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My circuit need to be plugged into a normal (canadian) 120V outlet. But everything on it is made to run 5V.

I'm very beginner, so yet, I'm thinking of adding a bunch of resistance, but I feel that it would be a terrible way to proceed ... if it would work, a lot of power would be dissipated in heat.

How do you proceed to lower voltage from 120V to 5V ?

Thanks !

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    \$\begingroup\$ Use a wall wart. \$\endgroup\$ – user207421 May 26 '13 at 1:53
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    \$\begingroup\$ Using a bunch of resistors is super dangerous, especially for a beginner. But even an experienced EE would not use resistors for that except in very specific situations. The other answers (Wall Wart, isolated switcher, transformer) are all acceptably safe. \$\endgroup\$ – user3624 May 26 '13 at 2:58
  • \$\begingroup\$ My input IS 120V, I can't use a wall wart. I need to ebbed one into the circuit I'm making, as a second circuit require 120V. Sorry I didn't explain that clearly. \$\endgroup\$ – FMaz008 May 26 '13 at 19:26
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Use a transformer to efficiently reduce your 120 V a.c. from the wall outlet to something like 9 V a.c. Add a bridge rectifier to convert the 9 V a.c. to pulsing d.c., and then a capacitor to smooth the d.c. Finally, add a linear regulator, like a 7805 to give you a nice steady 5 V power supply.

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Lots of things run on 5V these days; any charger that has a USB connection (and a lot that don't). If you look at the fine print on the charger, it will tell you the voltage and the amperage, and you can use that to figure out whether it will work for you.

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  • \$\begingroup\$ Yes, I understand, my question may have lacked of precision. I know adapters exist, but I want to figure out how to embbed this in my circuit... I don't want to use a transformer; my circuit has to do the job. ( Part of the circuit require 120V , but most use 5V... so I don't want to have 2 power plugs ) \$\endgroup\$ – FMaz008 May 26 '13 at 19:21
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For best efficiency use an isolated switcher module to convert the AC voltage to your 5V DC requirement. This will offer less heat build up and much better efficiency than even trying to use a 60Hz stepdown transformer with bridge rectifiers and a linear regulator.

Since attaching circuits to the AC line represents a huge safety hazard it may be best to acquire a ready made 5V output switcher type wall wart. These days these are readily available. You could even re-duty one from a powered USB hub or some other USB charger device. These will offer current capability of 2 or 2.5A.

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