SMPS Problem, push pull topology w/gs3525 - Page 2 - diyAudio
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Old 20th April 2004, 02:04 AM   #11
alexv is offline alexv  Romania
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I am using this core:
http://www.kaschke.de/pdf/ferrite/ringe/R40.pdf

Al=3400nH
Material: K2006
http://www.kaschke.de/pdf/material/K2006.PDF

On the net I have found diferent equations.I tried some but did not solve a thing. How should I use this data that the producer of the core is offering?????
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Old 21st April 2004, 07:41 PM   #12
alexv is offline alexv  Romania
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Please can somebody post some photos with their primary wave, so I can see the diference. Please.

I tried everything I could think of. Rewind the transformer, I don't know how many times. No change. I don't kow if it is working well or not.

Should I try to change the topology with full brigde pushpull??? I don't need more than 300W or so but If I can't make this one work I try again.

I'm in the dark here.
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Old 21st April 2004, 10:54 PM   #13
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Default SMPS problem

Hi alexv,

Greetings from the USA. As far as the power supply goes, switch-mode power supplies (SMPS) are tricky and take a great amount of time to really master. I've been designing such as part of my job for many years, and I still have to really be careful. I've designed six to seven dozen, and I'm still learning new stuff with each new design. I would recommend that you visit web sites such as Texas Instruments, National Semiconductor, Linear Technology, etc. and download some application notes re SMPS. For your first project, start with a simple non-isolated (transformerless), "buck" dc-dc converter. Then, I would suggest studying the boost, and the buck-boost converters. Once familiar with these circuits, tackle the transformer-based networks, starting with flyback, and simple forward converters. Then proceed to the symmetrical converters (push-pull center-tap, half-bridge, full-bridge). That wil take more time than most are willing to spend, but troubleshooting an SMPS over the web takes very long and produces much frustration. Also, I would use a newer control IC. The 3524/3525 have served us well for more than two decades, but many newer controllers have come out since then, and offer much better performance. Also, I would steer clear of any SMPS that doesn't have an inductor (except flybacks, since the transformer stores energy the way an inductor would). Inductors reduce noise and stress on the parts, and increase efficiency. I'm not trying to discourage you from experimenting, just trying to spare you some frustration. As far as the current SMPS you're working on goes, read the SG3524 or SG3525 data sheet and observe the example circuits shown. These use inductors. They work well. Please be careful. Best regards.
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Old 21st April 2004, 11:50 PM   #14
alexv is offline alexv  Romania
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Hello Claude,

In the past few weeks I've read hundrets of application notes form all the websites you mentioned and more irf, on maginc .. and so on.
I have a dial-up connection (if you remember what that is, stone age for a normal country, but Romania is not )and I've dounloaded almost 1Gb of documents, pictures and schematics.
I want to tell you a leattle story to show you how hard it is to find component in R.
I tried to buy a toroidal form the only store that seals them in the capital city of R. after they order it form Germany they call me in a week and tell me to come and pick up a diferent core made of difrent, not sutable material. Today I descovered that kaschke produces the ferrites in Romania, and from 50 products they manufacture I can only order 3-4 and form thouse 4 I get the wrong one.
hope I did not bore you, not my intention, but I am angry. sorry.

About that inductor. I put inductors on the secondary after the rectifiers and before the caps, but I saw in many circuits another inductor placed on the center tap of primary. Not the filter on power supply but an inductor. Should I try to place one or were you refering to other inductors.

thank you very much for your answer.
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Old 22nd April 2004, 12:02 PM   #15
alexv is offline alexv  Romania
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I made the schmatic EVA presented in other thread for fast turnoff and slow turnon for the mosfets. the spikes ar now very short. bigger with 200W load but not more than 15V.
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Old 22nd April 2004, 01:54 PM   #16
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increasing the value of the resistance of gate of the MOS it increases the turn on time.
Increasing the turn on time of the MOS do not diminish the spike?
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Old 22nd April 2004, 10:24 PM   #17
alexv is offline alexv  Romania
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the spikes are when the mos turns off. so if the turnoff time si very short the spikes are lower.

I tryed to rewind the transformer again and i get the best resaults when the primary wires are layed side by side. for example 6 strands that form one primary are layed one after the other not crossing and then the other primary the same. I will try the same with the secondary because nou the secondarys have 4 strands twisted together.
Is iti normal??? What is improved in this way?

I also experimented with difrent numbers of turns for the primary. There is no change. also I changed the freq and there was still no change. One formula stated that the number of turn are tightly related to freq and B (magnetix flux). So changing the variables in the equation, something must change, at least for the worst if not for better. The core can go up to 300khz but with the same number of turn and very diferent f the flux shuld change and afect the wave form, doesn't it.
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Old 23rd April 2004, 10:40 PM   #18
Grucho is offline Grucho  Croatia
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Hi.

Well about type of winding Im also confused.

In Elektor magazine (electronics magazine), they published car smps, but they used copper foil for primary, and couple of normal wires for secondary (secondary was wounded first - EE core).

On Internet you will find primary first then secondary and revers.
Whats best I dont know.

All of them use winding side by side.

One guy toled me that its best to wind primary parallel (that bot primaries at one time), and secondary serial (that x turns - center tap - x turns).
I havent tried that, I dont have nervs to wind anymore.

Good luck, and report your progess
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Old 6th May 2004, 11:45 AM   #19
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To reduce the spike i've found this: TOSHIBA

Click the image to open in full size.

Click the image to open in full size.

What do you think about this???
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Old 15th July 2004, 03:02 PM   #20
2pist is offline 2pist  United States
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Quote:
Originally posted by alexv
they heat up a leattle but i changed them with 2,2 ohm and the spikes ar smaller.

with 56 ohm - 20V spikes
with 2,2 ohm - 7-8V spikes
same load.

I intend to do the same, to wind the transformer for a higher voltage and lower it with pwm. also with optoisolator.
but first I want to see how to solve this problem.

Where in the circuit are you placing these resistors? (and I suppose the 100n caps) I am having the same issue since going with the SG chip. I was using a 556 timer chip for control but went with the SG for the slow turn on.
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