[ARC5] [Milsurplus] If You Need a Regulated Low B+ Supply

[J. Forster]

Hi Brooke,

I'm not a real fan of switching ICs or of buck/boost transformerless
topologies.

My interest is mostly in quiet DC/DC converters for the B+ on things like
WS58s, which can nicely operate on D cells and a string of 20 ea 9V
transistor batteries (but that gets to be expensive). At one point, I
designed a replacement unit for that set's "Battle Battery" that used two
Ds for the filament and an inverter running at about 60 Hz off 6 Cs for
the +90, +180, and -22.5, but I never packaged it in a battery shaped box.
The thing used a standard filament transformer and a modified reed relay
in the filament line to turn the HV inverter on/off. By the time you get
to the 100th harmonic of the switching frequency, there isn't a lot of
trash left.

As to topology in high frequency inverters, the important thing to avoid
radiated EMI is keeping the circuits carrying the high currents such that
there is no net projected area, so they don't look like loop antennas in
the far field. Tightly twisting the current carrying leads in a non-PCB PS
does the same thing.



> Hi John:
>
> National Semi has an app note about noise generation in switch mode
> power supplies and the key factor is the topology used.  Some
> arrangements are inherently noisy while others tend to generate a lot
> less noise and can be easily filtered.
>
> For one off circuits I just get the eval board for the IC which is a
> ready made power supply.  But if you want to roll your own supply it
> often turns out that NS has chosen some very special inductors.  Those
> inductors make the IC look very good in terms of specs like efficiency
> and small circuit size (comes with higher switching frequencies).  They
> often are only available in full rolls of SMT parts.  But for me size is
> not a big factor so going to a much larger inductor to get efficiency
> and give up the size is an easy choice.
>
> Have Fun,
>
> Brooke Clarke
> http://www.PRC68.com