CN111642042B

CN111642042B - Linear LED drive circuit and drive method thereof

Info

Publication number: CN111642042B
Application number: CN201910156206.6A
Authority: CN
Inventors: 刘军; 吴泉清
Original assignee: CRM ICBG Wuxi Co Ltd
Current assignee: CRM ICBG Wuxi Co Ltd
Priority date: 2019-03-01
Filing date: 2019-03-01
Publication date: 2023-02-28
Anticipated expiration: 2039-03-01
Also published as: CN111642042A

Abstract

The invention provides a linear LED drive circuit and a drive method thereof, wherein the drive method comprises the following steps: the anode of the first constant current control module is connected with the voltage input module, and the cathode of the first constant current control module is connected with the first LED lamp section of the first constant current control module; the output end of the first constant current control module is connected with the second end of the first sampling resistor and the first end of the second sampling resistor; the second end of the first sampling resistor is connected with the second sampling resistor in series, and the first end of the first sampling resistor is grounded; the anode of the first LED lamp section is connected with the cathode of the first sampling resistor, and the cathode of the first LED lamp section is connected with the first sampling resistor through the first constant current control module; the first diode and the second diode are connected in series and then connected in parallel with the first LED lamp section; one end of the capacitor is connected with the cathode of the second diode, and the other end of the capacitor is connected with the first end of the second sampling resistor through the third constant current control module. The invention can realize high power factor, no stroboflash, low cost and high efficiency; the device is compatible with silicon controlled rectifier dimming and has wide application range; the operation is still kept at low input voltage; meanwhile, the structure is simple and easy to realize.

Description

Linear LED driving circuit and driving method thereof

Technical Field

The invention relates to the field of integrated circuit design, in particular to a linear LED driving circuit and a driving method thereof.

Background

An LED is a semiconductor electronic component capable of emitting light, which can emit only low-intensity red light at an early stage, and with the continuous progress of technology, the light intensity has been improved to such an extent that visible light, infrared light and ultraviolet light are emitted. LEDs have the advantages of high efficiency, long life, low probability of damage, high switching speed, high reliability, and the like, which are not well-known in the conventional light sources, and have been widely used in the fields of indicator lights, displays, and illumination.

Generally, the overall efficiency in single-segment linear LED driving is determined by the LED on-voltage and the input voltage, and satisfies the following relationship:

as shown in fig. 1, in a linear LED driving scheme, in order to obtain a high Power Factor (PF), an electroless single-stage driving structure 1 is often adopted, which includes: the AC voltage Vin _ ac is converted into an input voltage V through a rectifier bridge 11 _IN And supplying power to the LED lamp section, wherein the LED lamp section is formed by connecting n LED lamps in series; the output end of the LED lamp section is connected with a constant current control chip 12, constant current control is realized through the switch of a constant current control tube in the constant current control chip 12, and a capacitor C1' and a resistorR1' is connected in parallel with two ends of the input voltage and is an adjustable device. Since the number of LEDs connected in series is fixed, when the input voltage exceeds the forward voltage drop of the LEDs, the redundant voltage is borne by the constant current control tube below the LEDs, V _IN -V _LED The voltage on the tube is adjusted, and the higher the input voltage is, the lower the efficiency of the system is; and the structure has the problem of power frequency flicker.

In order to filter the power frequency flicker and improve the efficiency, an electrolytic capacitor needs to be added to the input, as shown in fig. 2, an improved linear LED driving circuit 2 includes a power input module 21 for providing an input voltage; the LED lamp string 22 is connected to the power input module 21, the resistor R2 'is connected to the output end of the LED lamp string 22, and two ends of the resistor R2' are connected to the constant current control chip 23; the output end of the power input module 21 is connected to the constant current control chip 23 through an electrolytic capacitor C2 'and a diode D', the anode of the diode D 'is connected to the electrolytic capacitor C2', the cathode of the diode D 'is connected to the constant current control chip 23, the anode of the diode D' is further connected to a control tube M, and the control end of the control tube M is connected to the constant current control chip 23; the constant current control chip 23 is grounded through capacitors C3 'and C4' and resistors R3 'and R4', respectively. The linear LED driving circuit 2 filters stroboscopic light and accordingly improves some efficiency by the stored energy of the electrolytic capacitor C2', but the power factor is reduced accordingly, and is 0.5-0.7.

The two performances of high power factor and no stroboflash in the existing linear LED driving scheme are a pair of spears, and cannot be perfectly solved.

Disclosure of Invention

In view of the above-mentioned shortcomings of the prior art, an object of the present invention is to provide a linear LED driving circuit and a driving method thereof, which are used to solve the problem that high power factor and no strobe cannot be compatible in the prior art.

To achieve the above and other related objects, the present invention provides a linear LED driving circuit, comprising:

the LED lamp comprises a voltage input module, a first LED lamp section, a second LED lamp section, a first constant current control module, a second constant current control module, a third constant current control module, a first diode, a second diode, a first sampling resistor, a second sampling resistor and a capacitor;

the anode of the first LED lamp section is connected with the output end of the voltage input module, and the cathode of the first LED lamp section is connected with the first constant current control module;

the first constant current control module comprises a first power switch tube and a first operational amplifier, the first power switch tube is connected between the negative electrode of the first LED lamp section and the first end of the first sampling resistor, the control end of the first power switch tube is connected with the output end of the first operational amplifier, and the input end of the first operational amplifier is respectively connected with the first end of the second sampling resistor and a first reference voltage; the second end of the first sampling resistor is grounded, and the second end of the second sampling resistor is connected with the first end of the first sampling resistor;

the anode of the second LED lamp section is connected with the cathode of the first LED lamp section, and the cathode of the second LED lamp section is connected with the first end of the second sampling resistor through the second constant-current control module;

the cathode of the first diode is connected with the anode of the first LED lamp section, the anode of the first diode is connected with the cathode of the second diode, and the anode of the second diode is connected with the cathode of the first LED lamp section;

one end of the capacitor is connected with the cathode of the second diode, and the other end of the capacitor is connected with the first end of the second sampling resistor through the third constant current control module.

Optionally, the turn-on voltage of the first LED lamp segment is not greater than half of the average value of the output voltage of the voltage input module.

More optionally, the number of the lamp beads of the first LED lamp segment is greater than the number of the lamp beads of the second LED lamp segment.

More optionally, the ratio of the number of the lamp beads of the first LED lamp segment to the number of the lamp beads of the second LED lamp segment includes 2:1.

more optionally, the second constant current control module includes a second power switch tube and a second operational amplifier; the second power switch tube is connected between the negative electrode of the second LED lamp section and the first end of the second sampling resistor, and the control end of the second power switch tube is connected with the output end of the second operational amplifier; and the input end of the second operational amplifier is respectively connected with the first end of the second sampling resistor and the second reference voltage.

More optionally, the third constant current control module includes a third power switch tube, a third operational amplifier, a third diode, and a fourth diode; the third power switch tube is connected between the capacitor and the anode of the third diode, and the control end of the third power switch tube is connected with the output end of the third operational amplifier; the input end of the third operational amplifier is respectively connected with the cathode of the third diode and a third reference voltage; the cathode of the third diode is connected with the first end of the second sampling resistor; the anode of the fourth diode is grounded, and the cathode of the fourth diode is connected with the anode of the third diode.

More optionally, the linear LED driving circuit further includes a reference voltage generating module, and the reference voltage generating module is configured to provide a reference voltage for the linear LED driving circuit.

More optionally, the reference voltage generation module is further connected to a voltage detection module, the voltage detection module detects the input voltage, and the reference voltage generation module adjusts each reference voltage based on a detection signal of the voltage detection module to achieve constant input power.

More optionally, the linear LED driving circuit further includes a discharging current control module, where the discharging current control module is connected to the output end of the voltage input module and the first end of the second sampling resistor, and is configured to enable a current flowing through the thyristor to be greater than or equal to a holding current of the thyristor.

More optionally, the bleed-off current control module includes a fifth diode, a fourth power switch tube, a sampling unit, a fourth operational amplifier, and a current detection unit; the anode of the fifth diode is connected with the output end of the voltage input module, and the cathode of the fifth diode is connected with the anode of the first LED lamp section; the fourth power switch tube is connected between the output end of the voltage input module and one end of the sampling unit, and the control end of the fourth power switch tube is connected with the output end of the fourth operational amplifier; one end of the sampling unit is grounded; the current detection unit is connected with the sampling unit and the second sampling resistor and sums the currents flowing through the sampling unit and the LED lamp sections; the input end of the fourth operational amplifier is respectively connected with the current detection unit and the discharge threshold voltage, and the discharge current flowing through the sampling unit is adjusted based on the output current of the voltage input module.

To achieve the above and other related objects, the present invention provides a driving method of the linear LED driving circuit, including at least:

when the input voltage is greater than the conduction voltage of the first LED lamp section and less than the sum of the conduction voltages of the first LED lamp section and the second LED lamp section, performing constant current control on the current flowing through the first LED lamp section based on a first constant current control module;

when the input voltage is greater than the sum of the conduction voltages of the first LED lamp section and the second LED lamp section and is less than the sum of the conduction voltage of the first LED lamp section and the voltage at two ends of a capacitor, performing constant current control on the current flowing through the first LED lamp section and the second LED lamp section based on a second constant current control module;

when the input voltage is larger than the sum of the conducting voltage of the first LED lamp section and the voltage at two ends of the capacitor, the current flowing through the first LED lamp section is subjected to constant current control based on a third constant current control module, and the capacitor is charged by the input voltage;

when the input voltage is smaller than the voltage at two ends of the capacitor, the capacitor starts to discharge; when the input voltage is greater than the sum of the conduction voltages of the first LED lamp section and the second LED lamp section, performing constant current control on the current flowing through the first LED lamp section and the second LED lamp section based on the second constant current control module; and when the input voltage is smaller than the sum of the conduction voltages of the first LED lamp section and the second LED lamp section and is greater than the conduction voltage of the first LED lamp section, performing constant current control on the current flowing through the first LED lamp section based on the first constant current control module.

Optionally, a ratio of the first sampling resistor and the second sampling resistor is adjusted to make the output power constant.

More optionally, the output power of the linear LED driving circuit satisfies the following relation:

vref1 × VLED1/Rs1= Vref2 × (VLED 1+ VLED 2)/(Rs 1+ Rs 2) = Vref3 × VLED 1/(Rs 1+ Rs 2) where VLED1 is the on-voltage of the first LED segment, VLED2 is the on-voltage of the second LED segment, vref1 is the first reference voltage, vref2 is the second reference voltage, vref3 is the third reference voltage, rs1 is the resistance value of the first sampling resistor, and Rs2 is the resistance value of the second sampling resistor.

More optionally, the voltage of the positive electrode of the first LED lamp segment is detected, and the reference voltage of each constant current control module is reduced when the voltage of the positive electrode of the first LED lamp segment is greater than a set voltage.

More optionally, the output current of the voltage input module is detected, and when the output current of the voltage input module is smaller than the holding current of the thyristor, the bleeding path is increased, so that the current flowing through the thyristor is greater than or equal to the holding current of the thyristor.

As described above, the linear LED driving circuit and the driving method thereof according to the present invention have the following advantageous effects:

1. according to the linear LED driving circuit and the driving method thereof, the conduction time of the input voltage is longer, stroboflash is removed based on constant power output, and the high power factor and no stroboflash can be realized.

2. According to the linear LED driving circuit and the driving method thereof, the using number of the LED lamp beads is reduced through a specific framework, the voltage loss of the power switch tube at high voltage is reduced through capacitor charging, and the cost and the efficiency can be considered.

3. The linear LED driving circuit and the driving method thereof can be compatible with silicon controlled rectifier dimming, and have wide application range.

4. The linear LED driving circuit and the driving method thereof can still work under low input voltage through the energy stored by the capacitor.

5. The linear LED driving circuit and the driving method thereof have simple structure and are easy to realize.

Drawings

FIG. 1 is a schematic diagram of a non-electrolytic single-stage driving structure in the prior art.

Fig. 2 shows a schematic diagram of an improved linear LED driving circuit in the prior art.

Fig. 3 is a schematic diagram of a linear LED driving circuit according to the present invention.

Fig. 4 is a schematic diagram showing the waveform configuration of each node of the linear LED driving circuit according to the present invention.

Fig. 5 is a schematic diagram illustrating the operation of the linear LED driving circuit of the present invention when the circuit is powered by ac voltage.

Fig. 6 is a schematic diagram illustrating the operation principle of the linear LED driving circuit of the present invention when the capacitor is discharged.

Fig. 7 is a schematic diagram of another structure of the linear LED driving circuit according to the present invention.

Fig. 8 is a schematic diagram of another linear LED driving circuit according to the present invention.

Fig. 9 is a schematic diagram of another linear LED driving circuit according to the present invention.

Description of the element reference numerals

1. Non-electrolytic single-section driving structure

11. Rectifier bridge

12. Constant current control chip

2. Linear LED drive circuit

21. Power input module

22 LED lamp string

23. Constant current control chip

3. Linear LED drive circuit

31. Voltage input module

311. Silicon controlled rectifier

32. First constant current control module

33. Second constant current control module

34. Third constant current control module

35. Reference voltage generating module

351. Reference voltage generating unit

36. Working voltage generation module

37. Voltage detection module

38. Digital filtering module

39. Discharge current control module

391. Sampling unit

392. Current detection unit

393. Threshold voltage generating unit

Detailed Description

The embodiments of the present invention are described below with reference to specific embodiments, and other advantages and effects of the present invention will be easily understood by those skilled in the art from the disclosure of the present specification. The invention is capable of other and different embodiments and of being practiced or of being carried out in various ways, and its several details are capable of modification in various respects, all without departing from the spirit and scope of the present invention.

Please refer to fig. 3 to fig. 9. It should be noted that the drawings provided in this embodiment are only for schematically illustrating the basic idea of the present invention, and the components related to the present invention are only shown in the drawings and not drawn according to the number, shape and size of the components in actual implementation, and the form, quantity and proportion of each component in actual implementation may be arbitrarily changed, and the component layout may be more complicated.

Example one

As shown in fig. 3, the present embodiment provides a linear LED driving circuit 3, where the linear LED driving circuit 3 includes:

the LED lamp comprises a voltage input module 31, a first LED lamp section LED1, a second LED lamp section LED2, a first constant current control module 32, a second constant current control module 33, a third constant current control module 34, a first diode D1, a second diode D2, a first sampling resistor Rs1, a second sampling resistor Rs2 and a capacitor C1.

As shown in fig. 3, the voltage input module 31 supplies power.

Specifically, in this embodiment, the voltage input module 31 includes a rectifier bridge BD1 connected to two ends of the alternating voltage Vin _ ac, the rectifier bridge BD1 is composed of 4 end-to-end diodes, and a fuse F1 is connected between the alternating voltage Vin _ ac and the rectifier bridge BD 1. The alternating voltage Vin _ ac is a sine wave, and after passing through the rectifier bridge BD1, the output voltage of the voltage input module 31 is an absolute value of the alternating voltage Vin _ ac, and the period of the output voltage is half of the alternating voltage Vin _ ac. In practical applications, any circuit structure capable of converting ac power into dc power is suitable for the present invention, and is not described herein.

As shown in fig. 3, the first LED segment LED1 and the second LED segment LED2 are sequentially connected in series to the output end of the voltage input module 31.

Specifically, the positive electrode of the first LED segment LED1 is connected to the output end of the voltage input module 31, the negative electrode of the first LED segment LED1 is connected to the positive electrode of the second LED segment LED2 and the first constant current control module 32, and the negative electrode of the second LED segment LED2 is connected to the second constant current control module 33.

It should be noted that, in order to consider both system efficiency and lamp bead cost, in this embodiment, the turn-on voltage of the first LED lamp segment LED1 is equal to half of the average value of the output voltage of the voltage input module, and the number of lamp beads in the first LED lamp segment LED1 may be set according to different turn-on voltages of the LED lamp beads; the ratio of the number of the lamp beads of the first LED lamp section LED1 to the number of the lamp beads of the second LED lamp section LED2 is set to be 2:1. then, relative to the single-segment LED driving circuit, the total number of beads connected in series in the present invention is only (2 + 1)/(2 + 2) =75%. In practical use, the on-state voltage of the first LED lamp segment LED1 is less than half of the average value of the output voltage of the voltage input module; the quantity and the proportion of the lamp beads can also be adjusted, the quantity of the total lamp beads is less than the quantity of single-section LED lamp beads, the quantity of the lamp beads of the first LED lamp section LED1 is not more than half of the quantity of the single-section LED lamp beads, and the quantity of the lamp beads in the first LED lamp section LED1 is more than the quantity of the lamp beads in the second LED lamp section LED 2.

As shown in fig. 3, the first constant current control module 32 is connected to the first LED lamp segment LED1, the first sampling resistor Rs1 and the second sampling resistor Rs2, and is configured to perform constant current control on the first LED lamp segment LED 1.

Specifically, the first constant current control module 32 includes a first power switch Q1 and a first operational amplifier OP1. In this embodiment, the first power switch Q1 is an NMOS transistor, and then a drain of the first power switch Q1 is connected to a cathode of the first LED lamp segment LED1, a source is connected to a first end of the first sampling resistor Rs1, and a gate is connected to an output end of the first operational amplifier OP1, where in actual use, the first power switch Q1 may be of another type, including but not limited to an insulated gate bipolar transistor; the input end of the first operational amplifier OP1 is connected to the first end of the second sampling resistor Rs2 and the first reference voltage Vref1, in this embodiment, the inverting input end of the first operational amplifier OP1 is connected to the first end of the second sampling resistor Rs2, and the non-inverting input end is connected to the first reference voltage Vref1, in actual use, the correspondence between the input signal and the polarity of the input port can be changed by adding a phase inverter, which is not limited by this embodiment; the second end of the first sampling resistor Rs1 is grounded, and the second end of the second sampling resistor Rs2 is connected to the first end of the first sampling resistor Rs1.

As shown in fig. 3, the second constant current control module 33 is connected to the second LED lamp segment LED2 and the second sampling resistor Rs2, and is configured to perform constant current control on the first LED lamp segment LED1 and the second LED lamp segment LED 2.

Specifically, the second constant current control module 33 includes a second power switch Q2 and a second operational amplifier OP2. In this embodiment, the second power switch Q2 is an NMOS transistor, and then the drain of the second power switch Q2 is connected to the cathode of the second LED segment LED2, the source is connected to the first end of the second sampling resistor Rs2, and the gate is connected to the output end of the second operational amplifier OP2, in practical use, the second power switch Q2 may adopt other types, including but not limited to an insulated gate bipolar transistor; in this embodiment, an inverting input terminal of the second operational amplifier OP2 is connected to the first terminal of the second sampling resistor Rs2, and a non-inverting input terminal of the second operational amplifier OP2 is connected to the second reference voltage Vref 2.

As shown in fig. 3, a cathode of the first diode D1 is connected to an anode of the first LED segment LED1, an anode of the first diode D1 is connected to a cathode of the second diode D2, and an anode of the second diode D2 is connected to a cathode of the first LED segment LED 1; one end of the capacitor C1 is connected to the cathode of the second diode D2, and the other end is connected to the third constant current control module 34. The first diode D1 is used to form a discharge path, the second diode D2 is used to form a charge path, and the capacitor C1 is used for charging and discharging.

As shown in fig. 3, the third constant current control module 33 is connected to the capacitor C1 and the second sampling resistor Rs2, and is configured to perform constant current control on the first LED segment LED 1.

Specifically, the third constant current control module 33 includes a third power switch Q3, a third operational amplifier OP3, a third diode D3, and a fourth diode D4. In this embodiment, the third power switch Q3 is an NMOS transistor, and then the drain of the third power switch Q3 is connected to the capacitor C1, the source is connected to the anode of the third diode D3, and the gate is connected to the output end of the third operational amplifier OP3, in actual use, the third power switch Q3 may adopt other types, including but not limited to an insulated gate bipolar transistor; the input end of the third operational amplifier OP3 is connected to the cathode of the third diode D3 and a third reference voltage Vref3, respectively, in this embodiment, the inverting input end of the third operational amplifier OP3 is connected to the cathode of the third diode D3, and the non-inverting input end is connected to the third reference voltage Vref3, in practical use, the corresponding relationship between the input signal and the polarity of the input port can be changed by adding a phase inverter, which is not limited in this embodiment; the cathode of the third diode D3 is connected to the first end of the second sampling resistor Rs 2; the anode of the fourth diode D4 is grounded, and the cathode is connected to the anode of the third diode D3.

As an implementation manner of this embodiment, the linear LED driving circuit 3 further includes a reference voltage generating module 35, configured to provide a reference voltage for the linear LED driving circuit 3.

Specifically, in the present embodiment, the reference voltage generating module 35 includes a first setting resistor Rset1, a reference voltage generating unit 351, a first voltage dividing resistor R1, a second voltage dividing resistor R2, and a third voltage dividing resistor R3. The first setting resistor Rset1 is connected to the reference voltage generating unit 351 and is used for setting the reference voltage output by the reference voltage generating unit 351; the third voltage dividing resistor R3, the second voltage dividing resistor R2, and the first voltage dividing resistor R1 are sequentially connected in series to an output terminal of the reference voltage generating unit 351, and are configured to obtain a plurality of reference voltages with different voltage values. Any circuit structure capable of generating the reference voltage is suitable for the reference voltage generating module 35 of the present invention, and is not limited to this embodiment.

As an implementation manner of this embodiment, the linear LED driving circuit 3 further includes a working voltage generating module 36, where the working voltage generating module 36 is connected to the anode of the first LED lamp segment LED1, and obtains electric energy through the anode of the first LED lamp segment LED1 to provide stable working voltage for each module.

It should be noted that the first constant current control module 32, the second constant current control module 33, the third constant current control module 34, the first sampling resistor Rs1, the second sampling resistor Rs2, the reference voltage generating unit 351, the first voltage dividing resistor R1, the second voltage dividing resistor R2, the third voltage dividing resistor R3, and the operating voltage generating module 36 may be integrated into a chip.

The operation principle of the linear LED driving circuit 3 of the present embodiment is as follows:

step 1) when the input voltage is larger than the conduction voltage of the first LED lamp section and smaller than the sum of the conduction voltages of the first LED lamp section and the second LED lamp section, performing constant current control on the current flowing through the first LED lamp section based on a first constant current control module.

Specifically, as shown in fig. 4, in the initial state, the alternating voltage Vin _ ac is 0; the voltage across the capacitor C1 is VC1, and in this embodiment, the lowest discharge voltage across the capacitor C1 is set to be greater than the conduction voltage VLED1 of the first LED segment LED1 (at least, it is ensured that the first LED segment LED1 is turned on). The linear LED driving circuit 3 is started, the potential of the input voltage VHV is lower than the potential of the upper plate of the capacitor C1, the capacitor C1 starts to discharge, and the input voltage VHV gradually rises.

Specifically, as shown in fig. 4, as the ac voltage Vin _ ac increases, the input voltage VHV continuously increases, and when VLED1< VHV < VLED1+ VLED2 (where VLED2 is the on-state voltage of the second LED segment LED 2), the linear LED driving circuit 3 operates in a steady state, as shown in fig. 5, a current I1 flows through the first LED segment LED1, the first constant current control module 32 and the first sampling resistor Rs1, the second sampling resistor Rs2 divides the voltage of the first sampling resistor Rs1 into the first operational amplifier OP1, and the first operational amplifier OP1 controls the constant current of the first power switch Q1 based on the voltage of the second sampling resistor Rs2 and the first reference voltage Vref1, at this time, the first LED segment LED1 is turned on, the second LED segment LED2 is turned off, and the output LED power P1= I1 × VLED1, where I1= vlvref 1/Rs1.

And 2) when the input voltage is greater than the sum of the conduction voltages of the first LED lamp section and the second LED lamp section and is less than the sum of the conduction voltage of the first LED lamp section and the voltage at two ends of a capacitor, performing constant current control on the current flowing through the first LED lamp section and the second LED lamp section based on a second constant current control module.

Specifically, as shown in fig. 4, the ac voltage Vin _ ac is increased, accordingly, the input voltage VHV continues to be increased, when VLED1+ VLED2< VHV < VLED1+ VC1, at this time, VC1 is greater than or equal to VLED1, as shown in fig. 5, a current I2 flows through the first LED segment LED1, the second LED segment LED2, the second constant current control module 33, the second sampling resistor Rs2 and the first sampling resistor Rs1, sampling voltages on the second sampling resistor Rs2 and the first sampling resistor Rs1 are fed back to the second operational amplifier OP2, and the second operational amplifier OP2 controls the second power switch Q2 to have a constant current based on the sampling voltage and the second reference voltage Vref 2. At this time, the first LED segment LED1 and the second LED segment LED2 are both turned on, and the total output LED power P2= I2 × (VLED 1+ VLED 2), where I2= Vref 2/(Rs 1+ Rs 2), in order to ensure constant output power, P1= P2, thereby obtaining Vref1 ×/Rs1= Vref2 × (VLED 1+ VLED 2)/(Rs 1+ Rs 2), in this embodiment, since VLED1=2 × VLED2, vref1/Rs1= Vref 2/(Rs 1+ Rs 2) 1.5 can be obtained, and suitable Rs1, rs2 are set, and Vref2> Vref1 is set, so that the first power switch Q1 can be turned off when a constant current flows through the second power switch Q2, and the total output power remains unchanged.

And 3) when the input voltage is greater than the sum of the conduction voltage of the first LED lamp section and the voltage at the two ends of the capacitor, performing constant current control on the current flowing through the first LED lamp section based on a third constant current control module, and charging the capacitor by the input voltage.

Specifically, as shown in fig. 4, the ac voltage Vin _ ac continues to increase, and accordingly, the input voltage VHV also continues to increase, when VHV > VLED1+ VC1 (in this embodiment, the turning point VLED1+ VC1 is a fixed value for convenience), as shown in fig. 5, the input voltage VHV passes through the first LED segment LED1, the second diode D2, the third diode D2 starts to charge the capacitor C1, a current I3 passes through the first LED segment LED1, the second diode D2, the third constant current control module 34, the second sampling resistor Rs2 and the first sampling resistor Rs1, a sampling voltage on the second sampling resistor Rs2 and the first sampling resistor Rs1 is fed back to the third operational amplifier OP3, and the third operational amplifier OP3 controls the constant current of the third power switching tube Q3 based on the sampling voltage and the third reference voltage Vref 3. At this time, the first LED segment LED1 is turned on, the second LED segment LED2 is turned off, and the total output LED power P3= I3 × VLED1, where I3= Vref 1/(Rs 1+ Rs 2), and P1= P2= P3 to ensure constant output power, thereby obtaining Vref1 × VLED1/Rs1= Vref2 × (VLED 1+ VLED 2)/(Rs 1+ Rs 2) = Vref3 × VLED 1/(Rs 1+ Rs 2), so that Vref3> Vref2> Vref1, and during the constant current of the third power switch Q3, the second power switch Q2 and the third power switch Q3 are turned off. During the period, the voltage across the charging terminals of the capacitor C1 continuously rises, and VC1> VLED1, and the voltage loss VQ3 borne by the third power switch Q3= VHV-VLED1-VC1< VHV-2 × VLED1, so that the driving efficiency of the single-stage LED is still improved under the condition of reducing the number of the lamp beads.

Specifically, as shown in fig. 4, the ac voltage Vin _ ac starts to decrease after reaching the peak value, and accordingly, the input voltage VHV starts to decrease, and the state of charging the capacitor C1 via the first LED segment LED1 and the second diode D2 is maintained until VHV > VLED1+ VC1, and as shown in fig. 5, the voltage VC1 across the capacitor C1 continuously increases.

Step 4) when the input voltage is smaller than the voltage at the two ends of the capacitor, the capacitor starts to discharge; when the input voltage is larger than the sum of the conduction voltages of the first LED lamp section and the second LED lamp section, performing constant current control on the current flowing through the first LED lamp section and the second LED lamp section based on the second constant current control module; and when the input voltage is smaller than the sum of the conduction voltages of the first LED lamp section and the second LED lamp section and larger than the conduction voltage of the first LED lamp section, performing constant current control on the current flowing through the first LED lamp section based on the first constant current control module.

Specifically, as shown in fig. 4, the ac voltage Vin _ ac continues to drop, and accordingly, the input voltage VHV also continues to drop, when VHV < VLED1+ VC1, the capacitor C1 stops charging, as shown in fig. 5, a current I2 flows through the first LED segment LED1, the second LED segment LED2, the second constant current control module 33, the second sampling resistor Rs2, and the first sampling resistor Rs1, and a constant current is realized based on the second power switch tube Q2.

Specifically, as shown in fig. 4, the ac voltage Vin _ ac continues to drop, and accordingly, the input voltage VHV also continues to drop, and when VHV < VC1 (in this embodiment, the ac voltage Vin _ ac < VLED1+ VLED 2), the capacitor C1 starts to discharge; when VHV < VLED1+ VLED2, as shown in fig. 6, the capacitor C1 discharges the first LED segment LED1 through the first diode D1 and the fourth diode D4, a current I1 flows through the first LED segment LED1, the first constant current control module 32, the second sampling resistor Rs2, and the first sampling resistor Rs1, and a constant current is realized based on the first power switch tube Q1.

It should be noted that the current flowing through the LED during discharging is still controlled by I1, I2 to maintain constant output power until VC1 discharges to VLED1 to stop discharging. Due to the discharging effect of the capacitor C1, the LED can still be conducted during the valley period of the input voltage VHV, and therefore stroboscopic is reduced. Because the input minimum on-state voltage is VLED1, the on-state time of the input voltage VHV is longer, so that high power factor can be obtained (the power factor of the linear LED driving circuit 3 is more than 0.9), and compared with single-stage LED driving, the LED can still be lightened at lower voltage, so that the working voltage range is expanded, and the special application occasions are met.

It should be noted that, in this embodiment, it is assumed that VC1_ max = VLED1+ VLED2, where IC1 is the charging and discharging current of the capacitor C1, and a shaded area a of the charging current of the capacitor C1 is equal to a shaded area B of the discharging current of the capacitor C1.

In this embodiment, after the ac voltage Vin _ ac < VLED1+ VLED2, the capacitor C1 starts to discharge. In practical use, when VLED1+ VLED2< Vin _ ac < VC1, the capacitor C1 starts to discharge, as shown in fig. 6, after the capacitor C1 discharges, the capacitor C1 discharges the first LED lamp segment LED1 and the second LED lamp segment LED2 through the first diode D1 and the fourth diode D4, a current I2 flows through the first LED lamp segment LED1, the second LED lamp segment LED2, the second constant current control module 33, the second sampling resistor Rs2, and the first sampling resistor Rs1, and a constant current is realized based on the second power switch tube Q2. When the ac voltage Vin _ ac < VC1< VLED1+ VLED2, the capacitor C1 starts to discharge, as shown in fig. 6, after the capacitor C1 discharges, the capacitor C1 discharges the first LED lamp segment LED1 through the first diode D1 and the fourth diode D4, and the current I1 flows through the first LED lamp segment LED1, the first constant current control module 32, the second sampling resistor Rs2, and the first sampling resistor Rs1, and the constant current is realized based on the first power switch tube Q1. According to the actual circuit situation, the discharge is naturally realized when Vin _ ac < VC1, and the discharge path I1 and/or I2 is formed, which is not limited by the present embodiment.

Example two

As shown in fig. 7, the present embodiment provides a linear LED driving circuit 3, which is different from the first embodiment in that the present embodiment further includes a voltage detection module 37.

As shown in fig. 7, the voltage detection module 37 is connected to the output end of the voltage input module 31, and detects the input voltage VHV.

Specifically, in this embodiment, the voltage detection module 37 includes a first detection resistor Rx1, a second detection resistor Rx2, a filter resistor Rx3, and a filter capacitor Cx. The first detection resistor Rx1 and the second detection resistor Rx2 are connected in series and then connected in parallel to two ends of the voltage input module 31; one end of the filter resistor Rx3 is connected with a connection node of the first detection resistor Rx1 and the second detection resistor Rx2, and the other end of the filter resistor Rx3 outputs a detection signal LN; one end of the filter capacitor Cx is connected with the detection signal, and the other end of the filter capacitor Cx is grounded.

It should be noted that the voltage detection module 37 may be replaced by a digital filtering module 38, as shown in fig. 8, which filters the input voltage VHV by a digital filtering technique and obtains a detection signal LN. The digital filtering module 38 may be integrated on-chip.

Although the efficiency of the present invention is improved compared to a single-stage method, the efficiency still decreases with the increase of the input voltage, so that the input voltage VHV can be detected and the line voltage compensation can be performed, and the linear LED driving circuit 3 of this embodiment adjusts the reference voltage on the basis of the first embodiment to achieve the constant input power, and the specific principle is as follows:

the reference voltage generating module 35 receives the detection signal LN output by the voltage detecting module 37, and adjusts the first reference voltage Vref1, the second reference voltage Vref2, and the third reference voltage Vref3 based on the detection signal LN; when the voltage value of the detection signal is greater than the set voltage, the values of the first reference voltage Vref1, the second reference voltage Vref2, and the third reference voltage Vref3 are reduced, so that the output current when the input voltage is a high voltage is reduced, the output power is reduced, and the input power is kept constant.

It should be noted that the setting voltage can be set according to actual needs, which is not described in detail herein.

EXAMPLE III

As shown in fig. 9, the present embodiment provides a linear LED driving circuit 3, which is different from the first and second embodiments in that the present embodiment further includes a compatible scr dimming application.

As shown in fig. 9, a thyristor 311 is connected in series in the voltage input module 31, and the discharging current control module 39 is connected to the output end of the voltage input module 311 and the first end of the second sampling resistor, and is configured to make the current flowing through the thyristor 311 greater than or equal to the holding current of the thyristor 311.

Specifically, the bleeding current control module 39 includes a fifth diode D5, a fourth power switch Q4, a sampling unit 391, a fourth operational amplifier OP4 and a current detection unit 392. The anode of the fifth diode D5 is connected to the output end of the voltage input module 31, and the cathode is connected to the anode of the first LED lamp segment LED 1. The fourth power switch tube Q4 is connected between the output end of the voltage input module 31 and the sampling unit 391, and the control end is connected to the output end of the fourth operational amplifier OP 4; in this embodiment, the fourth power switch Q4 is an NMOS transistor, and then the drain of the fourth power switch Q4 is connected to the anode of the fifth diode D5, the source is connected to the sampling unit 391, and the gate is connected to the output end of the fourth operational amplifier OP4, in practical use, the fourth power switch Q4 may adopt other types, including but not limited to an insulated gate bipolar transistor. One end of the sampling unit 391 is connected to the source of the fourth power switch Q4, and the other end is grounded; in this embodiment, the sampling unit 391 is implemented by using a third sampling resistor Rs 3. The current detecting unit 392 is connected to the sampling unit 391 and the first end of the second sampling resistor Rs1, and sums the currents flowing through the sampling unit 391 and the LED lamp segments. The input end of the fourth operational amplifier OP4 is connected to the current detection unit 392 and the dumping threshold voltage, respectively, and the dumping current flowing through the sampling unit 391 is adjusted based on the output current of the voltage input module 31. The dumping threshold voltage is obtained based on the threshold voltage generating unit 393, and the threshold voltage generating unit 393 adjusts the dumping threshold voltage through the grounded second set resistor Rset2, so that the flexibility is greatly improved; in practical applications, the bleeding threshold voltage may also be generated by the reference voltage generating module 35, which is not limited to this embodiment.

When the output current of the voltage input module is smaller than the holding current of the thyristor, the fourth power switch tube Q4 is turned on, and part of the current generates a discharge current through the fourth power switch tube Q4 and the sampling unit 391, so that the current flowing through the thyristor is greater than or equal to the holding current of the thyristor 311, and the thyristor 311 is maintained to work normally.

Compared with single-segment LED driving, since the on-state voltage of the first LED segment LED1 is relatively low, the drain current consumption required by the system is relatively reduced, and the overall efficiency can be improved.

In summary, the present invention provides a linear LED driving circuit and a driving method thereof, including: the LED lamp comprises a voltage input module, a first LED lamp section, a second LED lamp section, a first constant current control module, a second constant current control module, a third constant current control module, a first diode, a second diode, a first sampling resistor, a second sampling resistor and a capacitor; the anode of the first LED lamp section is connected with the output end of the voltage input module, and the cathode of the first LED lamp section is connected with the first constant current control module; the first constant-current control module comprises a first power switch tube and a first operational amplifier, the first power switch tube is connected between the negative electrode of the first LED lamp section and the first end of the first sampling resistor, the control end of the first power switch tube is connected with the output end of the first operational amplifier, and the input end of the first operational amplifier is respectively connected with the first end of the second sampling resistor and a first reference voltage; the second end of the first sampling resistor is grounded, and the second end of the second sampling resistor is connected with the first end of the first sampling resistor; the anode of the second LED lamp section is connected with the cathode of the first LED lamp section, and the cathode of the second LED lamp section is connected with the first end of the second sampling resistor through the second constant-current control module; the cathode of the first diode is connected with the anode of the first LED lamp section, the anode of the first diode is connected with the cathode of the second diode, and the anode of the second diode is connected with the cathode of the first LED lamp section; one end of the capacitor is connected with the cathode of the second diode, and the other end of the capacitor is connected with the first end of the second sampling resistor through the third constant current control module. The linear LED driving circuit and the driving method thereof can realize high power factor, no stroboflash, low cost and high efficiency; the device can be compatible with silicon controlled rectifier dimming, and has wide application range; the operation is still kept at low input voltage; meanwhile, the structure is simple and easy to realize. Therefore, the invention effectively overcomes various defects in the prior art and has high industrial utilization value.

The foregoing embodiments are merely illustrative of the principles and utilities of the present invention and are not intended to limit the invention. Those skilled in the art can modify or change the above-described embodiments without departing from the spirit and scope of the present invention. Accordingly, it is intended that all equivalent modifications or changes which can be made by those skilled in the art without departing from the spirit and technical spirit of the present invention be covered by the claims of the present invention.

Claims

1. A linear LED driving circuit, characterized in that the linear LED driving circuit comprises at least:

the anode of the first LED lamp section is connected with the output end of the voltage input module, and the cathode of the first LED lamp section is connected with the first constant current control module; the on-state voltage of the first LED lamp section is not more than half of the average value of the output voltage of the voltage input module, and the number of the lamp beads of the first LED lamp section is more than that of the lamp beads of the second LED lamp section;

the anode of the second LED lamp section is connected with the cathode of the first LED lamp section, and the cathode of the second LED lamp section is connected with the first end of the second sampling resistor through the second constant current control module;

one end of the capacitor is connected with the cathode of the second diode, and the other end of the capacitor is connected with the first end of the second sampling resistor through the third constant current control module;

the third constant-current control module comprises a third power switch tube, a third operational amplifier, a third diode and a fourth diode; the third power switch tube is connected between the capacitor and the anode of the third diode, and the control end of the third power switch tube is connected with the output end of the third operational amplifier; the input end of the third operational amplifier is respectively connected with the cathode of the third diode and a third reference voltage; the cathode of the third diode is connected with the first end of the second sampling resistor; the anode of the fourth diode is grounded, and the cathode of the fourth diode is connected with the anode of the third diode.

2. The linear LED driving circuit of claim 1, wherein: the lamp bead quantity ratio of the first LED lamp section to the second LED lamp section comprises 2:1.

3. the linear LED driving circuit of claim 1, wherein: the second constant-current control module comprises a second power switch tube and a second operational amplifier; the second power switch tube is connected between the negative electrode of the second LED lamp section and the first end of the second sampling resistor, and the control end of the second power switch tube is connected with the output end of the second operational amplifier; and the input end of the second operational amplifier is respectively connected with the first end of the second sampling resistor and the second reference voltage.

4. The linear LED driving circuit of claim 1, wherein: the linear LED driving circuit further comprises a reference voltage generating module, and the reference voltage generating module is used for providing reference voltage for the linear LED driving circuit.

5. The linear LED drive circuit of claim 4, wherein: the reference voltage generation module is also connected with a voltage detection module, the voltage detection module detects the input voltage output by the voltage input module, and the reference voltage generation module adjusts each reference voltage based on the detection signal of the voltage detection module so as to realize constant input power.

6. The linear LED driving circuit of claim 1, wherein: the linear LED driving circuit further comprises a discharging current control module, wherein the discharging current control module is connected with the output end of the voltage input module and the first end of the second sampling resistor and is used for enabling the current flowing through the controllable silicon to be larger than or equal to the holding current of the controllable silicon.

7. The linear LED driving circuit of claim 6, wherein: the discharge current control module comprises a fifth diode, a fourth power switch tube, a sampling unit, a fourth operational amplifier and a current detection unit; the anode of the fifth diode is connected with the output end of the voltage input module, and the cathode of the fifth diode is connected with the anode of the first LED lamp section; the fourth power switch tube is connected between the output end of the voltage input module and one end of the sampling unit, and the control end of the fourth power switch tube is connected with the output end of the fourth operational amplifier; one end of the sampling unit is grounded; the current detection unit is connected with the sampling unit and the second sampling resistor and sums the currents flowing through the sampling unit and the LED lamp sections; the input end of the fourth operational amplifier is respectively connected with the current detection unit and the discharging threshold voltage, and the discharging current flowing through the sampling unit is adjusted based on the output current of the voltage input module.

8. A driving method of the linear LED driving circuit according to any one of claims 1 to 7, wherein the driving method of the linear LED driving circuit at least comprises:

9. The driving method of a linear LED driving circuit according to claim 8, wherein: and adjusting the ratio of the first sampling resistor and the second sampling resistor to ensure that the output power is constant.

10. The driving method of a linear LED driving circuit according to claim 9, wherein: the output power of the linear LED driving circuit satisfies the following relational expression:

11. The method of driving a linear LED driving circuit according to any one of claims 8 to 10, wherein: and detecting the positive voltage of the first LED lamp section, and reducing the reference voltage of each constant current control module when the positive voltage of the first LED lamp section is greater than a set voltage.

12. The method of driving a linear LED driving circuit according to any one of claims 8 to 10, wherein: and detecting the output current of the voltage input module, and increasing a discharge path when the output current of the voltage input module is less than the holding current of the controllable silicon so that the current flowing through the controllable silicon is more than or equal to the holding current of the controllable silicon.