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Variable laptop power supply

Discussion in 'Electronic Projects Design/Ideas/Reviews' started by Mr_Max, Aug 30, 2017.

  1. Mr_Max

    Mr_Max New Member

    Joined:
    Mar 16, 2006
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    Hi everyone

    Kindly I need your help, I have a Compaq PA-1500-051 18.5v 4.9A that I need to use as a variable power supply, I can't find schematic for this
    Particular model, but a close one Liteon PA-1500-05 19v 4.47A, I found that a 28.7K and 4.4K resistors form a voltage divider connected to Pin 2 of the (unknown 8 pin IC it might be TSM103) I tried changing the 28.7K resistor with 20K pot in series with a 10K resistor
    strangely while I set the 20K Pot combined with 10K to the value of 28.7K the output goes up and down from as low as .75v to 3.7v no matter how I change
    the value the output never change accordingly !
    I soldered the 28.7K resistor back the output is 18.53v & drops down with no load, and then when I put a 21w 12v car bulb the output voltage is not stable
    goes up and down from 11v to 13v

    liteon_pa-1900_05_out_power_schematic.pdf_1.png Liteon PA-1500-05.jpg 20170829_190046.jpg
     

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