[ARC5] Transformers in low-voltage to B+ supplies

[Tim]

Hi Les - OK, sounds like you are off on a good adventure with DC-DC power
supply experiments!  The circuit I did for my Type 12 set is as basic as it
gets, nothing novel there - just built from junk I had available.  It also
took some experimenting with that ferrite core as I learned the Black
Art... The running frequency is determined by "magnetics dynamics"...But it
works quite well.  For an HF Command set the guru's all recommend less than
the issued dyno's 220 volts.  Much less can work fine.
Also, regarding Iron cores, eons ago I built a 12VDC - 120VAC "inverter".
It used paralleled 24VCT filament transformers, backwards to produce an
~120V square wave for general purpose usage.  It consisted of a 555 timer
running at 60 cps, driving a 4013 flip flop.  Its outputs drove 2N2222
transistor drivers for MOSFET switching transistors into the primary, CT
fed with + 12 volts.  A real kludge but it was fun and worked well.  With
suitable filament transformers easy to adapt to provide higher output
voltage with a filter for HVDC radio service.

Regarding Google:
"When you control the information you control the people."
Nazi Reichminister of Propaganda Josef Google (er, Goebbels)....

Full disclosure:  this message sent via GMail!

73, Tim
N6CC

On Sat, Oct 29, 2022 at 10:49 AM Leslie Smith <lnsmith99 at gmail.com> wrote:

> Re-posting a message that appears to be 'lost'.
> Original mentioned a sketch - not attached in this case.
>
> Hello Tim (and others):
>
> Thanks for your reply (and particularly your circuit Tim).  Speaking
> generally the circuit you sent is similar to others seen on VMARS (hope I
> got that right).  Except:  Your cct runs at 25kHz, not a iron-core power
> transformer frequency.
>
> So - for the moment - I changed my plan.  (My  purpose in posting on ARC-5
> forum was to seek info.  The system is working.)
> I will move the switching frequency to 25 or 50kHz.  Up from ~100Hz (or
> iron-core power transformer frequency).  Still thinking xtal control for
> the switching frequency.
>
> I intend to use a driver circuit that does not switch polarity of the
> winding instantly.  The circuit here inserts one "off" clock pulse interval
> between the reversal of polarity in the transformer.  With a small RC I can
> soften the sharpness of the signal when each clock pulse switches off.  My
> be un-necessary; time (and a CRO) will tell.
>
> Yesterday:  I went to the local electronics shop and bought x3 pot cores
> to wind the transformer.  Don't have the specs for this particular ferrite
> so I will engage in some experimentation.  I hope to tap the secondary to
> give 60-90-120V to run the BC-454.  I will begin with the same number of
> turns on the* primary *winding shown in your circuit.  The secondary will
> have fewer turns.
>
> Reading earlier postings about optimum B+ voltages I understand I'm
> running well below the recommended 180 .. 250V but from experience I can
> say a  command set from the BC-45x series will work well on a 60V B+ supply.
>
> I attached a sketch to the previous e-mail.  It appears to have
> disappeared into that place where lost things are never seen again. Sketch
> is absent this time.  Let's see if I make it this time ...
>
> Leslie
>
> PS:  Here's an interesting observation.  A moment ago I clicked 'send'.
> Mr. Google reminded me that I wrote "I attached a sketch ... " in the body
> of my text but no attachement was found.  You know why.  That suggests some
> 'automaton' is reading my mail.  It appears nothing is private.  Not even
> an innocent message about hobby electronics.
>
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