Electricity: electrical systems and devices – Housing or mounting assemblies with diverse electrical... – For electronic systems and devices
Reexamination Certificate
1998-12-03
2001-03-13
Gaffin, Jeffrey (Department: 2841)
Electricity: electrical systems and devices
Housing or mounting assemblies with diverse electrical...
For electronic systems and devices
C361S752000, C361S799000, C361S800000, C361S816000, C361S818000, C174S051000, C211S041170, C220S004020
Reexamination Certificate
active
06201706
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to an electric power supply device having an internal electromagnetic interference filter.
BACKGROUND OF THE INVENTION
Electromagnetic interference (“EMI”) is an electrical noise current which is usually present in the radio-wave frequency range. This current originates from within a system of electrical devices rather than an outside source such as a radio signal transmitter. Electric power supplies are known to be significant generators of EMI. In connection with electric power supplies, EMI is undesirable because, for example, it can disturb the operation or degrade the performance of other equipment connected to the same source of AC power.
EMI filters frequently incorporate “Y” capacitors (“Y-caps”) as part of their noise suppression circuitry. These circuit elements typically connect near a power supply's input terminals and terminate at an electrical ground. By diverting common-mode current to an electrical ground, undesirable electrical noise current can be suppressed thereby preventing EMI from leaving the power supply via its input terminals and disturbing other equipment electrically connected to the same AC source.
In most known power supplies, EMI filtering incorporates a Y-cap circuit which is permanently connected to the power supply ground within the power supply's housing. This configuration typically allows the capacitor to be located very close to the electrical ground, thereby optimizing EMI suppression. However, the internally mounted Y-caps of conventional power supply devices are very difficult to disconnect from the power supply ground.
For a variety of reasons, some power supply end-users do not want a Y-cap circuit permanently connected to the power supply ground. One drawback in using a Y-cap circuit for EMI suppression is the attendant “leakage current” which flows into the electrical ground. For instance, whenever an alternating current (AC) voltage is applied across a Y-cap circuit, some amount of current will “leak” through it.
Some power supply users prefer a supply with minimal or no leakage current, even at the expense of reduced EMI suppression. For example, electric power supplies are frequently used to drive medical equipment. In this application of a power supply, leakage current must be reduced in order to ensure the safety of medical patients and equipment operators.
It is therefore an object of the present invention to provide a power supply device which has externally detachable “Y” capacitors located within the power supply.
It is a further object of the present invention to provide a power supply with an EMI suppression circuit which has a low-impedance path to an electrical ground.
SUMMARY OF THE INVENTION
The disadvantages of conventional power supplies have been overcome by the power supply device of the present invention. This power supply features an externally detachable, internally mounted Y-cap circuit having a low-impedance path for optimal EMI suppression.
One embodiment of the present invention features a power supply device including a chassis, a printed circuit board attached to the chassis, and a housing sheltering the printed circuit board. This embodiment further includes input terminals for connecting the power supply to its power source, wherein the input terminals are electrically connected to the printed circuit board, and an electromagnetic interference suppression circuit is connected to the input terminals. The electromagnetic interference suppression circuit may include capacitors electrically connected to the printed circuit board and to the input terminals. This circuit may also include a grounding mechanism of electrically conducting material detachably and electrically connected to both an electrical ground and the printed circuit board for electrically grounding the capacitors, wherein the grounding mechanism is accessible from outside the power supply device.
The power supply device of the present invention includes several advantages over conventional power supply devices. For example, the technique employed is advantageous because EMI can be suppressed without the need for an extra power supply terminal. A second advantageous feature of the power supply device of the present invention is the short impedance path between the capacitors in the Y-cap circuit and their corresponding connection to ground.
A further advantage of the power supply of the present invention is the ease with which an operator can safely and quickly detach the Y-cap circuit—which is located within the power supply's housing—without opening the housing. Typically, manufacturers construct power supplies such that it is not convenient for the customer or operator to open the housing. The power supply of the present invention allows the customer or operator to disconnect the internally mounted Y-cap circuit by simply removing a fastener accessible from outside the power supply. Thus, the Y-cap circuit can be detached easily, safely and without damaging the power supply housing, chassis or internal components.
A power supply device featuring externally detachable Y capacitors is particularly advantageous in two situations. In some applications, a power supply is connected to a source that has its own EMI filter. Here, the internal Y-cap circuit would be detached so that the resulting combination would not pay the leakage-current penalty twice. Disconnecting the Y-cap circuit located within the power supply causes a significant reduction in leakage current. In other applications, the device powered by the supply cannot perform optimally, or sometimes even adequately, if leakage current exists. In this second scenario, the power supply operator avoids leakage current by detaching the internal Y-cap circuit for some uses while retaining the ability to reconnect the Y-cap circuit when the power supply is put to alternative uses.
REFERENCES:
patent: 3816911 (1974-06-01), Knappenberger
patent: 4580112 (1986-04-01), Winslow
patent: 4661888 (1987-04-01), Jewell et al.
patent: 4686614 (1987-08-01), Costello
patent: 4717989 (1988-01-01), De Barros et al.
patent: 5107404 (1992-04-01), Tam
patent: 5252782 (1993-10-01), Cantrell et al.
patent: 5329422 (1994-07-01), Sasaki
patent: 5513088 (1996-04-01), Williamson
patent: 5815771 (1998-09-01), Dhande et al.
International Search Report for corresponding International Application No. PCT/US99/28523, dated Mar. 28, 2000.
1998 Lambda catalog pp. 58-61 (LZS/SE Series power supply specifications).
Gustavsen Gary G.
Nicollet James
Dinh Tuan
Gaffin Jeffrey
Lambda Electronics Inc.
Morgan & Finnegan , LLP
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