An adjustable constant current output circuit

Abstract

This invention discloses an adjustable constant current output circuit, solving the problems of low accuracy, poor stability, and insufficient adaptability of existing circuits. The circuit includes a signal processing unit, a constant current control unit, and a noise suppression unit: the signal processing unit generates a reference voltage through a first operational amplifier, resistors, and capacitors; the constant current control unit uses a second operational amplifier and a PNP transistor to output the current; the noise suppression unit filters out ground loop noise through a capacitor. This circuit achieves precise milliampere-level current adjustment through a DAC1 signal and a resistor network, with an error ≤ ±0.5mA; the capacitor and feedback loop suppress power supply ripple, with current fluctuation <1% under 100mV ripple; it is specifically optimized for low current, offering flexible adjustment and low power consumption, making it suitable for scenarios such as precision sensor power supply, LED lighting driver, and chip testing equipment, improving equipment accuracy, stability, and battery life.

Description

Technical Field

[0001] This utility model relates to the field of electronic circuit technology, specifically a low-current constant-current adjustable circuit suitable for output current ≤1A, especially suitable for precision sensor power supply, LED lighting driver and chip testing equipment. Background Technology

[0002] In low-current applications, such as milliampere-level or even smaller current scenarios, there are many special requirements and challenges for the design and performance of constant current circuits. Existing constant current circuit solutions have shortcomings in several aspects and are difficult to meet the high precision, high stability and high adaptability requirements of practical applications.

[0003] Many low-current applications, such as powering precision sensors, have extremely high requirements for current accuracy. For example, in some temperature or pressure sensors, the operating current is typically in the milliampere or microampere range. Even small current fluctuations can cause significant changes in the sensor's output signal, thus affecting measurement accuracy. Some existing constant current circuits, especially those based on simple linear regulators or low-cost operational amplifiers, often fail to provide the required accuracy. These circuits can be affected by factors such as component aging, temperature drift, and power supply voltage fluctuations, leading to deviations in the output current. Furthermore, some circuits are not designed to adequately account for nonlinear effects at low current levels, such as the input bias current of op-amps and the leakage current of transistors. These factors can become significant in low-current applications, further reducing the accuracy of the current output.

[0004] Low-current circuits are more susceptible to various interference factors, leading to unstable output current. Power supply noise is a major issue, especially in cases of poor power quality or when the circuit requires portable power, such as battery-powered devices. Ripple and noise in the power supply can directly couple into the constant current circuit, causing fluctuations in the output current. Furthermore, electromagnetic interference (EMI) is also a significant problem. Industrial environments or complex electronic devices contain numerous sources of EMI, such as motors, switching power supplies, and wireless communication devices. The electromagnetic fields generated by these sources can couple into the wiring or components of the constant current circuit, causing current instability. Some existing constant current circuits lack effective noise suppression and anti-interference measures, such as insufficient filter capacitors, lack of shielding, or unoptimized circuit layout, making the circuit prone to output current fluctuations in practical applications, affecting the normal operation of the equipment.

[0005] General-purpose constant current circuits are typically designed to meet a wide range of current output requirements, making them less than ideal for low-current applications. In terms of regulation range, these circuits may not offer sufficiently fine regulation resolution, struggling to meet the precise regulation needs in the milliamp range or even smaller current ranges. For example, some constant current circuits based on switching power supplies have large regulation steps, which may not achieve smooth current regulation in low-current regions. Regarding power consumption, general-purpose constant current circuits may not be optimized for low power consumption, resulting in excessive power consumption in low-current applications. For instance, some linear regulators still consume significant quiescent current at low current outputs, which is unacceptable in power-sensitive applications such as battery-powered portable devices. Furthermore, general-purpose circuits may not meet the specific requirements of low-current applications in terms of dynamic performance such as startup time and response speed. Summary of the Invention

[0006] In order to solve the above-mentioned technical problems, this utility model provides an adjustable constant current output circuit.

[0007] The technical solution of this utility model is implemented as follows:

[0008] An adjustable constant current output circuit includes:

[0009] The signal processing unit's power supply voltage is connected to the non-inverting input of the first operational amplifier via resistor R59; the external voltage regulation signal is connected to its inverting input via resistor R61; resistor R60 and capacitor C34 are connected in parallel and then connected across the inverting input and output of U30-A to generate a reference voltage, VA=VP−DAC1×(R60 / R61).

[0010] The constant current control unit has its non-inverting input terminal grounded via resistor R50; its inverting input terminal is connected to the emitter of transistor Q17 and resistor R57 (connected to VP); the base of Q17 is connected to the output terminal of U30-B via resistor R55, and the collector is connected to the output terminal via resistor R56. The output current satisfies IOUTA=(VP−VA) / R57.

[0011] The noise suppression unit, with capacitor C24 connected in parallel across resistor R50, is used to filter out ground loop noise.

[0012] The constant current adjustable circuit of this invention has significant advantages over the prior art.

[0013] First, precise milliampere-level current regulation is achieved through the synergistic effect of the DAC1 signal and the resistor network. For example, when VP=5V, DAC1=1V, and R60 / R61=2, VA is precisely calculated to be 3V, and the output current IOUTA=20mA, with an error controlled within ±0.5mA. This high-precision regulation capability is crucial for devices such as precision sensors, ensuring the accuracy and reliability of measurement data. Second, capacitors C24 and C34 effectively filter out noise, and the feedback loop compensates for current fluctuations in real time, improving circuit stability. Even with a 100mV ripple in the power supply, the output current fluctuation can still be suppressed to less than 1%. This effectively prevents light flickering in applications such as small LED lighting equipment, improving the user experience and extending equipment lifespan. Finally, this circuit is optimized for low-current scenarios, offering flexible adjustment range and low power consumption. By precisely configuring the DAC1 signal and external resistor values, flexible adjustment within the milliampere current range can be achieved to meet the needs of different devices. The low-power design helps extend battery life, reduce heat dissipation issues, and improve equipment reliability and operating efficiency. Attached Figure Description

[0014] Figure 1 This is a circuit diagram of the present invention.

[0015] In the diagram, operational amplifiers: U30-A and U30-B;

[0016] Transistor: Q17;

[0017] Resistors: R50, R55, R57, R59, R61;

[0018] Capacitors: C24, C34;

[0019] Power supply voltage: VP;

[0020] Current output terminal: IOUTA. Detailed Implementation

[0021] Example 1

[0022] This utility model discloses an adjustable constant current output circuit, comprising:

[0023] In the signal processing unit, the power supply voltage VP is connected to the non-inverting input of the first operational amplifier U30-A via resistor R59; the external voltage regulation signal DAC1 is connected to its inverting input via resistor R61; resistor R60 and capacitor C34 are connected in parallel and then connected across the inverting input and output of U30-A to generate a reference voltage, VA=VP−DAC1×(R60 / R61).

[0024] The constant current control unit has a non-inverting input terminal of the second operational amplifier U30-B connected to ground via resistor R50; its inverting input terminal is connected to the emitter of transistor Q17 (PNP type) and resistor R57; the base of Q17 is connected to the output terminal of U30-B via resistor R55, and the collector is connected to the output terminal IOUTA via resistor R56. The output current satisfies IOUTA=(VP−VA) / R57.

[0025] The noise suppression unit, with capacitor C24 connected in parallel across resistor R50, is used to filter out ground loop noise.

[0026] The specific circuit of the adjustable constant current output circuit of this utility model includes:

[0027] First operational amplifier U30-A and second operational amplifier U30-B;

[0028] Transistor Q17 is a PNP type transistor;

[0029] Resistor group R59, R61, R60, R57, R50, R55, R56;

[0030] First capacitor C34 and second capacitor C24; where:

[0031] The power supply voltage VP is connected to the non-inverting input of the first operational amplifier U30-A via resistor R59;

[0032] The external voltage-regulated signal DAC1 is connected to the inverting input of the first operational amplifier U30-A via resistor R61;

[0033] Resistor R60 and first capacitor C34 are connected in parallel and then connected across the inverting input and output terminals of the first operational amplifier U30-A.

[0034] One end of resistor R50 is grounded, and the other end is connected to the non-inverting input of the second operational amplifier U30-B;

[0035] The inverting input of the second operational amplifier U30-B is connected to the emitter of transistor Q17 and one end of resistor R57, and the other end of resistor R57 is connected to the power supply voltage VP.

[0036] The base of transistor Q17 is connected to the output terminal of the second operational amplifier U30-B via resistor R55, and the collector is connected to the current output terminal IOUTA via resistor R56.

[0037] The second capacitor C24 is connected in parallel across the resistor R50.

[0038] Preferably, the output voltage VA of the first operational amplifier U30-A satisfies the following relationship: VA=VP−DAC1×(R60 / R61)

[0039] Preferably, the output current IOUTA satisfies the following relationship: IOUTA=(VP−VA) / R57

[0040] Preferably, the second capacitor C24 is used to filter out noise signals across the resistor R50.

[0041] The circuit is used in low-current scenarios where the output current is ≤1A.

[0042] The above description is merely a preferred embodiment of the present utility model and is not intended to limit the present utility model in any way. Although the present utility model has been disclosed above with reference to a preferred embodiment, it is not intended to limit the present utility model. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present utility model. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present utility model without departing from the scope of the present utility model shall still fall within the scope of the present utility model.

Claims

1. An adjustable constant current output circuit, comprising: First operational amplifier (U30-A) and second operational amplifier (U30-B); Transistor (Q17) is a PNP type transistor; The resistor group includes resistor (R59), resistor (R61), resistor (R60), resistor (R57), resistor (R50), resistor (R55), and resistor (R56). First capacitor (C34) and second capacitor (C24); Its features are, The power supply voltage (VP) is connected to the non-inverting input of the first operational amplifier (U30-A) via resistor (R59); An external voltage-regulated signal (DAC1) is connected to the inverting input of the first operational amplifier (U30-A) via a resistor (R61); The resistor (R60) and the first capacitor (C34) are connected in parallel and then connected across the inverting input and output terminals of the first operational amplifier (U30-A); One end of the resistor (R50) is grounded, and the other end is connected to the non-inverting input of the second operational amplifier (U30-B); The inverting input of the second operational amplifier (U30-B) is connected to the emitter of the transistor (Q17) and one end of the resistor (R57), and the other end of the resistor (R57) is connected to the power supply voltage (VP). The base of transistor (Q17) is connected to the output of the second operational amplifier (U30-B) via resistor (R55), and the collector is connected to the current output terminal (IOUTA) via resistor (R56).

2. The adjustable constant current output circuit according to claim 1, characterized in that, The output voltage (VA) of the first operational amplifier (U30-A) satisfies the following relationship: VA=VP-DAC1×(R60 / R61), VA=VP-DAC1×(R60 / R61).

3. The adjustable constant current output circuit according to claim 1, characterized in that, The current output terminal (IOUTA) satisfies the following relationship: IOUTA=(VP−VA) / R57, IOUTA=(VP−VA) / R57.

4. The adjustable constant current output circuit according to claim 1, characterized in that, The second capacitor (C24) is connected in parallel across the resistor (R50).

5. The adjustable constant current output circuit according to claim 1, characterized in that, The second capacitor (C24) is used to filter out noise signals across the resistor (R50).

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