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In this lesson, we talk about the current phenomenon of power connection protection and its related circuits

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Let's first look at the common current phenomenon of power connection protection

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We power this mainboard with 4.2 volts,

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snap the battery to the battery holder,

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and we can see that the current jumps back and forth between 0-3-0-4-0-6 mA,

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and the jump is very fast, from 0 to 3 mA and goes to 0 soon

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This current phenomenon is the power connection protection

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After the normal mainboard is powered on,

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without pressing the power button,

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the current jumps from 0 to a dozen mA or tens of mA,

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and then returns to zero

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The current changes only once

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This is called power self-test,

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only available on individual mainboards

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The power connection protection is that when the power is connected once,

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the current will jump once,

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and then when the power is turned off and then connected,

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it will jump again

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There are similarities between the two cases,

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so we must pay attention to the distinction

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The power connection protection is that the current jumps very fast,

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and then returns to 0 immediately,

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and the current is very small, it is irregular

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As for the mainboard with normal power-on self-test,

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the current jumps to thirty or forty,

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then to fifty or sixty, and then returns to 0

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It has an incremental process

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Let's take a look at which circuits or components are related to power-on protection

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We learned earlier that in the power-on circuit,

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the power supply of the battery is converted into the main power supply through the charging chip,

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which is supplied to the power chip, display chip,

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WIFI chip or radio frequency

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What is the problem with the power connection protection?

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It is the main power supply that has a short circuit,

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which leads to the phenomenon of power connection protection,

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which causes the mobile phone to not be turned on

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Let's see where the main power lines go

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Here, we also need to pay attention

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This main power supply code VPH_PWR is commonly used on Xiaomi or Oppo

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There is also a code for the main power supply called VBAT_SYS,

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which is commonly used by Huawei

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Android phones generally use two codes on the drawing

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In the actual maintenance,

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what will cause this short circuit phenomenon in the main power supply,

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we conclude that any damage to the components connected to the main power supply line

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may cause the main power supply line to have connection protection

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How can we detect the short circuit of the main power supply?

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We use the diode gear of the multimeter to measure the diode value to ground,

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that is, the resistance value to ground

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If it shows 0, this is called a short circuit to ground,

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that is, the main power supply is short circuited

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If the main power supply is short-circuited,

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power-on protection will occur,

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so we call it power-on short-circuit

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Ok, that's it for this lesson