I was looking at this outlet for home use and wondered what they could be using that would switch power to the DC converter when the USB is plugged in? I would love to use something similar in my car as I want to add a USB port to charge my phone as the power port gets in the way of shifting.

Here is the link to the product:
http://store.fastmac.com/product_info.php?products_id=458

 

They most likely used a small transformer, coupled with a voltage regulator to get the 5 volt DC power for the USB charge ports, can be easily accomplished for a vehicle by getting a 5 volt Voltage regulator, a couple of .1uf capacitors and building a simple circuit....

 

That sounds like it is on all the time though. The item in the link claims to draw NO power until a USB device (like a phone) is plugged in. In the car this will always be connected to the vehicle power, and I don't want to drain my battery unless my phone is plugged in.

 

Well, with the device you linked to, the actual USB port charge controller circuit may not be powered all the time, but, there is circuitry in there that monitors that part of the circuit, so it still draws power no matter what...... You can simply add a switch to turn it off and on.... or if you are really clever, you could add a switch on the USB port, so that when a connector is plugged in, it actuates the switch and turns on the power to the port..... plus the LM7805 has a quiescent power draw of only 5mA, so it does not draw much power when nothing is connected to it...

But there are IC's out there (check www.Maxim-ic.com) available for this type of thig, but, they will still draw some power in order to be able to monitor the USB port...


B. Morse

 

Thanks for the idea about a switch. I do have some small lever type micro switches that I could hack onto the port, so that when the cable is plugged in it activates the switch. That would probably work the best anyhow. I plan to use an old phone charger for the 5v source so I don't have to re-invent the wheel

 

Let us know how it works out for you...