Linear LED driving circuit and electronic device

Abstract

The application provides a linear LED driving circuit and electronic equipment, comprising two constant current control modules, when the bus voltage is lower than the forward conduction voltage of the LED, the input capacitor is used for power supply, and the first / third constant current control module is used for constant current control; when the bus voltage is higher than the forward conduction voltage of the LED but lower than the voltage on the input capacitor, the bus voltage is used for power supply, and the second / fourth constant current control module is used for constant current control; when the bus voltage is higher than the voltage on the input capacitor, the bus voltage is used for power supply and charging the input capacitor, and the second / fourth constant current control module is used for constant current control. The linear LED driving circuit and electronic equipment of the application use the switch module and the two constant current control modules to optimize the high-order harmonic to meet the requirement of the standard in the simplest way; the parasitic diode of the power tube itself can be used to reduce the requirement for external elements, and the overall cost of the system is further reduced.

Description

Linear LED driver circuits and electronic equipment Technical Field

[0001] This invention relates to the field of integrated circuit design, and in particular to a linear LED driving circuit and electronic device. Background Technology

[0002] With the implementation of the EU ERP standard, LED drivers need to meet requirements in terms of harmonics, flicker, and other aspects. Figure 1 shows a common flicker-free linear LED driver system 1. The AC input is converted into an input voltage Vin through a rectifier bridge BD1. The input capacitor Cin is connected in parallel across the rectifier bridge BD1 to store energy and ensure that the LED can still flow current normally when the input voltage is at its lowest. One end of the LED is connected to the input voltage, and the other end is grounded through the power transistor Q and the sampling resistor Rcs. The operational amplifier OP (the power transistor Q and the operational amplifier OP are integrated in chip 11) compares the feedback signal on the sampling resistor Rcs with the reference Ref. Throughout the entire power frequency cycle, the reference Ref controls the power transistor Q to conduct with constant current through the operational amplifier OP, so that the LED flows with a constant current to achieve flicker-free operation. As shown in Figure 2, from time t0 to t1, the input voltage Vin is less than the voltage across the input capacitor (the minimum voltage across the input capacitor is Vrec_min), and the LED is powered by the input capacitor Cin, with no input current Iin. From time t1 to t4, the input voltage Vin is greater than or equal to the voltage across the input capacitor Vcap, and the LED is powered by the input voltage Vin. The peak current Ipk is reached at time t2, and the conduction angle is 90 degrees at time t3. From time t4 to t5, the input voltage Vin is less than the voltage across the input capacitor, and the LED is powered by the input capacitor Cin, with no input current Iin. Diode D is a parasitic diode of the power transistor Q (there is also a parasitic diode between the GND and OUT pins; since the external sampling resistor Rcs is relatively small, it can ultimately be connected in parallel and attributed to D).

[0003] The IEC 61000-3-2 standard (Harmonic Current Emission Standard) specifies input current harmonic requirements for lighting equipment with input currents of 5W-25W. Three different test standards can meet these requirements. Linear LED drivers must at least meet test standard 2, which focuses on: ① the 3rd harmonic being less than 86% of the fundamental frequency amplitude; ② the 5th harmonic being less than 61% of the fundamental frequency amplitude; ③ the input current being greater than 5% of the peak input current before a conduction angle of 60 degrees; ④ reaching the peak current before a conduction angle of 65 degrees; and ⑤ the input current not being less than 5% of the peak current after a conduction angle of 90 degrees. Therefore, this standard has requirements regarding both higher harmonics and conduction angle.

[0004] However, due to the presence of the input capacitor Cin, the waveform of the input current Iin is a pulse current, as shown in Figure 2. When the input capacitor C is selected with an appropriate capacitance, 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 urgently needs to be solved by those skilled in the art.

[0006] It should be noted that the above description of the technical background is only for the purpose of providing a clear and complete explanation of the technical solutions of the present invention and facilitating understanding by those skilled in the art. It should not be assumed that the above technical solutions are known to those skilled in the art simply because they have been described in the background section of this invention. Summary of the Invention

[0007] In view of the shortcomings of the prior art described above, the purpose of this invention is to provide a linear LED driving circuit and electronic device to solve the problem that the third and fifth harmonics of the LED input current are prone to exceed the standard in the prior art.

[0008] To achieve the above and other related objectives, the present invention provides a linear LED driving circuit, the linear LED driving circuit comprising at least:

[0009] The system comprises a first voltage input module, a switching 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 the bus voltage;

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

[0012] The output terminal of the first constant current control module is connected to the second terminal of the switching module, and the sampling terminal is connected to the first terminal of the second sampling module via the first sampling module.

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

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

[0015] Wherein, the impedance of the first sampling module is less 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, both the first constant current control module and the second constant current control module include a first power switch and a first operational amplifier;

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

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

[0019] Optionally, the switching module is implemented using a diode; the anode of the diode serves as the first terminal of the switching module, and the cathode of the diode serves as the second terminal of the switching module.

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

[0021] To achieve the above and other related objectives, the present invention also provides a linear LED driving circuit, the linear LED driving circuit comprising at least:

[0022] The system 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.

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

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

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

[0026] The impedance of the third sampling module is greater than that of the fourth sampling module.

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

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

[0029] Optionally, 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 terminal of the second LED load.

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

[0031] To achieve the above and other related objectives, the present invention also provides an electronic device, which includes at least the above-described 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 standard requirements in the simplest way through a switching module and two constant current control modules.

[0034] 2. The linear LED driving circuit and electronic device of the present invention can also reduce the need for external components by utilizing the parasitic diode of the power transistor itself, thereby further reducing the overall system cost. Attached Figure Description

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

[0036] Figure 2 shows a waveform diagram of the LED driving system in Figure 1.

[0037] Figure 3 shows a schematic diagram of one structure of the linear LED driving circuit of the present invention.

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

[0039] Figure 5 shows a schematic diagram of the working principle of the linear LED driving circuit in Figure 3 when the bus voltage is lower than the forward conduction voltage of the LED.

[0040] Figure 6 shows a schematic diagram of the working principle of the linear LED driving circuit in Figure 3 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 shows a schematic diagram of the working principle of the linear LED driving circuit in Figure 3 when the bus voltage is higher than the voltage on the first input capacitor.

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

[0043] Figure 9 shows a schematic diagram of the working principle of the linear LED driver circuit in Figure 8 when the bus voltage is lower than the forward conduction voltage of the LED.

[0044] Figure 10 shows a schematic diagram of the working principle of the linear LED driver circuit in Figure 8 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] Figure 11 shows a schematic diagram of the working principle of the linear LED driving circuit in Figure 8 when the bus voltage is higher than the voltage on the second input capacitor.

[0046] Component designation explanation

[0047] 1. Flicker-free linear LED driving system

[0048] 11 chips

[0049] 2 Linear LED Driver 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 Third constant current control module

[0056] 27. Fourth Constant Current Control Module Detailed Implementation

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

[0058] Please refer to Figures 3 to 11. It should be noted that the illustrations provided in this embodiment are only schematic representations of the basic concept of the present invention. Therefore, the figures only show the components related to the present invention and are not drawn according to the actual number, shape and size of the components in the actual implementation. In the actual implementation, the form, quantity and proportion of each component can be arbitrarily changed, and the layout of the components may also be more complex.

[0059] Example 1

[0060] As shown in Figure 3, this embodiment provides a linear LED driving circuit 2, which includes:

[0061] The system comprises 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] As shown in Figure 3, the first voltage input module 21 provides the 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 terminal 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 at the non-inverting input terminal or the inverting input terminal of the rectifier unit BD to provide protection. Any circuit structure capable of providing bus voltage is applicable to the first voltage input module of the present invention, and is not limited to this embodiment.

[0064] As shown in Figure 3, the first terminal of the switch module 22 is connected to the output terminal of the first voltage input module 21, and the second terminal 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 switching module 22 is implemented using a diode D1. The anode of the diode D1 serves as the first terminal of the switching module 22, and the cathode of the diode D1 serves as the second terminal of the switching module 22. When the bus voltage Vin_rec is greater than the voltage on the first input capacitor C1, the diode D1 is forward-biased; 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-biased. In practical use, any device or circuit structure that can achieve the above functions is applicable to this invention, and will not be described in detail here.

[0066] As shown in Figure 3, the output terminal of the first constant current control module 23 is connected to the second terminal of the switching module 22, and the sampling terminal is connected to the first terminal of the second sampling module via the first sampling module, for controlling the current flowing through the first constant current control module 23 to maintain a constant current. The output terminal of the second constant current control module 24 is connected to the output terminal of the first voltage input module 21, and the sampling terminal is connected to the first terminal of the second sampling module, for controlling the current flowing through the second constant current control module 24 to maintain a constant current.

[0067] Specifically, in this embodiment, the first constant current control module 23 includes a first power switch M1 and a first operational amplifier OP1. The drain of the first power switch 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 M1 is implemented using an NMOS transistor; in actual use, any device capable of power switching adjustment can be selected as needed. The first input terminal of the first operational amplifier OP1 is connected to the source of the first power switch 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 M1. As an example, the inverting input terminal of the first operational amplifier OP1 is connected to the source of the first power switch M1, and the non-inverting 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 to achieve constant current control logic. 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 will not be described in detail here. In this embodiment, the reference grounds (GND1 and GND2) of the first and second constant current control modules are connected to the positive terminal of the first LED load LED1. In practical use, any circuit structure capable of achieving constant current control is applicable to the first and second constant current control modules of this invention.

[0068] Specifically, in this embodiment, both the first sampling module and the second sampling module are implemented using resistors. The first sampling module includes a first resistor Rcs1, one end of which 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 which 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 practical use, any circuit structure capable of implementing sampling functionality is applicable to the first and second sampling modules of this invention.

[0069] It should be noted that in the present invention, the impedance of the first sampling module is less than that of the second sampling module (i.e., the resistance value of the first resistor Rcs1 is less than that 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 operates.

[0070] As shown in FIG. 3, 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 shown in FIGS. 4 to 7, the working principle of the linear LED driving circuit 2 of this embodiment is as follows:

[0072] As shown in FIGS. 4 and 5, 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 of 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, successively passing through the first sampling module and the second sampling module (current I1 path), ensuring no stroboscopic. Since the impedance of the first sampling module is much less than that 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 shown in FIGS. 4 and 6, at the time t1 - t2, the bus voltage Vin_rec is higher than the forward conduction voltage Vled of the LED but lower than the voltage Vcap of 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 of the sampling terminal CS2 of the second constant current control module 24 squeezes the voltage of the sampling terminal CS1 of the first constant current control module 23, and the first constant current control module 23 is turned off, and the first input capacitor C1 cannot discharge, and the voltage Vcap of the first input capacitor C1 remains unchanged. At this time, the requirement that the input current should be greater than 5% of the input peak current before the conduction angle of 60 degrees can be satisfied (Iin > Ipk * 5%).

[0074] As shown in Figures 4 and 7, from time t2 to t5, as the bus voltage Vin_rec continuously increases, the input current Iin not only supplies power to the first LED load LED1 (current path I2), but also charges the first input capacitor C1 through the switch module 22 (current path I3, the voltage Vcap on the first input capacitor C1 changes with the bus voltage Vin_rec). Therefore, the actual input current Iin is I2 + I3, where the peak current Ipk appears at time t3, satisfying the requirement that the peak current Ipk must be reached before the conduction angle reaches 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 reaches 90 degrees (Iin ≥ Ipk * 5%).

[0075] As shown in Figures 4 and 6, at time t5-t6, the bus voltage Vin_rec begins to decrease. 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 and the second sampling module. The voltage at the sampling terminal CS2 of the second constant current control module 24 blocks the voltage at the sampling terminal CS1 of the first constant current control module 23, thereby turning off the first constant current control module 23 (leaving only the current I2 path). At this time, the first input capacitor C1 cannot charge or discharge and its voltage remains unchanged.

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

[0077] Therefore, the LED current throughout the entire power frequency cycle is I1→I2→I2→I2→I1. By setting appropriate impedances for the first and second sampling modules (resistors Rcs1 and Rcs2 in this embodiment), I1≈I2 is achieved, thus realizing flicker-free operation. In this embodiment, the addition of the switching module 22 and the first constant current control module 23 extends the input current waveform from time t2-t5 (relative to time t1-t4 in Figure 2) to time t1-t6, thereby ensuring that the 3rd and 5th harmonics of the input current 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] Example 2

[0080] Considering that the MOSFET inside the constant current control module has a parasitic diode, this embodiment uses this diode to replace the switching module 22 in embodiment one by changing the circuit connection. As shown in Figure 8, the linear LED driving circuit 2 in this embodiment includes:

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

[0082] As shown in Figure 8, 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 Embodiment 1, and will not be described in detail here.

[0083] As shown in Figure 8, 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 through the second input capacitor C2, which is used to control the current flowing through the third constant current control module 26 to maintain a constant current.

[0084] Specifically, the third constant current control module 26 includes a second power switch M2 and a second operational amplifier OP2. The source of the second power switch 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. A parasitic diode D2 also exists between the source and drain of the second power switch M2. The anode of the parasitic diode D2 is connected to the source of the second power switch M2, and the cathode is connected to the drain of the second power switch M2. As an example, the second power switch M2 is implemented using an NMOS transistor. In actual use, any device can be selected as needed, as long as the device can realize power switching adjustment and has a diode with the anode connected to the sampling terminal and the 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 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 M2. As an example, the inverting input terminal of the second operational amplifier OP2 is connected to the source of the second power switch M2, and the non-inverting input terminal is connected to the third reference voltage Ref3. In practical use, the relationship between the input signal and the polarity of the corresponding input port can be adjusted as needed to achieve constant current control logic. In this embodiment, the reference ground (GND3) of the third constant current control module 26 is connected to the connection node between the third sampling module and the fourth constant current control module 27. In practical use, any circuit structure capable of achieving constant current control is applicable to the third constant current control module of this invention.

[0085] It should be noted that the parasitic diode D2 of the second power switch M2 conducts forward 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 be in a holding state.

[0086] As shown in Figure 8, 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 terminal of the second LED load LED2 via the fourth sampling module. The negative terminal 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 will not be described in detail here; the reference ground of the fourth constant current control module 27 is connected to the positive terminal of the second LED load LED2, and any circuit structure that can realize constant current control is applicable to the fourth constant current control module of the present invention, and is not limited to this embodiment.

[0088] Specifically, in this embodiment, both the third sampling module and the fourth sampling module are implemented using 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 practical use, any circuit structure capable of implementing sampling functionality is suitable for the third and fourth sampling modules of this invention.

[0089] It should be noted that, in this 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 value of the third resistor Rcs3 is greater than the resistance value 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] As shown in Figures 4 and 9-11, the working principle of the linear LED driving circuit 2 in this embodiment is as follows:

[0091] As shown in Figures 4 and 9, at 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. At this time, the voltage Vcap on the second input capacitor C2 is relatively high. 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 (current I1 path), ensuring no flicker. Since the impedance of the third sampling module is greater than that 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 dominant role. The third constant current control module 26 and the fourth constant current control module 27 carry the same current. At this time, the voltage sampled 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 conducting state and cannot control the current, which is equivalent to a short circuit in a wire.

[0092] As shown in Figures 4 and 10, at time 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 passes through the third sampling module, the fourth constant current control module 27, and the fourth sampling module to perform constant current control on the second LED load LED2. Since the impedance of the third sampling module is greater than the impedance of the fourth sampling module, the voltage sampled by the third sampling module will be higher than the voltage set by the third constant current control module 26, thereby turning off the third constant current control module 26 (leaving only the current I2 path). At this time, the requirement that the input current must be greater than 5% of the input peak current before the conduction angle is 60 degrees is met (Iin > Ipk * 5%).

[0093] As shown in Figures 4 and 11, between times t2 and t5, as the bus voltage Vin_rec continuously increases, it becomes 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 (current path I3, where the voltage Vcap on the second input capacitor C2 changes with the bus voltage Vin_rec). Simultaneously, the bus voltage Vin_rec sequentially passes through the third sampling module, the fourth constant current control module 27, and the fourth sampling module to perform constant current control on the second LED load LED2 (current path I2). The input current Iin is I2 + I3, where the peak current Ipk occurs at time t3, satisfying the requirement that the peak current Ipk must be reached before the conduction angle reaches 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 reaches 90 degrees (Iin ≥ Ipk * 5%).

[0094] As shown in Figures 4 and 10, at times t5-t6, the bus voltage Vin_rec begins to decrease. 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 passes through the third sampling module, the fourth constant current control module 27, and the fourth sampling module to perform constant current control on the second LED load LED2. Since the impedance of the third sampling module is greater than the impedance of the fourth sampling module, the voltage sampled by the third sampling module is higher than the voltage set by the third constant current control module 26, thereby turning off the third constant current control module 26 (leaving only the current I2 path). The second input capacitor C2 cannot charge or discharge at this time, thus maintaining a constant voltage.

[0095] As shown in Figures 4 and 9, during the time intervals t6-t7, the bus voltage Vin_rec is lower than the LED forward conduction voltage Vled. At this time, the voltage Vcap on the second input capacitor C2 is relatively high. The second input capacitor C2 discharges the second LED load LED2 (current I1 path) sequentially through the third constant current control module 26, the third sampling module, the fourth constant current control module 27, and the fourth sampling module, ensuring flicker-free operation. During this stage, the third constant current control module 26 plays a dominant role in current control, while the fourth constant current control module 27 is in a fully open conducting state.

[0096] Therefore, the LED current throughout the entire power frequency cycle is I1→I2→I2→I2→I1. By setting appropriate impedances for the third and fourth sampling modules (resistors Rcs3 and Rcs4 in this embodiment), I1≈I2 is achieved, resulting in flicker-free operation. Similarly, the parasitic diode D2 extends the input current waveform from t2-t5 to t1-t6, ensuring that the 3rd and 5th harmonics of the input current meet the standards.

[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 elaborated here.

[0098] Example 3

[0099] This embodiment also provides an electronic device, which includes a linear LED driving circuit 2 of Embodiment 1 or Embodiment 2. The LED in this electronic device can achieve stable output and provide a high level of customer experience.

[0100] In summary, this invention provides a linear LED driver circuit and electronic device, comprising: two constant current control modules. When the bus voltage is lower than the forward conduction voltage of the LED, the input capacitor supplies power, 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, the bus voltage supplies power, 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, the bus voltage supplies power and charges the input capacitor, and the constant current is controlled by the second / fourth constant current control module. The linear LED driver circuit and electronic device of this invention, through a switching module and two constant current control modules, optimizes high-order harmonics to meet standard requirements in the simplest way; it also utilizes the parasitic diodes of the power transistor itself to reduce the need for external components, further reducing the overall system cost. Therefore, this invention effectively overcomes the various shortcomings of the prior art and has high industrial applicability.

[0101] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can 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 those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should 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 includes at least: 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 the bus voltage; the sampling terminal of the third constant current control module is connected to the output terminal of the second voltage input module, and the output terminal is grounded via the second input capacitor; the output terminal of the fourth constant current control module is connected to the output terminal of the second voltage input module via the third sampling module, and the sampling terminal is connected to the positive terminal of the second LED load via the fourth sampling module; the negative terminal 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.

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

3. The linear LED driving circuit according to claim 1, 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 terminal of the second LED load.

4. The linear LED driving circuit according to claim 1, characterized in that: The third and fourth sampling modules are implemented using resistors.

5. An electronic device, characterized in that, The electronic device includes at least the linear LED driving circuit as described in any one of claims 1-4.

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