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I've been watching through hole film caps disappear. I've used a bunch of these in thermal control loops,

http://www.digikey.com/product-detail/en/ECQ-E1106KF/EF1106-ND/56416

Still making 'em, but I'm seeing a lifetime buy in the future.

The current project will again need thermal control.
Can I use a ceramic X7R as an integrator? Maybe one of these (50V 10uF), http://www.digikey.com/product-detail/en/CL32B106KBJNNNE/1276-3387-1-ND/3891473 I'd run it from +/- 15 V supplies. Time constant no more than one minute.

The question really is, what's the leakage current, and what's the voltage, temperature dependence?

I can hear many of you saying "George, get with it! and get a uC."

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MLCC capacitors, especially of large values, are notoriously voltage dependent so NO, I would never use one of them for an integrator if you care about the precision of your time constants. Typical dynamic capacitance of these capacitors can drop to as little as 30% of their nominal value by the time you have reached half of their rated voltage.

Also, be very careful not to crack it by bending your PCB even slightly, as when inserting connectors. Don't place them anywhere near a board edge that will be removed. If removing board edges, please don't use priers (!).

I use MLCC capacitors for decoupling supplies and to get scared. Their failure mode is typically a short-circuit. Presumably, in your application, a short-circuit means run-away heating in your control loop.

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  • \$\begingroup\$ Thanks, I thought the X-series might be OK, 15V is ~1/3 the rated voltage. I think I could live with a ~10-20% change in C. Not all MLCC's are bad, NPO's are certainly sweet. \$\endgroup\$ – George Herold Jul 30 '14 at 2:31
  • \$\begingroup\$ The voltage dependence depends on the dielectric. C0G capacitors are way less voltage dependent than X7R. There is also an effect called dielectric absorption that can cause integration errors on long time scales (see the Wikipedia article). The magnitude of this is again dielectric dependent. X7R is one of the worst, polypropylene film among the best. \$\endgroup\$ – Patrick Pribyl Dec 10 '16 at 10:56

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