Dear experts,

I have been searching the net and especially this site for a dc to dc adjustable output boost converter schematic allowing for a 4A output for many days and I've not found one, especially with the specs I need. I am hoping someone can point me in the right direction and or provide a schematic??? I am only begining in electronics and I don't have any formal education in it (so please be kind). I have recently built a few things (schematics provided) and I'm liking it a lot. But this has led me to try something more difficult.

The problem is that I would like to convert a 12vdc (solar/battery) power system (11vdc to 13.8vdc) to run my Direcway DW7000 satelite modem, instead of running a DC-AC inverter to convert my 12vdc system to 120AC then back into DC again (its a huge drain on my battery system to do that). The normal power supply is an AC-DC dual output supply, and I'll give the specs below. I have seen a site which gives an example of what is needed for this and suggests contacting an email address for the 12to24 adjustable converter (set to 19.55vdc). That email no longer works and so I will need to build my own (which I'm happy to do if I can find out how). Not being to far in my self education of electronics I'm hoping to get some help. The website with this DC-DC power solution is: http://www.dustyfoot.com/DirecWAY/. I've even contacted the dustyfoot domain owner and he says he just hosts the information, and doesn't have any contact for the writter of the page. So following its instructions I feel confident that if I can get the schematic and parts list for the 12-24 adjustable converter that I can build these pieces into what they show. Perhaps there is a better solution, I don't know, but if its easy for a beginner and gives the necessary volts and current, I'm up for it. I can solder and do all of the wiring, etc., so if I can get a schematic for the 12-24 I should be able to make this happen. I'm trying to give a lot of information because a lot of the posts I've seen suggest that the "OP" didn't give enough information. So I hope all of this isn't overkill.

I have not seen anything commerical that can do this, so it looks like my only option is to build it if I can get the necessary help.

The original AC-DC Power supply specs:
Input 100-240V~ 2.0A(MAX.) 50-60Hz
Max. Ouptput Power: 64W
Pin No. 1,2 = +6.5V 1.3A
Pin No. 6,7 = +19.5V 2.85A

So can anyone help me? I have recently built a DC-DC buck mode converter found here: http://solorb.com/elect/solarcirc/buckreg1/index.html and I got it to work (suprizingly). I built it on a cheap radio shack perf board and I'm considering trying to design a PCB in eagle and do it better. But at least I know I can follow a schematic and parts list.

Thanks for your help,
John

 

The buck converter might be fine for the 6.5V, although the output current falls a little short at only 1A.

The following manufacturers all sell products that will be able to do what you want. Some will even do the design work for you if you provide them with the input and output voltage/current you require.

http://www.linear.com/pc/viewCategor...03,C1042,C1031
http://www.national.com/appinfo/power/
http://para.maxim-ic.com/cache/en/results/4631.html

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please download EPE magazine august2006. there is an article on adjustable dc-dc converter from 12v-13.8v to24V but at 2amps.

__________________
Regards,
Sarma.

 

Thanks folks, I'll take your suggestios and look into them. Hero999, I'm sorry to have confused you about the buck converter. I built it for another project and was referring to it just to show that as a newbie I can actually follow a schematic. However, I won't be using it in this situation. I'll be following the instructions on the dustyfoot website.

But again, thank you both, I'll post again if I need anything additional.

Thanks
John

 

I downloaded the article and it shows 2amps at 15volts but drops as you increase volts. Thus this one won't work and I'm not smart enough to know what needs to be redesigned to make it work. But thanks for the suggestion.

John

 

Yes the graph and related explanation has really discouraged me too. i will indicate a better one that could be assembled by you, shortly

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Regards,
Sarma.

 

This is almost like the circuit you built, but its 5 Amps (current limit is adjustable as is voltage)
http://www.national.com/pf/LM/LM2679.html

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Please see the Laptop power supply with 12V battery from January2006 issue of Elektor UK edition. Again, this gives an output of 19V at almost 5amps out. as regards your other voltage, you can manage with the design at http://solorb.com/elect/solarcirc/buckreg1/index.html ,what you have located, for 6.5V1Amp low voltage. this appears suitable. Some how you have to sit and make it coolly. the article can be downloaded at 0.8 British Pounds (10elektor credits) from
http://www.elektor.com/magazines/200...or.58015.lynkx Thus a combination of both will serve your needs and efficiently too.
All the best John.

__________________
Regards,
Sarma.

 

Use the design wizard on National's or Linear's website and they'll give you the schematic together with advice on board layout for free.

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Thanks Hero999, I have visited the 3 links you gave me and tried to use them. I didn't quite understand them at first, and with National you have to register. So now that I've done that and tried them, I'm understanding that better.

Thank you,
John

 

Thanks, I'll go look at that article. On the dustfoot website it also shows how to get the 6.5v, so now I have several ways of getting that voltage. I'm not sure if you were saying that I need to make it look cool, or if I need to add some "cooling" like a heatsink/fan, but I intend to do both.

Thanks for the info again,
John

 

Overclocked that's Great. I've visited the page and I have a couple of questions. 1) There are 2 schematic graphics on this page and I'm not sure which one is the one you are referring to (although I'll presume its the first one - top) as it does look a lot like the one I built already. 2) can I follow that schematic as is? Is it a valid proven schematic? Or do they just show that for referrence (expecting that you/I know how to make it work right)? 3) Why do they list/show the "Block Diagram" schematic further down? Its considerably more intensive than the "Typical Application" graphic on top of the page. 4) since they give you the schematic (ie. "Typical Application"), why do they have the link on the right showing "Start Your Design" if its already designed? 5) and I think this is my final question, down in the "Package Availability, Models, Samples & Pricing" area, their first item listed is a "SIMPLE SWITCHER 5A Step-Down Voltage Regulator with Adjustable Current Limit" for $30 bucks, but the rest of the items there are $3.30 (1K qty pricing). But I'm looking for a boost, not a step-down, so why would they list a step-down here (maybe this IC can be used either way?)? And since its the only one with a qty price for 1, which of these chips do I select for purchase? In the top schematic they show a 7 pin IC chip, but right after that initial product (step-down regulator), they list IC's with 14 pins, and then the 7pins after that. I'm presuming I should just look at the 7pin chips (is that right)? But they don't list those with a price for a qty of 1. Can you help me pick the right chip? The schematic shows the IC as part "LM2679-5.0, but the parts at the bottom of the page don't show that exactly. They have part#'s "LM2679-5.0EVAL", "LM2679SD-5.0", "LM2679SDX-5.0", "LM2679T-5.0", "LM2679S-5.0" and "LM2679SX-5.0". I had thought I should be looking for an -ADJ for "adjustable"?

I'm sorry to ask you so many questions (really), especially about someone else's site, but Nationals website is rather confusing especially to someone who has never used it before and you seem more knowledgable than I. Your help is very appreciated.

Thanks
John

 

Actually Overclocked, I've just been looking carefully at the top schematic and it shows a 5V output, not 20 or 40 or whatever. Is this the right chip/schematic?

Thanks
John

 

1,2. Yes. Some people here have built it. I have built it, but Ive gotten side tracked with other projects. The Data sheet itself is simple, there are No Complex Calcs just one or two calcs and then some thinking and choosing parts.

3) Block diagram just shows the internals. Dont be too concerned with this.

4) They have a ADJ. Version the schematic they show is with a 5V Output. The LM2679 is a better replacement for the LM78xx Series.

5) Get the ADJ Version. There are a couple different packages, one is Through hole, and 2 are SMD. I suggested this on the grounds that you had already built a buck converter, you just needed more current from the same family of converters.

There is a a ADJ Version that is Much like the LM317, except it is a switching regulator and not a linear type

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Insinuating that they hold the bomb.
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Hi Teksaport,

1. If you just go to http://www.national.com/appinfo/power/webench.html and enter your 11 and 13.8 DC input voltages, and your 19.5 desired output voltage and max output current (4?), it will automatically design a boost converter for you, using either the LM3478 or LM3488.

Then you can try the same thing for the stepped-down (6.5v) supply, and probably have a choice of either an SMPS or a linear regulator.

2. Also, download and install http://ltspice.linear.com/software/swcadiii.exe . Then run it and select File-->Switch Selector Guide. Then enter your requirements, similarly, and it will automatically design a boost converter for you, using something like an LT1680 or an LT1270A. For the 6.5v supply, there will be more choices for the IC.

There will only be eight or nine components, for the boost converters.

Note: If you need a super-quiet output, you might want to use linear regulators after the SMPS outputs. In that case, remember to design each SMPS so that its output voltage is about three volts higher than your final desired output voltage, so you'll have enough headroom for the linear regulator's dropout voltage plus a little extra.

You might also want to add an LC lowpass filter stage, to the SMPS output (before any linear regulator, if you use one), to drastically-attenuate the switching noise. That could just be a high-current inductor, say 10 uH, in series with the output, and then a large-ish electrolytic cap to ground, maybe 1000 uF or 2200 uF.

With 2, above, you'll also have the LTspice circuit simulator. Then you can easily play around with adding a filter and/or a linear regulator circuit, and see exactly what will happen.

- Tom Gootee

http://www.fullnet.com/~tomg/index.html