Realization of current detection in automotive electronic systems

Here we mainly introduce the current detection method and find some factors that are easily overlooked in the design. First consider two different methods: a magnetic field based detection method and a shunt based detection method.

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1. Magnetic field-based detection methods (represented by current transformers and Hall sensors) have many advantages, such as good isolation and low power loss, which makes it more applicable in power drive technology and high current applications, but It also has shortcomings, such as large size, compensation characteristics, linearity and temperature characteristics are not ideal.

2. Method of shunt The high-precision and low-resistance resistors are currently characterized by high power and small volume. This method has lower cost and higher precision. More used in automotive electronics.

In order to realize the function of anti-pinch, it is usually to use two methods to detect at the same time. The following is an example of window control.

The operating current of the body electronic control system is generally between 1-100A, but we need to pay attention to the fact that most of the load has Inrush current. What is needed today is the method of the shunt. The principle of our detection is this: the shunt method is to insert a low-resistance sense resistor in series in the current path to form a small voltage drop, which can be amplified to be treated as a A signal proportional to the current. Of course there are two most basic topologies:

Of course there are two most basic topologies:

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Low side current detection

Place the sense resistor between the load and the circuit ground, then use the op amp to amplify the voltage drop across the resistor.

High side detection

Place the sense resistor between the power supply and the load.

If you want to subdivide more, you can take into account the position of the switch, because we are dealing with inductive loads.

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The op amp circuit for the high-end detection is shown in the figure below (these two graphs are of principle level, there are actually many problems that deserve to be considered):

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