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Old 12th March 2009, 02:37 AM   #1
poptart is offline poptart  Canada
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Default looking for a DC to DC converter

I suck at finding ICs. I'm embarrassed of this fact, but it's true. I'm looking for an appropriate IC to convert approximately 12vdc to 14.5vdc. One amp is probably sufficient but if it could do a few amps that's gravy. If it can be configured to limit it output current that's gravy with a cherry on top.

Now how do you guys go about searching for a part like this? I'm not getting anywhere...
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Old 12th March 2009, 04:13 AM   #2
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I don't think there's any such thing as an IC that will do that by itself. (could easily be wrong)

There are IC's to control a couple of FET's and make a switch mode boost converter - along with a cap or two and an inductor. There are also some with built-in FET's. All of these usually require careful PCB layout.

There are also ready made modules for this.

google buck-boost converters

BTW, is it really that critical it be 14.5V? 12V won't work?
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Old 12th March 2009, 04:24 AM   #3
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Finding ICs is easier if you can narrow the search to a couple companies that make what you need. National Semi has various switching ICs and a web page to help you select one based on your specific needs. Linear Technology also has a line of excellent switcher ICs, many that are self contained with the FET. It was easier back in the old days when semiconductor data books were given out free and in huge quantities. You could just sit down and page through the sections and app notes, making a mental note of anything potentially useful for your sorts of designs. Today it takes more time to read pdf files, plus there are a lot more chips available to consider.
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Old 12th March 2009, 04:42 AM   #4
poptart is offline poptart  Canada
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eclectic2k,

I'll take as much on chip stuff as I can get but I'm sure some external components are going to be required. This is for a lead acid battery charger project so accurate voltage control is pretty much the whole point. Needs to reach around 14.5v when re-charging then drop down to 13.5v. I know there's a huge selection of commercial products, I just like re-inventing the wheel (seriously though I don't think there are any dc to dc chargers and I have tight space constraints so I want to make my own)

Conrad Hoffman,

Thanks for the names, I'll see what I can google tonight.
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Old 12th March 2009, 04:54 AM   #5
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understand the voltage requirement now, makes a bit more sense
that's why this is a DIY forum after all.

I'm guessing you're using some stuff you have on hand then, but might it not be easier to start with 15v and then regulate down? off the top of my head, seems a bit easier. Or maybe you're working from some existing 12v supply... ah, well, I'll stop making guesses. I'm sure you've got your reasons

either way, good luck with the project!
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Old 16th March 2009, 01:22 AM   #6
dangus is offline dangus  Canada
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If this is to be used in a vehicle to recharge some 12V gel cell, how about just exploiting the fact that the nominal 12V will reach more like 13.8 to 14.4 volts when the engine is running and the alternator is charging?

If it has to run from just 12V, then take a look at switching power supply regulator chips. They usually have application notes with various examples, and often there's a circuit that is pretty close to what you need. Like the Motorola MC34166/MC33166.
http://www.onsemi.com/PowerSolutions....do?id=MC33166
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Old 18th March 2009, 10:24 PM   #7
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So long as your 12V supply will never get above about 13V you could happily use a national LM2586-ADJ for this. As a bonus if you go tothe national website you can use their new (ish) flash version of the webench design tool to do all of the tricky parts selection for you once you've told it what you'd like the circuit to do.

However if as one of the previous posts states you are using this ina car and your input voltage starts to get too close to your desired output voltage the circuit will probably stop working as you won't be boosting the input voltage any more (which is what this part is designed to do).

LM2586@National
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Old 18th March 2009, 10:24 PM   #8
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Sorry for the double post, but I'm still under modderation at the moment and can't edit the previous post I just made.

If you are looking for something with an adjustable output voltage (this is the bit I just noticed) I do have a design for a 0-40V 5A varaible switched supply at work using a clever linear dual mode switcher. However this currently runs on a 24V input so may require quite a bit more effert to get up and runnig than the national part I mentioned above (it's also a far more complex and costly circuit whaich can be a bit of a pain to get running properly even with an existing design to start from). If you're interested though I can probably dig out a rough schematic and definately the controller part number while I'm at work tomorrow.
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