The detection and control of the output current of the ground vehicle power system is directly related to the stability and reliability of the power system operation, and affects the running condition of the vehicle and the operability of the vehicle. Due to the complicated use conditions of the vehicle, the load of the vehicle power supply changes greatly, and the output power of the power supply will also change greatly. If the output current of the power supply is not limited, the power supply will be heated due to overload, affecting its power. Output, in severe cases, will cause permanent power failure.
The application of the closed-loop Hall current sensor in the vehicle power system realizes the isolated measurement of the output current of the power system and controls the output current of the power system through feedback. When the output current of the power supply is close to the designed power output of the power system, the power output current will not increase, which limits the output power of the power system and protects the power system from damage due to changes in the power load.
With the development of component process technology, the performance of Hall current and voltage sensors developed by Hall device applications has also been greatly improved, especially the successful development of closed-loop Hall current and voltage sensors, which greatly expanded the technology. Application area.
The Hall effect is the theoretical basis for the application of Hall technology. When a semiconductor wafer with a small current is placed in a magnetic field, the carriers in the semiconductor are deflected by the Lorentz force, causing a potential difference across the semiconductor. The potential difference is the Hall voltage VH, VH is proportional to the magnetic induction intensity and the control current IC. The following formula is theoretically derived:
VH=(RH/d)×B×IC
Where: B is the magnetic induction strength;
IC is the control current;
RH is the Hall coefficient;
d is the thickness of the semiconductor.
In the formula, if the control current IC is kept constant, under certain conditions, the magnitude of the magnetic induction can be calculated by measuring the Hall voltage, thereby establishing a relationship between the magnetic field and the voltage signal.
The closed-loop Hall current sensor is a modular product that uses a Hall device as a core sensitive component to isolate the detected current. Its working principle is Hall magnetic balance. It is well known that when a current flows through a wire, a magnetic field is generated around the wire. The magnitude of the magnetic field is proportional to the amount of current flowing through the wire. This magnetic field can be concentrated by a soft magnetic material and then detected by a Hall device. Since the change of the magnetic field has a good linear relationship with the output voltage signal of the Hall device, the output signal measured by the Hall device can directly reflect the current in the wire, and the formula is as follows:
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IâˆBâˆVH
Where: I is the current through the wire;
B is the magnetic induction intensity generated after the wire is passed through.
When the appropriate scale factor is selected, the above relationship can be expressed as an equation.
For the processing of the Hall output voltage signal VH, a variety of circuits are designed, but generally can be divided into two categories, one is open-loop (or direct-test, direct-check) Hall current sensor; the other It is a closed loop (or zero magnetic, magnetic balance) Hall current sensor.
For the circuit form of the Hall sensor, it is most easy to think that the output voltage of the Hall device is directly amplified by an operational amplifier to obtain a desired signal voltage, and thereby the voltage value is used to calibrate the current measured by the primary side. This form of Hall sensor is commonly referred to as an open loop Hall current sensor. The advantage of the open-loop Hall sensor is that the circuit form is simple and the cost is relatively low; its disadvantage is that its accuracy, linearity is poor, response time is slow, and temperature drift is large.
The working principle of the closed-loop Hall current sensor is magnetically balanced, that is, the magnetic field generated by the primary current (IN) is compensated by the magnetic field generated by the current (IM) of a secondary coil, so that the Hall device is always in the detection. The working state of zero flux. When the magnetic field generated by the primary secondary compensation current reaches equilibrium in the core, the formula is as follows:
N1×IN=N2×IM
Where: N1 is the number of turns of the primary coil;
N2 is the number of turns of the secondary coil.
When the number of primary and secondary coils of the sensor is known, by measuring the magnitude of the secondary compensation current IM, the value of the primary current IN can be derived, thereby achieving the isolation measurement of the primary current.
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