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    189. Conduction conditions, judgment and replacement of MOS tube
    In this lesson, we mainly learn the conduction conditions of MOS tubes, the judgment of MOS tubes and the principle of replacement.
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    Recognition and Measurement of Electronic Components

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    In this lesson, we mainly learn the conduction conditions of MOS tubes,

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    the judgment of MOS tubes and the principle of replacement

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    The MOS tube is not easy to distinguish the N channel and the P channel in the real thing,

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    we can distinguish it through the schematic diagram

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    In the schematic diagram, the inner arrow pointing inward is the N channel,

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    and the arrow pointing outward is the P channel

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    N-channel MOS tube, the current flows from the D pole to the S pole

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    P-channel MOS tube, the current generally flows from the S pole to the D pole

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    MOS tube conduction condition

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    The condition of the N-channel is that the G pole voltage is greater than the S pole voltage by 4-10V

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    D and S will communicate with each other,

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    and the voltage at both ends is the same

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    The P-channel conduction condition is when the G pole voltage is less than the S pole voltage by 4-10V

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    S and D are interconnected, and the voltage of S pole and D pole is the same

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    Because the voltage in the mainboard of the mobile phone is relatively low

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    During the actual measurement,

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    we will find that when the G pole voltage is about 1.8V greater than the S pole voltage,

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    the conduction can be achieved

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    MOS tube quality judgment

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    First short-circuit the three pins of the MOS tube, discharge them,

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    and adjust the multimeter to the diode range

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    When judging whether the N channel is good or bad,

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    the black marker needs to be connected to the D pole,

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    and the red marker is connected to the S pole

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    Then there is a value of about 500,

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    and other pins will display OL when measuring

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    If there are values measured on other pins,

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    it means that the MOS tube is damaged

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    When judging whether the P-channel MOS tube is good or bad,

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    we need to connect the red marker to the D pole,

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    and the black marker to the S pole

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    At this time, the measured value is about 500,

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    and the other pins are OL when measured

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    If there are values when other pins are measured,

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    it also means that the MOS tube is damaged

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    The MOS tubes in mobile phone are relatively small,

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    or they are all in the shape of BGA

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    We don't need to measure the quality of the MOS tubes

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    MOS tube replacement principle

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    In other circuit boards, the MOS tubes need to be replaced with the same parameters after damage

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    If the MOS tube is suspected to be damaged,

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    we directly remove it, and then directly short the D and S poles

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    Because in the iPhone, the small MOS tube acts as a fuse,

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    so it can be shorted

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    The large MOS tube is only used in the charging circuit,

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    and it will not affect the charging after short circuit

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    iPhone XS and above models do not have a charging tube

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    Ok, that's all for this video

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