Foldable transformer

Details Foldable transformer Foldable transformer

2001-09-12

2002-10-08

Berhane, Adolf Deneke (Department: 2838)

Electric power conversion systems

Current conversion

Encased in plug housing

Reexamination Certificate

active

06462975

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to AC-DC transformers where the AC power supply is of the type commonly available in homes, offices and the like, and the DC power supply is compatible with electronic devices such as radios, cellular telephones and the like. In particular, the present invention relates to transformers having a plug for plugging into a typical AC power source outlet, wherein the plug is foldable so that the transformer can be compactly stored when not in use.
2. Description of the Prior Art
Power transformers are often used with portable devices, and have been developed to be easily transported along with portable devices. Accordingly, such transformers are typically small, light, convenient to manufacture and safe to use.
A conventional foldable transformer is shown in FIG.
7
. The transformer includes a housing
100
having a storage cavity
102
at a top end thereof, a plug assembly
103
, and wires
108
. The plug assembly
103
is moveable between a folded position for storage and an unfolded position for use. The plug assembly
103
includes a rotatable rod
106
, and a pair of pins
104
for connecting with an external power source. The pins
104
are made of conductive material, and are insert-molded in the rod
106
. The wires
108
are respectively soldered at each end of the pins
104
in the rod
106
. Thus the pins
104
can both rotate together with the rod
106
between the folded position and the unfolded position, and are easily connected with the wires
108
to transmit power from an external source to a power transforming circuit (not shown) within the transformer itself. Because the pins
104
and the wires
108
are soldered together, rotation of the pins
104
generates stress to the solder joints between the wires
108
and the pins
104
. After repeated use, the solder joints are liable to become fatigued. Electrical connection between the wires
108
and the pins
104
may be lost, whereupon power transmission from the pins
104
through the wires
108
to the power transforming circuit is lost. Thus the transformer is prone to be unreliable after repeated use.
Another conventional transformer is shown in FIG.
8
. The transformer includes a housing
200
having a storage cavity
202
at a top portion thereof, and a plug assembly
203
. The plug assembly
203
further comprises a pair of rotary pins
204
, a pair of fixed pins
206
, a rotatable transverse rod
208
, an engaging block
210
, and a spring
212
. Each rotary pin
204
is pivotally connected to a corresponding fixed pin
206
via a pivot located at an end of the rod
208
. The rotary pins
204
are pivotally foldable while maintaining constant electric connection with the fixed pins
206
. The rod
208
also has a groove
209
, and the engaging block
210
has an engaging ridge
211
for engaging in the groove
209
. A blind hole
213
is defined in a side of the engaging block
210
opposite to the engaging ridge
211
, for receiving one end of the spring
212
. The storage cavity
202
further has a pair of pin holes
215
for receiving the fixed pins
206
, and an opening
217
for receiving the other end of the spring
212
to thereby fix the plug assembly
203
to the housing
200
.
In assembly, each fixed pin
206
is inserted into a corresponding pin hole
215
. When the rotary pins
204
and rod
208
are rotated to an unfolded position, the spring
212
exerts force such that the ridge
211
firmly engages in the corresponding groove
209
. The pins
204
are thus securely held in position, allowing the plug to be conveniently inserted into an AC power source outlet.
The above-mentioned foldable transformer does not have wires directly soldered to the rotary pins
204
. Thus the problem of the transformer of
FIG. 7
is resolved. However, the above-mentioned foldable transformer has at least the following drawbacks:
First, it has many components and a complicated structure, making it unduly difficult to manufacture.
Second, the spring
212
is not a reliable component. In particular, the force exerted by various springs
212
is not always constant. Thus the quality of the plug assembly
203
is not always uniform. Secondly, after repeated use of the plug assembly
203
, the resiliency of the spring
212
may be reduced to an unworkable level.
Accordingly, a foldable transformer having an improved plug assembly is desired.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to provide a plug assembly for a foldable transformer that has a reduced number of components, is easily assembled and manufactured, and is reliable.
To achieve the above object, a foldable transformer in accordance with a preferred embodiment of the present invention comprises an enclosure, a plug assembly and a locating assembly. The enclosure has a storage cavity at a top end thereof. A window is defined in the enclosure in communication with a bottom portion of the storage cavity, for receiving the plug assembly therethrough. A pair of tabs extends inwardly from the enclosure above the window, and a locating block extends inwardly from each tab. The plug assembly includes a pair of inserting pins, a rotatable rod having an arched profile, a pair of metal ears, and a pair of spring pins. Each inserting pin is made of conductive material, is insert-molded in the rod, and electrically connects with a corresponding ear. A protrusion is formed on a central portion of an apex of an arched surface of the rod. A pair of parallel projections extends outwardly from an arcuate portion of the arched surface of the rod proximate the protrusion. Each spring pin is made by folding a metal strip back over itself. Each spring pin comprises a first portion and a second portion connecting with each other via a neck. A dimple is formed in a free end of the second portion, to increase a contact area between the spring pin the corresponding metal ear. The locating assembly includes a pair of slots for receiving the spring pins, and a cam for resiliently engaging with the plug assembly so that the plug assembly can be disengagably fixed in a folded position or an unfolded position. The locating assembly also includes a pair of locating holes for locating the locating blocks.


REFERENCES:
patent: 4954940 (1990-09-01), Chandler et al.
patent: 5159545 (1992-10-01), Lee
patent: 5243510 (1993-09-01), Chemey, II
patent: RE35190 (1996-03-01), Zylstra et al.
patent: 5838554 (1998-11-01), Lanni
patent: 5973948 (1999-10-01), Hahn et al.
patent: 6086395 (2000-07-01), Lloyd et al.
patent: 6091611 (2000-07-01), Lanni
patent: 6266261 (2001-07-01), Liao

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