Hello, I need to boost 12V from parallel array of batteries to 85V. The desired output current must be around 1.5A - 2.0A. I want to use a buck-boost topology for space efficiency. My search for national parts was unsuccessful, as I could not find anything that suits my needs. What are my options for this project?

Thanks

__________________
"The people who cast the votes don't decide an election, the people who count the votes do."
-Joseph Stalin

 

You could always build your own - it wouldn't be easy though, that's a huge output current requirement for such a large voltage boost. What kind of batteries are you using?

This might work:
http://www.linear.com/pc/downloadDoc...,P38055,D25148

 

They are all SLA batteries (9 of them to be exact). Wired in parallel, to give a total of 45Ampere/hour rating. These batteries can supply a lot of current if that’s what you worry about.

__________________
"The people who cast the votes don't decide an election, the people who count the votes do."
-Joseph Stalin

 

Don't use a buck-boost, but rather just a straight boost. Since the output is never less than the input, a boost is the right topology. A buck-boost has 2 transistors & 2 diodes, vs. 1 of each for the boost.

Keep in mind that for 2.0 amp output at 85V, the input current at 12V must be a little more than 14.2 amp average.

I would use a UCC28C43 peak current mode controller. It operates with a supply of 8.4 to 18 volts, perfect for a 12V application. It has a totem pole FET driver, low side, perfect for a boost topology. The FET & rectifier must withstand 85V, so I'd use 100V parts for each. I'd operate the inductor in the continuous conduction mode. All in all it looks pretty straightforward.

__________________
Claude

 

Thank you, I will look into that. Sometimes I wish for the school curriculum to at least introduce me to switching regulators, but instead our provincial government forces everyone to take useless subjects such as psychology, economics, workplace safety (biggest joke ever), and other useless crap that have no relevance to electronics. So my only option for side project is to do my own research and pay a little visit to this place.

Thank you for your help.

__________________
"The people who cast the votes don't decide an election, the people who count the votes do."
-Joseph Stalin

 

If you have 9 twelve volt batteries, why don’t you connect 7 of them in series and get the voltage you need. You can then charge them individually and this will cost you NOTHING.

 

at low battery you are talking about 17A average in so you are looking at something on the order of 150A peak from the battery which makes for a 200A inductor and 400A FET.

Dan

 

You'd be far better off connecting all the batteries in series and using a buck step down converter.

If you must use 12V in then use an autotransformer as a flyback rather than a simple inductor.

__________________

I do not answer private messages asking for help because no one else can: benefit from advice I may give or correct me if I'm wrong.

Please ask on the open forum if you have a question and I'll be happy to help, if I know the answer.

 

But one can *section* the design so that each section carries a portion of the total current. Current mode control readily lends itself to this practice. Using 8 to 10 sections makes the design quite feasible.

At low battery, however, it depends on whether or not a full 2.0 amps is needed. If a reduction in max output current can be tolerated, maybe it can't be as I don't know the function, then it gets even easier. At 12.0V input, with 85V/2.0A output, the power is 170W, which when divided by an efficiency of 0.90 gives 188.9W. At 12V in, this gives 15.74A average current at the input, but the average inductor current is 123.9 amp, quite a lot. With 8 sections, it is 15.5 amp per section.

Not easy, but feasible.

__________________
Claude

 

sure you can. you can parallel components or use multiphase converters.

I can not count the times I have seen hobbyists ask for directions to do things that are not practical for any other than power or RF engineers and that wonder why they can not get a complete schematic, step by step instructions, and hand holding when their dreams collapse into rubble at their feet.

And then I get scolded for trying to explain life in the real world to them! So I usually just do what I did here: point out the component requirement and let them go find the price on the part, if they *find* it. Quite often what they are asking for requires custom parts or parts from a MFG that laughs at my ordering a single 1K reel, never mind a hobbyist looking for just one or two parts.

In this case it would be the custom. At any rate, the best bet would be a very high frequency multiphase switcher with custom magnetics: transformers of at least a 1:10 turns ratio capable of 15-20A peak on the primary running full bridge.

Dan

 

If someone has to ask about a problem like this it is way beyond their capability.
That's why I suggested connecting 7 batteries in series and using a simple $25.00 battery charger to charge each battery in turn. This is about the maximum capability of the poster.

Whenever you get currents greater than 3 amp, you need to be an engineer to deal with the heating effect.

 

better watch out: I get yelled at pretty regularly for pointing that out

 

So I guess this isn’t the place to ask for detailed design files on a 2kw inverter ,with 120% conversion efficiency that operates off a single 9Vdc alkaline?

 

How did you come up with such calculations ? Last night I used one of Ipk formulas from some book on switching regulators, and the peak current came up to be 45Amps - 49.8Amps.

__________________
"The people who cast the votes don't decide an election, the people who count the votes do."
-Joseph Stalin

 

I do not want to do that because if one battery drains, the whole chain fails! even if the rest of the batteries still have plenty of charge on them.

I experienced this issue before with one of the 6V battery being more drained than the other 6V battery in series.

__________________
"The people who cast the votes don't decide an election, the people who count the votes do."
-Joseph Stalin