For an RM ferrite core (RM8 in my case) you can buy two types of bobbin, a single section and two sections, though the latter is less often stocked.
Assuming there are two windings and that the wire will fit on either type, it seems to me that the two section bobbin would have less inherent inter-winding capacitance and better isolation, though you can't easily wrap a copper tape screen between windings.
What other differences/pros/cons are there? When would one type be preferable?
Cheers
-- Clive
Two sections formers have a smaller copper window, so your winding resistance ends up higher.
On the other hand being able to wind two banks does offer you smaller intra-winding-capacitance and a higher self-resonant frequency, which can be important if you need high turns ratios.
I posted a bit about this here back in 2013 and there's discussion about it on my web-site. The example is a different core, and there wasn't a two-section former available, but I did discuss winding in banks anyway.
-- Bill Sloman, Sydney
Exactly, they are useful but hard to get, so whenever you see a two-section version in stock, you should purchase some, unless you're already well stocked.
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Thanks,
- Win
Mouser has some:
-- John Larkin Highland Technology, Inc lunatic fringe electronics
Thanks, I'd need 12 pin ones to be compatible with existing PCB and the only one they have is 5 pins.
Cheers
-- Clive
Picky, picky, picky!
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Thanks,
- Win
What impedance is the transformer?
Split bobbin design probably has too much leakage inductance for use as a SMPS transformer.
Heck, they're barely passable at mains frequency -- the leakage inductance is high enough that the smaller sizes can be rated as "impedance limited". (The high impedance also limits rectifier harmonics, increasing power factor -- both come at the expense of output voltage regulation.) They have a bandwidth of a few kHz tops.
Tim
-- Seven Transistor Labs, LLC Electrical Engineering Consultation and Design Website: https://www.seventransistorlabs.com/
Maybe some of them. The common-mode chokes I've been testing as 1:1 transformers to give me 5V on the secondary, with 10kV insulation (vacuum potted in Sylgard), are working well. Primary inductance 1.5mH (spec says 1mH), and leakage inductance 28uH, or under 2%. These are Taiyo Yuden, type TLF9UA.
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Thanks,
- Win
Oh, and optimum operating frequency, 70kHz.
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Thanks,
- Win
About 1mH, 10kHz to 100kHz, linear.
Cheers
-- Clive
It's a strong function of low source impedance and low load capacitance and current (high-Z).
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Thanks,
- Win
Yeah, those work alright as transformers for a couple of watts; it's hard to get much more, even with a resonant controller. The bandwidth is pretty narrow. (What's so special about 70kHz? Exactly, the transformer is. ;-) )
Tim
-- Seven Transistor Labs, LLC Electrical Engineering Consultation and Design Website: https://www.seventransistorlabs.com/
1mH where? What's the source and load impedances?
Tim
-- Seven Transistor Labs, LLC Electrical Engineering Consultation and Design Website: https://www.seventransistorlabs.com/
You can always remove a barrier, in prototyping. Three sections is not uncommon. Bobbins dedicated to HV inverters may not be available without them.
It's only in large volumes, that you have to worry about exact dimensions, part numbers etc.
. . . . but it's pointless prototyping using shapes that aren't actually available, if you're not prepared to go through hoops to make them available.
RL
Thanks Bill.
-- Clive
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