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In this class, we will talk about the power supply circuit of the LCD backlight screen

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Let's take a look

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This is an Android phone screen power supply circuit

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This is the chip U1701,

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which is the screen power supply chip, or the display chip

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How can we understand this circuit diagram?

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This is the input power supply,

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the LCD_VSP and LCD_VSN on the right are the outputs

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What does this chip do?

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In fact, it is the conversion of power supply

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Under control conditions,

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it can complete the output of different power supplies that the circuits want

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What is the name of this input power supply?

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Main power supply

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We know that the highest voltage of the main power supply is equal to the battery voltage,

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Here on the left, ENP is the positive voltage enable signal,

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and ENN is the negative voltage enable signal

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I2C4 is the control signal of the chip

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Regarding the I2C bus, we must have a basic common sense

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There is a voltage of 1.8 volts on the I2C bus

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SCL is the serial clock

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SDA is the serial data

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For the same reason, we just need to know that it has 1.8 volts on it

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OK, here's the power and signal on the left side of it,

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what about the right side?

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This is a positive voltage output,

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this is a negative voltage output,

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what are their voltages in general?

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Positive voltage is general 5.5V,

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and negative voltage is general -5.5V

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It outputs OUTP and OUTN to the display connector

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There are magnetic beads LB in series in this circuit,

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which is actually an inductor

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Some lines are connected in series with an inductor FL, or a 0 ohm resistor

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If this component is damaged, it can be shorted

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Everyone must be clear, only this component can be short-circuited

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Then let's take a look at the key components we need to pay attention to here

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Why is it called a key component? It is essential, it must not be broken

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The first key component is this 4.7 uH inductor,

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which is energy storage, one end is connected to SW,

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the other end is connected to the input

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This circuit is known to be a boost circuit at a glance,

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so this chip U1701 is also a boost chip

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The second key component is the chip U1701, which must be the key

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And this 2.2 uF capacitor, C1703,

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which is a fast charging capacitor

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There is a power supply capacitor C1702,

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which is the capacitor connected to the pins D3 and E2,

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and it is also a key component

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When we actually repair,

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we should pay attention these components cannot be damaged,

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nor can they be replaced at will

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If they are corroded by water, then when we replace them,

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we need to find capacitors with the same capacity and withstand voltage value

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Ok, this is the description of the power supply circuit of the LCD backlight screen on the drawing

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Okay, that's it for this lesson