I'm working on trying to figure out how to wind transformers myself and picking values etc. I currently have PQ26/25 Bobbins with PC95PQ26/25Z-12 ferrite cores (N95).
I have some smaller E cores somewhere as well but I'm not entirely sure what/where or their specs.
I'm trying to design a practical example of a 60W SMPS flyback power supply / 85-260VAC Input / 12.1VDC Output
Basically: 85-260VAC input 12.1VDC Output
I mostly followed along with https://techweb.rohm.com/knowledge/acdc/acdc_pwm/acdc_pwm01/1311 and came up with these values:
Vin 95V Vout 12.1V Vo 13.05V Vor 95V Duty Max 0.5 Ratio 7.28
Iout 5A Lmax 6A Ispk 24A Ls 4.18uH Lp 221.68uH Ippk 3.16A
The ferrite cores that I have say they have an AL-Value of 6520 ungapped and gapped 630 Which following the calculations I arrived at 6 turns for the primary. and a NI of 18.99
Most examples I've seen have turns from 30-50 on the primary side and then 6-20 on the secondary side. In order to get the Np turns to 30-40 and a similar NI value, that AL-value needs to be closer to 100.
Using a small amount of turns like that makes it impossible to get close to the ratio. I have no idea if this is alright or not. I feel like picking a different core with different material (N47) and an air gap might make the most sense - or machining down the center leg to get the AL-value I'm looking for.
Based on the graph from the spec sheet https://product.tdk.com/system/files/dam/doc/product/ferrite/ferrite/ferrite-core/catalog/ferrite_mz_sw_pq_en.pdf If I machine a center gap (on the center leg) to be about 2mm I should have an AL-value around 100 but I can't figure out how to calculate that. I'm also not sure how to figure out how big the gap is to achieve the 630AL-value (I can't find that particular product code anywhere and the specs)
One thing I did notice is that if I lower the Iout the number of required turns goes up (and so does the inductance for Ls and Lp)
I guess my questions are these:
- Am I even remotely on the right track with my understanding (and/or) calculations?
- Is there other important metrics I should be looking at?
- Any direction or suggestions?
After reading @Verbal Kint 's answer I went ahead and built the first part of the circuit (in my kitchen lab, since I have these things on hand), the AC to DC adapter. I omitted the EMI filter/inductor and used:
- 600V 1μF safety cap
- 400V 120μF cap
- GBU806 Bridge Rectifier
- 60W load (old incandescent light bulb)
This might not have been the best format for a question on here. It's easier when you can narrow it down to a specific item. What I really needed was general design direction. I think I got that and quite a bit more.