Hello,

I'm looking to do a project where I need multiple isolated regulated outputs. I understand how to wire the regulator but am unsure how to isolate them from each other. They need to be isolated for groundloops. I've attached a portion of a schematic for illustration of what I think may work. Am I on the right track with the diodes? Or should I do something different?

I've searched for similar circuits with "isolation" but all I get is simple wiring circuits of the V reg's.

Thanks

 

hi dlad,
Welcome to AAC.
That method will not give isolation from each other or ground.
How many outputs do you require and is it complete isolation from ground and the other Vouts.?
E

 

Thank you.

I need (8) outs and yes complete isolation from ground and each of the other regulator out's.

Thank you!

 

hi,
What is the source of your 12V.?
One option would 12Vdc to 5Vdc isolated miniature SMPS modules.
E
This is the type I am suggesting.
https://www.google.com/search?client=firefox-b-d&q=12Vdc+to+5Vdc+smps

https://www.digikey.co.uk/product-d...I4d60LdDw2sN1BEvCJeqpfHtEQUZf1zQaAvHcEALw_wcB

 

The 12V would be a linear supply. A transformer into a bridge rectifier.

I wonder to get the isolation I need if i would need a transformer with several secondaries? Or could this be accomplished with discrete components?

Thanks

 

They need to be isolated for groundloops.

Please explain what you mean by this. I am skeptical. In your schematic the ground and output of each regulator is connected together!

Bob

 

hi 87,
You could use transformer with 8 off windings , say 8v output, you would need a rectifier, smoothing and 7805 for each winding.
Can you tell us what it will be used for.?

E

 

It will be for a guitar pedal supply. Instead of 7805's it will be 7809's and LM317's.

Thanks

 

hi,
OK, for a 7809, ie: 9Vout you will need about 12Vdc in from the rect and smoothing.
What are the current loads on the 9Vouts.?
E

 

Yes,
12-13V IN is what I planned for the 7809's. Most pedals draw 100mA or less but some can draw up to 400mA for high current pedals. Taking that into account, I think STMicroelectronics L78M09ABDT-TR should work as it is rated for 500mA.

https://www.digikey.com/en/products/detail/stmicroelectronics/L78M09ABDT-TR/4503547

 

hi,
One option would be to strip the secondary windings from an old transformer and rewind on 8 secondaries,
So a transformer capable of 8 * 0.5A say would be required.
You may have to use a higher VA rated transformer that has enough clearance for 8 secondaries

E

 

Another thought I just had is to use these Meanwell SPBW06F-12 isolated dc-dc converters ahead of the regulators. I would use one of these converters to supply each regulator. The converters would be powered by the transformer secondary after the rectifier and filter. I think it would allow me to use a transformer with one secondary and still maintain isolation of each regulator output from each other. Is my understanding correct? https://www.digikey.com/en/products/detail/mean-well-usa-inc/SPBW06F-12/7707012

Thanks

 

hi,
These are the type as I suggested in post #4.

The type you have posted are +12Vout , so a single 9V thru 36Vdc input would be OK.
E

 

Ha, I didn't realize these were SMPS's. I've attached an updated schematic showing how I think it should be wired. Let me know what you think.

 

hi,
There is a 9Vout version of that type, it would eliminate the need for the 7809's.
E
This is your PDF circuit.

Update:
added a PDF

 

If you need complete galvanic isolation among all outputs, then your options are capacitive coupling or transformers. One primary and multiple secondaries will work fine, but I doubt there is an off-the-shelf transformer that meets your requirements.

One option is several dual-secondary transformers, but the size, weight, and cost might be too much. Another is small isolated DC/DC converters, each with one output. For ausio applications you probably will need to add extra filtering to each output.

https://www.ebay.com/sch/i.html?_from=R40&_nkw=isolated+dc-dc+converter&_sacat=0&_sop=15

ak

 

Multiple secondaries are my preference but I can’t find a transformer that is 8x12V for secondary taps. I could run multiple dual secondary transformers such as ones from Antek but that takes a lot of space. Cost of the smaller Antek transformers are about the same as one of the Meanwell dc-dc converters so it is likely cheaper going with multiple toroids but the enclosure will have to be bigger.

 

I can’t find a transformer that is 8x12V for secondary taps.

hi dlad,
If you decide on a transformer solution, you do not want a tapped transformer secondary, it must be 8 independent secondary windings.
E

 

Correct, I said taps in error. But yes, 8 separate windings

 

I've attached another schematic going the dc-dc converter route. This one includes low pass filters between the SMPS and the Vreg's. I believe it should filter down to 3.4kHz.