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RE: LF: Stacking toroids

To: <[email protected]>
Subject: RE: LF: Stacking toroids
From: "Clemens Paul" <[email protected]>
Date: Sat, 25 Mar 2017 18:55:11 +0100
In-reply-to: <[email protected]>
References: <[email protected]> <[email protected]>,<[email protected]> <[email protected]> <[email protected]>
Reply-to: [email protected]
Sender: [email protected]
Thread-index: AQHSpNQOhV/0hE8CTkKw3ST47I99vqGkVIyAgAAMqQCAABNZWoAADszggAFQ5DA=
>I have no hands on experience with Class D PAs,only with my 
>own class B MW PA.

Here is a picture of a professional made Class D 500W MW PA
by ID Elektronik.
It uses also DC feeding by a separate choke, not via the output transformer 
center tap.
The blue core on the left side is the DC choke, the output xfm is on the right 
At full output power there is only very little heating.
For extended key down modes like WSPR ID Elektronik recommends laying a small 
on the output xfm.


>-----Original Message-----
>From: [email protected] 
>[mailto:[email protected]] On Behalf Of Clemens Paul
>Sent: Friday, March 24, 2017 10:43 PM
>To: [email protected]
>Subject: RE: LF: Stacking toroids
>Hi Rik,
>I have no hands on experience with Class D PAs,only with my 
>own class B MW PA.
>But also without bias current the FET(s) are drawing lots of 
>DC current when conducting
>which causes flux in the output transformer core(s) which adds 
>up to the flux caused by the RF signal.
>>-----Original Message-----
>>From: [email protected] 
>>[mailto:[email protected]] On Behalf Of Rik Strobbe
>>Sent: Friday, March 24, 2017 9:43 PM
>>To: [email protected]
>>Subject: Re: LF: Stacking toroids
>>Hello Clemens, all,
>>would that make a difference for a class D PA (no bias current)?
>>73, Rik  ON7YD - OR7T
>>Van: ow[email protected] 
>><[email protected]> namens Clemens Paul 
>><[email protected]>
>>Verzonden: vrijdag 24 maart 2017 21:32
>>Aan: [email protected]
>>Onderwerp: RE: LF: Stacking toroids
>>Another way - a bit more complicated - to reduce heating 
>>significantly is to
>>feed DC not via the center tap of the output XFM but via 
>>separate DC chokes.
>>This would eliminate the DC bias of the core(s).
>>>-----Original Message-----
>>>From: [email protected]
>>>[mailto:[email protected]] On Behalf Of 
>Markus Vester
>>>Sent: Friday, March 24, 2017 8:48 PM
>>>To: [email protected]
>>>Subject: Re: LF: Stacking toroids
>>>Yes Chris, this will work. Doubling the core cross section
>>>will halve the flux density, and reduce the per-core
>>>dissipation by at least a factor of four. The improvement may
>>>be more if the flux was so high that losses were dominated by
>>>hysteresis (up to a factor of 8).
>>>73, Markus (DF6NM)
>>>-----Ursprüngliche Mitteilung-----
>>>Von: Chris Wilson <[email protected]>
>>>An: rsgb_lf_group <[email protected]>
>>>Verschickt: Fr, 24. Mrz 2017 20:15
>>>Betreff: LF: Stacking toroids
>>>Hello LF people,
>>>If I have a ferrite toroidal output transformer for a push
>>>pull Class D 136kHz amp, that gets warmish after a WSPR15
>>>session, what would happen if I wound the same number of
>>>primary and secondary turns on two cores stacked together,
>>>all else remaining the same? Would it run cooler, but
>>>retain its transformation ratio, or would other things
>>>occur to make it not that simple? Thanks.
>>>Best regards,
>>>Chris 2E0ILY mailto:[email protected] <mailto:[email protected]?>

Attachment: Class D 500W MW PA.jpg
Description: JPEG image

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