"robb" wrote in message
...
yes i googled and found lots of different mods to the basic
5v
*7805* regulator power supply
that is {AC in, bridge, 7805, 5v out}

(images on a.b.s.e)

i built and experimenting with the 5v DC psu
i came across a strange (to me) oscope waveform.

using most basic psu {18vac in, bridge, 7805, 5v out}
with a (470 Ohm + standard LED) power indicator on the 5v side

1st
i oscope the (bridge +) and (7805 out) and i see typical
expected waves... that is bridge + positive 16 v sine peaks
squashed together and 7805 out is 5v DC but with small dips at
intervals cooresponding to positive sine peak dips

2nd (**problem here **)
i add .1uF cap between 7805 out and ground (high frequency
decoupling ) and the bridge + output changes to some high
frequency fuzz on the tops of positive sine peaks.

When i zoom in on the ?fuzz? it is a series of about 1 uSec wide
spikes that are space about 10 uSec apart and the magnitude
follows shape of the sine wave ? (see pic in a.b.s.e) thats the
best this amateur can dexcribe

3rd ( ? problem fix ? )
all of these things by themselves will make fuzz go away....
- add a .1uF cap between the -/+ bridge output
- remove the LED
- add smoothing cap to either side

any ideas to help understand what this fuzz is ?

thanks for any help ,
robb