Modify output voltage of a Dell power brick

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  • tom66
    EVs Rule
    • Apr 2011
    • 32560
    • UK
    #21
    Re: Modify output voltage of a Dell power brick

    The output voltage was probably too low. Try turning the voltage up. If this is the case you will need to modify the main transformer and increase the turns on the auxillary winding for the Vcc for the controller.
    Please do not PM me with questions! Questions via PM will not be answered. Post on the forums instead!
    For service manual, schematic, boardview (board view), datasheet, cad - use our search.

      Comment

      • RCKadath
        Member
        • Jun 2013
        • 16
        • Canada
        #22
        Re: Modify output voltage of a Dell power brick

        Thanks for the suggestion Tom but the output voltage was set for 17V (nominal was 19.5V). I can't go higher because 17V is the max my charger will support. I nvereless tried to increase the voltage but it doesn't help. Looks like I broke it somehow.

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          • Th3_uN1Qu3
            Believe in
            • Jul 2010
            • 6031
            • Romania
            #23
            Re: Modify output voltage of a Dell power brick

            Originally posted by tom66
            I think that decreasing the 69.8k resistor will decrease the output voltage.
            That is a bad idea. Do not modify the top resistor of the feedback divider in ANY SMPS unless you have a good reason to do so. If you need to change the output voltage, adjust the lower resistor only. The reason is that the top resistor plays an important role in the feedback loop, and altering it will, most of the time, lead to oscillations and related nasties.
            Originally posted by PeteS in CA
            Remember that by the time consequences of a short-sighted decision are experienced, the idiot who made the bad decision may have already been promoted or moved on to a better job at another company.
            A working TV? How boring!

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              • ben7
                Capaholic
                • Jan 2011
                • 4059
                • USA
                #24
                Re: Modify output voltage of a Dell power brick

                Originally posted by Th3_uN1Qu3
                That is a bad idea. Do not modify the top resistor of the feedback divider in ANY SMPS unless you have a good reason to do so. If you need to change the output voltage, adjust the lower resistor only. The reason is that the top resistor plays an important role in the feedback loop, and altering it will, most of the time, lead to oscillations and related nasties.
                Agreed, learned that the hard way before. It can even cause the PSU to appear to not work at all.
                Muh-soggy-knee

                  Comment

                  • RCKadath
                    Member
                    • Jun 2013
                    • 16
                    • Canada
                    #25
                    Re: Modify output voltage of a Dell power brick

                    Thanks for the warning guys. In my case I modified the lower resistor.

                    I have another 65W Dell brick that I'll try the modification on. Hopefully I won't destroy that 2nd one. I kinda lost motivation however...

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