Advices needed for modifying smps power supply

[jmx66]

Hi all,
View attachment Schematic1.pdf
I just want to modify this switch mode power supply:

https://uzzors2k.4hv.org/index.php?page=benchsmps1

In short i'd want

Output: 12 to 30-40 V and 20 A continuous not peak. SMPS Frequency: 50 kHz

So many questions to ask:

1 Where to connect power ground? See:

2 With 15 v from an auxiliary power card, must change resistor value of 220 ? See: View attachment Schematic1.pdf

3 What iron core for Gate Drive Transformer:

- FT140-77 https://www.reichelt.de/Amidon-Ferr...446;ARTICLE=7921;GROUPID=3187;artnr=FT+140-77

- FT240-77 https://www.reichelt.de/Amidon-Ferr...446;ARTICLE=7928;GROUPID=3187;artnr=FT+240-77

Higher inductance and core area "" Ae "" , maybe too , and price :sad::sad:


With this litz wire, is it perfect for the job?

4 Full bridge rectifier replaced original half-wave rectifier, so 2 x 30 CDPUO4 ----> 4 x DSP-30-12A View attachment A400_DSEP30-12A_IXY.pdf. Good choice?

5 What core for 33 µH inductor:

- T80- 2 :
- T80- 6 :View attachment AMI.pdf
- T80-10


If you could give me advices would be great.... :wink:


Thanks a lot.

jm

 

[schmitt trigger]

50 Khz is low enough frequency that you may not require Litz wire.

According to a Wikipedia table, at 50 Khz you have a skin depth of around 0.25 mm. Over 98% of the current will flow within a layer 4 times the skin depth from the surface, or 1 mm.

The AWG equivalent for the proposed Litz wire is #16, which has a 1.291 mm diameter.....but since your skin depth is 1mm on each side of the circle and that equals 2 mm, which is larger than 1.291 mm, then very little or nothing is gained by using Litz wire.

 

[jmx66]

Hi schmitt trigger,

Thanks for you reply, but in fact i read docs from a manufacturer.

View attachment Litz Wire Termination guide 4th Edition.pdf

View attachment Round_Litz_Catalog.pdf

Is it a commercial argument, i don't know, as in a multistrand wire, it's a bundle.

Now, is proximity effect greater than skin effect, that's the question?????

jm

 

[schmitt trigger]

Proximity effect...now that is heavy stuff. I would not know which one would have a greater effect.

 

[jmx66]

Hi Schmitt trigger,

I thought you were talking about greater efficiency ....

I used this AN, and a small openoffice calc sheet, to know windings number:

View attachment appnote11.28.10.pdf

Is it also good for smps transformer with foils?

Thanks a lot.

jm

 

[schmitt trigger]

This is an excellent app note.
And yes, a turn will be always a turn, whether its wound with foil, litz or solid wire.

Eventually, as the app notes clearly mentions, "the final choice will depend on the specific requirements of each design".
Since a solid wire's actual copper cross section for a given wire area is larger compared to that of the Litz wire, the DC resistance will be lower. Litz wire wastes much of the area with insulation.

One must balance AC versus DC losses, and the point I was driving across is for your relatively low frequency, the AC losses may not be that high, and efficiency may improve with the lower DC losses of a solid wire.

Now, on the gate drive transformer...I always advice to purchase a catalog component than attempting to do one. Why I say so? Because to achieve both a low-leakage inductance with a high degree of isolation between windings, it would be difficult for a beginner without the proper equipment.
You could use one like these: https://coilcraft.com/pwrbase.cfm

 

[jmx66]

Hi schmitt trigger,

Thanks a lot for your link.Always great to talk with someone in the field.
It's really interesting to read,as purchasing and winding different parts over ebay or other, is more costly than on-shelf component.....

Regards.

jm

 

[jmx66]

Hi all,

Now I think i do some misunderstanding, on some terms......

So:

1° question:

- say 2 gapped N27 with gap= 0,10 x 2

In this case, calculation is:




- '' s '' is for 0,2 mm? and so i must correct Al value of datasheet?

- or '' s '' is for '' new gap '' , and with Al initial value, in right side,I can get it?





View attachment PDF_ECoresGeneralInformation.pdf


2° question: if i add 2 N27 cores :

- ungapped N27 core with Al value of 2400 nH

- gapped N27 core with Al value of 790 nH

What's the resulting value , if it is possible ?


In short: - for an inductor, gap needed, or for a ring choke '' in the material grains ''

- transformer no gap needed?


3° question:

I plan to replace initial power trany - central tapped secondary - with a 1:3 with no CT secondary, than rectifying bridge of course, L and C also for output filtering.

I know from google and google a lot - and stiiiiill to do - that with this, I'm going to get double ripple: choice for ease of building a foil smps transformer only.

What do you think of all above?



Gate drive transformer: - Coilcraft products SD2503L

View attachment CoilCraft-Datasheet.pdf

- Murata products 76602/1C or 1026C by example.




As usual, thanks a lot.

jm

 

[schmitt trigger]

I'm not sure I understand your questions.

What I can tell you is that for a transformer you must have NO gap,
For an inductor which carries DC current, you must have a gap. Or as you mentioned, distributed throughout the magnetic material itself.
I find the latter case the best, as keeping consistent gaps of less than 1mm very difficult. Even small amounts of dirt can make significant changes in the total gap.

 

[jmx66]

Hi schmitt trigger,

Firstly thanks for your reply of course, i must admit that my questions are not really well expressed.... :-(
I'm surrounded by bad magnetic forces ;-)

More seriously, your replies cleared me about gap/ no gap for inductors or transformers.

Now i am on L output filter - value 33µH for 45 kHz 10 30-40 V output and about 20 A -, made a few calculations , and if someone could read them, tell me if i'm wrong or right, would be great.

1°: First step: Turn calculations: Material FT-240-77 from AMI

https://www.reichelt.de/Amidon-Ferr...446;ARTICLE=7928;GROUPID=3187;artnr=FT+240-77



2°: Al value to see if result < 0,3 T to avoid saturation

- for 2000 nH - 2725 x 0,75= 2000nh - tolerance 25%




- for 2725 nH




In short is it right way to build this inductor ?

Datasheet needed:

AMI: View attachment AMI-Iron-Core-Materials.pdf

Toroidal-Inductor: View attachment Lecture 17 The Toroidal Inductor.pdf For formula p17-3

As Al value has tolerance of 25%, checking for real Al is mandatory with '' core on hand ''???


Thanks a lot.

jm

 

[schmitt trigger]

Jm:

Your calculations for the ferrite cores are correct, if you were using it as an inductor without any DC bias.
However........since your inductor will carry a DC bias, it is best if you use iron cores; as they have a distributed air gap.

I'm quite busy today, hopefully tomorrow I'll be able to check your calculations.

 

[jmx66]

Hi schmitt trigger,

Thanks a lot for your help.

I'm going to use my friend google to find differences between inductors, with/without DC bias....

I thought using ring core was better, saving space and cost also, an other wrong idea:-(

jm

- - - Updated - - -

Hi schmitt trigger,

My first ''choice'': E-Core ETD49/25/16, but as i saw many examples with ring cores output filter,i thought it was a mistake...



Then some lines after, i discarded:
- E-Core 16-8-5

- E-Core 20-10-6

- E-Core 25-13-17

Reason: not enough winding space.




Next step: with 30 A for safety margin - maybe too much??? - diameter for wiring.




Datasheet for ETD 49/25/16 joined, and also in .zip format : Inductor design and Design of inductors and high frequency transformers.

View attachment Epcos-ETD-49-15-26.pdf

View attachment Inductors-Design.zip


One more time , really thanks for your help.

jm

 

[schmitt trigger]

Toroidal and E-cores, or PQ cores, or any other core geometry, is not the issue.

The issue is that when you carry DC bias, an air gap is required.

For Ferrite material, you have to create that gap.
For Iron powder material, the gap is distributed in the material, as the resin that holds all the iron particles together, serve the purpose of creating a distributed air gap.

There is a company called Fair-Rite, google it. It has a wonderful iron-core design software.

 

[jmx66]

Hi schmitt trigger,

Thanks a lot for your help and reply.

I'm going to google to reach Fair-Rite site.


One last question, as you are a busy man,and it's really kind to help me.
Tell me ''yes'' or ''no'', no need to expand the answer.

1° In following picture, ''s'' is gap needed to get ''Al'' value?
If value is different than : 0,2 ----> 2 mm like in ''standard'' gapped E49 cores - by example - , you have to make it, so ''custom" air gapped core?




2° About IC magnetising current, following page: ?




EPCOS Documentation '' Ferrites and accessories - E Cores General information ":

View attachment PDF_ECores.pdf


Thanks a lot.

jm

Regards.

jm

 

[pplus]

1 Where to connect power ground?

Output labelled "Power ground" is power ground for load R2 is current sensor for I load.

4 Full bridge rectifier replaced original half-wave rectifier, so 2 x 30 CDPUO4 ----> 4 x DSP-30-12A View attachment 90363. Good choice?

I mean it is bad choice.
DSEP 30-12A
VF ② IF = 30 A 1.79-2.74 V
If You use full bridge drop on diodes is 2*2.7=5.4V Loss 5.4V*30A=162W
I suggest schottky diodes and half bridge rectifier



DF30JC10 100V 30A
VF ② IF = 15 A 0.86 V
Loss ~1V*30A=30W

 

[jmx66]

Hi pplus,

Thanks a lot for your reply.

jm