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What is the principle of current sensor?

by:Transmart     2022-08-03

With the continuous development of science and technology, the current power supply equipment is becoming more and more compact, and integrates many new scientific and technological achievements. Such as switching power supply, hard switching, soft switching, voltage regulation, linear feedback voltage regulation, magnetic amplification, NC voltage regulation, PWM, SPWM, EMC, etc. The continuous development and advancement of power technology is directly driven by practical needs. In order to realize the automatic detection and display of current, in dangerous situations, such as overcurrent, overvoltage, etc., it has automatic protection function and high intelligent control function. Power supply technology with functions such as inductive detection, inductive sampling, and inductive protection has gradually become a development trend. Inductors that detect current or voltage have gradually become a trend in China, and are gradually favored by power supply designers.​​

In general, the function of the current sensor is to sample, that is, to convert the current of the circuit under test into a voltage value through electromagnetic induction or resistance, and then convert the ADC dedicated ADC into a digital signal for analysis. The core controller can adjust the flux of the FET according to the detected signal, thereby changing the current value of the controlled circuit.​​

operating mode. Using Hall magnetic balance principle (closed loop) and Hall direct measurement (open loop).​​

1. Principle of open-loop current sensor: The magnetic flux generated by the original current IP current is gathered in the magnetic circuit by using a high-quality magnetic core, and the Hall element is fixed in a small air gap to linearly detect the flux. After special circuit processing, the Hall voltage output by the device is consistent with the original side wave, and the output voltage in line with the original side wave is obtained.​​

2. The magnetic balance current sensor, also known as the compensation sensor, is the magnetic field generated by the measured current Ip on the magnetic concentrating ring, and the magnetic field generated by the compensation current is compensated by the secondary coil, so that the Hall device is in a state of zero magnetic flux.​​

The specific working process of the magnetic balance current sensor is: when the main loop current passes through the magnetic field generated by the magnetic focusing ring, the magnetic field is induced on the Hall device through the magnetic focusing ring, and the generated signal output drives the corresponding power tube and conducts, thereby obtaining Compensation current Is. This current generates a magnetic field through multiple turns, which is opposite to the magnetic field produced by the current under test, compensating for the original magnetic field and gradually reducing the output of the device. Is does not increase when the number of turns is equal to the magnetic field produced by Ip. At this point, the Hall device acts like zero flux and can be balanced by Is. Any change in the measurement current will upset this balance. When the Hall device generates a signal, the magnetic field is out of balance. After the energy is amplified, the secondary coil immediately generates a corresponding current to compensate for the unbalanced magnetic field. The time from magnetic unbalance to unbalance rebalance is less than 1 microsecond, which is a dynamic process.​​
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