Quickly-started precise positive and negative constant current source

Abstract

The invention relates to a quick-start precise positive and negative constant current source. The constant current source comprises an operational amplifier N, an operational amplifier N2, a reference voltage source N1, a field effect transistor V1, a transistor V2, a field effect transistor V3, a transistor V4, a field effect transistor V6, a resistor R1, a resistor R2, a resistor R4, a resistor R5, a resistor R7, a resistor Ro + and a resistor Ro-. The constant current source is realized by adopting a circuit structure in which the field-effect tube and the triode are compositely connected, and the amplification factor of the triode is effectively improved, so that the starting time of a constant current source product is greatly prolonged, and the starting time of a high-precision positive and negative constant current source product is prolonged to be within 30 seconds from the conventional starting time of about 800 seconds. The constant current source provided by the invention can meet the requirement of a user I / F converter on the quick start of a high-precision positive and negative constant current source, so that the whole system achieves the requirements of quick conversion and quick response. According to the constant current source, the circuit structure is simple, and the starting time of a constant current source product is greatly prolonged.

Description

Technical Field

[0001] The invention relates to the technical field of high-precision positive and negative constant current sources, and in particular to a fast-starting precision positive and negative constant current source. Background Art

[0002] The I / F converter of the 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, and it is an important internal component of the I / F converter.

[0003] At present, the average launch preparation time of a missile is 15 minutes. The launch preparation time of some airborne and shipborne intelligent defense, ground-to-ground, and anti-ship missiles is even shorter, and some even require direct ignition and launch without preparation. The shorter the startup time of the constant current source, the faster the conversion speed of the I / F converter, and the faster the response speed of the whole system. Users require that a fast-starting positive and negative dual-channel constant current source be applied to the whole machine to improve its overall performance. The startup time of ordinary constant current source products can no longer meet the user's overall machine indicator requirements.

[0004] Therefore, in order to meet user requirements, it is necessary to realize a fast-start precision positive and negative constant current source. Summary of the invention

[0005] In order to solve the deficiencies in the prior art, the object of the present invention is to provide a fast-starting precision positive and negative constant current source.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

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

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

[0009] Preferably according to the present invention, the positive end of the power supply is a +15V voltage, and the negative end of the power supply is a -15V voltage.

[0010] Preferably according to the present invention, the reference N1 is a low temperature coefficient reference of the output voltage, and the temperature coefficient is as low as 1 ppm / °C.

[0011] Preferably, according to the present invention, the operational amplifier N2 and the operational amplifier N4 are low offset voltage temperature coefficient operational amplifiers, and the offset voltage temperature coefficient thereof is as low as 0.3uV / °C.

[0012] Preferably, according to the present invention, the sampling resistor R2 and the sampling resistor R5 are both high-precision resistors, and the temperature coefficient of resistance of the two resistors is required to be extremely high, and the temperature coefficient is as low as 2ppm / °C.

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

[0014] The present invention realizes a constant current source by adopting a circuit structure of a composite connection of a field effect tube and a triode, which effectively improves the amplification factor of the triode, thereby greatly improving the startup time of the constant current source product, and realizing that the startup time of a high-precision positive and negative constant current source product is improved from the conventional startup time of about 800 seconds to less than 30 seconds. The constant current source described in the present invention can meet the user's I / F converter's requirements for fast startup of a high-precision positive and negative constant current source, so that the system complete machine meets the requirements of fast conversion and fast response. The constant current source described in the present invention has a simple circuit structure and greatly improves the startup time of the constant current source product. The present invention solves the user's IF complete machine's requirements for fast startup, meets the user's high index requirements, and achieves the technical effect that the user's complete machine can be applied in batches. The fast startup of the product output current is the innovation point of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 This is the circuit schematic diagram of high-precision positive and negative constant current source;

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

[0017] Figure 3 This is the constant current source startup characteristic curve diagram using a single field effect tube as the adjustment tube;

[0018] Figure 4 The schematic diagram of the circuit of the fast-start precision positive and negative constant current source proposed by the present invention;

[0019] Figure 5 This is a startup characteristic curve diagram of the fast-start precision positive and negative constant current source proposed by the present invention. DETAILED DESCRIPTION

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

[0021] like Figure 1 As shown in the figure, the constant current source startup time is defined as the time required for the constant current source to reach the lower limit of the current nominal value accuracy (0.998 times the current nominal value) from the start of power-on. Among them, the output current nominal value is the output current when the constant current source is powered on for half an hour (1800 seconds).

[0022] When designing the precise positive and negative constant current source with quick start shown in the present invention, the output current mechanism of the constant current source circuit is first analyzed to determine the main factors affecting the output current start-up time. Figure 1 This is the circuit schematic diagram of a high-precision positive and negative constant current source. Figure 1 Analyze the constant current source shown in the figure. According to the principle of DC negative feedback, the output current is:

[0023]

[0024] Wherein, 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 circuit sampling resistor of the circuit.

[0025] Perform total differentiation on formula (1):

[0026]

[0027] Right now

[0028]

[0029] Wherein, a1 represents the influence caused by the instability of the reference voltage of N1.

[0030]

[0031] Wherein, a2 represents the influence caused by the instability of the sampling resistor R5.

[0032] It can be seen from formula (3) and formula (4) that the startup characteristics of the output current are mainly determined by the startup characteristics of the voltage reference source N1 and the resistance stability of the sampling resistor R5.

[0033] The voltage reference source N1 uses a high-precision voltage reference source, and its startup characteristics are: the startup time is 5 microseconds, which is a device with a relatively good startup time among similar devices. The relationship between the startup time required by the product and the multiple of the reference startup time is as follows:

[0034]

[0035] From formula (5), it can be seen that the startup time of the selected voltage reference source is 6 orders of magnitude faster than the startup time required by the product, which fully meets the product startup time requirement of 30 seconds.

[0036] exist Figure 2 In the circuit, the sampling resistor R5 is a passive device and uses a precision resistor with high resistance accuracy, low temperature drift, and high stability, which does not affect the startup characteristics of the product output current. However, the field effect tube V3 connected to it directly affects the establishment time of the DC negative feedback circuit, affects the establishment time of the sampling voltage at both ends of the sampling resistor R5, and thus affects the startup time of the constant current source output current.

[0037] Figure 2 The FETs V3 and V1 in the circuit are adjustment tubes. Their function is to sense the slight change of the output current and form a DC negative feedback with the sampling resistor, amplifier comparator and reference to keep the output current in a constant current state. The main characteristic indicators of the FETs V1 and V3 are transconductance g m :

[0038]

[0039] From formula (6), we can know that the transconductance g m It reflects the control ability of the gate-source voltage on the drain current, which is equivalent to the slope of the operating point on the transfer characteristic. m It is an important parameter to characterize the amplification ability of the field effect tube, and its unit is mS, which is generally within 10 millisieverts. Therefore, it can be seen that the amplification ability of a single field effect tube is limited.

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

[0041] In order to improve the amplification ability of the adjustment tube, the present invention Figure 2 The constant current source circuit shown in the figure is improved, with the focus on improving the design of the adjustment tube. The improved circuit diagram is shown in Figure 4 .

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

[0043] Preferably according to the present invention, the reference N1 is a low temperature coefficient reference of the output voltage, and the temperature coefficient is as low as 1 ppm / °C.

[0044] Preferably, according to the present invention, the operational amplifier N2 and the operational amplifier N4 are low offset voltage temperature coefficient operational amplifiers, and the offset voltage temperature coefficient thereof is as low as 0.3uV / °C.

[0045] Preferably, according to the present invention, the sampling resistor R2 and the sampling resistor R5 are both high-precision resistors, and the temperature coefficient of resistance of the two resistors is required to be extremely high, and the temperature coefficient is as low as 2ppm / °C.

[0046] In such Figure 4 In the fast-start precision positive and negative constant current source shown in the figure, operational amplifiers N and N4 are mainly used to provide feedback control to ensure the stability and accuracy of the output current, by comparing the voltage difference at the input terminal and adjusting the output to maintain the set constant current. Operational amplifier N2 is responsible for generating a control signal to field effect transistor V1 to adjust the forward current. Field effect transistor V1 and field effect transistor V3 are used as voltage-controlled switches to adjust the current in their respective paths. Field effect transistor V6 is used to assist in regulating or protecting the circuit to ensure that the circuit works normally during startup or overload. Transistor V2 and transistor V4 are used as current amplifiers, and together with the corresponding field effect transistors, they form a composite tube to enhance the current control capability. The main function is to amplify the weak signal from the field effect transistor to drive a larger load. The reference voltage source N1 provides a precise reference voltage for the circuit, which is essential to ensure 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, which are used to detect the output current and adjust the current size through a feedback mechanism to achieve the constant current source function. Resistors R1, R4, and R7 are used to provide the necessary bias and feedback paths to help the operational amplifier work correctly. The above components work together to form a positive and negative constant current source circuit that can quickly start and maintain high-precision output. Through a carefully designed feedback loop and composite tube structure, the circuit can effectively control the output current while having fast response and good stability.

[0047] In such Figure 4 In the fast-start precision positive and negative constant current source circuit shown, the present invention adopts a method of compound connection of field effect tube V3 and BJT transistor V4 to form a compound tube, and a method of compound connection of field effect tube V1 and BJT transistor V2 to form a compound tube to achieve fast start of the constant current source. By compound connection of field effect tube (FET) and bipolar transistor (BJT), this design makes full use of the advantages of two types of transistors: the high input impedance characteristics of field effect tube and the large current gain characteristics of bipolar transistor. Such a composite structure can significantly improve the response speed and stability of the circuit.

[0048] Taking the negative circuit adjustment tube analysis as an example, Figure 4 In the circuit of the fast-start precision positive and negative constant current source shown in FIG. 1 , the field effect transistor V3 used in the present invention is a voltage-driven device with a small gate current and a large drain current, which can provide a large base current to the transistor V4. The small signal mutual conductance of the field effect transistor V3 is g m , the AC small signal amplification factor of transistor V4 is β (usually within 100). The composite tube (the composite tube is formed by the composite connection of field effect tube V3 and BJT transistor V4) is equivalent to a field effect tube, and its transconductance is about (β+1)g according to the small signal equivalent model analysis.m . Compared with the transconductance of the field effect tube and the small signal amplification factor of the transistor, it can be seen that the small signal transconductance of the composite tube is larger, which can be increased by about 100 times, 2 orders of magnitude, or about several orders of magnitude, compared with the transconductance of a single field effect tube. Since the field effect tube equivalent to the composite tube has a larger transconductance, it has a sensitive small signal voltage sensing capability. Therefore, the gate-source voltage of the composite tube (the potential difference between the output end of the op amp and one end of the sampling resistor) can be used to control the drain current of the composite tube (the value is equal to the output current of the constant current source), that is, the shorter the output current establishment time, the faster the output current starts. The field effect tube V3 and the BJT transistor V4 are compositely connected to form a composite tube, and the field effect tube V1 and the BJT transistor V2 are compositely connected to form a composite tube. The field effect tube equivalent to the composite tube has the characteristics of good stability and low noise, which can make up for the shortcomings of a single field effect tube and help improve the stability of the constant current source. The analysis of the positive path adjustment tube is similar.

[0049] As can be seen from the above, for the negative-circuit adjustment tube part, the composite connection mode of field effect tube V3 and transistor V4 makes the entire composite tube have a higher transconductance (gm), because field effect tube V3 can provide enough gate voltage to drive the base of transistor V4, thereby controlling a larger current. This results in the equivalent transconductance of the composite tube being about 100 times that of the field effect tube alone, greatly enhancing the sensitivity to small signal changes. Therefore, when the voltage at the output of the op amp changes, the composite tube can react faster, thereby shortening the output current establishment time. This design achieves a significant reduction in the startup time of the constant current source from 800 seconds to 30 seconds, which is a very significant improvement. This means that the constant current source can reach a stable working state in a short time, which is very important for application scenarios such as I / F converters that require fast response. This design not only speeds up the startup speed, but also maintains good stability and low noise levels, which are important performance indicators pursued by high-performance constant current sources. In short, the fast-start precision positive and negative constant current source using composite tube technology is an innovative and practical design solution that can play an important role in a variety of application scenarios.

[0050] Figure 5 The starting characteristic curve of the quick-start precision positive and negative constant current source of the present invention using the composite tube as the adjustment tube is shown in FIG. Figure 5 It can be seen that the output current startup time of the constant current source is about 30 seconds. Compared with the existing constant current source, the startup time is shortened from 800 seconds to 30 seconds, which greatly improves the startup time characteristics of the constant current source product and meets the user's indicator usage requirements.

[0051] The above-described embodiments are merely descriptions of preferred implementations of the present invention and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the scope of protection determined by the claims of the present invention.

Claims

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

2. The fast-start precision positive and negative constant current source according to claim 1, characterized in that: The positive end of the power supply is a +15V voltage, and the negative end of the power supply is a -15V voltage.

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

4. The fast-start precision positive and negative constant current source according to claim 1, characterized in that: The operational amplifier N2 and the operational amplifier N4 are low offset voltage temperature coefficient operational amplifiers, and their offset voltage temperature coefficients are as low as 0.3uV / °C.

5. The fast-start precision positive and negative constant current source according to claim 1, characterized in that: The sampling resistor R2 and the sampling resistor R5 are both high-precision resistors, and their temperature coefficients are as low as 2 ppm / °C.

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