Push-Pull centre tap simple forward (buck) conveter

[prayami]

Hi...

I know this is not the question of this forum but I am sure you guys know it better.

In our project we want Full Bridge Push-Pull transformer. I tried to search online but could not find any proper tutorial for designing the one. Hope you guys will give some hints. I have allready made it and test it. But there are few lacking in that. The output voltage doesnot go above 25V and output having more ripple etc. That is why I require to study more about this type of transformers or converters.

Specification:
8V to 16V DC input to centre tap primary. And other ends will be driven with pulses from microprocessor 18F2420 by the MOSFETs. The frequency of the pulses will be above 24Khz.
We want output of 30V DC and 20A max on the output(using full bridge).

Thanks in advanced.....

[Humberto]

Googling "DC-DC converter" you will find hundreds of info regarding this. I want you
know that one thing is to build a converter in the range of <60 Watt and another matter
is to design (and build) a converter in the range of 600 Watts as you want. Only the
size of the components will keep a "10/1 ratio" but unfortunately the complexity
to control it will increase exponentially.

I dont want to be pessimistic, just want to alert you that this project will not be to
chew a mint tablet.


Humberto

[prayami]

Thanks...for reaply....

I have searched a lot about DC/DC converter but all searched is about converters avaible but not for designing the DC/DC converters. It is really hard to find any converter of our choice so we have to make it. I know it will be hard but we have to.

Please let me know if anybody know, from where can I get the tutorial to design the one. About formulae etc..

Thanks....

[Storic]

I was going to do a project like this for a power supply however I found http://www.onsemi.com/ or even http://www.coilcraft.com/prod_pwr.cfm.

this gives me my DC-DC converter. Down side they require 36 to 70V DC input. At lease I can use the NCP1200 chip for 240V AC input to get my 12V DC out at a resonable current. (smaller that a standard transformer).

ANdrew
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What has been learnt if you make the same mistake?

[Ttelmah]

There are a lot of 'guidance notes', on places like the National semi site, linked to their power supply ICs. Though the 'web' has a lot of data, this is an area where 'real' books win, and you will probably need to either use a library, or buy one or more of the switch mode design handbooks. The smps site in the US, has a lot of pointers to white papers covering such designs. A google search on 'switch mode inverter design', will turn up a huge amount of data. In general, the most complex single part, will be the magnetic component. Companies like Ferroxcube, do large data 'tomes' which help here, but some experience with magnetics, is the biggest aid. There will also be added complexities if you need to meet noise regulations etc.. Beware, that you need to design the drive, to try to ensure that power fed in both directions is balanced. Even a small imbalance, will result in the core gradually moving towards saturation.

Best Wishes

[Rocket]

Here is a link that might help, http://sound.westhost.com/project89.htm
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J.I.L.

[rnielsen]

Transformers don't like sudden 'pulses' input into them. They are coils and coils have a tendency to try and filter out sudden spikes and high frequencies. The best way to input your signal would be to create a simulated sine wave. This is more in line to what the transformer is looking for because it looks like the natural AC sine wave. The higher your frequency is the more the transformer will resist the voltage changes. Creating a simulated sine wave is rather complex but if you're able to do it it will give you the best performance. As it has been said, sizing the components will affect your output. Once the transformer is saturated it won't be able to pump any more current out.

Ronald

[SherpaDoug]

I wouldn't try to drive the transformer phases from a PIC. I would use a dedicated switching supply chip with a logic level enable and let the PIC control the supply by that logic input. 600W is kind of an awkward power level. It is very low for the complexity of push-pull, but kind of high for single ended. I would look into doing it single ended at 100kHz or 300kHz first. Only try push-pull if the single ended configuration really won't work.

This will be a real piece of electrical engineering. Good luck!
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The search for better is endless. Instead simply find very good and get the job done.

[prayami]

Thanks a lot to ....all of you guys...You guys doing greate work...

I think the link that "Rocket" gave, seems useful.....