I am a lighting designer that just released my first table/desk lamp design. I would like to add a USB charging port to the base, so people can light their desk and charge their phone or tablet.

What I would like to do is get a bulk amount of USB ports like I am finding on eBay ("DC-DC Converter Step Up Boost Module 1-5V to 5V 500mA USB Charger") and mount them right into my custom-designed lamp base and connect it to spt-1 or spt-2 standard lamp wire that plugs into the wall.

How can I connect the USB port to the lamp wire so when the lamp is turned on it will charge the consumer's device?

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    \$\begingroup\$ I don't know about you, but most people would want their phones to charge even if the light is off \$\endgroup\$
    – Passerby
    Jan 27 '15 at 21:29
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    \$\begingroup\$ The usb charger you mentioned is a boost converter that takes 1-5V and boosts it to 5V. Unless I'm missing something, the lamp does not use low DC voltage like this. What you really want is an adapter that will take ac mains and change it to 5Vdc \$\endgroup\$
    – I. Wolfe
    Jan 27 '15 at 22:15
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    \$\begingroup\$ Yeah that's not going to work take a look at this answer electronics.stackexchange.com/questions/33036/… \$\endgroup\$ Jan 27 '15 at 22:20
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    \$\begingroup\$ Also if you're going to plug something into the wall and convert it down to "safe" 5VDC at a USB plug there are definitely liability issues. You should be considering UL testing for safety at that point or at the very least carefully following their safety guidelines. Although to be fair you should probably be doing that already for the lamp :) \$\endgroup\$ Jan 27 '15 at 22:22

A DC-DC boost converter like the ones you're seeing on eBay doesn't do what you want. It converts low voltages (1-5V) to 5V for charging devices over USB. That would be useful to charge a USB device from a battery.

What you want is an AC to DC converter which can take an input voltage of 110V and output 5V / 500mA (although you'll find that 500mA doesn't charge a modern phone particularly quickly, so you might need something beefier). To charge at 500mA a USB charger doesn't need to have much more than 5V connected to a USB plug. To charge at a greater rate (modern phone chargers charge at up to 2.1A) the circuitry needs to be a little more complicated.

Every plug-in phone charger (from a reputable company) does what you want (including the necessary circuitry to negotiate a higher charging rate). The problem is, pulling one apart to build into a lamp that you sell would be ill-advised. Given that there's mains voltages present I'd imagine there's all sorts of liability issues.

The problem isn't particularly complicated as electronics go, but given the voltages involved and that you're planning to actually sell these devices it might be worth talking to an electronics engineer. Poorly designed mains voltage AC to DC converters have killed people before - this is something that you want to do right.

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    \$\begingroup\$ Also the fact that most people that get lamps do it for the look, and having the usb port there might ruin that. All in all probably not worth the hassle(risk/time investment) \$\endgroup\$
    – I. Wolfe
    Jan 27 '15 at 22:24

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