[R-390] Re: Tantulum Capacitors

[2002tii]

Jim wrote:

>Lower leakage and lower ESR. However, they are extremely vulnerable to
>death by surge. I've seen recommendations that you should derate the
>voltage rating to 1/3 in power filtering apps. So 50v for a 12 (or 9)
>volt supply is reasonable. I avoid using them for such applications. A
>good quality electrolytic rated for 105 degrees C tempertatures is
>prefereable IMO.

Ed wrote:

>47 mf @ 50v is 47 mf @ 50v, it does *not* matter what type of cap 
>you use, unless
>you are concerned about physical size. Tantalums are more compact and other
>than that, they are equivalent to regular electrolytics

There is often a good reason designers use the parts they specify, 
and as several people have said already, tantalum capacitors are 
particularly appropriate at the output of some linear regulators 
because they will oscillate if they don't see capacitive reactance 
with low ESR at the output terminal up to tens of MHz.  Aluminum 
electrolytics are not very good in this application, because they 
have higher ESR and actually exhibit inductive reactance above a 
resonant frequency, which is often less than 1 MHz.  As others have 
also said, one can install other, smaller caps in parallel with an 
aluminum electrolytic to improve the high frequency performance.  The 
best for this are monolythic ceramic caps, but they tend to be 
available only with low voltage ratings (50 V or less).  If I wanted 
to replace a 47 uf solid tantalum with a 47 uf aluminum electrolytic 
in this application, I would use a 1 or 2 uf monolythic ceramic and a 
01 uf monolythic ceramic in parallel with the 'lytic.

Best regards,

Don