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Home Brew USB Charger / Power Supply

Over the years I think we’ve all gathered some extra power supplies and wall adapters. Here is a quick guide to a home brew USB charger or USB power supply. This USB tutorial is from the Hacked Gadgets website and Alan runs a good site – check’em out.

This unit is great for charging your iPod, PSP or any USB device and only costs pennies to make.
usb power charger
The main unit needs to run from a regulated 5vdc wall adapter with at least 500ma or higher. These are very common and I’d think most households have at least one extra laying around. You’ll also need:
  • 330 ohm 1/4 watt resister
  • 10k ohm 1/4 watt resister
  • 3mm LED (any color)
  • USB type A jack (female)
So this is what we have for total parts:
Most cases are held together by drops of glue in the corners, snap these apart with a little care. Here is the schematic of what we are tying to accomplish.
usb charger schematic
Next, lets review the USB pins we will use for integrating the USB jack into the power supply.
usb pins
  • Pin 1 is bent over and soldered to the case of the jack. The case of the jack is then connected to the wallwart ground.
  • Pins 2 & 3 are connected together then soldered to one end of the 10k ohm resister. The other end of the 10k ohm resister is connected to +5vdc.
  • Pin 4 is connected to +5vdc. One end of the 330 ohm resister is also connected to +5vdc. The other end connects to the anode of the LED. The cathode of the LED is grounded.
  • The 10k ohm resister is used to pull the USB data lines high. Some devices require these lines to be at +5vdc before initiating charging.
The LED functions as a power indicator and supplies the switching regulator with a minimum load. Now increase the size of the hole the power cable came out of to fit the USB jack and drill a 3mm hole for the LED. The items should fit snug in the plastic case, but you can put some glue in there just to be sure.
usb charger
That’s it! Source: Hacked Gadgets

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