A linear LED driving circuit

Abstract

The present invention discloses a linear LED driving circuit, including a rectifier circuit, and also including: a constant current control circuit and a voltage conversion circuit; wherein the constant current control circuit includes a power transistor, a first resistor and a power transistor control circuit; when the duty cycle of the input PWM signal is greater than a threshold value, the linear LED driving circuit can realize that the LED current decreases as the PWM duty cycle decreases; when the duty cycle of the PWM signal is not greater than the threshold value, further deep dimming is realized, and the linear constant current driving of the LED device is realized; and the linear LED driving circuit can be applied to both Traic dimming and PWM dimming systems, and can also be applied to non-dimming systems, with a wide range of applications, and can reduce system losses when applied to Traic dimming systems. In addition, the present invention also discloses another linear LED driving circuit, which realizes the compatible use of Traic dimming and PWM dimming.

Description

Technical Field

[0001] The invention relates to the technical field of power electronics, and in particular to a linear LED drive circuit. Background Art

[0002] At present, the traditional PWM dimming system allows the system to output energy to the output when the PWM signal is high, and turns off the power device when the PWM signal is low, and does not allow the system to output energy to the output. In this way, the output LED current changes with the change of the PWM signal duty cycle, realizing the PWM dimming function, such as Figure 1 As shown, when the voltage (Vac) output by the rectifier circuit is greater than the voltage (Vled) of the LED device, the voltage (Vcs) of the control power tube changes accordingly with the duty cycle of the PWM signal, so that the output LED current changes with the duty cycle of the PWM signal. However, this method is not suitable for TRAIC (thyristor) dimming. Since a minimum holding current is required to keep the TRAIC dimmer on when the TRAIC dimmer is working, a large latching current is required to turn on the TRAIC dimmer when the TRAIC dimmer is turned off and then turned on again. Therefore, the intermittent opening of the power tube in the traditional PWM dimming system cannot meet the necessary conditions for TRAIC dimming. Figure 2 As shown, if a chip with a traditional PWM dimming function is used in a system with a leading TRAIC dimmer, it is necessary to extract a larger holding current from the line voltage at the cutting edge of the leading TRAIC dimmer (such as Figure 2 60mA of Ibleeder in the middle), so that the front-cut TRAIC dimmer starts normally; after the front-cut TRAIC dimmer starts, when PWM is turned off, the main power tube that provides current to the output is turned off, and it is necessary to draw a maintenance current from the line voltage (such as Figure 2 When the line voltage reaches its peak, the system loss is increased and the system efficiency is greatly reduced.

[0003] Therefore, how to provide a PWM dimming system that can meet TRAIC dimming, reduce system losses, and meet market demand is a problem that needs to be solved urgently. Summary of the invention

[0004] The purpose of the present invention is to provide a linear LED driving circuit to realize a PWM dimming system compatible with Traic dimming, reduce system losses and meet market demand.

[0005] In order to solve the above technical problems, the present invention provides a linear LED driving circuit, including a rectifier circuit and further comprising:

[0006] A constant current control circuit, comprising a power transistor, a first resistor and a power transistor control circuit; wherein the power transistor has a first terminal, a second terminal and a control terminal, the first output end of the rectifier circuit is connected to the first terminal through an LED device, the second terminal is grounded through the first resistor, and the control terminal is connected to the power transistor control circuit;

[0007] A voltage conversion circuit, connected to the power transistor control circuit, for converting an input PWM signal into a DC signal to participate in controlling the power transistor;

[0008] Among them, the power transistor control circuit is used to control the on-time of the power transistor to be proportional to the duty cycle when the duty cycle of the PWM signal is greater than a threshold value according to the DC signal; when the duty cycle of the PWM signal is less than or equal to the threshold value, control the on-time of the power transistor to remain unchanged and control the current passing through the power transistor to be proportional to the duty cycle.

[0009] Optionally, the power transistor control circuit comprises: an instantaneous current reference generating circuit, a current reference value generating circuit, a voltage control circuit, a first operational amplifier, a second operational amplifier and a conduction time control circuit;

[0010] The output terminal of the instantaneous current reference generating circuit is connected to the non-inverting input terminal of the first operational amplifier, and is used to generate a reference voltage signal corresponding to the input DC signal and the output voltage signal of the first output terminal of the rectifier circuit;

[0011] The output end of the current reference value generating circuit is connected to the non-inverting input end of the second operational amplifier, and is used to generate a reference voltage signal corresponding to the input DC signal;

[0012] The output end of the voltage control circuit is connected to the first input end of the conduction time control circuit, and is used to output a control voltage signal that continuously increases within a preset time period according to the input control signal;

[0013] The inverting input terminals of the first operational amplifier and the second operational amplifier are both connected to the second terminal, the output terminal of the first operational amplifier is connected to the control terminal, and the output terminal of the second operational amplifier is connected to the second input terminal of the on-time control circuit; the output terminal of the on-time control circuit is connected to the control terminal of the first operational amplifier, and is used to control the first operational amplifier to stop working when the control voltage signal is greater than the amplified signal output by the second operational amplifier.

[0014] Optionally, the third input terminal of the on-time control circuit is connected to the first output terminal of the rectifier circuit, and is used to control the first operational amplifier to stop working when the output voltage signal is greater than a voltage threshold and the control voltage signal is greater than the amplified signal output by the second operational amplifier; wherein the voltage threshold is less than the on-voltage of the LED device.

[0015] Optionally, the on-time control circuit includes: a comparator, an RS trigger and a voltage comparison circuit;

[0016] Wherein, the negative terminal of the comparator is connected to the output terminal of the second operational amplifier, the positive terminal of the comparator is connected to the output terminal of the voltage control circuit, and the output terminal of the comparator is connected to the R input terminal of the RS trigger;

[0017] The input end of the voltage comparison circuit is connected to the first output end of the rectifier circuit, and the output end of the voltage comparison circuit is connected to the S input end of the RS trigger, so as to output a high-level signal to the RS trigger when the output voltage signal is greater than the voltage threshold; the Q output end of the RS trigger is connected to the control end of the first operational amplifier.

[0018] Optionally, the power transistor control circuit further includes: a second resistor and a third resistor;

[0019] The instantaneous current reference generating circuit is connected to the first output end of the rectifier circuit through the second resistor, and a common end of the instantaneous current reference generating circuit connected to the second resistor is grounded through the third resistor.

[0020] Optionally, the power transistor control circuit further includes: a third capacitor;

[0021] Wherein, a first end of the third capacitor is connected to the output end of the second operational amplifier, and a second end of the third capacitor is grounded.

[0022] Optionally, the voltage control circuit is specifically a switched capacitor circuit, which is used to output a control voltage signal that increases in steps within a preset time period according to an input clock signal.

[0023] Optionally, the voltage control circuit includes: a first controllable switch, a second controllable switch, a first capacitor and a second capacitor;

[0024] The first end of the first controllable switch is connected to the output end of the preset DC voltage, the second end of the first controllable switch is connected to the first end of the second controllable switch, and the common end thereof is connected to the first end of the first capacitor;

[0025] The second end of the second controllable switch and the first end of the second capacitor are connected, and their common end is used as the output end of the voltage control circuit and connected to the first input end of the conduction time control circuit, for outputting the control voltage signal to the conduction time control circuit;

[0026] The second ends of the first capacitor and the second capacitor are both grounded; the control end of the first controllable switch is connected to the output end of the first clock signal, and is used to be turned on and off according to the first clock signal; the control end of the second controllable switch is connected to the output end of the second clock signal, and is used to be turned on and off according to the first clock signal; wherein the first controllable switch and the second controllable switch are not turned on at the same time.

[0027] Optionally, the linear LED driving circuit further includes:

[0028] The discharge current control circuit is connected to the first output terminal of the rectifier circuit and is used for drawing current from the rectifier circuit and discharging it when the power transistor is turned off.

[0029] Optionally, the discharge current control circuit comprises: a discharge circuit and a logic controller;

[0030] Among them, the first output end of the rectifier circuit is grounded through the discharge circuit, and the discharge circuit includes a constant current source and a logic control switch connected in series; the first input end and the second input end of the logic controller are respectively connected one-to-one with the first output end of the rectifier circuit and the control terminal, and the output end of the logic controller is connected to the control end of the logic control switch.

[0031] The present invention also provides a linear LED driving circuit, including a rectifier circuit and a TRAIC dimmer, and further comprising:

[0032] A constant current control circuit, comprising a power transistor, a first resistor and a power transistor control circuit; wherein the power transistor has a first terminal, a second terminal and a control terminal, the first output end of the rectifier circuit is connected to the first terminal through an LED device, the second terminal is grounded through the first resistor, and the control terminal is connected to the output end of the power transistor control circuit;

[0033] A voltage conversion circuit, connected to the power transistor control circuit, for converting an input PWM signal into a DC signal to participate in controlling the power transistor;

[0034] The discharge current control circuit is connected to the first output terminal of the rectifier circuit and is used for drawing current from the rectifier circuit and discharging it when the power transistor is turned off.

[0035] Optionally, the discharge current control circuit comprises: a discharge circuit and a logic controller;

[0036] Among them, the first output end of the rectifier circuit is grounded through the discharge circuit, and the discharge circuit includes a constant current source and a logic control switch connected in series; the first input end and the second input end of the logic controller are respectively connected one-to-one with the first output end of the rectifier circuit and the control terminal, and the output end of the logic controller is connected to the control end of the logic control switch.

[0037] Optionally, the power transistor control circuit comprises: an instantaneous current reference generating circuit, a current reference value generating circuit, a voltage control circuit, a first operational amplifier, a second operational amplifier and a conduction time control circuit;

[0038] The output terminal of the instantaneous current reference generating circuit is connected to the non-inverting input terminal of the first operational amplifier, and is used to generate a reference voltage signal corresponding to the input DC signal and the output voltage signal of the first output terminal of the rectifier circuit;

[0039] The output end of the current reference value generating circuit is connected to the non-inverting input end of the second operational amplifier, and is used to generate a reference voltage signal corresponding to the input DC signal;

[0040] The output end of the voltage control circuit is connected to the first input end of the conduction time control circuit, and is used to output a control voltage signal that continuously increases within a preset time period according to the input control signal;

[0041] The inverting input terminals of the first operational amplifier and the second operational amplifier are both connected to the second terminal, the output terminal of the first operational amplifier is connected to the control terminal, and the output terminal of the second operational amplifier is connected to the second input terminal of the on-time control circuit; the output terminal of the on-time control circuit is connected to the control terminal of the first operational amplifier, and is used to control the first operational amplifier to stop working when the control voltage signal is greater than the amplified signal output by the second operational amplifier.

[0042] A linear LED driving circuit provided by the present invention comprises a rectifier circuit and also comprises: a constant current control circuit, comprising a power transistor, a first resistor and a power transistor control circuit; wherein the power transistor has a first terminal, a second terminal and a control terminal, the first output end of the rectifier circuit is connected to the first terminal through an LED device, the second terminal is grounded through a first resistor, and the control terminal is connected to the power transistor control circuit; a voltage conversion circuit is connected to the power transistor control circuit and is used to convert an input PWM signal into a DC signal to participate in controlling the power transistor; wherein the power transistor control circuit is used to control the on-time of the power transistor to be proportional to the duty cycle according to the DC signal when the duty cycle of the PWM signal is greater than a threshold value; when the duty cycle of the PWM signal is less than or equal to the threshold value, the on-time of the power transistor is controlled to remain unchanged, and the current passing through the power transistor is controlled to be proportional to the duty cycle;

[0043] It can be seen that when the duty cycle of the input PWM signal of the linear LED driving circuit provided by the present invention is greater than the threshold, the on-time of the power transistor can be reduced as the PWM duty cycle decreases, thereby realizing that the LED current decreases as the PWM duty cycle decreases; when the duty cycle of the PWM signal is not greater than the threshold, the on-time of the power transistor remains unchanged, and the current passing through the power transistor decreases as the PWM duty cycle decreases, thereby realizing deep dimming and realizing the linear constant current drive of the LED device; and the linear LED driving circuit provided by the present invention can be applied to both Traic dimming and PWM dimming systems, and can also be applied to non-dimming systems, with a wide range of applications, and can reduce system losses when applied to Traic dimming systems. In addition, the present invention also provides another linear LED driving circuit to achieve compatible use of Traic dimming and PWM dimming. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0045] Figure 1 The waveform diagram of each node of the traditional PWM dimming method without using the Traic dimmer;

[0046] Figure 2 The waveform diagram of each node of the traditional PWM dimming method using the front-cut Traic dimmer;

[0047] Figure 3A schematic diagram of the structure of a linear LED driving circuit provided by an embodiment of the present invention;

[0048] Figure 4 A waveform diagram of each node of a linear LED driving circuit provided by an embodiment of the present invention;

[0049] Figure 5 A dimming curve of a linear LED driving circuit provided by an embodiment of the present invention with a duty cycle of a PWM signal of 0 to 100%;

[0050] Figure 6 A dimming curve of a linear LED driving circuit provided by an embodiment of the present invention when the duty cycle of a PWM signal is between 0 and 10%;

[0051] Figure 7 This is a schematic structural diagram of another linear LED driving circuit provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0052] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0053] Please refer to Figure 3 , Figure 3 This is a schematic diagram of the structure of a linear LED driving circuit provided by an embodiment of the present invention. The driving circuit includes a rectifier circuit 10 and may also include:

[0054] The constant current control circuit 20 includes a power transistor 21, a first resistor 22 (R3) and a power transistor control circuit 23; wherein the power transistor 21 has a first terminal, a second terminal and a control terminal, the first output end of the rectifier circuit 10 is connected to the first terminal through the LED device 60, the second terminal is grounded through the first resistor 22, and the control terminal is connected to the power transistor control circuit 23;

[0055] The voltage conversion circuit 30 is connected to the power transistor control circuit 23 and is used to convert the input PWM signal into a DC signal to participate in controlling the power transistor 21;

[0056] Among them, the power transistor control circuit 23 is used to control the on-time of the power transistor 21 to be proportional to the duty cycle according to the DC signal when the duty cycle of the PWM signal is greater than the threshold; when the duty cycle of the PWM signal is less than or equal to the threshold, control the on-time of the power transistor 21 to remain unchanged and control the current passing through the power transistor 21 to be proportional to the duty cycle.

[0057] It can be understood that the constant current control circuit 20 provided in this embodiment can use the power transistor control circuit 23 to control the on and off of the power transistor 21, thereby realizing the linear constant current drive of the LED device 60. That is to say, the power transistor control circuit 23 can use the DC signal output by the voltage conversion circuit 30 to control the on and off of the power transistor 21, so that when the duty cycle of the PWM signal is greater than the threshold, the on time of the power transistor 21 is proportional to the duty cycle, and when the duty cycle of the PWM signal is less than or equal to the threshold, the on time of the power transistor 21 remains unchanged, and the current passing through the power transistor 21 is proportional to the duty cycle, thereby realizing the deep dimming of PWM on the basis of ensuring the linear constant current drive of the LED device 60.

[0058] Specifically, the voltage conversion circuit 30 in this embodiment can convert the input PWM signal into a DC signal (i.e., a DC voltage signal), and participate in controlling the on and off of the power transistor 21 by inputting the DC signal converted from the PWM signal into the power transistor control circuit 23. The specific circuit structure of the voltage conversion circuit 30 in this embodiment can be set by the designer, such as being implemented in the same or similar manner as the duty cycle conversion circuit in the prior art, that is, the voltage conversion circuit 30 can convert the PWM signal into a DC signal corresponding to the duty cycle according to the duty cycle of the PWM signal; for example, the voltage conversion circuit 30 in this embodiment can convert the PWM signal into a DC signal proportional to the duty cycle, that is, the larger the duty cycle of the PWM signal input to the voltage conversion circuit 30, the larger the voltage value of the DC signal input to the voltage conversion circuit 30.

[0059] Correspondingly, the specific circuit structure of the power transistor control circuit 23 in this embodiment can be set by the designer according to practical scenarios and user needs, such as Figure 3As shown, the power transistor control circuit 23 may include an instantaneous current reference generating circuit 231, a current reference value generating circuit 232, a voltage control circuit 233, a first operational amplifier 234 (OPA1), a second operational amplifier 235 (OPA2) and an on-time control circuit 236; wherein the output end of the instantaneous current reference generating circuit 231 is connected to the in-phase input end of the first operational amplifier 234, and is used to generate a reference voltage signal (Vref_ref) corresponding to the input DC signal and the output voltage signal of the first output end of the rectifier circuit 10; the output end of the current reference value generating circuit 232 is connected to the in-phase input end of the second operational amplifier 235, and is used to generate a reference voltage signal (Vref) corresponding to the input DC signal. ; The output end of the voltage control circuit is connected to the first input end of the on-time control circuit 236, and is used to output a control voltage signal (SC_OUT) that continuously increases within a preset time period according to the input control signal; the inverting input ends of the first operational amplifier 234 and the second operational amplifier 235 are both connected to the second terminal, the output end of the first operational amplifier 234 is connected to the control terminal, and the output end of the second operational amplifier 235 is connected to the second input end of the on-time control circuit 236; the output end of the on-time control circuit 236 is connected to the control end of the first operational amplifier 234, and is used to control the first operational amplifier 234 to stop working when the control voltage signal is greater than the amplified signal (COMP) output by the second operational amplifier 235.

[0060] That is to say, in this embodiment, the power transistor control circuit 23 can realize the PWM dimming function through the following process: in the first stage, when the duty cycle of the input PWM square wave (PWM signal) is greater than the duty cycle D1 (threshold), the reference voltage signal output by the instantaneous current reference generating circuit 231 remains unchanged, and the reference voltage signal output by the current reference value generating circuit 232 decreases as the duty cycle of the PWM square wave decreases, the amplified signal output by the second operational amplifier 235 decreases as the reference voltage signal decreases, and the conduction time of the power transistor 21 decreases as the amplified signal decreases, thereby achieving the goal of reducing the current of the LED device 60 as the duty cycle of the PWM signal decreases. In the second stage, when the input PWM square wave is less than the duty cycle D1, since the amplified signal output by the second operational amplifier 235 remains unchanged, the conduction time of the power transistor 21 remains unchanged, and the reference voltage signal output by the instantaneous current reference generating circuit 231 decreases as the duty cycle of the PWM square wave decreases, that is, the real-time current value when the power transistor 21 is turned on decreases as the duty cycle of the PWM square wave decreases, thereby achieving a further reduction in the LED current, thereby realizing deep dimming of PWM dimming.

[0061] like Figures 3 to 6As shown in FIG. 1 , when the duty cycle (dutycycle) of the PWM signal input to the voltage conversion circuit 30 is greater than 10% (i.e., the threshold), the reference voltage signal (VCS_ref) output by the instantaneous current reference generating circuit 231 remains unchanged, the DC voltage signal (PWM_dc) output by the voltage conversion circuit 30 decreases as the duty cycle of the PWM signal decreases, the reference voltage signal (Vref) output by the current reference value generating circuit 232 also decreases as the duty cycle of the PWM signal decreases, and the amplified signal (CO_DC) output by the second operational amplifier 235 decreases. MP) decreases as Vref decreases, so that the on-time of the MOS tube (i.e., the power transistor 21) decreases as the amplified signal decreases, and the LED current decreases as the duty cycle of the PWM signal decreases; when the duty cycle of the PWM signal input to the duty cycle conversion circuit is less than 10%, as the duty cycle of the PWM signal decreases, COMP remains unchanged, the on-time of the MOS tube remains unchanged, and VCS_ref is reduced, that is, the real-time current value when the MOS tube is turned on is reduced, so that the LED current is further reduced, thereby achieving a dimming depth of less than 1%.

[0062] It should be noted that the first input terminal and the second input terminal of the instantaneous current reference generating circuit 231 in the power transistor control circuit 23 can be connected one-to-one with the output terminal of the voltage conversion circuit 30 and the first output terminal of the rectifier circuit 10, respectively, so as to utilize the DC signal output by the voltage conversion circuit 30 and the output voltage signal of the rectifier circuit 10 (such as Figure 3 The bus signal in the power transistor control circuit 23 generates a reference voltage signal that determines the real-time current of the loop operation; the input end of the current reference value generating circuit 232 in the power transistor control circuit 23 can be connected to the output end of the voltage conversion circuit 30 to convert the DC signal output by the voltage conversion circuit 30 into a reference voltage signal that determines the loop output current.

[0063] Specifically, the second input terminal of the instantaneous current reference generating circuit 231 can be connected to the first output terminal of the rectifier circuit 10 through a voltage divider circuit, so that the instantaneous current reference generating circuit 231 can receive a divided voltage signal (such as Figure 3 The Vbus signal in the input voltage divider is used to generate a reference voltage signal using the input voltage divider signal and the PWM signal. Figure 3 As shown, the linear LED driving circuit provided in this embodiment may further include: a second resistor (R1) and a third resistor (R2); wherein the second input terminal of the instantaneous current reference generating circuit 231 is connected to the first output terminal of the rectifier circuit 10 through the second resistor, and the common terminal where the second input terminal of the instantaneous current reference generating circuit 231 is connected to the second resistor is grounded through the third resistor.

[0064] Correspondingly, the voltage control circuit in the power transistor control circuit 23 can output a control voltage signal that continuously increases within a preset time period to the conduction time control circuit 236 according to the control signal, that is, the control voltage signal output by the voltage control circuit can continuously increase from an initial voltage value (such as 0) to a preset voltage value within a preset time period according to the control of the input control signal. The specific circuit structure of the voltage control circuit in this embodiment can be set by the designer. For example, when the control signal is a clock signal, the voltage control circuit can be specifically a switch capacitor circuit, which is used to output a control voltage signal that continuously increases within a preset time period according to the input clock signal.

[0065] like Figure 3 As shown, the voltage control circuit is a switched capacitor circuit (such as Figure 3 When the Switch cap in the circuit is switched, it may include: a first controllable switch (S1), a second controllable switch (S1), a first capacitor (C1) and a second capacitor (C2); wherein the first end of the first controllable switch is connected to the output end of the preset DC voltage (Vdc_sc), the second end of the first controllable switch is connected to the first end of the second controllable switch, and the common end thereof is connected to the first end of the first capacitor; the second end of the second controllable switch is connected to the first end of the second capacitor, and the common end thereof is connected as the output end of the voltage control circuit to the first input end of the conduction time control circuit 236, and is used to output a control voltage signal (SC_OUT) to the conduction time control circuit 236; the second ends of the first capacitor and the second capacitor are both grounded; the control end of the first controllable switch is connected to the output end of the first clock signal (clkL), and is used to be turned on and off correspondingly according to the first clock signal; the control end of the second controllable switch is connected to the output end of the second clock signal (clkR), and is used to be turned on and off correspondingly according to the first clock signal; wherein the first controllable switch and the second controllable switch may not be turned on at the same time. That is to say, the voltage control circuit is controlled by the first clock signal clkL and the second clock signal clkR. The first controllable switch controlled by clkL and the second controllable switch controlled by clkR are not turned on at the same time. When the first controllable switch is turned on and the second controllable switch is turned off, the Vdc_sc signal charges the first capacitor C1, so that the voltage on C1 is Vdc_sc. When the second controllable switch is turned on and the first controllable switch is turned off, the second capacitor C2 and the capacitor C1 share the charge Vdc_sc*C1 on the capacitor C1, and the voltage on C2 is Vdc_sc*C1 / (C1+C2). Taking the capacitance of C2 as 1000 times that of C1 as an example, the value of the voltage on C2 increased when the second controllable switch is turned on is about one thousandth of Vdc_sc. This ensures that the control voltage signal outputted from the output end of the voltage control circuit can reach the amplified signal (COMP) outputted by the second operational amplifier 235 within mS. The higher the COMP value, the longer the on-time of the power transistor 21, and vice versa.

[0066] Among them, the first input end of the on-time control circuit 236 in the power transistor control circuit 23 can be connected to the output end of the voltage control circuit, and the second input end of the on-time control circuit 236 can be connected to the output end of the second operational amplifier 235; the output end of the on-time control circuit 236 can be connected to the control end of the first operational amplifier 234, used to control the start and shutdown of the first operational amplifier 234; the on-time control circuit 236 can control the first operational amplifier 234 to stop working when the voltage value of the input control voltage signal reaches the amplified signal output by the second operational amplifier 235, thereby turning off the power transistor 21. As long as the on-time control circuit 236 can achieve the above functions, the present embodiment does not limit the specific circuit structure of the on-time control circuit 236. For example, the on-time control circuit 236 in the present embodiment can also be connected to the first output terminal of the rectifier circuit 10, that is, the third input terminal of the on-time control circuit 236 can be connected to the first output terminal of the rectifier circuit 10, and is used to control the first operational amplifier 234 to stop working when the voltage value of the output voltage signal is greater than the voltage threshold and the voltage value of the control voltage signal is greater than the amplified signal output by the second operational amplifier 235; wherein the voltage threshold is less than the on-voltage of the LED device 60.

[0067] Specifically, Figure 3 As shown, the on-time control circuit 236 may include: a comparator, an RS trigger and a voltage comparison circuit; wherein the negative end of the comparator is connected to the output end of the second operational amplifier 235 as the second input end of the on-time control circuit 236, the positive end of the comparator is connected to the output end of the voltage control circuit as the first input end of the on-time control circuit 236, and the output end of the comparator is connected to the R input end of the RS trigger; the input end of the voltage comparison circuit is connected to the first output end of the rectifier circuit 10 as the third input end of the on-time control circuit 236, and the output end of the voltage comparison circuit is connected to the S input end of the RS trigger, for outputting a voltage signal greater than a voltage threshold (such as Figure 3 When the voltage at the positive terminal of the comparator (SC_OUT) reaches the voltage at the negative terminal of the comparator (COMP), the output of the comparator changes from low to high, and the subsequent RS trigger stops the first operational amplifier 234 from working, turning off the power transistor 21 (MOS tube).

[0068] That is to say, in this embodiment, the power transistor control circuit 23 controls the on-time of the power transistor 21 to achieve linear constant current output and PWM dimming. The on-time control can be as follows: when the output of the rectifier circuit 10 is greater than the on-voltage of the LED device 60, the power transistor 21 is turned on; the on-time of the power transistor 21 can depend on whether the control voltage signal output by the voltage control circuit is greater than the amplified signal output by the second operational amplifier 235, and the amplified signal output by the second operational amplifier 235 is adjusted by a loop composed of an instantaneous current reference generating circuit 231, a current reference value generating circuit 232, a first operational amplifier 234 and a second operational amplifier 235, so as to achieve a constant loop output current, which is the quotient of the voltage value of the second voltage signal and the resistance value of the first resistor 22, that is, Figure 3 Vref / R3 in.

[0069] It should be noted that the specific circuit structure for supplying power to the anode of the LED device 60 in this embodiment can be set by the designer according to practical scenarios and user needs, such as being implemented in the same or similar manner as the power supply circuit for supplying power to the LED device 60 in the prior art, such as converting the direct output of the AC power supply or the AC power supply adjusted by the TRAIC dimmer 40 into a corresponding half-wave waveform through the rectifier circuit 10 to supply power to the LED device 60. Regardless of whether the TRAIC dimmer 40 is used, the LED drive circuit provided in this embodiment can achieve constant current output and PWM dimming by controlling the conduction time of the power transistor 21.

[0070] Specifically, when the linear LED driving circuit provided in this embodiment is applied to the front-cut TRAIC dimming system, the linear LED driving circuit may also include: a TRAIC dimmer 40; wherein the first input end of the rectifier circuit 10 is connected to the first output end of the AC power supply through the TRAIC dimmer 40, the second input end of the rectifier circuit 10 is connected to the second output end of the AC power supply, the first output end of the rectifier circuit 10 is connected to the anode of the LED device 60, and the second output end of the rectifier circuit 10 is grounded, for utilizing the input AC power to power the LED device 60; the cathode of the LED device 60 is grounded in turn through the power transistor 21 and the first resistor 22.

[0071] Correspondingly, such as Figure 3 As shown, the linear LED driving circuit provided in this embodiment may also include a diode (D1) arranged between the rectifier circuit 10 and the LED device 60 to avoid current reverse; that is, the first output end of the rectifier circuit 10 can be connected to the anode of the diode, and the cathode of the diode can be connected to the anode of the LED device 60.

[0072] Specifically, the specific circuit structure of the rectifier circuit 10 in this embodiment can be set by the designer. Figure 3 As shown, the rectifier circuit 10 may be a full-bridge rectifier circuit 10 including four diodes. As long as the rectifier circuit 10 can convert the input AC voltage waveform into a corresponding half-wave waveform, this embodiment does not impose any limitation on this.

[0073] It is understandable that if Figure 3 As shown, the linear LED driving circuit provided in this embodiment may also include a discharge current control circuit 50 connected to the first output end of the rectifier circuit 10, which is used to draw current from the rectifier circuit 10 and discharge it when the power transistor 21 is cut off (i.e., turned off), so that when applied to the TRAIC dimming system, when the power transistor 21 is cut off, the holding current required for starting the TRAIC dimmer 40 and the maintenance current required after starting can be drawn from the rectifier circuit 10.

[0074] Specifically, Figure 3 and Figure 4 As shown, when the linear LED driving circuit further includes a TRAIC dimmer 40, the discharge current control circuit 50 can extract a holding current (such as Figure 4 60mA in Ibleeder), and then adjust the drawn current to the holding current after a preset delay time (such as Figure 4 30mA of Ibleeder), and the power transistor 21 is turned off again and the voltage outputted from the first output terminal of the rectifier circuit 10 is detected (such as Figure 4 When Vac is less than the preset threshold voltage, the maintenance current is drawn from the rectifier circuit 10, which ensures the startup and use of the TRAIC dimmer 40. Figure 2 The prior art shown reduces the use of holding current, reduces system losses, and improves system efficiency.

[0075] Correspondingly, the discharge current control circuit 50 in this embodiment may include a discharge circuit 51 and a logic controller 52; wherein the first output terminal of the rectifier circuit 10 is grounded through the discharge circuit 51, and the discharge circuit 51 may include one or more constant current sources and a logic control switch connected in series; the first input terminal and the second input terminal of the logic controller 52 are respectively connected one-to-one with the first output terminal and the control terminal of the rectifier circuit 10, and the output terminal of the logic controller 52 is connected with the control terminal of the logic control switch. Figure 3 As shown, the first input terminal of the logic controller 52 can receive a divided voltage signal (such as Figure 3The Vbus signal in the logic controller 51 is connected to the first output terminal of the rectifier circuit 10 through the second resistor, and the common terminal of the first input terminal of the logic controller 52 and the second resistor is grounded through the third resistor.

[0076] That is, the logic controller 52 can generate a voltage signal (such as a voltage signal) corresponding to the output voltage signal outputted from the first output terminal of the rectifier circuit 10. Figure 4 The Vbus signal in the figure) and the voltage signal for controlling the power transistor 21 (such as Figure 4 The GATE signal in the discharge circuit 51 controls the on and off of the logic control switch. Figure 4 As shown, the logic controller 52 can control the corresponding logic control switch to be turned on when the power transistor 21 is turned off and the Vbus signal corresponding to the cutting edge voltage of the TRAIC dimmer 40 is detected, so that the discharge circuit 51 draws 60mA of current (i.e., holding current) from the first output end of the rectifier circuit 10, and adjusts the turned-on logic control switch to draw 30mA of current (i.e., maintaining current) after a preset delay time, and then turns off the logic control switch when the power transistor 21 is turned on to no longer draw current, and when the power transistor 21 is turned off again and it is detected by detecting the Vbus signal that the voltage output from the first output end of the rectifier circuit 10 is less than the preset threshold voltage, the corresponding logic control switch is controlled to be turned on, so that the discharge circuit 51 draws 30mA of current from the first output end of the rectifier circuit 10.

[0077] Specifically, the specific device types and quantities of the constant current source and the logic control switch in the upper discharge circuit 51 can be set by the designer, such as including two constant current sources and two logic control switches, that is, each constant current source is connected in series with a corresponding logic control switch one by one, and the first output end of the rectifier circuit 10 is grounded through the two series-connected constant current sources and logic control switches, so that when one logic control switch is turned on, the discharge circuit 51 extracts the holding current from the first output end of the rectifier circuit 10, and when the other logic control switch is turned on, the discharge circuit 51 extracts the holding current from the first output end of the rectifier circuit 10. As long as it is ensured that the logic controller 52 can control the discharge circuit 51 to extract the holding current and the holding current from the first output end of the rectifier circuit 10 by controlling the on and off of the logic control switch, this embodiment does not impose any restrictions on this.

[0078] Accordingly, this embodiment does not limit specific current values ​​of the holding current and the maintaining current. For example, the maintaining current may be a current value not less than 30 mA, and the holding current may be a current value greater than the maintaining current, such as 60 mA.

[0079] Further, such as Figure 3As shown, the power transistor control circuit 23 may further include: a third capacitor (loop compensation capacitor); wherein a first end of the third capacitor is connected to the output end of the second operational amplifier 235, and a second end of the third capacitor is grounded.

[0080] Further, such as Figure 3 As shown, the linear LED driving circuit provided in this embodiment may further include: a fourth capacitor (C3) and a fourth resistor (R4); wherein the first ends of the fourth capacitor and the fourth resistor are both used to connect to the anode of the LED device 60, and the second ends of the fourth capacitor and the fourth resistor are both used to connect to the cathode of the LED device 60.

[0081] In this embodiment, when the duty cycle of the input PWM signal of the linear LED driving circuit provided by the embodiment of the present invention is greater than a threshold value, the on-time of the power transistor 21 can be reduced as the PWM duty cycle decreases, thereby achieving a reduction in the LED current as the PWM duty cycle decreases; when the duty cycle of the PWM signal is not greater than the threshold value, the on-time of the power transistor 21 remains unchanged, and the current passing through the power transistor 21 decreases as the PWM duty cycle decreases, thereby achieving deep dimming and realizing the linear constant current drive of the LED device 60; and the linear LED driving circuit provided by the present invention can be applied to both Traic dimming and PWM dimming systems, and can also be applied to non-dimming systems, with a wide range of applications, and can reduce system losses when applied to Traic dimming systems.

[0082] In addition, the embodiment of the present invention also provides another linear LED driving circuit to achieve compatible use of Traic dimming and PWM dimming, so as to achieve compatible use of Traic dimming and PWM dimming. Figure 7 , Figure 7 This is a schematic diagram of the structure of another linear LED driving circuit provided by an embodiment of the present invention. The driving circuit includes a rectifier circuit 10 and a TRAIC dimmer 40, and may also include:

[0083] The constant current control circuit 20 includes a power transistor 21, a first resistor 22 (R3) and a power transistor control circuit 23; wherein the power transistor 21 has a first terminal, a second terminal and a control terminal, the first output terminal of the rectifier circuit 10 is connected to the first terminal through the LED device 60, the second terminal is grounded through the first resistor 22, and the control terminal is connected to the output terminal of the power transistor control circuit 23;

[0084] The voltage conversion circuit 30 is connected to the power transistor control circuit 23 and is used to convert the input PWM signal into a DC signal to participate in controlling the power transistor 21;

[0085] The discharge current control circuit 50 is connected to the first output terminal of the rectifier circuit 10 and is used to extract and discharge current from the rectifier circuit 10 when the power transistor 21 is turned off.

[0086] It can be understood that the linear LED driving circuit provided in this embodiment enables Traic dimming and PWM dimming to be compatible through the setting of the discharge current control circuit 50 and the constant current control circuit 20. The discharge current control circuit 50 in this embodiment can extract the holding current required for the start-up of the Traic dimmer 40 and the maintenance current required after the start-up from the rectifier circuit 10 and discharge them when the power transistor 21 is cut off (i.e., turned off).

[0087] Specifically, Figure 4 and Figure 7 As shown, the discharge current control circuit 50 can extract the holding current (such as ) from the rectifier circuit 10 when detecting the voltage at the cutting edge of the TRAIC dimmer 40 (ie, the cutting edge voltage). Figure 4 60mA in Ibleeder), and then adjust the drawn current to the holding current after a preset delay time (such as Figure 4 30mA of Ibleeder), and the power transistor 21 is turned off again and the voltage outputted from the first output terminal of the rectifier circuit 10 is detected (such as Figure 4 When Vac is less than the preset threshold voltage, the maintenance current is drawn from the rectifier circuit 10, which ensures the startup and use of the TRAIC dimmer 40. Figure 2 The prior art shown reduces the use of holding current, reduces system losses, and improves system efficiency.

[0088] Correspondingly, the discharge current control circuit 50 in this embodiment may include a discharge circuit 51 and a logic controller 52; wherein the first output terminal of the rectifier circuit 10 is grounded through the discharge circuit 51, and the discharge circuit 51 may include one or more constant current sources and a logic control switch connected in series; the first input terminal and the second input terminal of the logic controller 52 are respectively connected one-to-one with the first output terminal and the control terminal of the rectifier circuit 10, and the output terminal of the logic controller 52 is connected with the control terminal of the logic control switch. Figure 7 As shown, the first input terminal of the logic controller 52 can receive a divided voltage signal (such as ) corresponding to the output voltage signal of the first output terminal of the rectifier circuit 10 through a voltage divider circuit composed of a second resistor (R1) and a third resistor (R2). Figure 3 The Vbus signal in the logic controller 51 is connected to the first output terminal of the rectifier circuit 10 through the second resistor, and the common terminal of the first input terminal of the logic controller 52 and the second resistor is grounded through the third resistor.

[0089] That is, the logic controller 52 can generate a voltage signal (such as a voltage signal) corresponding to the output voltage signal outputted from the first output terminal of the rectifier circuit 10. Figure 4 The Vbus signal in the figure) and the voltage signal for controlling the power transistor 21 (such as Figure 4 The GATE signal in the discharge circuit 51 controls the on and off of the logic control switch. Figure 4 As shown, the logic controller 52 can control the corresponding logic control switch to be turned on when the power transistor 21 is turned off and the Vbus signal corresponding to the cutting edge voltage of the TRAIC dimmer 40 is detected, so that the discharge circuit 51 draws 60mA of current (i.e., holding current) from the first output end of the rectifier circuit 10, and adjusts the turned-on logic control switch to draw 30mA of current (i.e., maintaining current) after a preset delay time, and then turns off the logic control switch when the power transistor 21 is turned on to no longer draw current, and when the power transistor 21 is turned off again and it is detected by detecting the Vbus signal that the voltage output from the first output end of the rectifier circuit 10 is less than the preset threshold voltage, the corresponding logic control switch is controlled to be turned on, so that the discharge circuit 51 draws 30mA of current from the first output end of the rectifier circuit 10.

[0090] Specifically, the specific device types and quantities of the constant current source and the logic control switch in the upper discharge circuit 51 can be set by the designer, such as including two constant current sources and two logic control switches, that is, each constant current source is connected in series with a corresponding logic control switch one by one, and the first output end of the rectifier circuit 10 is grounded through the two series-connected constant current sources and logic control switches, so that when one logic control switch is turned on, the discharge circuit 51 extracts the holding current from the first output end of the rectifier circuit 10, and when the other logic control switch is turned on, the discharge circuit 51 extracts the holding current from the first output end of the rectifier circuit 10. As long as it is ensured that the logic controller 52 can control the discharge circuit 51 to extract the holding current and the holding current from the first output end of the rectifier circuit 10 by controlling the on and off of the logic control switch, this embodiment does not impose any restrictions on this.

[0091] Accordingly, this embodiment does not limit specific current values ​​of the holding current and the maintaining current. For example, the maintaining current may be a current value not less than 30 mA, and the holding current may be a current value greater than the maintaining current, such as 60 mA.

[0092] It can be understood that the constant current control circuit 20 provided in this embodiment can use the power transistor control circuit 23 to control the on and off of the power transistor 21, thereby realizing the linear constant current drive of the LED device 60. Further, the power transistor control circuit 23 can use the DC signal output by the voltage conversion circuit 30 to control the on and off of the power transistor 21, so that when the duty cycle of the PWM signal is greater than the threshold, the on time of the power transistor 21 is proportional to the duty cycle, and when the duty cycle of the PWM signal is less than or equal to the threshold, the on time of the power transistor 21 remains unchanged, and the current passing through the power transistor 21 is proportional to the duty cycle, thereby realizing PWM deep dimming on the basis of ensuring the linear constant current drive of the LED device 60; accordingly, the specific circuit structure of the constant current control circuit 20 and the voltage conversion circuit 30 of the linear LED drive circuit provided in this embodiment can be implemented in the same or similar manner as the drive circuit provided in the above embodiment, so that the linear LED drive circuit provided in this embodiment can further realize PWM deep dimming on the basis of compatible use of Traic dimming and PWM dimming.

[0093] Correspondingly, such as Figure 7 As shown, the power transistor control circuit 23 may include an instantaneous current reference generation circuit, a current reference value generation circuit, a voltage control circuit (Switch cap), a first operational amplifier (OPA1), a second operational amplifier (OPA2) and an on-time control circuit; wherein the output end of the instantaneous current reference generating circuit is connected to the in-phase input end of the first operational amplifier, and is used to generate a reference voltage signal (Vref_ref) corresponding to the input DC signal and the output voltage signal of the first output end of the rectifier circuit 10; the output end of the current reference value generating circuit is connected to the in-phase input end of the second operational amplifier, and is used to generate a reference voltage signal (Vref) corresponding to the input DC signal; the output end of the voltage control circuit is connected to the first input end of the on-time control circuit, and is used to output a control voltage signal (SC_OUT) that continuously increases within a preset time period according to the input control signal; the inverting input ends of the first operational amplifier and the second operational amplifier are both connected to the second terminal, the output end of the first operational amplifier is connected to the control terminal, and the output end of the second operational amplifier is connected to the second input end of the on-time control circuit; the output end of the on-time control circuit is connected to the control end of the first operational amplifier, and is used to control the first operational amplifier to stop working when the control voltage signal is greater than the amplified signal (COMP) output by the second operational amplifier.

[0094] In this embodiment, the linear LED driving circuit provided in this embodiment extracts and discharges the holding current required for starting the TRAIC dimmer 40 and the maintenance current required after starting from the rectifier circuit 10 through the setting of the discharge current control circuit 50 when the power transistor 21 is turned off, so that the TRAIC dimming and PWM dimming can be used compatibly.

[0095] It should also be noted that, in this specification, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "comprise", "include" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, an element defined by the statement "comprises a ..." does not exclude the presence of other identical elements in the process, method, article or device including the element.

[0096] The above is a detailed introduction to an LED driving circuit provided by the present invention. This article uses specific examples to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only used to help understand the method and core ideas of the present invention. It should be pointed out that for ordinary technicians in this technical field, without departing from the principles of the present invention, several improvements and modifications can be made to the present invention, and these improvements and modifications also fall within the scope of protection of the claims of the present invention.

Claims

1. A linear LED driving circuit, comprising a rectifier circuit, characterized in that: Also includes: A constant current control circuit, comprising a power transistor, a first resistor and a power transistor control circuit; wherein the power transistor has a first terminal, a second terminal and a control terminal, the first output end of the rectifier circuit is connected to the first terminal through an LED device, the second terminal is grounded through the first resistor, and the control terminal is connected to the power transistor control circuit; A voltage conversion circuit, connected to the power transistor control circuit, for converting an input PWM signal into a DC signal to participate in controlling the power transistor; Among them, the power transistor control circuit is used to control the on-time of the power transistor to be proportional to the duty cycle when the duty cycle of the PWM signal is greater than a threshold value according to the DC signal; when the duty cycle of the PWM signal is less than or equal to the threshold value, control the on-time of the power transistor to remain unchanged and control the current passing through the power transistor to be proportional to the duty cycle.

2. The linear LED driving circuit according to claim 1, characterized in that: The power transistor control circuit comprises: an instantaneous current reference generation circuit, a current reference value generation circuit, a voltage control circuit, a first operational amplifier, a second operational amplifier and a conduction time control circuit; The output terminal of the instantaneous current reference generating circuit is connected to the non-inverting input terminal of the first operational amplifier, and is used to generate a reference voltage signal corresponding to the input DC signal and the output voltage signal of the first output terminal of the rectifier circuit; The output end of the current reference value generating circuit is connected to the non-inverting input end of the second operational amplifier, and is used to generate a reference voltage signal corresponding to the input DC signal; The output end of the voltage control circuit is connected to the first input end of the conduction time control circuit, and is used to output a control voltage signal that continuously increases within a preset time period according to the input control signal; The inverting input terminals of the first operational amplifier and the second operational amplifier are both connected to the second terminal, the output terminal of the first operational amplifier is connected to the control terminal, and the output terminal of the second operational amplifier is connected to the second input terminal of the on-time control circuit; the output terminal of the on-time control circuit is connected to the control terminal of the first operational amplifier, and is used to control the first operational amplifier to stop working when the control voltage signal is greater than the amplified signal output by the second operational amplifier.

3. The linear LED driving circuit according to claim 2, characterized in that: The third input terminal of the on-time control circuit is connected to the first output terminal of the rectifier circuit, and is used to control the first operational amplifier to stop working when the output voltage signal is greater than a voltage threshold and the control voltage signal is greater than the amplified signal output by the second operational amplifier; wherein the voltage threshold is less than the on-voltage of the LED device.

4. The linear LED driving circuit according to claim 3, characterized in that: The on-time control circuit comprises: a comparator, an RS trigger and a voltage comparison circuit; Wherein, the negative terminal of the comparator is connected to the output terminal of the second operational amplifier, the positive terminal of the comparator is connected to the output terminal of the voltage control circuit, and the output terminal of the comparator is connected to the R input terminal of the RS trigger; The input end of the voltage comparison circuit is connected to the first output end of the rectifier circuit, and the output end of the voltage comparison circuit is connected to the S input end of the RS trigger, so as to output a high-level signal to the RS trigger when the output voltage signal is greater than the voltage threshold; the Q output end of the RS trigger is connected to the control end of the first operational amplifier.

5. The linear LED driving circuit according to claim 2, characterized in that: The power transistor control circuit further includes: a second resistor and a third resistor; The instantaneous current reference generating circuit is connected to the first output end of the rectifier circuit through the second resistor, and a common end of the instantaneous current reference generating circuit connected to the second resistor is grounded through the third resistor.

6. The linear LED driving circuit according to claim 2, characterized in that: The power transistor control circuit further includes: a third capacitor; Wherein, a first end of the third capacitor is connected to the output end of the second operational amplifier, and a second end of the third capacitor is grounded.

7. The linear LED driving circuit according to claim 1, characterized in that: The voltage control circuit is specifically a switched capacitor circuit, which is used to output a control voltage signal that increases in steps within a preset time period according to an input clock signal.

8. The linear LED driving circuit according to claim 7, characterized in that: The voltage control circuit comprises: a first controllable switch, a second controllable switch, a first capacitor and a second capacitor; The first end of the first controllable switch is connected to the output end of the preset DC voltage, the second end of the first controllable switch is connected to the first end of the second controllable switch, and the common end thereof is connected to the first end of the first capacitor; The second end of the second controllable switch and the first end of the second capacitor are connected, and their common end is used as the output end of the voltage control circuit and connected to the first input end of the conduction time control circuit, for outputting the control voltage signal to the conduction time control circuit; The second ends of the first capacitor and the second capacitor are both grounded; the control end of the first controllable switch is connected to the output end of the first clock signal, and is used to be turned on and off according to the first clock signal; the control end of the second controllable switch is connected to the output end of the second clock signal, and is used to be turned on and off according to the first clock signal; wherein the first controllable switch and the second controllable switch are not turned on at the same time.

9. The linear LED driving circuit according to any one of claims 1 to 8, characterized in that: Also includes: The discharge current control circuit is connected to the first output terminal of the rectifier circuit and is used for drawing current from the rectifier circuit and discharging it when the power transistor is turned off.

10. The linear LED driving circuit according to claim 9, characterized in that: The discharge current control circuit comprises: a discharge circuit and a logic controller; Among them, the first output end of the rectifier circuit is grounded through the discharge circuit, and the discharge circuit includes a constant current source and a logic control switch connected in series; the first input end and the second input end of the logic controller are respectively connected one-to-one with the first output end of the rectifier circuit and the control terminal, and the output end of the logic controller is connected to the control end of the logic control switch.

11. A linear LED driving circuit, comprising a rectifier circuit and a TRAIC dimmer, characterized in that: Also includes: A constant current control circuit, comprising a power transistor, a first resistor and a power transistor control circuit; wherein the power transistor has a first terminal, a second terminal and a control terminal, the first output end of the rectifier circuit is connected to the first terminal through an LED device, the second terminal is grounded through the first resistor, and the control terminal is connected to the output end of the power transistor control circuit; A voltage conversion circuit, connected to the power transistor control circuit, for converting an input PWM signal into a DC signal to participate in controlling the power transistor; The discharge current control circuit is connected to the first output terminal of the rectifier circuit and is used for drawing current from the rectifier circuit and discharging it when the power transistor is turned off.

12. The linear LED driving circuit according to claim 11, characterized in that: The discharge current control circuit comprises: a discharge circuit and a logic controller; Among them, the first output end of the rectifier circuit is grounded through the discharge circuit, and the discharge circuit includes a constant current source and a logic control switch connected in series; the first input end and the second input end of the logic controller are respectively connected one-to-one with the first output end of the rectifier circuit and the control terminal, and the output end of the logic controller is connected to the control end of the logic control switch.

13. The linear LED driving circuit according to claim 11 or 12, characterized in that: The power transistor control circuit comprises: an instantaneous current reference generation circuit, a current reference value generation circuit, a voltage control circuit, a first operational amplifier, a second operational amplifier and a conduction time control circuit; The output terminal of the instantaneous current reference generating circuit is connected to the non-inverting input terminal of the first operational amplifier, and is used to generate a reference voltage signal corresponding to the input DC signal and the output voltage signal of the first output terminal of the rectifier circuit; The output end of the current reference value generating circuit is connected to the non-inverting input end of the second operational amplifier, and is used to generate a reference voltage signal corresponding to the input DC signal; The output end of the voltage control circuit is connected to the first input end of the conduction time control circuit, and is used to output a control voltage signal that continuously increases within a preset time period according to the input control signal; The inverting input terminals of the first operational amplifier and the second operational amplifier are both connected to the second terminal, the output terminal of the first operational amplifier is connected to the control terminal, and the output terminal of the second operational amplifier is connected to the second input terminal of the on-time control circuit; the output terminal of the on-time control circuit is connected to the control terminal of the first operational amplifier, and is used to control the first operational amplifier to stop working when the control voltage signal is greater than the amplified signal output by the second operational amplifier.

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