RF transformer winding

Status
Not open for further replies.

neazoi

Advanced Member level 6
Joined
Jan 5, 2008
Messages
4,157
Helped
13
Reputation
26
Reaction score
15
Trophy points
1,318
Location
Greece
www.microwave.gr
Activity points
37,198
How do I wind this 1:1CT transformer when E point is connected to ground and C and D are of opposite phase?
AB turns are equal to CD turns.

I am thinking of using a bifilar winding for CD and wind it. Then connect the end of one of the windings to the beginning of the second one.
For the AB, a second winding independed for the CD will be wound on the other side of the toroidal core.

If the transformer was 1:2CT then I would wind all three windings together trifilar, but now that it is 1:1CT this is the only way I can think of.

Any suggestions?
 

Attachments

  • untitled.jpg
    1.7 KB · Views: 120

I can't see any attachment but the trick to making windings as equal as possible is to start with two wires and wind them side by side. When you have the desired number of turns, join the wire from one winding to the other end on the other winding. That becomes your CT point and the identical windings then work in opposite directions to give opposite phase signals.

Brian.
 
Reactions: neazoi

    neazoi

    Points: 2
    Helpful Answer Positive Rating

Can you see the attachment now?
The problem is, that there is a third winding, AB in the picture, of equal number of turns like the CD
If AB had the same turns as CE and also if AB had the same amount of turns as ED, then a trifilar winding could be made.

But in my case AB has the same number of windings as the whole CD.
So how should I wind AB then? In a totally separate winding at the other side of the toroidal core, apart from CED?
 

Attachments

  • untitled.jpg
    1.7 KB · Views: 112

Quadfilar winding, and join the 4 windings in the obvious way to give the ratio you need?
Or wind the thing with small coax, centre is primary, braid is secondary and tap the braid half way?

The bast way very much depends on how you wish to trade off leakage inductance for inter winding capacitance.

Regards, Dan.
 
Reactions: neazoi

    neazoi

    Points: 2
    Helpful Answer Positive Rating

Oh yes, I haven't thought that, quadrifilar winding.
However things become confusing now. The AB (and it's center tap, since we are talking about quadrifilar), needs to be all in one phase. But the C and D should be out of phase, and the center tap E connected to ground.
So how should I cinstruct this transformer?
I believe it should be constructed the next way, please correct me if I am wrong:

1. Take 4 wires and twist them together Suppose 4 wires are a, b, c, d and their starting points are a1, b1, c1, d1 and their end points a2, b2, c2, d2 respectively.
2. wind all four windings onto the toroidal core
3. Connect a2 to b1. Then a1 will be point "A" in the schematic and b2 will be point "B" in the schematic. The a2, b1 point will not be connected to anywhere else.
4. Connect c1 to d1. This point will be point "E" in the schematic. The other two points c2, d2, will be points "C" and "D" in the schematic.

Am I right?
 

Sorry for misunderstanding, the picture makes it clearer now. That should work fine, wind four identical coils and join them into two series pairs, ignore the center joint on one and use the ends as A & B. The secondary side is wired in exactly the same way but you use the cener tap as E. The CE and ED winding is the same way around, essentially it is a single coil with a tap in the middle. Looking at it from point E, the windings appear to go in opposite directions so C and D will be out of phase.

When you say "twist them together" I'm not sure if you mean to twist then along the whole length of the wires or only at the joints. Twisting them all the way will ensure they are subject to the same magnetic fields but at the expense of increased capacitive coupling between the wires. A compromise might be to twist the two primary wires along their length and seperately twist the two secondary wires together.

Brian.
 


Ok, I upload a picture to see if I have understood that correctly.
If there is any mistake please let me know.

I am a bit confused on the point you say "The secondary side is wired in exactly the same way but you use the cener tap as E. The CE and ED winding is the same way around, essentially it is a single coil with a tap in the middle. Looking at it from point E, the windings appear to go in opposite directions so C and D will be out of phase."
If the secondary windings are wound the same direction onto the core, then will their ends will be out of phase?
Based on the picture I have uploaded their common starting point is E and the other two ends are C and D. This makes effectively two windings wound on the opposite direction onto the core, as seen from the point E?
 

Attachments

  • untitled.jpg
    3.3 KB · Views: 77
Last edited:

Think of the secondary winding as being like a center tapped mains transformer. If it was a 12-0-12 transformer you would get 24V across the ends of the windings so they must be wound in the same direction. In a full wave rectifier using two diodes you would ground the center tap (the '0') and expect one end of the winding to be positive while the other was negative. Despite being physically wound in the same direction, when viewed from the center the winding seem to head off in opposite directions.

Brian.
 
Reactions: neazoi

    neazoi

    Points: 2
    Helpful Answer Positive Rating

So the secondary should be wound like AB primary winding in post #7 (the end of the first winding connected to the start of the second) and the only difference is that the tap E is taken at the point that the two windings are connected together?
 

betwixt said:
Correct!

Brian.
Click to expand...

Ok thanks Brian!
As a conclusion I draw the schematic.
All windings are supposed to wound together at the same time, in the same direction onto the core.
 

Attachments

  • untitled3.jpg
    3.3 KB · Views: 74

Yes, the convention is to draw a dot at the start end of the winding in schematics like that so it is obvious which end is which. Sorry but with the equipment available to me at the moment I can't draw schematics easily, I have to do it by hand and photograph the result with my mobile phone! Easier said than done when you are also using the phone to access Edaboard!

Brian.
 
Reactions: neazoi

    neazoi

    Points: 2
    Helpful Answer Positive Rating
Brian,
Use this tool for simple online schematics drawing, if your phone browser is firefox? and supports javascript **broken link removed**
It is a refinement I have made to the original author's program. Only for simple stuff, I do not know if it works perfectly ok in mobile.
 

Status
Not open for further replies.

Similar threads

Menu
Log in
Register
Cookies are required to use this site. You must accept them to continue using the site. Learn more…