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Looking generally at the 74FCT family, I saw that it's power pin should be held at \$5V \pm 5 \%\$ to be in specs. From my understanding, \$\pm5\%\$ power supplies are widely available, but are the top of the cheaply available ones.

Considering a reasonable (devoted layer) ground and power plane on a PCB, would it be reasonable to power a PCB from a 5% precise supply (at 5V) ? Or would the losses and parasitics be too much of a problem ?

If I needed a more precise voltage, how should I tackle that ?

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  • \$\begingroup\$ would it be reasonable to power from a ±5% supply? ... please clarify what you are asking \$\endgroup\$ – jsotola Feb 17 '18 at 16:49
  • \$\begingroup\$ What would you need me to add ? \$\endgroup\$ – Sachiko.Shinozaki Feb 17 '18 at 16:50
  • \$\begingroup\$ Yes it would be reasonable to use a +/- 5% supply for a +/- 5% IC. You can double-check the actual voltage with a volt meter if you like. So that you can feel more comfortable after you build the circuit. \$\endgroup\$ – mkeith Feb 17 '18 at 16:56
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    \$\begingroup\$ @Sachiko.Shinozaki, i was trying to figure out what you mean by "reasonable" ... i read your post several times, and i think that i understand. ... you may run into problems if you end up with a -5% power supply ... the voltage at the "far end" of the board may drop below the -5% level ........ find a power supply with an adjustable output \$\endgroup\$ – jsotola Feb 17 '18 at 17:07
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Choose any higher voltage power supply and bring it down with higher accuracy with a buck converter, a fixed or variable linear voltage regulator like 7805 or LM317, an LDO,...

Or think again if you really need a TTL device. Maybe you can do with a variable voltage device that does not need exactly 5V power supply.

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    \$\begingroup\$ The tolerance on the 7805 is almost 5%. Also, it needs 7V in to maintain 5V out. There is no need to do it this way. If you are really paranoid, just get a power supply with a tighter tolerance, or get one that can be trimmed over a range. \$\endgroup\$ – mkeith Feb 17 '18 at 23:09
  • \$\begingroup\$ If it's only one power supply and one TTL chip, you're right. But we don't know that and its probably not the case. 7805 is only one of several solutions and there are many reasons why a higher voltage power supply might be useful, but we don't know if we don't know the full application. \$\endgroup\$ – gommer Feb 18 '18 at 10:49

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