A fast-start precision positive and negative constant current source

Abstract

This invention relates to a precision positive and negative constant current source with fast startup. The constant current source includes operational amplifier N, operational amplifier N2, reference voltage source N1, field-effect transistor V1, transistor V2, field-effect transistor V3, transistor V4, field-effect transistor V6, resistors R1, R2, R4, R5, R7, resistor Ro+, and resistor Ro-. This invention achieves the constant current source by employing a circuit structure that combines field-effect transistors and transistors, effectively increasing the transistor's amplification factor and thus significantly improving the startup time of the constant current source product. It reduces the startup time of high-precision positive and negative constant current sources from approximately 800 seconds to less than 30 seconds. The constant current source described in this invention can meet the requirements of users' I / F converters for fast startup of high-precision positive and negative constant current sources, enabling the entire system to achieve rapid conversion and rapid response. The constant current source described in this invention has a simple circuit structure and greatly improves the startup time of constant current source products.

Description

Technical Field

[0001] This invention relates to the field of high-precision positive and negative constant current source technology, specifically to a precision positive and negative constant current source with fast start-up. Background Technology

[0002] The I / F converter in an inertial navigation system requires a high-precision positive and negative constant current source to provide charging and discharging current for the integrator inside the I / F converter. The accuracy, temperature drift, and startup characteristics of this current directly determine the key performance indicators of the I / F converter, such as conversion speed, resolution, and nonlinearity, making it an important internal component of the I / F converter.

[0003] Currently, the average launch preparation time for missiles is 15 minutes. Some airborne and shipborne intelligent air defense, land-attack, and anti-ship missiles require even shorter preparation times, sometimes even requiring no preparation and direct ignition and launch. The shorter the start-up time of the constant current source, the faster the conversion speed of the I / F converter, and the faster the response speed of the entire system. Users require fast-start dual-channel positive and negative constant current sources for the entire system to improve its overall performance. The start-up time of ordinary constant current source products can no longer meet the user's overall system performance requirements.

[0004] Therefore, in order to meet user requirements, a precision positive and negative constant current source with fast startup is needed. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a precision positive and negative constant current source that can start up quickly.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A precision positive and negative constant current source with fast start-up, the constant current source includes operational amplifier N, operational amplifier N2, reference voltage source N1, field-effect transistor V1, transistor V2, field-effect transistor V3, transistor V4, field-effect transistor V6, resistor R1, resistor R2, resistor R4, resistor R5, resistor R7, resistor Ro+, and resistor Ro-.

[0008] The positive input terminal of operational amplifier N2 is connected to the first terminal of resistor R4, and the second terminal of resistor R4 is connected to the positive power supply terminal. The negative input terminal of operational amplifier N2 is connected to the first terminal of resistor R2, and the second terminal of resistor R2 is connected to the positive power supply terminal. The positive power supply terminal of operational amplifier N2 is connected to the positive power supply terminal, and the negative power supply terminal is grounded. The output terminal of operational amplifier N2 is connected to the gate of field-effect transistor V1. The source of field-effect transistor V1 is connected to the base of transistor V2. The drain of field-effect transistor V1 is connected to the collector of transistor V2 and the first terminal of resistor Ro+. The emitter of transistor V2 is connected to the first terminal of resistor R2, and the second terminal of resistor R2 is connected to the positive power supply terminal. The second terminal of resistor Ro+ is grounded. The output terminal of operational amplifier N is connected to the gate of field-effect transistor V6. The drain of field-effect transistor V6 is connected to the first terminal of resistor R4 and the positive input terminal of operational amplifier N2. The source of field-effect transistor V6 is connected to the gate of resistor R4. The first end of resistor R7 is connected, and the second end of resistor R7 is connected to the first end of resistor R1. The first end of resistor R1 is also connected to the negative input terminal of operational amplifier N, and the second end of resistor R1 is connected to the negative power supply terminal. The positive input terminal of operational amplifier N is connected to the positive input terminal of operational amplifier N4. The input terminal of reference voltage source N1 is grounded, the grounded terminal is connected to the negative power supply of the circuit, and the output terminal is connected to the positive input terminal of operational amplifier N4 as a reference voltage. The positive power supply terminal of operational amplifier N4 is grounded, and the negative power supply terminal is connected to the negative power supply terminal. The output terminal of operational amplifier N4 is connected to the gate of field-effect transistor V3, the source of field-effect transistor V3 is connected to the base of transistor V4, the drain of field-effect transistor V3 is connected to the first end of resistor Ro-, and the second end of resistor Ro- is grounded. The emitter of transistor V4 is connected to the first end of resistor R5, the first end of resistor R5 is also connected to the negative input terminal of operational amplifier N4, and the second end of resistor R5 is connected to the negative power supply terminal.

[0009] According to a preferred embodiment of the present invention, the positive terminal of the power supply is +15V and the negative terminal of the power supply is -15V.

[0010] According to a preferred embodiment of the present invention, the reference N1 is a low temperature coefficient reference for the output voltage, with a temperature coefficient as low as 1 ppm / ℃.

[0011] According to a preferred embodiment of the present invention, the operational amplifiers N2 and N4 are low offset voltage temperature coefficient operational amplifiers, with an offset voltage temperature coefficient as low as 0.3uV / ℃.

[0012] According to a preferred embodiment of the present invention, both the sampling resistor R2 and the sampling resistor R5 are high-precision resistors, and their resistance temperature coefficients are required to be extremely high, with a temperature coefficient as low as 2ppm / ℃.

[0013] Compared with the prior art, the advantages of the present invention are:

[0014] This invention achieves a constant current source by employing a circuit structure that combines a field-effect transistor (FET) and a bipolar junction transistor (BJT), effectively increasing the amplification factor of the BJT and thus significantly improving the startup time of the constant current source product. This reduces the startup time of high-precision positive and negative constant current sources from approximately 800 seconds to less than 30 seconds. The constant current source described in this invention meets the requirements of users' I / F converters for rapid startup of high-precision positive and negative constant current sources, enabling the entire system to achieve rapid conversion and response. The constant current source described in this invention features a simple circuit structure, greatly improving the startup time of the constant current source product. This invention solves the rapid startup requirements of users' entire I / F systems, meeting their high performance requirements and achieving the technical effect of mass application of the entire system. The rapid startup of the product's output current is the innovation of this invention. Attached Figure Description

[0015] Figure 1 The circuit schematic for a high-precision positive and negative constant current source;

[0016] Figure 2 Schematic diagram of constant current source startup characteristics;

[0017] Figure 3 The starting characteristic curve of a constant current source using a single field-effect transistor as the regulating transistor is shown.

[0018] Figure 4 The circuit diagram shows the fast-start precision positive and negative constant current source proposed in this invention.

[0019] Figure 5 This is a startup characteristic curve of the precision positive and negative constant current source with rapid startup proposed in this invention. Detailed Implementation

[0020] The present invention will be further described below with reference to the accompanying drawings:

[0021] like Figure 1 As shown, the constant current source startup time is defined as the time required for the constant current source to start powering on until the output current reaches the lower limit of the nominal current value accuracy (0.998 times the nominal current value). The nominal output current value is the output current after the constant current source has been powered on for half an hour (1800 seconds).

[0022] When designing the precision positive and negative constant current source with fast start-up as shown in this invention, the mechanism of the output current of the constant current source circuit is first analyzed to determine the main factors affecting the start-up time of the output current. Figure 1 This is the circuit schematic for a high-precision positive and negative constant current source. Figure 1 Analyzing the constant current source shown, based on the principle of DC negative feedback, the output current is:

[0023]

[0024] Where Vref is the output voltage of the reference N1 output port relative to the negative power supply, and R5 is the resistance value of the negative sampling resistor of the circuit.

[0025] Taking the total differential of formula (1):

[0026]

[0027] Right now

[0028]

[0029] Where a1 represents the effect of the instability of the N1 reference voltage.

[0030]

[0031] Where a2 represents the effect of the instability of the sampling resistor R5.

[0032] As can be seen from formulas (3) and (4), the starting characteristics of the output current are mainly determined by the starting characteristics of the voltage reference source N1 and the resistance stability of the sampling resistor R5.

[0033] The voltage reference source N1 is a high-precision voltage reference source with a startup time of 5 microseconds, which is among the best in its class. The required startup time and its ratio to the startup time of this reference source are as follows:

[0034]

[0035] As can be seen from formula (5), the selected voltage reference source starts up 6 orders of magnitude faster than the product's required start-up time, which fully meets the product's 30-second start-up time requirement.

[0036] exist Figure 2 In this circuit, the sampling resistor R5 is a passive component and a precision resistor with high resistance accuracy, low temperature drift, and high stability, thus not affecting the start-up characteristics of the product's output current. However, the field-effect transistor V3 connected to it directly affects the settling time of the DC negative feedback circuit, which in turn affects the settling time of the sampling voltage across the sampling resistor R5, thereby affecting the start-up time of the constant current source output current.

[0037] Figure 2 In this circuit, field-effect transistors V3 and V1 are the regulating transistors. Their function is to sense minute changes in the output current and, together with the sampling resistor, amplifier, comparator, and reference, form DC negative feedback to maintain a constant output current. m :

[0038]

[0039] From formula (6), it can be seen that the transconductance g m This reflects the gate-source voltage's control over the drain current; it is equivalent to the slope of the operating point on the transfer characteristic. Transconductance g m It is an important parameter characterizing the amplification capability of a field-effect transistor (FET), measured in millisieverters (mS), and typically within 10 millisieverts. Therefore, it is known that the amplification capability of a single FET is limited.

[0040] Similar products use a single field-effect transistor as the regulating transistor in the DC negative feedback circuit. The establishment time for the constant current source feedback balance is relatively long, resulting in a long start-up time for the constant current source output current, approximately 800 seconds. Figure 3 This is a startup characteristic curve of a constant current source using a single field-effect transistor as the regulating transistor, from... Figure 3 It can be seen that the output current start-up time using a single field-effect transistor as the regulating transistor is about 800 seconds.

[0041] To improve the amplification capability of the regulating tube, this invention... Figure 2 This circuit is an improvement upon the constant current source circuit shown, with a focus on redesigning the regulating transistor. The improved circuit diagram is shown below. Figure 4 .

[0042] like Figure 4The diagram illustrates a fast-start precision positive and negative constant current source, comprising operational amplifier N, operational amplifier N2, reference voltage source N1, field-effect transistor V1, transistor V2, field-effect transistor V3, transistor V4, field-effect transistor V6, resistors R1, R2, R4, R5, R7, resistor Ro+, and resistor Ro-. The positive input terminal of operational amplifier N2 is connected to the first terminal of resistor R4, and the second terminal of resistor R4 is connected to a +15V power supply. The negative input terminal of operational amplifier N2 is connected to the first terminal of resistor R2, and the second terminal of resistor R2 is connected to a +15V power supply. The positive power supply terminal of operational amplifier N2 is connected to a +15V power supply, and the negative power supply terminal is grounded. The output terminal of operational amplifier N2 is connected to the gate of field-effect transistor V1. The source of field-effect transistor V1 is connected to the base of transistor V2, and the drain of field-effect transistor V1 is connected to the collector of transistor V2 and the first terminal of resistor Ro+. The emitter of transistor V2 is connected to the first terminal of resistor R2, and the second terminal of resistor R2 is connected to a +15V power supply. The second terminal of resistor Ro+ is grounded. The output of operational amplifier N is connected to the gate of field-effect transistor V6. The drain of field-effect transistor V6 is connected to the first terminal of resistor R4 and the positive input terminal of operational amplifier N2. The source of field-effect transistor V6 is connected to the first terminal of resistor R7. The second terminal of resistor R7 is connected to the first terminal of resistor R1. The first terminal of resistor R1 is also connected to the negative input terminal of operational amplifier N. The second terminal of resistor R1 is connected to a -15V power supply. The positive input terminal of operational amplifier N is connected to the positive input terminal of operational amplifier N4. The first terminal of reference voltage source N1 is connected to a -15V power supply, the second terminal is grounded, and the third terminal is connected to the positive input terminal of operational amplifier N4 as a reference voltage. The positive terminal of the power supply of operational amplifier N4 is grounded, and the negative terminal is connected to a -15V power supply. The output of operational amplifier N4 is connected to the gate of field-effect transistor V3. The source of field-effect transistor V3 is connected to the base of transistor V4. The drain of field-effect transistor V3 is connected to the first terminal of resistor Ro-, and the second terminal of resistor Ro- is grounded. The emitter of transistor V4 is connected to the first terminal of resistor R5, which is also connected to the negative input terminal of operational amplifier N4. The second terminal of resistor R5 is connected to a -15V power supply.

[0043] According to a preferred embodiment of the present invention, the reference N1 is a low temperature coefficient reference for the output voltage, with a temperature coefficient as low as 1 ppm / ℃.

[0044] According to a preferred embodiment of the present invention, the operational amplifiers N2 and N4 are low offset voltage temperature coefficient operational amplifiers, with an offset voltage temperature coefficient as low as 0.3uV / ℃.

[0045] According to a preferred embodiment of the present invention, both the sampling resistor R2 and the sampling resistor R5 are high-precision resistors, and their resistance temperature coefficients are required to be extremely high, with a temperature coefficient as low as 2ppm / ℃.

[0046] In such Figure 4 In the fast-start precision positive and negative constant current source shown, operational amplifiers N and N4 are mainly used to provide feedback control, ensuring the stability and accuracy of the output current. They maintain a set constant current by comparing the voltage difference at the input terminals and adjusting the output. Operational amplifier N2 generates a control signal for field-effect transistor V1 to regulate the forward current. Field-effect transistors V1 and V3 act as voltage control switches, regulating the current in their respective paths. Field-effect transistor V6 is used to assist in regulation or protection circuitry, ensuring normal operation during startup or overload. Transistors V2 and V4 act as current amplifiers, forming a composite transistor with the corresponding field-effect transistors to enhance current control capability. Their main function is to amplify the weak signal from the field-effect transistors to drive larger loads. The reference voltage source N1 provides a precise reference voltage, which is crucial for ensuring the accuracy of the output current. Resistors R2 and R5 are used to set the bias points of transistors V2 and V4; Ro+ and Ro- are output resistors used to detect the output current and adjust its magnitude through a feedback mechanism to achieve the constant current source function. Resistors R1, R4, and R7 provide the necessary bias and feedback paths to help the operational amplifier operate correctly. These components work together to form a positive and negative constant current source circuit capable of rapid startup and maintaining high-precision output. Through a carefully designed feedback loop and composite transistor structure, this circuit effectively controls the output current while exhibiting fast response and good stability.

[0047] In such Figure 4 In the fast-start precision positive and negative constant current source circuit shown, this invention employs a composite transistor formed by combining a field-effect transistor (FET) V3 and a BJT transistor V4, and a composite transistor formed by combining an FET V1 and a BJT transistor V2, to achieve fast start-up of the constant current source. By combining FETs and BJTs, this design fully utilizes the advantages of both types of transistors: the high input impedance of the FET and the high current gain of the BJT. This composite structure can significantly improve the circuit's response speed and stability.

[0048] Taking the analysis of the negative circuit regulating pipe as an example, in such Figure 4 In the circuit of the precision positive and negative constant current source with fast startup shown, the field-effect transistor V3 used in this invention is a voltage-driven device with a small gate current and a large drain current, which can provide a large base current to transistor V4. The small-signal transconductance of the field-effect transistor V3 is g. m The small-signal amplification factor of transistor V4 is β (typically less than 100). This composite transistor (formed by connecting field-effect transistor V3 and BJT transistor V4) is equivalent to a single field-effect transistor, and its transconductance, analyzed using the small-signal equivalent model, is approximately (β+1)g.m Compared to the transconductance of a field-effect transistor (FET) and the small-signal amplification factor of a transistor, the composite transistor has a significantly larger small-signal transconductance, increasing by approximately 100 times (two orders of magnitude, or several sieves) compared to the transconductance of a single FET. Because the composite transistor's equivalent FET has a larger transconductance, it possesses a sensitive small-signal voltage sensing capability. Therefore, a smaller gate-source voltage (the potential difference between the op-amp output and one end of the sampling resistor) can be used to control the composite transistor's drain current (equivalent to the output current of the constant current source), resulting in a shorter output current settling time and faster output current initiation. A composite transistor is formed by connecting FET V3 and BJT transistor V4, and by connecting FET V1 and BJT transistor V2. The composite transistor's equivalent FET exhibits good stability and low noise, compensating for the shortcomings of a single FET and contributing to improved stability of the constant current source. The analysis of the forward adjustment transistor is similar.

[0049] As shown above, for the negative circuit regulating transistor section, the combined connection of MOSFET V3 and transistor V4 results in a higher transconductance (gm) for the entire composite transistor. This is because MOSFET V3 can provide sufficient gate voltage to drive the base of transistor V4, thereby controlling a larger current. This leads to an equivalent transconductance of approximately 100 times that of using a MOSFET alone, significantly enhancing sensitivity to small signal changes. Therefore, when the voltage at the op-amp output changes, the composite transistor can react more quickly, thus shortening the output current settling time. This design significantly reduces the startup time of the constant current source from 800 seconds to 30 seconds, a remarkable improvement. This means that the constant current source can reach a stable operating state in a short time, which is crucial for applications requiring rapid response, such as I / F converters. This design not only accelerates startup speed but also maintains good stability and low noise levels, all important performance indicators sought after by high-performance constant current sources. In conclusion, the fast-start precision positive and negative constant current source using composite transistor technology is an innovative and practical design that can play an important role in various application scenarios.

[0050] Figure 5 This is a startup characteristic curve of the precision positive and negative constant current source for rapid startup described in this invention, which uses a composite tube as the regulating tube. Figure 5 It can be seen that the output current of this constant current source starts up in about 30 seconds. Compared with the existing constant current sources, the start-up time is shortened from 800 seconds to 30 seconds, which greatly improves the start-up time characteristics of the constant current source product and meets the user's performance requirements.

[0051] The above-described embodiments are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A precision positive and negative constant current source with rapid start-up, characterized in that, The constant current source includes operational amplifier N, operational amplifier N2, reference voltage source N1, field-effect transistor V1, transistor V2, field-effect transistor V3, transistor V4, field-effect transistor V6, resistor R1, resistor R2, resistor R4, resistor R5, resistor R7, resistor Ro+, and resistor Ro-. The positive input terminal of operational amplifier N2 is connected to the first terminal of resistor R4, and the second terminal of resistor R4 is connected to the positive power supply terminal. The negative input terminal of operational amplifier N2 is connected to the first terminal of resistor R2, and the second terminal of resistor R2 is connected to the positive power supply terminal. The positive power supply terminal of operational amplifier N2 is connected to the positive power supply terminal, and the negative power supply terminal is grounded. The output terminal of operational amplifier N2 is connected to the gate of field-effect transistor V1. The source of field-effect transistor V1 is connected to the base of transistor V2. The drain of field-effect transistor V1 is connected to the collector of transistor V2 and the first terminal of resistor Ro+. The emitter of transistor V2 is connected to the first terminal of resistor R2, and the second terminal of resistor R2 is connected to the positive power supply terminal. The second terminal of resistor Ro+ is grounded. The output terminal of operational amplifier N is connected to the gate of field-effect transistor V6. The drain of field-effect transistor V6 is connected to the first terminal of resistor R4 and the positive input terminal of operational amplifier N2. The source of field-effect transistor V6 is connected to the gate of resistor R4. The first end of resistor R7 is connected, and the second end of resistor R7 is connected to the first end of resistor R1. The first end of resistor R1 is also connected to the negative input terminal of operational amplifier N, and the second end of resistor R1 is connected to the negative power supply terminal. The positive input terminal of operational amplifier N is connected to the positive input terminal of operational amplifier N4. The input terminal of reference voltage source N1 is grounded, the grounded terminal is connected to the negative power supply of the circuit, and the output terminal is connected to the positive input terminal of operational amplifier N4 as a reference voltage. The positive power supply terminal of operational amplifier N4 is grounded, and the negative power supply terminal is connected to the negative power supply terminal. The output terminal of operational amplifier N4 is connected to the gate of field-effect transistor V3, the source of field-effect transistor V3 is connected to the base of transistor V4, the drain of field-effect transistor V3 is connected to the first end of resistor Ro-, and the second end of resistor Ro- is grounded. The emitter of transistor V4 is connected to the first end of resistor R5, the first end of resistor R5 is also connected to the negative input terminal of operational amplifier N4, and the second end of resistor R5 is connected to the negative power supply terminal.

2. The precision positive and negative constant current source with rapid start-up according to claim 1, characterized in that, The positive terminal of the power supply is +15V, and the negative terminal is -15V.

3. The precision positive and negative constant current source with rapid start-up according to claim 1, characterized in that, The reference voltage source N1 is a low temperature coefficient reference for the output voltage, with a temperature coefficient as low as 1ppm / ℃.

4. The precision positive and negative constant current source with rapid start-up according to claim 1, characterized in that, The operational amplifiers N2 and N4 are low offset voltage temperature coefficient operational amplifiers, with an offset voltage temperature coefficient as low as 0.3uV / ℃.

5. The precision positive and negative constant current source with rapid start-up according to claim 1, characterized in that, Both resistors R2 and R5 are high-precision resistors with a temperature coefficient as low as 2ppm / ℃.

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