bigheadted
Electrical
Are there any major considerations when changing from a linear to a switch mode power supply that feed assorted plc cards and components?
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power supplies
- Thread starter bigheadted
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Switchers are notorious for having lots of noise on their outputs. People who want quiet DC don't reach for switchers.
Also switchers have vastly more parts and so always die sooner. Lower MBTF.
They also, again because of all the parts, cost more!
All that said....
They are nicely done these days.
Because of the MTBF concerns they have been refined to where they last 'just about' as long as a any linear.
They give off less heat.
They are waaaaaay smaller.
And if you are feeding only digital devices like a PLC it won't make any difference.
Have I said too much?
Keith Cress
Flamin Systems, Inc.- <
Also switchers have vastly more parts and so always die sooner. Lower MBTF.
They also, again because of all the parts, cost more!
All that said....
They are nicely done these days.
Because of the MTBF concerns they have been refined to where they last 'just about' as long as a any linear.
They give off less heat.
They are waaaaaay smaller.
And if you are feeding only digital devices like a PLC it won't make any difference.
Have I said too much?
Keith Cress
Flamin Systems, Inc.- <
- Thread starter
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bigheadted
Electrical
the power supply is to feed only digital devices but there are some communiction links involved rs232/485 and dh+? i assume it should be ok with these
thanks for the reply
thanks for the reply
Yes a modern switcher should not cause any problems there.
Keith Cress
Flamin Systems, Inc.- <
Keith Cress
Flamin Systems, Inc.- <
coconutalley
Electrical
Considerations:
Linears are quieter but switchers have come a long ways.
You can get ones for <1% ripple & noise at less than $1 per watt these days. For digital, this is not a problem.
For analog, you can always add a small linear regulator off the switcher output to quiet things down.
Linears need more power and take up more space. Switchers are usually 75% - 90% efficient, so they need less power and space.
Switchers generate more EMI but if they have CE Mark they conform to a least 40 dB of shielding.
In rare cases, the resonant point in the load and switcher frequency need to be taken into account, though for most apps the switcher frequency is up there in 20kHz - 500 kHz depending on the size.
Some real cheap switchers need minimum load.
Also, in rare cases, the loop response of the switcher may be important.
Linears are quieter but switchers have come a long ways.
You can get ones for <1% ripple & noise at less than $1 per watt these days. For digital, this is not a problem.
For analog, you can always add a small linear regulator off the switcher output to quiet things down.
Linears need more power and take up more space. Switchers are usually 75% - 90% efficient, so they need less power and space.
Switchers generate more EMI but if they have CE Mark they conform to a least 40 dB of shielding.
In rare cases, the resonant point in the load and switcher frequency need to be taken into account, though for most apps the switcher frequency is up there in 20kHz - 500 kHz depending on the size.
Some real cheap switchers need minimum load.
Also, in rare cases, the loop response of the switcher may be important.
I've also seen plenty of switchers that have the CE mark and FCC, but in fact are broadband noise generators that will fail you at any test range.
Always check, never assume with those things.
-Bill
CE Designer Forum
Always check, never assume with those things.
-Bill
CE Designer Forum
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