What is the principle of current sensor?

The principle of current sensor mainly involves two basic aspects.

With the continuous advancement of science and technology, 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 technology, soft switching technology, voltage regulation technology, linear feedback voltage regulation, magnetic amplification technology, NC voltage regulation, PWM (pulse width modulation), SPWM (sinusoidal pulse width modulation) and EMC (electromagnetic compatibility). The continuous development and improvement of these power technologies are directly driven by practical needs. In order to realize the automatic detection and display of current, as well as the automatic protection function in dangerous situations such as overcurrent and overvoltage, and to achieve a higher level of intelligent control, power supply technology with functions such as inductive detection, inductive sampling, and inductive protection has become a development trend. In China, sensors that detect current or voltage are gradually becoming mainstream and are favored by the majority of power supply designers.

Generally speaking, the main function of the current sensor is sampling, that is, using the principle of electromagnetic induction or resistance to convert the current in the measured circuit into a voltage value, and then convert the voltage value into a digital signal for subsequent analysis through a dedicated ADC (analog-to-digital converter). The core controller can adjust the flux of the FET (field effect transistor) according to the detected signal, thereby changing the current value of the controlled circuit.

The working principle of the current sensor can be divided into two main operating modes:

1. Open-loop current sensor principle: Use a high-quality Magnetic Core to gather the magnetic flux generated by the original current (I_P ) in the magnetic circuit. The Hall element is fixed in a small air gap for linear detection of magnetic flux. After processing by a special circuit, the Hall voltage output by the device is consistent with the original current waveform, thereby obtaining an output voltage that conforms to the characteristics of the original waveform.

2. Magnetic balance current sensor (also known as compensation sensor): Its working principle is based on the magnetic field generated by the measured current (I_P ) on the magnetic ring, and the compensation current generated by the secondary coil is used to offset this magnetic field, so that the Hall device is in a zero flux state. The specific working process is: when the main circuit current passes through the magnetic ring, the generated magnetic field will induce a signal on the Hall device. This signal output will drive the corresponding power tube to turn on, thereby obtaining the compensation current (I_S ). The compensation current generates a magnetic field opposite to the magnetic field generated by the measured current through multiple turns, thereby compensating the original magnetic field. As the compensation process proceeds, the output of the device gradually decreases. When the magnetic field generated by the number of turns is equal to the magnetic field generated by the measured current (I_P ), the compensation current (I_S ) no longer increases. At this time, the Hall device is like being in a zero flux state and can be balanced by (I_S ). Any change in the measured current will destroy this balance, causing the Hall device to generate a signal. After the signal is energy amplified, the secondary coil will immediately generate a corresponding current to compensate for the unbalanced magnetic field. The time from magnetic imbalance to regaining balance is very short, usually less than 1 microsecond. This is a dynamic balance process.