Hello,

I'm trying to build an offline converter that has an input 150Vac-250Vac and outputs 24V 0.3A (about 7.2W). This converter will be used as an adapter to feed other digital and analog circuitry components and is not used as a charger.

I have TI's ucc28911 (CV/CC controller) and Power Intergration's LNK626PG which is a CV controller in mind. Both are PSR flyback ICs and can provide the output power required.
Based on your experience and if you were designing such converter how would you decide?

Thank you.

 

I would buy one.

 

That's not the easiest option. Custom transformers need to be built to try each one out. Have you built a flyback converter before?

 

That's not the easiest option. Custom transformers need to be built to try each one out. Have you built a flyback converter before?

Yes, as a matter of fact, I have designed and built a number of supplies for industrial control and monitoring equipment.
And my answer may have been a little vague. Unless you are going to be building a number of custom boards, and you are prepared to spend a lot of time and effort to get it right, I'd buy a complete power supply. Not the just the transformer.
There are quite a few ready built power supply modules that can be PCB or chassis mounted. And it will be hard to beat the price, particularly if you take your development time into account.

For example, these are just a couple from a quick search...
ZWS10B-24 https://au.mouser.com/ProductDetail/TDK-Lambda/ZWS10B-24/?qs=sGAEpiMZZMsPs3th5F8koIEW7SAQWhaR4B1mXDEZAYw=

MFM-20-24 https://au.mouser.com/productdetail/mean-well/mfm-20-24?qs=sGAEpiMZZMuWiaalG5TUgGqTPUILE6OSkR4MhNWQS%2bk/ae5Hh6CinQ==

And many have "C Tick" approval already, if that is needed.

 

This is a personal project that I am building where I want to fit everything on a single PCB. I don't want to buy external power supplies. So I will be working on the power supply too.

Now back to my quesiton, the thing is both claim to be great solutions however TI comes with more protection such as input undervoltage, output overtalge etc t which are not present in LNK626PG. PI claims to have better EMI reduction based on E-Shield™ transformer construction techniques present in their PI Expert design software. In addition PI states to be using On/Off controllers which they claim to be better than regular PWM controllers. And when I was trying PI Expert's suite and TI's Webench suite I found PI Expert's suite to more robust and detailed compared to TI's Webench and this a major reason that attracts me to PI's LNK626PG.

Have you tried designing any flyback based on any of the ICs mentioned?
Do you usually use design suites to come up with a design?
What can you advice?

Thank you

 

No, I did not use these parts. Someone else may be able to help.
Just be very careful when playing around with them and remember, an isolation transformer is a must while building and testing but then does not remove the danger. Just lessens it a little.
I hope you have a fair bit of electronics experience to begin with.
Some of the modules available solder to your PCB as a component.

 

Thank you for your advice. Yes I do, I've worked on couple of projects but this is the first time on trying to design and implement a SMPS.

Do you usually use design suites to come up with a design? If yes what do you use?
And how do you usually assess if you have done a good job in your design? I mean after receiving the PCB and placing the components, what do you look for?
And how do you make sure that the transformer that you ordered for prototyping complies with the specs you sent to the company? Because I'm trying to deal with companies that are not very popular just random companies I find on aliexpress.

Sorry for the lengthy list of questions but I'm sure I can benefit from your expertise .

Thank you

 

Do you usually use design suites to come up with a design? If yes what do you use?

I don't use design suites generally. My designs for power supplies were some time ago. Then I scanned the data sheets and wrote a spreadsheet to help.

And how do you usually assess if you have done a good job in your design? I mean after receiving the PCB and placing the components, what do you look for?

For me, the look of the PCB is important. I try to line things up well, and have no 90 degree bends in the PCB tracks.

And how do you make sure that the transformer that you ordered for prototyping complies with the specs you sent to the company? Because I'm trying to deal with companies that are not very popular just random companies I find on aliexpress.

My transformer designs started with me just getting cores and bobbins. Then winding them myself until I had the one that was the final design.
Then fully documenting it all, core type, bobbin type, wire gauge, winding order, turns and direction, core air gap size, and anything else you can think off. The batch of transformers were made, but locally, (here in Australia) so I could talk to the people if requited.
The supplied transformers worked well.

You will need to make your own transformer for a start I think. Making switch mode power supplies is easier nowadays, but I would still advise you to think of getting a ready made one from a company that has the proven design expertise. The supply has to be safe. And a mains powered switch mode supply is not simple. I doubt you could make one that is properly designed anywhere as cheap as you can buy one.
If you are going Aliexpress anyway, look and see the PCB mount supplies for under $15. That is pretty good.

 

Thank you for your reply.

For me, the look of the PCB is important. I try to line things up well, and have no 90 degree bends in the PCB tracks.

I meant how can you assess that you have a good converter based on your signals? Not just based on the PCB and its looks.

 

There are some guides for switchmode supply layouts on line. Keep the tracks thick, isolate high and low current paths, and make the tracks as short as you can.
Don't forget voltage isolation slots.
You could test for radiated noise and measure the efficiency. Then how well the output is regulated.
And further on the transformers made for you, measure resistance and inductance of each winding. Capacitance between windings and the breakdown voltage and insulation resistance between windings and the core. If you don't have them yet, you need to buy a capacitance and inductance meter. And a HiPot or Megger tester.

 

That's not the easiest option. Custom transformers need to be built to try each one out. Have you built a flyback converter before?

Power Integrations do various flyback chips, and some of their application notes include tables of suggested windings data.