Transformer-driven SEPP output stage.

[dkemppai]

Originally posted by Circlotron
I have an ETD49 style N87 core right in front of me and it has a centre pole diameter of... lets see... 16mm. How many turns would it take to get down to 30Hz at least?

/Circlotron - can wind really good SMPS transformers but can't do the hard sums.

How about 1800 turns, for Ferrite...
And around 750 for permalloy or similar...

-Dan

[Antoinel]

Originally Posted by dkemppai

Yes, it is true that the transformer need not supply a lot of power.

Maybe I'm wrong, but I thought that the transformer must be designed so that it cannot saturate at low frequencies. Assuming a small core you'd need a lot of turns on primary to get in the range of 20Hz. I guess this is what you mean by "appropraite # of turns"? (Something like a million turns of #80 copper )

Also, won't you want even more turns than the minimum needed to keep core in a more linear region of the BH loop?

-Dan

May consider a power toroid transformer for investigatiion. How ideal? It'll get the DIYer quickly in the groove. For example; a 25 VA made by TRIAD VPT24-1040. Two independent primaries [115VAC ea] and two independent secondaries [24VAC @ 1 A ea]. May work around the problems above; as a woofer amp or better.

[Osvaldo de Banfield]

Keep in mind that the MOSFET´s input is a big capacitance, an then, it will resonate in parallel with magnetizing inductance of secondaries, and that, both upper and lower resonances may be of different frequencies because of different capacitances in this circuit. If the resonance is of high Q, then the stage may oscillate. The conventional half bridge auto-oscillating is made of similar way, adding a saturated transformer. And finally, these resonances can cause phase bumps and or several distortion. Extremely, can cause the gate isolation to be destroyed if the signal oscillating goes to more than 30V in each secondary.

[kasey197]

Originally Posted by Antoinel

May consider a power toroid transformer for investigatiion. How ideal? It'll get the DIYer quickly in the groove. For example; a 25 VA made by TRIAD VPT24-1040. Two independent primaries [115VAC ea] and two independent secondaries [24VAC @ 1 A ea]. May work around the problems above; as a woofer amp or better.

I agree - I tried using power toroids, and it looks like anything north of 20-30VA gives you a VERY flat freq response at the low end down to 5Hz and decent THDs too. At the top end, depending on tx and source impednace of the driver, you can get good, average, and mediocre results.

I posted some results here: Ticle Zen Amp

issue regarding driving the input tx remain unsolved as yet ....

[Antoinel]

kasey197: Thank you for the above connection; quite useful and instructional. Are the output FETs in F6 driven IN phase or NOT like the older OTL technology?

[Antoinel]

Originally Posted by Osvaldo de Banfield

Keep in mind that the MOSFET´s input is a big capacitance, an then, it will resonate in parallel with magnetizing inductance of secondaries, and that, both upper and lower resonances may be of different frequencies because of different capacitances in this circuit. If the resonance is of high Q, then the stage may oscillate. The conventional half bridge auto-oscillating is made of similar way, adding a saturated transformer. And finally, these resonances can cause phase bumps and or several distortion. Extremely, can cause the gate isolation to be destroyed if the signal oscillating goes to more than 30V in each secondary.

Thank you Osvaldo for raising this caution flag regarding the use of power torroids in an F6 application.