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Old 13th January 2007, 07:05 PM   #41
djQUAN is offline djQUAN  Philippines
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and to add another question, suppose I get a different powdered iron core (different size), would it be perfectly fine to just wind it to get the same inductance value? operation not affected? (assuming I get the same or bigger core)

and also, you mention 24T bifilar wound on the core. is this 12T + 12T or 24T +24T?

I would like to do a TL494 version but realized I already had a couple of 3525's sitting here so I guess it wouldn't hurt to use them. besides, eliminating the drivers makes a little bit smaller PCB.
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Old 13th January 2007, 09:19 PM   #42
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Diffrent core diffrent inductance. 24-bifilar is 24T+24T same direction

Steve

How much inductance would I need for 13.8v/ a lot of amps one?
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Old 14th January 2007, 03:20 AM   #43
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DJ-

Go with the SG3525 then. And its outputs are good for +/-400mA, so driving a pairof TO-220 MOSFETS shouldn't be a problem withour a drive buffer. You will have to alter the number of turns if you're using a different size. Also, keep in mind how using a different material will affect things. Amidon Associates has a good datasheet for all their products, and the A(l) values for the different sizes/materials is on there. The basic equation for calculating the number of turns for powdered-iron toroids is as follows:

..............._____________________________
N= 100 x \/[(L(mH) / A(l) value].

Or, in plain English, the number of turns will be the square root of the desired inductance in microhenrys divided by the A(l)value, all multiplied by 100.

Example: for a 22mH indictor on a T-80-26 core, you will need-

................__________
N = 100 x \/22mH / 590 = 19.31T (Round this up to 20T).

Luka-

Not too sure. Is 13.8 your output? I assume this is a boost and not a buck, right? If it is a boost, then, I don't have the design procedure in front of me, but you could use the design procedure from Brown. Also, if it is a boost from 10-12V to a stable 13.8V, you need to give the NOV 04 issue of QST a look at. Another blogger here, dkempaii, wrote an article on just that. He is an Amateur Radio operator, and his project was for transmitting at a full 100W from a single 12v car battery while maintaining a steady 13.8V, even as the battery discharges.

His circuit uses an SG3524 (though a '3525 should work too), to drive a pair of N-CH TO-220's using a conventional (meaning out of a pc supply, and NOT a 50/60Hz one) transformer with center-tap primary & center-tap secondary, rectified, filtered, and the whole nine yards. The trick here, though, was the center-tap of the secondary joined the center-tap of the primary going to +V(in). Consequently, all the secondary side saw was the difference between 13.8V and whatever the incoming voltage was, ~1-3V. Anway, go to the
ARRL's website and download that issue. His pc boards are available from a US distributor of components for many of QST's projects. FAR Circuits is the place.
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Old 14th January 2007, 06:52 AM   #44
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I have an LC meter and I think that will be very handy. I have a few cores here where I already have written the AL value on them after measuring. I will need 33uH then.

although what type of cores are those with green/red paint on them? I have a couple and would be nice to know what they are. with their AL values, looks like they are powdered iron too? I see them used in motherboards I think for the 3.3V supplies.
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Old 14th January 2007, 08:18 AM   #45
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Hi Steve

No it is buck converter 40v->13.8v, but will use MC33025, I was able to get them , Hope/need to have current limiting too, or there won't be any way to stop the best

What freq should I use? And should I use only single phase?
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Old 14th January 2007, 08:53 AM   #46
luka is offline luka  Slovenia
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Hi Steve

Do you have any pictures of your converters operation, like before inductor..?
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Old 14th January 2007, 05:23 PM   #47
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Luka-

What do you mean? Like waveforms? I don't have the capability of transferring my readouts to computer. If I do, I am unaware of it. Anyway, if waveforms are what you're looking for, I will see if I can gin something up.

As for the 40V>13.8V converter, how many amps do you need? Do you want input-output isolation? If so, then use a transformer, either E-I or toroid. If not, then depending on the desired output current, I would choose either a T-130-26, or a T-200-26 powdered-iron ferrite. If you're using the MC33025, then I would make use of the 2-F topology because the '33025 has dual outputs. There are alot of datasheets out there on polyphase buck converters. I would go with a 100kHz clock for 50kHz on each output.

DJ-

Not sure what red-green cores are. Amidon Assicoates has the color code on their datasheets. If I see it later today, I will look it up.
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Old 14th January 2007, 05:33 PM   #48
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N-channel,
while you're at it, could you post what the other color combination means. will appreciate it very much. thanks

because I also have yellow/green, gray/white, all gray, all blue and some others.
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Old 14th January 2007, 06:05 PM   #49
DRZ1 is offline DRZ1  Canada
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Hi guys, i'm new on this forum, but i have some simple switching power supply designed.

Did you considered that development software from Linear Technologies

SwitcherCAD III

http://www.linear.com/company/software.jsp

It's free, and it's VERY accurate and their chips are awesome and very easy to work with.
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Old 14th January 2007, 06:37 PM   #50
luka is offline luka  Slovenia
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Hi Steve

By that i mean how does signal looks like just before inductor.
I have been looking at LM3485 and saw this picture

Click the image to open in full size.

So that is why I asked this in hope to see yours.If you have scope and camera and can take some picture of waveform of your converter.

I would like to go for 75A (+/-25A depends on what I will be able to get, best would be 100A, but that is very high number of amps ) for my converter, non-insulated.

Hi DRZ1

Well you can use it but you have to play with it a bit, I prefer real thing, where anything can go wrong.
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