What are design requirements of SMPS transformers need to be provided for manufacturer!?

Thread Starter

Younes Thabet

Joined Jan 9, 2019
28
Hello all,

I am designing a 12V, 18W Flyback SMPS and i can't figure exactly the characteristics of high-freq transformer (Both Core, Bobbin) to send for transformer manufacturer!!
Can someone already went through these procedures guide me little bit!?

Regards,
 

Papabravo

Joined Feb 24, 2006
14,847
Hello all,

I am designing a 12V, 18W Flyback SMPS and i can't figure exactly the characteristics of high-freq transformer (Both Core, Bobbin) to send for transformer manufacturer!!
Can someone already went through these procedures guide me little bit!?

Regards,
Not really. You haven't really provided sufficient information to even take a swag at defining your requirements. I would suggest that in the absence of any empirical data you should set about the process of acquiring some. It works like the following. Build it with an off the shelf part that has known and repeatable characteristics and make it work. Figure out what you need to do to make it more efficient, Then make it elegant.
 

Thread Starter

Younes Thabet

Joined Jan 9, 2019
28
Not really. You haven't really provided sufficient information to even take a swag at defining your requirements. I would suggest that in the absence of any empirical data you should set about the process of acquiring some. It works like the following. Build it with an off the shelf part that has known and repeatable characteristics and make it work. Figure out what you need to do to make it more efficient, Then make it elegant.
I used PI Expert to generate a Flyback SMPS based on TinySwitch3 PMIC ... which recommended a transformer that doesn't exist in my transformer supplier's catalog .. idk if u have seen it, but the PI Expert provides a lot of parameters (transformer construction, winding parameters) and i just didn't know if i should provide all these parameters or less !?

one other question please !!
what other parameters i should look for when comparing PMICs other than:
(1) Minimum continuous power in a typical non-ventilated enclosed adapter measured at +50 °C ambient.
(2) Output Frequency in Standard Mod.
(3) Maximum Duty Cycle.

Thank you very much for your help.
 

Papabravo

Joined Feb 24, 2006
14,847
It would be a huge mistake to use only one suppliers catalog for doing any design. You didn't say if that supplier will do custom jobs or not. Fact of the matter is that it doesn't matter if you get the one you want right out of the box. It appears that this is your first design and you are relying on automated tools to do your work. This is unlikely to be a successful approach. What you need to do is get some "ice time" (an ice hockey metaphor) with these type of power supplies. Unfortunately there is no easy way to go from your present level of understanding to a successful design without some pain. Use whatever you can get to "make one" so you can try things out. Component selection is only the first step. Layout will be far more critical in the long run.

Check the transformer stocks at distributors like Digi-key and Mouser. Then ask for more catalogs and datasheets. If you are doing this design for a company that wants the design to be proprietary then I can understand your reluctance to share your requirements.
 

Thread Starter

Younes Thabet

Joined Jan 9, 2019
28
It would be a huge mistake to use only one suppliers catalog for doing any design. You didn't say if that supplier will do custom jobs or not. Fact of the matter is that it doesn't matter if you get the one you want right out of the box. It appears that this is your first design and you are relying on automated tools to do your work. This is unlikely to be a successful approach. What you need to do is get some "ice time" (an ice hockey metaphor) with these type of power supplies. Unfortunately there is no easy way to go from your present level of understanding to a successful design without some pain. Use whatever you can get to "make one" so you can try things out. Component selection is only the first step. Layout will be far more critical in the long run.

Check the transformer stocks at distributors like Digi-key and Mouser. Then ask for more catalogs and datasheets. If you are doing this design for a company that wants the design to be proprietary then I can understand your reluctance to share your requirements.
Thanks for your valuable tips, btw you are right in every word you said ..

I have seen many "industrial psu" that has been made using this approach i.e using automated tools as you mentioned and some others use the recomanded circuit and layout in PMIC datasheet..
So why this approach undesirable if industrial products has been using it.!?

Thanks again,
 

Ian0

Joined Aug 7, 2020
1,120
This is what you need to tell your transformer manufacturer:
The type of bobbin
For each winding, starting with the one nearest the core.
The start pin, the finish pin, the number of turns and the wire gauge.
The dielectric strength of the insulation between windings.
The type of ferrite in the core.
They would also like to know the size of gap, but you can give them the inductance of a main winding and let them work it out.
 

Papabravo

Joined Feb 24, 2006
14,847
Thanks for your valuable tips, btw you are right in every word you said ..

I have seen many "industrial psu" that has been made using this approach i.e using automated tools as you mentioned and some others use the recomanded circuit and layout in PMIC datasheet..
So why this approach undesirable if industrial products has been using it.!?

Thanks again,
The design and production of a circuit involves many factors that are missing form datasheet example circuits. It is often the case that the components that you need for a specific application are not readily available. This is especially true with magnetic components. In this case you must find a reliable supplier that can work with you to get what you need. In order to do a design, suitable for manufacturing, you can start with the example circuit and adapt it to your needs. You have to understand the circuit well enough to VERIFY that this is the case. If you have no idea WTF you are doing how will you ever know what done means?
 

Papabravo

Joined Feb 24, 2006
14,847
This is what you need to tell your transformer manufacturer:
The type of bobbin
For each winding, starting with the one nearest the core.
The start pin, the finish pin, the number of turns and the wire gauge.
The dielectric strength of the insulation between windings.
The type of ferrite in the core.
They would also like to know the size of gap, but you can give them the inductance of a main winding and let them work it out.
Assuming that you do all of that, how will you verify that they have produced a part to those specification? How will you know what to do if the first samples do not come up to your expectations? Please tread carefully and don't end up as the fall guy if things don't work out. I have seen this scenario play out multiple times. The only way to go is for you to assume total responsibility for the results. You'll end up with that responsibility regardless.
 

schmitt trigger

Joined Jul 12, 2010
367
In a previous company, we didn’t have sufficient transformer experience and ended using PI expert software.

My take on the software is that it will get you close enough to the requirements.
“Close Enough” means that several times you will have to make trade offs. Or start some technical talks with the transformer’s engineers on optimizing the design.
One example: to meet the safety margins, you may have to reduce the wire diameter, impacting efficiency.
 

Ian0

Joined Aug 7, 2020
1,120
When you get samples back from the manufacturer, put one in the prototype circuit, measure all the resistances and inductances, then flash test the insulation, then dismantle one. If it is varnished, a hot-air gun will soften the varnish so that the cores can be removed, and the accuracy of the gap can be checked.
 

Ian0

Joined Aug 7, 2020
1,120
Transformer winding machines are very smart these days. Whatever you can make by hand, they can make a better one. It's all a matter of communication.
If you state "this winding is one complete layer" a decent transformer firm will tell you if it overlaps onto a second layer or leaves a gap, so you can adjust the number of turns or the wire gauge.
I find that some "offshore" manufacturers are too eager to follow the specification to the letter, that they don't tell you if it doesn't quite fit. Some manufacturers are too keen to ignore your specifications entirely and do it their way. Somewhere in the middle is your perfect transformer.
 
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