Analog Devices isoPower devices (ADuM524x)
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Posted by Steve on February 13, 2008, 10:34 am
Please log in for more thread options applications that uses these isoPower devices. The parts work well for our purposes but the power supply is horribly inefficient and produces severe radiated emissions at 300mHz (integrated PS switching frequency) and higher harmonics. We've tried everything from PWB layout changes, multi layer boards, ferrites/caps/filters, etc. but still have not been able to reduce the emissions to meet the CE requirments for industrial environments. Anyone have any experience with this part? Thanks, Steve | ||||||||||||||||||||||
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Posted by John Larkin on February 13, 2008, 11:38 am
Please log in for more thread options We used transformer coupled supplies, at 60 KHz with deliberately slowed edges, to avoid problems like that: http://www.highlandtechnology.com/DSS/V450DS.html Probably cheaper, too. We do use their logic isolators, which seem fine, but not the self-powered ones. John | ||||||||||||||||||||||
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Posted by Joerg on February 13, 2008, 3:33 pm
Please log in for more thread options John Larkin wrote:
> On Wed, 13 Feb 2008 07:34:35 -0800 (PST), Steve
> >> We have developed an isolated thermocouple product for industrial
>> applications that uses these isoPower devices. The parts work well for >> our purposes but the power supply is horribly inefficient and produces >> severe radiated emissions at 300mHz (integrated PS switching >> frequency) and higher harmonics. We've tried everything from PWB >> layout changes, multi layer boards, ferrites/caps/filters, etc. but >> still have not been able to reduce the emissions to meet the CE >> requirments for industrial environments. >> >> Anyone have any experience with this part? >> >> Thanks, >> Steve >
> > We used transformer coupled supplies, at 60 KHz with deliberately > slowed edges, to avoid problems like that: > > http://www.highlandtechnology.com/DSS/V450DS.html > > Probably cheaper, too. > That's the way to do it. > We do use their logic isolators, which seem fine, but not the
> self-powered ones. > I mostly use a modulation scheme, essentially a clock and then a DC restore (clamping) on the system side. That way there are no single-sourced parts in the machine. -- Regards, Joerg http://www.analogconsultants.com/ | ||||||||||||||||||||||
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Posted by Robert Adsett on February 13, 2008, 11:42 am
Please log in for more thread options > We have developed an isolated thermocouple product for industrial
> applications that uses these isoPower devices. The parts work well for > our purposes but the power supply is horribly inefficient and produces > severe radiated emissions at 300mHz (integrated PS switching MHz Presumably ;) > frequency) and higher harmonics. We've tried everything from PWB
> layout changes, multi layer boards, ferrites/caps/filters, etc. but > still have not been able to reduce the emissions to meet the CE > requirments for industrial environments. All the switching currents are within the chip (other than maybe transient input) so there may not be much you can do externally to reduce EMI. Have you tried shielding it? Robert | ||||||||||||||||||||||
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Posted by Robert Adsett on February 13, 2008, 2:23 pm
Please log in for more thread options >
> > We have developed an isolated thermocouple product for industrial
> > applications that uses these isoPower devices. The parts work well for > > our purposes but the power supply is horribly inefficient and produces > > severe radiated emissions at 300mHz (integrated PS switching >
> MHz Presumably ;) > > > frequency) and higher harmonics. We've tried everything from PWB
> > layout changes, multi layer boards, ferrites/caps/filters, etc. but > > still have not been able to reduce the emissions to meet the CE > > requirments for industrial environments. >
> All the switching currents are within the chip (other than maybe > transient input) so there may not be much you can do externally to > reduce EMI. Have you tried shielding it? Apparently I wasn't thinking clearly. A conductive shield across the isolation gap might not be very good for the isolation. I take it you've implemented there suggestion about providing 100Ohms or so of impedance at 300MHz and adding caps to slow down the transition edges? Robert | ||||||||||||||||||||||
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>applications that uses these isoPower devices. The parts work well for
>our purposes but the power supply is horribly inefficient and produces
>severe radiated emissions at 300mHz (integrated PS switching
>frequency) and higher harmonics. We've tried everything from PWB
>layout changes, multi layer boards, ferrites/caps/filters, etc. but
>still have not been able to reduce the emissions to meet the CE
>requirments for industrial environments.
>
>Anyone have any experience with this part?
>
>Thanks,
>Steve