Run an inductor twice current if half the duty cycle?

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Hi guys,

 

I am looking at a buck switching regulator, but the inductor for it is very large in expensive. The price suddenly goes up.

However if I go for half the current rating of inductor, but I am only using it for a on time of 25%, can I use the inductor?

Will the core reach saturation before then and limit the current (or is this only for transformers)?

Is the only risk burning out the wire like a motor?

 

Thanks for any help

This topic has a solution.

Just a noob in this crazy world trying to get some electrons to obey me.

Last Edited: Thu. Sep 24, 2015 - 09:46 PM
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Core saturation would be the major problem methinks. Crank up the frequency to cut the inductor size.

This reply has been marked as the solution. 
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It depends on what establishes the current rating for that specific inductor.

 

If it is core saturation, then PEAK current has to be limited. Changing frequency may "fix" this as  higher frequency means lower peaks for the same average.

 

If it is I*R losses in the wire, then AVERAGE has to be limited.  Typically, changing frequency won't fix this.

 

The inductor specs may  include limits on both peak and average, and your design will have to conform to both.

 

Core design has a strong influence on both saturation and wire requirement. Sometimes, a small change in the core (gapped vs non-gapped, for example)  can mean big differences in performance. But, you often have to go to a different manufacturer. It is often necessary to search across several manufacturers to find one with the performance and cost you need. Occasionally, however, you cannot "get it all" (performance AND cost).

 

Jim

Jim Wagner Oregon Research Electronics, Consulting Div. Tangent, OR, USA http://www.orelectronics.net

Last Edited: Thu. Sep 24, 2015 - 04:59 PM
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Thanks Jim you legend! I will see if I can find more specs on the inductor and deduce something intelligent.

Just a noob in this crazy world trying to get some electrons to obey me.

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Kartman, omw! You have always given me helpful advice. I remember asking about making PLC like IO for a MCU about 8 years ago and you gave me brilliant advice that really helped me, so glad you are still around, thanks mate! smiley

Just a noob in this crazy world trying to get some electrons to obey me.

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An important point for a switch-mode power supply. 

 

At normal load, you may, indeed, be running at at 1/4 duty cycle. BUT, when it is first turning on, the duty cycle may be much higher as it charges up the output capacitor. While the time duration of this event may be relatively short, lots of things can go wrong if the inductor is being run beyond its specs. 

 

Usually, a SMPS chip will have some kind of mechanism to limit the MAXIMUM current. You need to design for proper operation at the designed load AND within the component extreme limits at the maximum current. Been there, done that, smelled the smoke.

 

Jim

Jim Wagner Oregon Research Electronics, Consulting Div. Tangent, OR, USA http://www.orelectronics.net

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Kartman, omw! You have always given me helpful advice

Kartman should be a moderator

 

Its a disgrace he isnt IMO

 

 

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Thanks for the vote Jamie. If i were a moderator, that would mean more work for the other moderators to moderate me! Besides, i'd only do it for the free stuff!

Anyways, thanks for the appreciation.

Jim gave a more complete answer. Like most things, it's a tradeoff. For a given physical size, going down in inductance usually means a better current rating - less turns. But going higher in frequency brings other problems - more critical layout and selection of components.
Even with current limiting, running the inductor into saturation is going to worsen your EMI problems. (The Sex Pistols had a song about that!)

Last Edited: Thu. Sep 24, 2015 - 10:32 PM
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Man you have really helped out sh!t loads of people, everyone likes you and you are well regarded

 

Like I said its a disgrace whoever it is that holds the decision to promote moderators has not chosen you, in a good organisation hard work, passion and results are rewarded

 

Kartman i know your modest dude and thats great but you know that you are an asset to this site

 

Can someone tell me who is it that has the power to promote Kartman to a moderator?

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What is your output current requirement for the buck-switching regulator?   If it is 3 amps or less, then use one of these tiny pre-made buck-convertor breakout-boards that cost $1 US.  They use very fast switching components that can regulate high currents for their sizes. 

http://www.ebay.com/itm/5pcs-goo...

 

For 12 amps, use this kind of module:

http://www.ebay.com/itm/DC-DC-CC...

 

If more than 12 amps, don't build anything; buy something professional.

 

Building your own power supply is like building your own car.  It can be done, and it's a wonderful learning experience, as the saying goes.  But there are better alternatives.