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Author Topic: [Req] Step-Up Converter  (Read 2267 times)
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max
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« on: February 06, 2011, 12:56:01 12:56 »

Hi Friends
I need to build a step up converter with following specs

vin   16v to 24v
vo    32v
iout  25A max (with current limit)

please advise...
tia

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aisvo
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« Reply #1 on: April 03, 2011, 11:35:27 11:35 »

25A is pretty steep I think.

I've used lt3755 multi-mode regulator to step 12V to 32V, but only with 1.2A.
What kind of devices are you trying to drive with that massive current?
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picavr
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« Reply #2 on: April 06, 2011, 10:49:43 10:49 »

you can try a current somator with diode from lm2577   (3A)
www.national.com/ds/LM/LM1577.pdf 
10x3A----->10 x lm2577 and 10 x Diodes (plastic 6A)
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« Reply #3 on: April 10, 2011, 10:20:43 22:20 »

The high output current/power you specify is making the design a bit challenging.

 I would consider dividing the task in two halves: First, constructing an isolated converter with specification 16-24 V input, output controllable between 16 and 8 V, 32 A. Then "adding up" the voltages by connecting the "negative end" of that converter to the positive input rail (which you said is 16-24V), and controlling that converter's output voltage in a way it always adds up to 32V when summed up with the input voltage.

That way the converter's topology can be made to be more suitable for high currents than the usual "flyback-boost" regulators, storing all of the energy in an inductor, and having very high current peak values and thus also extreme ripple currents. Very high peak currents and ripple makes the practical implementation of flyback-family converters extremely challenging on high power levels.

There are many good articles and Application Notes around for switchmode DC/DC converters, for instance Microchip AN1114:
 http://www.microchip.com/stellent/idcplg?IdcService=SS_GET_PAGE&nodeId=1824&appnote=en532115 . Our friend Google will bring you to many more with suitable keywords (such as: high power switchmode converter application note  -- and similar wordings)

Of course, all output power might pass through the converter instead of connecting it in series with  the input, but then it will be nearly twice as large ( about 1024 W versus about 512W ).

The current limit may need some consideration, but if a "fold-back" type operation is OK, you could even use a series (mosfet) transistor as an automatic circuit breaker -style current  limit. Easy to design, and easy to make very robust and reliable.

« Last Edit: April 10, 2011, 10:22:50 22:22 by tedz » Logged
DreamCat
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« Reply #4 on: April 11, 2011, 01:02:16 13:02 »

I think you can use UC3842 and a MOSFET do it.
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« Reply #5 on: April 12, 2011, 07:02:23 19:02 »

I've use National Semiconductor LM3478 for some step up converter project but all far below the amperage as your requirement. If i remember correctly some people talking about such a high amperage on their forum and answered by NS technical support. You may try to search there, and worth to try the webbench first.

-ichan
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« Reply #6 on: April 13, 2011, 11:48:16 23:48 »

Humm... I think this current asks for bigger dimension of implementation like
those small step-up-converters from Analog Devices or so.

Maybe this can be made with a two system design. I remember on another board there
was a similar question. The solutions was a design where a simple small step up converter
did what he was told to do and a workaround with MOSFET, PWM and some OPA did the
high current/voltage part.

I'm not very skilled in power things but I think this is method to think about.

And if you have a solution, maybe you can post it here? It would be very interesting.
I sure will follow this topic Smiley
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« Reply #7 on: April 15, 2011, 01:26:04 13:26 »

Hy,

I accidentally stumbled over the SIMPLE SWITCHER Power Modules from National Semiconductor.
It seems that they can be the solve of your problem.
There are many different devices and I'm sue one would fit. If you have found any distributor,
please tell me. They are perfect for my projects Wink

Here is the link to National Semiconductor:
http://www.national.com/analog/power/simple_switcher_power_modules#overview


Greets DarkClover
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« Reply #8 on: May 04, 2011, 12:31:15 00:31 »

At 800 watts peak output and a low input voltage a Push-Pull topology would work well.  Synchronous rectification should be considered too.

Take a look at these National controllers:

http://www.national.com/pf/LM/LM5030.html
http://www.national.com/pf/LM/LM5033.html
http://www.national.com/pf/LM/LM5037.html
http://www.national.com/pf/LM/LM5041.html

The LM5041 doesn't fit your needs all that well, it's best in step-down and multiple output voltages; but I thought I'd mention it anyway.
NXP and ST has some nice SMPS controllers too!

To use off the shelf power inductors, consider LT's polyphase boost converter:
http://www.linear.com/product/LTC3787
« Last Edit: May 04, 2011, 03:51:32 15:51 by Tanuki » Logged
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