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Author Topic: DC to DC voltage step down  (Read 1976 times)
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Hello Friends

We have an Arduino ready to integrate into an electrical appliance for additional functions. Just want to post a question regarding power, see below for details:

Circuit #1: Electrical appliance's transformer converting AC main (120V AC) to 110V DC
Circuit #2: Need 5V DC circuit powering the Arduino (minimal current needed)
Circuit #3: Also need a separate 12V DC circuit (minimal current needed)

Circuit #1 is the original appliance circuit, circuit #2 and #3 are new requirements. Just wondering if there is a DC to DC step down out there with 2 outputs that fits the job?

Thoughts?

Thanks in advance, BTF
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Here's one: http://www.mpja.com/5V-9A-and-12V-300mA-Cisco-Power-Supply/productinfo/18465+PS/
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I don't know what your trying to do, but do you have the mains(120v AC) available to you for circuit 2 and 3?? A computer power supply is cheap and readily available and provides 5v and 12v.. T
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Idk what exactly you are trying to do.

But I can give you theoretical answers.

For a 120V Ac to Dc you can use a rectifier.

7805 and 7812 can be used for 5v and 12 v.

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Is it acceptable for the Arduino to have a common ground with the 12v supply? If so, then just get a 12v supply and power the Arduino from it too through the barrel jack or the Vin pin.
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Thank you for all your replies.

Let me elaborate further.

Circuit #1: Electrical appliance's transformer converting AC main (120V AC) to 110V DC
Circuit #2: Need 5V DC circuit powering the Arduino
Circuit #3: Also need a separate 12V DC circuit to drive some automotive light bulbs

Circuit #1 is the original circuit of the appliance (AC 120V main, power cable to transformer). Circuit #2 and #3 are new requirements. As mentioned before, we are to "Integrate" an Ardunio solution into this appliance, hence we do not want to introduce a extra/external power supply to user.

Also, these 5V & 12V circuits is next to 110V DC source but physically far from AC main. This is what prompt us to see if there is a device which:

1. Has input of 110V DC
2. Provides dual output of 5V DC and 12V DC

Thanks, BTF
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You don't need dual output, you can derive the 5v supply from the 12v supply. I found this one http://uk.farnell.com/synqor/iq1b120qtc12nrs-g/inqor-dc-dc-converters/dp/1817944 that is specifically a DC-DC converter but is rather expensive. However, most switch mode PSUs are just as happy running off DC as AC, for example these http://uk.farnell.com/jsp/search/browse.jsp?N=203411+110032328+110372221+110371633+110383842+110372213+110387003+731&No=0&getResults=true&appliedparametrics=true&locale=en_UK&divisionLocale=en_UK&catalogId=&skipManufacturer=false&skipParametricAttributeId=&prevNValues=203411+110032328+110372221+110371633+110383842+110372213+110387003&mm=1000645||,1003617||,&filtersHidden=false&appliedHidden=false&autoApply=false&originalQueryURL=%2Fjsp%2Fsearch%2Fbrowse.jsp%3FN%3D203411%26No%3D0%26getResults%3Dtrue%26appliedparametrics%3Dtrue%26locale%3Den_UK%26divisionLocale%3Den_UK%26catalogId%3D%26skipManufacturer%3Dfalse%26skipParametricAttributeId%3D%26prevNValues%3D203411 are specified for minimum DC inputs of 85v or 90v.
« Last Edit: February 01, 2012, 04:56:47 pm by dc42 » Logged

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Sure, you can get a DC-DC converter that will chop up the DC to make AC, run it thru a transformer reduce it to a more manageable level, and rectify it again into a DC level that can then be regulated to 12V and 5V.

Is there a need for the 110VDC? Be easier to work from the 120V AC.
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You realise the original post is asking about DC--DC step down supply?  Probably want somewhat less than 9A at 5V...

I've seen nice Murata units that go from 72V down to 12 and 5, see if they do a higher-input-voltage range?  I couldn't see anything.

A 12V power blob from the mains is a possible solution, followed by 12V to 5V converter or regulator?
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What you need is another "power supply" mainly a small stepdown transformer from 120 12 V AC. Go through a ful wave bridge rectifier and a regulator (7812) for your 12V needs, and through a 5 V regulator (7805)  for your 5 volt needs. All this is assuming you need less than 1Amp of low voltage DC. If you need more at 12V then you would have to size that part of the power supply for the 12V needs and still use the 7805 for the 5 V needs. A few appropriate Capacitors at each stage of the DC would clean it up and make the devices connected happy.
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