Murata's Power MONO ceramic capacitor saves board space in Hybrid Electric Scooter application

Four Murata Power MONO capacitors are utilised in the scooter's power conversion system, on a board designed for smoothing the inverter. The capacitors are used to reduce the surge generated by the IGBT (insulated gate bipolar transistor). Until now, film or aluminium electrolytic capacitors were used in this application, however these types suffer from low heat resistance as they both contain organic material. Murata's ceramic capacitors are made entirely from inorganic materials and have a very high intrinsic resistance to high temperatures. The capacitors used in the hybrid electric scooter application can be used in the standard automotive temperature range, up to 125ºC.

These Power MONO ceramic capacitors are by far the largest in Murata's product range, measuring 32 x 40 x 4 mm each. The next largest footprint in Murata's range is 5.7 x 5.0 mm, so with a footprint around 87 times larger, the Power MONO capacitors are considered to be 'huge'. Despite their relatively large size, they are actually helping to reduce the footprint of the scooter's inverter circuit as they are still smaller than their film and aluminium counterparts for a given capacitance. Murata's technology allows its ceramic capacitors a capacitance per unit volume of 2.4µF/cm3, compared to 1.2µF/cm3 for film capacitors and 1.89µF/cm3 for aluminium electrolytic types.

Other desirable characteristics of ceramic capacitors include their high allowable ripple current. Power MONO capacitors have an allowable ripple current of 1.56A/cm3, an order of magnitude higher than film capacitors and two orders of magnitude higher than aluminium electrolytic types. Their capacitance is 52µF, effectively 38µF at 150VDC, with rated voltage of 200VDC.

Murata has designed innovative metal terminals for the Power MONO that prevent cracks forming in the capacitor due to expansion or contraction of the PCB on which the capacitor is mounted. These gull-wing shaped metal terminals absorb any expansion, contraction or deflection of the PCB, whilst allowing the part to be reflow soldered.