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I am trying to use a BCD converter 7447 to display numbers on a seven segment display. Even before I apply any inputs or outputs, I observe that the VCC voltage of the 7447 drops (which is powered by a 7805 voltage regulator). The voltage drops to around 3V. I need this voltage to power up other ICs so can't afford it to go so low. I am unsure why is the voltage dropping so drastically. I have done some debugging and found the the 7447 is drawing just 7mA from the 7805 while the voltage is dropped to approximately 3V. I tried putting a resistor that draws 50mA and that only caused the voltage to drop to 4.85V. I am really confused why is the voltage dropping so much. I encourage the maker community to share their thoughts. I am stuck on this for the last two days.

ps. the input power supply to the 7805 is a 12V adapter capable of delivering 1A. It's output remained stable at 12V throughout all experimentation.

Thanks,

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    \$\begingroup\$ Have you used the recommended decoupling capacitors close to the 7805? \$\endgroup\$
    – Transistor
    Commented Jun 14, 2021 at 8:29
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    \$\begingroup\$ Please include a schematic. Did you connect the 7805 correctly? Are you measuring the supply voltage at the output of the 7805 or at the 7447s? \$\endgroup\$
    – StarCat
    Commented Jun 14, 2021 at 8:30
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    \$\begingroup\$ Hi Usman! this is really impossible to answer without knowing the schematic of exactly what you've built, I'm afraid – could you add that to your question? Also, details on where you measured (i.e. between which points) voltages and where (i.e. in between which nodes) current might help! \$\endgroup\$
    – Marcus Müller
    Commented Jun 14, 2021 at 8:37
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    \$\begingroup\$ @Transistor, I haven't added any decoupling capacitors. I have used 7805 earlier and apparently it works just fine without them. What values should I add there are a few different schematics circulating online? \$\endgroup\$
    – Usman Ashraf
    Commented Jun 14, 2021 at 8:58
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    \$\begingroup\$ Thanks for the suggestion @MarcusMüller. I just added a schematic. \$\endgroup\$
    – Usman Ashraf
    Commented Jun 14, 2021 at 9:01

1 Answer 1

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Thanks for everyone who commented and pointed in the right direction specially @Transistor. The problem was resolved by adding decoupling capacitors at input and output.

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