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Two basic principles of current sensors.
With the continuous development of science and technology, the current power supply equipment is becoming more and more compact and exquisite, and incorporates many new scientific and technological achievements. Such as switching power supply, hard switching, soft switching, voltage stabilization, linear feedback voltage stabilization, magnetic amplification, NC voltage regulation, PWM, SPWM, EMC, etc. The continuous development and progress of power technology is directly driven by actual needs. In order to realize the automatic detection and display of current, in dangerous situations, such as over-current, over-voltage, 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. Sensors that detect current or voltage have gradually become a trend in China, and are gradually being favored by the majority of power supply designers.
Generally speaking, the function of a current sensor is to sample, that is, 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.
Use 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 collected in the magnetic circuit 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 an output voltage that conforms to 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 concentrator ring, and the magnetic field generated by the secondary coil compensation current, 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 circuit current passes through the magnetic field generated by the magnetic concentrating ring, the Hall device is induced on the Hall device through the magnetic concentrating 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 turn groups, which is opposite to the magnetic field generated by the measured current, compensates the original magnetic field, and gradually reduces the output of the device. When the number of turns is equal to the magnetic field generated by Ip, Is does not increase. At this time, the Hall device is like zero magnetic flux and can be balanced by Is. Any change in the measured current will disrupt this balance. When the Hall device generates a signal, the magnetic field loses 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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