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This lesson talks about the overvoltage protection circuit of Huawei and Xiaomi mobile phones

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In this circuit, the power supply VCHG_USB_CON is the 5V voltage from the tail connector

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Here, Q1601 and Q1604 are two MOS tubes, used as switches

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After the 5V power supply comes from the tail plug, it passes through the D pole of this MOS,

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and at the same time reaches the D pole of another MOS tube

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Through the D pole to the S pole of the MOS tube

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After reaching the S level, they merge into a line and output to the charging chip

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It should be noted during maintenance that the 5V power supply is supplied to the charging chip

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through these two MOS tubes.

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If the MOSE tube is damaged, 5 volts can be measured at this end,

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but no voltage can be measured at the output end

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The fastest way to repair is to replace these two MOS tubes, Q1601 and Q1604

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You can also remove the two MOS tubes and short-circuit the D pole and S pole of one of the MOS tubes

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Also note here that there is also a diode in this line, D1601

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If this diode is damaged, it will pull down this 5 volt voltage, resulting in no charging

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This diode is a Zener diode, which can be removed without installation

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This is Huawei's overvoltage protection component

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Next, look at Xiaomi's overvoltage protection circuit

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In this circuit, USB_VBUS is the 5V power supply from the tail plug

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The power supply is supplied to the overvoltage protection chip U5400

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The B3, C2 and C3 pins on the left of this chip are input, and the right is output

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When we can measure 5 volts on the left line, but not 5 volts on the right output,

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it will cause no charging, usually because the chip U5400 is damaged

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Just remove the chip and short the input and output pins

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Of course, it can also be solved by replacing the chip.

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If you can't find the same type of chip, then directly short the input and output pins of the chip to repair the fault

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That's all for this lesson