. 5. When the peak value of the ac input voltage Vin is higher than the preset value, the filtered voltage sampling signal Vs _ a is always greater than the second voltage threshold Vref 2. Therefore, the comparator cmp2 always outputs the invalid switch control signal S2. I.e., the switch control signal S2 that controls the transistor Q21 is always inactive.

At time t 0-time t1, the linear LED driving circuit 2 operates in the second state. As shown in fig. 5, the voltage sampling signal Vs is less than the first voltage threshold Vref1, the comparator cmp1 outputs an active switch control signal S1, and the control transistor Q22 remains on. At this time, since the voltage of the first intermediate terminal CN is lower than the voltage of the second intermediate terminal LP, the one-way conduction element D21 is not conducted at this time. Therefore, the first branch 21 where the energy storage element C21 is located is not connected to the circuit, and the current Ic flowing through the energy storage element C21 is 0. Therefore, at time t 0-time t1, the output energy of the rectifier circuit 24 powers only the LED load LED 1. And, due to the regulation of the controllable current source 221, the current Iled flowing through the LED load LED1 is substantially maintained at I2 at this time. It is to be understood that the controllable current source 221 may adjust the current in the branch depending on the variation of the ac input voltage Vin.

At time t 1-time t2, the linear LED driving circuit 2 operates in the third state. As shown in fig. 5, the voltage sampling signal Vs is greater than the first voltage threshold Vref 1. Therefore, the comparator cmp1 outputs an inactive switch control signal S1, which controls the transistor Q22 to remain off. At this time, the output energy of the rectifying circuit 24 charges the capacitor C21, and the voltage across the unidirectional conductive element D21 reaches its conduction voltage, so that the unidirectional conductive element D21 is turned on. Therefore, at time t 1-time t2, the output energy of the rectifying circuit 24 simultaneously powers the energy storage element C21 and the LED load LED 1. It should be understood that, since it takes a certain time for the voltage across the unidirectional conducting element D21 to reach its conducting voltage, a current flows through the energy storage element C21 and the LED load LED1 after a delay at time t 1. During the time that the energy storage element C21 and the LED load LED1 are turned on, the currents Ic and Iled flowing through the energy storage element C21 and the LED load LED1 are substantially maintained at I2 due to the regulation of the controllable current source 221. After the energy storage element C21 and the LED load LED1 are turned on for a period of time, since the voltage across the LED load gradually decreases to be less than its turn-on voltage, the currents Ic and Iled flowing through the energy storage element C21 and the LED load LED1 gradually decrease to 0.

At time t 2-time t3, the linear LED driving circuit 2 operates in the second state. As shown in fig. 5, the voltage sampling signal Vs is less than the first voltage threshold Vref 1. Therefore, the comparator cmp1 outputs an active switch control signal S1, which controls the transistor Q22 to remain on. At this time, since the voltage of the first intermediate terminal CN is lower than the voltage of the second intermediate terminal LP, the one-way conduction element D21 is not conducted at this time. Therefore, the first branch 21 where the energy storage element C21 is located is not connected to the circuit, and the current Ic flowing through the energy storage element C21 is 0. Therefore, at time t 2-time t3, the output energy of the rectifier circuit 24 powers only the LED load LED 1. And, due to the regulation of the controllable current source 221, the current Iled flowing through the LED load LED1 is substantially maintained at I2 at this time.

At time t 3-time t4, the linear LED driving circuit 2 operates in the fourth state. As shown in fig. 5, the voltage sampling signal Vs is less than the first voltage threshold Vref1, and the comparator cmp1 outputs an active switch control signal S1 to control the transistor Q22 to remain on. At this time, the output voltage of the rectifying circuit 24 is 0 or approximately 0, and thus the LED load is supplied with power through the energy storage element C21. At this time, the voltage of the first middle terminal CN is less than the voltage of the second middle terminal LP and less than the voltage of the second terminal i2 of the rectification output port, the unidirectional conducting element D21 is not conducting, the transistor Q21 is conducting through its parasitic diode, and a path of C21-Q22-led1-Q23-R1-Q21-C21 is formed. Due to the regulation of the controllable current source 221, the absolute values of the currents Ic and Iled flowing through the energy storage element C21 and the LED load LED1 are substantially maintained at I2 for a period of time after time t 3. It should be understood that the current Ic and Iled flowing through the energy storage element C21 and the LED load LED1 at this time are in opposite directions. However, since the energy in the energy storage element C21 decreases, the voltage across the LED load LED1 gradually decreases to be less than its turn-on voltage, so the current Ic flowing through the energy storage element C21 gradually increases to 0, and the current Iled flowing through the LED load LED1 gradually decreases to 0. At time t4, a new cycle begins.

In the present embodiment, the linear LED driving circuit switches among the second state, the third state and the fourth state to supply power to the LED load when the ac input voltage Vin is in the high-voltage state. The energy storage element is used for absorbing the peak energy of the mains supply and releasing the peak energy to the LED load, so that the LED driving circuit is prevented from generating large loss when the alternating current input voltage is in a high-voltage state, meanwhile, the LED on-state voltage in a wide range is allowed, and the design flexibility is improved. Compared with the linear LED drive circuit in the prior art, the linear LED drive circuit in the embodiment can control the LED load to be conducted when the alternating-current input voltage is in a low-voltage state, so that the input voltage range is widened, the conduction angle of the input current is increased, and the power factor and the efficiency of the linear LED drive circuit are improved.

In another alternative implementation, the switching control signal of the transistor Q21 is always inactive when the ac input voltage Vin is in a high-voltage state, and is turned on through its parasitic diode when the output voltage of the rectifying circuit 24 is 0 or approximately 0. Therefore, the transistor Q21 can be replaced by a diode when the ac input voltage Vin is in a high-voltage state. The anode of the diode is connected to the second terminal i2 of the rectified output port and the cathode is connected to the first intermediate terminal CN. It is thus achieved that at time t 0-t 3 the diode is non-conducting and at time t3-t4 the diode is conducting such that the energy storage element supplies the load. That is, when the ac input voltage Vin is in a high-voltage state, replacing the transistor Q21 with a diode also can achieve the function of making the output voltage of the linear LED driving circuit smaller to improve the power factor and efficiency of the linear LED driving circuit.

Fig. 6 is a circuit diagram of a linear LED driving circuit according to a second embodiment of the present invention. As shown in fig. 6, the linear LED driving circuit 6 of the present embodiment includes a first branch circuit 61, a second branch circuit 62, a third branch circuit 63, and a rectifying circuit 64. The rectifying circuit 64 is configured to convert an ac input voltage Vin into dc and output the dc to the dc BUS. The first branch 61 and the second branch 62 are both connected between the rectified output ports (i.e., the output ports of the rectification circuit 64).

The first branch 61 includes a storage element C61 and a transistor Q61. Wherein the transistor Q61 is connected between the rectified output port i3 and the second intermediate terminal LP1 (i.e. the second terminal of the third branch 63). The energy storage element C61 is connected between the second intermediate terminal LP1 and the second terminal i4 of the rectified output port. The second terminal i4 of the rectifying output port is a ground terminal. The transistor Q61 is controlled by the switch control signal S2 to turn on or off.

The second branch 62 comprises an LED load LED2, a controllable current source 621 and a transistor Q62. The transistor Q62 is connected between the first intermediate terminal CN1 and the second terminal i4 of the rectified output port. The controllable current source 621 and the LED load LED2 are connected in series between the first end i3 of the rectified output port and a first intermediate terminal CN1 (i.e., a first end of the third branch 63). The transistor Q62 is controlled by the switch control signal S1 to be turned on or off. The controllable current source 621 is configured to maintain the current flowing through the LED load LED2 at a preset value. The controllable current source 621 includes a transistor Q63, an error amplifier gm2, and a resistor R2.

The third leg 63 is connected between the first intermediate end CN1 and the second intermediate end LP 1. Third branch 73 includes a one-way pass element D61. The anode of the one-way conduction element D61 is connected to the first intermediate terminal CN1, and the cathode is connected to the second intermediate terminal LP 1.

The linear LED driving circuit 6 further includes a controller (not shown) for generating switching control signals S1 and S2 to control the transistors Q62 and Q61, respectively, according to the voltage sampling signal. The voltage sampling signal is used to characterize the output voltage of the rectifying circuit 64. The circuit diagram of the controller is shown in fig. 3, and is not described herein again.

The linear LED driving circuit 6 of this embodiment is connected in a different manner from the linear LED driving circuit 2 of the first embodiment, but the operating states thereof are basically the same, that is, the linear LED driving circuit 6 operates in four different states according to the magnitude of the ac input voltage Vin. The operation waveforms of the linear LED driving circuit 6 in different operation states are also shown in fig. 3 and 4. And therefore will not be described in detail herein.

Therefore, even when the ac input voltage Vin is low, the linear LED driving circuit 6 can improve the linear adjustment rate of the linear LED driving circuit 6 in a low voltage state by connecting the energy storage element C61 in parallel to the circuit, thereby improving the stability of the output voltage. The linear LED driving circuit 6 is also switched among the second state, the third state and the fourth state to supply power to the LED load when the ac input voltage Vin is in the high-voltage state. Compared with the linear LED drive circuit in the prior art, the output voltage of the linear LED drive circuit 6 is smaller, and the power factor and the efficiency of the linear LED drive circuit are improved.

In another alternative implementation, the switching control signal S2 of the transistor Q61 is always inactive when the ac input voltage Vin is in a high-voltage state, and is turned on through its parasitic diode when the output voltage of the rectifying circuit 64 is 0 or approximately 0. Therefore, the transistor Q61 can be replaced by a diode when the ac input voltage Vin is in a high-voltage state. The anode of the diode is connected to the second intermediate terminal LP1 and the cathode is connected to the first terminal i3 of the rectified output port. Therefore, it can be realized that the diode is not conducted from time t0 to time t3, and at time t3 to time t4, the diode is conducted so that the energy storage element C61 supplies power to the LED load LED 2. That is, when the ac input voltage Vin is in a high-voltage state, replacing the transistor Q61 with a diode also can achieve the function of making the output voltage of the linear LED driving circuit smaller to improve the power factor and efficiency of the linear LED driving circuit.

Fig. 7 is a circuit diagram of a linear LED driving circuit according to a third embodiment of the present invention. Fig. 8 is a circuit diagram illustrating a linear LED driving circuit according to a third embodiment of the present invention operating in a first state. Fig. 9 is a circuit diagram illustrating a linear LED driving circuit according to a third embodiment of the present invention operating in a second state. Fig. 10 is a circuit diagram illustrating a third embodiment of a linear LED driving circuit according to the present invention operating in a third state. Fig. 11 is a circuit diagram illustrating the linear LED driving circuit according to the third embodiment of the present invention in a fourth state.

As shown in fig. 7, the linear LED driving circuit 7 of the present embodiment includes a first branch 71, a second branch 72, a third branch 73, a rectifying circuit 74, and a logic circuit 75. The rectifier circuit 74 converts an ac input voltage Vin into dc and outputs the dc to the dc BUS. The first branch 71 and the second branch 72 are both connected between the rectified output ports (i.e., the output ports of the rectification circuit 74).

The first branch 71 includes an energy storage element C71, a transistor Q71, and a transistor Q73. Wherein the transistor Q71 is connected between the rectified output port i5 and the second intermediate terminal LP2 (i.e. the second terminal of the third branch 73). The energy storage element C71 and the transistor Q73 are connected in series between the second intermediate terminal LP2 and the second terminal i6 of the rectified output port. The second terminal i6 of the rectifying output port is a ground terminal. The transistor Q71 is controlled by the switch control signal S1 to turn on or off. The transistor Q73 is controlled to switch between a constant current state, an on state or an off state.

The second branch 72 comprises an LED load LED3 and a controllable current source 721. The controllable current source 721 includes a transistor Q72. The transistor Q72 is connected between the first intermediate terminal CN1 (i.e., the first terminal of the third branch 73) and the second terminal i6 of the rectified output port. The LED load LED3 is connected between the first end i5 of the rectified output port and the first intermediate end CN 2. The transistor Q72 operates in a constant current state or an off state under the control of the switch control signals S1 and S2. The controllable current source 721 is configured such that the current through the LED load LED3 is kept at a set value.

The third leg 73 is connected between the first intermediate end CN2 and the second intermediate end LP 2. Third branch 73 includes a one-way pass element D71. The anode of the one-way conduction element D71 is connected to the first intermediate terminal CN2, and the cathode is connected to the second intermediate terminal LP 2.

The logic circuit 75 is configured to control the transistor Q71 to be turned on or off, and the transistors Q73 and Q72 to be turned on or off or operated in a constant current state according to the switch control signals S1 and S2. The logic circuit 75 includes an or gate or1, inverters inv1 and inv2, and switches K1-K4.

The linear LED driving circuit 7 further includes a controller (not shown) for generating switching control signals S1 and S2 to control the transistor Q71, the transistor Q72, and the transistor Q73 according to the voltage sampling signal. The voltage sample signal is used to characterize the output voltage of the rectifier circuit 74. The circuit diagram of the controller is shown in fig. 3, and is not described herein again.

In the present embodiment, the linear LED driving circuit 7 still operates in four different states according to the peak state of the ac input voltage Vin. That is, when the peak value of the ac input voltage Vin is lower than the preset value, the linear LED driving circuit 7 operates in the first state. When the peak value of the ac input voltage Vin is higher than the preset value, the linear LED driving circuit 7 switches in the second state, the third state, and the fourth state.

The linear LED driving circuit 7 operates in the first state when the ac input voltage Vin is a low voltage (i.e. the peak value of the ac input voltage Vin is lower than the predetermined value), and the operating waveform diagram is still as shown in fig. 4. When the peak value of the alternating-current input voltage Vin is lower than the preset value, the voltage sampling signal Vs is smaller than the first voltage threshold, the filtered voltage sampling signal is smaller than the second voltage threshold Vref2, and the comparator cmp1 and the comparator cmp2 always output valid switch control signals S1 and S2 respectively. As shown in fig. 7, the control transistor Q71 is continuously turned on when the switch control signal S2 is asserted. The or gate or1 outputs an active signal to control the switches K1 and K3 to be on and the switches K2 and K4 to be off. That is, the transistor Q72 operates in a constant current state at this time (i.e., the transistor Q72, the differential amplifier gm3, and the resistor R3 constitute the controllable current source 721).

Further, the linear LED driving circuit 7 further includes a breakdown diode D72 and a resistor R5. The breakdown diode D72 and the resistor R5 are connected in series between the second intermediate terminal LP2 and the ground terminal. A control terminal of the transistor Q73 is connected to a common terminal of the breakdown diode D72 and the resistor R5. Since the transistor Q71 is controlled to be turned on, the voltage of the second intermediate terminal LP2 is increased to cause the breakdown diode D72 to be broken down. Therefore, the transistor Q73 is in a conducting state controlled by the voltage of the breakdown diode D72.

Thus, when the ac input voltage Vin is low, the linear LED driving circuit 7 turns on the transistor Q71, turns on the transistor Q73, and turns on the transistor Q72 to be in a constant current state. And at this time, the voltage of the first intermediate terminal CN2 is less than the voltage of the second intermediate terminal LP2, and the unidirectional conducting element D71 is non-conducting, and the circuit diagram thereof is shown in fig. 8 (the dashed line is used to indicate that the branch is non-conducting). When the peak value of the ac input voltage Vin is lower than the preset value, the first branch 71 and the second branch 72 are connected in parallel to the output port of the rectifying circuit 74, and both can receive the output energy of the rectifying circuit 74. As shown in fig. 4, when the bus voltage Vbus is greater than the on-state voltage Vled of the LED load, the current Iled flowing through the LED load is substantially maintained at I1 due to the adjustment of the controllable current source 721. When the BUS voltage BUS is smaller than the turn-on voltage Vled of the LED load, the current Iled flowing through the LED load LED3 gradually decreases to 0.

Therefore, when the ac input voltage Vin of the linear LED driving circuit 7 is low, the energy storage element C71 is connected in parallel to improve the linear adjustment rate of the linear LED driving circuit 7 in a low voltage state, thereby improving the stability of the output voltage.

When the ac input voltage Vin is at a high voltage (i.e. the peak value of the ac input voltage Vin is higher than the predetermined value), the linear LED driving circuit 7 still has the working waveform as shown in fig. 5. When the peak value of the ac input voltage Vin is higher than the preset value, the filtered voltage sampling signal Vs _ a is always greater than the second voltage threshold Vref 2. Therefore, the comparator cmp2 always outputs an invalid switch control signal S2, and the transistor Q71 is controlled to be turned off.

At time t 0-time t1, the linear LED driving circuit 7 operates in the second state. As shown in fig. 5, the voltage sampling signal Vs is less than the first voltage threshold Vref 1. Therefore, the comparator cmp1 outputs an active switch control signal S1. When the switch control signal S1 is active, the or gate or1 outputs an active signal to control the switches K1 and K3 to be turned on, the switches K2 and K4 to be turned off, and the transistor Q72 is in a constant current state. That is, at time t0 to time t1, since the transistor Q71 is turned off, the energy storage element C71 is not connected to the circuit, and the current Ic flowing through the energy storage element C71 is 0.

At time t 0-time t1, switches K1 and K3 are turned on, and transistor Q72 operates in a constant current state (i.e., transistor Q72, differential amplifier gm3, and resistor R3 constitute controllable current source 721). And, at this time, the voltage of the first intermediate terminal CN2 is less than the voltage of the second intermediate terminal LP2, the unidirectional conducting element D71 is not conducting, and the circuit diagram of the linear LED driving circuit 7 operating in the second state is shown in fig. 9 (the dashed line is used to indicate that the branch is not conducting). Thus, the output energy of the rectifier circuit 74 only powers the LED load LED 3. And, due to the regulation of the controllable current source 721, the current Iled flowing through the LED load LED3 at this time is substantially maintained at I2.

At time t 1-time t2, the linear LED driving circuit 7 operates in the third state. As shown in fig. 5, the voltage sampling signal Vs is greater than the first voltage threshold Vref 1. Therefore, the comparator cmp1 outputs an inactive switch control signal S1. When both the switch control signals S1 and S2 are inactive, the control transistor Q71 is turned off. The or gate or1 outputs an inactive signal to control switches K1 and K3 to remain off and switches K2 and K4 to remain on. That is, at this time, the transistor Q72 is controlled to be in an off state, and the transistor Q73 is controlled to be in a constant current state (that is, the transistor Q73, the resistor R4, the error amplifier gm3, and the like may constitute a controllable current source). At this time, the output energy of the rectifying circuit 74 charges the capacitor C71 so that the voltage across the one-way conducting element D71 reaches its conducting voltage, so that the one-way conducting element D71 is conducting, and a circuit diagram of the linear LED driving circuit 7 operating in the third state is shown in fig. 10 (the dashed line is used to indicate that the branch circuit is not conducting). At time t 1-time t2, the output energy of the rectifying circuit 74 simultaneously powers the energy storage element C71 and the LED load LED 3. It should be understood that, since it takes a certain time for the voltage across the unidirectional conducting element D71 to reach its conducting voltage, a current flows through the energy storage element C71 and the LED load LED3 after a delay at time t 1. During the period when the energy storage element C71 and the LED load LED3 are turned on, since the transistor Q73 is in a constant current state, the currents Ic and Iled flowing through the energy storage element C71 and the LED load LED3 are both substantially maintained at I2. After the energy storage element C71 and the LED load LED3 are turned on for a while, the currents Ic and Iled flowing through the energy storage element C71 and the LED load LED3 drop to 0 due to the gradual decrease of the voltage of the LED load LED 3.

At time t 2-time t3, the voltage sampling signal Vs is less than the first voltage threshold Vref 1. At this time, the operating state of the linear LED driving circuit 7 is the same as that at time t 0-t 1, and will not be described again.

At time t 3-time t4, the linear LED driving circuit 7 operates in the fourth state. As shown in fig. 5, the voltage sampling signal Vs is less than the first voltage threshold Vref 1. Therefore, the comparator cmp1 outputs an active switch control signal S1. When the switch control signal S1 is active, the or gate or1 outputs an active signal to control the switches K1 and K3 to be turned on, the switches K2 and K4 to be turned off, and the transistor Q72 is in a constant current state. At this time, the output voltage of the rectifying circuit 74 is 0 or approximately 0, and therefore, the energy storage element C71 supplies power to the LED load LED 3. Since the voltage of the first intermediate terminal CN2 is lower than the voltage of the second intermediate terminal LP2, the unidirectional conducting element D21 is not conducting. As shown in fig. 7, when the energy storage element C71 discharges, the transistor Q71 is turned on through its parasitic diode, a current flows through the resistor R5 to break down the breakdown diode D72, and the transistor Q73 is turned on by the voltage of the breakdown diode D72. A schematic circuit diagram of the linear LED driving circuit 7 operating in the fourth state is shown in fig. 11 (the dashed line is used to indicate that the branch is not conductive). The transistor Q73 is controlled to be conducted, the transistor Q71 is conducted through a parasitic diode of the transistor Q72 is controlled to work in a constant current state, and therefore a path of C71-Q71-led3-Q72-R4-Q73-C71 can be formed in the circuit. Due to the regulation of the controllable current source 721, the absolute values of the currents Ic and Iled flowing through the energy storage element C71 and the LED load LED3 are substantially maintained at I2 for a period of time after time t 3. It should be understood that the current Ic and Iled flowing through the energy storage element C71 and the LED load LED3 at this time are in opposite directions. However, since the energy in the energy storage element C71 decreases, the voltage across the LED load LED3 gradually decreases, and thus the current Ic flowing through the energy storage element C71 gradually increases to 0, and the current Iled flowing through the LED load LED3 gradually decreases to 0. At time t4, a new cycle begins.

In the present embodiment, the linear LED driving circuit switches between different states to supply power to the LED load when the ac input voltage Vin is in a high-voltage state. The energy storage element is used for absorbing the peak energy of the mains supply and releasing the peak energy to the LED load, so that the LED driving circuit is prevented from generating large loss when the alternating current input voltage is in a high-voltage state, meanwhile, the LED on-state voltage in a wide range is allowed, and the design flexibility is improved. Compared with the linear LED drive circuit in the prior art, the linear LED drive circuit in the embodiment can control the LED load to be conducted when the alternating-current input voltage is in a low-voltage state, so that the input voltage range is widened, the conduction angle of the input current is increased, and the power factor and the efficiency of the linear LED drive circuit are improved.

In another alternative implementation, the switching control signal S2 of the transistor Q71 is always inactive when the ac input voltage Vin is in a high-voltage state, and is turned on through its parasitic diode when the output voltage of the rectifying circuit 74 is 0 or approximately 0. Therefore, the transistor Q71 can be replaced by a diode when the ac input voltage Vin is in a high-voltage state. The anode of the diode is connected to the second intermediate terminal LP2 and the cathode is connected to the first terminal i5 of the rectified output port. Therefore, it can be realized that the diode is not conducted from time t0 to time t3, and at time t3 to time t4, the diode is conducted so that the energy storage element C71 supplies power to the LED load LED 3. That is, when the ac input voltage Vin is in a high-voltage state, replacing the transistor Q71 with a diode also can achieve the function of making the output voltage of the linear LED driving circuit smaller to improve the power factor and efficiency of the linear LED driving circuit.

Fig. 12 is a circuit diagram of a linear LED driving circuit according to a fourth embodiment of the present invention. As shown in fig. 12, the linear LED driving circuit 8 of the present embodiment includes a first branch 81, a second branch 82, a third branch 83, a rectifying circuit 84, and a logic circuit 85. The rectifying circuit 84 is configured to convert an ac input voltage Vin into a dc voltage and output the dc voltage to the dc BUS. The first branch 81 and the second branch 82 are both connected between the rectified output ports (i.e., the output ports of the rectification circuit 84).

The first branch 81 includes a storage element C81 and a transistor Q81. Wherein the energy storage element C81 is connected between the first end i7 of the rectified output port and the first intermediate end CN3 (i.e., the first end of the third branch 83). The transistor Q81 is connected between the first intermediate terminal CN3 and the second terminal i8 of the rectified output port. The second terminal i8 of the rectified output port is a ground terminal. The transistor Q81 is controlled by the switch control signal S2 to turn on or off.

The second branch 82 comprises an LED load LED4 and a controllable current source 821. The controllable current source 821 comprises a transistor Q82, a resistor R6 and a differential amplifier gm 4. The transistor Q82 is connected between the first end i7 of the rectified output port and the second intermediate end LP3 (i.e., the second end of the third branch 83). The LED load LED3 and the resistor R6 are connected in series between the second intermediate terminal LP3 and the second terminal i8 of the rectified output port. The transistor Q82 is controlled by the switching control signals S1 and S2 to be in a constant current state or an off state. The controllable current source 821 is configured to maintain the current through the LED load LED3 at a set value.

The third branch 83 is connected between the first intermediate end CN3 and the second intermediate end LP 3. The third branch comprises a unidirectional conducting element D81 and a transistor Q84. The unidirectional conducting element D81 and the transistor Q84 are connected in series between the first intermediate terminal CN3 and the second intermediate terminal LP 3. The transistor Q84 is controlled by the switching control signals S1 and S2 to be in a constant current state or an off state.

The logic circuit 85 is configured to control the transistor Q82 and the transistor Q84 to be in an off state or an on state according to the switch control signals S1 and S2. The logic circuit 85 includes an or gate or3, an inverter inv3, and switches K5 and K6.

The linear LED driving circuit 8 further includes a controller (not shown) for generating switching control signals S1 and S2 to control the transistor Q81, the transistor Q82, and the transistor Q84 according to the voltage sampling signal. The voltage sampling signal is used to characterize the output voltage of the rectifier circuit 84. The circuit diagram of the controller is shown in fig. 3, and is not described herein again.

In the present embodiment, the linear LED driving circuit 8 still operates in four different states according to the magnitude of the ac input voltage Vin. That is, when the peak value of the ac input voltage Vin is lower than the preset value, the linear LED driving circuit 8 operates in the first state. When the peak value of the ac input voltage Vin is higher than the preset value, the linear LED driving circuit 8 switches in the second state, the third state, and the fourth state.

The linear LED driving circuit 8 operates in the first state when the ac input voltage Vin is a low voltage (i.e. the peak value of the ac input voltage Vin is lower than the predetermined value), and the operating waveform diagram is still as shown in fig. 4. When the peak value of the ac input voltage Vin is lower than the preset value, the voltage sampling signal Vs is always smaller than the first voltage threshold Vref1, and the comparator cmp1 always outputs an active switch control signal S1. As shown in fig. 12, when the switch control signal S1 is asserted, the or gate or3 outputs an asserted signal to control the switch K6 to be turned on and the switch K5 to be turned off. That is, at this time, the transistor Q82 operates in a constant current state (i.e., the transistor Q82, the differential amplifier gm4, and the resistor R6 constitute the controllable current source 821), and the transistor Q84 is in an off state. The filtered voltage sampling signal Vs _ a is always smaller than the second voltage threshold Vref2 when the ac input voltage Vin is low. Therefore, the comparator cmp2 always outputs the active switch control signal S2, and the control transistor Q81 is continuously turned on.

Thus, when the ac input voltage Vin is low, the linear LED driving circuit 8 turns on the transistor Q81, turns off the transistor Q84, and turns on the transistor Q82 to be in a constant current state. That is, in this case, the first branch 81 and the second branch 82 are connected in parallel to the output port of the rectifier circuit 84, and both can receive the output energy of the rectifier circuit 84. Here, the waveform diagram of the current Iled flowing through the LED load LED4 is as shown in fig. 4, and when the bus voltage Vbus is greater than Vled (i.e. the on-state voltage of the LED load), the current Iled flowing through the LED load is substantially maintained at I1 due to the adjustment of the controllable current source 821. When the BUS voltage BUS is less than Vled, the current Iled flowing through the LED load LED4 gradually drops to 0.

Therefore, when the ac input voltage Vin of the linear LED driving circuit 8 is low, the energy storage element C81 is connected in parallel to improve the linear adjustment rate of the linear LED driving circuit 8 in a low voltage state, thereby improving the stability of the output voltage.

When the ac input voltage Vin is at a high voltage (i.e. the peak value of the ac input voltage Vin is higher than the predetermined value), the operating waveform of the linear LED driving circuit 8 is still as shown in fig. 5. When the peak value of the ac input voltage Vin is higher than the preset value, the filtered voltage sampling signal Vs _ a is always greater than the second voltage threshold Vref 2. Therefore, the comparator cmp2 always outputs the invalid switch control signal S2.

At time t 0-time t1, the linear LED driving circuit 8 operates in the second state. As shown in fig. 5, the voltage sampling signal Vs is less than the first voltage threshold Vref 1. Therefore, the comparator cmp1 outputs an active switch control signal S1. When the switch control signal S1 is asserted, the or gate or3 outputs an asserted signal to control the switch K6 to be turned on and the switch K5 to be turned off. The transistor Q82 is controlled to operate in a constant current state, and the transistor Q84 is controlled to be in an off state. Since the switch control signal S2 is inactive at this time, the transistor Q81 is controlled to be turned off. Therefore, at time t0 to time t1, the energy storage element C81 is not connected to the circuit, and the current Ic flowing through the energy storage element C81 is 0. The output energy of the rectifier circuit 84 only powers the LED load LED 4. Also, due to the regulation of the controllable current source 821, the current Iled flowing through the LED load LED4 is maintained substantially at I2 at this time.

At time t 1-time t2, the linear LED driving circuit 8 operates in the third state. As shown in fig. 5, the voltage sampling signal Vs is greater than the first voltage threshold Vref 1. Therefore, the comparator cmp1 outputs an inactive switch control signal S1. When both the switch control signals S1 and S2 are inactive, the or gate or3 outputs an inactive signal to control the switch K6 to turn off and the switch K5 to turn on. That is, at this time, the transistor Q81 is controlled to be in an off state, the transistor Q82 is controlled to be in an off state, and the transistor Q84 is controlled to be in a constant current state. At this time, the output energy of the rectifying circuit 84 charges the capacitor C81 so that the voltage across the one-way conduction element D81 is greater than the conduction voltage thereof, so that the one-way conduction element D81 is conducted. Therefore, at time t 1-time t2, the output energy of the rectifying circuit 84 simultaneously powers the energy storage element C81 and the LED load LED 4. It should be understood that, since it takes a certain time to make the voltage across the unidirectional conducting element D81 greater than the conducting voltage thereof, a current flows through the energy storage element C81 and the LED load LED4 after a delay at time t 1. During the period when the energy storage element C81 and the LED load LED4 are turned on, since the transistor Q84 is in a constant current state, the currents Ic and Iled flowing through the energy storage element C81 and the LED load LED4 are both substantially maintained at I2. After the energy storage element C81 and the LED load LED4 are turned on for a period of time, the currents Ic and Iled flowing through the energy storage element C81 and the LED load LED4 drop to 0 because the voltage across the LED load gradually decreases to be less than its turn-on voltage.

At time t 2-time t3, the voltage sampling signal Vs is less than the first voltage threshold Vref 1. At this time, the operating state of the linear LED driving circuit 8 is the same as that at time t 0-t 1, and will not be described again.

At time t 3-time t4, the linear LED driving circuit 8 operates in the fourth state. As shown in fig. 5, the voltage sampling signal Vs is less than the first voltage threshold Vref 1. Therefore, the comparator cmp1 outputs an active switch control signal S1. When the switch control signal S1 is active, the or gate or3 outputs an active signal to control the switch K6 to be turned on and the switch K5 to be turned off. The transistor Q82 is in a constant current state and the transistor Q84 is in an off state. At this time, the output voltage of the rectifying circuit 84 is 0, and thus the energy storage element C81 supplies power to the LED load LED 4. As shown in fig. 12, when the energy storage element C81 discharges, the transistor Q81 may be turned on through its parasitic diode. Thus, a path of C81-Q82-R6-led4-Q81-C81 can be formed in the circuit. Due to the regulation of the controllable current source 821, the absolute values of the currents Ic and Iled flowing through the energy storage element C81 and the LED load LED4 are substantially maintained at I2 for a period of time after time t 3. It should be understood that the current Ic and Iled flowing through the energy storage element C81 and the LED load LED4 at this time are in opposite directions. However, since the energy in the energy storage element C81 decreases, the voltage across the LED load gradually decreases, and therefore the current Ic flowing through the energy storage element C81 gradually increases to 0, and the current Iled flowing through the LED load LED4 gradually decreases to 0. At time t4, a new cycle begins.

In another alternative implementation, the switching control signal of the transistor Q81 is always inactive when the ac input voltage Vin is in a high-voltage state, and is turned on through its parasitic diode when the output voltage of the rectifying circuit 24 is 0. Therefore, the transistor Q81 can be replaced by a diode when the ac input voltage Vin is in a high-voltage state. The anode of the diode is connected to the second terminal i8 of the rectified output port, and the cathode is connected to the first intermediate terminal CN 3. Thus, it is achieved that the diode is non-conducting from time t0 to time t3 and conducting from time t3 to time t 4. That is, when the ac input voltage Vin is in a high-voltage state, replacing the transistor Q81 with a diode also can achieve the function of making the output voltage of the linear LED driving circuit smaller to improve the power factor and efficiency of the linear LED driving circuit.

The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A linear LED drive circuit, comprising:

the first branch circuit comprises an energy storage element and a first transistor which are connected in series, and the second branch circuit comprises an LED load and a controllable current source which are connected in series, so that when the linear LED driving circuit is in a first state, the first branch circuit and the second branch circuit both receive output energy of the rectifying circuit;

the linear LED driving circuit further includes:

2. The linear LED driving circuit according to claim 1, wherein the third branch comprises a unidirectional conducting element.

3. The linear LED drive circuit of claim 2, wherein the second branch further comprises a second transistor connected in series with the LED load and the controllable current source.

4. The linear LED drive circuit of claim 2, wherein the first branch further comprises a third transistor connected in series with the energy storage element.

5. The linear LED driving circuit of claim 2, wherein the third branch further comprises a fourth transistor connected in series with the unidirectional conducting element, wherein the fourth transistor is configured to switch between a constant current state and an off state.

6. The linear LED drive circuit of claim 1, wherein the linear LED drive circuit is configured to be in the first state when a peak value of an ac input voltage is below a preset value.

7. The linear LED drive circuit of claim 2, wherein the linear LED drive circuit is configured to switch between the second state, the third state, and the fourth state when a peak value of an ac input voltage is above a preset value.

8. The linear LED drive circuit of claim 7, wherein the linear LED drive circuit is configured to be in the second state when a voltage sampling signal characterizing an instantaneous value of an output voltage of the rectifier circuit is less than a first voltage threshold, in the third state when the voltage sampling signal is greater than the first voltage threshold, and in the fourth state when the output voltage of the rectifier circuit is zero or approximately zero.

9. The linear LED drive circuit of claim 2, further comprising:

10. The linear LED driving circuit according to claim 3, wherein the energy storage element is connected between the first end of the rectified output port and the first end of the third branch; the LED load and the controllable current source are connected in series between the second end of the third branch and the second end of the rectification output port.

11. The linear LED drive circuit of claim 10, wherein the first transistor is connected between the first end of the third branch and the second end of the rectified output port; the second transistor is connected between the first end of the rectified output port and the second end of the third branch.

12. The linear LED driving circuit according to claim 3, wherein the LED load and the controllable current source are connected in series between a first end of a rectified output port and a first end of the third branch; the energy storage element is connected between the second end of the third branch and the second end of the rectification output port.

13. The linear LED driving circuit of claim 12, wherein the second transistor is connected between the first end of the third leg and the second end of the rectified output port; the first transistor is connected between a first end of the rectified output port and a second end of the third branch.

14. The linear LED drive circuit of claim 4, wherein the LED load is connected between the first end of the third leg and the first end of the rectified output port; the energy storage element and the third transistor are connected in series between the second end of the third branch and the second end of the rectification output port;

15. The linear LED driving circuit according to claim 14, wherein the controllable current source is connected between the first end of the third branch and the second end of the rectified output port; the first transistor is connected between a first end of the rectified output port and a second end of the third branch.

16. The linear LED drive circuit of claim 5, wherein the energy storage element is connected between the first end of the rectified output port and the first end of the third branch; the LED load is connected between the second end of the third branch and the second end of the rectified output port.

17. The linear LED drive circuit of claim 16, wherein the first transistor is connected between the first end of the third leg and the second end of the rectified output port; the controllable current source is connected between the first end of the rectified output port and the second end of the third branch.

18. The linear LED driving circuit according to claim 11 or 13, wherein in the first state, the first transistor and the second transistor are controlled to conduct; in the second state, the first transistor is controlled to be turned off, and the second transistor is controlled to be turned on; in the third state, the first transistor and the second transistor are controlled to be turned off; in the fourth state, the first transistor is turned on through a parasitic diode, and the second transistor is controlled to be turned on.

19. The linear LED drive circuit of claim 15, wherein in the first state, the first transistor and the third transistor are controlled to conduct; in the second state, the first transistor and the third transistor are controlled to be turned off; in the third state, the transistor in the controllable current source and the first transistor are controlled to be turned off, and the third transistor is controlled to work in a constant current state; in the fourth state, the third transistor is controlled to be turned on, and the first transistor is turned on through a parasitic diode.

20. The linear LED driving circuit of claim 17, wherein in the first state, the first transistor is controlled to be on and the fourth transistor is controlled to be off; in the second state, the first transistor and the fourth transistor are controlled to be turned off; in the third state, the first transistor is controlled to be turned off, the fourth transistor is controlled to work in a constant current state, and the transistor in the controllable current source is controlled to be turned off; in the fourth state, the first transistor is turned on through a parasitic diode, and the fourth transistor is controlled to be turned off.

21. A linear LED drive circuit, comprising:

a first branch and a second branch connected in parallel between output ports of the rectifying circuit; the first branch circuit comprises an energy storage element and a switching tube which are connected in series, and the second branch circuit comprises an LED load and a controllable current source which are connected in series; and

a third branch connected between the first branch and the second branch;

the first branch, the second branch and the third branch are configured such that when the linear LED driving circuit is in a first state, only the second branch receives output energy of a rectifying circuit, when the linear LED driving circuit is in a second state, the energy storage element and the LED load receive output energy of the rectifying circuit through the third branch, and when the linear LED driving circuit is in a third state, the LED load receives output energy of the energy storage element;

wherein the third branch comprises a unidirectional conducting element.

22. The linear LED driving circuit according to claim 21, wherein when the linear LED driving circuit is in a fourth state, the first branch and the second branch are connected in parallel between output ports of a rectifying circuit, such that the first branch and the second branch both receive output energy of the rectifying circuit.

23. The linear LED drive circuit of claim 21, wherein the second branch further comprises a first transistor connected in series with the LED load and the controllable current source.

24. The linear LED drive circuit of claim 21 wherein the first branch further comprises a second transistor connected in series with the energy storage element.

25. The linear LED drive circuit of claim 21, wherein the third branch further comprises a fourth transistor connected in series with the unidirectional conducting element, wherein the fourth transistor is configured to switch between a constant current state and an off state.

26. The linear LED driving circuit of claim 21, wherein the switching tube is a transistor or a diode.