A couple different adapters plugged into a 12V battery
My USB adapter quit working. I opened it up to see what the circuit looks like and determine what caused it to fail.
Also shown: Charging a cell phone with a wind turbine.
As shown in the video below, the problem appears to be a cheap electronic part that may have overheated. A voltage regulator, IC 78L05, costs about 25 cents but is not rated for the spec’s shown on the label. The IC can handle up to 100mA while the adapter had a label indicating it was designed for 1,000 mA!
VIDEO
I did not say in the video, but the red LED on the USB adapter finally went out and never came back on, indicating permanent damage. I read that these IC’s work better if they have a heat sink. This circuit had no heat sink. I bought this device through eBay. It was cheap and made in China. I guess I got what I paid for.
I might try to replace the part and see if I get it working again. If so, I’ll update this page.
jammit says:
Yep, the regulator blew, although that’s pretty hard to do. The reg is definitely underpowered. The reason for the odd power cycling at the beginning is because the regulator has built in thermal limiting. It tries to put out high current, it overheats, and shuts down until it cools enough to turn on. This is supposed to save the regulator, but a lot of thermal cycling will cause the chip bonded inside the plastic shell to break loose internally. The LM7805 with a heatsink can put out 1.5 amps, but will dissipate 7 watts at one amp, and 3.5 watts at 500ma when run from 12 volts. If you run it from 24 volts the power loss doubles. If you don’t feel like making a switching regulator, which can easily control a lot of current with very little power loss to heat, you may want to try these guys:
http://www.dimensionengineering.com
I would suggest the micro regulator http://www.dimensionengineering.com/AnyVoltMicro.htm
It’s a drop in replacement for the 78XX series regulator, except you need to adjust this for an output of 5 volts. The only problem is that the 7805 linear regulator can be found for only a few bucks, the switcher is selling for about $20.
If you don’t mind slinging some solder around, you may even want to try this:
http://www.romanblack.com/smps/smps.htm
It’s OK to contact me by my email.
October 30, 2010, 6:34 pmEarl says:
Thank you for that detailed feedback. I did not realize that the regulator had a thermal protection circuit and now that makes more sense why the power supply turned off and on repeatedly before getting completely toasted. Interesting links.
November 5, 2010, 12:37 pmWatson says:
I’ve written more on this in my blog.
watsonseblog.blogspot.com/2011/04/2011-apr-11-12-to-5v-usb-adapter-junk.html
April 17, 2011, 8:42 pmWatson says:
The Roman Black regulator circuit has a deficiency that may be very important; everyone should know about it. You can find out more at the end of my blog below.
watsonseblog.blogspot.com/2010/02/roman-blacks-black-regulator-modd-to-1.html
April 17, 2011, 9:09 pmEarl says:
Thanks for sharing your results.
April 17, 2011, 10:41 pm