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In this lesson, we will talk about the screen circuit principle of LCD backlight screen

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First, let's look at the working conditions of its circuit

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In general, the power supply of the backlight screen circuit has the following four power supplies

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1.8 volts,

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positive and negative voltage power supplies,

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VSP is positive voltage power supply,

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and VSN is negative voltage power supply

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LED+ and WLED are the positive poles of the backlight,

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which are the power supplies  for the backlight,

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usually a high voltage of 14 to 21 volts

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When it reaches 14 volts, basically this screen can light up

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Well, there is another one that is 1.8 volts for this power supply

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What is shown here is the real thing

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There is a set of lamp beads behind the screen,

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which is the light source of the backlight

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These are all backlights, that is, light-emitting diodes

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Well, let's look at another working condition of it, reset

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This is generally described in the drawings

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The reset signal identifier starting with GPIO is Huawei's

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What does N mean?

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N means low level active

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The reset signal has a characteristic

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When it is high, there is a voltage, usually 1.8 volts,

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indicating that it has no problem

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Next we look at the detection signal

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There are two types of detection signals on the circuit,

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one is ID and the other is DET

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For example, in the drawing,

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what we see is a detection signal that starts with ID

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This display screen detection can read screen information, manufacturer information

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If there is a problem with it,

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it will also cause the phone to have a black screen

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OK, let's look at another operating condition, the bus

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On Android phones, the bus usually starts with DSI and has clock pins

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This is the clock signal of the bus, not the clock signal of the display

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This is DATA, which usually has 3 sets of data,

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that is, 6 roots, which are used to transmit image information

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Then there is the synchronization signal, TE,

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which has another name, called anti-tearing signal

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What is a key point we need to know?

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If the line is disconnected,

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or the components in the line are falsely welded,

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the signal cannot communicate with the screen and the CPU normally

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We call it an open circuit,

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which will cause a black screen, that is, no display

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What we focus on are these conditions,

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how do we judge whether it is good or bad

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This is the working condition of the backlight screen

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Okay, that's all for this lesson