A constant current source circuit

Abstract

The application provides a constant current source circuit, which comprises a three-terminal adjustable voltage reference chip, an operational amplifier and a power supply end, a first resistor, an NMOS tube, a load resistor and a power supply ground end connected in series; the three-terminal adjustable voltage reference chip is connected with the power supply end and the operational amplifier; the NMOS tube comprises a D pole, an S pole and a G pole; the NMOS tube is connected with the first resistor through the D pole, connected with the load resistor through the S pole and connected with the output end of the operational amplifier through the G pole; the current flowing through the load resistor is controlled by controlling the voltage between the S pole and the G pole; and the constant control of the current flowing through the load resistor by the NMOS tube is realized. The constant current source circuit provided by the application not only does not generate common-mode voltage, but also improves the constant current source output current and the stability of the constant current source.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of electronic devices, and in particular to a constant current source circuit. BACKGROUND

[0002] With the rapid development of electronic devices, the application of constant current source circuit will be involved in various fields. The conventional constant current source circuit is composed of a power supply end, a three-terminal adjustable voltage reference chip, an operational amplifier, a resistor, a grounding resistor, a load resistor and a power supply ground end, and a constant current is generated by using the voltage on the grounding resistor as a negative feedback.

[0003] However, the constant current source circuit has some defects: on the one hand, the voltage generated by the constant current flowing through the load resistor RL is a common-mode voltage, which is inconvenient to extract; on the other hand, the driving capability of the constant current source circuit generated by the operational amplifier is limited by the driving capability of the operational amplifier itself. SUMMARY

[0004] The present application provides a constant current source circuit to improve the defects of the existing constant current source circuit.

[0005] On the one hand, the present application provides a constant current source circuit, which comprises a three-terminal adjustable voltage reference chip, an operational amplifier and a power supply end, a first resistor, an NMOS tube, a load resistor and a power supply ground end connected in series.

[0006] The three-terminal adjustable voltage reference chip is connected to the power supply end and the operational amplifier at the same time;

[0007] The NMOS tube comprises a D pole, an S pole and a G pole; the NMOS tube is connected to the first resistor through the D pole, connected to the load resistor through the S pole, and connected to the output end of the operational amplifier through the G pole;

[0008] The voltage between the S pole and the G pole is controlled to control the current flowing through the load resistor, so as to realize the constant control of the current on the load resistor by the NMOS tube.

[0009] Further, the three-terminal adjustable voltage reference chip comprises a K pole, an R pole and an A pole; the K pole and the R pole are both connected to the power supply end, and the A pole is connected to one end of a second resistor, and the other end of the second resistor is connected to the power supply ground end.

[0010] Further,

[0011] The positive end of the operational amplifier is connected between the first resistor and the D pole as a positive feedback of the operational amplifier;

[0012] The negative end of the operational amplifier is connected between the A pole and the second resistance as the negative feedback of the operational amplifier.

[0013] Further, the constant current source circuit further comprises a first capacitor; the first capacitor is connected in parallel between the K pole and the A pole.

[0014] Further, the constant current source circuit further comprises a second capacitor; the second capacitor is connected in parallel across the first resistance.

[0015] Further, the constant current source circuit further comprises a diode; the diode is connected in series between the NMOS tube and the load resistance.

[0016] Further, the positive pole of the diode is connected to the S pole, and the negative pole of the diode is connected to the load resistance.

[0017] Further, the voltage of the power supply end is greater than the reference voltage between the K pole and the A pole.

[0018] Further, by controlling the current flowing through the three-terminal adjustable voltage reference chip, the reference voltage is stabilized at a constant value.

[0019] Further,

[0020] The constant current I flowing through the load resistance is calculated as follows:

[0021]

[0022] Overall, compared with the prior art, the technical scheme conceived by the present application can achieve the following beneficial effects:

[0023] (1) The present application provides a constant current source circuit, which adds an NMOS tube in the circuit to adapt to the load resistance, and takes the load resistance as the grounding resistance of the ground end, so as to not generate common-mode voltage, and at the same time, improve the output current of the constant current source.

[0024] (2) The present application provides a constant current source circuit, which sets the position of the three-terminal adjustable voltage reference chip, connects the K pole and the R pole to the power supply end, connects the A pole to one end of the second resistance, and connects the other end of the second resistance to the power supply ground end, so that the driving capability of the operational amplifier itself is no longer limited, and the driving capability of the constant current source circuit to generate constant current flowing through the load resistance is also no longer limited.

[0025] (3) The application provides a constant current source circuit, which filters out noise on a reference voltage by connecting a first capacitor in parallel between K and A poles of a three-terminal adjustable voltage reference chip, filters out noise on two ends of a first resistor caused by power supply end fluctuation and noise caused by unstable closed loop of an operational amplifier by connecting a second capacitor in parallel on two ends of the first resistor, and makes the whole circuit more stable and the output constant current source more stable.

[0026] (4) The application provides a constant current source circuit, which is universal in components, low in price, simple in composition and wide in practical range. BRIEF DESCRIPTION OF DRAWINGS

[0027] In order to more clearly illustrate the technical solutions of the present application or prior art, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings described below are some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor on the basis of these drawings.

[0028] Figure 1 is a schematic diagram of a constant current source circuit commonly used in prior art provided by the present application;

[0029] Figure 2 is a circuit schematic diagram of a constant current source circuit provided by the present application. DETAILED DESCRIPTION

[0030] In order to make the purpose, technical solutions and advantages of the present application more clear, the following will combine the drawings and embodiments in the present application to clearly and completely describe the technical solutions in the present application. Obviously, the described embodiments are some embodiments of the present application, not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the protection scope of the present application.

[0031] It should be noted that in the description of the embodiments of the present application, the terms "comprise", "include" or any other variants thereof are intended to cover non-exclusive inclusion, so that the circuit comprising a series of elements not only includes those elements, but also includes other elements not explicitly listed or inherent to such circuit. Without more limitation, the element defined by the statement "comprising a" does not exclude the existence of another same element in the circuit comprising the element.

[0032] As Figure 1As shown, the constant current source circuit commonly used in the prior art is composed of a power supply end VCC, a three-terminal adjustable voltage reference chip U, an operational amplifier F, a resistor R1, a grounding resistor R0, a load resistor RL and a power supply ground end AGND; wherein the power supply end VCC, the resistor R1, the three-terminal adjustable voltage reference chip U and the power supply ground end AGND are connected in series, the K pole and the R pole of the three-terminal adjustable voltage reference chip U are connected to the resistor R1 at the same time, and the A pole of the three-terminal adjustable voltage reference chip U is directly connected to the power supply ground end AGND; the output end of the operational amplifier F is connected to the power supply ground end AGND through the load resistor RL and the grounding resistor R0 connected in series, the positive end of the operational amplifier F is connected between the resistor R1 and the K pole, and the negative end of the operational amplifier F is connected between the resistor R1 and the grounding resistor R0. The constant current is generated by using the voltage on the grounding resistor R0 as negative feedback.

[0033] However, the voltage generated by the commonly used constant current source circuit flowing through the load resistor RL is a common-mode voltage, which is inconvenient to extract; and the driving capability of the constant current source flowing through the load resistor is limited by the driving capability of the operational amplifier itself.

[0034] In order to solve these problems, the present application provides a constant current source circuit which has no common-mode voltage, the driving capability of the operational amplifier itself is not limited, and the practical range is wider on the basis of the commonly used constant current source circuit.

[0035] The present application provides a constant current source circuit, which comprises a three-terminal adjustable voltage reference chip, an operational amplifier and a power supply end, a first resistor, an NMOS tube, a load resistor and a power supply ground end connected in series.

[0036] The three-terminal adjustable voltage reference chip is connected to the power supply end and the operational amplifier at the same time; the NMOS tube comprises a D pole, an S pole and a G pole; the NMOS tube is connected to the first resistor through the D pole, connected to the load resistor through the S pole and connected to the output end of the operational amplifier through the G pole; the voltage between the S pole and the G pole is controlled to control the current flowing through the load resistor, so as to realize the constant control of the current flowing through the load resistor by the NMOS tube.

[0037] The constant control of the current flowing through the load resistor is realized by using the voltage-current characteristic of the NMOS tube: when the voltage between the S pole and the G pole of the NMOS tube increases, the current flowing through the load resistor increases; when the voltage between the S pole and the G pole of the NMOS tube decreases, the current flowing through the load resistor decreases until zero. It should be noted that the voltage between the S pole and the G pole is controlled by introducing negative feedback and the output of the operational amplifier.

[0038] As an embodiment of the present application, the constant current source circuit further comprises a second resistor; the three-terminal adjustable voltage reference chip comprises a K terminal, an R terminal and an A terminal; the K terminal and the R terminal are both connected to a power supply terminal, and the A terminal is connected to one end of the second resistor, and the other end of the second resistor is connected to a power supply ground terminal.

[0039] As an embodiment of the present application, the positive terminal of the operational amplifier is connected between the first resistor and the D terminal, as the positive feedback of the operational amplifier; and the negative terminal of the operational amplifier is connected between the A terminal and the second resistor, as the negative feedback of the operational amplifier.

[0040] As an embodiment of the present application, in order to further filter out the noise on the reference voltage between the K terminal and the A terminal, the constant current source circuit of the present application further comprises a first capacitor connected in parallel between the K terminal and the A terminal.

[0041] As an embodiment of the present application, in order to further filter out the noise caused by the fluctuation of the power supply terminal on both ends of the first resistor and the noise caused by the instability of the closed loop of the operational amplifier, the constant current source circuit of the present application further comprises a second capacitor connected in parallel between both ends of the first resistor.

[0042] Since there is a parasitic diode inside the NMOS tube, in order to prevent the current from flowing back on the load resistor, as a preferred embodiment of the present application, a diode is connected in series between the NMOS tube and the load resistor; further, the anode of the diode is connected to the S terminal, and the cathode of the diode is connected to the load resistor.

[0043] In addition, in order to ensure the normal operation of the constant current source circuit, the voltage of the power supply terminal should be greater than the reference voltage between the K terminal and the A terminal. The current limited by the second resistor should be able to ensure that the three-terminal adjustable voltage reference chip works normally within the voltage stable range, and the power supply terminal should be able to ensure the effective work of the operational amplifier.

[0044] The reference voltage is stabilized at a constant value by controlling the current flowing through the three-terminal adjustable voltage reference chip. Therefore, the calculation method of the constant current flowing through the load resistor is: the reference voltage between the K terminal and the A terminal divided by the first resistor.

[0045] As a specific embodiment of the present application, as shown in Figure 2 the constant current source circuit comprises a power supply terminal VCC, a first resistor R1, an NMOS tube Q, a diode D1, a load resistor RL and a power supply ground terminal AGND connected in series; further comprising a three-terminal adjustable voltage reference chip U, an operational amplifier F, a second resistor R2, a first capacitor C1 and a second capacitor C2.

[0046] The power supply end VCC is +5VA, the first resistor R1 is 300Ω, the NMOS tube Q is 2N7002 type, the diode D1 is IN5819 type, the power supply ground end AGND, the three-terminal adjustable voltage reference chip U is CD431 type, the operational amplifier F is LM2904XS8G / TR type, and the second resistor R2 is 1.2kΩ. The first capacitor C1 and the second capacitor C2 are both 0.1μF.

[0047] The K pole and the R pole of the three-terminal adjustable voltage reference chip U are both connected to the power supply +5VA, the A pole is connected to one end of the second resistor R2, and the other end of the second resistor R2 is connected to the power supply ground AGND; the current flowing through the three-terminal adjustable voltage reference chip U1 in the constant current source circuit is about 2mA, so that the voltage between the A pole and the K pole of the three-terminal adjustable voltage reference chip U1 can be stabilized at about 2.5V.

[0048] The G pole of the NMOS tube Q is connected to the output 1 pin of the operational amplifier F, the positive input end 3 pin of the operational amplifier F is connected between the first resistor R1 and the D pole, and the positive feedback of the operational amplifier F is introduced; the negative end 2 pin of the operational amplifier F is connected between the A pole and the second resistor R2, and the negative feedback of the operational amplifier F is introduced. Through the introduced negative feedback, the output of the operational amplifier F is controlled, so that the voltage between the G pole and the S pole of the NMOS tube is controlled.

[0049] The power supply end +5VA is greater than the reference voltage 2.5V between the K pole and the A pole, and the current 2mA limited by the second resistor R2 can ensure that the working voltage of the three-terminal adjustable voltage reference chip U is stabilized at 2.5V, and the power supply end +5VA can ensure the effective working of the operational amplifier F.

[0050] Therefore, the constant current I flowing through the load resistor RL can be obtained as:

[0051]

[0052] So as to realize the constant control of the current on the load resistor by the NMOS tube.

[0053] In summary, the constant current source circuit provided by the application does not generate common-mode voltage, and the output current of the constant current source is improved.

[0054] It should be noted that, for the foregoing circuit embodiments, in order to simply describe, they are all expressed as a series of action combinations, but those skilled in the art should know that the application is not limited by the action sequence described, because according to the application, certain steps can be performed in other sequences or simultaneously. Secondly, those skilled in the art should know that the embodiments described in the specification all belong to preferred embodiments, and the actions and modules involved are not necessarily required by the application.

[0055] In the above-described embodiments, the description of each embodiment focuses on different aspects, and the parts not described in detail in a certain embodiment can be referred to the relevant description of other embodiments.

[0056] In several embodiments provided in the present application, it should be understood that the disclosed circuit can be implemented by other manners. For example, the above-described circuit embodiments are only schematic, and the division of the units is only a logical function division, and actual implementation can have another division manner, for example, a plurality of units or components can be combined or integrated into another system, or some features can be ignored or not executed. In addition, the coupling or direct coupling or communication connection between the units shown or discussed can be indirect coupling or communication connection through some service interface, and the coupling or communication connection can be electrical or other forms.

[0057] The units described as separate components can or can not be physically separate, and the components shown as units can or can not be physical units, that is, they can be located in one place or distributed on a plurality of network units. Part or all of the units can be selected according to actual needs to achieve the purpose of the embodiment.

[0058] In addition, each functional unit in each embodiment of the present application can be integrated in one processing unit, or each unit can exist physically, or two or more units can be integrated in one unit. The integrated unit can be realized in the form of hardware or in the form of a software functional unit.

[0059] When the integrated unit is realized in the form of a software functional unit and sold or used as an independent product, it can be stored in a computer readable storage medium. Based on this understanding, the technical solutions of the present application essentially or the part that contributes to the prior art or the whole or part of the technical solutions can be embodied in the form of a software product, and the computer software product is stored in a storage medium, including a plurality of instructions to make a computer device (which can be a personal computer, a server or a network device, etc.) execute all or part of the steps of the method described in each embodiment of the present application. The foregoing storage medium includes: a U disk, a read-only memory (ROM), a random access memory (RAM), a mobile hard disk, a magnetic disk or an optical disk, and various media that can store program codes.

[0060] Those skilled in the art can understand that all or part of the circuits in the above embodiments can be programmed to instruct the relevant hardware to complete, and the program can be stored in a computer readable memory, which can include a flash disk, a read-only memory (ROM), a random access memory (RAM), a magnetic disk or an optical disk, etc.

[0061] The above merely describes exemplary embodiments of the present disclosure, and cannot limit the scope of the present disclosure. Any equivalent changes and modifications made according to the teachings of the present disclosure are still within the scope of the present disclosure. Those skilled in the art will easily think of the embodiments of the present disclosure after considering the specification and practicing the disclosure herein. The present application is intended to cover any variations, uses, or adaptive changes of the present disclosure that follow the general principles of the present disclosure and include common knowledge or conventional technical means in the technical field not recorded in the present disclosure. The specification and examples are only considered to be exemplary, and the scope and spirit of the present disclosure are defined by the claims.

[0062] The technical features of the above embodiments can be combined in any way, and for the sake of brevity, not all possible combinations of the technical features in the above embodiments are described, however, as long as the combination of the technical features does not exist contradictory, it should be considered as the scope recorded in the present disclosure.

[0063] Those skilled in the art can understand that the above only describes preferred embodiments of the present application and is not intended to limit the present application, and any modifications, equivalent replacements and improvements made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A constant current source circuit, characterized by comprising: The constant current source circuit comprises a three-terminal adjustable voltage reference chip, an operational amplifier, a second resistor, and a power supply end, a first resistor, an NMOS tube, a load resistor and a power supply ground end connected in series. The three-terminal adjustable voltage reference chip is connected to the power supply end and the operational amplifier; the three-terminal adjustable voltage reference chip comprises a K pole, an R pole and an A pole; the K pole and the R pole are connected to the power supply end, and the A pole is connected to one end of the second resistor, and the other end of the second resistor is connected to the power supply ground end. The NMOS tube comprises a D pole, an S pole and a G pole. The NMOS tube is connected to the first resistor through the D pole, connected to the load resistor through the S pole, and connected to the output end of the operational amplifier through the G pole. The positive end of the operational amplifier is connected between the first resistor and the D pole as positive feedback of the operational amplifier, and the negative end of the operational amplifier is connected between the A pole and the second resistor as negative feedback of the operational amplifier. The voltage between the S pole and the G pole is controlled to control the current flowing through the load resistor, so as to realize constant control of the current flowing through the load resistor by the NMOS tube.

2. A constant current source circuit as claimed in claim 1, characterized in that The constant current source circuit further comprises a first capacitor; the first capacitor is connected in parallel between the K pole and the A pole.

3. A constant current source circuit as claimed in claim 1 or 2, characterized in that The constant current source circuit further comprises a second capacitor; the second capacitor is connected in parallel across the first resistor.

4. A constant current source circuit as claimed in claim 1, characterized in that The constant current source circuit further comprises a diode; the diode is connected in series between the NMOS tube and the load resistor.

5. A constant current source circuit as claimed in claim 4, characterized in that The positive pole of the diode is connected to the S pole, and the negative pole of the diode is connected to the load resistor.

6. A constant current source circuit as claimed in claim 1, characterized in that The voltage of the power supply end is greater than the reference voltage between the K pole and the A pole.

7. A constant current source circuit as claimed in claim 6, characterized in that The reference voltage is stabilized at a constant value by controlling the current flowing through the three-terminal adjustable voltage reference chip.

8. The constant current source circuit of claim 7, wherein a constant current flowing through the load resistor is calculated as 。

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