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Old 27th August 2003, 11:06 PM   #1
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Default SMPS controller advice

I'm thinking of building and constructing a SMPS circuit, and I have a general question. What controller chip to use?

When I did a search on the board, I found that the SG2525 and SG3525 is still very popularm but I have heard that they ain't the best chip for the job.

Any comments?

/Johan Ch
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Old 29th August 2003, 09:46 PM   #2
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I have build a SMPS with the MC33167 from www.onsemi.com
There is a pcb layout in the datasheet as well
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Old 30th August 2003, 12:26 AM   #3
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the LM3524/SG3524 were among the first dedicated switcher chips, so they are showing their age -- they are cheap, less than $0.50 here in the States. I use them for motor control -- it's easy to press into service to control an H-bridge -- like the LMD18200/1

it's not a "quiet" device by any means.

before you dig to far into it, consider reading a book like Pressman's "Switching Power Supply Design" , also take a look at the application notes at Texas Instruments, On-Semi, Linear Tech, Nat Semi websites -- if you spend a little more money on the chip you just might well have a more robust, quieter design.
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Old 30th August 2003, 12:53 AM   #4
subwo1 is offline subwo1  United States
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Here are some considerations. How much power do you need? What is the application? One advantage of SMPS's is small size and higher power density. Most of the controller chips with special features like synchronous rectification are intended for low to medium power uses.
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Old 30th August 2003, 11:09 AM   #5
subwo1 is offline subwo1  United States
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I ended up with a simple way of controlling pulse width which uses a 74C14 and an optocoupler. I find it provides stable performance. The differentor method it uses is resistant to shutting off the pulses to the mosfets completely which keeps the transformer resonating, thus boosting efficiency. The other methods which use a timing ramps need special care to avoid that problem.
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Old 30th August 2003, 01:17 PM   #6
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Default i didn't know there was an SMPS Forum

not many respondents -- some of the Yahoo groups just whither -- I think that their (Yahoo Groups) problem relates to the number of advertisments which you have to plow through to get to messages.
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Old 30th August 2003, 02:55 PM   #7
subwo1 is offline subwo1  United States
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Hi jackinnj,

That observation about my link is perceptive. I need some format that is easy, free, reliable, and solid. A regular Web-site is a problem for me because I am not talented at programming--Basic computer language was hard enough for me. My focus of interest may be narrow and almost fanatical since I do not really have much talent with computers at all. My work on the project is totally non-profit. If something happens to me, I hope my discoveries can live on through the Yahoo Group. I am actually hoping to find some good folks who can find the same passion about the concept and design to become moderators also. I would hope that could allow the Group to live on even if I were no longer able to tend to it.
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Old 31st August 2003, 09:04 PM   #8
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wow,
you really have take my favorite one-gate-oscillator
to new heights
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Old 31st August 2003, 10:15 PM   #9
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Default Re which controller to use

You don't mention what voltages you are planning to extract from your SMPS controller and your input voltage. These parameters are kind of important , as is desired power level and any preference on topology that you might have.

Now, I would recommend that you start looking at the Linear Technology data sheets first, simply because the "black art" is reduced to simple explanations illustrated with formulae and design examples. Also, the very latest data sheets from TI (previously Unitrode) are very easy to evaluate for the same reasons.

Unitrode devices (now TI) are typically considered the reference standard for whatever reason - probably performance (it certainly is not the original data sheets). If you are really keen, you can download a bunch of application notes from www.ti.com (search for SEM600 and keep incrementing/decrementing the number by 100 until you have exhausted all the SEMX00 series). There is A LOT of information there.

Linear Technologies www.linear.com (I have been warned about stability of these devices from a member of this site) end up being my choice in the design process pretty much every time - typically based on the collection of features which just happen to fit well with my needs. They certainly have some highly specified units, some of which just happen to have very appropriate features for me. I guess you can call that well researched product planning which I am grateful for.

You should also head on over to www.infineon.com and look at their application notes / reference designs - they are very helpful, particularly their 200W demo board. They do have some controller IC's which seem OK but they seem hard to get, and to be frank, I was only swayed in their direction based on the incredibly helpful application note on the aforementioned demo board. If your power needs are low, I would strongly recommend that you consider their series of integrated devices (controller + switch) but you may be topologically or power level constrained.

Based on my limited experience, other manufacturers don't seem to have great controller devices (subjectively based on my relatively specialized needs). Your selection will probably end up being based on the features you desire. In my personal case, my desires just about force the selection of manufacturer. If your needs are more general, you should be able to get by with any manufacturer's device.

Petter
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Old 31st August 2003, 10:21 PM   #10
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Quote:
How much power do you need? What is the application?
Well, the first application where I want to try a SMPS PSU is in my current tube preamp. The SMPS should be used to supply the B+ voltage, around 300VDC and very little power.

I have been following the discussion that started a while ago in the Pass forum about a SMPS for power amplifier. Enlightning reading. But, is there acually much to gain over a conventienell design when talking about this much power?

/Johan Ch
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