After what seemed, for many of us, to be an interminable winter it's finally June and that means Mother Nature is getting ready to turn up the burners.
But before summer gets too hot to handle and we occupy ourselves with such important tasks as finding the SPF 50 block to prevent sunburn, I thought it a perfect time to take a look at how passives—and specifically capacitors—are meeting the challenge of very high temperature applications. Temperature-critical applications such as down-hole drilling, aerospace (in particular jet engines) and automotive use are generating the need for capacitors with very high operating temperatures, often approaching or exceeding 200 °C.
The need to drill deeper has significantly increased temperatures in today's wells. Customary high-pressure/high temperature (HPHT) wells with pressures up to 69MPa (MegaPascals, 1 MPa = 145.037738 pound-force/square inch [PSI]) and temperatures of up to 177 °C, have now been expanded to what are being called "extreme high-pressure/high-temperature" (xHPHT) wells with pressures up to 138 MPa and temperatures of 200 °C and above. These applications also involve strong vibration and shock. In this application high temperature capacitors are needed for the DC/DC converters used in drilling heads that experience rising ambient temperatures the deeper you drill.
In automotive electronics the most temperature demanding locations are in the engine, transmission and brake systems (some of the wheel-mounted components can reach or exceed 250 °C). The ambient temperature of engine control systems, which are typically placed very close to the engine itself can range from – 55 °C to 200 °C. Power electronics for fuel pumps, motor controls and electric braking require high temperature capacitors that can withstand extensive and stressful thermal cycling over a long operating life.
In the capacitive discharge ignition (CDI) systems used to ignite jet engines the operating temperature can reach 200 °C or more. High temp capacitors also are used in conjunction with jet exhaust sensor systems, landing systems, fuel pumps and other aviation applications.
Several dielectrics including plastic (e.g., polytetrafluoroethylene [PTFE] or PEI polyester), micaMineral silicates H2KA13(Si04 )3 naturally occurring. An excellent insulator resistant to temperatures. Used as a dielectric in capacitors and as insulation in high voltage, high temperature environments., aluminum electrolyticA polarized capacitor exhibiting a very high capacitanceThat property of a system of conductors and dielectrics which permits the storage of electricity when potential difference exists between the conductors. Its value is expressed as the ratio of a quantity of electricity to a potential difference. A capacitance value is always positive./volume ratio that consists of two electrodes immersed in an electrolyte, with a chemical film that acts as a dielectricThe insulating material between the plates of the capacitor. The material is chosen for its ability to permit electrostatic attraction and repulsion to take place across it. The material will have the property that energy required to establish an electric field is recoverable in whole or in part, as electric energy. In other words, a good dielectric material is a poor conductor of electricity while being an effective supporter of electrostatic fields. on one or both electrodes. Electrolytic capacitors are made by winding either plain or etched foils on which an oxide has been formed on the surface of one (either anodeAn electrodeA solid electric conductor through which an electric current enters or leaves in a medium through which current enters any nonmetallic conductor. or cathodeThe negative electrodeA solid electric conductor through which an electric current enters or leaves in a medium of a capacitor.) film. The etching of the foil increases the surface area and a considerable increase in capacitanceThat property of a system of conductors and dielectrics which permits the storage of electricity when potential difference exists between the conductors. Its value is expressed as the ratio of a quantity of electricity to a potential difference. A capacitance value is always positive. can thus be obtained., tantalum and ceramic are used for manufacturing high temperature capacitors. These technologies provide very high stability and good mechanical and electrical characteristics in temperatures ranging from of -55 °C to +200 °C, depending on the dielectricThe insulating material between the plates of the capacitor. The material is chosen for its ability to permit electrostatic attraction and repulsion to take place across it. The material will have the property that energy required to establish an electric field is recoverable in whole or in part, as electric energy. In other words, a good dielectric material is a poor conductor of electricity while being an effective supporter of electrostatic fields. technology, and some do not require voltage de-rating.
In these high temperature apps the two dominant capacitor technologies are ceramic and tantalum capacitorsThe tantalum capacitor distinguishes itself from other capacitors in having high capacitanceThat property of a system of conductors and dielectrics which permits the storage of electricity when potential difference exists between the conductors. Its value is expressed as the ratio of a quantity of electricity to a potential difference. A capacitance value is always positive. per volume and weight. Relative to other electrolytic capacitors, tantalum capacitors have low resistance, low leakage, and can operate in higher temperature environments, but non-electrolytics are even better in these regards.. With operation temperatures exceeding +200 °C and even approaching +250 °C ceramic and tantalum capacitorsThe tantalum capacitor distinguishes itself from other capacitors in having high capacitanceThat property of a system of conductors and dielectrics which permits the storage of electricity when potential difference exists between the conductors. Its value is expressed as the ratio of a quantity of electricity to a potential difference. A capacitance value is always positive. per volume and weight. Relative to other electrolytic capacitors, tantalum capacitors have low resistance, low leakage, and can operate in higher temperature environments, but non-electrolytics are even better in these regards. are available that incorporate advanced designs and construction methods to operate reliably at these elevated temperatures.
