LED driving circuit and control method

Abstract

The present invention discloses an LED driving circuit and control method, wherein the circuit includes a first field effect tube, the drain of the first field effect tube outputs an operating current; a charging module connected to the gate of the first field effect tube to charge its gate to control the rising slope of the output working current; a discharging module connected to the gate of the first field effect tube to discharge its gate to control the falling slope of the output working current; a signal generating module to output a pulse width modulation signal; a first input terminal of a comparator connected to the gate of the first field effect tube, a second input terminal of the comparator connected to a target voltage, and a first output terminal of the comparator outputting a switching signal; a logic control module connected between the signal generating module, the comparator and the charging module and the discharging module, and the logic control module controls the on and off of the charging module and the discharging module according to the pulse width modulation signal and the switching signal. The present invention discloses an LED driving circuit and control method, which can control the slope change of the output working current.

Description

Technical Field

[0001] The present invention relates to the field of chip technology, and in particular to an LED drive circuit and a control method. Background Art

[0002] The LED driver chip converts the corresponding pulse width control signal, i.e., PWM signal, input from the front end into the required output current square wave to drive the external light-emitting lamp beads, i.e., LEDs, through the internal high-precision current source and the corresponding drive-level circuit, thereby achieving the control of producing the required different brightness.

[0003] Both direct display LED systems and backlight LED systems have strict requirements on electromagnetic interference (EMI), and the PWM square wave high current output by the LED driver chip in the system is the biggest contributor to EMI problems.

[0004] In order to improve the EMI characteristics of the system, there are generally strict requirements on the change rate of the output PWM current of the driver stage in the LED driver chip. Regardless of the current conduction speed or the shutdown speed, the current edge change is generally required to be controlled in the range of 50ns-500ns. At the same time, for slower current edge changes, when displaying low gray brightness, that is, when the PWM pulse width is very narrow, the controlled current edge duration will increase relative to the PWM pulse width. Because of the process changes in chip production, large errors will be generated, resulting in poor low gray consistency when displaying low gray.

[0005] like Figure 1 As shown, the conventional LED driving circuit for output current slope control is usually implemented by using a controllable resistor. The specific method is to control the change slope of the final output current by controlling the series resistor R1 from the driving stage to the final switch tube 10 and the resistance value of the discharge resistor R2 of the switch tube 10 when it is turned off, thereby improving electromagnetic compatibility EMI and power supply noise.

[0006] However, since the initial charging slope is determined by the voltage difference between the output voltage of the operational amplifier and the gate voltage of the switch tube 10 divided by the resistance value of the resistor R1, and the initial discharging slope is determined by the voltage difference between the steady-state gate voltage of the switch tube 10 and the reference ground voltage divided by the resistance value of the resistor R2, even if R1 and R2 are perfectly matched, the two slopes will deviate with the process angle, that is, the two voltage differences cannot remain constant or the same, so the rising edge and falling edge of the output current cannot be perfectly compensated, that is Figure 2 The time width of T1-T2 and the time width of T3-T4 are inconsistent, resulting in low gray precision offset and inconsistency between slices.

[0007] Therefore, it is necessary to improve the prior art to overcome the above defects in the prior art. Summary of the invention

[0008] The object of the present invention is to provide an LED driving circuit and a control method, which can control the slope change of the output working current.

[0009] In order to solve the above technical problems, in a first aspect, the present invention provides an LED driving circuit, comprising:

[0010] A first field effect transistor, wherein a drain of the first field effect transistor outputs an operating current;

[0011] A charging module, connected to the gate of the first field effect transistor, to charge the gate of the first field effect transistor to control the rising slope of the output working current;

[0012] A discharge module, connected to the gate of the first field effect transistor, discharges the gate of the first field effect transistor to control the falling slope of the output working current;

[0013] A signal generating module outputs a pulse width modulation signal;

[0014] The first input terminal of the comparator is connected to the gate of the first field effect transistor, the second input terminal of the comparator is connected to the target voltage, and the first output terminal of the comparator outputs a switching signal;

[0015] The logic control module is connected between the signal generating module, the comparator and the charging module and the discharging module. The logic control module controls the on and off of the charging module and the discharging module according to the pulse width modulation signal and the switching signal.

[0016] Preferably, when the pulse width modulation signal is a high level signal and the gate voltage of the first field effect transistor is less than the target voltage, the charging module is turned on and the discharging module is turned off;

[0017] When the pulse width modulation signal is a low level signal, the charging module is turned off and the discharging module is turned on.

[0018] Preferably, the logic control module comprises:

[0019] A first AND gate, wherein a third input terminal of the first AND gate is connected to the signal generating module, a fourth input terminal of the first AND gate is connected to the first output terminal of the comparator, the fourth input terminal is an inverting input terminal, and a second output terminal of the first AND gate is connected to the charging module;

[0020] A NOT gate, wherein the fifth input terminal of the NOT gate is connected to the signal generating module, and the third output terminal of the NOT gate is connected to the discharge module.

[0021] Preferably, the charging module comprises:

[0022] A charging current source connected to the gate of the first field effect transistor;

[0023] A first switch is connected in series with the charging current source, and a second output terminal of the first AND gate is connected to the first switch.

[0024] Preferably, the discharge module comprises:

[0025] A discharge current source connected between the gate of the first field effect transistor and ground;

[0026] A second switch is connected in series with the discharge current source, and a third output terminal of the NOT gate is connected to the second switch.

[0027] Preferably, the LED driving circuit further includes:

[0028] A reference current module, connected between the gate and source of the first field effect transistor, to provide an output target current for the first field effect transistor;

[0029] The logic control module is connected between the signal generation module, the comparator and the reference current module, and controls the on and off of the reference current module according to the pulse width modulation signal and the switching signal.

[0030] Preferably, when the pulse width modulation signal is a high level signal and the gate voltage of the first field effect transistor is greater than or equal to the target voltage, the charging module is turned off, the discharging module is turned off, and the reference current module is turned on.

[0031] Preferably, the logic control module further includes:

[0032] A second AND gate, wherein the sixth input terminal of the second AND gate is connected to the signal generating module, the seventh input terminal of the second AND gate is connected to the first output terminal of the comparator, and the fourth output terminal of the second AND gate is connected to the reference current module.

[0033] Preferably, the reference current module comprises:

[0034] an error amplifier, wherein an eighth input terminal of the error amplifier is connected to a first reference voltage;

[0035] a third switch connected between the fifth output terminal of the error amplifier and the gate of the first field effect transistor, and a fourth output terminal of the second AND gate is connected to the third switch;

[0036] A second field effect transistor, wherein the gate of the second field effect transistor is connected to the second reference voltage, the drain of the second field effect transistor is respectively connected to the ninth input terminal of the error amplifier and the source of the first field effect transistor, and the source of the second field effect transistor is grounded.

[0037] Preferably, the LED driving circuit further comprises a protection module connected to the gate of the first field effect transistor, and the protection module comprises a fourth switch connected between the gate of the first field effect transistor and ground.

[0038] In a second aspect, the present invention further provides a control method for an LED driving circuit, comprising:

[0039] Provide an LED driving circuit as described in the first aspect;

[0040] Output pulse width modulation signal;

[0041] Comparing the gate voltage of the first field effect transistor with the target voltage, and outputting a switching signal;

[0042] The charging module and the discharging module are controlled to be turned on and off according to the pulse width modulation signal and the switching signal.

[0043] Preferably, controlling the on and off of the charging module and the discharging module according to the pulse width modulation signal and the switching signal includes:

[0044] Determine whether the pulse width modulation signal is a low level signal, and if so, control the charging module to be turned off and control the discharging module to be turned on so that the gate of the first field effect transistor discharges to control the falling slope of the output working current;

[0045] If not, determine whether the gate voltage of the first field effect transistor is less than the target voltage. If so, control the charging module to turn on to charge the gate of the first field effect transistor to control the rising slope of the output working current and control the discharge module to turn off.

[0046] Preferably, while controlling the on and off of the charging module and the discharging module, the on and off of the reference current module is synchronously controlled according to the pulse width modulation signal and the switching signal, including:

[0047] It is determined whether the gate voltage of the first field effect transistor is less than the target voltage. If not, the charging module is controlled to be turned off, the discharging module is controlled to be turned off, and the reference current module is controlled to be turned on to provide the output target current for the first field effect transistor.

[0048] Compared with the prior art, the present invention has the following advantages:

[0049] The present invention adopts a highly matched charging module and a discharging module at the gate of the first field effect tube, and adopts a logic control module to control the on and off of the charging module and the discharging module according to a pulse width modulation signal and a switching signal. By charging the gate of the first field effect tube to control the rising slope of the output working current IOUT, and discharging the gate of the first field effect tube to control the falling slope of the output working current IOUT, the slope change of the working current output by the first field effect tube is directly controlled, so that the rising slope and the falling slope of the output working current IOUT are consistent, so that the rising cycle and the falling cycle complement each other, and the low gray precision is improved while the electromagnetic interference is improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] The drawings described herein are only for explanation purposes and are not intended to limit the scope of the present invention in any way. In addition, the shapes and proportional dimensions of the components in the drawings are only for illustration purposes and are used to help understand the present invention. They do not specifically limit the shapes and proportional dimensions of the components of the present invention. Under the guidance of the present invention, those skilled in the art can select various possible shapes and proportional dimensions to implement the present invention according to specific circumstances. In the drawings:

[0051] Figure 1 It is a schematic diagram of a conventional LED driving circuit with output current slope control;

[0052] Figure 2 It is a signal waveform diagram of a traditional LED driving circuit with output current slope control;

[0053] Figure 3 is a schematic diagram of an LED driving circuit in the present invention;

[0054] Figure 4 It is a circuit diagram of the charging module, the discharging module and the reference current module in the present invention;

[0055] Figure 5 It is a circuit diagram of a comparator and a logic control module in the present invention;

[0056] Figure 6 It is a schematic diagram of the signal waveform of the LED driving circuit in the present invention;

[0057] Figure 7 is a flow chart of a control method of an LED driving circuit in the present invention;

[0058] Figure 8 It is a flow chart of step S4 of the control method of the LED driving circuit in the present invention. DETAILED DESCRIPTION

[0059] In order to enable those skilled in the art to better understand the technical solutions in the present invention, the technical solutions 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 only 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 should fall within the scope of protection of the present invention.

[0060] It should be noted that when an element is referred to as being "disposed on" another element, it may be directly on the other element or there may be a central element. When an element is considered to be "connected to" another element, it may be directly connected to the other element or there may be a central element at the same time. The terms "vertical", "horizontal", "left", "right" and similar expressions used herein are for illustrative purposes only and are not intended to be the only embodiment.

[0061] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those generally understood by those skilled in the art of the present invention. The terms used herein in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The term "and / or" used herein includes any and all combinations of one or more related listed items.

[0062] like Figure 3 As shown, the LED driving circuit corresponding to a preferred embodiment of the present invention comprises: a first field effect tube 1, a charging module 2 connected to the gate of the first field effect tube 1, a discharging module 3 connected to the gate of the first field effect tube 1, a reference current module 4 connected between the gate and the source of the first field effect tube 1, a signal generating module 5, a comparator 6, and a logic control module 7 connected between the signal generating module 5, the comparator 6 and the charging module 2, the discharging module 3, and the reference current module 4. Among them, the signal generating module 5 is used to output a pulse width modulation signal PWM, the comparator 6 is used to compare the gate voltage V1 of the first field effect tube 1 with the target voltage V2, and output a switching signal, and the logic control module 7 controls the charging module 2, the discharging module 3, and the reference current module 4 to turn on and off according to the pulse width modulation signal PWM and the switching signal.

[0063] Specifically, Figure 4As shown, the first field effect transistor 1 is used as a switch tube of the LED driving circuit, and preferably a cascade field effect transistor CAS_FET is used, which can achieve lower switching voltage, lower power consumption and more dense design. The drain of the first field effect transistor 1 outputs the working current IOUT, the charging module 2 is connected to the gate of the first field effect transistor 1 to charge the gate of the first field effect transistor 1 to control the rising slope of the output working current IOUT, the discharge module 3 discharges the gate of the first field effect transistor 1 to control the falling slope of the output working current IOUT, and the reference current module 4 is connected between the gate and source of the first field effect transistor 1 to provide the first field effect transistor 1 with an output target current I1.

[0064] The charging module 2 includes a charging current source 21 and a first switch 22 connected in series with the charging current source 21. The charging current source 21 is connected to the gate of the first field effect tube 1. Preferably, the first control terminal F2 of the first switch 22 is connected between the charging current source 21 and the gate of the first field effect tube 1. The tenth input terminal F1 of the first switch 22 is connected to the logic control module 7. The charging current source 21 is preferably a constant charging current source. When the charging module 2 is turned on, the charging current source 21 charges the gate of the first field effect tube 1, and the current size depends on the required output current change rate. The larger the charging current, the faster the rise rate of the drain output working current IOUT of the first field effect tube 1 generated by the parasitic capacitance and the partial miller effect, and finally the linear and controllable rise rate of the LED output working current IOUT is achieved.

[0065] The discharge module 3 includes a discharge current source 31 connected between the gate of the first field effect transistor 1 and the ground and a second switch 32 connected in series with the discharge current source 31. Preferably, the second control terminal G2 of the second switch 32 is connected between the discharge current source 31 and the gate of the first field effect transistor 1, and the eleventh input terminal G1 of the second switch 32 is connected to the logic control module 7. The discharge current source 31 is preferably a constant discharge current source, which is equal to the charging current source 21. When the discharge module 3 is turned on, the discharge current source 31 discharges the gate of the first field effect transistor 1, and the same principle as the charging module 2, the larger the discharge current, the faster the rate of change of the drain output working current IOUT of the first field effect transistor 1 generated by the parasitic capacitance and the partial miller effect, and finally the linear and controllable rate of decrease of the LED output working current IOUT is achieved.

[0066] The reference current module 4 includes an error amplifier 41, a third switch 42 and a second field effect transistor 43. The eighth input terminal E1 of the error amplifier 41 is connected to the first reference voltage V3, the third control terminal H2 of the third switch 42 is connected between the fifth output terminal E3 of the error amplifier 41 and the gate of the first field effect transistor 1, the gate of the second field effect transistor 43 is connected to the second reference voltage V5, the second reference voltage is a reference voltage corresponding to the required output target current I1, the drain of the second field effect transistor 43 is respectively connected to the ninth input terminal E2 of the error amplifier 41 and the source of the first field effect transistor 1, the source of the second field effect transistor 43 is grounded, and the twelfth input terminal H1 of the third switch 42 is connected to the logic control module 7. When the reference current module 4 is turned on, the second field effect transistor 43 provides the first field effect transistor 1 with an output working current IOUT which is a constant output target current I1. Furthermore, the drain voltage V4 of the second field effect transistor 43 is loop-controlled with the first reference voltage V3, that is, a loop is formed by the error amplifier 41 and the first field effect transistor 1 to ensure that in the final steady state, the drain voltage V4 of the second field effect transistor 43 (that is, the source voltage of the first field effect transistor 1) is the same as the first reference voltage V3, thereby eliminating the channel modulation effect of the second field effect transistor 43 as a current source reference, ensuring that the current reference is more accurate.

[0067] like Figure 5 As shown, the first input terminal A1 of the comparator 6 is connected to the gate of the first field effect tube 1, the second input terminal A2 of the comparator 6 is connected to the target voltage V2, and the first output terminal A3 of the comparator 6 outputs a switching signal. The target voltage V2 is obtained by sampling and matching the gate voltage obtained by the field effect tube of the same type as the first field effect tube 1 through the set final set output current. The signal generation module 5 outputs a pulse width modulation signal PWM alternating between a high level signal PWM_ON and a low level signal PWM_OFF. When the pulse width modulation signal PWM is a high level signal and the gate voltage V1 of the first field effect tube 1 is less than the target voltage V2, the logic control module 7 controls the charging module 2 to turn on, the discharging module 3 to turn off, and the reference current module 4 to turn off. When the pulse width modulation signal PWM is a high level signal and the gate voltage V1 of the first field effect tube 1 is greater than or equal to the target voltage V2, the charging module 2 is turned off, the discharging module 3 is turned off, and the reference current module 4 is turned on. When the pulse width modulation signal PWM is a low level signal, the charging module 2 is turned off, the discharging module 3 is turned on, and the reference current module 4 is turned off.

[0068] In this embodiment, the Figure 5In the connection method shown, when the gate voltage V1 of the first field effect tube 1 is less than the target voltage V2, the first output terminal A3 of the comparator 6 outputs a switching signal as a low level signal; when the gate voltage V1 of the first field effect tube 1 is greater than or equal to the target voltage V2, the first output terminal A3 of the comparator 6 outputs a switching signal as a high level signal. It can be understood that if the target voltage V2 and the gate voltage V1 of the first field effect tube 1 are interchanged at the input terminal, then under the same circumstances, the switching signal output by the first output terminal A3 of the comparator 6 is also correspondingly interchanged between high and low.

[0069] In order to realize that the charging module 2, the discharging module 3, and the reference current module 4 are turned on and off according to the above logic, preferably, in this embodiment, the logic control module 7 includes a first AND gate 71, a second AND gate 72, and a NOT gate 73. The third input terminal B1 of the first AND gate 71 is connected to the signal generating module 5, the fourth input terminal B2 of the first AND gate 71 is connected to the first output terminal A3 of the comparator 6, the fourth input terminal B2 is an inverting input terminal, the second output terminal B3 of the first AND gate 71 is connected to the tenth input terminal F1 of the first switch 22 of the charging module 2, and the second output terminal B3 of the first AND gate 71 outputs the first control signal PWM_PRE to control the on and off of the first switch 22. The sixth input terminal D1 of the second AND gate 72 is connected to the signal generating module 5, the seventh input terminal D2 of the second AND gate 72 is connected to the first output terminal A3 of the comparator 6, the fourth output terminal D3 of the second AND gate 72 is connected to the twelfth input terminal H1 of the third switch 42 of the reference current module 4, and the fourth output terminal D3 of the second AND gate 72 outputs the second control signal PWM_SEC to control the on-off of the third switch 42. The fifth input terminal C1 of the NOT gate 73 is connected to the signal generating module 5, the third output terminal C2 of the NOT gate 73 is connected to the eleventh input terminal G1 of the second switch 32 of the discharge module 3, and the third output terminal C2 of the NOT gate 73 outputs the third control signal PWM_OFF_1 to control the on-off of the second switch 32. It should be noted that the above is only a preferred implementation and connection mode of the logic control module 7, and other implementations and connection modes can also be adopted. For example, when the target voltage V2 and the gate voltage V1 of the first field effect tube 1 are interchanged in input terminals, the first AND gate 71 and the second AND gate 72 are also interchanged in connection modules accordingly, which is not further limited here.

[0070] The LED driving circuit also includes a protection module 8 connected to the gate of the first field effect tube 1. The protection module 8 includes a fourth switch 81 connected between the gate of the first field effect tube 1 and the ground. The protection module 8 is configured to prevent the working voltage VLED of the drain of the first field effect tube 1 from ringing due to external noise or parasitic inductance, and to prevent the gate of the first field effect tube 1 from being charged by the parasitic capacitance of the first field effect tube 1, causing false start. When the gate voltage V1 of the first field effect tube 1 is lower than the threshold voltage Vth, the fourth switch 81 can be controlled to be turned on through a certain delay signal PWM_OFF_DLY, and the discharge module 3 is switched to the protection module 8 for complete shutdown.

[0071] like Figure 7 As shown, the present invention also provides a control method for an LED driving circuit, comprising the following steps:

[0072] S1: Set up the above-mentioned LED driving circuit.

[0073] S2: Output pulse width modulation signal PWM, the pulse width modulation signal PWM alternately outputs high level signal and low level signal;

[0074] S3: Compare the gate voltage V1 of the first field effect transistor 1 with the target voltage V2, and output a switching signal.

[0075] Use Figure 5 In the connection method shown, when the gate voltage V1 of the first field effect transistor 1 is less than the target voltage V2, the switching signal is a low level signal; when the gate voltage V1 of the first field effect transistor 1 is greater than or equal to the target voltage V2, the switching signal is a high level signal.

[0076] S4: Controlling the on and off of the charging module 2 and the discharging module 3 according to the pulse width modulation signal PWM and the switching signal.

[0077] like Figure 8 As shown, step S4 specifically includes:

[0078] S400: Determine whether the PWM signal is a low level signal, if so, execute step S410, if not, execute S420.

[0079] S410: When the pulse width modulation signal PWM is a low-level signal PWM_OFF, no matter the switching signal is a low-level signal or a high-level signal, the first AND gate 71 outputs the first control signal PWM_PRE, which is a low-level signal, and controls the charging module 2 to be turned off. The second AND gate 72 outputs the second control signal PWM_SEC, which is a low-level signal, and controls the reference current module 4 to be turned off. The NOT gate 73 outputs the third control signal PWM_OFF_1 as a high-level signal, and the discharge module 3 is turned on to discharge the gate of the first field effect tube 1 and control the falling slope of the output working current IOUT. During the discharge process, step S411 is executed synchronously.

[0080] S411: Determine whether the gate voltage V1 of the first field effect transistor 1 is lower than the threshold voltage Vth. If so, a certain delay signal PWM_OFF_DLY is used to control the discharge module 3 to be turned off and the protection module 8 to be turned on, and a traditional strong pull-down tube is used to completely turn off the first field effect transistor; if not, the discharge module 3 continues to be turned on.

[0081] S420: Determine whether the gate voltage V1 of the first field effect transistor 1 is less than the target voltage V2, if so, execute step S421, if not, execute step S422.

[0082] S421: When the pulse width modulation signal PWM is a high-level signal PWM_ON and the gate voltage V1 of the first field effect tube 1 is less than the target voltage V2, that is, the switching signal is a low-level signal, the first AND gate 71 outputs the first control signal PWM_PRE as a high-level signal to control the charging module 2 to be turned on, the NOT gate 73 outputs the third control signal PWM_OFF_1 as a low-level signal to control the discharge module 3 to be turned off, the second AND gate 72 outputs the second control signal PWM_SEC as a low-level signal to control the reference current module 4 to be turned off, and the charging module 2 charges the gate of the first field effect tube 1 and controls the rising slope of the output working current IOUT.

[0083] While controlling the on and off of the charging module 2 and the discharging module 3, the control method also synchronously controls the on and off of the reference current module 4 according to the pulse width modulation signal PWM and the switching signal, specifically including:

[0084] S422: When the pulse width modulation signal PWM is a high-level signal PWM_ON, and the gate voltage V1 of the first field effect tube 1 is greater than or equal to the target voltage V2, that is, the switching signal is a high-level signal, the first AND gate 71 outputs the first control signal PWM_PRE as a low-level signal, controls the charging module 2 to be turned off, the NOT gate 73 outputs the third control signal PWM_OFF_1 as a low-level signal, controls the discharge module 3 to be turned off, and the second AND gate 72 outputs the second control signal PWM_SEC as a high-level signal, controls the reference current module 4 to be turned on, and the reference current module 4 provides the first field effect tube 1 with an output working current IOUT which is a constant output target current I1.

[0085] Step S420 is continuously and repeatedly executed until the pulse width modulation signal PWM becomes a low level signal.

[0086] It should be noted that the control method of the LED driving circuit provided in the above embodiment belongs to the same concept as the LED driving circuit, that is, the method is based on the circuit. The specific circuit implementation is detailed in the circuit embodiment and will not be repeated here.

[0087] like Figure 6As shown, it is a signal waveform diagram of the LED driving circuit of the present invention, from top to bottom respectively: pulse width modulation signal PWM waveform, gate voltage V1 signal waveform of the first field effect tube 1, switching signal waveform, drain output working current IOUT signal waveform of the first field effect tube 1, first control signal PWM_PRE waveform for controlling charging module 2, second control signal PWM_SEC waveform for controlling reference current module 4, third control signal PWM_OFF_1 waveform for controlling discharge module 3, and delay signal PWM_OFF_DLY waveform for controlling protection module 8. When the pulse width modulation signal PWM is a high level signal, and the gate voltage V1 of the first field effect tube 1 does not reach the target voltage V2 (i.e., T0-T2), the charging module 2 is turned on. When the gate voltage V1 of the first field effect tube 1 does not reach the threshold voltage Vth, i.e., T0-T1, the drain of the first field effect tube 1 does not output the working current IOUT. When the gate voltage V1 of the first field effect tube 1 reaches the threshold voltage Vth (i.e., T1-T2), the drain output working current IOUT of the first field effect tube 1 increases at a certain linear rate. When the pulse width modulation signal PWM is When the signal is high, and the gate voltage V1 of the first field effect tube 1 reaches the target voltage V2 (i.e., T2-T3), the reference current module 4 is turned on, and the drain output working current IOUT of the first field effect tube 1 is the output target current I1 provided by the reference current module 4; when the pulse width modulation signal PWM is a low level signal (i.e., T3-T4), the discharge module 3 is turned on, and when the gate voltage V1 of the first field effect tube 1 does not drop to the threshold voltage Vth, i.e., (T3-T4), the drain output working current IOUT of the first field effect tube 1 decreases at a certain linear rate.

[0088] The LED drive circuit and control method of the present invention utilize a highly matched charging and discharging current source to directly control the slope change of the output current (since the parasitic capacitance and the Miller effect seen during the rising and falling processes are the same), the robustness and reliability of PVT (i.e., process / voltage / temperature) are better, and the rising slope and the falling slope of the chip LED output current are consistent, so that the rising cycle and the falling cycle of the output current complement each other, and the low-gray accuracy is improved while meeting the requirements of improving EMI, i.e., the rated output current slope.

[0089] It should be understood that the above description is for illustration and not for limitation. Many embodiments and many applications beyond the examples provided will be apparent to those skilled in the art upon reading the above description. Therefore, the scope of the present teachings should not be determined with reference to the above description, but rather with reference to the foregoing claims and the full scope of equivalents to which such claims are entitled. For the purpose of comprehensiveness, all articles and references, including disclosures of patent applications and publications, are incorporated herein by reference. The omission of any aspect of the subject matter disclosed herein in the foregoing claims is not intended to be a waiver of such subject matter, nor should it be considered that the applicant has not considered such subject matter to be part of the disclosed inventive subject matter.

Claims

1. An LED driving circuit, characterized in that: include: A first field effect transistor, wherein a drain of the first field effect transistor outputs an operating current; A charging module, connected to the gate of the first field effect transistor, to charge the gate of the first field effect transistor to control the rising slope of the output working current; A discharge module, connected to the gate of the first field effect transistor, discharges the gate of the first field effect transistor to control the falling slope of the output working current; A signal generating module outputs a pulse width modulation signal; A comparator, wherein a first input terminal of the comparator is connected to the gate of the first field effect transistor, a second input terminal of the comparator is connected to a target voltage, and a first output terminal of the comparator outputs a switching signal; A logic control module, connected between the signal generating module, the comparator and the charging module and the discharging module, and the logic control module controls the on and off of the charging module and the discharging module according to the pulse width modulation signal and the switching signal; When the pulse width modulation signal is a high level signal and the gate voltage of the first field effect transistor is less than the target voltage, the charging module is turned on and the discharging module is turned off; When the pulse width modulation signal is a low level signal, the charging module is turned off and the discharging module is turned on.

2. The LED driving circuit according to claim 1, characterized in that: The logic control module comprises: A first AND gate, wherein a third input terminal of the first AND gate is connected to the signal generating module, a fourth input terminal of the first AND gate is connected to the first output terminal of the comparator, the fourth input terminal is an inverting input terminal, and a second output terminal of the first AND gate is connected to the charging module; A NOT gate, wherein the fifth input terminal of the NOT gate is connected to the signal generating module, and the third output terminal of the NOT gate is connected to the discharge module.

3. The LED driving circuit according to claim 2, characterized in that: The charging module comprises: A charging current source connected to the gate of the first field effect transistor; A first switch is connected in series with the charging current source, and a second output terminal of the first AND gate is connected to the first switch.

4. The LED driving circuit according to claim 2, characterized in that: The discharge module comprises: A discharge current source connected between the gate of the first field effect transistor and ground; A second switch is connected in series with the discharge current source, and a third output terminal of the NOT gate is connected to the second switch.

5. The LED driving circuit according to any one of claims 1 to 4, characterized in that: The LED driving circuit further includes: A reference current module, connected between the gate and source of the first field effect transistor, to provide an output target current for the first field effect transistor; The logic control module is connected between the signal generation module, the comparator and the reference current module, and controls the on and off of the reference current module according to the pulse width modulation signal and the switching signal.

6. The LED driving circuit according to claim 5, characterized in that: When the pulse width modulation signal is a high level signal and the gate voltage of the first field effect transistor is greater than or equal to the target voltage, the charging module is turned off, the discharging module is turned off, and the reference current module is turned on.

7. The LED driving circuit according to claim 6, characterized in that: The logic control module also includes: A second AND gate, wherein the sixth input terminal of the second AND gate is connected to the signal generating module, the seventh input terminal of the second AND gate is connected to the first output terminal of the comparator, and the fourth output terminal of the second AND gate is connected to the reference current module.

8. The LED driving circuit according to claim 7, characterized in that: The reference current module comprises: an error amplifier, wherein an eighth input terminal of the error amplifier is connected to a first reference voltage; a third switch connected between the fifth output terminal of the error amplifier and the gate of the first field effect transistor, and a fourth output terminal of the second AND gate is connected to the third switch; A second field effect transistor, wherein the gate of the second field effect transistor is connected to the second reference voltage, the drain of the second field effect transistor is respectively connected to the ninth input terminal of the error amplifier and the source of the first field effect transistor, and the source of the second field effect transistor is grounded.

9. The LED driving circuit according to claim 5, characterized in that: The LED driving circuit further includes a protection module connected to the gate of the first field effect transistor, and the protection module includes a fourth switch connected between the gate of the first field effect transistor and ground.

10. A control method for an LED driving circuit, characterized in that: include: Provide an LED driving circuit as described in any one of claims 1 to 9; Output pulse width modulation signal; Comparing the gate voltage of the first field effect transistor with the target voltage, and outputting a switching signal; Controlling the on and off of the charging module and the discharging module according to the pulse width modulation signal and the switching signal; the controlling the on and off of the charging module and the discharging module according to the pulse width modulation signal and the switching signal comprises: Determine whether the pulse width modulation signal is a low level signal, and if so, control the charging module to be turned off and control the discharging module to be turned on so that the gate of the first field effect transistor discharges to control the falling slope of the output working current; If not, determine whether the gate voltage of the first field effect transistor is less than the target voltage. If so, control the charging module to turn on to charge the gate of the first field effect transistor to control the rising slope of the output working current and control the discharge module to turn off.

11. The control method of the LED driving circuit according to claim 10, characterized in that: While controlling the on and off of the charging module and the discharging module, the on and off of the reference current module is synchronously controlled according to the pulse width modulation signal and the switching signal, including: It is determined whether the gate voltage of the first field effect transistor is less than the target voltage. If not, the charging module is controlled to be turned off, the discharging module is controlled to be turned off, and the reference current module is controlled to be turned on to provide the output target current for the first field effect transistor.

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