PowerSource

After seeing the role played by electrolytic capacitors in the lifetime of solar inverters and the importance of accurately derating them,, I asked the technical folks at AVX to talk about ceramic capacitors appropriate for another application that requires long lifetimes: LED lighting. Ron Demcko, application engineering manager at AVX, got back to me. Here’s Ron’s reply.

The perceived disparity between the life of LEDs (60,000 hours) and that of capacitors (perceived as 8000 hours) is a hot topic within the Solid State Lighting (SSL) world.

Many different types of capacitor technologies already exist that yield very reliable capacitors. Power film capacitors for example, have internal fuses within the electrodes. It’s not uncommon to talk about 100,000 hour reliability at rated voltage and 70°C. These devices are physically large and may be most applicable to stadium and large light schemes.

Existing ceramic capacitors are capable of meeting the reliability requirements of smaller-size LED-based lighting. For example, a ceramic capacitor operating at half-rated voltage and 50ºC can offer an operational life > 800,000 hours. [You can read the AVX research paper (pdf) here.]

Conservative voltage and temperature derating methods in conjunction with careful capacitor selection are critical to a long life design.

Next-generation ceramic capacitors for use in solid state lighting with temperature ratings of 150ºC in the X8R classification offer over a million hours of life even at temperatures of up to 85ºC. These capacitors are now being used in under-the-hood applications in automotive designs and can withstand harsh environments. Higher-temperature dielectric systems for operation up to 200ºC are expected to come to the market soon offering a wide range of operating temperatures.

With additional features like thermal cycle events becoming important for performance, special terminations have been developed for various dielectric materials. To address these issues, ceramic capacitors utilize a conductive epoxy material system between the first metallization of a MLCC and the Ni barrier layer. This conductive epoxy allows a MLCC to withstand > 1000 thermal cycles without failure and to perform reliably in applications where high vibration/board flexure is present. This termination can be utilized with all dielectric classes and operate up to 150ºC. The Flexi termination is also capable of high-voltage operation.

Next-generation low distortion ceramic capacitors can also help improve the noise emitted in PWM drivers associated with SSL circuitry.

With time expanded data bases and new products will dispel the concerns of ceramic capacitor applicability to solid state lighting circuits.