Another Ceramic Cap Anecdote

[Tim Williams]

Anecdote, since the plural of "anecdote" is not "data". It is suggestive
though...

0.47uF 16V X7R 0603, Samsung CL10B474KO8NNNC. Withstands over 120V without
breakdown.

Tested in a LLC resonant converter. Variable range quite large, and
variability doesn't go away when hot. By "hot", we're talking on the order
of 20 VAR.

Startup of the converter is interesting. It drifts severely at first, as
the capacitors heat up. It reaches equilibrium, seemingly somewhere below
Curie temperature. Possibly the core temperature is over, and varying
amounts of chip are depolarizing?

Even when hot, the adjustable range is quite good. Hm, didn't seem like
there was a big tail after adjustment, but there should because of the
change in reactive power? May've been masked by the large time constant I
used for biasing.

Tim

--
Seven Transistor Labs, LLC
Electrical Engineering Consultation and Design
Website: https://www.seventransistorlabs.com/

 

[George Herold]

On Wednesday, August 7, 2019 at 2:01:30 AM UTC-4, Tim Williams wrote:

Anecdote, since the plural of "anecdote" is not "data". It is suggestive
though...

0.47uF 16V X7R 0603, Samsung CL10B474KO8NNNC. Withstands over 120V without
breakdown.

Tested in a LLC resonant converter. Variable range quite large, and
variability doesn't go away when hot. By "hot", we're talking on the order
of 20 VAR.
What's VAR?

Startup of the converter is interesting. It drifts severely at first, as
the capacitors heat up. It reaches equilibrium, seemingly somewhere below
Curie temperature. Possibly the core temperature is over, and varying
amounts of chip are depolarizing?

Curie temperature makes me think of ferro-magnetics.. but I assume you mean
the curie temp of the ceramic. (And what is a ceramic Curie temperature?)

George H.

Even when hot, the adjustable range is quite good. Hm, didn't seem like
there was a big tail after adjustment, but there should because of the
change in reactive power? May've been masked by the large time constant I
used for biasing.

Tim

--
Seven Transistor Labs, LLC
Electrical Engineering Consultation and Design
Website: https://www.seventransistorlabs.com/

 

[Tim Williams]

"George Herold" <gherold@teachspin.com> wrote in message
news:1ef29a14-fed9-4ea9-a679-62c017f3a1b5@googlegroups.com...

of 20 VAR.
What's VAR?

Volt-amps reactive. It's power, but sideways (i.e., imaginary). It has
units of power but it's actually energy -- if you know the frequency it's
being "sloshed" at (give or take some pi, E = VAR / (2*pi*F)).

Analogous to torque having the units of work (i.e., N.m), but being
"sideways", so it's not real work, it's imaginary work. In other words,
rotating force.

Curie temperature makes me think of ferro-magnetics.. but I assume you
mean
the curie temp of the ceramic. (And what is a ceramic Curie temperature?)

Yes, exactly: ferroelectricity is so named because the physics is almost
identical to ferromagnetism. It's just with electric charges rather than
magnetic spins.

So, that's the temperature where the charges are unable to maintain
spontaneous, collective polarization. Also relevant: leading up to that
temperature, the field strength that causes saturation drops exponentially
(hrm, actually, hyperbolically shouldn't it?). Meaning that the C(V) curve
should be shifted left as T --> Tc.

I guess X7Rs being good up to 125C means they're Tc >= 150C or something
like that. Probably about as high as BaTiO3 and relatives go, from what I
understand?

Tim

--
Seven Transistor Labs, LLC
Electrical Engineering Consultation and Design
Website: https://www.seventransistorlabs.com/