Patent Application
20080297275
1. Field of the Invention
The subject matter described herein relates generally to devices and methods for filtering electrical energy and, more particularly, to devices and methods for filtering noise carried by, or induced in, power source lines.
2. Related Art
Electromagnetic noise, such as electromagnetic interference (sometimes referred to herein as “EMI”) is induced in power source lines and may originate from local sources. One local source known to create EMI is a switching power source. A typical device to reduce EMI is a power line filter circuit such as that described in U.S. Pat. No. 5,179,362. This patent illustrates in
However, to date, no suitable device or method of filtering electrical energy supplied by power source lines is available.
In accordance with an embodiment of the present invention, a low current leakage circuit for power source lines that comprise a first power line at one potential and a second power line at another potential with respect to the first power line and that carry energy to power a device is provided. The low leakage circuit may comprise a filter circuit connected in parallel with the device and between the first power line and the second power line. The filter circuit may have a junction in circuit with a local ground and a switch may be connected in series between the junction and the local ground.
In accordance with another embodiment of the present invention, a method of reducing current leakage in a filter circuit for power source lines carrying energy for powering a device is provided. The power source lines may comprise a first power line at one potential and a second power line at another potential with respect to the first power line. The method comprises connecting a filter circuit in parallel with the device and between the first power line and the second power line, the filter circuit having a junction in circuit with a local ground; connecting a switch in series between the junction and the local ground; and closing the switch when the device is energized.
The following detailed description is made with reference to the accompanying drawings, in which:
One embodiment of the present invention concerns a device and a method for eliminating a leakage current in filter circuits such as those used for filtering electrical energy conducted by power source lines while maintaining relatively high filtering capability. It has been found that in current filter circuits, such as that described above and used in the energizing of a device, have a leakage current that increases when filtering capability is increased by using higher valued Y capacitors. One embodiment of the present invention overcomes this disadvantage by switching the Y capacitors to, e.g., green wire, chassis or local ground only when the inverter is operating and itself may be generating high frequency noise. By closing the switch upon energization of the device, a leakage current, measured when the device is de-energized, is eliminated. Accordingly, the capability of the filter circuit may be increased without consequence of a corresponding increase in leakage current.
Referring now to
In the illustrated embodiment of
In accordance with an embodiment of the invention, the low leakage circuit 100 comprises a filter circuit 124 and is shown in a configuration that shunts high frequency noise to ground when switch 132 is closed. The filter circuit 124 may comprise a pair of capacitors 126 and 128 each in circuit with a respective power line 120 and 122 and a junction 130. The capacitors 126 and 128 are illustrated as Y safety rated as they are connected to green wire safety ground by switch 132.
In accordance with this embodiment, the low leakage circuit 100 also comprises a normally open relay switch 132 that is interposed in series between the junction 130 and a local ground 134. The switch 132 may comprise an actuator 136 connected in circuit with a power switch 138 that is, in turn, connected with the device 112. The power switch 138 is configured to energize the actuator 136 and the device 112 whereby when the device is operating, the switch 132 is closed shunting the noise to ground. It will be understood that while the switch 132 and actuator 136 are shown as discreet components, other components might be utilized.
A method of reducing current leakage in a filter circuit for power source lines in accordance with another embodiment of the present invention is shown generally at 200 in
While the present invention has been described in connection with what are presently considered to be the most practical and preferred embodiments, it is to be understood that the present invention is not limited to these herein disclosed embodiments. Rather, the present invention is intended to cover all of the various modifications and equivalent arrangements included within the spirit and scope of the appended claims.
