High-precision constant current source circuit

Abstract

The utility model discloses a high-precision constant current source circuit, and belongs to the field of constant current source circuits. Comprising an operational amplifier U1 and an operational amplifier U2. The reverse input end of the operational amplifier U1 is grounded through a serially connected resistor R3, and the paying-off input end of the operational amplifier U1 is further connected with the output end of the operational amplifier U1 after being serially connected with a resistor R4; the positive input end of the operational amplifier U1 is connected with a reference voltage through a serially connected resistor R1; the output end of the operational amplifier U1 is grounded through a serially connected resistor RS; the positive input end of the operational amplifier U2 is connected with a resistor RS; and the output end of the operational amplifier U2 is connected with the positive input end of the operational amplifier U1 through a serially connected resistor R2. The constant current source generating circuit has the beneficial effects that compared with an existing constant current source circuit constructed by using triodes, the constant current source generating circuit has higher precision; a user can select corresponding operational amplifiers to realize constant current output according to different precision requirements.

Description

Technical Field

[0001] The utility model relates to a high-precision constant current source circuit, belonging to the field of constant current source circuits. Background Art

[0002] The constant current source is a unit circuit widely used in analog integrated circuits. This article emphasizes its use in resistance measurement. A known constant current source is passed through the resistor to be measured, and the voltage across the resistor to be measured can be measured to calculate the resistance value of the resistor to be measured.

[0003] The closest existing constant current source circuit is composed of an operational amplifier and a triode. Figure 2 As shown, RL is the load, RS is the sampling resistor, and Iout is the output constant current source.

[0004] Its working principle is to amplify the voltage across the sampling resistor through the operational amplifier and feed it back to the base of the transistor to adjust the current flowing through. When Iout is greater than the set constant current, the voltage U- on the sampling resistor increases, the operational amplifier output voltage Uout=A*(U+-U-) decreases, and then the base current of the transistor decreases, and the current flowing through the transistor decreases until it reaches a stable constant current. The same applies when Iout is less than the set constant current value.

[0005] Please see the instruction manual for details. Figure 2 ;

[0006] In the prior art, the collector current (Ic) and emitter current (Ie) of a transistor are approximately equal, but in fact the emitter current also includes the base current (Ib). At this time, the output constant current includes the error of the transistor base current (Ib), which cannot meet the requirements of some high-precision constant current sources. Utility Model Content

[0007] The purpose of the utility model is to provide a high-precision constant current source circuit, which can effectively solve the above-mentioned problems.

[0008] In order to solve the above technical problems, the utility model is achieved through the following technical solutions:

[0009] It includes an operational amplifier U1 and an operational amplifier U2; the reverse input terminal of the operational amplifier U1 is grounded via a series resistor R3, and the discharge input terminal of the operational amplifier U1 is also connected to the output terminal of the operational amplifier U1 via a series resistor R4;

[0010] The positive input terminal of the operational amplifier U1 is connected to the reference voltage via the series-connected resistor R1;

[0011] The output end of the operational amplifier U1 is grounded via a series resistor RS;

[0012] The positive input terminal of the operational amplifier U2 is connected to the resistor RS;

[0013] The output terminal of the operational amplifier U2 is connected to the positive input terminal of the operational amplifier U1 via a series resistor R2.

[0014] Furthermore: the inverting input terminal of the operational amplifier U2 is suspended.

[0015] Furthermore: the output end of the operational amplifier U1 is connected in series with a resistor RL after being connected in series with a resistor RS.

[0016] Furthermore: the positive input terminal of the operational amplifier U1 is grounded via a series capacitor.

[0017] The beneficial effects are:

[0018] The constant current source generating circuit described in this article has higher accuracy than the existing constant current source circuit constructed using triodes; users can select the corresponding operational amplifier to achieve constant current output according to different accuracy requirements. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] For ease of explanation, the present invention is described in detail by the following specific implementations and drawings.

[0020] Figure 1 A circuit diagram of the utility model;

[0021] Figure 2 This is a circuit diagram for comparing the prior art of the present utility model. DETAILED DESCRIPTION

[0022] The embodiments of the present invention are described in detail below, and examples of the embodiments are shown in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and intended to be used to explain the present invention, but cannot be understood as limiting the present invention.

[0023] See also Figure 1 This is an embodiment of a high-precision constant current source circuit of the utility model.

[0024] It includes an operational amplifier U1 and an operational amplifier U2; the reverse input terminal of the operational amplifier U1 is grounded via a series resistor R3, and the discharge input terminal of the operational amplifier U1 is also connected to the output terminal of the operational amplifier U1 via a series resistor R4;

[0025] The positive input terminal of the operational amplifier U1 is connected to the reference voltage via the series resistor R1;

[0026] The output terminal of the operational amplifier U1 is grounded via a series resistor RS;

[0027] The positive input terminal of the operational amplifier U2 is connected to the resistor RS;

[0028] The output terminal of the operational amplifier U2 is connected to the positive input terminal of the operational amplifier U1 via a series resistor R2.

[0029] The inverting input terminal of operational amplifier U2 is left floating.

[0030] The output end of the operational amplifier U1 is connected in series with a resistor RS and then connected in series with a resistor RL.

[0031] The non-inverting input terminal of the operational amplifier U1 is grounded via a series capacitor.

[0032] The resistor R4 of this circuit is used to perform negative feedback compensation on the output end of the operational amplifier U1, thereby helping the operational amplifier U1 to stabilize the current.

[0033] The resistor R2 in this circuit helps to increase the input impedance of the operational amplifier. The input impedance of the operational amplifier affects the matching degree between the signal source and the operational amplifier.

[0034] At the same time, the positive input terminal of the operational amplifier U1 in this circuit is grounded through a series capacitor to help improve the input impedance of the operational amplifier.

[0035] In this circuit, the output end of the operational amplifier U1 is connected to a resistor RL in series after being connected to a resistor RS. The resistor RL is a load resistor. The output end of the operational amplifier is connected to the load resistor, which converts the output voltage signal into a current signal. According to Ohm's law, the relationship between voltage and current can be converted by the resistance value of the load resistor. Therefore, by connecting a suitable load resistor, the output voltage signal of the operational amplifier can be converted into an actual current output.

[0036] In the prior art, the collector current (Ic) and emitter current (Ie) of the transistor are approximately equal, but in fact the emitter current also includes the base current (Ib). At this time, the output constant current includes the error of the transistor base current (Ib), which cannot meet the requirements of some high-precision constant current sources.

[0037] This circuit adds an operational amplifier U2 and replaces the transistor with a resistor RS. By using the operational amplifier U2 and the resistor RS, when external conditions change, the operational amplifier will adjust the output to ensure that the voltage drop on the resistor RS remains unchanged and is always Vref, thereby ensuring a constant output current.

[0038] Specifically:

[0039] R1=R2,R3=R4

[0040] In op amp U2: According to the virtual short principle, U2+=U2-.

[0041] In op amp U1: U1-=U1+=(Vref+U2-) / 2;

[0042] U1out=(1+R4 / R3)*U1-=Vref+U2-;

[0043] The voltage drop URS on RS = U1out-U2+ = Vref+U2-- U2+=Vref.

[0044] When external conditions change, the op amp will adjust the output to ensure that the voltage drop across the RS resistor remains constant at Vref, thereby ensuring a constant output current: the constant current source output Iout = Vref / RS; selecting different reference voltages and RS resistors can set the desired constant current value.

[0045] The above description is only a specific embodiment of the present invention, but the technical features of the present invention are not limited thereto. Any changes or modifications made by any technician in the field of the present invention are included in the patent scope of the present invention.

Claims

1. A high-precision constant current source circuit, characterized in that: It includes an operational amplifier U1 and an operational amplifier U2; the reverse input terminal of the operational amplifier U1 is grounded via a series resistor R3, and the discharge input terminal of the operational amplifier U1 is also connected to the output terminal of the operational amplifier U1 via a series resistor R4; The positive input terminal of the operational amplifier U1 is connected to the reference voltage via the series-connected resistor R1; The output end of the operational amplifier U1 is grounded via a series resistor RS; The positive input terminal of the operational amplifier U2 is connected to the resistor RS; The output terminal of the operational amplifier U2 is connected to the positive input terminal of the operational amplifier U1 via a series resistor R2.

2. The high-precision constant current source circuit according to claim 1, characterized in that: The inverting input terminal of the operational amplifier U2 is left floating.

3. The high-precision constant current source circuit according to claim 2, characterized in that: The output end of the operational amplifier U1 is connected in series with a resistor RL after being connected in series with a resistor RS.

4. The high-precision constant current source circuit according to claim 3, characterized in that: The positive input terminal of the operational amplifier U1 is grounded via a series capacitor.

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