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Hello everyone, today we will learn about the protective isolation circuit during the startup process of the laptop

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This lesson consists of two parts

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The first one is the introduction of protective isolation circuit

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The second is the three common ways of generating common points

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First of all, the protective isolation circuit is used to isolate the power supply of the battery and the adapter

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to prevent two different voltages from being connected together to cause a short circuit

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The point where the battery and adapter voltages meet is called the common point

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When the adapter is plugged in,

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the adapter power supply will flow to the common point through the adapter isolation tube

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At the same time, the battery isolation tube will be cut off,

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and the adapter will supply power to the public point at this time

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The common point voltage goes to the D poles of all power supply upper tubes

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The D poles of all PWM circuits are powered by the common point

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If any PWM circuit is abnormal, it may cause a short circuit at the common point

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The resistance to ground of the common point of ordinary machines is above 400

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Like some common points generated by PWM, its resistance to ground is above 100

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This is the common point-to-ground resistance we actually measured

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It is more than 500 here, which is a normal phenomenon

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Next, let's take a look at the three common common point generation methods

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The first, which is the most common

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These two are adapter isolation tubes

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This VIN is the adapter power supply

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The first isolation tube uses a P-channel, which uses resistors in series to divide the voltage,

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divides the low level, and controls its self-conduction

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The second isolation tube uses N-channel, which is controlled by the charging chip

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After the charging chip meets the working conditions,

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it outputs a high level to control the conduction of the N-channel to generate a common point

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If the second isolation tube is not turned on,

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the common point also has a small current voltage,

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which flows from the body diode of PQ102

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The small current common point is also a false common point, which cannot make the machine work normally

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The first isolation tube and the second isolation tube

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are controlled by the charging chip at the same time

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The battery isolation tubes of some models are also controlled by the charging chip

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Some are when inserting the adapter, after the first isolation tube is turned on,

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the P1 voltage provides a high level to the G pole of the battery isolation tube

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to control the cut-off of the battery isolation tube

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Well, this is the first, most common common point

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When the adapter is plugged in, it can only be powered by the adapter

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When the adapter is not plugged in or the adapter is damaged,

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it will control the adapter isolation tube to cut off,

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and use the battery to provide power to the common point

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The second type, the common point is generated by PWM step-down

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In this case, after the adapter power supply is turned on through the adapter isolation tube,

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it needs to be stepped down by PWM

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The power supply after PW step-down,

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it is the charging voltage and the power supply voltage to the common point

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That is to say, the common point voltage is equal to the charging voltage

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With the common point generated in this way,

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it supports battery and adapter to power the common point at the same time

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The third type, the common point is generated by 4-switch BUCK or BOOT mode

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if the voltage of the adapter is 20V,

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it will be stepped down by PWM to the common point,

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and the battery will be charged at the same time

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The common point voltage at this time is not equal to the adapter voltage

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After the Type-C adapter is inserted,

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it will communicate with the mainboard through the CC bus,

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the CC bus is pulled low by the U4701 here

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Then the adapter will output a pre-boosted 5V to supply power to the PD protocol controller here

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After the PD protocol controller is powered,

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it will generate linearity and provide power to its FLASH chip

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Then the PD protocol controller reads the information in the flash through the SPI bus,

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and then communicates with the adapter through the CC bus,

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requesting the adapter to provide a voltage that can satisfy the normal operation of the mainboard

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The adapter will perform voltage conversion internally according to the request of the mainboard,

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and output a boosted 20V power supply

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When the PD controller detects that the adapter voltage has risen to 20V,

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it will send a turn-on signal to convert the adapter power supply 20V

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to provide power for the subsequent common point circuit

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Next, after the charging chip is powered by 20V,

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it will generate linearity, supply power to its own VDDA,

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and then output a CHRG_OK signal

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Then, the charging chip will control the four MOS tubes here to turn on in turn

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according to the voltage set by its CELL pin,

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and step down the 20V power supply of the adapter to the charging voltage to supply power to the common point

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and charge the battery at the same time

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When no adapter is plugged in, for example,

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I plug in an extended peripheral in the Type-C interface

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The power supply of this interface will be powered by the battery voltage,

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and the charging chip will control it to boost the battery voltage

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and reverse it to supply power to the Type-C peripherals

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Well, this is the third common point generation method, 4-switch buck, boost to generate a common point