Constant current control circuit and constant current control system

Abstract

The utility model discloses a constant current control circuit and a constant current control system, a turn-off control unit compares a first sampling voltage with a turn-off reference voltage and outputs a turn-off control signal, and if the first sampling voltage is greater than the turn-off reference voltage, a driving unit outputs a driving signal for controlling a power tube to be turned off, so that the inductive current is reduced, and the power tube is turned off. It is ensured that no overshoot current occurs during starting, and then the problem of starting overcharge is solved; the turn-on control unit receives the first sampling voltage, the second sampling voltage and the constant-current reference voltage and outputs a turn-on control signal, if the first sampling voltage is smaller than the constant-current reference voltage, the driving unit outputs a driving signal for controlling the turn-on of the power tube according to the turn-on control signal, so that the inductive current rises, and in each period, the power tube is turned on; the switch-on control unit obtains the compensation voltage by integrating the difference value between the first sampling voltage signal and the constant current reference voltage, and performs real-time adjustment by comparing the compensation voltage with the second sampling voltage, so that the precision of the constant current is improved.

Description

Technical Field

[0001] The utility model relates to the field of power supply management, in particular to a constant current control circuit and a constant current control system. Background Art

[0002] With the rapid development of electronic products, the requirements for LED constant current control are getting higher and higher, requiring higher performance and more complete internal protection current, while also having better conversion efficiency.

[0003] The LED constant current control in the prior art usually adopts the hysteresis control method, and the control points of the turn-on threshold and the turn-off threshold are set at 20% above and below the reference value. The inductor current is continuously charged and discharged within the current range corresponding to the turn-on threshold and the turn-off threshold, thereby obtaining a constant output current. However, since there is no cycle-by-cycle feedback regulation, the accuracy of the constant current is low.

[0004] The LED constant current control in the related art does not set an upper limit value for the inductor current in the LED constant current control system, resulting in excessive current ripple and a startup overshoot problem. Therefore, it is urgent to provide a constant current control circuit and a constant current control system that can balance constant current accuracy and reduce current ripple. Utility Model Content

[0005] The utility model provides a constant current control circuit and a constant current control system, which are used to solve the problems in the prior art that the LED constant current control system has no cycle-by-cycle feedback adjustment, resulting in low precision of the constant current, and has no set upper limit value, resulting in excessive current ripple and startup overshoot.

[0006] In a first aspect, the utility model provides a constant current control circuit, comprising: a sampling unit, a shut-off control unit, an opening control unit and a driving unit:

[0007] The sampling unit is connected between the input terminal and the sampling terminal, and the sampling unit outputs a first sampling voltage and a second sampling voltage;

[0008] The shutdown control unit receives the first sampling voltage and the shutdown reference voltage, and outputs a shutdown control signal according to a comparison result between the first sampling voltage and the shutdown reference voltage: when the first sampling voltage is greater than or equal to the shutdown reference voltage, the shutdown control signal is valid, and when the first sampling voltage is less than the shutdown reference voltage, the shutdown control signal is invalid;

[0009] The opening control unit receives the first sampling voltage, the second sampling voltage and the constant current reference voltage, and outputs an opening control signal: when the first sampling voltage is less than the constant current reference voltage, the opening control signal is valid, and when the first sampling voltage is greater than or equal to the constant current reference voltage, the opening control signal is invalid;

[0010] The driving unit receives the on control signal and the off control signal, and outputs a driving signal.

[0011] In a possible implementation, it further includes a reference voltage generating unit, which is connected to the input end, receives an input voltage, and outputs a shutdown reference voltage and a constant current reference voltage according to the input voltage.

[0012] In a possible implementation, the activation control unit includes a first transconductance amplifier, a first comparator, and a compensation module;

[0013] The first sampling voltage is input into a first input terminal of the first transconductance amplifier, the constant current reference voltage is input into a second input terminal of the first transconductance amplifier, and a compensation voltage is output from an output terminal of the first transconductance amplifier;

[0014] The compensation module is connected between the output terminal of the first transconductance amplifier and the ground terminal, and is used for integrating the difference between the first sampling voltage input by the first transconductance amplifier and the constant current reference voltage to obtain a compensation voltage;

[0015] The compensation voltage is inputted into a first input terminal of the first comparator, the second sampling voltage is inputted into a second input terminal of the first comparator, and the turn-on control signal is outputted into an output terminal of the first comparator.

[0016] In a possible implementation, the shutdown control unit includes a second comparator;

[0017] The first sampling voltage is input into a first input terminal of the second comparator, the shutdown reference voltage is input into a second input terminal of the second comparator, and the shutdown control signal is output from an output terminal of the second comparator.

[0018] In a possible implementation, the sampling unit includes: a second transconductance amplifier, a second resistor and a third resistor;

[0019] The sampling unit is connected to two ends of the sampling resistor, the first end of the sampling resistor is the input end, and the second end of the sampling resistor is the sampling end;

[0020] The first input terminal of the second transconductance amplifier is connected to the input terminal, the second input terminal of the second transconductance amplifier is connected to the sampling terminal, the output terminal of the second transconductance amplifier is connected to the first terminal of the second resistor, and outputs the second sampling voltage;

[0021] The second end of the second resistor is electrically connected to the first end of the third resistor, and outputs the first sampling voltage;

[0022] The second end of the third resistor is electrically connected to the ground end.

[0023] In a possible implementation, the reference voltage generating unit includes a voltage reduction module and a voltage division module;

[0024] The voltage reduction module is connected between the input terminal and the voltage dividing module, receives the input voltage, reduces the input voltage, and outputs a first voltage;

[0025] The voltage division module receives the first voltage, divides the first voltage, and outputs the shutdown reference voltage and the constant current reference voltage.

[0026] In a possible implementation, the driving unit includes: a trigger, a first inverter, a first switch tube, and a second switch tube;

[0027] The reset end of the trigger inputs the shutdown control signal, the set end of the trigger inputs the startup control signal, and the output end of the trigger is connected to the input end of the first inverter and the control end of the first switch tube;

[0028] The output end of the first inverter is connected to the control end of the second switch tube;

[0029] The first switch tube and the second switch tube are connected between a power supply terminal and a ground terminal;

[0030] The first end of the first switch tube is connected to the power supply end, the second end of the second switch tube is connected to the ground end, and a connection node between the second end of the first switch tube and the first end of the second switch tube outputs the driving signal.

[0031] In a possible implementation, the shutdown reference voltage represents an upper limit value of the inductor current in a constant current control system, and the inductor current does not exceed the upper limit value of the inductor current corresponding to the shutdown reference voltage.

[0032] In a second aspect, the utility model further provides a constant current control system, comprising a sampling resistor, a light-emitting unit, an inductor, a power tube, a freewheeling diode, and a constant current control circuit as described in any one of the first aspects;

[0033] The first end of the sampling resistor is electrically connected to the input end of the sampling unit in the constant current control circuit and the cathode of the freewheeling diode, and the second end of the sampling resistor is electrically connected to the sampling end of the sampling unit and the input end of the light emitting unit;

[0034] The output end of the light emitting unit is electrically connected to the first end of the inductor;

[0035] The second end of the inductor is electrically connected to the anode of the freewheeling diode and the first end of the power tube;

[0036] The control end of the power tube is electrically connected to the output end of the driving unit in the constant current control circuit, and the second end of the power tube is electrically connected to the ground end.

[0037] In one possible implementation, an input capacitor and an output capacitor are also included;

[0038] The first end of the input capacitor is electrically connected to the first end of the sampling resistor, and the second end of the input capacitor is electrically connected to the ground end;

[0039] The first end of the output capacitor is electrically connected to the input end of the light emitting unit, and the second end of the output capacitor is electrically connected to the output end of the light emitting unit.

[0040] The beneficial effects of the utility model are as follows:

[0041] The utility model provides a constant current control circuit and a constant current control system, wherein a shutdown control unit compares a first sampling voltage and a shutdown reference voltage, outputs a shutdown control signal, and if the first sampling voltage is greater than the shutdown reference voltage, a driving unit outputs a driving signal for controlling the power tube to be disconnected according to the shutdown control signal, thereby causing the inductor current to drop, ensuring that no overshoot current occurs during startup, thereby solving the problem of overcharging during startup; an opening control unit receives the first sampling voltage, the second sampling voltage and the constant current reference voltage, outputs an opening control signal, and if the first sampling voltage is less than the constant current reference voltage, the driving unit outputs a driving signal for controlling the power tube to be turned on according to the opening control signal, thereby causing the inductor current to rise, and in each cycle, the opening control unit integrates the difference between the first sampling voltage signal and the constant current reference voltage to obtain a compensation voltage, and performs real-time adjustment by comparing the compensation voltage with the second sampling voltage, thereby improving the accuracy of the constant current. The compensation voltage represents the difference between the actual current and the preset constant current reference in each cycle. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0043] Figure 1 A structural schematic diagram of a constant current control system provided by an embodiment of the utility model;

[0044] Figure 2 A structural schematic diagram of a constant current control circuit provided by an embodiment of the utility model;

[0045] Figure 3 A structural schematic diagram of a constant current control circuit provided by an embodiment of the utility model;

[0046] Figure 4 It is a peak current control waveform diagram;

[0047] Figure 5 It is a hysteresis control waveform diagram;

[0048] Figure 6 A waveform diagram of a constant current control circuit provided in an embodiment of the utility model. DETAILED DESCRIPTION

[0049] In order to make the purpose, technical solution and advantages of the utility model clearer, the utility model will be further described in detail below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the utility model, not all of the embodiments. Based on the embodiments of the utility model, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the utility model.

[0050] In the description of the embodiments of the present application, the terms "first" and "second" are used for descriptive purposes only and should not be understood as suggesting or implying relative importance or implicitly indicating the number of technical features indicated. Thus, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features.

[0051] With the rapid development of electronic products, the requirements for LED constant current control are getting higher and higher, requiring higher performance and more perfect internal protection current, while having better conversion efficiency. In related technologies, LED constant current control usually adopts hysteresis control. For example, by setting the turn-on reference voltage and the turn-off reference voltage at 20% above and below the reference value, the sampling voltage is obtained by collecting the voltage across the sampling resistor, and the turn-off control signal is output by comparing the sampling voltage and the turn-off reference voltage, and the turn-on control signal is output by comparing the sampling voltage and the turn-on reference voltage. The inductor current is continuously charged and discharged within the current range corresponding to the turn-on reference voltage and the turn-off reference voltage, thereby obtaining a constant output current. However, since this method does not have feedback regulation, the accuracy of the constant current obtained is low.

[0052] Based on the above problems, the present invention provides a constant current control system, such as Figure 1 As shown, the constant current control system includes a sampling resistor RCS, a light-emitting unit LED1, an inductor L, a power tube M0, a freewheeling diode D and a constant current control circuit 101;

[0053] The first end of the sampling resistor RCS is electrically connected to the input end VIN of the sampling unit in the constant current control circuit 101 and the cathode of the freewheeling diode D, and the second end of the sampling resistor RCS is electrically connected to the sampling end VCS of the sampling unit and the input end of the light emitting unit LED1;

[0054] The output end of the light emitting unit LED1 is electrically connected to the first end of the inductor L;

[0055] The second end of the inductor L is electrically connected to the anode of the freewheeling diode D and the first end of the power tube M0;

[0056] The control end of the power tube M0 is electrically connected to the output end GATE of the driving unit in the constant current control circuit, and the second end of the power tube M0 is electrically connected to the ground end.

[0057] like Figure 1 As shown, the constant current control provided by the embodiment of the utility model further includes an input capacitor Cin and an output capacitor Cout;

[0058] A first end of the input capacitor Cin is electrically connected to a first end of the sampling resistor RCS, and a second end of the input capacitor Cin is electrically connected to a ground end;

[0059] A first end of the output capacitor Cout is electrically connected to an input end of the light emitting unit LED1 , and a second end of the output capacitor Cout is electrically connected to an output end of the light emitting unit LED1 .

[0060] In the embodiment of the utility model, the input terminal VIN of the constant current control circuit 101 and the sampling terminal VCS of the constant current control circuit 101 are electrically connected to the two ends of the sampling resistor RCS respectively, and the voltage across the sampling resistor RCS is collected through the input terminal VIN of the constant current control circuit 101 and the sampling terminal VCS of the constant current control circuit 101. The output terminal GATE of the constant current control circuit 101 is electrically connected to the control end of the power tube M0. The driving signal is output through the output terminal GATE of the constant current control circuit 101 to control the opening or disconnection of the power tube M0, thereby controlling the LED1 to light up or stop lighting up.

[0061] like Figure 2 As shown, it is a structural schematic diagram of a constant current control circuit provided by an embodiment of the utility model, from Figure 2 It can be seen that the constant current control circuit includes: a sampling unit 201, a shutdown control unit 203, an opening control unit 204 and a driving unit 205:

[0062] The sampling unit 201 is connected between the input terminal and the sampling terminal, and the sampling unit 201 outputs a first sampling voltage VSAMP1 and a second sampling voltage VSAMP2;

[0063] The shutdown control unit 203 receives the first sampling voltage VSAMP1 and the shutdown reference voltage Vref_off, and outputs a shutdown control signal according to the comparison result of the first sampling voltage VSAMP1 and the shutdown reference voltage Vref_off: when the first sampling voltage VSAMP1 is greater than or equal to the shutdown reference voltage Vref_off, the shutdown control signal is valid, and when the first sampling voltage VSAMP1 is less than the shutdown reference voltage Vref_off, the shutdown control signal is invalid;

[0064] The opening control unit 204 receives the first sampling voltage VSAMP1, the second sampling voltage VSAMP2 and the constant current reference voltage Vref1, and outputs an opening control signal: when the first sampling voltage VSAMP1 is less than the constant current reference voltage Vref1, the opening control signal is valid; when the first sampling voltage VSAMP1 is greater than or equal to the constant current reference voltage Vref1, the opening control signal is invalid;

[0065] The driving unit 205 receives the on control signal and the off control signal, and outputs a driving signal.

[0066] In the utility model, the shutdown control unit 203 compares the first sampling voltage VSAMP1 and the shutdown reference voltage Vref_off, and outputs a shutdown control signal. If the first sampling voltage VSAMP1 is greater than or equal to the shutdown reference voltage Vref_off, the driving unit 205 outputs a driving signal for controlling the power tube M0 to be disconnected according to the shutdown control signal, thereby reducing the inductor current, ensuring that there is no overshoot current at startup, and solving the problem of overcharging at startup; the opening control unit 204 receives the first sampling voltage VSAMP1, the second sampling voltage VSAMP2 and the constant current reference voltage Vref1, and outputs an opening control signal. If the first sampling voltage is less than the constant current reference voltage Vref1, the driving unit 205 According to the turn-on control signal, a driving signal for controlling the turn-on of the power tube M0 is output, so that the inductor current increases, and in each cycle, the turn-on control unit 204 integrates and maintains the difference between the first sampling voltage signal VSAMP1 and the constant current reference voltage Vref1 to obtain a compensation voltage Vcomp, compares the compensation voltage Vcomp with the second sampling voltage VSAMP2, and outputs an turn-on control signal to the driving unit to control the action of the power tube M0, wherein the compensation voltage Vcomp represents the difference between the actual current in each cycle and the preset constant current reference, and is adjusted in real time by comparing the compensation voltage Vcomp with the second sampling voltage VSAMP2, thereby improving the accuracy of the constant current.

[0067] Specifically, the embodiment of the present application also includes a reference voltage generating unit 202, which is connected to the input end, receives the input voltage VIN, and outputs a shutdown reference voltage Vref_off and a constant current reference voltage Vref1 according to the input voltage VIN.

[0068] It should be noted that, by comparing the off reference voltage Vref_off with the first sampling voltage VSAMP1, an off control signal is output, and the off control signal limits the upper limit of the inductor current ripple. Therefore, the off reference voltage Vref_off is used to limit the upper limit of the inductor current ripple.

[0069] In a specific implementation, the turn-off reference voltage Vref_off may be a preset ratio M times of the constant current reference voltage Vref1 , where M is a positive number greater than 1, and the preset ratio M may be 1.1-1.2, ie, Vref_off=Vref1*M.

[0070] In addition, the sampling unit 201 in the utility model collects the voltages VIN and VCS across the sampling resistor RCS, calculates the difference between the voltages VIN and VCS across the sampling resistor RCS, outputs the first sampling voltage VSAMP1 according to the product of the first preset coefficient and the voltage difference across the two ends, and outputs the second sampling voltage VSAMP2 according to the product of the second preset coefficient and the voltage difference across the two ends, wherein the first sampling voltage VSAMP1 is less than the second sampling voltage VSAMP2, and when the DC input is about 80V and the constant current is controlled at about 1A, the first preset coefficient can be 3 to 5, and the second preset coefficient can be 6 to 15, and the second coefficient is 2 to 3 times the first coefficient.

[0071] like Figure 3 , which is a schematic diagram of the structure of an opening control unit provided by the utility model. Specifically, the opening control unit 204 includes a first transconductance amplifier 301, a first comparator 302 and a compensation module 303;

[0072] The first input terminal of the first transconductance amplifier 301 inputs the first sampling voltage VSAMP1, the second input terminal of the first transconductance amplifier 301 inputs the constant current reference voltage Vref1, and the output terminal of the first transconductance amplifier 301 outputs the compensation voltage Vcomp;

[0073] The compensation module 303 is connected between the output terminal of the first transconductance amplifier 301 and the ground terminal, and is used to integrate the difference between the first sampling voltage VSAMP1 input by the first transconductance amplifier 301 and the constant current reference voltage Vref1 to obtain a compensation voltage Vcomp;

[0074] The first input terminal of the first comparator 302 inputs the compensation voltage Vcomp, the second input terminal of the first comparator 302 inputs the second sampling voltage VSAMP2, and the output terminal of the first comparator 302 outputs the turn-on control signal.

[0075] In a specific embodiment, the first input terminal of the first transconductance amplifier 301 inputs the first sampling voltage VSAMP1; the second input terminal of the first transconductance amplifier 301 inputs the constant current reference voltage Vref1, the first transconductance amplifier 301 performs a difference integration on the first sampling voltage VSAMP1 and the constant current reference voltage Vref1, and the output terminal of the first transconductance amplifier 301 outputs the compensation voltage Vcomp, wherein the first input terminal of the first transconductance amplifier 301 is the negative input terminal of the first transconductance amplifier 301, and the second input terminal of the first transconductance amplifier 301 is the positive input terminal of the first transconductance amplifier 301;

[0076] The compensation voltage Vcomp is input to the first input terminal of the first comparator 302, and the second sampling voltage VSAMP2 is input to the second input terminal of the first comparator 302. The first comparator 302 compares the compensation voltage Vcomp with the second sampling voltage VSAMP2. If the compensation voltage Vcomp is greater than the second sampling voltage VSAMP2, the turn-on control signal output from the output terminal of the first comparator 302 is a high level, and the driving unit 205 outputs a driving signal for controlling the power tube M0 to turn on according to the input high level turn-on control signal. The first input terminal of the first comparator 302 is the positive input terminal of the first input terminal of the first comparator 302, and the second input terminal of the first comparator 302 is the negative input terminal of the first comparator 302.

[0077] The compensation module 303 is connected between the output terminal of the first transconductance amplifier 301 and the ground terminal. The compensation module 303 is used to integrate and hold the difference signal input by the first transconductance amplifier 301 to obtain a compensation voltage Vcomp.

[0078] It should be noted that the compensation module 303 includes a first capacitor C1 and a first resistor R1:

[0079] A first end of the first resistor R1 is connected to the output end of the first transconductance amplifier 301, and a second end of the first resistor R1 is electrically connected to a first end of the first capacitor C1;

[0080] The second end of the first capacitor C1 is connected to the ground.

[0081] The first resistor R1 and the first capacitor C1 in the embodiment of the utility model integrate and maintain the difference between the first sampling signal VSAMP1 input to the operational amplifier and the constant current reference voltage Vref1 to obtain the compensation voltage Vcomp. Selecting appropriate resistor R1 and capacitor C1 can ensure the accuracy of the operational amplifier and the speed of the loop response.

[0082] In addition, if Figure 3 As shown in the shutdown control unit 203, the shutdown control unit 203 includes a second comparator 401;

[0083] The first sampling voltage VSAMP1 is input to the first input terminal of the second comparator 401, the off reference voltage Vref_off is input to the second input terminal of the second comparator 401, and the off control signal is output to the output terminal of the second comparator 401. The first input terminal of the second comparator 401 is the positive input terminal of the second comparator 401, and the second input terminal of the second comparator 401 is the negative input terminal of the second comparator 401.

[0084] In a specific embodiment, the first input terminal of the second comparator 401 inputs the first sampling voltage VSAMP1; the second input terminal of the second comparator 401 inputs the shutdown reference voltage Vref_off; the output terminal of the second comparator 401 outputs a shutdown control signal. If the first sampling voltage VSAMP1 is greater than or equal to the shutdown reference voltage Vref_off, the shutdown control signal output by the second comparator 401 is a high level, and the driving unit outputs a driving signal for controlling the shutdown of the power tube according to the input high level shutdown control signal.

[0085] In one embodiment, if Figure 3 As shown in the sampling unit 201, the sampling unit 201 includes a second transconductance amplifier 501, a second resistor R2 and a third resistor R3;

[0086] The sampling unit 201 is connected to two ends of the sampling resistor, the first end of the sampling resistor is the input end VIN, and the second end of the sampling resistor is the sampling end VCS;

[0087] A first input terminal of the second transconductance amplifier 501 is connected to the input terminal VIN, a second input terminal of the second transconductance amplifier 501 is connected to the sampling terminal VCS, an output terminal of the second transconductance amplifier 501 is connected to the first terminal of the second resistor R2, and outputs a second sampling voltage VSAMP2;

[0088] The second end of the second resistor R2 is electrically connected to the first end of the third resistor R3, and outputs a first sampling voltage VSAMP1;

[0089] The second end of the third resistor R3 is electrically connected to the ground.

[0090] In a specific embodiment, the first input terminal of the second transconductance amplifier 501 inputs a voltage VIN, the second input terminal of the second transconductance amplifier 501 inputs a voltage VCS, the second transconductance amplifier 501 outputs a first sampling voltage VSAMP1 according to the product of the first preset coefficient and the voltage difference between the two ends, and the second transconductance amplifier 501 outputs a second sampling voltage VSAMP2 according to the product of the second preset coefficient and the voltage difference between the two ends, wherein the first preset coefficient and the second preset coefficient are adjusted according to the proportional relationship between the second resistor and the third resistor in the sampling unit, for example, the first preset coefficient can be 3 to 5, and the second preset coefficient can be 6 to 15. It can also be said that the second sampling voltage VSAMP2 is K times the first sampling voltage VSAMP1, K is a positive number greater than 1, and K is generally 2 to 3.

[0091] It should be noted that the first input terminal of the second transconductance amplifier 501 is the positive input terminal of the second transconductance amplifier 501 , and the second input terminal of the second transconductance amplifier 501 is the negative input terminal of the second transconductance amplifier 501 .

[0092] In one embodiment, if Figure 3 As shown in the reference voltage generating unit 202, the reference voltage generating unit 202 includes a voltage reduction module 601 and a voltage dividing module 602;

[0093] The voltage reduction module 601 is connected between the input terminal and the voltage dividing module 602, receives the input voltage VIN, reduces the voltage of the input voltage VIN, and outputs a first voltage;

[0094] The voltage dividing module 602 receives the first voltage, divides the first voltage, and outputs a turn-off reference voltage Vref_off and a constant current reference voltage Vref1 .

[0095] In a specific embodiment, the buck module 601 may be a JFET tube or a LDO structure.

[0096] It should be noted that the voltage divider module 602 includes a fourth resistor R4, a fifth resistor R5 and a sixth resistor R6; the fourth resistor R4, the fifth resistor R5 and the sixth resistor R6 are connected in sequence between the step-down module 601 and the ground terminal, and the connection node between the fourth resistor R4 and the fifth resistor R5 outputs the shutdown reference voltage Vref_off, and the connection node between the fifth resistor R5 and the sixth resistor R6 outputs the constant current reference voltage Vref1.

[0097] In a specific embodiment, the voltage reduction module 601 is used as the input terminal of the reference voltage generating unit 202 to input the input voltage VIN, the connection node of the fourth resistor R4 and the fifth resistor R5 is used as the first output terminal of the reference voltage generating unit 202 to output the off reference voltage Vref_off, and the connection node of the fifth resistor R5 and the sixth resistor R6 is used as the second output terminal of the reference voltage generating unit 202 to output the constant current reference voltage Vref1. According to the proportional relationship between the resistance values ​​of the fourth resistor R4, the fifth resistor R5 and the sixth resistor R6, the proportional relationship M between the off reference voltage Vref_off and the constant current reference voltage Vref1 can be adjusted, and M is a positive number greater than 1, and M can be 1.1-1.2, that is, Vref_off=Vref1*M.

[0098] In one embodiment, if Figure 3 As shown in the driving unit 205, the driving unit 205 includes a trigger 701, a first inverter 702, a first switch tube Q1 and a second switch tube Q2;

[0099] The reset terminal of the trigger 701 inputs a shutdown control signal, the set terminal of the trigger 701 inputs an on control signal, and the output terminal of the trigger 701 is connected to the input terminal of the first inverter 702 and the control terminal of the first switch tube Q1;

[0100] The output end of the first inverter 702 is electrically connected to the control end of the second switch tube Q2;

[0101] A first end of the first switch tube Q1 is electrically connected to the power supply end, and a second end of the second switch tube Q2 is electrically connected to the ground end;

[0102] A connection node between the second end of the first switch tube Q1 and the first end of the second switch tube Q2 outputs a driving signal. In the above specific embodiment, both the first switch tube Q1 and the second switch tube Q2 are NMOS.

[0103] It should be noted that the description of the circuit implementation method related to the above-mentioned driving unit 205 is a description of the preferred embodiment of the present application. It should be understood that the description here is only used to illustrate and explain the present application, and is not used to limit the present application, nor is it used to limit the specific circuit and connection method of the driving unit 205, and in possible implementation methods, it may be other types of switching tubes.

[0104] In addition, the first end of the first switch tube Q1 is the source of the first switch tube Q1, the second end of the first switch tube Q1 is the drain of the first switch tube Q1, and the control end of the first switch tube Q1 is the gate of the first switch tube Q1; the first end of the second switch tube Q2 is the source of the second switch tube Q2, the second end of the second switch tube Q2 is the drain of the second switch tube Q2, and the control end of the second switch tube Q2 is the gate of the second switch tube Q2.

[0105] In a specific embodiment, when the constant current control system is started, the first sampling voltage VSAMP1 is less than the constant current reference voltage Vref1, the turn-on control signal is high level, and the turn-off control signal is low level, so the output end of the trigger 701 is high level, the first switch tube Q1 is turned on, and the second switch tube Q2 is turned off, and the corresponding output drive signal controls the power tube M0 to turn on; thereafter, the first sampling voltage VSAMP1 is greater than or equal to the constant current reference voltage Vref1, and is less than the turn-off reference voltage Vref_off, the turn-on control signal flips to a low level, and the turn-off control signal is a low level. Since the output end of the trigger 701 maintains a high level at this time, the corresponding output drive signal The power tube M0 is turned on by the corresponding signal; until the current rises to the point where the corresponding first sampling voltage VSAMP1 is greater than the turn-off reference voltage Vref_off, the turn-off control signal is flipped to a high level, and the turn-on control signal remains at a low level, so the output end of the trigger 701 is at a low level, the first switch tube Q1 is turned off, and the second switch tube Q2 is turned on, and the corresponding output drive signal controls the power tube M0 to turn off; the current starts to decrease, the turn-off control signal is flipped to a low level, and the turn-on control signal is flipped to a high level, so the output end of the trigger 701 is at a high level, and the corresponding output drive signal controls the power tube M0 to turn on. In the specific implementation, the above steps are repeated to finally obtain a stable current.

[0106] In addition, the constant current control circuit of the present invention is applied in a constant current control system. Since the control unit is turned on in each cycle, it will make a difference between the constant current reference voltage Vref1 representing the constant current target value and the first sampling voltage VS AMP1 to obtain the compensation voltage Vcomp, and compare the second sampling voltage VSAMP2 with the compensation voltage Vcomp to control the conduction of the power tube M0, thereby realizing feedback regulation of the output current. Therefore, the output current of the constant current control system of the present invention is stable and has high accuracy, and there will be no large constant current point offset.

[0107] On the other hand, since the shutdown control unit compares the first sampling voltage VSAMP1 with the shutdown reference voltage Vref_off, when the sampling voltage representing the inductor current exceeds the shutdown reference voltage, the power tube M0 is controlled to be shut down to reduce the inductor current, that is, the upper limit value of the inductor current ripple is limited. Therefore, the constant current control system of the utility model will not generate a large overshoot current at startup, thereby solving the problem of overcharging at startup.

[0108] It should be noted that if Figure 4 As shown in FIG. 1 , it is a peak current control waveform diagram, and there is an overshoot phenomenon at the initial startup; Figure 5 As shown, it is a hysteresis control waveform diagram, by setting the turn-on reference voltage and the turn-off reference voltage at 20% above and below the constant current target value respectively. However, since this method has no feedback adjustment, the actual current will deviate from the constant current target value, so the accuracy of the constant current obtained is low.

[0109] like Figure 6 As shown, it is a waveform diagram of the constant current control circuit of the utility model. The shutdown control unit outputs a shutdown control signal by comparing the first sampling voltage VSAMP1 and the shutdown reference voltage Vref_off. The driving unit outputs a driving signal for controlling the power tube M0 to be disconnected according to the shutdown control signal, thereby reducing the inductor current. Therefore, no overshoot current occurs at startup, and in each cycle, the start-up control unit compares the difference between the compensation voltage Vcomp and the constant current reference voltage Vref1, and performs feedback adjustment on the compensation voltage Vcomp according to the difference comparison result, thereby improving the accuracy of the constant current.

[0110] It should be noted that the turn-off reference voltage Vref_off represents the upper limit value of the inductor current in the constant current control system, and the inductor current does not exceed the upper limit value of the inductor current corresponding to the turn-off reference voltage Vref_off.

[0111] Based on the same utility model concept, the embodiment of the present application also provides a constant current control method, which is similar in principle to the above-mentioned constant current control circuit, and the repeated parts will not be repeated.

[0112] A constant current control method provided by an embodiment of the utility model is applied to any of the above-mentioned LED constant current control systems, and the method comprises the following steps:

[0113] In step 1, the sampling unit 201 collects the voltage across the sampling resistor RCS, calculates the voltage difference across the sampling resistor RCS, outputs a first sampling voltage VSAMP1 based on the voltage difference across the sampling resistor RCS and based on a first preset coefficient, and outputs a second sampling voltage VSAMP2 based on the voltage difference across the sampling resistor RCS and based on a second preset coefficient.

[0114] Step 2, the reference voltage generating unit 202 inputs the voltage VIN of the first end of the sampling resistor RCS, outputs the constant current reference voltage Vref1, and calculates the turn-off reference voltage Vref_off based on the preset ratio and the constant current reference voltage Vref1.

[0115] Step 3: The shutdown control unit 203 compares the first sampling voltage VSAMP1 with the shutdown reference voltage Vref_off, and outputs a shutdown control signal.

[0116] Step 4, the opening control unit 204 integrates the difference between the first sampling voltage VSAMP1 and the constant current reference voltage Vref1 to obtain a compensation voltage Vcomp, compares the difference compensation voltage Vcomp with the second sampling voltage VSAMP2, and outputs an opening control signal.

[0117] Step 5, the driving unit 205 inputs a shut-off control signal and an on control signal, and outputs a driving signal for controlling the power tube M0 to be turned on or off.

[0118] The constant current control method provided by the embodiment of the utility model, in the constant current control circuit, collects the voltage across the sampling resistor through the sampling unit, calculates the difference of the voltage across the sampling resistor, outputs the first sampling voltage according to the difference of the voltage across the sampling resistor according to the first preset coefficient, and outputs the second sampling voltage according to the second preset coefficient. The voltage at the first end of the sampling resistor is input through the reference voltage generating unit, and the constant current reference voltage is output, and the shutdown reference voltage obtained by calculating the preset ratio and the constant current reference voltage is output. The first sampling voltage and the shutdown reference voltage are compared by the shutdown control unit, and the shutdown control signal is output. The first sampling voltage and the constant current reference voltage are integrated by the opening control unit to obtain the compensation voltage, and the compensation voltage is compared with the second sampling voltage to output the opening control signal. Finally, the driving unit outputs the driving signal for controlling the power tube to be turned on or off.

[0119] Among them, the shutdown reference voltage in the utility model is used to limit the upper limit of the ripple of the inductor current. The shutdown control unit compares the first sampling voltage and the shutdown reference voltage, and outputs a shutdown control signal. If the first sampling voltage is greater than the shutdown reference voltage, the driving unit outputs a driving signal for controlling the power tube to be disconnected according to the shutdown control signal, thereby reducing the inductor current and ensuring that there is no overshoot current at startup; the opening control unit receives the first sampling voltage, the second sampling voltage and the constant current reference voltage, and outputs an opening control signal. If the first sampling voltage is less than the constant current reference voltage, the driving unit outputs a driving signal for controlling the power tube to be turned on according to the opening control signal, thereby increasing the inductor current, and in each cycle, the opening control unit integrates the difference between the first sampling voltage signal and the constant current reference voltage to obtain a compensation voltage, and performs real-time adjustment by comparing the compensation voltage with the second sampling voltage, thereby improving the accuracy of the constant current. Among them, the compensation voltage Vcomp represents the difference between the actual current and the preset constant current reference in each cycle.

[0120] Those skilled in the art may make various modifications and variations to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is intended to include these modifications and variations.

Claims

1. A constant current control circuit, characterized in that: include: Sampling unit, shutdown control unit, opening control unit and drive unit: The sampling unit is connected between the input terminal and the sampling terminal, and the sampling unit outputs a first sampling voltage and a second sampling voltage; The shutdown control unit receives the first sampling voltage and the shutdown reference voltage, and outputs a shutdown control signal according to a comparison result between the first sampling voltage and the shutdown reference voltage: when the first sampling voltage is greater than or equal to the shutdown reference voltage, the shutdown control signal is valid, and when the first sampling voltage is less than the shutdown reference voltage, the shutdown control signal is invalid; The opening control unit receives the first sampling voltage, the second sampling voltage and the constant current reference voltage, and outputs an opening control signal: when the first sampling voltage is less than the constant current reference voltage, the opening control signal is valid, and when the first sampling voltage is greater than or equal to the constant current reference voltage, the opening control signal is invalid; The driving unit receives the on control signal and the off control signal, and outputs a driving signal.

2. The circuit according to claim 1, characterized in that It also includes a reference voltage generating unit, which is connected to the input terminal, receives an input voltage, and outputs a shutdown reference voltage and a constant current reference voltage according to the input voltage.

3. The circuit according to claim 1, characterized in that The opening control unit includes a first transconductance amplifier, a first comparator and a compensation module; The first sampling voltage is input into a first input terminal of the first transconductance amplifier, the constant current reference voltage is input into a second input terminal of the first transconductance amplifier, and a compensation voltage is output from an output terminal of the first transconductance amplifier; The compensation module is connected between the output terminal of the first transconductance amplifier and the ground terminal, and is used for integrating the difference between the first sampling voltage input by the first transconductance amplifier and the constant current reference voltage to obtain a compensation voltage; The compensation voltage is input into a first input terminal of the first comparator, the second sampling voltage is input into a second input terminal of the first comparator, and the turn-on control signal is output from an output terminal of the first comparator.

4. The circuit according to claim 1, characterized in that The shutdown control unit includes a second comparator; The first sampling voltage is input into a first input terminal of the second comparator, the shutdown reference voltage is input into a second input terminal of the second comparator, and the shutdown control signal is output from an output terminal of the second comparator.

5. The circuit according to claim 1, characterized in that The sampling unit includes a second transconductance amplifier, a second resistor and a third resistor; The sampling unit is connected to two ends of the sampling resistor, the first end of the sampling resistor is the input end, and the second end of the sampling resistor is the sampling end; The first input terminal of the second transconductance amplifier is connected to the input terminal, the second input terminal of the second transconductance amplifier is connected to the sampling terminal, the output terminal of the second transconductance amplifier is connected to the first terminal of the second resistor, and outputs the second sampling voltage; The second end of the second resistor is electrically connected to the first end of the third resistor, and outputs the first sampling voltage; The second end of the third resistor is electrically connected to the ground end.

6. The circuit according to claim 2, characterized in that The reference voltage generating unit includes a voltage step-down module and a voltage dividing module; The voltage reduction module is connected between the input terminal and the voltage dividing module, receives the input voltage, reduces the input voltage, and outputs a first voltage; The voltage division module receives the first voltage, divides the first voltage, and outputs the shutdown reference voltage and the constant current reference voltage.

7. The circuit according to claim 1, characterized in that The driving unit includes a trigger, a first inverter, a first switch tube and a second switch tube; The reset end of the trigger inputs the shutdown control signal, the set end of the trigger inputs the startup control signal, and the output end of the trigger is connected to the input end of the first inverter and the control end of the first switch tube; The output end of the first inverter is connected to the control end of the second switch tube; The first switch tube and the second switch tube are connected between a power supply terminal and a ground terminal; The first end of the first switch tube is connected to the power supply end, the second end of the second switch tube is connected to the ground end, and a connection node between the second end of the first switch tube and the first end of the second switch tube outputs the driving signal.

8. The circuit according to claim 1, characterized in that The shutdown reference voltage represents an upper limit value of the inductor current in a constant current control system, and the inductor current does not exceed the upper limit value of the inductor current corresponding to the shutdown reference voltage.

9. A constant current control system, characterized in that: It comprises a sampling resistor, a light-emitting unit, an inductor, a power tube, a freewheeling diode and a constant current control circuit as claimed in any one of claims 1 to 8; The first end of the sampling resistor is electrically connected to the input end of the sampling unit in the constant current control circuit and the cathode of the freewheeling diode, and the second end of the sampling resistor is electrically connected to the sampling end of the sampling unit and the input end of the light emitting unit; The output end of the light emitting unit is electrically connected to the first end of the inductor; The second end of the inductor is electrically connected to the anode of the freewheeling diode and the first end of the power tube; The control end of the power tube is electrically connected to the output end of the driving unit in the constant current control circuit, and the second end of the power tube is electrically connected to the ground end.

10. The system according to claim 9, characterized in that It also includes input and output capacitors; The first end of the input capacitor is electrically connected to the first end of the sampling resistor, and the second end of the input capacitor is electrically connected to the ground end; The first end of the output capacitor is electrically connected to the input end of the light emitting unit, and the second end of the output capacitor is electrically connected to the output end of the light emitting unit.

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