Typically, the range switch on the cost-sensitive (cheap) power supplies
changes the front-end topology from conventional capacitor input to a
voltage -doubled one. Since the power load stays the same, the current
will double. But the nature of the input current to these supplies is
gulps of current rather than sinusoidal draw. At the higher voltage the
conduction angle of the current pulse gets very narrow so the current
spike grows even more in magnitude. This can take the cores into
saturation and lead to low frequency (25-100 kHz) conducted emissions
problems. The effect is related more to voltage than frequency. The
logic-created frequencies are not afffected by the AC input voltage or
frequency.
> ----------
> From: Gary McInturff[SMTP:gmcintu...@packetengines.com]
> Reply To: Gary McInturff
> Sent: Monday, July 06, 1998 6:30 PM
> To: hmellb...@aol.com; dwight.hunnic...@vina-tech.com;
> emc-p...@ieee.org
> Cc: eric.lif...@natinst.com
> Subject: RE: Ce versus FCC
>
> That's interesting. The change from 50 to 60 Hz would change some
> input
> components and that could effect the input impedance and hence the
> conducted emissions signature but the voltage, especially if its a
> well
> regulated and filtered supply should be invisible. The components that
> radiate at that point are all of the secondary 5 or 3.3 volt
> oscillators
> and stuff. They shouldn't even know the difference in the input
> voltage.
> If using a switcher power supply it seems even more odd. The input
> voltage is rectified and then chopped to "#$@ then more regulating and
> filtering stuff happens. Then it hits the electronics.
> Anybody else see this and have an idea why it might. I may be living
> in
> a fools paradise here.
> Gary McInturff
> Packet Engines
>
>
> -----Original Message-----
> From: hmellb...@aol.com [SMTP:hmellb...@aol.com]
> Sent: Monday, July 06, 1998 11:16 AM
> To: dwight.hunnic...@vina-tech.com; emc-p...@ieee.org
> Cc: eric.lif...@natinst.com
> Subject: Re: Ce versus FCC
>
> I have encountered certain European agencies requesting that not
> only are the
> conducted emissions required to be performed at 230V 50Hz but
> radiated
> emissions as well. I agree that for conducted emissions it may
> make a
> difference but I have not seen radiated emissions change when
> the power source
> is changed from 60 to 50 Hz (while keeping Voltage the same). I
> did, however,
> see recently a product change emissions when the voltage was
> changed from 120
> to 230 V. And, it did not matter if it was 50 or 60 Hz, only the
> voltage was
> significant. Go figure!
> Hans
>
