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DC-DC converter ---- 24V input 5V output
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din.gulu.er

Posted: Jun 06, 2012 - 07:58 AM

Joined: Mar 03, 2010
Posts: 535
Location: New Delhi, India

Hi,

I need to convert 24 V supply from battery to 5V on an distributed network for CAN bus.

Shall i use normal switching regulator or DC-DC converter. Which is more efficient Question

What will be advantage of DC-DC converter over normal switching regulator Question

Please suggest.

Regards,

Dinesh

valusoft

Posted: Jun 06, 2012 - 08:08 AM

Joined: Jul 02, 2005
Posts: 5946
Location: Melbourne, Australia

Dinesh,

What is your definition of a "normal switching regulator"? (I suspect that you meant to say "linear regulator", but heck I may be wrong ... Laughing

Cheers,

Ross

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Ross McKenzie
ValuSoft
Melbourne Australia

Kartman

Posted: Jun 06, 2012 - 08:59 AM

Joined: Dec 30, 2004
Posts: 8780
Location: Melbourne,Australia

A switching regulator is a dc/dc converter! My interpretation is the isolated dc/dc converters vs a non-isolated dc/dc converter. Both are switching. As for efficiency, then you'll need to refer to the relevant datasheets. Expect over 70% efficiency for either. The isolated dc/dc converter's advantage is that it is isolated! That may be a benefit or maybe not - depends on what you want to achieve. The isolation uses a transformer so that may add cost.If you have a common suppply rail then the isolation might give you the benefit of not passing the supply current through your comms common wire.

din.gulu.er

Posted: Jun 06, 2012 - 09:11 AM

Joined: Mar 03, 2010
Posts: 535
Location: New Delhi, India

Quote:

I suspect that you meant to say "linear regulator"

linear regulator will led to lot of power loss, i will prefer switching regulator.

Quote:

The isolated dc/dc converter's advantage is that it is isolated! That may be a benefit or maybe not - depends on what you want to achieve. The isolation uses a transformer so that may add cost

Transformer is used to step down AC voltage, what will it find use in DC to DC conversion

I need efficient way of converting 24V on common bus power line into 5V to be used for microcontroller. Thats why question is "Shall i use normal switching regulator or DC-DC converter."

Quote:

.If you have a common suppply rail then the isolation might give you the benefit of not passing the supply current through your comms common wire.

Will it also help in noise suppression Question

Regards,

Dinesh

valusoft

Posted: Jun 06, 2012 - 09:33 AM

Joined: Jul 02, 2005
Posts: 5946
Location: Melbourne, Australia

Dinesh,

Kartman and I have both tried to help you clarify your terminology ... so that we can help you. You still say "Shall i use normal switching regulator or DC-DC converter." The ball is back in your court ...

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Ross McKenzie
ValuSoft
Melbourne Australia

jan_dc

Posted: Jun 06, 2012 - 09:45 AM

Joined: Feb 09, 2011
Posts: 322
Location: Turnhout, Belgium

Both switching regulators (e.g. 7805 variants) and DC-DC converters (= convert 1 voltage level to an other) use AC to convert the voltage levels. In isolated DC-DC converters the isolation is thus done with a pulse transformer.

A switching regulator has a higher efficiency and a wide input range (about 9V to 35V). A typical DC-DC converter is isolated but can only be used with 1 input voltage (24V input in your case).

Since you're running from batteries there is *no* need for an isolated DC-DC converter. There is also a large benefit of a switching regulator in battery opperated situations: it the battery voltage level must drop below 8 or 9 V before the switching regulator will give up.

Noise reduction can be done with good copper ground planes, lots of decoupling capacitors and shielding.

Last edited by jan_dc on Jun 06, 2012 - 11:31 AM; edited 1 time in total

din.gulu.er

Posted: Jun 06, 2012 - 09:46 AM

Joined: Mar 03, 2010
Posts: 535
Location: New Delhi, India

Quote:

The ball is back in your court ...

my mistake. I have correctly mentioned below.

Quote:

My interpretation is the isolated dc/dc converters vs a non-isolated dc/dc converter.

Actually i means to say Isolated DC-DC converter. You are suggesting transformer, but Transformer is used to step down AC voltage, what will it find use in DC to DC conversion, DC 24V to 5V Question

Kartman

Posted: Jun 06, 2012 - 11:27 AM

Joined: Dec 30, 2004
Posts: 8780
Location: Melbourne,Australia

I think you'll find isolated dc/dc converters use transformers. The switching action is causing the AC. Will it help with noise? Probably not- in fact it may give you more problems. I think it is time you do some research on power conversion and gain some knowlege rather than asking obscure questions and telling us about how transformers work.

What happens if you poke dc to dc converter into wikipedia?

markus_b

Posted: Jun 06, 2012 - 11:39 AM

Joined: Mar 20, 2001
Posts: 1517
Location: Switzerland

din.gulu.er wrote:

You are suggesting transformer, but Transformer is used to step down AC voltage, what will it find use in DC to DC conversion, DC 24V to 5V Question

A switching DC/DC converter does convert your DC input voltage into an (internal) AC voltage. It then uses either a simple inductor or a transformer to reduce/step down the voltage to the desired level and rectifies the result to obtain a DC voltage again at the output.

If you want a isolation you need a transformer, otherwise an inductor is sufficient. A transformer and the somewhat more complex circuit for isolation is more expensive than a simple switching (non-isolated) converter.

_________________
Markus

markus_b

Posted: Jun 06, 2012 - 11:56 AM

Joined: Mar 20, 2001
Posts: 1517
Location: Switzerland

Some more thoughts: Switching regulators are non-trivial to implement, so you may want to buy a module. Searching on Ebay you'll find plenty. Non-isolated ones start at $3.49, isolated ones are more expensive: $21.

_________________
Markus

MBedder

Posted: Jun 06, 2012 - 12:12 PM

Joined: Nov 02, 2009
Posts: 3239
Location: Zelenograd, Russia

If you do not need isolation between 24V GND and 5V GND, use something like this:

If you do, use something like this:

And if you need your system really working, do not even think about building whatever DC/DC converter yourself. Period.

jan_dc

Posted: Jun 06, 2012 - 12:29 PM

Joined: Feb 09, 2011
Posts: 322
Location: Turnhout, Belgium

He's powering from a battery, there is absolutely no need for a isolated DC-DC...

MBedder

Posted: Jun 06, 2012 - 01:19 PM

Joined: Nov 02, 2009
Posts: 3239
Location: Zelenograd, Russia

I could provide tons of examples when isolated DC-DC is absolutely needed in battery powered systems, but I won't waste my time.

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Warning: Grumpy Old Chuff. Reading this post may severely damage your mental health.

jan_dc

Posted: Jun 06, 2012 - 02:03 PM

Joined: Feb 09, 2011
Posts: 322
Location: Turnhout, Belgium

1 example would suffice

MBedder

Posted: Jun 06, 2012 - 02:22 PM

Joined: Nov 02, 2009
Posts: 3239
Location: Zelenograd, Russia

Any device with both power actuators (motors, solenoids etc.) and multiple, precision analog input signals - is this sufficient?

_________________
Warning: Grumpy Old Chuff. Reading this post may severely damage your mental health.

jan_dc

Posted: Jun 06, 2012 - 03:05 PM

Joined: Feb 09, 2011
Posts: 322
Location: Turnhout, Belgium

I fail to understand the need for a DC-DC converter at the battery side.

Yes I do understand the need for DC-DC converters to have different ground planes between the actuators and measurements but not at the battery.

Maybe it's just me but I tend to only read what I can see. I read 24V battery and convert that to 5V for CAN bus. A battery does not generate noise hence galvanic isolation is not needed. Switching regulators generate noise and unless the TP is identifying the other items that could generate noise I will not guess for anything that the TP could or would probably make. I only answer to the question given, nothing more.

IMHO this forum would be a lot more efficient if all experienced people would only answer the actual questions, not the probable questions. It's a waste of time give answers to questions not asked...

valusoft

Posted: Jun 06, 2012 - 03:25 PM

Joined: Jul 02, 2005
Posts: 5946
Location: Melbourne, Australia

Jan,

With respect, sometimes the answer to an actual question can be dangerous "in the wrong hands". Efficiency is not always the best measure of "good". I would sooner provide a little more information and avoid an accident every time.

And yes ... probably in this topic, it would be safe ... but it was clear from the first post that the OP was not asking a question that could be answered without more questions.

Cheers,

Ross

_________________
Ross McKenzie
ValuSoft
Melbourne Australia

jan_dc

Posted: Jun 06, 2012 - 04:21 PM

Joined: Feb 09, 2011
Posts: 322
Location: Turnhout, Belgium

Ross, I'm a strong believer of the principles of the "Darwin Awards" and I've absolutely no desire to reduce the possible errors in a probable design which I have to guess based on little information.

For me there is sometimes a too high level of Hyacinth from "Keeping up appearences" (TV show from the BBC). If you know the show, I like to refer to things like this: http://www.imdb.com/title/tt0098837/quotes?qt=qt1517339

DocJC

Posted: Jun 06, 2012 - 05:02 PM

Joined: Dec 11, 2007
Posts: 6849
Location: Cleveland, OH

Quote:

Shall i use normal switching regulator or DC-DC converter.

Actually, I'm glad they asked a few other questions.

I found this original statement to be rather vague.

My first guess was that this referred to switching vs linear regulators.

In this case switching is generally the way to go, as a linear regulator with 24 V in and 5 V out will get very hot with even a small current draw.

I'm not blaming the OP for the vagueness of his question. I am continually amazed at how well so many people speak English as a second language.

JC

valusoft

Posted: Jun 07, 2012 - 03:57 AM

Joined: Jul 02, 2005
Posts: 5946
Location: Melbourne, Australia

DocJC wrote:

I am continually amazed at how well so many people speak English as a second language.

Including some born in an "English speaking country" Laughing

_________________
Ross McKenzie
ValuSoft
Melbourne Australia

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