This application claims benefit of priority to Japanese Application No. JP2000-282196 filed on Sep. 18, 2000, the entire content of which is incorporated by reference herein.
1. Field of the Invention
The present invention relates to mounting structure for capacitors located, for instance, on a circuit comprising a power semiconductor device.
2. Description of the Related Art
Generally speaking, where a power semiconductor device is used as a switching device, the semiconductor device is provided with a snubber circuit or smoothing circuit including a capacitor.
In the case of a snubber circuit, the collector and emitter of the semiconductor device are provided with a series circuit with capacitor and diode to absorb surge voltage of the semiconductor device during switching.
With a smoothing circuit, it is generally provided on the input side of a three-phase inverter or other main switching circuit to control variations in voltage.
Inductance in a snubber circuit must he kept very low in order to reduce surge voltage. However, in high-capacity apparatus using high levels of current and voltage, increased capacitor size and length of wiring mean that it is difficult to reduce inductance.
Film capacitors (oil type or dry type) are in frequent use, and there is a limit to the extent to which they can be made more compact and inductance reduced.
In the case of smoothing circuits, film capacitors are used for high voltages, while electrolytic capacitors are used where the main circuit voltage is less than about 3 kV. The volume and lengthy wiring of the electrolytic capacitors used for medium and low voltages in particular make it difficult to reduce inductance, and increase the external dimensions of the equipment in which they are used.
Meanwhile, ceramic capacitors offer high permittivity and compact size. Moreover, the fact that they are sintered bodies gives them a freedom of structure, it is easy to achieve low inductance, and the inorganic nature of the material makes them non-combustible and stable. It also means that in order to achieve high capacity it is necessary to have a serial or parallel structure of unit capacities.
Recent advances have led to the realization of 1 kV/1 xcexcF capacitors for use in snubber circuits and 600 V/10-1001 xcexcF devices for use in smoothing circuits. Consequently, there is a demand for mounting structures which allow unit capacitors of this sort to be connected in serial or parallel fashion compactly and with low inductance.
Accordingly, one object of the present invention is to provide a novel mounting structure for capacitors which permits of high capacity in a compact form achieved by connected ceramic unit capacitors in serial or parallel fashion compactly and with low inductance.
With a view to fulfilling this object, the present invention is a mounting structure for capacitors having a plurality of unit capacitors comprising ceramic capacitor devices with pairs of positive and negative terminals, and a three-tier (layer) substrate comprising an insulating layer sandwiched between two electrodes, wherein a plurality of apertures is formed in the first electrode, in which are positioned bosses being continuous with the second electrode, while the plurality of unit capacitors are arranged on the first electrode, one terminal of each unit capacitor being in contact with the first electrode and the other with the second electrode via a boss so as to connect all the unit capacitors electrically in parallel fashion.