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Understanding Motherboard Power Supply in Schematics

zentech

Mar 8, 2021
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Hi everyone,
this is my first post, I need help understanding the difference in power supply voltages in my hp laptop motherboard. I have the diagram of a driver ic which controls 2 mosfet. and I'm trying to find out why I don't have 3.3v on source of PQ55, also I need to understand the difference between all these voltages, why I have 3.3v and +3VAWL. If someone can explain the difference in the following voltages and what they mean and when are they present. This is for an HP Pavilion g6 laptop motherboard
+3V, +3VSUS, +3VS5, +VAD, ACIN, +VAD_1, +12ALW, MAIND, +VIN_VCC_CORE, +VIN, +VCC_CORE, G5934PG, +VH28
thanks for the help!
u55_power_supply.PNG
u55_power_supply.PNG
 

Harald Kapp

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Nov 17, 2011
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I'm trying to find out why I don't have 3.3v on source of PQ55
Check the voltage at the gate of the transistor. It needs to be at least 6 V or higher (the VGSth of the transistor is max. 3 V plus the volateg at the source add up to > 6 V Vgate - measured from gate to GND).
If someone can explain the difference in the following voltages and what they mean and when are they present.
To answer this question would require deep knowledge of the circuit design of the motherboard. It is unlikely you find someone with knowledge of that much detail. Different voltages are used to satisfy different requirements of sub-circuits on the motherboard. Sometimes it is even necessary to control turn-on and turn-off of voltages in a precisely timed sequence to avoid destruction of components due to stray currents. The gs7502q3-r seems to be a controller for just that purpose. I couldn't find a datasheet, though.
 
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