DC linear constant current mode constant current chip

Abstract

The application discloses a DC linear constant-current mode constant-current chip, and belongs to the technical field of chip linear constant-current, in particular to a DC power supply linear constant-current mode constant-current chip with reverse connection protection, input overvoltage protection and voltage and current clamping. The DC linear constant-current mode constant-current chip is composed of a PMOS reverse connection protection circuit, an internal power supply circuit of a three-terminal voltage regulator, a voltage and current clamping switch constant-current circuit and an overvoltage protection circuit. The linear constant-current chip adopts the PMOS as the reverse connection protection circuit, adopts the three-terminal voltage regulator to supply power to the internal operational amplifier circuit, adopts the voltage and current clamping switch constant-current circuit composed of the operational amplifier and a switch device, and adopts the overvoltage protection circuit composed of the operational amplifier and a triode, so that the relatively high-precision constant-current effect of the LED lamp strip / LED hard light bar is realized, and the problem of the brightness difference between the head and the tail of the LED lamp strip / LED hard light bar caused by the voltage drop of the copper sheet of the PCB when the LED lamp strip / LED hard light bar is connected in length is solved.

Description

Technical Field

[0001] This invention relates to the field of negative pressure cleaning device technology, specifically a DC linear constant current mode constant current chip. Background Technology

[0002] Traditional LED strips / rigid LED strips use resistor-based constant current. When multiple LED strips / rigid LED strips are connected together, a significant brightness difference occurs between the beginning and end of the strip due to the voltage drop across the copper foil on the PCB board.

[0003] Traditional LED strips / rigid LED strips all use constant voltage switching power supplies, which are characterized by providing a relatively constant output voltage to the LED strips / rigid LED strips. The first LED strip / rigid LED strip, such as... Figure 1 as well as Figure 2 As shown, the output voltage of the switching power supply is named V0, the supply voltage of the LED strip / LED rigid light strip is named V1, and the output current is named I1. The supply voltage of the first connected LED strip / LED rigid light strip is V1 = V0. The LED bead is equivalent to a constant voltage device. The sum of the voltages of all LED beads connected in series is named V2, the current flowing through the LED bead is named I2, the voltage across resistor R1 is named V3, and the current flowing through resistor R1 is named I3. Then V3 = V1 - V2 = V0 - V2, I3 = V3 / R1. According to the principle that the current in a series circuit is equal, I1 = I2 = I3. When multiple LED strips / LED rigid light strips are connected in parallel and extended, such as... Figure 2 As shown, the first and last LED strips / rigid LED light bars experience a significant voltage difference due to voltage drop across the copper foil on the PCB board. This voltage difference is named V4. Therefore, the supply voltage of the last LED strip / rigid LED light bar is V1 = V0 - V4. The voltage across resistor R1 on the last LED strip / rigid LED light bar is V3 = V1 - V2 = V0 - V4 - V2. Consequently, the current I3 flowing through resistor R1 decreases, and the current I2 flowing through the LEDs on the last LED strip / rigid LED light bar decreases, resulting in a significant brightness difference between the first and last LED strips / rigid LED light bars. Summary of the Invention

[0004] The purpose of this invention is to provide a DC linear constant current mode constant current chip to solve the problem of brightness difference between the beginning and end of LED light strips / LED rigid light strips when they are used in extended applications due to the voltage drop of the copper foil on the PCB board.

[0005] To achieve the above objectives, the present invention provides the following technical solution: a DC linear constant current mode constant current chip, comprising a reverse connection protection circuit to prevent reverse connection of the circuit, wherein the input terminal of the reverse connection protection circuit is connected to VDD; an internal operational amplifier power supply circuit, comprising a three-terminal regulator U1, wherein the output terminal of the reverse connection protection circuit is connected to the IN terminal of the three-terminal regulator U1; a voltage and current clamping switch constant current circuit, comprising a ninth resistor R9, a tenth resistor R10, an eleventh resistor R11, a twelfth resistor R12, a thirteenth resistor R13, a third operational amplifier U3, and a control switch; the three-terminal regulator U1 The OUT terminal of the three-terminal regulator U1 is connected to the V+ terminal of the third operational amplifier U3 through the tenth resistor R10. The OUT terminal of the three-terminal regulator U1 is connected to one end of the thirteenth resistor R13 through the ninth resistor R9, and the other end of the thirteenth resistor R13 is grounded. The node between the ninth resistor R9 and the thirteenth resistor R13 outputs a reference voltage signal Vref2 to the + terminal of the third operational amplifier U3. The - terminal of the third operational amplifier U3 is connected to one end of the twelfth resistor R12, and the other end of the twelfth resistor R12 outputs the CS terminal. The OUT terminal of the third operational amplifier U3 is connected to the control switch through the eleventh resistor R11.

[0006] As a further optimization, the control switch is a third transistor Q3, wherein the base of the third transistor Q3 is connected to the eleventh resistor R11, the collector of the third transistor Q3 forms the LED terminal, and the emitter of the third transistor Q3 is grounded through the fifteenth resistor R15.

[0007] As a further optimization, the control switch is a third MOSFET Q3, wherein the gate (G) of the third MOSFET Q3 is connected to the eleventh resistor R11, the drain (D) of the third MOSFET Q3 forms the LED terminal, and the source (S) of the third MOSFET Q3 is grounded through the fifteenth resistor R15.

[0008] As a further optimization, the reverse connection protection circuit includes a first capacitor C1, a first resistor R1, a second resistor R2, and a first MOSFET Q1. One end of the first capacitor C1 is connected to VDD, and the other end is grounded. The drain (D) of the first MOSFET Q1 is connected to VDD, and the gate (G) of the first MOSFET is grounded through the second resistor R2. One end of the first resistor R1 is connected to the gate (G) of the first MOSFET, and the other end is connected to the source (S) of the first MOSFET. The source (S) of the first MOSFET is connected to the IN terminal of the three-terminal regulator U1.

[0009] As a further optimization, an overvoltage protection circuit is also included. This overvoltage protection circuit includes a second operational amplifier U2, a third resistor R3, a fourth resistor R4, a fifth resistor R5, a sixth resistor R6, a seventh resistor R7, an eighth resistor R8, a fourteenth resistor R14, and a second transistor Q2. One end of the third resistor R3 is connected to VDD, and the other end of the third resistor R3 is grounded through the fourth resistor R4. The voltage divider signal A output from the node between the third resistor R3 and the fourth resistor R4 is connected to the positive terminal of the second operational amplifier U2. One end of the fifth resistor R5 is connected to the OUT terminal of the three-terminal regulator U1, and the other end of the fifth resistor R5 is connected to the OUT terminal of the three-terminal regulator U1 through the sixth resistor R6. The reference voltage signal Vref1, located at the node between the fifth resistor R5 and the sixth resistor R6, is connected to the negative terminal of the second operational amplifier U2. The output terminal of the second operational amplifier U2 is connected to the base of the second transistor Q2 through the eighth resistor R8. The emitter of the second transistor Q2 is grounded, and the collector of the second transistor Q2 is connected at the node between the ninth resistor R9 and the thirteenth resistor R13. One end of the seventh resistor R7 is connected to the OUT terminal of the three-terminal regulator U1, and the other end of the seventh resistor R7 is connected to the V+ terminal of the second operational amplifier U2. The V+ terminal of the second operational amplifier U2 is connected to the OUT terminal of the second operational amplifier U2 through the fourteenth resistor R14.

[0010] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0011] By using an operational amplifier to compare the voltage across the CS constant current resistor connected to the sampling switching device, and controlling the switching device to turn on / off in PWM mode, the voltage and current across the CS constant current resistor remain constant under different voltage input conditions, achieving a relatively high-precision constant current purpose. This solves the problem of brightness difference between the beginning and end of LED light strips / LED rigid light strips caused by voltage drop across the copper foil of the PCB board when they are extended.

[0012] The DC linear constant current mode constant current chip of the present invention solves the problem of brightness difference between the beginning and end of LED light strips / LED rigid light strips caused by voltage drop of PCB copper foil when used in extended applications, through a voltage and current clamping switch constant current chip structure composed of operational amplifiers and switching devices. Attached Figure Description

[0013] Figure 1 This is a schematic diagram of a traditional LED strip / LED rigid light bar that uses constant current through resistance.

[0014] Figure 2 This is a schematic diagram of multiple parallel LED light strips / LED rigid light bars that use constant current through resistance.

[0015] Figure 3 This is a block diagram of the chip of the present invention.

[0016] Figure 4This is the internal schematic diagram of the AD62-X chip of this invention.

[0017] Figure 5 This is the internal schematic diagram of the AD63-X chip of this invention.

[0018] Figure 6 This is a detailed explanation of the internal schematic diagram of the AD62-X chip of this invention.

[0019] Figure 7 This is a schematic diagram of multiple parallel LED light strips / LED rigid light bars using the AD62-X chip in this invention.

[0020] Figure 8 This is a schematic diagram of the PMOS reverse connection protection circuit of the present invention.

[0021] Figure 9 This is a schematic diagram of the constant current circuit of the voltage and current clamping switch of the present invention.

[0022] Figure 10 This is a schematic diagram of the LED strip / LED rigid light bar of the operational amplifier voltage and current clamping switch constant current circuit of the present invention.

[0023] Figure 11 This is a schematic diagram of the overvoltage protection circuit composed of operational amplifiers and transistors of the present invention. Detailed Implementation

[0024] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0025] To address the issue of brightness difference between the beginning and end of LED light strips / LED rigid strips caused by voltage drop across the PCB copper foil when they are extended, the following preferred technical solutions are provided:

[0026] A DC linear constant current mode constant current chip includes a reverse connection protection circuit to prevent reverse connection of the circuit, wherein the input terminal of the reverse connection protection circuit is connected to VDD; an internal operational amplifier power supply circuit including a three-terminal regulator U1, wherein the output terminal of the reverse connection protection circuit is connected to the IN terminal of the three-terminal regulator U1; a voltage and current clamping switch constant current circuit including a ninth resistor R9, a tenth resistor R10, an eleventh resistor R11, a twelfth resistor R12, a thirteenth resistor R13, a third operational amplifier U3, and a control switch; the OUT terminal of the three-terminal regulator U1 is connected to the tenth resistor. Resistor R10 is connected to the V+ terminal of the third operational amplifier U3. The OUT terminal of the three-terminal regulator U1 is connected to one end of the thirteenth resistor R13 through the ninth resistor R9, and the other end of the thirteenth resistor R13 is grounded. The node between the ninth resistor R9 and the thirteenth resistor R13 outputs a reference voltage signal Vref2 to the + terminal of the third operational amplifier U3. The - terminal of the third operational amplifier U3 is connected to one end of the twelfth resistor R12, and the other end of the twelfth resistor R12 outputs the CS terminal. The OUT terminal of the third operational amplifier U3 is connected to the control switch through the eleventh resistor R11.

[0027] As a further optimization, the control switch in the AD62-X chip is a third transistor Q3, wherein the base of the third transistor Q3 is connected to the eleventh resistor R11, the collector of the third transistor Q3 forms the LED terminal, and the emitter of the third transistor Q3 is grounded through the fifteenth resistor R15.

[0028] As a further optimization, the control switch in the AD63-X chip is the third MOSFET Q3, where the gate (G) of the third MOSFET Q3 is connected to the eleventh resistor R11, the drain (D) of the third MOSFET Q3 forms the LED terminal, and the source (S) of the third MOSFET Q3 is grounded through the fifteenth resistor R15.

[0029] Depend on Figure 4 Figure 5 It can be seen that the difference between the AD62-X and AD63-X lies in the switching device used for constant current. Since transistors are current-controlled devices, the emitter current and collector current are approximately equal. However, the emitter current actually includes the base current, Iled = Ics + Ib. Therefore, when the AD62-X constant current chip uses a transistor in the op-amp output stage, the output current will have a base current component, resulting in an error. It can also be seen that the higher the transistor's amplification factor, the higher the accuracy of the constant current. MOSFETs are voltage-controlled devices, requiring very little gate current. Iled and Ics can be very close. Compared to the AD62-X constant current chip using a transistor in the op-amp output stage, the AD63-X constant current chip using a MOSFET in the op-amp output stage achieves higher constant current accuracy.

[0030] In the specific embodiments discussed below, the AD62-X chip is used. The principle is the same as that of the AD63-X, so the AD63-X will not be described in detail.

[0031] The voltage and current clamping switch constant current circuit composed of the third operational amplifier U3 and a control switch Q3, such as Figure 9 This route, combined with Figure 7 By analyzing and combining the results, and simplifying the process (first removing the protection circuit), we arrive at the diagram above. Figure 10 The arrow indicates the direction of current flow. Figure 10 The current flows from the switching power supply V+ to the LED, then from the LED to the third transistor Q3, then from the third transistor Q3 to the CS current-limiting resistor R1 (the CS current-limiting resistor R1 is an external resistor and is not an internal component of the chip), and then flows back to the negative terminal V- of the switching power supply, forming a series current loop. Therefore, i1 = i2 = i3. The three-terminal regulator U1 is the power supply for the operational amplifier and the sampling point for the reference voltage signal Vref2. The tenth resistor R10 is the current-limiting resistor for the operational amplifier. A reference voltage signal Vref2 is obtained by sampling through the voltage division ratio of the ninth resistor R9 and the thirteenth resistor R13. The reference voltage signal Vref2 of the AD6X-X constant current chip of this invention is 0.5V. When the LED strip / LED rigid light bar is powered on, the three-terminal regulator U1 outputs a regulated 5V to power the third operational amplifier U3. A 0.5V reference voltage signal Vref2 is obtained by sampling through the voltage division ratio of the ninth resistor R9 and the thirteenth resistor R13, and connected to the positive terminal of the third operational amplifier U3. At this time, a 0.5V voltage difference is formed between the positive and negative terminals of the third operational amplifier U3, and the third operational amplifier U3 outputs a high potential. This potential flows through the current-limiting resistor eleventh resistor R11 to the base of the third transistor Q3, turning Q3 on. After Q3 turns on, the current flows from the switching power supply V+ to the LED bead, then from the LED bead to the collector (C) terminal of the transistor Q3, then from the collector (C) terminal of the transistor Q3 to the emitter (E) terminal of the transistor Q3, then from the emitter (E) terminal of the transistor Q3 to the current-limiting resistor R1, and finally back to the negative terminal V- of the switching power supply, forming a series current loop, and the LED strip / LED rigid light bar lights up.

[0032] When the voltage across the current-limiting resistor R1 rises from 0V to 0.5V, it is connected to the negative terminal of the third operational amplifier U3 through a twelfth current-limiting resistor R12. At this time, the voltage difference between the positive and negative terminals of the third operational amplifier U3 becomes 0V, the third operational amplifier U3 outputs a low potential, and the third transistor Q3 is cut off. Therefore, the high potential voltage V3 across the current-limiting resistor R1 is 0.5V, and the low potential voltage V3 is 0V. The high potential V3 = V1 - V2 - V5 = V0 - V2 - V5 = Vref2 = 0.5V, where V5 is the voltage across the collector and emitter of transistor Q3. The current i3 = i1 = i2 = V3 / R1 = 0.5 / R1. This cycle repeats, achieving the purpose of constant current for the voltage and current clamping switch.

[0033] When multiple LED light strips / LED rigid light bars are connected in parallel and extended, such as Figure 7 As shown, the first and last LED strips / LED rigid strips have a large voltage difference due to the voltage drop of the copper foil on the PCB board. This voltage difference is named V4. At this time, V1 = V0 - V4, so V5 = V1 - V2 - V3 = V0 - V2 - V3 - V4. Since V3 is at a high potential = Vref2 = 0.5V, which is a constant value, and V2 is the sum of the LED voltages, which is also a constant value, the voltage V5 decreases. Therefore, the Ton time of the third transistor Q3 increases, and the Toff time decreases. Since the high potential of V3 = Vref2 = 0.5V, the current i3 = i1 = i2 = V3 / R1 = 0.5 / R1. Therefore, it can be seen that the voltage drop across the PCB copper foil only changes the voltage V5 across the collector and emitter terminals of transistor Q3 and the times of Ton and Toff. The current is not affected by the voltage drop across the PCB copper foil when LED strips / rigid LED strips are extended. The current of the first and last LED strips / rigid LED strips is exactly the same, thus solving the problem of brightness difference between the beginning and end of LED strips / rigid LED strips caused by the voltage drop across the PCB copper foil when they are extended.

[0034] As a further optimization, the reverse connection protection circuit includes a first capacitor C1, a first resistor R1, a second resistor R2, and a first MOSFET Q1. One end of the first capacitor C1 is connected to VDD, and the other end is grounded. The drain (D) of the first MOSFET Q1 is connected to VDD, and the gate (G) of the first MOSFET is grounded through the second resistor R2. One end of the first resistor R1 is connected to the gate (G) of the first MOSFET, and the other end is connected to the source (S) of the first MOSFET. The source (S) of the first MOSFET is connected to the IN terminal of the three-terminal regulator U1.

[0035] The reverse connection protection circuit is a PMOS reverse connection protection circuit, such as... Figure 8As shown, when the input voltage V0's VDD and GND are not reversed, the input voltage V0 reaches the source (S) through the first MOSFET Q1, specifically a PMOS transistor (hereinafter referred to as the PMOS transistor Q1). The body diode (the drain-source junction is not yet conducting) inside Q1 is approximately V0 - 0.7V. At this time, Ugs = negative voltage (V - 0.7V), and the PMOS transistor Q1 conducts (the drain-source junction is conducting). The internal body diode is short-circuited, and the current flows entirely through the drain-source junction. After the PMOS transistor Q1 conducts, the internal resistance between the drain and source junctions is very small, and the resulting voltage drop is negligible. Therefore, V0 is approximately equal to V1. The first resistor R1 and the second resistor R2 form a bias circuit, and the first capacitor C1 acts as a soft-start circuit. When the input voltage V0's VDD and GND are reversed, the source (G) is at a high level, Ugs > 0, and the PMOS transistor Q1 will not conduct, thus providing reverse connection protection.

[0036] As a further optimization, an overvoltage protection circuit is also included. This overvoltage protection circuit includes a second operational amplifier U2, a third resistor R3, a fourth resistor R4, a fifth resistor R5, a sixth resistor R6, a seventh resistor R7, an eighth resistor R8, a fourteenth resistor R14, and a second transistor Q2. One end of the third resistor R3 is connected to VDD, and the other end of the third resistor R3 is grounded through the fourth resistor R4. The voltage divider signal A output from the node between the third resistor R3 and the fourth resistor R4 is connected to the positive terminal of the second operational amplifier U2. One end of the fifth resistor R5 is connected to the OUT terminal of the three-terminal regulator U1, and the other end of the fifth resistor R5 is connected to the OUT terminal of the three-terminal regulator U1 through the sixth resistor R6. The reference voltage signal Vref1, located at the node between the fifth resistor R5 and the sixth resistor R6, is connected to the negative terminal of the second operational amplifier U2. The output terminal of the second operational amplifier U2 is connected to the base of the second transistor Q2 through the eighth resistor R8. The emitter of the second transistor Q2 is grounded, and the collector of the second transistor Q2 is connected at the node between the ninth resistor R9 and the thirteenth resistor R13. One end of the seventh resistor R7 is connected to the OUT terminal of the three-terminal regulator U1, and the other end of the seventh resistor R7 is connected to the V+ terminal of the second operational amplifier U2. The V+ terminal of the second operational amplifier U2 is connected to the OUT terminal of the second operational amplifier U2 through the fourteenth resistor R14.

[0037] The overvoltage protection circuit of this application, such as Figure 11As shown, the dashed line encloses the overvoltage protection and power supply circuits composed of operational amplifiers and transistors. The three-terminal regulator U1 is the sampling point for the operational amplifier power supply and the reference voltage signal Vref1. The second operational amplifier U2 acts as a voltage comparator in this circuit. The seventh resistor R7 is the current-limiting resistor for the operational amplifier power supply. A reference voltage signal Vref1 is obtained by sampling through the voltage division ratio of the fifth resistor R5 and the sixth resistor R6 and connected to the negative terminal of the second operational amplifier U2. The reference voltage signal Vref1 of the AD62-X constant current chip of this invention is 3V. The third resistor R3 and the fourth resistor R4 form a voltage division ratio signal A, which is connected to the positive terminal of the second operational amplifier U2. When the input voltage is lower than the maximum voltage set by the AD62-X constant current chip, the voltage division ratio signal A is less than 3V, the second operational amplifier U2 outputs a low potential, the second transistor Q2 is cut off, the subsequent voltage and current clamping switch constant current circuit works normally, and the LED strip / LED rigid light strip works normally. When the input voltage exceeds the maximum voltage set by the AD6X-X constant current chip, the voltage divider ratio signal A is greater than 3V. The second operational amplifier U2 continuously outputs a high potential, which flows through the current-limiting resistor R8 to the base of the second transistor Q2. The second transistor Q2 remains in the on state, and the second transistor Q2 short-circuits the positive terminal of the third operational amplifier U3 to GND. The voltage between the positive and negative terminals of the third operational amplifier U3 is 0V, and the output of the third operational amplifier U3 remains at a low potential. The third transistor Q3 remains in the off state, and the LED strip / LED rigid light bar does not work, thus achieving the overvoltage protection function.

[0038] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0039] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A DC linear constant current mode constant current chip, characterized in that: It includes a reverse connection protection circuit to prevent reverse wiring, wherein the input terminal of the reverse connection protection circuit is connected to VDD; an internal operational amplifier power supply circuit, including a three-terminal regulator U1, wherein the output terminal of the reverse connection protection circuit is connected to the IN terminal of the three-terminal regulator U1; a voltage and current clamping switch constant current circuit, including a ninth resistor R9, a tenth resistor R10, an eleventh resistor R11, a twelfth resistor R12, a thirteenth resistor R13, a third operational amplifier U3, and a control switch; the OUT terminal of the three-terminal regulator U1 is connected to the third operational amplifier U3 through the tenth resistor R10. The V+ terminal of op-amp U3 is connected to the OUT terminal of the three-terminal regulator U1. The OUT terminal of the three-terminal regulator U1 is connected to one end of the thirteenth resistor R13 through the ninth resistor R9, and the other end of the thirteenth resistor R13 is grounded. The node between the ninth resistor R9 and the thirteenth resistor R13 outputs a reference voltage signal Vref2 to the + terminal of the third op-amp U3. One terminal of the third op-amp U3 is connected to one end of the twelfth resistor R12, and the other end of the twelfth resistor R12 outputs the CS terminal. The OUT terminal of the third op-amp U3 is connected to the control switch through the eleventh resistor R11. It also includes an overvoltage protection circuit, which comprises a second operational amplifier U2, a third resistor R3, a fourth resistor R4, a fifth resistor R5, a sixth resistor R6, a seventh resistor R7, an eighth resistor R8, a fourteenth resistor R14, and a second transistor Q2. One end of the third resistor R3 is connected to VDD, and the other end is grounded through the fourth resistor R4. The voltage divider signal A output from the node between the third resistor R3 and the fourth resistor R4 is connected to the positive terminal of the second operational amplifier U2. One end of the fifth resistor R5 is connected to the OUT terminal of the three-terminal regulator U1, and the other end is grounded through the sixth resistor R6. The reference voltage signal Vref1 output from the node between resistor R5 and resistor R6 is connected to one terminal of the second operational amplifier U2. The output terminal of the second operational amplifier U2 is connected to the base of the second transistor Q2 through resistor R8. The emitter of the second transistor Q2 is grounded, and the collector of the second transistor Q2 is connected to the node between resistor R9 and resistor R13. One end of resistor R7 is connected to the OUT terminal of the three-terminal regulator U1, and the other end of resistor R7 is connected to the V+ terminal of the second operational amplifier U2. The V+ terminal of the second operational amplifier U2 is connected to the OUT terminal of the second operational amplifier U2 through resistor R14.

2. The DC linear constant current mode constant current chip according to claim 1, characterized in that: The control switch is a third transistor Q3, wherein the base of the third transistor Q3 is connected to the eleventh resistor R11, the collector of the third transistor Q3 forms the LED terminal, and the emitter of the third transistor Q3 is grounded through the fifteenth resistor R15.

3. The DC linear constant current mode constant current chip according to claim 1, characterized in that: The control switch is the third MOSFET Q3, where the gate (G) of the third MOSFET Q3 is connected to the eleventh resistor R11, the drain (D) of the third MOSFET Q3 forms the LED terminal, and the source (S) of the third MOSFET Q3 is grounded through the fifteenth resistor R15.

4. A DC linear constant current mode constant current chip according to claim 2, characterized in that: The reverse connection protection circuit includes a first capacitor C1, a first resistor R1, a second resistor R2, and a first MOSFET Q1. One end of the first capacitor C1 is connected to VDD, and the other end is grounded. The drain (D) of the first MOSFET Q1 is connected to VDD, and the gate (G) of the first MOSFET is grounded through the second resistor R2. One end of the first resistor R1 is connected to the gate (G) of the first MOSFET, and the other end is connected to the source (S) of the first MOSFET. The source (S) of the first MOSFET is connected to the IN terminal of the three-terminal regulator U1.

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