Re: DRSSTC Noise source found

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: robert heidlebaugh <rheidlebaugh@xxxxxxxxxxxxxx>

Ed; Large value capacitors have enough internal inductanve to become an open
circuit at high frequencies. That is why standard practice was to shunt
large value capacitors with a disk capacitor and to instal a o.1 u disk
ceramic at  each IC on a printed circuit board as close to the IC as
possible across the ground and power lead. In TC circuits where current
pulses are so high unwanted current pulses can cause problems not found in
low current circuits.
     Robert    H
--


> From: "Tesla list" <tesla@xxxxxxxxxx>
> Date: Fri, 18 Feb 2005 08:00:11 -0700
> To: tesla@xxxxxxxxxx
> Subject: Re: DRSSTC Noise source found
> Resent-From: tesla@xxxxxxxxxx
> Resent-Date: Fri, 18 Feb 2005 08:01:35 -0700 (MST)
>
> Original poster: Ed Phillips <evp@xxxxxxxxxxx>
>
> ">Its Probably the inductance of the caps resonating with the C and not
>> related to the fact the dielectric is polypropylene.
>
> Yep!!  I have heard poly turns into resistive mush at say 10MHz, but
> that
> is typically far past poly cap's resonant frequency.  We have fancy
> spectrum analyzers at work, but they have more buttons than I have brain
> cells 0;o))  Maybe in a dull moment I could try to measure them if I can
> get someone there to help me."
>
> Polypropylene isn't a bad HF dielectric.  Problem is undoubtedly in
> method of construction and lead inductance.  Of course, lots of smaller
> capacitors (of any type) in parallel will have a lot less ESR and higher
> resonant frequencies, leading to better bypassing performance.
>
> Ed
>
>