Electricity: electrical systems and devices – Housing or mounting assemblies with diverse electrical... – For electronic systems and devices
Reexamination Certificate
2000-04-19
2002-02-12
Gandhi, Jayprakash N. (Department: 2841)
Electricity: electrical systems and devices
Housing or mounting assemblies with diverse electrical...
For electronic systems and devices
C361S753000, C361S801000, C361S825000, C312S223100, C206S719000, C174S051000
Reexamination Certificate
active
06347043
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to power supplies and system grounding, and more particularly to power supplies and systems having electrically conductive chassis electrically coupled to an earth ground electrical potential.
2. Description of the Related Art
Most electronic devices require direct current (DC) electrical power. Portable electronic devices typically dissipate relatively small amounts of electrical power during use, and are typically powered by a battery producing DC electrical power. Electronic devices designed for stationary indoor operation typically include a power supply which converts alternating current (AC) power, e.g. from an electrical outlet in a wall, to DC power.
FIG. 1
is a diagram of a typical power supply
10
including a power supply circuit
12
producing a DC voltage between a DC voltage (DCV) terminal
14
and a return terminal
16
. Power supply circuit
12
may be a portion of a linear power supply circuit or a switching power supply circuit. Power supply circuit
12
includes a transformer
18
, a rectifier
20
, and a filter
22
. Transformer
18
produces an AC voltage between opposed first and second ends of a secondary winding
24
. A first end of secondary winding
24
is connected to rectifier
20
, and a second end of secondary winding
24
is connected to return terminal
16
. The second end of secondary winding
24
forms a common ground electrical potential for components of circuit
12
as indicated by symbol
26
. Rectifier
20
rectifies the AC voltage produced by transformer
18
, producing a time-varying DC voltage. Filter
22
receives the time-varying DC voltage produced by rectifier
20
and smoothes the time-varying DC voltage, producing a substantially constant DC voltage at an output terminal. The output terminal of filter
22
is connected to DCV terminal
14
. Where power supply circuit
12
is a switching circuit, an output voltage feedback signal may be conducted from the output terminal of filter
22
to a switching circuit driving a primary winding of transformer
18
as indicated in FIG.
1
.
Power supply circuit
12
is housed within an electrically conductive metal enclosure or chassis
18
. Metal chassis
18
is typically connected to an earth ground electrical potential for safety reasons as indicated by symbol
28
. Metal chassis
18
completely surrounds power supply circuit
12
, thus preventing a user from contacting high voltages present within power supply circuit
12
during operation. Where power supply circuit
12
is a switching circuit, grounded metal chassis
18
also provides a measure of shielding which reduces an amount of electromagnetic radiation produced by the switching circuit during operation and received by other electronic circuits located near power supply
10
.
As is typical, the common ground of power supply circuit
12
is electrically connected to chassis
18
within chassis
18
. In
FIG. 1
, this electrical connection is represented by conductor
30
. Conductor
30
presents a problem in that conductor
30
provides a path for noise voltages to be conducted between the common ground potential of power supply circuit
12
and chassis
18
. For example, a system including power supply
10
also includes other electronic devices having different connections to earth ground. Where the connections to earth ground of two or more of the devices are physically separated from one another, the earth ground potentials may be different, causing “ground loop” currents to flow between the differing potentials. Noise voltages are created when ground loop currents flow through conductor resistances. In
FIG. 1
, any noise voltage present upon chassis
18
is conducted into the common ground potential of power supply circuit
12
by conductor
30
, and into any electronic device receiving DC electrical power from power supply
10
. It is also true that any noise voltage coupled into the common ground potential of power supply circuit
12
(e.g., by an electronic device receiving DC electrical power from power supply
10
) is coupled into chassis
18
by conductor
30
, and into any other device coupled to chassis
18
.
It would thus be desirable to have a power supply which provides electrical isolation between a common ground electrical potential and a metallic chassis. Such isolation would eliminate the noise voltage conduction path present between the common ground potential and the metallic chassis of typical power supplies.
SUMMARY OF THE INVENTION
A system (e.g., a power supply) is presented which allows a user to electrically couple a common ground electrical potential of a circuit (e.g., a common power supply return) to an earth grounded chassis, or to electrically isolate the common ground electrical potential from the earth grounded chassis, without having to open the chassis. The circuit is formed upon a printed circuit board (PCB). The system includes an electrically conductive fastener having a threaded shaft (e.g., a metal bolt), and an electrically conductive bracket (e.g., a metal “L” bracket). The bracket is mounted upon the PCB and electrically coupled to the common ground electrical potential. The bracket is adapted for receiving the threaded shaft of the fastener.
The system includes an electrically insulating bushing having a washer-like first portion and a sleeve-like second portion. A hole in the isolating bushing passes through both the washer-like first portion and the sleeve-like second portion, and is dimensioned to pass the threaded shaft of the fastener. An outer diameter of the washer-like first portion is greater than an outer diameter of the sleeve-like second portion.
The electrically conductive chassis houses the PCB, and is adapted for coupling to an earth ground potential (e.g., for safety reasons). A portion of the chassis is adjacent to the bracket, and has a hole dimensioned to receive the sleeve-like second portion of the insulating bushing. The hole in the portion of the chassis adjacent to the bracket may, for example, have a diameter greater than or equal to the outer diameter of the sleeve-like second portion of the insulating bushing, and less than the outer diameter of the washer-like first portion of the insulating bushing.
In one embodiment, the fastener is a metal bolt. The bracket has a hole dimensioned to pass the threaded shaft of the bolt, and an electrically conductive nut is mechanically and electrically coupled to the bracket. The nut has a hole therethrough and a threaded inner surface for receiving the threaded shaft of the bolt.
The system may include an electrically insulating member disposed between, and in physical contact with, the bracket and the portion of the chassis adjacent to the bracket. The insulating member may have a hole dimensioned to pass the threaded shaft of the bolt.
In order to electrically isolate the common ground electrical potential of the circuit from the earth grounded chassis, the user may insert the sleeve-like second portion of the insulating bushing into the hole in the portion of the chassis adjacent to the bracket. The user may push the threaded shaft of the bolt through the hole in the insulating bushing, the hole in the insulating member, and the hole in the bracket. The user may turn the bolt to engage the threaded shaft of the bolt and the threaded inner surface of the nut, thereby tightening the bolt. When adequately tightened, the bolt holds the insulating bushing in place. The bracket is electrically isolated from the chassis, and the common ground electrical potential is electrically isolated from the earth ground potential.
The system may also include an electrically conductive washer having a hole dimensioned to pass the threaded shaft of the bolt. In order to electrically couple the common ground electrical potential of the circuit to the earth grounded chassis, the user may align the hole in the conductive washer with the hole in the portion of the chassis adjacent to the bracket, and push the threaded shaft of the bolt through the hole in the cond
Beck Alan
Heffernan Peter
Natarajan Thiagarajan
Conley Rose & Tayon PC
Gandhi Jayprakash N.
Kivlin B. Noäl
Sun Microsystems Inc.
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