Linear LED driving circuit and electronic equipment

Abstract

The invention provides a linear LED driving circuit and electronic equipment, and the circuit comprises two constant-current control modules which are powered by an input capacitor when the bus voltage is lower than the forward conduction voltage of an LED, and are controlled by a first / third constant-current control module to realize constant current; when the bus voltage is higher than the forward break-over voltage of the LED but lower than the voltage on the input capacitor, the bus voltage supplies power, and the second / fourth constant current control module controls the constant current. When the bus voltage is higher than the voltage on the input capacitor, the bus voltage supplies power and charges the input capacitor, and the second / fourth constant current control module controls constant current. According to the linear LED driving circuit and the electronic equipment, through the switch module and the two constant-current control modules, higher harmonics are optimized through the simplest method to meet the standard requirement; and a parasitic diode of the power tube can be utilized to reduce the requirements on external elements, so that the overall cost of the system is further reduced.

Description

Technical Field

[0001] The present invention relates to the field of integrated circuit design, and in particular to a linear LED drive circuit and electronic equipment. Background Art

[0002] With the implementation of the EU ERP standard, LED drivers need to meet requirements in many aspects such as harmonics and flicker. Figure 1 It is a common linear LED driving system 1 without flicker. The AC input AC is converted into the input voltage Vin through the rectifier bridge BD1. The input capacitor Cin is connected in parallel at both ends of the rectifier bridge BD1. Energy storage is used to ensure that the LED can still flow current normally when the input voltage is at the bottom. One end of the LED is connected to the input voltage, and the other end is connected to the ground through the power tube Q and the sampling resistor Rcs in turn. The operational amplifier OP (the power tube Q and the operational amplifier OP are integrated in the chip 11) compares the feedback signal on the sampling resistor Rcs with the reference Ref. During the entire power frequency cycle, the reference Ref controls the power tube Q to conduct constant current through the operational amplifier OP, so that the LED flows through a constant current to achieve no flicker. Figure 2 As shown, at t0-t1, the input voltage Vin is less than the voltage on the input capacitor (the minimum voltage on the input capacitor is Vrec_min), the input capacitor Cin powers the LED, and there is no input current Iin; at t1-t4, the input voltage Vin is greater than or equal to the voltage Vcap on the input capacitor, the input voltage Vin powers the LED, and reaches the current peak Ipk at t2, and the conduction angle is 90 degrees at t3; at t4-t5, the input voltage Vin is less than the voltage on the input capacitor, the input capacitor Cin powers the LED, and there is no input current Iin. Among them, the diode D is the parasitic diode of the power tube Q (there is also a parasitic diode between the GND and OUT pins, and because the external sampling resistor Rcs is relatively small, it can also be connected in parallel to D in the end).

[0003] The standard IEC61000-3-2 (harmonic current emission standard) has input current harmonic requirements for lighting equipment with 5W-25W input. There are 3 different test standards to meet the regulatory requirements. Among them, linear LED drivers must at least meet test standard 2, which focuses on: ① The 3rd harmonic is lower than 86% of the fundamental amplitude, ② The 5th harmonic is lower than 61% of the fundamental amplitude, ③ The input current must be greater than 5% of the input peak current before the conduction angle is 60 degrees, ④ The peak current must be reached before the conduction angle is 65 degrees, and ⑤ The input current cannot be lower than 5% of the peak current after the conduction angle is 90 degrees. It can be seen that this standard has both high-order harmonic requirements and conduction angle requirements.

[0004] However, due to the presence of input capacitor Cin, the input current Iin waveform is a pulse current, such as Figure 2As shown in the figure, when the input capacitor C is selected with appropriate capacity, its conduction angle can meet the above requirements, but the harmonics generally cannot meet the requirements, and the 3rd and 5th harmonics are prone to exceed the standard.

[0005] Therefore, how to further optimize the waveform of the input current to meet the above standards has become one of the problems that technicians in this field need to solve urgently.

[0006] It should be noted that the above introduction to the technical background is only for the convenience of providing a clear and complete description of the technical solutions of the present invention and for the convenience of understanding by those skilled in the art. It cannot be considered that the above technical solutions are well known to those skilled in the art simply because these solutions are described in the background technology section of the present invention. Summary of the invention

[0007] 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 electronic equipment, which are used to solve the problem that the third and fifth harmonics of the LED input current are easily exceeded in the prior art.

[0008] To achieve the above-mentioned object and other related objects, the present invention provides a linear LED driving circuit, wherein the linear LED driving circuit at least comprises:

[0009] A first voltage input module, a switch module, a first input capacitor, a first constant current control module, a second constant current control module, a first sampling module, a second sampling module and a first LED load;

[0010] The first voltage input module provides bus voltage;

[0011] The first end of the switch module is connected to the output end of the first voltage input module, and the second end is grounded via the first input capacitor; when the bus voltage is greater than the voltage on the first input capacitor, the switch module is turned on; when the bus voltage is less than or equal to the voltage on the first input capacitor, the switch module is turned off;

[0012] The output end of the first constant current control module is connected to the second end of the switch module, and the sampling end is connected to the first end of the second sampling module via the first sampling module;

[0013] The output end of the second constant current control module is connected to the output end of the first voltage input module, and the sampling end is connected to the first end of the second sampling module;

[0014] The second end of the second sampling module is connected to the positive electrode of the first LED load, and the negative electrode of the first LED load is grounded;

[0015] The impedance of the first sampling module is smaller than the impedance of the second sampling module, so that the first constant current control module is turned off when the second constant current control module is working.

[0016] Optionally, the first constant current control module and the second constant current control module both include a first power switch tube and a first operational amplifier;

[0017] The drain of the first power switch tube serves as the output end of the corresponding constant current control module, and the source serves as the sampling end of the corresponding constant current control module; the first input end of the first operational amplifier is connected to the source of the first power switch tube, the second input end is connected to the corresponding reference voltage, and the output end is connected to the gate of the first power switch tube.

[0018] Optionally, the reference grounds of the first constant current control module and the second constant current control module are connected to the positive electrode of the first LED load.

[0019] Optionally, the switch module is implemented by a diode; the anode of the diode serves as the first end of the switch module, and the cathode of the diode serves as the second end of the switch module.

[0020] Optionally, the first sampling module and the second sampling module are implemented by resistors.

[0021] In order to achieve the above-mentioned object and other related objects, the present invention further provides a linear LED driving circuit, wherein the linear LED driving circuit at least comprises:

[0022] A second voltage input module, a second input capacitor, a third constant current control module, a fourth constant current control module, a third sampling module, a fourth sampling module and a second LED load;

[0023] The second voltage input module provides a bus voltage;

[0024] The sampling end of the third constant current control module is connected to the output end of the second voltage input module, and the output end is grounded via the second input capacitor;

[0025] The output end of the fourth constant current control module is connected to the output end of the second voltage input module via the third sampling module, and the sampling end is connected to the positive electrode of the second LED load via the fourth sampling module; the negative electrode of the second LED load is grounded;

[0026] Wherein, the impedance of the third sampling module is greater than the impedance of the fourth sampling module.

[0027] Optionally, the third constant current control module and the fourth constant current control module both include a second power switch tube and a second operational amplifier;

[0028] The drain of the second power switch tube serves as the output end of the corresponding constant current control module, and the source serves as the sampling end of the corresponding constant current control module; the first input end of the second operational amplifier is connected to the source of the second power switch tube, the second input end is connected to the corresponding reference voltage, and the output end is connected to the gate of the second power switch tube.

[0029] Optionally, the reference ground of the third constant current control module is connected to a connection node between the third sampling module and the fourth constant current control module, and the reference ground of the fourth constant current control module is connected to the positive electrode of the second LED load.

[0030] Optionally, the third sampling module and the fourth sampling module are implemented by resistors.

[0031] In order to achieve the above object and other related objects, the present invention also provides an electronic device, which at least includes: the above linear LED driving circuit.

[0032] As described above, the linear LED driving circuit and electronic device of the present invention have the following beneficial effects:

[0033] 1. The linear LED driving circuit and electronic device of the present invention optimizes high-order harmonics to meet the requirements of the standard in the simplest way through a switch module and two constant current control modules.

[0034] 2. The linear LED driving circuit and electronic device of the present invention can also utilize the parasitic diode of the power tube itself to reduce the demand for external components, further reducing the overall cost of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 It is a schematic structural diagram of a flicker-free linear LED driving system in the prior art.

[0036] Figure 2 Display as Figure 1 Schematic diagram of the waveform of the LED driving system.

[0037] Figure 3 Shown is a structural schematic diagram of the linear LED driving circuit of the present invention.

[0038] Figure 4 Shown is a waveform diagram of the linear LED driving circuit of the present invention.

[0039] Figure 5 Display as Figure 3 Schematic diagram of the working principle of the linear LED driving circuit when the bus voltage is lower than the forward conduction voltage of the LED.

[0040] Figure 6 Display as Figure 3Schematic diagram of the working principle of the linear LED driving circuit when the bus voltage is higher than the forward conduction voltage of the LED but lower than the voltage on the first input capacitor.

[0041] Figure 7 Display as Figure 3 Schematic diagram of the working principle of the linear LED driving circuit when the bus voltage is higher than the voltage on the first input capacitor.

[0042] Figure 8 Shown is another structural schematic diagram of the linear LED driving circuit of the present invention.

[0043] Fig. 9 Display as Figure 8 Schematic diagram of the working principle of the linear LED driving circuit when the bus voltage is lower than the forward conduction voltage of the LED.

[0044] Fig.10 Display as Figure 8 Schematic diagram of the working principle of the linear LED driving circuit when the bus voltage is higher than the forward conduction voltage of the LED but lower than the voltage on the second input capacitor.

[0045] Fig.11 Display as Figure 8 Schematic diagram of the working principle of the linear LED driving circuit when the bus voltage is higher than the voltage on the second input capacitor.

[0046] Component number description

[0047] 1 Flicker-free linear LED drive system

[0048] 11 Chip

[0049] 2 Linear LED drive circuit

[0050] 21 First voltage input module

[0051] 22 Switch module

[0052] 23. First constant current control module

[0053] 24. Second constant current control module

[0054] 25 Second voltage input module

[0055] 26 The third constant current control module

[0056] 27 Fourth constant current control module DETAILED DESCRIPTION

[0057] The following describes the embodiments of the present invention through specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention.

[0058] See also Figure 3 to Figure 11 It should be noted that the illustrations provided in this embodiment are only used to illustrate the basic concept of the present invention in a schematic manner, and the drawings only show components related to the present invention rather than being drawn according to the number, shape and size of components in actual implementation. In actual implementation, the type, quantity and proportion of each component may be changed arbitrarily, and the component layout may also be more complicated.

[0059] Embodiment 1

[0060] like Figure 3 As shown, this embodiment provides a linear LED driving circuit 2, and the linear LED driving circuit 2 includes:

[0061] A first voltage input module 21 , a switch module 22 , a first input capacitor C1 , a first constant current control module 23 , a second constant current control module 24 , a first sampling module, a second sampling module and a first LED load LED1 .

[0062] like Figure 3 As shown, the first voltage input module 21 provides a bus voltage Vin_rec.

[0063] Specifically, in this embodiment, the first voltage input module 21 includes a rectifier unit BD and a fuse F; the input end of the rectifier unit BD receives an AC input voltage AC, rectifies the AC input voltage AC into the bus voltage Vin_rec and outputs it; the fuse F is connected in series to the positive phase input end or the negative phase input end of the rectifier unit BD to provide protection. Any circuit structure that can provide a bus voltage is applicable to the first voltage input module of the present invention, and is not limited to this embodiment.

[0064] like Figure 3 As shown, the first end of the switch module 22 is connected to the output end of the first voltage input module 21, and the second end is grounded via the first input capacitor C1; when the bus voltage Vin_rec is greater than the voltage on the first input capacitor C1, the switch module 22 is turned on; when the bus voltage Vin_rec is less than or equal to the voltage on the first input capacitor C1, the switch module 22 is turned off.

[0065] Specifically, in this embodiment, the switch module 22 is implemented by a diode D1. The anode of the diode D1 serves as the first end of the switch module 22, and the cathode of the diode D1 serves as the second end of the switch module 22. When the bus voltage Vin_rec is greater than the voltage on the first input capacitor C1, the diode D1 is forward-conducted; when the bus voltage Vin_rec is less than or equal to the voltage on the first input capacitor C1, the diode D1 is reverse-cut off. In actual use, any device or circuit structure that can achieve the above functions is applicable to the present invention, and will not be described one by one here.

[0066] like Figure 3 As shown, the output end of the first constant current control module 23 is connected to the second end of the switch module 22, and the sampling end is connected to the first end of the second sampling module via the first sampling module, so as to control the constant current of the current flowing through the first constant current control module 23. The output end of the second constant current control module 24 is connected to the output end of the first voltage input module 21, and the sampling end is connected to the first end of the second sampling module, so as to control the constant current of the current flowing through the second constant current control module 24.

[0067] Specifically, in this embodiment, the first constant current control module 23 includes a first power switch tube M1 and a first operational amplifier OP1. The drain of the first power switch tube M1 serves as the output terminal OUT1 of the first constant current control module 23, and the source serves as the sampling terminal CS1 of the first constant current control module 23; as an example, the first power switch tube M1 is implemented by an NMOS tube, and any device that can realize power switch adjustment can be selected as needed in actual use. The first input terminal of the first operational amplifier OP1 is connected to the source of the first power switch tube M1, the second input terminal is connected to the first reference voltage Ref1, and the output terminal is connected to the gate of the first power switch tube M1; as an example, the inverting input terminal of the first operational amplifier OP1 is connected to the source of the first power switch tube M1, and the positive input terminal is connected to the first reference voltage Ref1; in actual use, the relationship between the input signal and the polarity of the corresponding input port can be adjusted as needed, and the logic of constant current control can be realized. In this embodiment, the second constant current control module 24 has the same structure as the first constant current control module 23, and the reference voltage is set to the corresponding second reference voltage Ref2, which is not repeated here. In this embodiment, the reference grounds (GND1 and GND2) of the first constant current control module and the second constant current control module are connected to the positive electrode of the first LED load LED1. In actual use, any circuit structure that can achieve constant current control is applicable to the first constant current control module and the second constant current control module of the present invention.

[0068] Specifically, in this embodiment, both the first sampling module and the second sampling module are implemented by resistors. Among them, the first sampling module includes a first resistor Rcs1. One end of the first resistor Rcs1 is connected to the sampling terminal CS1 of the first constant current control module 23, and the other end is connected to the second sampling module. The second sampling module includes a second resistor Rcs2. One end of the second resistor Rcs2 is connected to the sampling terminal CS2 of the second constant current control module 24, and the other end is connected to the first LED load LED1. In actual use, any circuit structure that can implement the sampling function is applicable to the first sampling module and the second sampling module of the present invention.

[0069] It should be noted that in the present invention, the impedance of the first sampling module is less than the impedance of the second sampling module (that is, the resistance value of the first resistor Rcs1 is less than the resistance value of the second resistor Rcs2), so that the first constant current control module 23 can be turned off when the second constant current control module 24 works.

[0070] As Figure 3 shown, the positive electrode of the first LED load LED1 is connected to the second end of the second sampling module, and the negative electrode of the first LED load LED1 is grounded.

[0071] As Figures 4 to 7 shown, the working principle of the linear LED driving circuit 2 of this embodiment is as follows:

[0072] As Figure 4 and Figure 5 shown, at the time t0 - t1, the bus voltage Vin_rec is relatively low (lower than the forward conduction voltage Vled of the LED), and no current can be input. The second constant current control module 24 cannot be turned on due to the insufficient bus voltage; while the voltage Vcap on the first input capacitor C1 is relatively high, and the first input capacitor C1 discharges the first LED load LED1 through the first constant current control module 23, the first sampling module, and the second sampling module in sequence (current I1 path), ensuring no stroboscopic. Since the impedance of the first sampling module is much less than the impedance of the second sampling module (in this example, Rcs1 << Rcs2), therefore, the current of the first LED load LED1 mainly depends on the impedance of the second sampling module.

[0073] As Figure 4 and Figure 6As shown, at the moment t1-t2, the bus voltage Vin_rec is higher than the forward conduction voltage Vled of the LED but lower than the voltage Vcap on the first input capacitor C1. At this time, the bus voltage Vin_rec supplies power to the first LED load LED1 through the second constant current control module 24 and the second sampling module (current I2 path); the voltage at the sampling end CS2 of the second constant current control module 24 squeezes the voltage at the sampling end CS1 of the first constant current control module 23, the first constant current control module 23 is turned off, the first input capacitor C1 cannot be discharged, and the voltage Vcap on the first input capacitor C1 remains unchanged. At this time, the requirement that the input current is greater than 5% of the input peak current before the conduction angle is 60 degrees (Iin>Ipk*5%) can be met.

[0074] like Figure 4 and Figure 7 As shown, at time t2-t5, as the bus voltage Vin_rec continues to increase, the input current Iin can not only supply power to the first LED load LED1 (current I2 path), but also charge the first input capacitor C1 through the switch module 22 (current I3 path, the voltage Vcap on the first input capacitor C1 changes with the bus voltage Vin_rec), so the actual input current Iin is I2+I3, wherein the peak current Ipk appears at time t3, satisfying the requirement that the peak current Ipk can be reached before the conduction angle is 65 degrees; at time t4, the conduction angle is 90 degrees, satisfying the requirement that the input current cannot be lower than 5% of the peak value after the conduction angle is 90 degrees (Iin≥Ipk*5%).

[0075] like Figure 4 and Figure 6 As shown, at time t5-t6, the bus voltage Vin_rec begins to decrease, and the bus voltage Vin_rec is lower than the voltage Vcap on the first input capacitor C1, but higher than the LED forward conduction voltage Vled. The bus voltage Vin_rec supplies power to the first LED load LED1 through the second constant current control module 24 via the second sampling module; the voltage at the sampling end CS2 of the second constant current control module 24 squeezes the voltage at the sampling end CS1 of the first constant current control module 23, thereby turning off the first constant current control module 23 (only the current I2 path remains). At this time, the first input capacitor C1 cannot be charged or discharged and the voltage remains unchanged.

[0076] like Figure 4 and Figure 5As shown, at time t6-t7, the bus voltage Vin_rec is lower than the LED forward conduction voltage Vled, and the first input capacitor C1 discharges the first LED load LED1 with a constant current (current I1 path) through the first constant current control module 23 and the first sampling module and the second sampling module in sequence to ensure no flicker. At this time, the second constant current control module 24 cannot be turned on due to insufficient bus voltage.

[0077] It can be seen that the LED current of the entire power frequency cycle is I1→I2→I2→I2→I1. The first sampling module impedance and the second sampling module impedance are set appropriately (in this embodiment, the resistance values ​​are Rcs1 and Rcs2) so that I1≈I2, thereby achieving no flicker. In this embodiment, by adding the switch module 22 and the first constant current control module 23, the input current waveform is adjusted from t2-t5 (relative to Figure 2 The t1-t4 moment) is expanded to the t1-t6 moment, so that the third and fifth harmonics of the input current can meet the standard requirements.

[0078] It should be noted that the switch module 22 , the first constant current control module 23 and the second constant current control module 24 can be integrated into a single chip to simplify system application, which will not be described in detail here.

[0079] Embodiment 2

[0080] Considering that the MOS tube inside the constant current control module has a parasitic diode, this embodiment uses this diode to replace the switch module 22 in the first embodiment by changing the circuit connection method, such as Figure 8 As shown, the linear LED driving circuit 2 of this embodiment includes:

[0081] The second voltage input module 25, the second input capacitor C2, the third constant current control module 26, the fourth constant current control module 27, the third sampling module, the fourth sampling module and the second LED load LED2.

[0082] like Figure 8 As shown, the second voltage input module 25 provides the bus voltage Vin_rec; as an example, the structure of the second voltage input module 25 is the same as that of the second voltage input module 25 in the first embodiment, which will not be described in detail here.

[0083] like Figure 8 As shown, the sampling terminal CS3 of the third constant current control module 26 is connected to the output terminal of the second voltage input module 25 , and the output terminal is grounded via the second input capacitor C2 , so as to control the constant current of the current flowing through the third constant current control module 26 .

[0084] Specifically, the third constant current control module 26 includes a second power switch tube M2 and a second operational amplifier OP2. The source of the second power switch tube M2 serves as the sampling terminal CS3 of the third constant current control module 26, and the drain serves as the output terminal OUT3 of the third constant current control module 26; there is also a parasitic diode D2 between the source and drain of the second power switch tube M2, the anode of the parasitic diode D2 is connected to the source of the second power switch tube M2, and the cathode is connected to the drain of the second power switch tube M2; as an example, the second power switch tube M2 is implemented by an NMOS tube, and any device can be selected as needed in actual use, and the device can realize power switch adjustment and has a diode with an anode connected to the sampling terminal and a cathode connected to the output terminal. The first input terminal of the second operational amplifier OP2 is connected to the source of the second power switch tube M2, the second input terminal is connected to the third reference voltage Ref3, and the output terminal is connected to the gate of the second power switch tube M2; as an example, the inverting input terminal of the second operational amplifier OP2 is connected to the source of the second power switch tube M2, and the non-inverting input terminal is connected to the third reference voltage Ref3; in actual use, the relationship between the input signal and the polarity of the corresponding input port can be adjusted as needed, and the logic of constant current control can be realized. In this embodiment, the reference ground (GND3) of the third constant current control module 26 is connected to the connection node of the third sampling module and the fourth constant current control module 27. In actual use, any circuit structure that can realize constant current control is applicable to the third constant current control module of the present invention.

[0085] It should be noted that the parasitic diode D2 of the second power switch tube M2 is forward-conducted when the bus voltage Vin_rec is greater than the voltage on the second input capacitor C2, and is reverse-cut off when the bus voltage Vin_rec is less than or equal to the voltage on the second input capacitor C2, thereby controlling the second input capacitor C2 to charge, discharge or maintain.

[0086] like Figure 8 As shown, the output terminal OUT4 of the fourth constant current control module 27 is connected to the output terminal of the second voltage input module 25 via the third sampling module, and the sampling terminal CS4 is connected to the positive electrode of the second LED load LED2 via the fourth sampling module. The negative electrode of the second LED load LED2 is grounded.

[0087] Specifically, in this embodiment, the fourth constant current control module 27 has the same structure as the third constant current control module 26, and the reference voltage is set to the corresponding fourth reference voltage Ref4, which is not described here one by one; the reference ground of the fourth constant current control module 27 is connected to the positive electrode of the second LED load LED2, and any circuit structure that can achieve constant current control is suitable for the fourth constant current control module of the present invention, not limited to this embodiment.

[0088] Specifically, in this embodiment, the third sampling module and the fourth sampling module are both implemented by resistors. The third sampling module includes a third resistor Rcs3, one end of which is connected to the sampling terminal CS3 of the third constant current control module 26, and the other end is connected to the reference ground GND3 of the third constant current control module 26. The fourth sampling module includes a fourth resistor Rcs4, one end of which is connected to the sampling terminal CS4 of the fourth constant current control module 27, and the other end is connected to the second LED load LED2. In actual use, any circuit structure that can realize the sampling function is applicable to the third sampling module and the fourth sampling module of the present invention.

[0089] It should be noted that, in the present invention, the impedance of the third sampling module is greater than (can be set to be slightly greater than) the impedance of the fourth sampling module (that is, the resistance of the third resistor Rcs3 is greater than the resistance of the fourth resistor Rcs4), so that the fourth constant current control module 27 can turn off the third constant current control module 26 when performing constant current control.

[0090] like Figure 4 , Figures 9 to 11 As shown, the working principle of the linear LED driving circuit 2 of this embodiment is as follows:

[0091] like Figure 4 and Fig. 9 As shown, at the moment t0-t1, the bus voltage Vin_rec is relatively low (lower than the forward conduction voltage Vled of the LED), and current cannot be input. At this time, the voltage Vcap on the second input capacitor C2 is relatively high, and the second input capacitor C2 discharges to the second LED load LED2 through the third constant current control module 26, the third sampling module, the fourth constant current control module 27 and the fourth sampling module in sequence (current I1 path), ensuring no flicker; since the impedance of the third sampling module is greater than the impedance of the fourth sampling module (in this example, Rcs3>Rcs4), and the third constant current control module 26 and the fourth constant current control module 27 are in series, the third constant current control module 26 plays a leading role; the third constant current control module 26 and the fourth constant current control module 27 flow through the same current, at this time, the voltage collected by the fourth sampling module is lower than the voltage set by the fourth constant current control module 27, therefore, the fourth constant current control module 27 is in a fully open conduction state, unable to control the current, equivalent to a short circuit of a wire.

[0092] like Figure 4 and Fig.10As shown, at the moment t1-t2, the bus voltage Vin_rec is higher than the LED forward conduction voltage Vled but lower than the voltage Vcap on the second input capacitor C2. At this time, the bus voltage Vin_rec sequentially controls the constant current of the second LED load LED2 through the third sampling module, the fourth constant current control module 27 and the fourth sampling module. Since the impedance of the third sampling module is greater than the impedance of the fourth sampling module, the voltage collected by the third sampling module will be higher than the voltage set by the third constant current control module 26, so that the third constant current control module 26 is turned off (only the current I2 path remains). At this time, the input current is greater than the input peak current by 5% before the conduction angle is 60 degrees (Iin>Ipk*5%).

[0093] like Figure 4 and Fig.11 As shown, at time t2-t5, as the bus voltage Vin_rec continues to increase, the bus voltage Vin_rec is higher than the voltage Vcap on the second input capacitor C2. At this time, the bus voltage Vin_rec charges the second input capacitor C2 through the parasitic diode D2 on the one hand (current I3 path, the voltage Vcap on the second input capacitor C2 changes with the bus voltage Vin_rec); on the other hand, the bus voltage Vin_rec sequentially controls the constant current of the second LED load LED2 through the third sampling module, the fourth constant current control module 27 and the fourth sampling module (current I2 path); at this time, the input current Iin is I2+I3, wherein the peak current Ipk appears at time t3, satisfying the requirement that the peak current Ipk must be reached before the conduction angle is 65 degrees, and at time t4, the conduction angle is 90 degrees, satisfying the requirement that the input current cannot be lower than 5% of the peak value after the conduction angle is 90 degrees (Iin≥Ipk*5%).

[0094] like Figure 4 and Fig.10 As shown, at time t5-t6, the bus voltage Vin_rec begins to decrease, and the bus voltage Vin_rec is lower than the voltage Vcap on the second input capacitor C2, but higher than the LED forward conduction voltage Vled. The bus voltage Vin_rec sequentially controls the constant current of the second LED load LED2 through the third sampling module, the fourth constant current control module 27 and the fourth sampling module. Since the impedance of the third sampling module is greater than the impedance of the fourth sampling module, the voltage collected by the third sampling module is higher than the voltage set by the third constant current control module 26, so that the third constant current control module 26 is turned off (only the current I2 path remains); the second input capacitor C2 cannot be charged or discharged at this time, so the voltage remains unchanged.

[0095] like Figure 4 and Fig. 9 As shown, at time t6-t7, the bus voltage Vin_rec is lower than the LED forward conduction voltage Vled, and at this time, the voltage Vcap on the second input capacitor C2 is relatively high, and the second input capacitor C2 discharges the second LED load LED2 (current I1 path) through the third constant current control module 26, the third sampling module, the fourth constant current control module 27 and the fourth sampling module in sequence to ensure no flicker. At this stage, the third constant current control module 26 plays a leading role in current control, and the fourth constant current control module 27 is in a fully open conduction state.

[0096] It can be seen that the LED current of the entire power frequency cycle is I1→I2→I2→I2→I1, and the third sampling module impedance and the fourth sampling module impedance are set appropriately (in this embodiment, the resistance values ​​are Rcs3 and Rcs4) so ​​that I1≈I2, and no flicker is achieved. The parasitic diode D2 also makes the input current waveform extend from the time t2-t5 to the time t1-t6, so that the third and fifth harmonics of the input current can meet the standard.

[0097] It should be noted that the third constant current control module 26 and the fourth constant current control module 27 can be packaged into a single chip to simplify system application, which will not be described in detail here.

[0098] Embodiment 3

[0099] This embodiment further provides an electronic device, which includes the linear LED driving circuit 2 of the first embodiment or the second embodiment. The LED in the electronic device can achieve stable output and provide a high customer experience.

[0100] In summary, the present invention provides a linear LED drive circuit and electronic device, including: two constant current control modules, when the bus voltage is lower than the forward conduction voltage of the LED, it is powered by the input capacitor, and the constant current is controlled by the first / third constant current control module; when the bus voltage is higher than the forward conduction voltage of the LED but lower than the voltage on the input capacitor, it is powered by the bus voltage, and the constant current is controlled by the second / fourth constant current control module; when the bus voltage is higher than the voltage on the input capacitor, it is powered by the bus voltage and charges the input capacitor, and the constant current is controlled by the second / fourth constant current control module. The linear LED drive circuit and electronic device of the present invention optimizes high-order harmonics to meet the requirements of the standard in the simplest way through the switch module and two constant current control modules; the parasitic diode of the power tube itself can also be used to reduce the demand for external components, further reducing the overall cost of the system. Therefore, the present invention effectively overcomes the various shortcomings of the prior art and has a high industrial utilization value.

[0101] The above embodiments are merely illustrative of the principles and effects of the present invention, and are not intended to limit the present invention. Anyone familiar with the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by a person of ordinary skill in the art without departing from the spirit and technical concept disclosed by the present invention shall still be covered by the claims of the present invention.

Claims

1. A linear LED driving circuit, characterized in that: The linear LED driving circuit at least comprises: A first voltage input module, a switch module, a first input capacitor, a first constant current control module, a second constant current control module, a first sampling module, a second sampling module and a first LED load; The first voltage input module provides bus voltage; The first end of the switch module is connected to the output end of the first voltage input module, and the second end is grounded via the first input capacitor; when the bus voltage is greater than the voltage on the first input capacitor, the switch module is turned on; when the bus voltage is less than or equal to the voltage on the first input capacitor, the switch module is turned off; The output end of the first constant current control module is connected to the second end of the switch module, and the sampling end is connected to the first end of the second sampling module via the first sampling module; The output end of the second constant current control module is connected to the output end of the first voltage input module, and the sampling end is connected to the first end of the second sampling module; The second end of the second sampling module is connected to the positive electrode of the first LED load, and the negative electrode of the first LED load is grounded; The impedance of the first sampling module is smaller than the impedance of the second sampling module, so that the first constant current control module is turned off when the second constant current control module is working.

2. The linear LED driving circuit according to claim 1, characterized in that: The first constant current control module and the second constant current control module both include a first power switch tube and a first operational amplifier; The drain of the first power switch tube serves as the output end of the corresponding constant current control module, and the source serves as the sampling end of the corresponding constant current control module; the first input end of the first operational amplifier is connected to the source of the first power switch tube, the second input end is connected to the corresponding reference voltage, and the output end is connected to the gate of the first power switch tube.

3. The linear LED driving circuit according to claim 1, characterized in that: The reference grounds of the first constant current control module and the second constant current control module are connected to the positive electrode of the first LED load.

4. The linear LED driving circuit according to claim 1, characterized in that: The switch module is implemented by a diode; the anode of the diode serves as the first end of the switch module, and the cathode of the diode serves as the second end of the switch module.

5. The linear LED driving circuit according to claim 1, characterized in that: The first sampling module and the second sampling module are implemented by resistors.

6. A linear LED driving circuit, characterized in that: The linear LED driving circuit at least comprises: A second voltage input module, a second input capacitor, a third constant current control module, a fourth constant current control module, a third sampling module, a fourth sampling module and a second LED load; The second voltage input module provides a bus voltage; The sampling end of the third constant current control module is connected to the output end of the second voltage input module, and the output end is grounded via the second input capacitor; The output end of the fourth constant current control module is connected to the output end of the second voltage input module via the third sampling module, and the sampling end is connected to the positive electrode of the second LED load via the fourth sampling module; the negative electrode of the second LED load is grounded; Wherein, the impedance of the third sampling module is greater than the impedance of the fourth sampling module.

7. The linear LED driving circuit according to claim 6, characterized in that: The third constant current control module and the fourth constant current control module both include a second power switch tube and a second operational amplifier; The drain of the second power switch tube serves as the output end of the corresponding constant current control module, and the source serves as the sampling end of the corresponding constant current control module; the first input end of the second operational amplifier is connected to the source of the second power switch tube, the second input end is connected to the corresponding reference voltage, and the output end is connected to the gate of the second power switch tube.

8. The linear LED driving circuit according to claim 6, characterized in that: The reference ground of the third constant current control module is connected to the connection node between the third sampling module and the fourth constant current control module, and the reference ground of the fourth constant current control module is connected to the positive electrode of the second LED load.

9. The linear LED driving circuit according to claim 6, characterized in that: The third sampling module and the fourth sampling module are implemented by resistors.

10. An electronic device, characterized in that: The electronic device at least comprises: the linear LED driving circuit as described in any one of claims 1-9.

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