On Wed, 10 Feb 2010 06:44:25 -0800 (PST), Control Freq
wrote:


Hi,

Is this normal?
I have a plug top power supply, for UK. The sticker shows:
AC/DC Adaptor
Input 230V ~ 50Hz 11.2W
Output 9v 500mA 4.5VA

I have just measured the voltage at 13.5 volts (DC).

I guess I have bought a non-standard item!!

Anyone else experience this sort of thing before?

For devices that have their own internal regulation and that don't need
a tightly regulated supply (e.g., one that can run from a battery), this
kind of supply is simple and cheap. Think of it as a 13.5 VDC "pure"
supply in series with a source impedance of about 9 ohms. When it is
supplying a 500 mA load, that internal resistance will drop about 4.5 V,
so at the terminals you'll see the expected 9 VDC.

--
Rich Webb Norfolk, VA