[time-nuts] Switching regulator replacement for 7805

Tim Shoppa tshoppa at gmail.com
Mon Dec 5 07:55:09 EST 2016


Attila - I certainly do not differentiate between "ferrite bead" and "single turn toroidal choke".

I think the SMT inductor manufacturers think of them in the same bucket too.

what I think of as a "ferrite core for winding a multi turn inductor on", is invariably listed as a "ferrite bead" in the catalog these days.

Most of my switchers run in the very low MHz and I like to have at least several hundred ohms at that frequency before a bus or wiring run. This often means ten or more turns. 

Tim N3QE

Sent from my iPhone

> On Dec 5, 2016, at 7:24 AM, Attila Kinali <attila at kinali.ch> wrote:
> 
> On Sun, 4 Dec 2016 17:07:53 -0800
> jimlux <jimlux at earthlink.net> wrote:
> 
>>> Wouldn't it be better to use a ferrite bead instead, for this application?
>>> The much lower series capacitance and thus higher self-resonance frequency
>>> should help damping the spurs.
>>> 
>> sure, if you can get enough L.  The other thing is that SMD inductors 
>> can be placed by machine, which isn't necessarily the case with ferrite 
>> beads (depending on how you do them).
> 
> A BLM18 gets you into the order of 300Ω @ 100MHz, which is about
> the equivalent of about 480nH. Using a lower current version gets
> you into the 1kΩ @ 100MHz range (~1.6µH). Shouldn't that be enough
> inductance?
> 
> 
> Combined with some 10µF of capacitance and you already get ~15dB @ 1MHz
> for a simple LC-lowpass. For additional filtering, add something like an
> NFM18PS105 and you  get good filtering up to ~100MHz.
> 
> 
>            Attila Kinali
> -- 
> It is upon moral qualities that a society is ultimately founded. All 
> the prosperity and technological sophistication in the world is of no 
> use without that foundation.
>                 -- Miss Matheson, The Diamond Age, Neil Stephenson
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