Electricity: electrical systems and devices – Electrolytic systems or devices – Liquid electrolytic capacitor
Reexamination Certificate
2001-12-27
2003-04-29
Dinkins, Anthony (Department: 2837)
Electricity: electrical systems and devices
Electrolytic systems or devices
Liquid electrolytic capacitor
C361S518000
Reexamination Certificate
active
06556426
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention us directed to a low-inductance electrolytic capacitor having a pot accepting a winding and an insulating terminating disk into which a positive lead-through and a negative lead-through for the winding are introduced.
DE-U-298 20 720 discloses an electrolytic capacitor wherein a resin-bonde paper disk reinforced with a metal plate is employed instead of the known terminating disk composed of plastic in order to reduce the inductance.
Given rapid switching events, as known, the self-inductance of electrolytic capacitors effects a delay of their smoothing function for the voltages. Various efforts have already been made to reduce the self-inductance of electrolytic capacitors in order to keep this delay as low as possible (see, for example, DE 297 18 066 U1). Many of these efforts aim at reducing individual inductances that all contribute to the overall inductance of an electrolytic capacitor. Nonetheless, a low-inductance electrolytic capacitor has not yet been successfully created that is distinguished by such a low self-inductance that a delay of the smoothing function for voltages can be avoided given rapid switching events.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to specify a low-inductance electrolytic capacitor that is distinguished by an extremely low self-inductance, so that a delay of its smoothing function for voltages can be practically largely avoided.
This object is inventively achieved by an electrolytic capacitor having a pot accepting a winding and having an insulating disk into which a positive lead-through and a negative lead-through for the winding are introduced, the capacitor having an electrically conductive disk at least in the region between the pot edge and the negative lead-through and electrically separated from the positive lead-through, the conductive disk being electrically conductively connected to a flared flange on an edge of the pot and electrically contacting the negative lead-through at an end facing away from the winding.
The invention thus embarks upon a path that departs completely from the previous state of the art. Instead of having recourse to measures that aim at a reduction of the individual inductances, as has been hitherto standard, an additional current path for high-frequency currents is constructed given the new, low-induction electrolytic capacitor that is laid for the minus contact between the winding of the electrolytic capacitor via the pot floor to the negative lead-through. To this end, the electrically conductive disk is provided at least in the region between the pot edge, which, of course, is connected via the pot casing to the pot floor, and the negative lead-through, whereby this electrically conductive disk, of course, is arranged electrically separated from the positive lead-through. For example, a current path between the pot of the electrolytic capacitor and the negative lead-through is constructed without further ado with a standard screw-type terminal in an electrolytic capacitor.
The electrically conductive disk is preferably composed of metal and, for example, is secured and electrically contacted to the upper flared flange of the pot and the negative lead-through. A hole for the positive lead-through is provided in the disk, and additional holes that allow the electrolytic capacitor or, respectively, its terminating disk to be viewed can be potentially provided.
The disk applied in the new low-inductance electrolytic capacitor serves the sole purpose of opening up the additional current path for high-frequency currents for the negative contact between winding via the pot floor to the negative lead-through. The disk assumes no further functions such as, in particular, mechanical fastening tasks, etc. For this reason, the disk can be implemented in a simple way and, for example, can be composed of a metal lattice, a wire net or even of correspondingly conducted individual wires. The expression “disk” is thus to be understood very broadly and is intended to cover any “disk-shaped” arrangement that is in the position of producing the desired electrical connection.
In existing electrolytic capacitors with a solder star, the current is in fact conducted from the winding to the negative contact via the housing, i.e. the pot. In such an electrolytic capacitor, however, there is only this single electrical connection between the negative contact and the winding.
Differing therefrom, the new low-inductance electrolytic capacitor has both the usual, direct connection between upper side of the winding and negative contact or, respectively, negative lead-through as well as the additionally provided, “indirect” connection via the pot floor, pot and disk. Given the inventive low-inductance electrolytic capacitor, the current can thus “divide”, which leads to a corresponding reduction of the self-inductance of the electrolytic capacitor.
A critical advantage of the new low-inductance electrolytic capacitor is to be seen that the disk provided therein, which forms a critical feature of the invention, can also be installed without further ado in existing electrolytic capacitors. In other words, the application of the invention in existing electrolytic capacitors requires no difficult retrofitting for reducing the self-inductance.
The self-inductance can be reduced by about one-third through one-fourth by the planar electrical connection between the housing and the negative lead-through. Measurements undertaken by the inventor have shown that the inductances of electrolytic capacitors without the disk, having values of 17.7 nH, 14.8 nH or, respectively, 10.8 nH, can be reduced to values of 12.7 nH, 12.0 nH or, respectively, 7.65 nH given employment of a disk corresponding to the invention.
These values are obtained given utilization of a smooth or, respectively, planar disk that proceeds parallel to the surface of the terminating disk that is already present. In such an arrangement, the positive lead-through and the negative lead-through project beyond the disk since, in a preferred way as already set forth, the conductive disk is placed onto the flared flange of the pot and secured thereto.
In order to also reduce the current density in the upper region of the negative lead-through which projects beyond the disk, it is possible to design the disk so that the disk is initially contacted in the upper region of the negative lead-through. In other words, the disk contacts the negative lead-through at its end facing away from the winding. The self-inductance of the electrolytic capacitor can be reduced further in this way. However, greater demands are then to be made of the contactings of the electrolytic capacitor since the disk is arced “up” and proceeds practically in the plane of the end of the negative lead-through.
By employing a disk designed in this way, self-inductances in electrolytic capacitors of 17.7 nH or, respectively, 14.8 nH for capacitors without the disk can be reduced to values of 11.3 nH or, respectively, 10.0 nH for capacitors with the disk.
In order to additionally reduce the partial inductance of the positive lead-through, the disk can also be shaped so that the disks drops perpendicularly down to the height of the flared flange next to the positive lead-through, so that the disk has two different levels and the current in the disk can flow to the positive lead-through in a bifilar fashion. Given such a design of the disk, in other words, this proceeds up to the positive lead-through to a distance therefrom on the level of the upper end of the negative lead-through and, in the region of the positive lead-through, then drops onto the level of the flared flange of the pot. This is then what is referred to as a ¾ disk.
It is likewise possible to make exactly half the area of the disk respectively available to the positive lead-through and the negative lead-through and to provide the vertical drop-off of the disk in the region between the negative lead-through and the positive lead-through. Although a inductance as low as that w
Dinkins Anthony
EPCOS Aktiengesellschaft
Schiff & Hardin & Waite
Thomas Eric
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