The shell is made of metal, with a screw hole in the middle, which is connected to the earth. Here, through a 1M resistor and a 33 1nF capacitor in parallel, connected with the circuit board ground, what is the benefit of this?
If the shell is unstable or has static electricity, if it is directly connected to the circuit board, it will break the circuit board chip, add capacitors, and you can isolate the low frequency and high voltage, static electricity and so on to protect the circuit board. Circuit high-frequency interference and the like will be directly connected to the shell by the capacitor, which plays the function of separating the direct communication.
So why add a 1M resistor? This is because, if there is no such resistance, when there is static electricity in the circuit board, the 0.1uF capacitor connected to the earth is cut off from the connection with the shell earth, that is, suspended. These charges accumulate to a certain extent, there will be problems, must be connected to the earth, so the resistance here is used for discharge.
1M resistance is so large, if there is static electricity outside, high voltage and the like, it can also effectively reduce the current, and will not cause damage to the chip in the circuit.
Post time: Aug-08-2023