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I was working on building an induction furnace. What would be the difference in using a metal film capacitor or a ceramic capacitor with similar ratings and values.

From what I know, the ceramic show poor response in terms of high frequency and are highly non-linear in their behavior with frequency. However for this application I plan to run it at around 40KHZ, which isnt a high frequency. Is it fine to use a ceramic capacitor for this application?

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  • \$\begingroup\$ The respective datasheets should show you the performance of the capacitors vs. voltage, frequency and temperature and allow you to judge easily. \$\endgroup\$ – Adam Lawrence Dec 1 '13 at 1:48
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Multilayer ceramic capacitors (MLCCs) are actually quite good at high frequency operation by the nature of their inherently parallel construction (minimizing inductance and ESR). The type of dielectric used can cause significant variation of capacitance over temperature and applied voltage. Surface-mount varieties can crack under thermal and mechanical stress.

Film capacitors are also good for high frequency, have self-healing capabilities and excel at 'pulse' applications. They're also leaded devices, giving them advantages over surface-mount MLCCs in terms of size (read: higher capacitance values) and durability (they don't crack). The dielectrics used also don't tend to lead to large capacitance variations due to thermal and DC bias changes.

To me, given the choice of a film cap over a ceramic, I'd use the film. Space constraints can make ceramics the only practical choice under some conditions, but I'll use a film anywhere I can make it fit.

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  • \$\begingroup\$ Thanks,the constraint is the availability of the metal film, which is why I plan to use the ceramic. Would you consider 40Khz, a high enough frequency to really have a significant performance difference between the 2? \$\endgroup\$ – Sherby Dec 1 '13 at 1:59
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    \$\begingroup\$ 40kHz is low frequency as far as high-Q capacitors are concerned. I doubt frequency will be a significant factor either way you go. \$\endgroup\$ – Adam Lawrence Dec 1 '13 at 2:00

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