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| DIY Transformer for use with Bode Plots. |
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| mawyatt:
This is an extension of the previous thread: https://www.eevblog.com/forum/testgear/injection-transformers-bode-plots-application/ Awhile back when ordering parts from LCSC we picked up a couple Common Mode Filters C2832691 and C2924780 with the idea to attempt to convert into a Bode Injection Transformer. Finally got around to fooling around with the smaller filter, and decided to unwind the windings. After removing the center shield and yanking the wires from the black epoxy we were able to remove the windings. Since we didn't have any twisted pair wire, decided to use the wire from the filter and after straightening we used a hand drill to twist the wires in a light twist. This twisted pair was sewn into the core and the ends swapped and mounted onto a fixture we had created with a 3D print. Know our 3D print skills suck, and we need to get better adhesion, but that's another topic!! Anyway, after printing a lid and base, we mounted some BNC and Banana connectors as shown below. Decided to terminate the transformer with either 100 or 50 ohms, so used 4 2W 100 resistors, and soldered one set of resistors and clamp the other set with the Banana terminal nuts as shown. This allows the remove of a resistor pair for a 100 ohms termination, and 2W were used just in case we provided too much voltage ??? Here's a plot of the Transformer using a 50 ohm source @ 0.2Vpp (SDG2042) and Siglent SDS2104X Plus under Bode mode. Note IL at 100Hz is ~ 0.06dBV and at 1MHz 0.12dBV :) Not bad for a ~1$ reconfigured CM Filter using same wire, four 100 ohm 2W resistors, couple BNC connectors and 4 Banana terminals, total cost <$10 :-+ Edit: Added another plot out to 100MHz. Best, |
| mawyatt:
Was able to unwind the larger CM Filter and rewind with twisted pair made from the unwind wire. This is a larger core ($3), and larger wire so should be able to handle more DC current in applications where that's required. Performance looks good as does the smaller core. 3D Printed another front cover (Grey), and waiting on a deeper bottom, 12 hr print time :o Best, |
| RoGeorge:
I wouldn't have expected it to be so linear. Nice touch 3D-writing on the lid! :-DMM About getting bigger ferrite cores, the biggest yet easy to source (from scraped electronics) would be the magnet from (defective) audio speakers. Many audio speakers have the magnet made from something that looks like ferrite. Some can have a very large magnet, much bigger than the usual OTS ferrite cores. Not to say big ferrite cores tend to be very expensive. Magnets have a Curie point low enough so they should be easy to demagnetize by slowly heating them with a common stove/oven. Never tried, but it should work! :D |
| jonpaul:
Bonjour, BRAVO! nice job, in 1960s we used the ESI bode plotter with electrostatic paper. In 1980s we used the fine open loop stability plot system from Deane Venable. Speaker magnets material will be unsuitable, and strong BH curve bias due to the magnetization. The professional units have much lower LF cutoff than 100 Hz, 1..10 Hz. Bon chance! Jon PS: I might have old core larger sizes, better material, contact me by PM if interested in better cores |
| RoGeorge:
--- Quote from: jonpaul on May 19, 2022, 07:31:27 am ---strong BH curve bias due to the magnetization --- End quote --- Even after de-magnetising the ferrite by heating the magnet above the Curie point in an oven? |
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