I have designed a board with an UA78M33CDCY voltage regulato which is connected as recommended in the datasheet.

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When I hook it up to my 3.3v bench supply it boots fine. But powering it from the regulator does't give any response.

When a apply 12v power from a stable 3.3A psu the output of the regulator is reasonably stable at ~3.45v. Have I chosen the wrong voltage regulator or should I look for the problem somewhere else?

  • \$\begingroup\$ If you are concerned about the extra 0.15V your regulator is supplying when testing then don't. It is less than 5% over and will likely drop a little when you load your regulator. You will need to keep maximum current and power dissipation limits in mind though. \$\endgroup\$
    – KalleMP
    Jul 25, 2017 at 21:09
  • \$\begingroup\$ what's the question/problem? the ESP is spec'd at 3.0~3.6V \$\endgroup\$
    – dandavis
    Jul 25, 2017 at 22:11
  • \$\begingroup\$ I forgot to mention that it does't run from the regulator, I was already scratching my head why everyone thought I was afraid of the voltage being to high. \$\endgroup\$
    – thommie
    Jul 28, 2017 at 21:29
  • \$\begingroup\$ "When I hook it up to my 3.3v bench supply it boots fine." What does? The regulator? Your schematic shows it connected to +12 V. There are a few other funnies in your question. A small point: "V" for volt, "A" for amps, etc. \$\endgroup\$
    – Transistor
    Jul 28, 2017 at 21:34
  • \$\begingroup\$ Sorry for any confusions, let me clear it up. 12v 3.3A power supply connected to the regulator results in a stable ~3.45v from the regulator but the esp does not work. 3.3V bench supply connected directly to the esp (without the regulator) does work. This made me wonder if there is an error in my board or I overlooked something when I picked the regulator. \$\endgroup\$
    – thommie
    Jul 29, 2017 at 11:44

1 Answer 1


Have a look at the datasheet (Page 5) the 3.45v is still within the margin of error of the output voltage. If such small voltage changes are an issue for you, you may want to look for another more precise regulator. Its kinda difficult to tell if you can run the esp12 with more than 3.3v because there is no absolute max. rating in the datasheet.

  • \$\begingroup\$ i've been running an esp12 almost daily straight from an 18650 for over a year w/o problems. when i built it i didn't know better, but it never released its magic smoke and still works... \$\endgroup\$
    – dandavis
    Jul 25, 2017 at 22:14

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