Switch mode power supply output across capacitor increases i

Hi all,

The subject describes pretty much my question. I have been spending
several days trying to debug a circuit, only to find that it wasn't my
fault:

I have a normal (pretty cheap) switch-mode plug-pack power supply
(240V, 50Hz in; 12V, 200mA out), and nominal voltage appears to be
somewhere around 12V (so far so good). With an electrolytic cap across
the output (correctly polarised), the voltage rises to somewhere
around 17V - 18V. I had no idea this would occur, and was thus trying
to find the problem in my circuit.

Does anyone know why this happens? Presumerably a poor regulating
circuit in the plug pack, but does anyone have some more thorough
answers?

Thanks very much,

-Gus

 

[Jamie]

angus.oliver@gmail.com wrote:

Hi all,

The subject describes pretty much my question. I have been spending
several days trying to debug a circuit, only to find that it wasn't my
fault:

I have a normal (pretty cheap) switch-mode plug-pack power supply
(240V, 50Hz in; 12V, 200mA out), and nominal voltage appears to be
somewhere around 12V (so far so good). With an electrolytic cap across
the output (correctly polarised), the voltage rises to somewhere
around 17V - 18V. I had no idea this would occur, and was thus trying
to find the problem in my circuit.

Does anyone know why this happens? Presumerably a poor regulating
circuit in the plug pack, but does anyone have some more thorough
answers?

Thanks very much,

-Gus
its simple, You don't have a switch mode power supply..

Its your basic all wart type supply that is unfiltered or
you have something serious wrong with the supply.

http://webpages.charter.net/jamie_5"

 

thanks both of you - i guess I buy more expensive, properly regulated
supplies in the future!

Cheers...