Closed-loop control current source circuit based on NMOS (N-channel Metal Oxide Semiconductor) tube

Abstract

The invention discloses a closed-loop control current source circuit based on an NMOS tube, and belongs to the technical field of power electronics, when the state of a power supply or a load is changed and the current is changed, the closed-loop control current source circuit based on the NMOS tube can change the drain-source voltage of the NMOS tube through the closed-loop control of the NMOS tube in a feedback control sub-circuit, and the closed-loop control current source circuit based on the NMOS tube can change the current of the NMOS tube through the closed-loop control of the NMOS tube in the feedback control sub-circuit. Therefore, the working state of the closed-loop control current source circuit based on the NMOS tube is adjusted so as to keep the current constant. Therefore, the current source circuit provided by the invention can continuously and automatically adjust the states of the operational amplifier and the NMOS tube by continuously monitoring the value of the current flowing through the sampling resistor, ensures that the current flowing through the sampling resistor and the load is kept stable, and realizes a controllable current source.

Description

Technical Field

[0001] The invention belongs to the technical field of power electronics, and in particular relates to a closed-loop controlled current source circuit based on an NMOS tube. Background Art

[0002] A circuit often requires a current source that can provide a specific small current, but it is not easy to find a ready-made integrated circuit and you need to design it yourself.

[0003] In the related art, the common current source circuit is an open-loop control structure composed of a reference voltage, an operational amplifier, an NMOS tube, and a sampling resistor. Considering that the sampling resistor must be grounded and the load must be connected in series with the sampling resistor, the load that requires current can only be ungrounded; conversely, if the load must be grounded, then this traditional open-loop control current source will no longer be applicable. Summary of the invention

[0004] In order to solve the above problems existing in the prior art, the present invention provides a closed-loop controlled current source circuit based on an NMOS tube. The technical problem to be solved by the present invention is achieved through the following technical solutions: The present invention provides a closed-loop controlled current source circuit based on an NMOS tube. When the state of a power supply or a load changes and will cause a current change, the drain-source voltage of the NMOS tube is changed through the closed-loop control of the NMOS tube in a feedback control subcircuit, thereby adjusting the working state of the closed-loop controlled current source circuit based on the NMOS tube to keep the current constant.

[0005] Compared with the prior art, the present invention has the following beneficial effects: The present invention provides a closed-loop controlled current source circuit based on an NMOS tube. When the state of a power supply or a load changes and causes a current change, the drain-source voltage of the NMOS tube can be changed by closed-loop control of the NMOS tube in a feedback control subcircuit, thereby adjusting the working state of the closed-loop controlled current source circuit based on the NMOS tube to keep the current constant. It can be seen that the current source circuit can continuously and automatically adjust the state of the operational amplifier and the NMOS tube by continuously monitoring the current value flowing through the sampling resistor, ensuring that the current flowing through the sampling resistor and the load remains stable, thereby realizing a controllable current source.

[0006] In addition, the present invention uses low-cost and easily available discrete devices to form a closed-loop feedback, and the load can be connected to two positions in the current source circuit, making the design of the current source circuit more flexible and more practical.

[0007] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1It is a structural schematic diagram of a closed-loop controlled current source circuit based on an NMOS tube provided in an embodiment of the present invention; Figure 2 is a circuit diagram of a closed-loop controlled current source circuit based on an NMOS tube provided in an embodiment of the present invention; Figure 3 is a circuit diagram of a power supply circuit provided by an embodiment of the present invention; Figure 4 is a circuit diagram of a reference voltage generating subcircuit provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0009] The present invention is further described in detail below with reference to specific embodiments, but the embodiments of the present invention are not limited thereto.

[0010] Figure 1 Schematic diagram of the structure of the closed-loop control current source circuit based on NMOS tube provided by the embodiment of the present invention. Figure 1 As shown, an embodiment of the present invention provides a closed-loop controlled current source circuit based on an NMOS tube. When the state of a power supply or a load changes and will cause a current change, the drain-source voltage of the NMOS tube Q1 is changed through the closed-loop control of the NMOS tube Q1 in the feedback control subcircuit 10, thereby adjusting the working state of the closed-loop controlled current source circuit based on the NMOS tube to keep the current constant.

[0011] Figure 2 is a circuit diagram of a closed-loop controlled current source circuit based on an NMOS tube provided by an embodiment of the present invention. Figure 2 As shown, the closed-loop controlled current source circuit based on the NMOS tube also includes: a reference voltage generating subcircuit 20, a current-voltage conversion subcircuit 30, a power supply subcircuit 40, a first load access position 50 and a second load access position 60; wherein, The power supply subcircuit 40 is connected to a power source and is used to supply power to the feedback control subcircuit 10 , the current-voltage conversion subcircuit 30 , and the reference voltage generation subcircuit 20 ; The feedback control subcircuit 10 is used to adjust the gate-source voltage of the NMOS transistor Q1 according to the voltage value output by the current-voltage conversion subcircuit 30 and the reference voltage output by the reference voltage generation subcircuit 20, thereby controlling the drain-source voltage of the NMOS transistor Q1; The reference voltage generating subcircuit 20 is used to generate a reference voltage and output it to the feedback control subcircuit 10; The current-voltage conversion subcircuit 30 is used to collect the current value flowing through the two ends of the sampling resistor, and convert the current value into a voltage value and output it to the feedback control subcircuit 10; The first load access position 50 and the second load access position 60 are used to access loads.

[0012] In this embodiment, the closed-loop control current source circuit based on the NMOS tube includes: a feedback control subcircuit 10, a reference voltage generating subcircuit 20, a current-voltage conversion subcircuit 30, a power supply subcircuit 40, a first load access position 50 and a second load access position 60; specifically, the first load access position 50 and the second load access position 60 are used to access the load, the power supply subcircuit 40 is used to supply power to the first operational amplifier A1 in the feedback control subcircuit 10, the second operational amplifier A2 in the current-voltage conversion subcircuit 30 and the reference voltage generating subcircuit 20, and the reference voltage generating subcircuit 20 is used to supply power to the first operational amplifier A1 in the feedback control subcircuit 10, the second operational amplifier A2 in the current-voltage conversion subcircuit 30 and the reference voltage generating subcircuit 20. The reference voltage is generated under the power supply of the circuit 40 and output to the non-inverting input terminal of the first operational amplifier A1 in the feedback control sub-circuit 10. The current-voltage conversion sub-circuit 30 is used to extract the current value flowing through the sampling resistor and convert it into a voltage value, which is then sent to the inverting input terminal of the first operational amplifier A1 in the feedback control sub-circuit 10 after voltage division. In this way, the feedback control sub-circuit 10 can control the drain-source voltage of the NMOS tube Q1 according to the received voltage value and the reference voltage, so as to provide voltage compensation when the power supply or load changes, maintain the current unchanged, and the magnitude of the current can be accurately set by adjusting the value of the reference voltage.

[0013] In this embodiment, the load includes: a first load connected to the first load access position 50, and / or a second load connected to the second load access position 60; When only one load is connected to the closed-loop controlled current source circuit based on the NMOS tube Q1, the other load connection position that is not connected to the load is short-circuited.

[0014] Please continue to see Figure 2 , the feedback control subcircuit 10 includes a first resistor R1, a second resistor R2, a third resistor R3, a fourth resistor R4, an NMOS transistor Q1 and a first operational amplifier A1; Among them, the source of the NMOS tube Q1 serves as the output end of the feedback control subcircuit 10, connected to the first end of the first resistor R1 and the input end of the first load access position 50, the second end of the first resistor R1 is connected to the gate of the NMOS tube Q1 and the first end of the second resistor R2, the drain of the NMOS tube Q1 is connected to the power supply and the input end of the power supply subcircuit 40, the second end of the second resistor R2 is connected to the output end of the first operational amplifier A1, the first end of the third resistor R3 is connected to the output end of the current-voltage conversion subcircuit 30, the second end of the third resistor R3 is connected to the first end of the fourth resistor R4 and the inverting input end of the first operational amplifier A1, the second end of the fourth resistor R4 is grounded, the non-inverting input end of the first operational amplifier A1 is connected to the output end of the reference voltage generation subcircuit 20, and the power supply end of the first operational amplifier A1 is connected to the output end of the boost circuit in the power supply subcircuit 40.

[0015] Specifically, in the feedback control subcircuit 10, the drain of the NMOS tube Q1 is connected to the power supply, and the voltage difference between the voltage at the output end of the first operational amplifier A1 and the source of the NMOS tube Q1 is divided by the first resistor R1 and the second resistor R2, so that a voltage difference is formed between the gate and the source of the NMOS tube Q1, and the NMOS tube Q1 is kept working in an amplification state, so as to control the drain-source voltage of the NMOS tube Q1 to maintain a suitable value.

[0016] It should be understood that the voltage at the output terminal of the first operational amplifier A1 is determined by the voltages at its non-inverting input terminal and its inverting input terminal. According to the principle of a negative feedback circuit, the voltages at the two input terminals must be equal.

[0017] The above-mentioned closed-loop control current source circuit based on NMOS tube further includes a fifth resistor R5; The current-voltage conversion sub-circuit 30 includes: a sixth resistor R6, a seventh resistor R7, an eighth resistor R8, a ninth resistor R9, a tenth resistor R10 and a second operational amplifier A2; Among them, the sixth resistor R6 is a sampling resistor, the first end of the sixth resistor R6 is connected to the output end of the first load access position 50 and the first end of the seventh resistor R7, the second end of the sixth resistor R6 is connected to the first end of the fifth resistor R5 and the first end of the eighth resistor R8, the second end of the fifth resistor R5 is connected to the input end of the second load access position 60, the output end of the second load access position 60 is grounded, the second end of the seventh resistor R7 is connected to the in-phase input end of the second operational amplifier A2 and the first end of the tenth resistor R10, the second end of the tenth resistor R10 is grounded, the second end of the eighth resistor R8 is connected to the inverting input end of the second operational amplifier A2 and the first end of the ninth resistor R9, the output end of the second operational amplifier A2 is used as the output end of the current-voltage conversion sub-circuit 30, and is connected to the second end of the ninth resistor R9, and the power supply end of the second operational amplifier A2 is connected to the output end of the boost circuit in the power supply sub-circuit 40.

[0018] It should be understood that when the closed-loop controlled current source circuit based on the NMOS tube only includes a load located at the first load access position 50, the second load access position 60 needs to be short-circuited. At this time, the fifth resistor R5 can be used as a bias resistor to prevent zero voltage from occurring at any point in the current-voltage conversion subcircuit 30.

[0019] Optionally, the seventh resistor R7 and the eighth resistor R8 have the same resistance value, and the ninth resistor R9 and the tenth resistor R10 have the same resistance value.

[0020] In the current-voltage conversion subcircuit 30, the function of the sixth resistor R6 is to sample the current flowing through the drain-source of the NMOS tube Q1, the first load access position 50, the second load access position 60 and the fifth resistor R5, and convert the current value into the voltage value across the sixth resistor R6. The second operational amplifier A2 and the seventh resistor R7, the eighth resistor R8, the ninth resistor R9 and the tenth resistor R10 form a differential voltage amplifier circuit, which is used to amplify the small voltage across the sixth resistor R6 and convert it into a single-ended voltage, and then output it from the output end of the second operational amplifier A2. Therefore, in the current-voltage conversion subcircuit 30, the resistance value of the seventh resistor R7 is equal to the resistance value of the eighth resistor R8, the resistance value of the ninth resistor R9 is equal to the resistance value of the tenth resistor R10, and the amplification factor of the differential voltage amplifier circuit is the ratio of the resistance value of the tenth resistor R10 to the resistance value of the seventh resistor R7, or the ratio of the resistance value of the ninth resistor R9 to the resistance value of the eighth resistor R8.

[0021] In this embodiment, the first operational amplifier A1 and the second operational amplifier A2 are both high-bandwidth operational amplifiers, using single-ended power supply, and the bandwidth parameter determines the response speed and dynamic performance of the entire current source circuit.

[0022] Figure 3 is a circuit diagram of a power supply circuit provided by an embodiment of the present invention. Figure 3 , the power supply circuit 40 includes: an inductor L1, a first capacitor C1 and a boost circuit; Among them, the input end of the boost circuit is connected to the power supply and the first end of the inductor L1, the output end of the boost circuit is connected to the power supply end of the first operational amplifier A1 and the power supply end of the second operational amplifier A2, the second end of the inductor L1 is connected to the first end of the first capacitor C1 and the input end of the reference voltage generating subcircuit 20, and the second end of the first capacitor C1 is grounded.

[0023] Figure 4 is a circuit diagram of a reference voltage generating subcircuit provided in an embodiment of the present invention. Figure 4 As shown, the reference voltage generating subcircuit 20 includes: an eleventh resistor R11 and a voltage reference chip D; Among them, the first end of the eleventh resistor R11 is the input end of the reference voltage generating sub-circuit 20, connected to the second end of the inductor L1 in the power supply sub-circuit 40, the second end of the eleventh resistor R11 is connected to the first end of the voltage reference chip D and the in-phase input end of the first operational amplifier A1, and the second end of the voltage reference chip D is grounded.

[0024] Specifically, the input of the reference voltage generating subcircuit 20 is the power supply voltage after filtering from the power supply subcircuit 40, and the output is a reference voltage with a lower value. The function of the reference voltage generating subcircuit 20 is to provide a stable reference voltage. The implementation method depends on the cost and performance requirements. A voltage reference chip D can be used to achieve higher performance, such as the TL431 voltage reference chip, or when the performance requirements are not high, two resistors can be used at the output end of the boost circuit to form a voltage divider network to achieve it.

[0025] The working principle of the closed-loop controlled current source circuit based on NMOS tube provided by the present invention is described below.

[0026] After the power supply is powered on, the power supply sub-circuit 40 and the reference voltage generating sub-circuit 20 work normally. Since the NMOS tube Q1 is not turned on temporarily, no matter which position of the two load access positions the load is in, the current flowing through the sixth resistor R6 is 0, and the output of the second operational amplifier A2 is also 0. The voltage at the non-inverting input terminal of the first operational amplifier A1 is higher than the voltage at the inverting input terminal, and its output voltage is close to its power supply voltage. The voltage across the first resistor R1 is high enough to gradually turn on the NMOS tube Q1, and the current flowing through the load and the fifth resistor R5 and the sixth resistor R6 gradually increases. The voltage value output by the second operational amplifier A2 also increases, and finally the voltages at the non-inverting input terminal and the inverting input terminal of the second operational amplifier A2 are nearly equal, and the inverting input terminal voltage reaches a state of following the non-inverting input terminal voltage. Under the action of closed-loop feedback, the voltage at the output terminal of the first operational amplifier A1 is automatically adjusted to a suitable value, so that the drain-source voltage of the NMOS tube Q1 reaches a suitable value, and finally the current is stabilized at the set value and continues to work.

[0027] When the power supply voltage fluctuates, there are two situations: the power supply voltage increases and decreases.

[0028] On the one hand, when the power supply voltage increases, the current flowing through the sixth resistor R6 tends to increase, and thus the voltage value at the output end of the second operational amplifier A2 also tends to increase, while the voltage at the inverting input end of the first operational amplifier A1 tends to be higher than the voltage at the non-inverting input end, so that the voltage value at the output end of the first operational amplifier A1 decreases, the gate-source voltage of the NMOS tube Q1 decreases, and further causes the drain-source voltage of the NMOS tube Q1 to increase, keeping the absolute value voltage of the source of the NMOS tube Q1 unchanged, and thus maintaining the state of the load and the fifth resistor R5 and the sixth resistor R6 unchanged, so that the current remains unchanged. On the other hand, when the power supply voltage decreases, there will be a trend opposite to that when the power supply voltage increases and the current remains unchanged, which will not be repeated here.

[0029] Based on the above analysis, it can be seen that the methods for changing the current size set by the above current source circuit include: changing the resistance value of the sixth resistor R6 (sampling resistor), or changing the resistance value of the seventh resistor R7, the eighth resistor R8, the ninth resistor R9, and the tenth resistor R10, or changing the resistance value of the third resistor R3 and the fourth resistor R4 (voltage dividing resistor), or changing the reference voltage output by the reference voltage generating subcircuit 20. One or more of these four methods may be used.

[0030] In addition, when the load state changes, the voltage across the load will also change accordingly, which can be equivalent to the power supply voltage fluctuation. At this time, the state change trend of the current source circuit is similar to the above-mentioned power supply voltage fluctuation, and will not be repeated here.

[0031] It can be seen from the above embodiments that the beneficial effects of the present invention are: The present invention provides a closed-loop controlled current source circuit based on an NMOS tube. When the state of a power supply or a load changes and causes a current change, the drain-source voltage of the NMOS tube can be changed by closed-loop control of the NMOS tube in a feedback control subcircuit, thereby adjusting the working state of the closed-loop controlled current source circuit based on the NMOS tube to keep the current constant. It can be seen that the current source circuit can continuously and automatically adjust the state of the operational amplifier and the NMOS tube by continuously monitoring the current value flowing through the sampling resistor, ensuring that the current flowing through the sampling resistor and the load remains stable, thereby realizing a controllable current source.

[0032] In addition, the present invention uses low-cost and easily available discrete devices to form a closed-loop feedback, and the load can be connected to two positions in the current source circuit, making the design of the current source circuit more flexible and more practical.

[0033] In the description of the present invention, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0034] The description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine different embodiments or examples described in this specification.

[0035] The above contents are further detailed descriptions of the present invention in combination with specific preferred embodiments, and it cannot be determined that the specific implementation of the present invention is limited to these descriptions. For ordinary technicians in the technical field to which the present invention belongs, several simple deductions or substitutions can be made without departing from the concept of the present invention, which should be regarded as falling within the protection scope of the present invention.

Claims

1. A closed-loop controlled current source circuit based on an NMOS tube, characterized in that: When the state of the power supply or the load changes and will cause the current to change, the drain-source voltage of the NMOS tube is changed through the closed-loop control of the NMOS tube in the feedback control subcircuit, thereby adjusting the working state of the closed-loop controlled current source circuit based on the NMOS tube to keep the current constant.

2. The closed-loop controlled current source circuit based on NMOS tube according to claim 1, characterized in that: Also includes: A reference voltage generating subcircuit, a current-voltage conversion subcircuit, a power supply subcircuit, a first load access position, and a second load access position; wherein, The power supply subcircuit is connected to a power source and is used to supply power to the feedback control subcircuit, the current-voltage conversion subcircuit and the reference voltage generation subcircuit; The feedback control subcircuit is used to adjust the gate-source voltage of the NMOS tube according to the voltage value output by the current-voltage conversion subcircuit and the reference voltage output by the reference voltage generation subcircuit, thereby controlling the drain-source voltage of the NMOS tube; The reference voltage generating subcircuit is used to generate a reference voltage and output it to the feedback control subcircuit; The current-voltage conversion subcircuit is used to collect the current value flowing through the two ends of the sampling resistor, and convert the current value into a voltage value and then output it to the feedback control subcircuit; The first load access position and the second load access position are used to access a load.

3. The closed-loop controlled current source circuit based on NMOS tube according to claim 2, characterized in that: The loads include: a first load connected to a first load access position, and / or a second load connected to a second load access position; When only one load is connected to the NMOS-based closed-loop controlled current source circuit, the other load connection position that is not connected to the load is short-circuited.

4. The closed-loop controlled current source circuit based on NMOS tube according to claim 2, characterized in that: The feedback control subcircuit comprises a first resistor (R1), a second resistor (R2), a third resistor (R3), a fourth resistor (R4), an NMOS tube (Q1) and a first operational amplifier (A1); The source of the NMOS transistor (Q1) is used as the output end of the feedback control subcircuit, connected to the first end of the first resistor (R1) and the input end of the first load access position, the second end of the first resistor (R1) is connected to the gate of the NMOS transistor (Q1) and the first end of the second resistor (R2), the drain of the NMOS transistor (Q1) is connected to the power supply and the input end of the power supply subcircuit, the second end of the second resistor (R2) is connected to the output end of the first operational amplifier (A1), the first end of the third resistor (R3) is connected to the output end of the current-voltage conversion subcircuit, the second end of the third resistor (R3) is connected to the first end of the fourth resistor (R4) and the inverting input end of the first operational amplifier (A1), the second end of the fourth resistor (R4) is grounded, the non-inverting input end of the first operational amplifier (A1) is connected to the output end of the reference voltage generation subcircuit, and the power supply end of the first operational amplifier (A1) is connected to the output end of the boost circuit in the power supply subcircuit.

5. The closed-loop controlled current source circuit based on NMOS tube according to claim 4, characterized in that: Also including a fifth resistor (R5); The current-voltage conversion subcircuit comprises: a sixth resistor (R6), a seventh resistor (R7), an eighth resistor (R8), a ninth resistor (R9), a tenth resistor (R10) and a second operational amplifier (A2); The sixth resistor (R6) is a sampling resistor, a first end of the sixth resistor (R6) is connected to the output end of the first load access position and the first end of the seventh resistor (R7), a second end of the sixth resistor (R6) is connected to the first end of the fifth resistor (R5) and the first end of the eighth resistor (R8), a second end of the fifth resistor (R5) is connected to the input end of the second load access position, and the output end of the second load access position is grounded, a second end of the seventh resistor (R7) is connected to the in-phase input end of the second operational amplifier (A2) and the first end of the tenth resistor (R10), a second end of the tenth resistor (R10) is grounded, a second end of the eighth resistor (R8) is connected to the inverting input end of the second operational amplifier (A2) and the first end of the ninth resistor (R9), an output end of the second operational amplifier (A2) is used as the output end of the current-voltage conversion sub-circuit and is connected to the second end of the ninth resistor (R9), and a power supply end of the second operational amplifier (A2) is connected to the output end of the boost circuit in the power supply sub-circuit.

6. The closed-loop controlled current source circuit based on NMOS tube according to claim 5, characterized in that: The seventh resistor (R7) and the eighth resistor (R8) have the same resistance value, and the ninth resistor (R9) and the tenth resistor (R10) have the same resistance value.

7. The closed-loop controlled current source circuit based on NMOS tube according to claim 5, characterized in that: The power supply circuit comprises: an inductor (L1), a first capacitor (C1) and a boost circuit; The input end of the boost circuit is connected to the power supply and the first end of the inductor (L1), the output end of the boost circuit is connected to the power supply end of the first operational amplifier (A1) and the power supply end of the second operational amplifier (A2), the second end of the inductor (L1) is connected to the first end of the first capacitor (C1) and the input end of the reference voltage generating subcircuit, and the second end of the first capacitor (C1) is grounded.

8. The closed-loop controlled current source circuit based on NMOS tube according to claim 7, characterized in that: The reference voltage generating subcircuit comprises: an eleventh resistor (R11) and a voltage reference chip (D); The first end of the eleventh resistor (R11) is the input end of the reference voltage generating subcircuit, connected to the second end of the inductor (L1) in the power supply subcircuit, the second end of the eleventh resistor (R11) is connected to the first end of the voltage reference chip (D) and the non-inverting input end of the first operational amplifier (A1), and the second end of the voltage reference chip (D) is grounded.

Images