Quote:
Originally Posted by ivanjt
Arcticmaniac, all of the LM78xx chips are voltage regulators, i.e. they regulate the input voltage, that must be HIGHER than the output voltage, to what ever the last two numbers are.
Next thing, when you say you want a USB charger what do you actually mean? If it is something that you plug into a computer USB socket then it will never work because the current available is too small. If, on the other hand, you want something that plugs into mains power then start with a 12v unit and add the 5v regulator and a USB socket.
When I get home tonight (midday here now) I'll take some pictures to show you.
If you added a concentric socket you could make an extremely small (10 mm x 25 mm x 5 mm) unit that you plug the 12v plug into and then plug the USB cable into for charging your USB charged devices.
12v mains charger ----> 5v regulator module ----> USB device.
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I just found out the hard way today. I actually got the LM7812 and noticed that any voltage that i place on it gives me back less than the input voltage. Which you are right, the input has to be higher than the output. What I wanted to build was 5V usb ---- > 12V -----> edge.
LM339 work?, not sure if I can use an op-amp to do it.
ivanjt. thanks for you help though. i think i'm gonna scrap the project for now between school and work and kids, gotta balance it out. was hoping for a simple project, but its been over 20 years since EE school. Will try wally world for one of those universal ac adapters for now. Hope those work.