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Current sense transformer leakage inductance?

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Flyback

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Hello,
Please advise which of the attached diagrams has less leakage inductance, as seen from the primary of the current sense transformer? Its for a 45khz boost pfc stage
 

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both will have lots of leakage.
Dont need to wrap a half turn , just insert wire at right angles and make the wire fit the hole for least leakage and make depth greater than hole size.(DELETE)

upload_2015-8-30_17-9-36.png
 
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I forgot this was 45kHz.

Use the W material (10k) and shoot for 200~250 mH with 100:1 ratio of AWG30
 
The lowest frequency the CT can see is related to you inductance and resistance on the 100 turns.
The highest frequency the CT can see is related to the self resonances of the 100 turns. So keep the wire to wire capacitance low.
**broken link removed****broken link removed**
 
Thanks, also, in the attached diagram, which Current sense transformer (CST) has the most leakage inductance, as seen from the primary? We need to minimise this leakage inductance, because the CST is situated in the Power FET loop of a boost converter PFC stage driven by UCC28070 driver. (as seen on page 1 of ucc28070 datasheet)

UCC28070 datasheet
https://www.ti.com/lit/ds/symlink/ucc28070.pdf
 

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I think you should spread the 100 turns out over the entire core.
reasons:
1) Every one does it that way.
2) The primary and secondary should take up the same spot in space to reduce LL.

Why not get your transformer from Coil Craft?
 
we have 39 amps peak and its for 45khz f(sw), there is nothing in stock off the shelf for this. The winders wont do us a few prototypes as qty is too small......well, they'll do it, but kind of whenever they get time, 2, 3 months..
 
we have 39 amps peak and its for 45khz f(sw), there is nothing in stock off the shelf for this.
I don't know what the problem is.
So the 45kz is not a problem.
The problem must b e the 39A.
Take the D1870L for example. 100:1 turns. 20mH 2khz to 1mhz. I think the self resonant frequency is about 10mhz. I could go check.
You need to test to see if the 298VuS is OK.
As for the 35A rating. That is at 2000 Gauss. If you change the 2.9 ohm Rt to 1.5 (1/2) you will reduce the VT by 2:1. I know the coil will work fine with the Rt=1.5 ohms. I don't know if it will work at 70A but I know it will work fine at 40A. You will have some errors because the CT was designed to work with 1.4 ohms of wire (internal) and 2.9 ohms external. If you reduce the Rt the 1.4 ohms becomes a bigger part of the equation.

Bottom line reduce Rt. I have used Rt/10 and Rt*10 and they work. In your case I would reduce Rt to 2 to 1.5 ohms. Use the "off the shelf" part. Don't make one.
upload_2015-8-31_16-5-32.png
 
Thanks, but also, it isn't available in-stock, off the shelf anywhere. We have to get a prototype working, on the bench, in a couple weeks.
oh, I see d1870L is for 298V.us, when we only need 4*20V.us....., anyway, it isn't in stock, nor are any others, so we have to make it ourselves.

You will have some errors because the CT was designed to work with 1.4 ohms of wire (internal) and 2.9 ohms external. If you reduce the Rt the 1.4 ohms becomes a bigger part of the equation.
Thanks, but since its a current output, does it matter that theres an internal secondary resistance of 1.4 ohms? It wont affect the current output.

V(sec) = 4v and its for 20us max....so 80us is well under the 298us, so we're ok there, as you also allude.
 
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it isn't in stock
I have 30; HM31-20200 from BI. 1:200, 20mH 1.4 ohms internal 1300VuS 20A
I have four; CS4200V Coil Craft 35A Rt=200
I have two; D1871 35A 200:1
I have two; D1870 24A 100:1
Also have some CS4050, CS4100, and some 60hz transformers. Also some odd CTs.
Might have some in boards that could be removed with work.
Make an offer.
 
Thanks very much for the offer, but you think that wrapping 100 turns of 30swg ECW, evenly round a VJ42106TC torroid, then standing it up on the PCB, and putting the primary conductor through its hole will not work?
If it won’t work, then is it because the coupling will be too poor between primary and secondary?

VJ42106TC torroid datasheet
**broken link removed**
 
It will work.
If the CT is across the isolation gap then it needs UL approval.
Do what you will. I am saying don't make if you can get it made.
I don't think there will be any leakage inductance problems.
I would look for a core with a slightly larger area than what BI or Coil Craft are using.
The center hole, when the 100T are on, needs to allow insulated wire to pass through.
 
Thanks, the VJ42106TC has an inner hole diameter of 12.9 mm, so the primary will easily pass through it, that's what I was a little worried about, maybe the hole should be as small as possible so that the primary conductor is kind of near to all the whole inner ring of the torroid?
There is no isolation requirement as such. The pri and sec are both on the same side of the isolation barrier in this case.
Please advise which of the attached digrams of current sense transformers do you think has the least leakage inductance as seen from the primary?
 

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