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electronic problem solving

Here's a problem that I can solve, it's for a portable rechargable usb charger. The original plan used mini relays, but they consumed too much energy, so I need to solve this somehow. There's 1 usb port, I need it so whenever you plug it in a computer it powers the charging circuit, but when it's not plugged in and some other thing, such as an ipod is attached to the same usb port, the boost circuit (i'm using a lithium battery) connects to the usb port, but it doesn't charge the battery in an inefficient cycle. The boost circuit I'm using is the max1709.

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tech-king9 years ago
i don't get it. is the problem replacing the mini relays? because you could simply use an scr.
guyfrom7up (author)  tech-king9 years ago
that might just work, but I don't think I can make this project, trying to fit like 30 components in a square inch, I have most of the pcb desgined in eagle, but I don't think I can do it, 1 solder bridge overlooked and it won't work, debugging would be impossible
of course it works. it came from tech-king's database of electrical problems and solutions
Patrik9 years ago
Hmm... interesting problem. The tricky part would be to avoid draining your battery when you connect to a sub-par powered port (e.g. your batteries are at 5V, but the computer USB port is only at 4.75V). The simplest solution would be to use a male USB connector to charge the battery from the computer, and a female USB connector to power devices from the battery.
guyfrom7up (author) 9 years ago
ok, I'll post a little picture soon, I should have explained it better
guyfrom7up (author)  guyfrom7up9 years ago
here's a rough diagram
lion usb.gif
guyfrom7up (author)  guyfrom7up9 years ago
Any ideas?
Goodhart9 years ago
I was temporarily confused by the first line, then I realized you meant: Here's a problem I can't solve.....rather then can solve

But I agree with gmoon, we need a wee bit more info.
gmoon9 years ago
The second para seems self-contradictory:
....whenever you plug it in a computer it powers the charging circuit, but when it's not plugged in.....the boost circuit (i'm using a lithium battery) connects to the usb port...

We're a little unsure what you're doing.

Maybe give us a block schematic to clarify the description. One that illustrates the different states--what's plugged in where (or unplugged, as the case may be), as well as the battery, charging circuit, etc.
guyfrom7up (author) 9 years ago
any ideas?