What is an operational amplifier? Let you know how to use it in one minute!
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What is an operational amplifier? Let you know how to use it in one minute!

Posted Date: 2024-01-19

High-precision operational amplifiers can be used to configure shunt resistor current sensors. High-precision current sensors can be implemented over the entire temperature and operating voltage range using high-precision operational amplifiers, especially ABLIC's zero-drift amplifiers. But have you ever encountered design issues such as op amp oscillation, failure to meet design goals for detection accuracy, or inability to reduce the impact of external noise?

This article presents an easy-to-follow example of designing a low-side or high-side shunt resistor current sensor using a high-precision op amp.

Table of Contents

1. Types and characteristics of current sensors and why shunt resistor current sensors are used
2. What type of operational amplifier (signal amplifier circuit) is required for a shunt resistor current sensor?
3. Types of high-precision operational amplifiers and advantages of zero-drift amplifiers
4. Solve your design problems!
5. ABLIC’s development support services align with customers’ design efforts
6.ABLIC recommended zero-drift amplifier

1. Types and characteristics of current sensors and why shunt resistor current sensors are used

●Types and characteristics of current sensors

Current sensors are used to measure the current flowing through a circuit.
There are many types of current sensors (shunt resistors, magnetic, etc.) as shown in the figure below, and the type of sensor required depends on the current area it is intended to be used in.
Therefore, it is crucial to understand the different sensor types and use the correct current sensor for the application.

●Why use shunt resistor current sensor?

The low cost and high accuracy of current sensing of the shunt resistor current sensor make it the most commonly used of the three current sensors mentioned above. Therefore, it is widely used in applications such as battery current monitoring in automobiles and industrial equipment that require high-precision detection to tens of amps or less, and current control applications in solenoid valve-operated hydraulic actuators.

2. What type of operational amplifier (signal amplifier circuit) is required for a shunt resistor current sensor?

A shunt resistor current sensor consists of a shunt resistor and an amplifier (signal amplification circuit) to amplify the voltage drop in the sensor.

Since a few tens of amps flowing through a shunt resistor is enough to cause power loss and heating problems, a shunt resistor with low resistance is used. Since the voltage drop that occurs across the shunt resistor is tiny, this requires an amplifier that can accurately amplify tiny input signals. This amplifier uses a high precision operational amplifier.

Use 1mΩ shunt resistor to detect 10A current with an accuracy of ±1%

3. Types of high-precision operational amplifiers and advantages of zero-drift amplifiers

The input bias voltage amplifies with the input signal. Therefore, high-precision operational amplifiers with low input bias voltage and low temperature drift are widely used in current sensors and other applications that require high-precision amplification of small signals.

●Types of high-precision operational amplifiers

High-precision operational amplifiers are divided into two types according to the correction method of the input bias voltage.

1. Ordinary high-precision operational amplifier with zero drift
This is an op amp that does not automatically correct the input offset voltage. Each op amp is trimmed at the factory to minimize input offset voltage.

2.Zero-drift amplifier
This type of op amp automatically corrects the input offset voltage. This op amp incorporates a circuit that automatically minimizes the input offset voltage during operation.

●Advantages of zero-drift amplifiers

The difference in how the input bias voltage is corrected is reflected in the output voltage characteristics. The zero-drift amplifier automatically corrects the input offset voltage and will minimize the input offset voltage at all times, regardless of ambient temperature or op amp common-mode input voltage fluctuations.

ABLIC offers a full range of zero-drift operational amplifier products for general purpose and automotive applications.

3. Solve your design problems!

An example of the design of a parallel resistive current sensor using a zero-drift amplifier is introduced.

A detailed design example of a shunt resistor current sensor configured using the S-19630A zero-drift amplifier is described below.

The S-19630A is a zero-drift operational amplifier with a wide operating range (4.0 to 36V) and low input offset voltage of ±50μV maximum. Low input bias voltage drift of ±25nV/°C

Using S-19630A to design a current sensor can do the following.

●Due to its low input bias voltage and low input bias voltage drift characteristics, very high-precision current sensors can be designed whose current detection results are not affected by temperature and power supply voltage fluctuations.
●Its wide operating range allows direct connection to 5V, 12V or 24V systems.
●Input rail-to-rail allows low-side and high-side current sensing.

1. Low-side current sensing design example

●Current sensor design specifications
●Design process
●Current sensor design results
●Road diagram

2. High-side current sensing design example

●Current sensor design specifications
●Design process
●Current sensor design results
●Road diagram

5. ABLIC’s development support services align with customers’ design efforts

ABLIC's operational amplifier products offer a variety of services to help customers overcome issues or issues at every step of circuit development. Our products comply with all major automotive standards.

●Support service to assist in suggesting circuits and setting constants
ABLIC provides circuit design consulting. In order to reduce the number of prototypes, development time and development costs, and to optimize the cost performance of the application, we propose the best combination of peripheral components and integrated circuits.

●Circuit simulation services
After the circuit design is complete, the op amp starts oscillating during device evaluation! Have you ever encountered such a problem? ABLIC performs circuit simulation services to confirm that the op amp will operate without oscillation

●Provide PSpice model services
ABLIC's zero-drift amplifier products offer PSpice models to reduce the number of prototypes customers must develop. You can download the model from the page listed below. We also provide consulting services to help customers analyze simulation results using PSpice models. If you are interested, please feel free to call our sales department.

●Evaluation board service
ABLIC provides evaluation boards to help customers evaluate the equipment. And not just evaluation boards, but boards with op amp ICs and other peripherals mounted on them. If you are interested, please feel free to call our sales department.

6.ABLIC recommended zero-drift amplifier

ABLIC offers an extensive family of general-purpose and automotive operational amplifiers. These operational amplifiers are recommended for high-accuracy, high-voltage and rail-to-rail current sensing applications.

They are used by our customers in a wide range of applications. ABLIC zero-drift op amps are highly recommended.

●Automotive operational amplifier

●General purpose operational amplifier


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