>>>>>>>>>>>>>>>>>> Original Message <<<<<<<<<<<<<<<<<<
On 30/07/2003, 15:31:14, Pat Lawler <pat.law...@verizon.net> wrote
regarding Synchronizing DC-DC converters to reduce emissions?:
> We are designing a switching power supply for a customer that has
> multiple outputs. Due to the tight regulation requirements, all
> outputs have their own PWM modulators and control loops.
> The customer feels the RF emissions (as measured by CISPR 11) will be
> reduced by synchronizing the frequencies of all the converters. I
> think synchronizing the PWM sections will make the total power supply
> emissions as high as possible (emissions are coherent?).
Although we have not used dc-dc convertors, our experience with switch
mode power supplies may be of interest. We often run multiple power
supplies on the same chassis and although they are not synchronised,
their switching frequencies are not far different. The lower harmonics,
the main cause of conducted emission problems, on all units are very
close and do add to the levels at each frequency.
Just thinking about it, and I have no experience of this aspect, if
switching frequencies on individual units could be adjusted such that no
harmonics from any unit fell within the measurement instrument's band
width of any of the other unit's harmonics, then the result may be the
measurement of only one unit at each frequency of the spectrum. ok, I
expect to be shown that this wouldn't work but it's worth a try!
Regards,
Neil Helsby
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