John Larkin wrote:

I think multilayer ceramics are pushing 100 uF these days.

Yes, but alas, only with zero volts across them. Capacitance
drops precipitously with DC bias. For a cap with Y5V dielectric,
at half the rated DC voltage, there's only 10% of the initial
capacitance left. Most manufacturers don't tell you.

"Jeroen" wrote in message
...
John Larkin wrote:

I think multilayer ceramics are pushing 100 uF these days.

Yes, but alas, only with zero volts across them. Capacitance
drops precipitously with DC bias. For a cap with Y5V dielectric,
at half the rated DC voltage, there's only 10% of the initial
capacitance left. Most manufacturers don't tell you.


I didn't think it was quite as bad as that. Also very temperature
dependent. These type of ceramics are also pyroelectric as well as being
piezoelectric!

In article , Fred
writes

"Jeroen" wrote in message
...
John Larkin wrote:

I think multilayer ceramics are pushing 100 uF these days.

Yes, but alas, only with zero volts across them. Capacitance
drops precipitously with DC bias. For a cap with Y5V dielectric,
at half the rated DC voltage, there's only 10% of the initial
capacitance left. Most manufacturers don't tell you.

The high k types vary to +-10% and +20-80% from memory if full temp is
allowed for.
High K doped with piezo material, they can be heard to click if hit with
a square wave.

I've seen more than one problem with high-value ceramics causing problems
during operational vibe tests because of microphonics. In our case it
usually seems to be the vibration causing capacitance change rather than
true piezoelectricity, but it happens in any case. The last one that I
remember we replaced the ceramic caps with back-to-back tantalums, in fact.
Worked like a charm.

"ddwyer" wrote in message
...
In article , Fred
writes

"Jeroen" wrote in message
...
John Larkin wrote:

I think multilayer ceramics are pushing 100 uF these days.

Yes, but alas, only with zero volts across them. Capacitance
drops precipitously with DC bias. For a cap with Y5V dielectric,
at half the rated DC voltage, there's only 10% of the initial
capacitance left. Most manufacturers don't tell you.

The high k types vary to +-10% and +20-80% from memory if full temp is
allowed for.
High K doped with piezo material, they can be heard to click if hit with
a square wave.

On Thu, 22 Jan 2004 08:54:58 +0100, Jeroen
wrote:

John Larkin wrote:

I think multilayer ceramics are pushing 100 uF these days.

Yes, but alas, only with zero volts across them. Capacitance
drops precipitously with DC bias. For a cap with Y5V dielectric,
at half the rated DC voltage, there's only 10% of the initial
capacitance left. Most manufacturers don't tell you.


Which opens up the possibility of using them as parametric amplifiers
or modulators. I have a paper somewhere that uses the nonlinearity of
ceramic caps to make a nonlinear transmission line - a shock line -
that sharpens the rising edge speed of kilovolt pulses.

John