[sdiy] Tempcos of Xicon and LCR polystyrene caps

[Andre Majorel]

For anyone who has been wondering about that :

Mouser has cheap polystyrene caps (Xicon 23P series). The data
sheet does not give a figure for their tempcos, but looking at the
graph, the slope is about -250 PPM/°C at 25°C.

The LCR FSCEX polystyrene caps are five times more expensive. That
may be because they are more precise (1% vs. 5% for the Xicon
parts) but they also claim -50/+110 PPM/°C.

That "+110" bit is interesting. The capacitance vs temperature
curve in the Xicon data sheet is downward over the full range
(-40°C through 85°C).

Assuming the relationship between capacitance and frequency is
linear, 250 PPM/°C amount to 0.4 cent/°C (0.1 Hz/°C at 440 Hz).
Not bad, though the temperature better be stable if you want fine
control of beating between VCOs.

The Panasonic ECHS PPS (*not* PS) caps perform as well as the LCR
FSCEX (i.e. 0.04 Hz/°C at 440 Hz) for slightly lower price.

-- 
André Majorel <amajorel at teaser.fr>
http://www.teaser.fr/~amajorel/