Analysis and Design of a Flyback, Part 19, Tranformer Design B.

In this video lecture, I review the design procedure in more detail in how to select the core, the material, the number of turns, and how to size the wire to fit all the primary winding in one layer. I also cover skin and proximity effects. Questions and comments can be sent to [e-mail]

[@satd2024]

Very much informative and helpful. Especialy why proximity loss - clearly understood.Thanks.

[@biteshtiwari]

Thanks a lot for taking time out to make such an informative video.It helps to learn about nuances of flyback for a newbie like me.

[@RobertBolanos]

Thank you Bitesh!

[@azdinator]

Excellent video Robert. Thanks for sharing.

[@RobertBolanos]

Thank you Younes

[@harin188]

really helping allot with ur updates

[@anandparalkar]

Great! I did not know about Dowell's equations. Bet commercial tools use these equations. Could you please give us an idea if Dowell's equations can be applied for interleaved winding (two consecutive layers are not from the same winding).

[@supersilve]

I had been following your videos and they are very informative and well explained. I wish you could explain how to minimize losses using Litz wire and where to put primary and secondary turns, Ex half pri, half sec. half pri etc. Which is the best option regarding coupling effects and losses.

[@RobertBolanos]

Yes, I will try to do that.

[@azdinator]

Very good idea.

[@ttkoh123]

The formula don't seem to be the same as Part 18. Can you please clarify it. Thanks for another great video.

[@titeman9374]

You have two different formula for Ipri_rms which one is correct looking at part 18 and 19

[@babotvoj]

Do these calculations need to be adjusted for a pull-push topology or we can use the same calculations and use 2 primary windings?

[@RobertBolanos]

The flyback and the push-pull operate differently. The flyback stores the energy in the Gap during the time the primary mosfet is turned on. When the mosfet is turned off, the energy stored in the GAP will be release into the secondary. The push-pull does not store energy but only transfers. So the equation are not the same. In the flyback you need to calculate the primary inductance while in a push pull you dont. I hope this makes sense. Robert

[@jimis04]

Hello again Mr Bolanos. About eddy current calculations and the plot you use could you please clarify how we calculate AC resistance if for instance we have 4 layers with different AWG wires.
1st layer main primary 26AWG (half turns)
2nd layer(feedback) 26AWG
,3rd layer secondary 24 AWG
4th layer main primary 26AWG (the other half turns)
I mean i dont want you to make the calculations for me but the procedure. I will calculate 4 different Rac? is the secondary Rac the most crucial or the primary?

[@RobertBolanos]

Hi Liis04, Can you clarify your question. Are you asking how to treat if you have four different winding with different AWG? Not sure of the question.

[@cezarymakulec1749]

Hello Robert. Thanks a lot for putting all this info together. It is very useful indeed. Could you possibly clarify that if the input voltage has a range say 8V to 60V then we have to design Lm for the maximum voltage? I guess yes but... Also, would it be possible to get your excel spreadsheet, please? Thank you very much. It would be very useful to get the procedure for and Air Gap calculations. Thanks again. Cezary

[@RobertBolanos]

Please reply to [e-mail] and I will send my files including my excel spreadsheet

[@anandparalkar]

...personally for me....I think the pace is fine or a wee bit faster would be fine....

[@chintukota757]

while designing how to choose DCM OR CCM?

[@RobertBolanos]

Hi, Chintu, that is a very good question. The depends on your specifications. For most low power less than 100W, a DCM would be better provided that you can handle the peak currents. Keep in mind that the Ipeak current at both the input and output are about 4 times the average current. For example, let say that the output current is 10A at 12V, then the peak current will be 40A. That is a lot of current. However, if you use a CCM then the peak current are reduced depending on the size of the primary inductance of the flyback. However, when you use CCM, you get a right hand plane zero which makes compensating the loop response more difficult. Using DCM is much more simpler to compensate the loop. I hope this make sense. Robert

[@chintukota757]

sir thanks for reply sir.i want to desin 5v/5a ouput .input is 70v dc to 240v dc

[@chintukota757]

duty cycle max iam confusing sir how to choose duty cycle max

[@RobertBolanos]

For a DCM, the theoretical max duty cycle is 50% However, some PWM can not achieve the 50% duty cycle. So you have to look at the PWM and see what the maximum duty cycle is. So if the datasheet say that the max duty is 46% then you want to margin to ensure that you have enough. So I would then 5% and set the dytycyle to 46%-5% = 41%. This way you have enough margin at low line (low voltage) and for tolerance in your parts. Hope this helps. Robert