Electric power conversion systems – Current conversion – With cooling means
Reexamination Certificate
2001-02-22
2002-04-02
Patel, Rajnikant B. (Department: 2838)
Electric power conversion systems
Current conversion
With cooling means
C361S707000
Reexamination Certificate
active
06366486
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a switching power supply (SPS), and more particularly to a packing structure and a packing method of a mini-size power supply.
BACKGROUND OF THE INVENTION
Presently, for the development of electronic device, the volume trends to be smaller and smaller, and the current and power requirements trend to be bigger and bigger, especially for a high density switching power supply (SPS). Therefore, it is an important issue to achieve excellent heat-dissipating effect and reduce the current loading in such tiny space.
FIG. 1A
is a diagram illustrating a switch circuit used in the switching power supply according to the prior art. Referring to
FIG. 1A
, an induced current is generated and inputted to a secondary winding
101
via a transformer
10
. A set of rectifiers
102
and
103
then rectify the induced current to generate the output DC current to output through inductances
104
and
105
connected with a positive terminal (Vo) and a negative terminal (−Vo). The rectifiers
101
and
102
can either be a diode or a metal-oxide-semiconductor field effect transistor (MOSFET).
FIG. 1B
is a diagram illustrating an alternate circuit used in the switching power supply arranged slightly differently than that of FIG.
1
A.
FIG. 2
is an exploded three-dimensional view illustrating a packed circuit in
FIG. 1A
which is a general packed structure used in the industry. Cores
200
,
201
and a windings
202
shown in
FIG. 2
is corresponded to the secondary winding
101
in FIG.
1
A. Cores
203
,
204
and a windings
207
shown in
FIG. 2
are corresponded to the inductance
104
in
FIG. 1A
, and cores
205
,
206
and a winding
208
shown in
FIG. 2
are corresponded to the inductance
105
in FIG.
1
A. The MOSFETs
211
and
212
are corresponded to the rectifiers
103
and
102
in
FIG. 1A
, respectively.
Currently, most rectifiers applied in SPS are MOSFETs.
FIG. 3
is a perspective view illustrating the typical structure of a packed MOSFET. As shown in
FIG. 3
, a chip
301
is soldered onto a copper plate
300
which is a drain of the MOSFET. A source and a gate are bonding to two pins
302
and
304
via metal lines
306
and
305
. After testing the electricity, the top of the chip
301
is packed by epoxy. Generally, the conductivity of copper is about 380 W/mk, while that of epoxy is smaller than 1 W/mk. For the general heat-dissipating mechanism, the MOSFET is connected onto a pad or a metal of a substrate by soldering or screwing, and a thermal pad is placed between the MOSFET and the substrate for heat-dissipating. Usually, the substrate is a FR4 printed circuit board and the metal is aluminum. Thus, the heat conduction pathway is to transfer the heat generated from the MOSFET to the pad of the substrate via the copper plate
300
, and then dissipate the heat to the air by natural convection or forced convection.
On the other hand, most electric devices are soldered on the surface of substrate by the surface mounting technology (SMT). For SPS, the surface mounted device (SMD) is generally used in SPS designation.
FIG. 4A
is an exploded diagram illustrating a standard packed MOSFET bound to a printed circuit board according to the prior art. Generally, MOSFET has three pins, i.e. a gate
401
, a source
402
, and a drain
400
which is a copper plate. The copper plate
400
is soldered on a pad
404
of a printed circuit board
403
, and the gate
401
and the source
402
are soldered on plates
405
,
406
of the printed circuit board
403
respectively. After assembling, the structure is as shown in FIG.
4
B. As shown in
FIG. 4C
, the heat conduction pathway is from the drain
400
located at the back of MOSFET to the printed circuit board
403
via a soldering material
407
, i.e. the conductive materials such as tin or silver. Generally, since the material of printed circuit board is FR4 having conductivity of about 0.8 W/mk, the conduction effect is very small, i.e. the heat resistance is very large. Hence, most heat is directly transferred to the position just under the printed circuit board
403
, i.e. under the MOSFET, by conduction, and dissipated into the air by convection as shown in FIG.
4
C. Thus, if an electronic device which is not tolerance to heat such as capacitance is placed under the MOSFET, then the device lifetime will reduce because of high temperature generated by the MOSFET. However, since the device which could generate heat is soldered on the printed circuit board which is a FR4 material and is a bad conductor for heat, the generated heat is not easily taken away. According to the law of the conservation of energy, the temperature of the device which could generate heat will keep increasing because the generated heat cannot be dissipated, and further results in losing efficacy of the device because of the thermal run away effect.
In addition, for the power supply design having high current and high power characteristics, many MOSFETs are generally parallel connection for enhancing the efficiency, so the printed circuit board requires more thick copper line for loading larger current. Therefore, the space on the printed circuit board is occupied.
Summarily, the problems of the heat-dissipating effect, loading larger current and the space-consumption are still required to be solved in current industry. Therefore, the purpose of the present invention is to develop a method to deal with the above situations encountered in the prior art.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to propose a packing structure of a switching power supply for enhancing heat-dissipating effect.
It is therefore another object of the present invention to propose a packing structure of a switching power supply for loading and outputting more current.
It is therefore an additional object of the present invention to propose a packing structure of a switching power supply having the smaller packaged volume.
According to one aspect of the present invention, there is provided a packing structure of a switching power supply for enhancing heat-dissipating effect. The packing structure includes a printed circuit board, a transformer, an inductor having an inductive winding, a converter placed on a pad of the printed circuit board, wherein the pad is electrically connected to a secondary winding of the transformer and the inductive winding, and a metal cover directly covered on the converter.
Certainly, the metal cover can be made of copper.
Certainly, the converter can be a metal-oxide-semiconductor field effect transistor (MOSFET) having a drain directly connected to the metal cover and a source and a gate directly connected to the pad of the printed circuit board.
Preferably, the packing structure further includes a heatsink placed on the metal cover for enhancing heat-dissipating, or/and a thermal pad placed between the metal cover and the heatsink for conducting heat.
Preferably, the packing structure further includes a metal strip electrically connected to the metal cover, the inductive winding and the secondary winding of the transformer. The metal strip and the inductive winding can be integrally formed. The metal strip can be made of copper.
Certainly, the converter can be a diode having an anode electrically connected to the inductor and a cathode directly connected to a pad of the printed circuit board.
Certainly, the printed circuit board can be made of a material selected from FR4 and thermal clad.
According to another aspect of the present invention, there is provides a packing structure of a switching power supply for enhancing heat-dissipating effect. The packing structure includes a printed circuit board, a transformer, an inductor having an inductive winding, a metal strip electrically connected to the inductive winding, and a converter electrically connected to the metal strip and covered by the metal strip.
According to an additional aspect of the present invention, there is provides a method for packing a switching power supply to enhance heat-dissipatin
Chen Kun-Feng
Hsiao Ko-Yu
Hsieh Yi-Hwa
Delta Electronics , Inc.
Patel Rajnikant B.
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