Run Switching Type AC Power Adapters on DC
designed by David A. Johnson, P.E.

May 15, 2007

I have received a couple emails from people looking for inexpensive DC to DC converters, which can convert 40v to 60v DC into say +5 or +12v.  Such input voltages are often found in new automotive and industrial applications with a typical DC voltage of 48 volts. It turns out that many, not all, but many, standard AC line operated power adapters, which use switch mode techniques, will indeed work great when supplied with DC instead of AC. The unit below works down to about 30v DC and delivers 500ma at 5v. If you draw less current, it will operate at even lower DC input voltages.

How do you know if your adapter will work on DC?  First, pick it up and shake it.  If it feels heavy, then it is most likely a transformer type power converter and will not work on DC.  If it is light, it is a switching type power converter and will work on DC.  You will have to test it to determine what input voltage is needed to produce the rated output voltage.  Since these adapters are readily available it would be an inexpensive solution.