LED driving system, chip, LED driving control circuit and method

Abstract

The invention provides an LED driving system, a chip, and an LED driving control circuit and method, and the system comprises an overcurrent detection module which generates an overcurrent detection signal of an output current; the maximum conduction time control module is used for setting the maximum conduction time; the negative pressure detection module is used for generating a negative pressure detection signal of the driving signal; the maximum turn-off time control module is used for setting maximum turn-off time; the squeal removing module is used for generating a turn-off ending signal when the power switch tube is turned off for a preset time when the power supply voltage is abnormal; the logic control module is used for generating a PWM signal; the driving module generates a driving signal. According to the invention, a squeal-removing mode is added, and the turn-off time of the power switch tube is shortened, so that the working frequency in the squeal-removing mode exceeds a human ear recognizable range, and a user has good use experience; and self-adaptive time delay is carried out on the negative voltage detection signal, so that the drain voltage of the power switch tube is reduced to the preset voltage and then is switched to 0V, and the efficiency is improved.

Description

Technical Field

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

[0002] In the past, in the actual application of LED constant current driver chips (circuits), electrolytic capacitors were mostly connected to the outside of the chip (in the circuit). However, with the market demand for LED driver chips in the high-frequency field and the consideration of reducing costs, electrolytic capacitors are gradually being replaced by ceramic capacitors that are more suitable for high-frequency and high-voltage circuits. Ceramic capacitors have the advantages of high dielectric constant, good stability and small size. However, ceramic capacitors will expand and contract (vibrate) due to the piezoelectric effect when voltage is applied. When the vibration period is within the range that the human ear can recognize (generally 20Hz~20KHz), the human ear will hear a chirping sound, that is, "howling".

[0003] In the application of the existing chip (circuit) design connected to the ceramic capacitor (for example, the ceramic capacitor is used as the input capacitor), the signal frequency during the power-off process is within the range that the human ear can recognize, so the power-off howling phenomenon will occur during use. How to avoid the power-off howling phenomenon and improve the customer experience has become one of the problems that technicians in this field need to solve urgently.

[0004] It should be noted that the above introduction to the technical background is only for the convenience of providing a clear and complete description of the technical solutions of the present invention and for the convenience of understanding by those skilled in the art. It cannot be considered that the above technical solutions are well known to those skilled in the art simply because these solutions are described in the background technology section of the present invention. Summary of the invention

[0005] In view of the above-mentioned shortcomings of the prior art, the purpose of the present invention is to provide an LED drive system, chip, LED drive control circuit and method, which are used to solve the problem of power-off howling when using ceramic capacitors in the LED constant current drive circuit in the prior art.

[0006] To achieve the above-mentioned object and other related objects, the present invention provides an LED drive control circuit, wherein the LED drive control circuit at least comprises:

[0007] Overcurrent detection module, maximum on-time control module, negative pressure detection module, maximum off-time control module, anti-howling module, logic control module and drive module;

[0008] The overcurrent detection module detects the output current of the LED and generates an overcurrent detection signal when the output current is greater than a preset peak current;

[0009] The maximum on-time control module times the on-time of the power switch tube that controls the output current, and generates a maximum on-time signal when the preset maximum on-time is reached;

[0010] The negative pressure detection module detects the voltage of the driving signal of the power switch tube, and generates a negative pressure detection signal when it is detected that the voltage of the driving signal is less than zero;

[0011] The maximum off-time control module times the off-time of the power switch tube and generates a maximum off-time signal when the preset maximum off-time is reached;

[0012] The anti-howling module is connected to the overcurrent detection module, the maximum on-time control module, the maximum off-time control module and the output end of the logic control module; when the overcurrent detection signal and the negative pressure detection signal cannot be detected, and the maximum on-time signal and the maximum off-time signal appear alternately, a shutdown end signal is generated when the power switch tube is turned off for a preset time; wherein the frequency corresponding to the sum of the maximum on-time and the preset time exceeds the range recognizable by the human ear;

[0013] The logic control module generates a PWM signal for controlling the on and off of the power switch tube based on the output signals of the overcurrent detection module, the maximum on time control module, the negative pressure detection module, the maximum off time control module and the anti-howling module;

[0014] The driving module is connected to the output end of the logic control module, and generates a driving signal for the power switch tube based on the PWM signal.

[0015] Optionally, the preset time is less than 10 μs.

[0016] Optionally, the anti-howling module includes a power-off detection unit, a delay unit and a logic unit;

[0017] The power-off detection unit receives the overcurrent detection signal, the maximum conduction signal and the maximum shutdown signal, and generates a first judgment signal when the overcurrent detection signal is valid; and generates a second judgment signal when the overcurrent detection signal is invalid and the maximum conduction signal and the maximum shutdown signal appear alternately;

[0018] The delay unit receives the PWM signal, and generates the shutdown end signal when the falling edge of the PWM signal is delayed to the preset time;

[0019] The logic unit is connected to the output ends of the power-off detection unit and the delay unit, shields the shutdown end signal when the first judgment signal is valid, and outputs the shutdown end signal when the second judgment signal is valid.

[0020] More optionally, the power-off detection unit includes a first RS trigger, a second RS trigger and a frequency divider;

[0021] The set terminal of the first RS flip-flop is connected to the maximum on-signal, and the reset terminal is connected to the maximum off-signal;

[0022] The clock end of the frequency divider is connected to the output end of the first RS trigger, and the reset end is connected to the overcurrent detection signal, so as to divide the output signal of the first RS trigger;

[0023] The set end of the second RS trigger is connected to the overcurrent detection signal, the reset end is connected to the output end of the frequency divider, and the inverting output end outputs the first judgment signal or the second judgment signal.

[0024] More optionally, the frequency divider is a divide-by-two frequency circuit composed of two stages of D flip-flops.

[0025] More optionally, the delay unit includes a current source, a first capacitor, a switch tube and a Schmitt trigger;

[0026] One end of the current source is connected to the power supply voltage, and the other end is connected to the upper plate of the first capacitor; the lower plate of the first capacitor is grounded; the switch tube is connected in parallel to the two ends of the first capacitor, and the control end receives the PWM signal; the input end of the Schmitt trigger is connected to the upper plate of the first capacitor, and outputs the shutdown end signal.

[0027] More optionally, the logic unit is a NAND gate.

[0028] More optionally, the LED drive control module further includes an adaptive delay module;

[0029] The adaptive delay module is connected between the negative pressure detection module and the logic control module, and receives the drain voltage of the power switch tube. When the negative pressure detection signal is valid, the negative pressure detection signal is delayed based on the falling slope of the drain voltage of the power switch tube, so that the drain voltage of the power switch tube gradually drops to a preset voltage and then turns on the power switch tube; wherein the delay time is negatively correlated with the falling slope.

[0030] More optionally, the adaptive delay module includes a slope detection unit, a second capacitor, a comparator and an AND logic unit;

[0031] The slope detection unit receives the negative voltage detection signal and the drain voltage of the power switch tube, and when the negative voltage detection signal is valid, detects the falling slope of the drain voltage of the power switch tube and converts it into a corresponding current signal;

[0032] The upper plate of the second capacitor is connected to the output end of the slope detection unit, and the lower plate is grounded;

[0033] The comparator has a positive input terminal connected to the upper plate of the second capacitor, an inverting input terminal receiving a reference voltage, and outputting a comparison result;

[0034] One end of the AND logic unit is connected to the output end of the comparator, and the other end receives the negative pressure detection signal and outputs a delayed signal of the negative pressure detection signal.

[0035] Optionally, the LED drive control circuit further includes a power supply module and a protection module; the power supply module provides a power supply voltage for the LED drive control circuit; and the protection module is used to provide a protection signal.

[0036] In order to achieve the above-mentioned purpose and other related purposes, the present invention further provides a chip, which at least includes: the above-mentioned LED drive control circuit.

[0037] To achieve the above-mentioned object and other related objects, the present invention further provides an LED driving system, the LED driving system at least comprising:

[0038] A switching power supply circuit, an LED load, a ceramic capacitor, and an LED drive control circuit as claimed in any one of claims 1 to 10;

[0039] The switching power supply circuit is connected to the LED load and provides a driving current for the LED load based on the on and off of the power switch tube;

[0040] The LED drive control circuit is connected to the switch power supply circuit to provide a drive signal for the power switch tube in the switch power supply circuit; the ceramic capacitor is connected to the LED drive control circuit.

[0041] To achieve the above-mentioned object and other related objects, the present invention further provides an LED driving control method, the LED driving method at least comprising:

[0042] In the normal working mode, the overcurrent detection signal of the LED output current and the negative voltage detection signal of the power switch tube drive signal are detected and obtained, and when the overcurrent detection signal is valid, the power switch tube is controlled to be turned off, and when the negative voltage detection signal is valid, the power switch tube is controlled to be turned on;

[0043] As the power supply voltage decreases, the overcurrent detection signal and the negative pressure detection signal cannot be detected, and the abnormal working mode is entered; at this time, when the on-time of the power switch tube reaches the preset maximum on-time, the power switch tube is controlled to be turned off, and when the off-time of the power switch tube reaches the preset maximum off-time, the power switch tube is controlled to be turned on;

[0044] The power supply voltage keeps decreasing, the overcurrent detection signal and the negative pressure detection signal cannot be detected, and the on-time and off-time of the power switch tube alternately reach the maximum on-time and the maximum off-time, and the anti-howling mode is entered; at this time, when the on-time of the power switch tube reaches the preset maximum on-time, the power switch tube is controlled to be turned off, and when the power switch tube is turned off for a preset time, the power switch tube is controlled to be turned on; wherein, the frequency corresponding to the sum of the maximum on-time and the preset time exceeds the range recognizable by the human ear.

[0045] Optionally, the preset time is less than 10 μs.

[0046] Optionally, the LED drive control method also includes: when the negative voltage detection signal is valid, delaying the negative voltage detection signal based on the falling slope of the drain voltage of the power switch tube, so that the drain voltage of the power switch tube gradually drops to a preset voltage and then the power switch tube is turned on; wherein the delay time is negatively correlated with the falling slope.

[0047] As described above, the LED driving system, chip, LED driving control circuit and method of the present invention have the following beneficial effects:

[0048] 1. The LED drive system, chip, LED drive control circuit and method of the present invention have added a howling elimination mode. By shortening the off-time of the power switch tube, the operating frequency in the howling elimination mode is made greater than 20KHz, which is beyond the recognizable range of the human ear, thereby realizing the power-off howling elimination function; thereby solving the problem of howling caused by the use of ceramic capacitors and providing users with a good user experience.

[0049] 2. The LED drive system, chip, LED drive control circuit and method of the present invention adaptively delay the negative voltage detection signal, so that the drain voltage of the power switch tube drops to a preset voltage and then switches to 0V, thereby improving efficiency and customer experience. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Figure 1 Shown is a structural schematic diagram of an LED drive control circuit.

[0051] Figure 2 Display as Figure 1Schematic diagram of waveforms of key nodes when the LED drive control circuit works normally.

[0052] Figure 3 Display as Figure 1 Schematic diagram of waveforms of key nodes when the LED drive control circuit works abnormally.

[0053] Figure 4 Display as Figure 1 Schematic diagram of the inefficient LED drive control circuit.

[0054] Figure 5 Shown is a structural schematic diagram of the LED drive control circuit of the present invention.

[0055] Figure 6 It is a schematic diagram of the structure of the anti-howling module of the present invention.

[0056] Figure 7 It is a schematic structural diagram of the power-down detection module unit of the present invention.

[0057] Figure 8 Shown is a schematic structural diagram of the delay unit of the present invention.

[0058] Fig. 9 Another structural schematic diagram of the LED driving control circuit of the present invention is shown.

[0059] Fig.10 Shown is a schematic structural diagram of the adaptive delay module of the present invention.

[0060] Fig.11 Shown is a schematic structural diagram of the LED driving system of the present invention.

[0061] Fig.12 It is a schematic diagram showing the principle of howling removal of the LED driving control method of the present invention.

[0062] Fig.13 It is a schematic diagram showing the principle of improving the efficiency of the LED driving control method of the present invention.

[0063] Component number description

[0064] 1 LED drive control circuit

[0065] 11 Overcurrent detection module

[0066] 12. Maximum on-time control module

[0067] 13 Negative pressure detection module

[0068] 14 Maximum off time control module

[0069] 15 Logic Control Module

[0070] 16 Driver Module

[0071] 2 LED drive control circuit

[0072] 20 Overcurrent detection module

[0073] 21. Maximum on-time control module

[0074] 22 Negative pressure detection module

[0075] 23 Maximum off time control module

[0076] 24 Howling Reduction Module

[0077] 241 Power-off detection unit

[0078] 241a First RS flip-flop

[0079] 241b Crossover

[0080] 241c Second RS flip-flop

[0081] 242 Delay Unit

[0082] 242a Schmitt trigger

[0083] 243 Logic Unit

[0084] 25 Logic Control Module

[0085] 251 First logic control unit

[0086] 252 Second logic control unit

[0087] 253 PWM signal generation unit

[0088] 26 Driver Module

[0089] 27 Power Module

[0090] 28 Protection module

[0091] 29 Adaptive Delay Module

[0092] 291 Slope Detection Unit

[0093] 292 Comparator

[0094] 293 AND logic unit

[0095] 3 Switching power supply circuit DETAILED DESCRIPTION

[0096] The following describes the embodiments of the present invention through specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention.

[0097] See also Figures 1 to 13 It should be noted that the illustrations provided in this embodiment are only used to illustrate the basic concept of the present invention in a schematic manner, and the drawings only show components related to the present invention rather than being drawn according to the number, shape and size of components in actual implementation. In actual implementation, the type, quantity and proportion of each component may be changed arbitrarily, and the component layout may also be more complicated.

[0098] like Figure 1 The figure shows an LED drive control circuit 1, comprising: an overcurrent detection module 11, a maximum on-time control module 12, a negative pressure detection module 13, a maximum off-time control module 14, a logic control module 15 and a driving module 16. The logic control module 15 generates a PWM signal of a corresponding level based on the output signals of the overcurrent detection module 11 and the maximum on-time control module 12, and controls the power switch tube (not shown) to be turned off through the drive signal DRV output by the driving module 16; the logic control module 15 generates a PWM signal of a corresponding level based on the output signals of the negative pressure detection module 13 and the maximum off-time control module 14, and controls the power switch tube to be turned on through the drive signal DRV output by the driving module 16.

[0099] like Figure 2 As shown, when the LED drive control circuit 1 is in a normal working state (normal power supply), the negative pressure detection module 13 detects the drive signal DRV of the power switch tube. After detecting the negative pressure, the negative pressure detection signal ZC is valid, and the PWM signal is controlled based on the logic control module 15 to achieve the flip from low level to high level; at the same time, the overcurrent detection module 11 detects the sampling voltage Vcs. When the sampling voltage Vcs reaches the set voltage, it is considered that the output current Iout reaches the set peak current Ipk, the overcurrent detection signal OC is valid, and the PWM signal is controlled based on the logic control module 15 to flip from high level to low level. Since the peak value of the output current Iout is constant, the average value of the output current Iout is also constant, thereby realizing constant current drive.

[0100] like Figure 3As shown, when the LED drive control circuit 1 is in an abnormal working state (including but not limited to the power-off process), the power supply voltage of the LED drive control circuit 1 will gradually decrease and gradually approach the voltage of the load LED. At this time, the effective over-current detection signal OC cannot be detected, and the maximum on-time t is set by the maximum on-time control module 12. onmax When the output signal Tonmax of the maximum on-time control module 12 is valid, the PWM signal is controlled by the logic control module 15 to achieve the flip from high level to low level. Considering the situation that the LED drive control circuit 1 works at low frequency, the maximum on-time t onmax It is usually set to tens of microseconds; at the same time, as the power supply voltage drops, the effective negative pressure detection signal ZC cannot be detected. At this time, the maximum off time control module 14 sets the maximum off time t offmax When the output signal Toffmax of the maximum off-time control module 14 is valid, the PWM signal is controlled by the logic control module 15 to achieve a flip from a low level to a high level. In order to reduce the short-circuit power consumption of the system output, the maximum off-time t offmax is set to several hundred microseconds. In this state, the period of the PWM signal is T = t onmax +t offmax , the order of magnitude is about several hundred microseconds, and the frequency is within the range recognizable by the human ear, so howling will occur during use.

[0101] In addition, according to the above control logic, when a negative voltage is detected (negative voltage detection signal ZC is valid), the drive signal DRV is quickly switched from a low level to a high level, which makes the drain voltage Vsw of the power switch tube quickly switch from a high voltage close to the external power supply voltage to 0V. Figure 4 As shown; that is, the high voltage falls on the power switch tube, resulting in low efficiency.

[0102] In order to solve the above problems, the present invention proposes an LED driving system, a chip, an LED driving control circuit and a method. Figure 1 A power-off anti-howling mode is added on the basis of the LED drive control circuit 1, and the flip logic of the PWM signal is optimized, so that the signal frequency during the power-off process exceeds the recognizable range of the human ear, so as to realize the anti-howling function and improve the efficiency in the normal working state.

[0103] Embodiment 1

[0104] like Figure 5 As shown, the present invention provides an LED drive control circuit 2, and the LED drive control circuit 2 includes:

[0105] An overcurrent detection module 20 , a maximum on-time control module 21 , a negative pressure detection module 22 , a maximum off-time control module 23 , a howling removal module 24 , a logic control module 25 and a driving module 26 .

[0106] like Figure 5 As shown, the over-current detection module 20 detects the output current Iout of the LED and generates an over-current detection signal OC when the output current Iout is greater than a preset peak current Ipk.

[0107] Specifically, in this embodiment, the overcurrent detection module 20 receives a sampling voltage Vcs, and the sampling voltage Vcs samples the output current Iout of the LED; as an example, the sampling voltage Vcs is the voltage on the sampling resistor at the source end of the power switch tube. A set voltage is set inside the overcurrent detection module 20, and when the sampling voltage Vcs reaches the set voltage, the overcurrent detection signal OC is output (it is considered that the output current Iout reaches the set peak current Ipk).

[0108] like Figure 5 As shown, the maximum on-time control module 21 counts the on-time of the power switch tube that controls the output current, and when the preset maximum on-time t is reached, onmax The maximum conduction signal Tonmax is generated at this time.

[0109] Specifically, in this embodiment, the maximum on-time control module 21 receives the PWM signal and times the high-level time of the PWM signal (i.e., the on-time of the power switch tube). When the high-level time of the PWM signal reaches the maximum on-time t onmax When , the maximum conduction signal Tonmax is output; as an example, the maximum conduction signal Tonmax is a positive pulse.

[0110] like Figure 5 As shown, the negative pressure detection module 22 detects the voltage of the driving signal DRV of the power switch tube, and generates a negative pressure detection signal ZC when it is detected that the voltage of the driving signal DRV is less than zero.

[0111] Specifically, in this embodiment, the negative pressure detection module 22 receives the driving signal DRV, and compares the driving signal DRV with a reference signal (0V), and outputs the negative pressure detection signal ZC when the voltage of the driving signal DRV is less than 0V.

[0112] like Figure 5 As shown, the maximum off-time control module 23 counts the off-time of the power switch tube and turns off the power switch tube when the preset maximum off-time t is reached. offmaxThe maximum shutdown signal Toffmax is generated at this time.

[0113] Specifically, in this embodiment, the maximum off-time control module 23 receives the PWM signal and times the low-level time of the PWM signal (i.e., the off-time of the power switch tube). When the low-level time of the PWM signal reaches the maximum off-time t offmax When the maximum off-state signal Toffmax is output, as an example, the maximum off-state signal Toffmax is a positive pulse.

[0114] like Figure 5 As shown, the anti-howling module 24 is connected to the output end of the overcurrent detection module 20, the maximum on-time control module 21, the maximum off-time control module 23 and the logic control module 25; when the overcurrent detection signal OC and the negative pressure detection signal ZC cannot be detected, and the maximum on-time signal Tonmax and the maximum off-time signal Toffmax appear alternately, the power switch tube is turned off at the preset time t delay The shutdown end signal PWM_delay is generated.

[0115] Specifically, Figure 6 As shown, in this embodiment, the anti-howling module 24 includes a power-off detection unit 241 , a delay unit 242 and a logic unit 243 .

[0116] More specifically, if Figure 6 As shown, the power-off detection unit 241 receives the overcurrent detection signal OC, the maximum conduction signal Tonmax and the maximum off signal Toffmax, and generates a first judgment signal when the overcurrent detection signal OC is valid; when the overcurrent detection signal OC is invalid, and the maximum conduction signal Tonmax and the maximum off signal Toffmax appear alternately, a second judgment signal is generated; in this example, the first judgment signal and the second judgment signal are represented by different levels of the output signal VINOFF of the power-off detection unit 241. Figure 7As shown, as an example, the power-off detection unit 241 includes a first RS trigger 241a, a frequency divider 241b and a second RS trigger 241c; the set terminal S of the first RS trigger 241a is connected to the maximum on-state signal Tonmax, the reset terminal R is connected to the maximum off-state signal Toffmax, and the output terminal Q outputs a trigger signal. The clock terminal CLK of the frequency divider 241b is connected to the output terminal Q of the first RS trigger 241a, and the reset terminal RST is connected to the overcurrent detection signal OC, so as to divide the output signal of the first RS trigger 241a; in this example, the frequency divider 241b is a two-division circuit composed of two stages of D triggers, that is, the clock terminal CLK of the first D trigger is connected to the output terminal Q of the first RS trigger 241a, the data input terminal D of the first D trigger is connected to the inverting output terminal QB, the clock terminal CLK of the second D trigger is connected to the inverting output terminal QB of the first D trigger, the data input terminal D of the second D trigger is connected to the inverting output terminal QB and outputs a divided signal; in actual use, the frequency divider can be configured as four-division or six-division, which can reflect the alternating appearance of the maximum on-signal Tonmax and the maximum off-signal Toffmax. Of course, the larger the frequency division number of the frequency divider, the longer the delay time for detecting the power supply voltage drop (that is, the longer the reaction time). The set terminal S of the second RS trigger 241c is connected to the overcurrent detection signal OC, the reset terminal R is connected to the output terminal of the frequency divider 241b, and the inverting output terminal QB outputs the first judgment signal or the second judgment signal. Any circuit structure that can detect a drop in power supply voltage is applicable to the present invention, not limited to this embodiment.

[0117] More specifically, if Figure 6 As shown, the delay unit 242 receives the PWM signal, and when the falling edge of the PWM signal is delayed to the preset time t delay The shutdown end signal PWM_delay is generated when Figure 8As shown, as an example, the delay unit 242 includes a current source I1, a first capacitor C1, a switch tube M1 and a Schmitt trigger 242a. One end of the current source I1 is connected to the power supply voltage, and the other end is connected to the upper plate of the first capacitor C1; the lower plate of the first capacitor C1 is grounded. The switch tube M1 is connected in parallel to the two ends of the first capacitor C1, and the control end receives the PWM signal; in this embodiment, the switch tube M1 is implemented by an NMOS tube, the drain of the switch tube M1 is connected to the upper plate of the first capacitor C1, the source is grounded, and the gate is connected to the PWM signal. The input end of the Schmitt trigger 242a is connected to the upper plate of the first capacitor C1, and the shutdown end signal PWM_delay is output. When the PWM signal is at a high level, the switch tube M1 is turned on, and the first capacitor C1 is discharged quickly; when the PWM signal is at a low level, the switch tube M1 is turned off, and the current source I1 charges the first capacitor C1; from the falling edge of the PWM signal to the preset time t delay The shutdown end signal PWM_delay is output after a delay of ; as an example, the shutdown end signal PWM_delay is a positive pulse. Any circuit structure that can generate the shutdown end signal when the falling edge of the PWM signal is delayed to a preset time is applicable to the present invention, and is not limited to this embodiment.

[0118] More specifically, if Figure 6 As shown, the logic unit 243 is connected to the output end of the power-off detection unit 241 and the delay unit 242, shields the shutdown end signal PWM_dealy when the first judgment signal is valid, and outputs the shutdown end signal PWM_dealy when the second judgment signal is valid; in this embodiment, the first judgment signal is valid at a low level, and the second judgment signal is valid at a high level. Figure 6 As shown, as an example, the logic unit 243 is a NAND gate, the first input end of the NAND gate is connected to the output end of the power-off detection unit 241, and the second input end is connected to the output end of the delay unit 242; when the power-off detection unit 241 outputs a low level, the NAND gate outputs a low level (the shutdown end signal PWM_dealy is shielded), and when the power-off detection unit 241 outputs a high level, the NAND gate outputs the shutdown end signal PWM_dealy. Any circuit structure that can control the output or shielding of the PWM signal according to the judgment signal is applicable to the present invention, and is not limited to this embodiment.

[0119] It should be noted that the maximum on-time t onmax With the preset time t delay The setting meets the condition: the maximum on-time t onmax With the preset time tdelay The frequency corresponding to the sum is beyond the range that can be recognized by the human ear. Considering the situation that the LED drive control circuit 2 works at a low frequency, the maximum on time t onmax It is usually set to tens of μs; the preset time t delay It is generally set to be within 100 μs, preferably less than 10 μs. In this example, t onmax +t offmax <50μs, the frequency of the PWM signal in the howling removal mode is greater than 20KHz, which is beyond the recognizable range of the human ear, thereby achieving the howling removal function.

[0120] like Figure 5 As shown, the logic control module 25 generates a PWM signal for controlling the on and off of the power switch tube based on the output signals of the overcurrent detection module 20, the maximum on time control module 21, the negative pressure detection module 22, the maximum off time control module 23 and the anti-howling module 24.

[0121] Specifically, when the overcurrent detection signal OC and the negative pressure detection signal ZC can be detected, a PWM signal for controlling the on and off of the power switch tube is generated based on the overcurrent detection signal OC and the negative pressure detection signal ZC; when the overcurrent detection signal OC and the negative pressure detection signal ZC cannot be detected, the PWM signal is generated based on the maximum on-signal Tonmax and the maximum off-signal Toffmax; when the overcurrent detection signal OC and the negative pressure detection signal ZC cannot be detected, and the maximum on-signal Tonmax and the maximum off-signal Toffmax appear alternately, the PWM signal is generated based on the maximum on-signal Tonmax and the off-end signal PWM_delay.

[0122] Specifically, Figure 5As shown, in this embodiment, the logic control module 25 includes a first logic control unit 251, a second logic control unit 252 and a PWM signal generating unit 253. The first logic control unit 251 receives the overcurrent detection signal OC and the maximum conduction signal Tonmax, and generates a control signal for controlling the power switch tube to be turned off based on the overcurrent detection signal OC or the maximum conduction signal Tonmax in different working states (normal working state, abnormal working state and anti-howling working state). The second logic control unit 252 receives the negative pressure detection signal ZC, the maximum turn-off signal Toffmax and the turn-off end signal PWM_delay, and generates a control signal for controlling the power switch tube to be turned on based on the negative pressure detection signal ZC, the maximum turn-off signal Toffmax or the turn-off end signal PWM_delay in different working states (normal working state, abnormal working state and anti-howling working state). The PWM signal generating unit 253 is connected to the output ends of the first logic control unit 251 and the second logic control unit 252, and generates a PWM signal based on the control signals output by the first logic control unit 251 and the second logic control unit 252. In actual use, any circuit structure that can generate a PWM signal for controlling the power switch tube based on the overcurrent detection signal OC, the maximum conduction signal Tonmax, the negative voltage detection signal ZC, the maximum shutdown signal Toffmax and the shutdown end signal PWM_delay is suitable for the present invention.

[0123] like Figure 5 As shown, the driving module 26 is connected to the output end of the logic control module 25, and generates a driving signal DRV of the power switch tube based on the PWM signal.

[0124] like Figure 5 As shown, as another implementation of the present invention, the LED drive control circuit 2 further includes a power supply module 27 , and the power supply module 27 provides a power supply voltage for the LED drive control circuit 2 .

[0125] like Figure 5 As shown, as another implementation of the present invention, the LED drive control circuit 2 also includes a protection module 28, and the protection module 28 is used to provide a protection signal to improve reliability; including but not limited to an over-temperature protection signal, an over-voltage protection signal, and a short-circuit protection signal, which are not described one by one here.

[0126] This embodiment further provides a chip, and the chip includes the LED drive control circuit 2.

[0127] Embodiment 2

[0128] like Fig. 9 As shown, this embodiment provides an LED drive control module 2 and a chip, which are different from the first embodiment in that the LED drive control module 2 further includes an adaptive delay module 29 to improve efficiency.

[0129] like Fig. 9 As shown, the adaptive delay module 29 is connected between the negative pressure detection module 22 and the logic control module 25, and receives the drain voltage Vsw of the power switch tube. When the negative pressure detection signal ZC is valid, the negative pressure detection signal ZC is delayed based on the falling slope of the drain voltage Vsw of the power switch tube, so that the drain voltage Vsw of the power switch tube gradually decreases to the preset voltage Vset and then the power switch tube is turned on; wherein, the delay time is negatively correlated with the falling slope.

[0130] Specifically, Fig.10 As shown, in this embodiment, the adaptive delay module 29 includes a slope detection unit 291, a second capacitor C2, a comparator 292 and an AND logic unit 293. The slope detection unit 291 receives the negative voltage detection signal ZC and the drain voltage Vsw of the power switch tube. When the negative voltage detection signal OC is valid, the falling slope of the drain voltage Vsw of the power switch tube is detected (the detection of the falling slope can be performed within a fixed time period, and there is no need to detect it during the entire falling process when the negative voltage detection signal OC is valid) and converted into a corresponding current signal I1. The upper plate of the second capacitor C2 is connected to the output end of the slope detection unit 291, and the lower plate is grounded; the current I1 output by the slope detection unit 291 charges the second capacitor C2. The positive input end of the comparator 292 is connected to the upper plate of the second capacitor C2, the negative input end receives the reference voltage Vref, and outputs the comparison result. One end of the AND logic unit 293 is connected to the output end of the comparator 292, and the other end receives the negative voltage detection signal ZC, and outputs a delay signal ZC_DLY of the negative voltage detection signal; the delay time is related to the current I1 output by the slope detection unit 291, and the greater the falling slope of the drain voltage Vsw of the power switch tube, the greater the current I1 output by the slope detection unit 291, and the shorter the delay time; the smaller the falling slope of the drain voltage Vsw of the power switch tube, the smaller the current I1 output by the slope detection unit 291, and the longer the delay time.

[0131] It should be noted that, in this embodiment, the current I1 is calculated by detecting the slope, and then the current is used to charge the second capacitor C2. After reaching the set voltage (that is, the flip voltage of the drain voltage Vsw of the power switch tube: the preset voltage Vset), the PWM signal flips. In other words, the purpose of setting the delay time is to make the drain voltage Vsw of the power switch tube drop to the preset voltage Vset. Any circuit structure that can make the drain voltage Vsw of the power switch tube drop to the preset voltage Vset and then turn on is applicable to the present invention, and is not limited to this embodiment.

[0132] The other structures and principles are the same as those in the first embodiment and will not be described in detail here.

[0133] Embodiment 3

[0134] like Fig.11 As shown, this embodiment provides an LED driving system, and the LED driving system includes:

[0135] The LED drive control circuit 2, the switch power supply circuit 3, the LED load and the ceramic capacitor C3.

[0136] like Fig.11 As shown, the switching power supply circuit 3 is connected to the LED load and provides a driving current for the LED load based on the on and off of the power switch tube.

[0137] Specifically, the structure of the switching power supply circuit 3 is not limited, and any circuit structure that can realize drive current regulation based on a power switch tube is applicable, including but not limited to BUCK, BOOST, BUCK-BOOST, forward, and flyback. Fig.11 As shown, as an example, the switching power supply circuit 3 includes a power switch tube M2, a freewheeling diode D, an inductor L, a capacitor C4 and a sampling resistor Rcs; the cathode of the freewheeling diode D is connected to the bus voltage Vbus, and the anode is connected to the drain of the power switch tube M2; the upper plate of the capacitor C4 is connected to the cathode of the freewheeling diode D, and the lower plate is connected to the anode of the freewheeling diode D via the inductor L; the source of the power switch tube is grounded via the sampling resistor Rcs, and the gate receives the drive signal DRV provided by the LED drive control circuit 2.

[0138] Specifically, in this example, the positive electrode of the LED load is connected to the upper plate of the capacitor C4, and the negative electrode is connected to the lower plate of the capacitor C4.

[0139] like Fig.11 As shown, the LED drive control circuit 2 is connected to the switch power circuit 3 to provide a drive signal DRV for the power switch tube M2 in the switch power circuit 3 .

[0140] Specifically, the LED driving control circuit 2 adopts the structure of the first embodiment or the second embodiment, which will not be described in detail here.

[0141] like Fig.11 As shown, the ceramic capacitor C3 is connected to the LED drive control circuit 2.

[0142] Specifically, in this embodiment, the ceramic capacitor C3 is used as the input capacitor of the LED drive control circuit 2; in actual use, the ceramic capacitor C3 can be set with corresponding functions and connection relationships as needed, which will not be described in detail here.

[0143] The LED driving system of the present invention solves the problem of howling caused by using ceramic capacitors, so that users have a good use experience.

[0144] Embodiment 4

[0145] like Fig.12 As shown, this embodiment provides an LED driving control method. In this embodiment, the LED driving method is implemented based on the LED driving control circuit 2 of the first or second embodiment. In actual use, any hardware circuit that can implement this method is applicable. The LED driving method includes:

[0146] 1) In normal working mode, the overcurrent detection signal OC of the LED output current and the negative voltage detection signal ZC of the power switch tube drive signal are detected and obtained. When the overcurrent detection signal OC is valid, the power switch tube M2 is controlled to be turned off, and when the negative voltage detection signal ZC is valid, the power switch tube M2 is controlled to be turned on.

[0147] Specifically, Fig.12 As shown, in the normal working mode, the power supply voltage Vin supplies power normally, the output current Iout of the LED can reach the preset peak current Ipk, and the gate voltage of the power switch tube M2 (the voltage of the drive signal DRV) will have a negative voltage; at this time, the output current Iout of the LED is detected based on the overcurrent detection module 20, and the gate voltage of the power switch tube M2 is detected based on the negative voltage detection module 22. When the overcurrent detection signal OC is detected, the power switch tube M2 is turned off, and when the negative voltage detection signal ZC is detected, the power switch tube M2 is turned on, thereby realizing constant current control. For specific principles, please refer to Figure 1 The working principle of the controller is not described in detail here.

[0148] It should be noted that, in this state, the anti-howling module 24 outputs a low level, and the anti-howling function is not enabled.

[0149] 2) As the power supply voltage Vin decreases, the overcurrent detection signal OC and the negative voltage detection signal ZC cannot be detected, and the abnormal working mode is entered; at this time, when the on-time of the power switch tube M2 reaches the preset maximum on-time t onmax When the off time of the power switch tube M2 reaches the preset maximum off time t offmax The power switch tube M2 is controlled to be turned on.

[0150] Specifically, Fig.12 As shown, when the circuit is in an abnormal working state (including but not limited to the power-off process), the power supply voltage Vin gradually decreases and gradually approaches the voltage Vout of the load LED. At this time, the output current Iout of the LED cannot reach the preset peak current Ipk, and the gate voltage of the power switch tube M2 cannot detect a negative voltage. Based on the maximum on-time t onmax and the maximum off time t offmax Control the power switch tube M2 to turn on and off. For the specific principle, please refer to Figure 1 The working principle of the controller is not described in detail here.

[0151] 3) The power supply voltage Vin continues to decrease, the overcurrent detection signal OC and the negative voltage detection signal ZC cannot be detected, and the on-time and off-time of the power switch tube M2 alternately reach the maximum on-time t onmax and the maximum off time t offmax , enter the anti-howling mode; at this time, when the on-time of the power switch tube M2 reaches the preset maximum on-time t onmax When the power switch tube M2 is turned off, the power switch tube M2 is turned off for a preset time t delay Then the power switch tube M2 is controlled to be turned on; wherein the maximum on-time t onmax With the preset time t delay The frequency corresponding to the sum is beyond the range that can be detected by the human ear.

[0152] Specifically, Fig.12 As shown, when the overcurrent detection signal OC and the negative voltage detection signal ZC cannot be detected, and the on-time and off-time of the power switch tube M2 alternately reach the maximum on-time t onmax and the maximum off time t offmax , it is determined to enter the anti-howling mode. As an example, if Figure 7As shown, the overcurrent detection signal OC is at a low level. At this time, the frequency divider 241b is released from reset and starts working. When the maximum on-signal Tonmax is 1, the output signal of the first RS trigger 241a is 1; when the maximum off-signal Toffmax is 1, the output signal of the first RS trigger 241a is 0; when the maximum on-signal Tonmax and the maximum off-signal Toffmax are both 0, the output signal of the first RS trigger 241a maintains the previous state; according to the generation logic of the maximum on-signal Tonmax and the maximum off-signal Toffmax, the prohibited state in which the maximum on-signal Tonmax and the maximum off-signal Toffmax are both 1 will not occur (because the maximum on-signal Tonmax and the maximum off-signal Toffmax are both generated by the PWM signal, the maximum on-signal Tonmax is 1 when the PWM signal is at a high level, and the maximum off-signal Toffmax is 1 when the PWM signal is at a low level). Therefore, when the maximum on-state signal Tonmax and the maximum off-state signal Toffmax appear alternately and continuously, the output signal of the first RS trigger 241a will present a square wave alternating between 0 and 1, which serves as the clock signal of the frequency divider 241b. When the maximum on-state signal Tonmax is received for the first time, the output signal of the first-stage D trigger is flipped (to 0), and the output signal of the second-stage D trigger is not flipped (remains 0); when the maximum off-state signal Toffmax is received for the first time, the output signal of the first-stage D trigger is not flipped (remains 0), and the output signal of the second-stage D trigger is not flipped (remains 0); when the maximum on-state signal Tonmax is received for the second time, the output signal of the first-stage D trigger is flipped again (to 1), and the output signal of the second-stage D trigger is also flipped (to 1); the inverted output signal VINOFF of the second RS trigger 241c is set to 1, and the anti-howling mode is entered. The anti-howling module is reset by the overcurrent detection signal OC. When the power supply voltage Vin returns to the normal working voltage, the overcurrent detection signal OC is at a high level, and the divider 241b and the second RS trigger 241c are reset. At this time, the inverting output signal VINOFF of the second RS trigger 241c is reset to 0, and the anti-howling mode is exited.

[0153] Specifically, Fig.12 As shown, when entering the anti-howling mode, the off time of the power switch tube M2 is shortened to the preset time t delay , so that the maximum on-time t onmax With the preset time t delayThe frequency corresponding to the sum of is beyond the range that can be recognized by the human ear. In this embodiment, the preset time t is set based on the delay unit 242. delay ,like Figure 8 As shown, the charge and discharge of the first capacitor C1 is controlled based on the PWM signal. When the PWM signal is at a low level, the first capacitor C1 is slowly charged by the charging current. When the voltage on the first capacitor C1 reaches the flip voltage of the Schmitt trigger 242a, the shutdown end signal PWM_delay is effective. As an example, the preset time t delay is set to less than 10μs, so that t onmax +t offmax <50μs, the frequency of the PWM signal in the howling removal mode is greater than 20KHz, thereby achieving the howling removal function.

[0154] like Fig. 9 , Fig.10 and Fig.13 As shown, as another implementation method of the present invention, the LED drive control method also includes: when the negative voltage detection signal ZC is valid, the negative voltage detection signal is delayed based on the falling slope of the drain voltage Vsw of the power switch tube, so that the drain voltage of the power switch tube gradually drops to a preset voltage and then the power switch tube is turned off; wherein the delay time is negatively correlated with the falling slope.

[0155] Specifically, Fig.11 As shown, due to the series resonance generated by the inductor L and the coupling capacitor of the power switch tube M2, after the energy storage of the inductor L is exhausted and negative voltage detection occurs, the coupling capacitor discharges to charge the inductor L, and the drain voltage Vsw of the power switch tube will decrease, and the magnitude of the decrease is controlled by the delay time. Fig.10 As shown, the drain voltage Vsw of the power switch tube is sampled in a fixed time period, and the voltage difference between the start time and the end time of the fixed time period is calculated, so as to detect the falling slope of the drain voltage Vsw of the power switch tube and convert it into a current I1. The voltage generated by charging the second capacitor C2 by the current is compared with the reference voltage Vref by the comparator 292, and a suitable delay time will be adaptively determined (that is, if the slope of SW is larger when it decreases, the output current is larger, and the adaptive delay time is shorter; if the slope of SW is smaller when it decreases, the output current is smaller, and the adaptive delay time is longer). The delay time can make the drain voltage Vsw of the power switch tube drop to a lower preset voltage Vset. At this time, the drive signal DRV is controlled to flip from a low level to a high level (the power switch tube M2 is turned on), and the drain voltage Vsw of the power switch tube is switched from a lower voltage to 0V, thereby realizing an efficient design.

[0156] It should be noted that any method that can delay the drain voltage Vsw of the power switch tube to drop to the preset voltage Vset and then switch to 0V is applicable to the present invention.

[0157] In summary, the present invention provides an LED driving system, a chip, an LED driving control circuit and a method, comprising: an overcurrent detection module, a maximum on-time control module, a negative pressure detection module, a maximum off-time control module, a howling removal module, a logic control module and a driving module; the overcurrent detection module detects the output current of the LED, and generates an overcurrent detection signal when the output current is greater than a preset peak current; the maximum on-time control module times the on-time of the power switch tube that controls the output current, and generates a maximum on-time signal when the preset maximum on-time is reached; the negative pressure detection module detects the voltage of the driving signal of the power switch tube, and generates a negative pressure detection signal when it is detected that the voltage of the driving signal is less than zero; the maximum off-time control module times the off-time of the power switch tube, and generates a maximum off-time signal when the preset maximum off-time is reached. signal; the anti-howling module is connected to the output end of the overcurrent detection module, the maximum on-time control module, the maximum off-time control module and the logic control module; when the overcurrent detection signal and the negative pressure detection signal cannot be detected, and the maximum on-time signal and the maximum off-time signal appear alternately, a shutdown end signal is generated when the power switch tube is turned off for a preset time; wherein the frequency corresponding to the sum of the maximum on-time and the preset time exceeds the range recognizable by the human ear; the logic control module generates a PWM signal for controlling the on and off of the power switch tube based on the output signals of the overcurrent detection module, the maximum on-time control module, the negative pressure detection module, the maximum off-time control module and the anti-howling module; the driving module is connected to the output end of the logic control module, and generates a driving signal for the power switch tube based on the PWM signal. The LED drive system, chip, LED drive control circuit and method of the present invention have added a de-howling mode. By shortening the turn-off time of the power switch tube, the operating frequency in the de-howling mode is made >20KHz, which is beyond the recognizable range of the human ear, thereby realizing the power-off de-howling function; thereby solving the problem of howling caused by the use of ceramic capacitors, so that users have a good user experience. The present invention also adaptively delays the negative pressure detection signal, so that the drain voltage of the power switch tube drops to a preset voltage and then switches to 0V, thereby improving efficiency and customer experience. Therefore, the present invention effectively overcomes the various shortcomings of the prior art and has a high industrial utilization value.

[0158] The above embodiments are merely illustrative of the principles and effects of the present invention, and are not intended to limit the present invention. Anyone familiar with the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by a person of ordinary skill in the art without departing from the spirit and technical concept disclosed by the present invention shall still be covered by the claims of the present invention.

Claims

1. An LED drive control circuit, characterized in that: The LED drive control circuit at least includes: Overcurrent detection module, maximum on-time control module, negative pressure detection module, maximum off-time control module, anti-howling module, logic control module and drive module; The overcurrent detection module detects the output current of the LED and generates an overcurrent detection signal when the output current is greater than a preset peak current; The maximum on-time control module times the on-time of the power switch tube that controls the output current, and generates a maximum on-time signal when the preset maximum on-time is reached; The negative pressure detection module detects the voltage of the driving signal of the power switch tube, and generates a negative pressure detection signal when it is detected that the voltage of the driving signal is less than zero; The maximum off-time control module times the off-time of the power switch tube and generates a maximum off-time signal when the preset maximum off-time is reached; The anti-howling module is connected to the overcurrent detection module, the maximum on-time control module, the maximum off-time control module and the output end of the logic control module; when the overcurrent detection signal and the negative pressure detection signal cannot be detected, and the maximum on-time signal and the maximum off-time signal appear alternately, a shutdown end signal is generated when the power switch tube is turned off for a preset time; wherein the frequency corresponding to the sum of the maximum on-time and the preset time exceeds the range recognizable by the human ear; The logic control module generates a PWM signal for controlling the on and off of the power switch tube based on the output signals of the overcurrent detection module, the maximum on time control module, the negative pressure detection module, the maximum off time control module and the anti-howling module; The driving module is connected to the output end of the logic control module, and generates a driving signal for the power switch tube based on the PWM signal.

2. The LED drive control circuit according to claim 1, characterized in that: The preset time is less than 10 μs.

3. The LED drive control circuit according to claim 1, characterized in that: The anti-howling module includes a power-off detection unit, a delay unit and a logic unit; The power-off detection unit receives the overcurrent detection signal, the maximum conduction signal and the maximum shutdown signal, and generates a first judgment signal when the overcurrent detection signal is valid; and generates a second judgment signal when the overcurrent detection signal is invalid and the maximum conduction signal and the maximum shutdown signal appear alternately; The delay unit receives the PWM signal, and generates the shutdown end signal when the falling edge of the PWM signal is delayed to the preset time; The logic unit is connected to the output ends of the power-off detection unit and the delay unit, shields the shutdown end signal when the first judgment signal is valid, and outputs the shutdown end signal when the second judgment signal is valid.

4. The LED drive control circuit according to claim 3, characterized in that: The power-off detection unit includes a first RS trigger, a second RS trigger and a frequency divider; The set terminal of the first RS flip-flop is connected to the maximum on-signal, and the reset terminal is connected to the maximum off-signal; The clock end of the frequency divider is connected to the output end of the first RS trigger, and the reset end is connected to the overcurrent detection signal, so as to divide the output signal of the first RS trigger; The set end of the second RS trigger is connected to the overcurrent detection signal, the reset end is connected to the output end of the frequency divider, and the inverting output end outputs the first judgment signal or the second judgment signal.

5. The LED drive control circuit according to claim 4, characterized in that: The frequency divider is a divide-by-two frequency circuit composed of two stages of D flip-flops.

6. The LED drive control circuit according to claim 3, characterized in that: The delay unit includes a current source, a first capacitor, a switch tube and a Schmitt trigger; One end of the current source is connected to the power supply voltage, and the other end is connected to the upper plate of the first capacitor; the lower plate of the first capacitor is grounded; the switch tube is connected in parallel to the two ends of the first capacitor, and the control end receives the PWM signal; the input end of the Schmitt trigger is connected to the upper plate of the first capacitor, and outputs the shutdown end signal.

7. The LED drive control circuit according to any one of claims 1 to 6, characterized in that: The LED drive control module also includes an adaptive delay module; The adaptive delay module is connected between the negative pressure detection module and the logic control module, and receives the drain voltage of the power switch tube. When the negative pressure detection signal is valid, the negative pressure detection signal is delayed based on the falling slope of the drain voltage of the power switch tube, so that the drain voltage of the power switch tube gradually drops to a preset voltage and then turns on the power switch tube; wherein the delay time is negatively correlated with the falling slope.

8. The LED drive control circuit according to claim 7, characterized in that: The adaptive delay module includes a slope detection unit, a second capacitor, a comparator and an AND logic unit; The slope detection unit receives the negative voltage detection signal and the drain voltage of the power switch tube, and when the negative voltage detection signal is valid, detects the falling slope of the drain voltage of the power switch tube and converts it into a corresponding current signal; The upper plate of the second capacitor is connected to the output end of the slope detection unit, and the lower plate is grounded; The comparator has a positive input terminal connected to the upper plate of the second capacitor, an inverting input terminal receiving a reference voltage, and outputting a comparison result; One end of the AND logic unit is connected to the output end of the comparator, and the other end receives the negative pressure detection signal and outputs a delayed signal of the negative pressure detection signal.

9. A chip, characterized in that: The chip at least includes: the LED drive control circuit according to any one of claims 1-8.

10. An LED driving system, characterized in that: The LED driving system at least comprises: A switching power supply circuit, an LED load, a ceramic capacitor, and an LED drive control circuit as claimed in any one of claims 1 to 8; The switching power supply circuit is connected to the LED load and provides a driving current for the LED load based on the on and off of the power switch tube; The LED drive control circuit is connected to the switch power supply circuit to provide a drive signal for the power switch tube in the switch power supply circuit; the ceramic capacitor is connected to the LED drive control circuit.

11. A LED driving control method, characterized in that: The LED driving method at least comprises: In the normal working mode, the overcurrent detection signal of the LED output current and the negative voltage detection signal of the power switch tube drive signal are detected and obtained, and when the overcurrent detection signal is valid, the power switch tube is controlled to be turned off, and when the negative voltage detection signal is valid, the power switch tube is controlled to be turned on; As the power supply voltage decreases, the overcurrent detection signal and the negative pressure detection signal cannot be detected, and the abnormal working mode is entered; at this time, when the on-time of the power switch tube reaches the preset maximum on-time, the power switch tube is controlled to be turned off, and when the off-time of the power switch tube reaches the preset maximum off-time, the power switch tube is controlled to be turned on; The power supply voltage keeps decreasing, the overcurrent detection signal and the negative pressure detection signal cannot be detected, and the on-time and off-time of the power switch tube alternately reach the maximum on-time and the maximum off-time, and the anti-howling mode is entered; at this time, when the on-time of the power switch tube reaches the preset maximum on-time, the power switch tube is controlled to be turned off, and when the power switch tube is turned off for a preset time, the power switch tube is controlled to be turned on; wherein, the frequency corresponding to the sum of the maximum on-time and the preset time exceeds the range recognizable by the human ear.

12. The LED driving control method according to claim 11, characterized in that: The LED drive control method also includes: when the negative voltage detection signal is valid, the negative voltage detection signal is delayed based on the falling slope of the drain voltage of the power switch tube, so that the drain voltage of the power switch tube gradually drops to a preset voltage and then the power switch tube is turned on; wherein the delay time is negatively correlated with the falling slope.

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