[SI-LIST] Re: Conducted Emissions and SMPSs help needed
- From: npatel@xxxxxxxxxx
- To: <Erin.McPhalen@xxxxxxxxxxxxxxxxxxxxxxxxx>, <si-list@xxxxxxxxxxxxx>
- Date: Fri, 9 Feb 2007 12:43:29 -0700
Erin,
In the past I have had very good luck using common mode chokes right at
the input of PS to pass conducted emissions. You can also try increasing
the X and Y cap values. Try to find the source of the frequency in
question. There are FET's switching at very high duty cycle on the
primary and secondary side especially if you have some DC-DC converters
in it that causes emissions. Try increasing the gate resistance of the
FET's to slow they down. You might run into thermal issues if you do
that. Ask the vendor what components, IC's are switching at what
frequency. I would also start near field probing the PS and see if you
can pick up anything there. Take the output of the spectrum analyzer and
feed it into a Oscilloscope to see if you spot the frequency. Check the
routing on the boards. Usually PS boards are single layer with big power
and ground loops. Also you might try snapping torrid on cables in the PS
including the input PS cable to see if one them is acting as an antenna.
Hope it helps.
Nikhil=20
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
On Behalf Of Erin.McPhalen@xxxxxxxxxxxxxxxxxxxxxxxxx
Sent: Friday, February 09, 2007 10:39 AM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Conducted Emissions and SMPSs help needed
Hi
Wondering if any of the Guru's out their might be able to provide some
advice on how to proceed on a problem I am having with a switch mode
power supply.
The power supply is a 3 Phase supply (L1,L2,L3,N, Gnd) operates from=20
90Volts to 300 Volts AC. Currently, it has a very low margin at 200
kHz=20
for CISPR 22 Class B conducted levels. The mains filter consists of 5
mH=20
inductors and the standard capacitor values for L-GND and phase to phase
(4n7 and 47n respectively). All my efforts have reduced everything
over=20
400 kHz considerably but has not budged the two spikes at 200 kHz and
300 kHz. Using a splitter(0deg and 180deg) and two LISNs, the source of
the conducted emissions is common mode.
Any ideas on how to reduce this low frequency conducted emissions would
be greatly appreciated.
Erin
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=20
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