What are methods of designing PWM flyback converter?

Thread Starter

Younes Thabet

Joined Jan 9, 2019
58
I have encountered 2 methods of designing a flyback smps. In the setp of designing the transformer:

The fist method goes like:
1. Setting the flyback voltage: VOR
2. Calculation for the inductance of secondary winding: Ls, and the secondary side peak current: Ispk
3. Calculation for the inductance of primary winding: Lp, and the secondary side peak current: Ippk
4. Fixing the core size of transformer
5. Calculation for turns of the primary winding: Np
6. Calculation for turns of the secondary winding: Ns
7. Calculation for turns of the VCC winding: Nd
NB: Found this in a
power supply design using BM1P061FJ document by ROHM Semiconductor.

The second method depicted in link below..

How to Design High Frequency SMPS Ferrite Core Transformer by Haseeb Electronics

I did not understand exactly the first one especially this VOR!! and the second one gets little bit confusing in the transformer core selection !!
Can you please say which method is best? and if there is a better method with clear instructions on how to design a flyback smps!
 

Papabravo

Joined Feb 24, 2006
16,938
The method you use is less important than articulating the requirements that the design must meet. Designing an SMPS of any topology bears nor relation to baking a cake by following a recipe. The method(s) you use, lead to a design, that either meets the requirements or it doesn't. In many ways it is like writing a novel. You write a paragraph, develop a character, and interweave different story arcs. Each element either works or it doesn't. When things don't work, the writer has no choice, but to revise and rewrite. So it is with the SMPS.
 

Thread Starter

Younes Thabet

Joined Jan 9, 2019
58
The method you use is less important than articulating the requirements that the design must meet. Designing an SMPS of any topology bears nor relation to baking a cake by following a recipe. The method(s) you use, lead to a design, that either meets the requirements or it doesn't. In many ways it is like writing a novel. You write a paragraph, develop a character, and interweave different story arcs. Each element either works or it doesn't. When things don't work, the writer has no choice, but to revise and rewrite. So it is with the SMPS.
So it is a matter of trial and error !! meaning i will do my calculations and choose my components and then assemble a prototype then perform tests to see if my design meets the initial requirements.. if not i will keep changing components values (transformer windings, capacitors, resistors) till i meet the requirements..
Gotcha!!
 

ronsimpson

Joined Oct 7, 2019
1,533
It is easy to make an error in the numbers and there are more than one right answer. So I use SPICE or LT Spice to test the circuit. That way I have not purchased parts or made a PCB based on wrong numbers.

Setting the flyback voltage: VOR
Here is one of the may places to have more than one right answer. You might choose to flyback 20V or 30V or 40V and all will work.

I would write down the input voltage (220vac or 24Vdc or ____)
What is the output voltage? 12V What power or current 2A or 25Watts.
Then go looking for a data sheet or application note for that type of supply.
Example: If I need a 120VAC input but found a example for 220VAC then that is easy to change.
Example: If I find a 25W 12V output but I need a 25W 24V that is easy change.
Compare my math to what the application note said.

If you can not find a application note we can help. We need good direction from you.
example from TI This one is too complicated because they did not use a simple diode in the output. That is easy to change.
 

Papabravo

Joined Feb 24, 2006
16,938
So it is a matter of trial and error !! meaning i will do my calculations and choose my components and then assemble a prototype then perform tests to see if my design meets the initial requirements.. if not i will keep changing components values (transformer windings, capacitors, resistors) till i meet the requirements..
Gotcha!!
Yes - that is exactly what I am saying. The solution to your design is not unique and there is no "cookie-cutter" approach that is guaranteed to work in all cases, and be robust enough to function properly, let alone to mass produce and sell. Using simulation can vastly improve your chances of getting to a viable design quickly because it allows you to experiment with alternatives without the expense of acquiring parts and building prototypes.
 
Top