[time-nuts] Switching regulator replacement for 7805
attila at kinali.ch
Mon Dec 5 07:24:13 EST 2016
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
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.
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