air caps
Luka
I have been working on my website and my new design and between the two have not had a lot of spare time to read post but it seems as this one has about run its course, however if I can help I will.
I am sure you mean air gaps in the inductor, if you use the right core you should not have to worry about gaps. The only time a core would need to be gapped is if you think it is in saturation or will approach saturation. You can confirm this with a simple scope of the inductor current or by calculations but if you still have the same design I don't think you have a saturation problem. Need more info on problems your are having and the final design schematic along with the values of the components.
Chas1
Luka
I have been working on my website and my new design and between the two have not had a lot of spare time to read post but it seems as this one has about run its course, however if I can help I will.
I am sure you mean air gaps in the inductor, if you use the right core you should not have to worry about gaps. The only time a core would need to be gapped is if you think it is in saturation or will approach saturation. You can confirm this with a simple scope of the inductor current or by calculations but if you still have the same design I don't think you have a saturation problem. Need more info on problems your are having and the final design schematic along with the values of the components.
Chas1
Gap in Xfrmr
Luka
Good, no gap in inductors. The transformer if designed properly needs no gap. What core set are you using and is the fsw still 50khz. It is always recommended to use the next larger core set than calculated for mechanical assembly problems such as enough window area to properly wind the transformer, if you do this you should not have an air gap. I would not recycle tranformers from PC's because of that . For your application an ETD39 or better yet the ETD44 core set should be ok and much easier to work with. You can get the spec's from the net. I am almost ready to launch my site just need to clean up a few things.
Almost forgot if you have Pressman read Part 2, there you will find a lot of good info that addresses your problem.
chas1
Luka
Good, no gap in inductors. The transformer if designed properly needs no gap. What core set are you using and is the fsw still 50khz. It is always recommended to use the next larger core set than calculated for mechanical assembly problems such as enough window area to properly wind the transformer, if you do this you should not have an air gap. I would not recycle tranformers from PC's because of that . For your application an ETD39 or better yet the ETD44 core set should be ok and much easier to work with. You can get the spec's from the net. I am almost ready to launch my site just need to clean up a few things.
Almost forgot if you have Pressman read Part 2, there you will find a lot of good info that addresses your problem.
chas1
Hi
Yes my Fsw will always stay 50kHz, and I use ETD44 and there is no problem winding that much turns on. Now trafo looks half empty
.
Yea a have been reading part 2 a lot, but there is so much info I mix everything up and have to read that part over and over again
Here is a link to a PDF file, where you can read how to measure inductance and see where core saturates.
Yes my Fsw will always stay 50kHz, and I use ETD44 and there is no problem winding that much turns on. Now trafo looks half empty
.Yea a have been reading part 2 a lot, but there is so much info I mix everything up and have to read that part over and over again
Here is a link to a PDF file, where you can read how to measure inductance and see where core saturates.
Saturation of transformer
Luka
ETD44 core set:
Ae = 1.74CM^2 and I will derate the Bmax to 2800 then to calculate Npri:
382 E8 / 4 x 50 E3 x 2800G x 1.74 = 40 Turns
Where 382 VDC is max bulk for high line input.
Some explanation, this will give you a Bmax of 1400 at regulation or 50% duty cycle and the core material that your are using has a spec of 3300 Bmax at 100 deg C. If you think you core is saturating you can derate the Bmax to 2400 and recaluate your primary and secondary windings. However Brown uses 2800G as a very conservative value which should keep any design at 100 kHz and below out of saturation.
Bottom line is 31 turns is not sufficent.
Bmax calculation:
382 E8 / (4 x 31Turns x 50000 x 1.74) = 3540G (saturation)
382 E8 / (4 x 40Turns x 50000 x 1.74) = 2745G well below saturation at any condition.
chas1
Luka
ETD44 core set:
Ae = 1.74CM^2 and I will derate the Bmax to 2800 then to calculate Npri:
382 E8 / 4 x 50 E3 x 2800G x 1.74 = 40 Turns
Where 382 VDC is max bulk for high line input.
Some explanation, this will give you a Bmax of 1400 at regulation or 50% duty cycle and the core material that your are using has a spec of 3300 Bmax at 100 deg C. If you think you core is saturating you can derate the Bmax to 2400 and recaluate your primary and secondary windings. However Brown uses 2800G as a very conservative value which should keep any design at 100 kHz and below out of saturation.
Bottom line is 31 turns is not sufficent.
Bmax calculation:
382 E8 / (4 x 31Turns x 50000 x 1.74) = 3540G (saturation)
382 E8 / (4 x 40Turns x 50000 x 1.74) = 2745G well below saturation at any condition.
chas1
Hi
I didn't put for max voltage 382, but did put 330. When would I get this 382v?High Line? I don't think that our voltage is fluctuating that much. Never saw this. And I did put more gausses almost to the max for this core set wich is 320mT. This 2800G seems to too far from core saturation, so I would like to put 3000G.
I didn't put for max voltage 382, but did put 330. When would I get this 382v?High Line? I don't think that our voltage is fluctuating that much. Never saw this. And I did put more gausses almost to the max for this core set wich is 320mT. This 2800G seems to too far from core saturation, so I would like to put 3000G.
Saturation
Luka
It is possible for a short duration for all lines to vary 10%, so use 382VDC for bulk max and 265 for bulk min. I use 3200G for my
calculations which gives about 1600G at 50% duty cycle. When calcuating values don't use 160 or 320 VDC for bulk voltages follow Browns examples and you will eliminate most problems.
chas1
Luka
It is possible for a short duration for all lines to vary 10%, so use 382VDC for bulk max and 265 for bulk min. I use 3200G for my
calculations which gives about 1600G at 50% duty cycle. When calcuating values don't use 160 or 320 VDC for bulk voltages follow Browns examples and you will eliminate most problems.
chas1
Hi
The schematic is here (Post #453). the start-up is diffrent and there is no feedback. It puts out 45Vdc with no load, and it puts out 36Vdc with 4 ohm load. This voltage is across both secondarys.
I check what voltage it will give me on this page. I have put in for Vin (min,max,for the calculations)=330v,Vout=35V(not important for the result), 10A current, 50kHz and 3.6 for N1/N2 (36/5+5). And you can see that it will give you something like 44,xxV
The ONLY diffrence that I can see is that I have put on core the complete primary first and then the secondary.
The schematic is here (Post #453). the start-up is diffrent and there is no feedback. It puts out 45Vdc with no load, and it puts out 36Vdc with 4 ohm load. This voltage is across both secondarys.
I check what voltage it will give me on this page. I have put in for Vin (min,max,for the calculations)=330v,Vout=35V(not important for the result), 10A current, 50kHz and 3.6 for N1/N2 (36/5+5). And you can see that it will give you something like 44,xxV
The ONLY diffrence that I can see is that I have put on core the complete primary first and then the secondary.
Calculations
Luka
According to my math you need 40 turns on the primary and 12 turns on the secondary center tapped or 40 - 6 - 0 - 6. I would think that using an ETD49 core set and winding according to the website you used for your calculations should solve all problems or you might change the fsw to 75 kHz.
chas1
Luka
According to my math you need 40 turns on the primary and 12 turns on the secondary center tapped or 40 - 6 - 0 - 6. I would think that using an ETD49 core set and winding according to the website you used for your calculations should solve all problems or you might change the fsw to 75 kHz.
chas1
transformer design
Luka
You should wind the transformer 1/2 Primary, complete secondary then finish the primary. Make sure you continue the primary in the same direction as it was started. Eva posted a good rough calculation for offline supplies, I will include it in this post I am sure she want mind.
(Vin-Vdrop_pri) * ratio * max_d_c = (Vout+Vdrop_sec)
(220-4) * X * .85 = 35 + 2
X = (35 + 2) / (216 * .85) = 0.2
So 0.2 secondary turns are required for each primary turn, a 5:1 ratio if we look at it in the other way.
The 220 VDC is the bulk min from a 220 VAC line input
The 4 VDC is est. loss for switches and other losses on primary side.
The .85 is an transfer efficency.
The 35 Volts is output desired and the 2 volts are the loss on secondary side.
By finding the value of X which in this example is .2
I hope she reads this post as she can explain it better than I can and I don't remember where the post was. Sorry!
You will need 2 times the required output across the secondary before rectification.
chas1
Luka
You should wind the transformer 1/2 Primary, complete secondary then finish the primary. Make sure you continue the primary in the same direction as it was started. Eva posted a good rough calculation for offline supplies, I will include it in this post I am sure she want mind.
(Vin-Vdrop_pri) * ratio * max_d_c = (Vout+Vdrop_sec)
(220-4) * X * .85 = 35 + 2
X = (35 + 2) / (216 * .85) = 0.2
So 0.2 secondary turns are required for each primary turn, a 5:1 ratio if we look at it in the other way.
The 220 VDC is the bulk min from a 220 VAC line input
The 4 VDC is est. loss for switches and other losses on primary side.
The .85 is an transfer efficency.
The 35 Volts is output desired and the 2 volts are the loss on secondary side.
By finding the value of X which in this example is .2
I hope she reads this post as she can explain it better than I can and I don't remember where the post was. Sorry!
You will need 2 times the required output across the secondary before rectification.
chas1