Not too long ago I created a design for an iPhone charger based off of the LM7805 5V/1A linear regulator and a 9V battery. It worked but, both because of limitations in the regulator and in the size of the battery, it was horribly inefficient and the large current draw of the iPhone ate through the battery without even charging it entirely. I decided to create a new design based off of 4 AA batteries outputting 3V (so that there were two groups of 2 parallel batteries that were in series). This worked off a high efficiency switching 1A DC/DC converter (the LT1308A by Linear Technologies). I’ve dug through the specs and the designed and routed the board and I think that I can get 3 maybe 4 good charges before the batteries run out. Before I send off the designs to be printed and before I start to order the parts, I wanted to get your opinion on my design and layout.
Any Ideas or comments?
Here is the file and the pictures in case you don’t have EAGLE:
On which parts are you talking about. I tried to keep to that layout on page nine. I updated the pictures with the new layout. It might be a little better now.
For instance, you should have a minimal length track for pin 1 and you should really be using surface-mount parts. Use the same parts they have in their schematic, or equivalents.
You need to read the data sheet very carefully, and follow their recommendations to the letter, unless you really know what you are doing. Switching power supplies like that are tricky things, and won’t work properly with a poor layout and the wrong parts.
The orientation of the switch looks like R3 and R3 will get in the way when you try to turn the device on and off. Double check the Eagle part drawing against the actual switch.
Edit: BTW, limit the size of your photos place a link to the photo. The large schematic image exceeded the width of my display and I have to scroll to see not only to view the image, but all the messages in the post.
Riden: The part that is sticking off of the switch is not actually the slider, it’s just a nib to help stabilize the switch. The slider hangs off of the board on the other side.
