[Premium-Rx] Tantalums and ceramic beads

[Francesco Ledda]

I was talking about ferrite beads….

Sent from my iPad

> On May 8, 2022, at 18:42, Francesco Ledda via Premium-Rx <premium-rx at mailman.qth.net> wrote:
> 
> The ferrite bead slows down the rising edge of any current demanded by a
> capacitor.  
> 
> Let say you have a logic device that is switching from low to high.  When
> the device switches to an high state, the device requires energy.  The local
> capacitor provides some of the energy required by the logic device;
> consequently, the current on the power trace rapidly increase to recharge
> the capacitor and power the load.  The current spike in the trace radiates
> RF (EMI). 
> 
> Proper design technique is to add another capacitor of the other side of the
> ferrite bead as a local charge storage. The capacitor on the other side of
> the ferrite bead, is  a "local" energy storage that further reduces the
> instantaneous current demand.  The idea is to reduce the risetime of the
> current demand. Faster the risetime, larger is its frequency content.  
> 
> Fixing EMI problems is very hard, but designing for EMI compliance is much
> easier. I did work on EMI problems and are a real pain to resolve.
> 
> Best, Francesco K5URG 
> 
> 
> 
> 
> 
> -----Original Message-----
> From: premium-rx-bounces at mailman.qth.net
> <premium-rx-bounces at mailman.qth.net> On Behalf Of Al via Premium-Rx
> Sent: Sunday, May 8, 2022 6:00 PM
> To: premium-rx at mailman.qth.net
> Subject: [Premium-Rx] Tantalums and ceramic beads
> 
> Why are the ceramic beads used when installing tantalum caps?
> 
> Sent from my iPad
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