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I want to put 3 leds as night light to some power outlets around the house. I also want to keep them discrete so the power adapter (110v to 5v) has to be small.

I don't want to use a simple resistor voltage divider (don't not think it is safe). But even smallest transformer is not small enough to put into space around outlet.

How can I get 5v dc from 110v safely with smallest possible way?

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  • \$\begingroup\$ "Safely" can be acheived by seperation and/or a physical barrier - it doesn't always have to rely on a transformer. \$\endgroup\$
    – Andy aka
    Feb 28, 2015 at 17:39
  • \$\begingroup\$ You also don't need to run an LED off DC; they will run off AC just fine, provided you don't mind the flicker. \$\endgroup\$ Feb 28, 2015 at 17:49
  • \$\begingroup\$ You might be better off with small mains neon bulbs (NE-2), which also require a resistor but are more traditional in this role. \$\endgroup\$
    – pjc50
    Feb 28, 2015 at 17:56

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There are several ways you can do this.

I'd start off by seeing if any of the cell-phone charger wall-warts are sufficiently small. These normally supply about 5V at current ranging from 100 mA to 2 Amps. The Apple cube adapters are nice and small (about 2.5cm cube).

If that's too large, you can purchase replacement wall receptacles that have a built-in 5V USB power supply. You could assemble the LEDs & current-limit resistors right onto a cut-down USB plug.

You can also do a capacitive-type power supply. However, I'm reluctant to steer you in this direction if you aren't aware of the hazards involved and know how to choose the appropriate components. This is one situation where choosing the correct capacitor and resistors means the difference between a safe circuit and a fire hazard.

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  • \$\begingroup\$ I already checked the Apple's cube adapter, it s not small enough. I want to do this in a safe way (with isolation) if possible. \$\endgroup\$
    – dvdmn
    Feb 28, 2015 at 21:54
  • \$\begingroup\$ @dvdnhm - do you have dimensions you are looking to fit into (LxWxH)? \$\endgroup\$
    – cowboydan
    Feb 28, 2015 at 21:59
  • \$\begingroup\$ The board can be 2x4.5 cm (.8x1.8 inch) and thickness cant be more than smd parts + the pcb \$\endgroup\$
    – dvdmn
    Mar 1, 2015 at 4:03
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There are even smaller Apple wall warts, about 1.5cm cube. Although that design you usually only get 1A current rating. You can design your board to go directly into the USB port card edge connector style, that will also reduce some space requirement and component count.

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