[Premium-Rx] Tantalums and ceramic beads

[frledda at att.net]

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
______________________________________________________________
Premium-Rx mailing list
Home: http://mailman.qth.net/mailman/listinfo/premium-rx
Help Page: http://mailman.qth.net/mmfaq.htm
Post: mailto:Premium-Rx at mailman.qth.net
Help Contact eMail:  73 at 73.am
Home Page:  http://www.premium-rx.org/