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

Abstract

The invention provides an LED driving system, a power supply system, a chip, a control circuit and a method, and the system comprises a constant-current conduction control module which detects the discharge time based on a feedback voltage, and continuously adjusts a conduction point of a constant-current conduction control signal, so that the average value of the ratio of the discharge time to a switching period is a preset fixed value, and the conduction point is located at the valley bottom of resonance; the comparison module is used for generating a constant-current turn-off control signal when the output current reaches the peak current; the trigger module generates a switch control signal based on the constant current conduction control signal and the constant current turn-off control signal. According to the invention, good constant current precision is ensured, and QR turn-on can be realized at the turn-on moment of each switching period, so that the system efficiency is improved; due to the fact that the frequencies of all periods are slightly different, the jittering frequency effect is indirectly achieved, and the EMI characteristic of a system can be improved.

Description

Technical Field

[0001] The present invention relates to the field of integrated circuit design, and particularly to an LED driving system, a power supply system, a chip, a control circuit and a method. Background Art

[0002] Constant current control and constant voltage control are common control methods for switching power supply circuits; for example, for an LED load, a constant current control method needs to be provided; for a charger, a constant current control method needs to be provided when the load is large to achieve constant current charging, and a constant voltage control method needs to be provided when the load is small to achieve constant voltage charging. How to achieve high-performance constant current and / or constant voltage control has always been a difficult problem to overcome in this field.

[0003] Taking an ACDC power supply as an example, medium and small power ACDC power supplies generally adopt a flyback topology structure, and small power ACDC generally adopts a PSR (primary-side regulator) architecture. The constant current and constant voltage control principle of the PSR architecture is as follows:

[0004] The constant voltage loop compares the feedback signal with the reference voltage inside the control chip, and then adjusts through an operational amplifier to form a peak current. This peak current serves as the turn-off point of the constant voltage control. At the same time, the VCO output by the operational amplifier control is also used to generate the turn-on point of the constant voltage control; the constant current loop forms the turn-off point of the constant current control based on a fixed peak current, and at the same time doubles the discharge time (tdis time) to form a switching period signal, that is, the turn-on point of the constant current control. When the system is in the constant current section (CC, Constant Current), the switching period is determined by T / tdis = const, and satisfies the following relationship: Where, n is the turns ratio of the primary and secondary sides of the transformer, Vcs is the primary peak voltage, Rcs is the primary sampling resistor, tdis is the discharge time (that is, the conduction time of the secondary diode, that is, the time between the turn-off of the power switch tube and the occurrence of resonance), and T is the switching period; among them, n and Rcs are known parameters determined by the system. Therefore, as long as Vcs is ensured to be a fixed value and T / tdis is constant, then Iout is constant.

[0005] In the above constant current and constant voltage control method, the constant voltage loop adopts closed-loop control, and the constant current loop adopts open-loop control. The advantage of this classic architecture is that the switching between the constant current and constant voltage modes is easy to understand, and the technology is mature and convenient for debugging; however, in the constant current section, since T / tdis is a fixed value, the next turn-on time point is controlled by the switching period T to ensure the accuracy of constant current, and QR (QuasiResonant) turn-on cannot be achieved, and the efficiency is relatively low.

[0006] Therefore, in today's increasingly fierce competition in terms of cost performance, it is necessary to find a control method that can achieve accurate constant current and QR turn-on in the constant current section, so as to enhance the competitiveness of the chip. This has become one of the problems that need to be urgently solved by those skilled in the art.

[0007] It should be noted that the above introduction to the technical background is only for the convenience of clearly and completely explaining the technical solution of the present invention and facilitating the understanding of those skilled in the art. It cannot be considered that the above technical solutions are well-known to those skilled in the art just because these solutions are described in the background art part of the present invention. Summary of the Invention

[0008] In view of the above-mentioned disadvantages of the prior art, the purpose of the present invention is to provide an LED driving system, a power supply system, a chip, a control circuit and a method, which are used to solve the problem that QR turn-on cannot be achieved in the constant current section of the prior art and the efficiency is relatively low.

[0009] To achieve the above object and other related objects, the present invention provides a control circuit, which at least includes:

[0010] A constant current conduction control module, a comparison module and a trigger module;

[0011] The constant current conduction control module receives the feedback voltage of the output signal of the switching power supply circuit, detects the discharge time based on the feedback voltage, and continuously adjusts the conduction point of the constant current conduction control signal, so that the average value of the ratio of the discharge time to the switching period is a preset fixed value and the conduction point is located at the bottom of the resonance; wherein, the discharge time is the period between the turn-off of the power switch tube and the generation of resonance.

[0012] The first comparison module receives the sampled voltage of the output current of the switching power supply circuit, and generates a constant current turn-off control signal when the output current reaches the peak current.

[0013] The trigger module is connected to the output ends of the constant current conduction control module and the first comparison module, and generates a switching control signal based on the constant current conduction control signal and the constant current turn-off control signal.

[0014] Optionally, the constant current conduction control module includes a discharge time detection unit, a charge and discharge control unit, a capacitor, a first comparator, a second comparator and a logic unit;

[0015] The discharge time detection unit receives the feedback voltage and detects the discharge time from the feedback voltage.

[0016] The control terminal of the charge and discharge control unit is connected to the output terminal of the discharge time detection unit, and the output terminal is connected to the upper plate of the capacitor; the lower plate of the capacitor is grounded; the charge and discharge control unit charges and discharges the capacitor respectively within and outside the time period of the discharge time;

[0017] The first input terminal of the first comparator is connected to the upper plate of the capacitor, and the second input terminal receives a first threshold; when outside the time period of the discharge time, when the voltage on the capacitor reaches the first threshold, it is determined that the turn-on preparation condition is satisfied, and a valid turn-on preparation signal is output;

[0018] The first input terminal of the second comparator is connected to the feedback voltage, and the second input terminal is connected to a second threshold for detecting the resonant valley bottom;

[0019] The logic unit is connected to the output terminals of the first comparator and the second comparator, and outputs a valid constant current conduction control signal at the first resonant valley bottom after the turn-on preparation condition is satisfied.

[0020] More preferably, the charge and discharge control unit includes a first current source, a second current source, a first switching tube and a second switching tube;

[0021] The first current source, the first switching tube, the second switching tube and the second current source are connected in series between the power supply voltage and the reference ground in sequence; outside the time period of the discharge time, the capacitor is charged based on the first current source; within the time period of the discharge time, the capacitor is discharged based on the second current source; when the voltage on the capacitor is greater than or equal to the first threshold, it is determined that the turn-on preparation condition is satisfied.

[0022] More preferably, the trigger module is an RS flip-flop, the set terminal of the RS flip-flop is connected to the output terminal of the constant current conduction control module, and the reset terminal is connected to the output terminal of the comparison module.

[0023] More preferably, the control circuit further includes: a constant voltage control module, a conduction signal generation module and a turn-off signal generation module;

[0024] The constant voltage control module receives the sampled voltage and the feedback voltage, and generates a constant voltage conduction control signal and a constant voltage turn-off control signal;

[0025] The conduction signal generation module receives the constant current conduction control signal and the constant voltage conduction control signal, takes the one with the larger period of the constant current conduction control signal and the constant voltage conduction control signal as the conduction control signal, and replaces the output signal of the constant current conduction control module to provide a conduction control signal for the trigger module;

[0026] The turn-off signal generation module receives the constant-current turn-off control signal and the constant-voltage turn-off control signal, takes the first-arriving one of the constant-current turn-off control signal and the constant-voltage turn-off control signal as the turn-off control signal, and replaces the output signal of the comparison module to provide the turn-off control signal for the trigger module.

[0027] Optionally, the constant-voltage control module includes an operational amplifier, a voltage-controlled oscillator, and a third comparator;

[0028] The operational amplifier receives the feedback voltage and the reference voltage, and generates the difference between the feedback voltage and the reference voltage;

[0029] The voltage-controlled oscillator is connected to the output end of the operational amplifier, and generates a constant-voltage conduction control signal based on the output signal of the operational amplifier. The greater the difference between the feedback voltage and the reference voltage, the shorter the period of the constant-voltage conduction control signal;

[0030] The third comparator is connected to the output end of the operational amplifier and receives the sampled voltage, and generates a valid constant-voltage turn-off control signal when the sampled voltage is greater than the output signal of the operational amplifier.

[0031] To achieve the above object and other related objects, the present invention further provides a chip, which at least includes: a driving circuit, a power switch tube, and the above control circuit;

[0032] The input end of the driving circuit is connected to the output end of the control circuit, and the output end is connected to the control end of the power switch tube. The driving circuit drives the power switch tube to work based on the switch control signal.

[0033] To achieve the above object and other related objects, the present invention further provides an LED driving system, which at least includes: a switching power supply circuit, an LED load, and the above control circuit;

[0034] The switching power supply circuit is connected to the LED load and provides a driving current for the LED load;

[0035] The control circuit provides a switch control signal for the switching power supply circuit to control the constant-current output of the switching power supply circuit.

[0036] To achieve the above object and other related objects, the present invention further provides a power supply system, which at least includes: a switching power supply circuit and the above control circuit;

[0037] The control circuit provides a switch control signal for the switching power supply circuit to control the constant-current output or constant-voltage output of the switching power supply circuit.

[0038] More optionally, the switching power supply circuit adopts a PSR topology structure.

[0039] To achieve the above object and other related objects, the present invention also provides a control method, which at least includes:

[0040] Obtain the feedback voltage of the output signal of the switching power supply circuit and the sampling voltage of the output current;

[0041] Continuously adjust the conduction point of the constant current conduction control signal so that the average value of the ratio of the discharge time to the switching period is a preset fixed value and the conduction point is at the bottom of the resonance;

[0042] Generate a constant current turn-off control signal when the output current reaches the peak current;

[0043] Control the power switch tube based on the constant current conduction control signal and the constant current turn-off control signal, thereby achieving constant current output.

[0044] More optionally, the method for generating the constant current conduction control signal further includes:

[0045] Detect the discharge time, and charge and discharge the capacitor respectively inside and outside the time period of the discharge time; outside the time period of the discharge time, when the voltage on the capacitor reaches the first threshold, it is determined that the turn-on preparation condition is satisfied, and an effective turn-on preparation signal is output;

[0046] And detect the bottom of the resonance, and output an effective constant current conduction control signal at the first bottom of the resonance after the turn-on preparation condition is satisfied.

[0047] More optionally, the control method further includes:

[0048] Generate a constant voltage conduction control signal and a constant voltage turn-off control signal based on a closed-loop control method;

[0049] When the period of the constant current conduction control signal is greater than the period of the constant voltage conduction control signal, and the constant current turn-off control signal is valid before the constant voltage turn-off control signal, control the power switch tube based on the constant current conduction control signal and the constant current turn-off control signal, thereby achieving constant current output;

[0050] When the period of the constant voltage conduction control signal is greater than the period of the constant current conduction control signal, and the constant voltage turn-off control signal is valid before the constant current turn-off control signal, control the power switch tube based on the constant voltage conduction control signal and the constant voltage turn-off control signal, thereby achieving constant voltage output.

[0051] More optionally, the method for generating the constant voltage conduction control signal and the constant voltage turn-off control signal includes:

[0052] Obtain the feedback voltage and the sampled voltage, and calculate the difference between the feedback voltage and the reference voltage;

[0053] Generate an oscillation signal based on the difference between the feedback voltage and the reference voltage, and the oscillation signal serves as a constant-voltage turn-on control signal;

[0054] When the sampled voltage reaches the difference between the feedback voltage and the reference voltage, generate a constant-voltage turn-off control signal.

[0055] As described above, the LED driving system, power supply system, chip, control circuit and method of the present invention have the following beneficial effects:

[0056] 1. The LED driving system, power supply system, chip, control circuit and method of the present invention can achieve QR turn-on at the turn-on moment of each switching cycle while ensuring good constant-current accuracy, thereby improving the system efficiency.

[0057] 2. Since the frequency of each cycle of the LED driving system, power supply system, chip, control circuit and method of the present invention is slightly different, the effect of frequency dithering is indirectly achieved, which helps to improve the EMI characteristics of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0058] Figure 1 Show the structural schematic diagrams of the control circuit (constant current) and the corresponding chip of the present invention.

[0059] Figure 2 Show the structural schematic diagram of the constant-current turn-on control module of the present invention.

[0060] Figure 3 Show the structural schematic diagrams of the control circuit (constant current and constant voltage) and the corresponding chip of the present invention.

[0061] Figure 4 Show the structural schematic diagram of the LED driving system of the present invention.

[0062] Figure 5 Show the structural schematic diagram of the power supply system of the present invention.

[0063] Figure 6 Show the principle schematic diagram of the control method of the present invention.

[0064] DESCRIPTION OF REFERENCE NUMERALS

[0065] 1 Control circuit

[0066] 11 Constant-current turn-on control module

[0067] 111 Discharge time detection unit

[0068] 112 Charge and discharge control unit

[0069] 113 First comparator

[0070] 114 Second comparator

[0071] 115 Logic unit

[0072] 12 Comparison module

[0073] 13 Trigger module

[0074] 14 Constant voltage control module

[0075] 141 Operational amplifier

[0076] 142 Voltage-controlled oscillator

[0077] 143 Third comparator

[0078] 15 Conducting signal generation module

[0079] 16 Shut-off signal generation module

[0080] 2 Driver circuit

[0081] 3 Power supply circuit

[0082] 4 Switching power supply circuit

[0083] 5 Chip Specific implementation manners

[0084] The following uses specific specific examples to illustrate the implementation manners of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific implementation manners. Various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0085] Please refer to Figures 1 to 6 . It should be noted that the diagrams provided in this embodiment only illustrate the basic concept of the present invention in a schematic manner. Therefore, only the components related to the present invention are shown in the diagrams, rather than being drawn according to the number, shape, and size of the components in actual implementation. The types, quantities, and proportions of the components in actual implementation can be arbitrarily changed, and the component layout type may also be more complex.

[0086] Embodiment 1

[0087] As Figure 1 shown, this embodiment provides a control circuit 1, and the control circuit 1 includes:

[0088] A constant current conduction control module 11, a comparison module 12, and a trigger module 13.

[0089] As Figure 1 shown, the constant current conduction control module 11 receives the feedback voltage FB of the output signal of the switching power supply circuit, detects the discharge time tdis based on the feedback voltage FB, and continuously adjusts the conduction point of the constant current conduction control signal on1 so that the average value of the ratio of the discharge time tdis to the switching period T is a preset fixed value const and the conduction point is located at the bottom of the resonance; wherein, the discharge time tdis is the period between the turn-off of the power switch tube and the generation of resonance.

[0090] Specifically, as Figure 2 shown, in this embodiment, the constant current conduction control module 11 includes a discharge time detection unit 111, a charge and discharge control unit 112, a capacitor C, a first comparator 113, a second comparator 114, and a logic unit 115.

[0091] More specifically, as Figure 2 shown, the discharge time detection unit 111 receives the feedback voltage FB and detects the discharge time tdis by detecting the feedback voltage FB. The feedback voltage FB contains the information of the discharge time tdis. As an example, the feedback voltage FB is compared with a preset reference voltage, and when the feedback voltage is greater than the preset reference voltage, it is determined as the discharge time tdis. The preset reference voltage is set according to actual needs, and it is only necessary to be able to detect the discharge time tdis based on the feedback voltage FB, and the details are not limited here one by one.

[0092] More specifically, as Figure 2As shown, the control terminal of the charge and discharge control unit 112 is connected to the output terminal of the discharge time detection unit 111, and the output terminal is connected to the upper plate of the capacitor C; the lower plate of the capacitor C is grounded. The charge and discharge control unit 112 charges and discharges the capacitor C respectively within and outside the time period of the discharge time tdis; in this embodiment, the capacitor is discharged within the time period of the discharge time tdis, and the capacitor is charged outside the time period of the discharge time tdis. As an example, the charge and discharge control unit 112 includes a first current source I1, a second current source I2, a first switching transistor M1 and a second switching transistor M2. In this example, the first switching transistor M1 is a PMOS transistor, and the second switching transistor M2 is an NMOS transistor; one end of the first current source I1 is connected to the power supply voltage, and the other end is connected to the source of the first switching transistor M1; the drain of the first switching transistor M1 is connected to the drain of the second switching transistor M2 and is connected to the upper plate of the capacitor C; one end of the second current source I2 is connected to the source of the second switching transistor M2, and the other end is grounded; the gates of the first switching transistor M1 and the second switching transistor M2 are connected to the output terminal of the discharge time detection unit 111. When no discharge is detected (outside the time period of the discharge time), the first switching transistor M1 is turned on, the second switching transistor M2 is turned off, and the capacitor C is charged, and the charging current is equal to the magnitude of the first current source I1; when discharge is detected (within the time period of the discharge time tdis), the first switching transistor M1 is turned off, the second switching transistor M2 is turned on, and the capacitor C is discharged, and the discharge current is equal to the magnitude of the second current source I2.

[0093] It should be noted that the ratio of the first current source I1 to the second current source I2 determines the preset fixed value const, and the specific ratio can be set according to actual needs. In addition, in actual use, it is also possible to charge within the time period of the discharge time tdis and discharge outside the time period of the discharge time tdis, and adjust the subsequent comparison logic accordingly, as long as the constant current conduction control logic of the present invention can be achieved, which will not be elaborated here one by one.

[0094] More specifically, as Figure 2As shown, the first input terminal of the first comparator 113 is connected to the upper plate of the capacitor C, and the second input terminal receives the first threshold value Vth1; when outside the time period of the discharge time tdis, the voltage on the capacitor C reaches (rises to or falls to) the first threshold value Vth1, it is determined that the turn-on preparation condition is satisfied, and a valid turn-on preparation signal is output. In this embodiment, the non-inverting input terminal of the first comparator 113 is connected to the upper plate of the capacitor C, the inverting input terminal receives the first threshold value Vth1, and the output signal is valid at a high level (or rising edge); when the voltage on the capacitor C is greater than or equal to the first threshold value Vth1, it is determined that the turn-on preparation condition is satisfied.

[0095] It should be noted that for the case where the time period corresponding to the charge and discharge of the discharge time tdis is opposite to that of the embodiment, or the effective level (or transition edge) of the output signal is opposite to that of this embodiment, the corresponding relationship between the input signal of the first comparator and the polarity of the input terminal can be interchanged, which will not be elaborated here one by one. In addition, the first threshold value Vth1 is a preset charge and discharge starting point, and any value can be set as needed to enable the voltage to return to the initial state after charge and discharge. In this embodiment, the first threshold value Vth1 is set to a voltage value between 0 and 1V.

[0096] More specifically, the first input terminal of the second comparator 114 is connected to the feedback voltage FB, and the second input terminal is connected to the second threshold value Vth2, which is used to detect the resonant valley bottom. In this embodiment, the inverting input terminal of the second comparator 114 is connected to the feedback voltage FB, and the non-inverting input terminal is connected to the second threshold value Vth2. When the feedback voltage FB is less than the second threshold value Vth2 (the specific value of the second threshold is set according to actual needs as long as the detection of the resonant valley bottom can be achieved), it is determined that the resonant valley bottom is detected, and the output detection signal is valid at a high level (or rising edge); for the case where the effective level (or transition edge) of the detection signal is opposite to that of this embodiment, the corresponding relationship between the input signal of the second comparator and the polarity of the input terminal can be interchanged as long as the resonant valley bottom can be detected, which will not be elaborated here one by one.

[0097] More specifically, the logic unit 115 is connected to the output terminals of the first comparator 113 and the second comparator 114, and outputs a valid constant current conduction control signal on1 at the first resonant valley bottom after the turn-on preparation condition is satisfied. When the turn-on preparation condition is satisfied, the logic unit 115 waits for the arrival of the resonant valley bottom, determines the conduction point when the first resonant valley bottom is detected, and thus realizes QR turn-on. When the turn-on preparation condition is not satisfied, even if the resonant valley bottom is detected, the power switch tube is not controlled to conduct.

[0098] It should be noted that any circuit structure that can turn on the control power switch tube at the resonant valley bottom and the average value of the ratio of the discharge time tdis to the switching period T is the preset fixed value const is applicable to the present invention, and is not limited to this embodiment.

[0099] As Figure 1 shown, the comparison module 12 receives the sampled voltage CS of the output current of the switching power supply circuit, and generates a constant current turn-off control signal off1 when the output current reaches the peak current Ipk.

[0100] Specifically, in this embodiment, the inverting input terminal of the comparison module 12 receives the sampled voltage CS, and the non-inverting input terminal receives the preset peak value PK; when the sampled voltage CS is greater than or equal to the preset peak value PK, it indicates that the output current reaches the peak current Ipk, and the peak current Ipk is a preset constant value. The relationship between the input signal of the comparison module 12 and the polarity of the input terminal can be adjusted according to needs, and is not limited to this embodiment.

[0101] As Figure 1 shown, the trigger module 13 is connected to the output terminals of the constant current turn-on control module 11 and the comparison module 12, and generates a switching control signal based on the constant current turn-on control signal on1 and the constant current turn-off control signal off1.

[0102] Specifically, in this embodiment, the trigger module 13 is an RS flip-flop. The set terminal S of the RS flip-flop 13 is connected to the output terminal of the constant current turn-on control module 11, and the reset terminal R is connected to the output terminal of the comparison module 12; when the constant current turn-on control signal on1 is valid, the output signal of the trigger module 13 jumps to a level that controls the power switch tube to turn on, and when the constant current turn-off control signal off1 is valid, the output signal of the trigger module 13 jumps to a level that controls the power switch tube to turn off.

[0103] The control circuit 1 of the present invention can achieve QR turn-on while ensuring constant current, thereby reducing switching losses and improving system efficiency.

[0104] As Figure 1 shown, this embodiment also provides a chip, which includes: the control circuit 1, the drive circuit 2 and the power switch tube Q.

[0105] Specifically, the input terminal of the drive circuit 2 is connected to the output terminal of the control circuit 1, and the output terminal is connected to the control terminal of the power switch tube Q. The drive circuit 2 drives the power switch tube Q to work based on the switching control signal to achieve constant current output; the drive circuit 2 includes, but is not limited to, a totem pole structure, which will not be elaborated here one by one.

[0106] Specifically, the drain of the power switch transistor Q is led out as the SW pin of the chip; the source of the power switch transistor Q is led out as the CS pin of the chip. The feedback signal FB is introduced through the chip pin.

[0107] Specifically, the chip further includes a power supply circuit 3. The power supply circuit 3 is connected to an external power supply through the chip pin VDD to generate the working power supply inside the chip. The power supply circuit 3 includes, but is not limited to, an LDO.

[0108] Embodiment 2

[0109] As Figure 3 shown, this embodiment provides a control circuit 1. The difference from Embodiment 1 is that the control circuit 1 further includes: a constant voltage control module 14, a conduction signal generation module 15, and a turn-off signal generation module 16.

[0110] As Figure 3 shown, the constant voltage control module 14 receives the sampling voltage CS and the feedback voltage FB, and generates a constant voltage conduction control signal on2 and a constant voltage turn-off control signal off2.

[0111] Specifically, in this embodiment, the constant voltage control module 14 realizes constant voltage control based on closed-loop control. In actual use, any circuit structure that can realize constant voltage control is applicable to the present invention and is not limited to this embodiment. As an example, the constant voltage control module 14 includes an operational amplifier 141, a voltage-controlled oscillator 142, and a third comparator 143.

[0112] More specifically, the operational amplifier 141 receives the feedback voltage FB and the reference voltage Vref (the reference voltage Vref is related to the conduction point and turn-off point of the constant voltage control, and specific values are set according to actual needs), and generates the difference between the feedback voltage FB and the reference voltage Vref. In this example, the inverting input terminal of the operational amplifier 141 receives the feedback voltage FB, the non-inverting input terminal receives the reference voltage Vref, and outputs an amplified signal of Vref - FB. In actual use, the relationship between the input signal of the operational amplifier 141 and the polarity of the input terminal can be adjusted according to needs and is not limited to this embodiment.

[0113] More specifically, the voltage-controlled oscillator 142 is connected to the output terminal of the operational amplifier 141, and generates a constant voltage conduction control signal on2 based on the output signal of the operational amplifier 141. The greater the difference between the feedback voltage FB and the reference voltage Vref, the shorter the period of the constant voltage conduction control signal on2. Any voltage-controlled oscillator structure is applicable to the present invention and will not be elaborated here one by one.

[0114] More specifically, the third comparator 143 is connected to the output terminal of the operational amplifier 141 and receives the sampling voltage CS. When the sampling voltage CS is greater than the output signal of the operational amplifier 141, a valid constant voltage turn-off control signal off2 is generated. In this embodiment, the non-inverting input terminal of the third comparator 143 is connected to the output terminal of the operational amplifier 14, and the inverting input terminal is connected to the sampling voltage CS. The output signal of the third comparator 143 is active low. In actual use, the relationship between the input signal of the third comparator 143 and the polarity of the input terminal can be adjusted as needed, and this embodiment is not limiting.

[0115] As Figure 3 shown, the conduction signal generation module 15 receives the constant current conduction control signal on1 and the constant voltage conduction control signal on2, takes the one with the larger period among the constant current conduction control signal on1 and the constant voltage conduction control signal on2 as the conduction control signal, and replaces the output signal of the constant current conduction control module 11 to provide the conduction control signal for the trigger module 13.

[0116] Specifically, in this embodiment, the conduction signal generation module 15 identifies the rising edges of the constant current conduction control signal on1 and the constant voltage conduction control signal on2, and determines which one has a larger period based on which rising edge arrives later. In actual use, any method that can implement the determination of the period size is applicable to the present invention, and this embodiment is not limiting.

[0117] As Figure 3 shown, the turn-off signal generation module 16 receives the constant current turn-off control signal off1 and the constant voltage turn-off control signal off2, takes the one that arrives first (becomes valid first) among the constant current turn-off control signal off1 and the constant voltage turn-off control signal off2 as the turn-off control signal, and replaces the output signal of the comparison module 12 to provide the turn-off control signal for the trigger module 13.

[0118] Specifically, in this embodiment, the turn-off signal generation module 16 identifies the falling edges of the constant current turn-off control signal off1 and the constant voltage turn-off control signal off2, and determines which one becomes valid first based on which falling edge arrives first. In actual use, any method that can implement the determination of the order of signal arrival is applicable to the present invention, and this embodiment is not limiting.

[0119] As Figure 3As shown, this embodiment also provides a chip, the chip includes: the control circuit 1, the drive circuit 2 and the power switch tube Q; as another example, the chip also includes a power supply circuit 3. The connection relationship of each circuit is the same as that of the chip in the first embodiment, except that the constant current control is implemented based on the control circuit 1 in the first embodiment, and the constant voltage control is also implemented based on the control circuit 1 in the present embodiment, and the conduction signal generation module 15 selects the conduction control signal and the shutdown signal generation module 16 selects the shutdown control signal, thereby realizing the constant current and constant voltage control in a time-sharing manner.

[0120] Embodiment 3

[0121] like Figure 4 As shown, this embodiment provides an LED driving system, which includes: a switching power supply circuit 4, an LED load and the control circuit 1 of the first embodiment.

[0122] like Figure 4 As shown, the switching power supply circuit 4 is connected to the LED load to provide a driving current for the LED load.

[0123] Specifically, in this embodiment, the switching power supply circuit 4 adopts a flyback topology structure, including a rectifier bridge, capacitors C1, C2, a transformer, a power switch tube Q, a resistor R1 and a diode D1. The rectifier bridge converts the AC voltage ACINPUT into a DC input voltage Vin; the capacitor C1 is connected in parallel to both ends of the rectifier bridge; one end of the primary winding of the transformer is connected to the input voltage Vin, and the other end is grounded via the power switch tube Q and the resistor R1 (sampling resistor); one end of the secondary winding of the transformer is connected to the anode of the diode D1, the cathode of the diode D1 is connected to the upper plate of the capacitor C2, and the lower plate is connected to the other end of the secondary winding of the transformer; the positive electrode of the LED load is connected to the upper plate of the capacitor C2, and the negative electrode is connected to the lower plate of the capacitor C2. In this embodiment, the discharge time tdis is the conduction time of the diode D1.

[0124] As an example, the switching power supply circuit 4 can provide the feedback voltage FB for the control circuit 1 based on primary-side feedback or secondary-side feedback, which will not be described in detail here.

[0125] It should be noted that the structure of the switching power supply circuit 4 includes but is not limited to a PSR topology, a BUCK topology, a BOOST topology, a BUCK-BOOST topology and their derived topologies, and is not limited to this embodiment.

[0126] like Figure 4As shown, the control circuit 1 provides a switching control signal for the switching power supply circuit 4 to control the constant current output of the switching power supply circuit 4.

[0127] Specifically, for the specific structure and working principle of the control circuit 1, refer to Embodiment 1, which will not be elaborated here one by one. The control circuit 1 can achieve QR turn-on while ensuring constant current, thereby enabling the LED load to emit light stably and having a high system efficiency.

[0128] Embodiment 4

[0129] As Figure 5 shown, this embodiment provides a power supply system, which includes: a switching power supply circuit and the control circuit 1 of Embodiment 2. In this embodiment, the control circuit 1 and the power switch transistor Q in the switching power supply circuit are integrated in the chip 5 (see Figure 3 ).

[0130] As Figure 5 shown, the switching power supply circuit is used to provide a DC power supply.

[0131] Specifically, in this embodiment, the switching power supply circuit adopts a PSR topology structure, including a rectifier bridge, capacitors C3, C4, C5, C6, resistors R2, R3, R4, R5, R6, R7, a transformer, and diodes D2, D3, D4. The rectifier bridge converts the AC voltage AC INPUT into a DC input voltage; the capacitor C3 is connected in parallel across the rectifier bridge; one end of the primary winding of the transformer is connected to the input voltage, and the other end is grounded via the SW pin of the chip 5, the power switch transistor Q, the CS pin of the chip 5, and the resistor R7 (sampling resistor); one end of the secondary winding of the transformer is connected to the anode of the diode D3, the cathode of the diode D3 is connected to the upper plate of the capacitor C6, and the lower plate of the capacitor C6 is connected to the other end of the secondary winding of the transformer; the resistor R4 is connected in parallel across the capacitor C6; one end of the capacitor C5 is connected to the input voltage, and the other end is connected to the cathode of the diode D2; the anode of the diode D2 is connected to the SW pin of the chip 5; the resistor R3 is connected in parallel across the capacitor C5; the resistor R2 and the capacitor C4 are connected in series between the input voltage and the reference ground, and the middle node supplies power to the chip 5; the resistors R5 and R6 are connected in series across the auxiliary winding of the transformer, and the middle node of the resistors R5 and R6 provides a feedback voltage FB for the chip 5; one end of the auxiliary winding of the transformer is grounded, and the other end is connected to the anode of the diode D4; the cathode of the diode D4 is connected to the VDD pin of the chip 5. In this embodiment, the discharge time tdis is the conduction time of the diode D3.

[0132] It should be noted that the structure of the switching power supply circuit includes, but is not limited to, the PSR topology structure listed in this embodiment. Any structure that can achieve constant current control based on the ratio of the discharge time tdis to the switching period T is applicable to the present invention, and will not be elaborated one by one here.

[0133] As Figure 5 shown, the control circuit 1 provides a switching control signal for the switching power supply circuit to control the constant current output or constant voltage output of the switching power supply circuit.

[0134] Specifically, for the structure and operation of the control circuit 1, refer to Embodiment 1, which will not be elaborated one by one here. When the control circuit 1 is in the constant current mode, it can achieve QR turn-on while ensuring constant current; when in the constant voltage mode, it can achieve efficient and stable constant voltage control.

[0135] Embodiment 5

[0136] This embodiment provides a control method. In this embodiment, based on the control circuit 1 of Embodiment 1, the (constant current) control method of the present invention is implemented. In actual use, any circuit that can implement this method is applicable to the present invention. The (constant current) control method includes:

[0137] 11) Obtain the feedback voltage FB of the output signal of the switching power supply circuit and the sampling voltage CS of the output current.

[0138] Specifically, in this embodiment, the feedback voltage FB is obtained based on primary side feedback. In actual use, the feedback voltage FB can be obtained based on any method that can reflect the output signal, not limited to this embodiment. The sampling voltage CS is obtained by sampling through a resistor connected in series with the power switch tube Q. In actual use, any method that can achieve sampling of the output current is applicable to the present invention, not limited to this embodiment.

[0139] 12) Continuously adjust the turn-on point of the constant current turn-on control signal so that the average value of the ratio of the discharge time tdis to the switching period T is a preset fixed value const and the turn-on point is located at the bottom of the resonance.

[0140] Specifically, the discharge time tdis is detected, and the capacitor C is charged and discharged respectively inside and outside the time period of the discharge time tdis; outside the time period of the discharge time tdis, when the voltage VC on the capacitor C reaches the first threshold Vth1, it is determined that the turn-on preparation condition is satisfied, and a valid turn-on preparation signal is output; and the bottom of the resonance is detected, and a valid constant current turn-on control signal on1 is output at the first bottom of the resonance after the turn-on preparation condition is satisfied.

[0141] More specifically, in this embodiment, the detection of the discharge time tdis is achieved based on the feedback voltage FB. As Figure 6 shown, the capacitor C is discharged during the period of the discharge time tdis and charged outside the period of the discharge time tdis; when the voltage VC on the capacitor C is greater than or equal to the first threshold Vth1 (necessarily outside the period of the discharge time tdis), it is determined that the turn-on preparation condition is satisfied, and a valid turn-on preparation signal is output. In this embodiment, the resonant valley bottom is detected based on the comparison result between the feedback voltage FB and the second threshold Vth2.

[0142] 13) A constant-current turn-off control signal off1 is generated when the output current Iout reaches the peak current Ipk.

[0143] Specifically, in this embodiment, the sampling voltage CS is compared with a preset peak value PK to determine whether the output current Iout reaches the peak current Ipk.

[0144] 14) The power switch Q is controlled based on the constant-current turn-on control signal on1 and the constant-current turn-off control signal off1, thereby achieving a constant-current output.

[0145] Specifically, the power switch Q is turned on when the constant-current turn-on control signal on1 is valid, and the power switch Q is turned off when the constant-current turn-off control signal off1 is valid.

[0146] As Figure 6As shown, in this example, it is assumed that the theoretical value of T / tdis is exactly stuck between the first valley and the second valley of resonance. During the first switching period, outside the time period of the discharge time tdis, when the voltage VC on the capacitor C reaches the first threshold Vth1, the first valley of resonance has passed. Therefore, the second valley of resonance is the first resonance valley after the turn-on preparation condition is met. At the second valley, the power switch Q conducts, and the voltage at the drain of the power switch Q (i.e., the SW terminal) is pulled down, and the switching period T is lengthened (in the prior art, it can only be turned on at a certain moment after the first valley and before the second valley). During the second switching period, the output current Iout reaches the peak current Ipk, the power switch Q is turned off again, the voltage at the drain of the power switch Q (i.e., the SW terminal) is pulled up, and it is recharged and discharged based on the discharge time tdis, and the voltage VC on the capacitor C is compared with the first threshold Vth1. During the second switching period, when the voltage VC on the capacitor C reaches the first threshold Vth1, the first valley of resonance has also passed. Therefore, it conducts at the second valley of resonance, and similarly, the switching period T is lengthened accordingly. During the third switching period, the above steps are repeated. Due to the accumulation of the previous two periods, the maximum value of the voltage VC on the capacitor C is continuously pushed up. During the third switching period, when the voltage VC on the capacitor C reaches the first threshold Vth1, the first valley of resonance has not passed yet. Therefore, the first valley of resonance is the first resonance valley after the turn-on preparation condition is met, and it conducts at the first valley of resonance. Compared with the previous two periods, the switching period T is shortened. And so on, the conduction point continuously switches between the first valley and the second valley of resonance, so that the ratio of the discharge time tdis to the switching period T is averaged to a preset fixed value const.

[0147] This embodiment also provides a (constant current and constant voltage) control method. In this embodiment, the (constant current and constant voltage) control method of the present invention is implemented based on the control circuit 1 of Embodiment 2. In actual use, any circuit that can implement this method is applicable to the present invention. The (constant current and constant voltage) control method includes:

[0148] 21) Generate the constant current turn-on control signal on1 and the constant current turn-off control signal off1 based on the control method of the present invention.

[0149] For the specific steps and methods, refer to the above (constant current) control method, and details are not repeated here.

[0150] 22) Generate the constant voltage turn-on control signal on2 and the constant voltage turn-off control signal off2 based on the closed-loop control method.

[0151] Specifically, obtain the feedback voltage FB and the sampling voltage CS, and calculate the difference between the feedback voltage FB and the reference voltage Vref. Generate an oscillation signal based on the difference between the feedback voltage FB and the reference voltage Vref. The period of the oscillation signal is inversely proportional to the difference, and the oscillation signal serves as the constant-voltage turn-on control signal on2. When the sampling voltage CS reaches the difference between the feedback voltage FB and the reference voltage CS, generate the constant-voltage turn-off control signal off2.

[0152] 23) When the period of the constant-current turn-on control signal on1 is greater than the period of the constant-voltage turn-on control signal on2, and the constant-current turn-off control signal off1 becomes effective prior to the constant-voltage turn-off control signal off2, control the power switch tube Q based on the constant-current turn-on control signal on1 and the constant-current turn-off control signal off1, thereby achieving constant-current output.

[0153] 24) When the period of the constant-voltage turn-on control signal on2 is greater than the period of the constant-current turn-on control signal on1, and the constant-voltage turn-off control signal off2 becomes effective prior to the constant-current turn-off control signal off1, control the power switch tube based on the constant-voltage turn-on control signal on2 and the constant-voltage turn-off control signal off2, thereby achieving constant-voltage output.

[0154] Specifically, in this embodiment, identify the rising edges of the constant-current turn-on control signal on1 and the constant-voltage turn-on control signal on2, and determine which one has a larger period based on which rising edge arrives later. Identify the falling edges of the constant-current turn-off control signal off1 and the constant-voltage turn-off control signal off2, and determine which one becomes effective first based on which falling edge arrives first.

[0155] The present invention controls T / tdis to be averaged at a fixed value within a period of time. Drawing on the control idea of delta-sigma, when a fixed T / tdis is required to ensure constant-current accuracy and this ratio cannot ensure resonant turn-on, extend the switching period T until the next resonant turn-on point is reached. Subsequently, this time extension will be stretched cycle by cycle until, after a certain cycle time, the previous resonant turn-on point has not yet arrived, thereby shifting the resonant turn-on point forward by one resonant peak. Within the entire large time period, the resonant turn-on point will switch between the Nth and (N + 1)th valleys (N >= 1), thereby ensuring constant-current accuracy within the large time period and achieving a certain auxiliary effect of spreading spectrum to reduce EMI.

[0156] In summary, the present invention provides an LED driving system, a power supply system, a chip, a control circuit and a method, including: a constant-current conduction control module, a comparison module and a trigger module; the constant-current conduction control module receives the feedback voltage of the output signal of the switching power supply circuit, detects the discharge time based on the feedback voltage, and continuously adjusts the conduction point of the constant-current conduction control signal, so that the average value of the ratio of the discharge time to the switching period is a preset fixed value and the conduction point is located at the bottom of the resonance; wherein, the discharge time is the period between the turn-off of the power switch tube and the generation of resonance; the comparison module receives the sampling voltage of the output current of the switching power supply circuit, and generates a constant-current turn-off control signal when the output current reaches the peak current; the trigger module is connected to the output ends of the constant-current conduction control module and the comparison module, and generates a switching control signal based on the constant-current conduction control signal and the constant-current turn-off control signal. The LED driving system, power supply system, chip, control circuit and method of the present invention can achieve QR turn-on at the conduction moment of each switching period while ensuring good constant-current accuracy, thereby improving the system efficiency; since the frequency of each period of the present invention is slightly different, the effect of frequency dithering is indirectly achieved, which helps to improve the EMI characteristics of the system. Therefore, the present invention effectively overcomes various disadvantages in the prior art and has high industrial utilization value.

[0157] The above embodiments are only illustrative of the principles and effects of the present invention, and are not used to limit the present invention. Any person familiar with this technology can modify or change the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or changes made by those with ordinary knowledge in the technical field without departing from the spirit and technical ideas disclosed by the present invention should still be covered by the claims of the present invention.

Claims

1. A control circuit, characterized in that, The control circuit at least includes: a constant-current conduction control module, a comparison module, and a trigger module; The constant-current conduction control module receives the feedback voltage of the output signal of the switching power supply circuit, detects the discharge time based on the feedback voltage, and continuously adjusts the conduction point of the constant-current conduction control signal so that the average value of the ratio of the discharge time to the switching period is a preset fixed value and the conduction point is at the bottom of the resonance; wherein, the discharge time is the period from when the power switch tube is turned off to when resonance occurs; The comparison module receives the sampled voltage of the output current of the switching power supply circuit and generates a constant-current turn-off control signal when the output current reaches the peak current; The trigger module is connected to the output ends of the constant-current conduction control module and the comparison module and generates a switch control signal based on the constant-current conduction control signal and the constant-current turn-off control signal.

2. The control circuit according to claim 1, characterized in that: The constant-current conduction control module includes a discharge time detection unit, a charge-discharge control unit, a capacitor, a first comparator, a second comparator, and a logic unit; The discharge time detection unit receives the feedback voltage and detects the discharge time from the feedback voltage; The control end of the charge-discharge control unit is connected to the output end of the discharge time detection unit, and the output end is connected to the upper plate of the capacitor; the lower plate of the capacitor is grounded; the charge-discharge control unit charges and discharges the capacitor respectively outside and inside the period of the discharge time; The first input end of the first comparator is connected to the upper plate of the capacitor, and the second input end receives a first threshold; when the voltage on the capacitor reaches the first threshold outside the period of the discharge time, it is determined that the turn-on preparation condition is met, and a valid turn-on preparation signal is output; The first input end of the second comparator is connected to the feedback voltage, and the second input end is connected to a second threshold for detecting the bottom of the resonance; The logic unit is connected to the output ends of the first comparator and the second comparator and outputs a valid constant-current conduction control signal at the first bottom of the resonance after the turn-on preparation condition is met.

3. The control circuit according to claim 2, characterized in that: The charge-discharge control unit includes a first current source, a second current source, a first switch tube, and a second switch tube; The first current source, the first switch tube, the second switch tube, and the second current source are connected in series between the power supply voltage and the reference ground in sequence; outside the period of the discharge time, the capacitor is charged based on the first current source; inside the period of the discharge time, the capacitor is discharged based on the second current source; when the voltage on the capacitor is greater than or equal to the first threshold, it is determined that the turn-on preparation condition is met.

4. The control circuit according to any one of claims 1 - 3, characterized in that: The trigger module is an RS flip-flop, the set end of the RS flip-flop is connected to the output end of the constant-current conduction control module, and the reset end is connected to the output end of the comparison module.

5. The control circuit according to any one of claims 1 - 3, characterized in that The control circuit further includes: a constant-voltage control module, a turn-on signal generation module, and a turn-off signal generation module; The constant-voltage control module receives the sampled voltage and the feedback voltage and generates a constant-voltage turn-on control signal and a constant-voltage turn-off control signal; The conduction signal generation module receives the constant-current conduction control signal and the constant-voltage conduction control signal, takes the one with a larger period among the constant-current conduction control signal and the constant-voltage conduction control signal as the conduction control signal, and replaces the output signal of the constant-current conduction control module to provide the conduction control signal for the trigger module; The turn-off signal generation module receives the constant-current turn-off control signal and the constant-voltage turn-off control signal, takes the one that arrives first among the constant-current turn-off control signal and the constant-voltage turn-off control signal as the turn-off control signal, and replaces the output signal of the comparison module to provide the turn-off control signal for the trigger module.

6. The control circuit according to claim 5, characterized in that: The constant-voltage control module includes an operational amplifier, a voltage-controlled oscillator, and a third comparator; The operational amplifier receives the feedback voltage and the reference voltage, and generates the difference between the feedback voltage and the reference voltage; The voltage-controlled oscillator is connected to the output end of the operational amplifier, generates a constant-voltage conduction control signal based on the output signal of the operational amplifier. The greater the difference between the feedback voltage and the reference voltage, the shorter the period of the constant-voltage conduction control signal; The third comparator is connected to the output end of the operational amplifier and receives the sampled voltage, and generates a valid constant-voltage turn-off control signal when the sampled voltage is greater than the output signal of the operational amplifier.

7. A chip, characterized in that, The chip at least includes: a drive circuit, a power switch, and the control circuit according to any one of claims 1-6; The input end of the drive circuit is connected to the output end of the control circuit, and the output end is connected to the control end of the power switch. The drive circuit drives the power switch to work based on the switch control signal.

8. An LED driving system, characterized in that, The LED drive system at least includes: a switch power supply circuit, an LED load, and the control circuit according to any one of claims 1-4; The switch power supply circuit is connected to the LED load to provide a drive current for the LED load; The control circuit provides a switch control signal for the switch power supply circuit to control the constant-current output of the switch power supply circuit.

9. A power supply system, characterized in that, The power supply system at least includes: a switch power supply circuit and the control circuit according to any one of claims 5 or 6; The control circuit provides a switch control signal for the switch power supply circuit to control the constant-current output or constant-voltage output of the switch power supply circuit.

10. The power supply system according to claim 8 or 9, characterized in that: The switch power supply circuit adopts a PSR topology structure.

11. A control method, characterized in that, The control method at least includes: Obtain the feedback voltage of the output signal of the switch power supply circuit and the sampled voltage of the output current; Continuously adjust the conduction point of the constant-current conduction control signal so that the average value of the ratio of the discharge time to the switching period is a preset fixed value and the conduction point is at the bottom of the resonance; Generate a constant-current turn-off control signal when the output current reaches the peak current; Control the power switch based on the constant-current conduction control signal and the constant-current turn-off control signal, thereby realizing constant-current output.

12. The control method according to claim 11, characterized in that: The method for generating the constant-current conduction control signal further includes: Detect the discharge time, and charge and discharge the capacitor respectively inside and outside the time period of the discharge time; outside the time period of the discharge time, when the voltage on the capacitor reaches the first threshold, it is determined that the turn-on preparation condition is satisfied, and a valid turn-on preparation signal is output; Detect the resonant valley bottom, and output a valid constant-current conduction control signal at the first resonant valley bottom after the turn-on preparation condition is satisfied.

13. The control method according to claim 11 or 12, characterized in that: The control method further includes: Generate a constant-voltage conduction control signal and a constant-voltage turn-off control signal based on a closed-loop control method; When the period of the constant-current conduction control signal is greater than the period of the constant-voltage conduction control signal, and the constant-current turn-off control signal is valid prior to the constant-voltage turn-off control signal, control the power switch tube based on the constant-current conduction control signal and the constant-current turn-off control signal, so as to achieve constant-current output; When the period of the constant-voltage conduction control signal is greater than the period of the constant-current conduction control signal, and the constant-voltage turn-off control signal is valid prior to the constant-current turn-off control signal, control the power switch tube based on the constant-voltage conduction control signal and the constant-voltage turn-off control signal, so as to achieve constant-voltage output.

14. The control method according to claim 13, characterized in that: The method for generating the constant-voltage conduction control signal and the constant-voltage turn-off control signal includes: Obtain the feedback voltage and the sampling voltage, and calculate the difference between the feedback voltage and the reference voltage; Generate an oscillation signal based on the difference between the feedback voltage and the reference voltage, and the oscillation signal serves as the constant-voltage conduction control signal; When the sampling voltage reaches the difference between the feedback voltage and the reference voltage, generate a constant-voltage turn-off control signal.

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