🚀 go-pugleaf

john@jjdesigns.fsnet.co.uk wrote:

> Eeyore wrote:
> > Rich Grise wrote:
> > > Sylvia Else wrote:
> > >
> > > > I've recently bought a D-Link DIR-300 wireless router. While
> > > > disconnecting its power supply from it, I got a tingling sensation when
> > > > I touched the plug (to be clear, I'm talking about the 5V DC plug, not
> > > > the mains plug).
> > > >
> > > > An AVO meter shows about 90V AC to earth from either side of the 5V
> > > > plug. Short circuit current to earth is about 0.1mA.
> > > >
> > > > Still, I thought these things were meant to be completely isolated. Has
> > > > there been a change of approach?
> > >
> > > If the wart is 2-prong, turn it around in the socket. If it's 3-prong,
> > > get an outlet tester.
> >
> > Sylvia's experience is 100% normal. I've even modelled it in the past which
> > is why I reckon the Y cap between the rectified pri and sec sides is 2n2.
> >
> > I was myself at the time specifically interested in the value of the leakage
> > current and its waveform shape. It gives a great 'buzz' with lots of
> > harmonics in poorly grounded audio systems. The audio groups regularly get a
> > question why their laptop buzzes on the mains but not on battery power. About
> > once a month on average.
> >
> > Cue EMC discussion ?
>
> I reckon whomsoever allowed a capacitor/resistor/whatever to straddle
> a magnetically isolated, electrical safety barrier, ought to be
> marched out of their keep-the-public-safe-committee office and shot.

I could be tempted to agree.

Needless to say there's a reason for the method which as I said you'll find in the
EXCELLLENT app notes at powerint.com. It surprised me too.

The transformer would have coupling capacitance anyway.

This one's a real little runner. It can make life very much more complicated.

BTW, try connecting a modern printer to your PC at night with low illumination.
Look out for the sparks.

Graham