Nope, sorry, don't see it. I've got lots of CM chokes that look closely like the one shown. The barrier serves the purpose of increasing the dielectric path between the two windings. This would have no purpose if the winding merely reversed. CM chokes must maintain 1500 VAC or more dielectric withstand to meet U/L CSA specs. From a certain angle you can be led to believe the wires reverse and run through the barrier, but the ones I have do not run through the barrier. I believe it is an optical illusion. The wire on the left merely crunches up and runs over the top of the previous wind, then back down into the center of the core. Additionally in one short clip, as the unit (SM17) is switched off, a spark is seen to jump between the two windings at exactly that point where you say the winding reverses. This video has been posted by cheapower 2012, and by myself. A spark could not jump between the two winds if this was just a turnaround. Obviously the dielectric withstand was exceeded due to stored core energy, much like an ignition coil.. Further, I have seen those exact chokes in a surplus store in Phila. in the past, many years ago. I can tell you why the Faston lugs are part of the bracket, and construction details that involve the type of bobbin used. To each his own, believe as you must, you may be right, but maybe not. Each man sees what he wants to see and plots his course accordingly. No need to argue, we just speak our own truth. I posted this a few years back: I have seen this type of common mode choke years ago in at least one of the surplus stores I used to visit. They are pulled from equipment complete with leads and mounting bracket.
I can state with almost certainty that they are common mode chokes (two matched dielectrically isolated windings, 1500 VAC minimun per U/L , CSA for 240 VAC line operation) But in SM's application, I don't believe they were for filtering noise because no other parts of the device are shielded in any way and will radiate beyond belief.
The common mode chokes are potted for two reasons; to fix the core to the plastic insulating assembly which is part of the white separator and "washer" seen between the core and the mounting plate and to secure the "flying" leadwires, which were part of the assembly. These devices were made for mounting rigidly to the side wall of a chassis when space on the pc board is at a premium. There might be a "PEM" insert or stud on the opposite face of the mounting bracket or the mounting screw taps directly into the center of the plastic insulator. What is being interpreted as mounting feet are male terminals for grounding by solder or "faston" type disconnects.
Better questions to ask are: why would someone nead a toroidal transformer that has tight coupling between 1kHz and 100 kHz, excelllent turns matching and high dielectric withstand? Which of these features are incidental, which are of prime importance?
these are just a few possible reasons, I'm sure others can think of more:.
1. Signals between the windings are in phase and must maintain electrical insulation in the required passband.
2. Signals between the windings are inverted and must maintain electrical insulation in the required passband
3. One side of the core is pulsed, producing a mirror image inverted pulse on the other winding. These identical opposite phased pulses drive "some other parts of the device".
4. A "fringe field" is produced by "bucking the windings". Possibly this is rotated in some manner.
5. This is a cheap way of getting a pre-wound transformer for an oscillator that can be driven many ways (colpitts, hartley, armstrong, blocking ,etc)
6. It is easily biased or saturated with a small weak magnet.
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Topic: The Small Toroid Discussion (Read 57746 times)
