To: rsgb_lf_group@blacksheep.org
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From: Tobias DG3LV <DG3LV@gmx.net>
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Date: Thu, 3 Mar 2016 20:01:40 +0100
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Subject: Re: LF: Re: [rsgb_lf_group] Re: MF: DC-Bias [was: EbNaut]
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Hi Clemens !

Please have a look at the website of Manfred, XQ6FOD to understand the 
necessity of this bifilar supply choke at a push-pull PA:

http://ludens.cl/Electron/mosfetamps/amps.html

("Output architectures of conventional class AB push-pull amplifiers")

Jochen DB1NV had held a lecture at Weinheim(2012?) about this, to be 
read in their scriptum.

This "choke" is used as a kind of auto-transformer. When one transistor 
pulls down on one wire, it pushes up an equal amount of current into the 
second wire of the twisted pair (at the same time). By this it is 
doubling the (supply-)voltage of the second transistor. There is a 
significant step-up of power-efficiency (and of output power) at a PA 
designed this way. Efficiencies of well above 50 % have been acheived at 
my recent linear PAs for MF and HF.

73 de dg3lv Tobias

Am 03.03.2016 um 16:44 schrieb Johan Bodin:
> But if the winding is bifilar, usually a twisted pair, then, from the
> core's point of view, it will look almost like a single wire carrying
> current in alternating directions. The core has no way of knowing that
> there are two wires instead of one so it will "see" a pure AC
> excitation. Am I missing something obvious?
>
> 73 de
> Johan SM6LKM
>
> cpaul@gmx.net wrote:
> Hi Markus,
>
>> Clemens, I think that saturation from DC-biasing would only be
>> a problem if the two transformer primaries (LP1 and LP2) were
>> wound on separate cores. On a single toroid, the flux from the
>> two DC currents should cancel.
> It would appear that the flux from the two DC currents will not cancel
> because they don't flow at one time.
> The current into the center tap alternates from travelling through one
> half of the winding then the
> other due to the push pull action of the FETs.
>
> 73
> Clemens
> DL4RAJ
>
>