Patent Application
20060164811
The present invention relates in general to electronic power supplies and, more particularly, to an integral molded heat sink on a DC-DC converter or other power supply.
Most modern electronic equipment requires a power supply to provide a direct current (DC) operating potential to the electronic components contained therein. Common types of electronic equipment which use power supplies include personal computers, energy systems, telecommunication systems, audio-video equipment, consumer electronics, automotive components, and other devices which utilize integrated circuits, semiconductor chips, or otherwise require DC operating potential. Most, if not all, semiconductor components require a low voltage DC operating potential. However, many sources of electric power are alternating current (AC), or high voltage DC, which must be converted to low voltage DC for the electronic equipment.
In one common arrangement, the AC/DC power supply receives an AC input voltage, e.g., between 110 and 240 VAC, and converts the AC input voltage to the DC operating voltage. The AC voltage is routed through a full-wave rectifier bridge and filtered to produce a high voltage DC signal. The high voltage DC signal is processed through a pulse width modulated (PWM) controller and transformer assembly to generate the low voltage, regulated DC output voltage, which is used as the operating potential for the semiconductor components and other devices requiring low voltage DC supply in the electronic equipment. The low voltage DC signal is typically in the range of 1 to 12 VDC. In other cases, a DC/DC power supply receives a high voltage DC signal and provides the low voltage DC signal necessary for the electronic equipment.
Power supplies are well-known to generate heat during normal operation. The energy transfer process across the transformer as well as switching losses in the power transistor are primary sources of the heat generation in power converters. In an effort to dissipate the heat, power supply manufacturers have mechanically attached heat sinks on individual components, e.g. pressure fit metal fins on the power transistor package, and utilized cooling fans to increase air flow across the unit. The heat sink increases the surface area of the heat generating device. The cooling fan increases air flow across the surface area of the heat generating device to dissipate the heat into the surrounding air.
As electronic equipment increase in functionality, there is less room for overhead functions like power supplies. This is particular true in telecommunication systems. The original equipment manufacturers (OEMs) demand more power from dimensionally smaller power supplies, or power supplies which at least are not proportionally larger. The heat generation is one factor limiting the operational parameters and power rating which can be achieved with conventional power converters.
A need exists for a power supply having a higher power rating without increasing its feature size or ambient operating temperature.
In one embodiment, the present invention is a power supply module comprising a printed circuit board having a plurality of electrical components mounted thereon for converting an input voltage to an output voltage. A heat sink is formed over substantially an entire surface area of the printed circuit board for providing heat dissipation.
In another embodiment, the present invention is a power supply module comprising a printed circuit board having a plurality of electrical components mounted thereon for converting an input voltage to an output voltage. An overmolded polymer compound is formed over at least a portion of the printed circuit board for providing heat dissipation.
In another embodiment, the present invention is a power supply comprising a chassis and a plurality of power supply modules mounted within the chassis. Each power supply module receives an input voltage and generates an output voltage. A heat sink is formed over the power supply modules for providing heat dissipation.
In another embodiment, the present invention is a method of dissipating heat from a power supply module comprising providing a printed circuit board having a plurality of electrical components mounted thereon for converting an input voltage to an output voltage, and forming a heat sink over the printed circuit board for providing heat dissipation.
In another embodiment, the present invention is a method of forming a heat sink on a power supply module comprising providing a power supply module, and depositing a thermally conductive polymer compound onto a surface of the power supply module.
The present invention is described in one or more embodiments in the following description with reference to the Figures, in which like numerals represent the same or similar elements. While the invention is described in terms of the best mode for achieving the invention's objectives, it will be appreciated by those skilled in the art that it is intended to cover alternatives, modifications, and equivalents as may be included within the spirit and scope of the invention as defined by the appended claims and their equivalents as supported by the following disclosure and drawings.
Referring to
Further detail of modular power supply 10 is shown in
Further detail of power supply module 14 is shown in
The DC output voltage VOUT1 is routed back through feedback regulation loop 42 to a control input of PWM controller 32. The DC output voltage VOUT1 generates the feedback signal which PWM controller 32 uses to regulate the power conversion process and maintain a relatively constant output voltage VOUT1 under changing loads. The aforedescribed electrical components of the power supply module are mounted to and electrically interconnected through a printed circuit board.
In the power conversion process, PWM controller 32 sets the conduction time duty cycle of MOSFET 28 to store energy in the primary side of transformer 26 and then transfer the stored energy to the secondary side during the off-time of MOSFET 28. The output voltage VOUT1 is determined by the energy transfer between the primary and secondary side of transformer 26. The energy transfer is regulated by PWM controller 32 via the duty cycle of the PWM control signal to MOSFET 28. Feedback regulation loop 42 generates the feedback signal to PWM controller 32 in response to the output voltage VOUT1 to set the conduction time duty cycle of MOSFET 28.
Consider the case where the load increases from zero to some nominal value. As load increases, the output current demand from power supply module 14 increases and the output voltage VOUT1 decreases. As the lower output voltage causes the feedback signal to be asserted for a longer time within the control cycle, which in turn causes PWM controller 32 to increase the pulse width to the power MOSFET 28. The longer conduction time of the power MOSFET 28 stores more energy in the primary side of transformer 26. Accordingly, more energy is transferred to the secondary side of transformer 26 during the off-time of the power MOSFET. The output voltage VOUT1 of power supply module 14 increases to compensate for the increased current demand. Power supply modules 16 and 18 may follow a similar design and operation.
Power supply 10 is constructed to meet the maximum power requirement of electronic equipment 12. The power supply requirements of electronic equipment 12 continue to grow with increasing equipment functionality. The designers of electronic equipment 12 continue to add more features and increase the speed of their equipment, which often takes more space and consumes more power. In order to supply the power demands of electronic equipment 12, the power supply modules within power supply 10 necessarily generate heat. The transformer 26, power MOSFET 28, and PWM controller 32 are primarily sources of the heat generated from power supply modules 14-18. However, more power usually involves larger components, more heat dissipation, and more printed circuit board area for the power supply module to dissipate the heat. Yet, because of the growing number and size of functional components within electronic equipment 12, equipment manufacturers also demand smaller overall feature size in the requisite power supplies.
In
As a feature of the present invention, power supply module 14 is overmolded with heat dissipating polymer compound to act as a heat sink for the print circuit board as a whole. The polymer compound is thermally conductive, electrically insulating, and covers substantially the entire surface area of PCB 50. The overmolded polymer compound is in intimate contact with the PCB 50 and electrical components 52, which allows the compound to operate as a thermal conductor to extract heat from the electrical components on the PCB and from substantially the entire surface area of the PCB itself.
A cross-sectional side view of power supply module 14 is shown in
In another embodiment, formed without the fins or posts, the overmolded heat sink 54 has a relatively flat surface. Alternatively, the overmolded polymer compound may have a uniform thickness and conform to the outline or shape of the electrical components 52.
In another embodiment, the overmolded heat sink can also be formed over only portion(s) of the PCB and electrical components 52 which generate the most heat, i.e. the hot spots. For example, the overmolded heat sink 54 may be formed over the area(s) of PCB 50 containing transformer 26 and power MOSFET 28. The overmolding polymer compound would cover the heat generating electric components and some portion of the PCB in proximity to the heat generating electric components. The heat sink over the hot spots can be formed with fins or posts.
The PCBs with overmolded heat sinks shown in
The overmolded polymer compound can be formed into heat sink 54 using an injection molding process. The polymer compound is a thermally conductive and electrically insulating material. Examples of a suitable polymer material include liquid crystalline polymer (LCP) available from Cool Polymer as part number D5502, and polyphenylene sulfide (PPS) available from Cool Polymer as part numbers D5104, D5106, and D5108. The LCP and PPS material may be filled with a ceramic, usually boron nitride. The thermal conductivity of such polymer materials are in the range of 1.5-10 W/mK. The electrical resistivity ranges from 1013 to 1016 ohm-cm and the dielectric strength ranges from 35-560 kV/mm.
The base polymer material comes in pellet form, which can be loaded into a thermoplastic injection molding apparatus. Power supply module 14 embodied as PCB 50 is placed within the cavity of mold 70. The cavity is formed to the shape of heat sink 54, including fins or posts 56 if desired. The pellets are melted and injected in semi-liquid state to a pre-formed mold 70 such as shown in
In another embodiment, the polymer compound can be deposited onto the surfaces of PCB 50 as a spray. The PCB may also be dipped into a polymer bath. In such cases, the polymer compound will create a heat sink of uniform thickness over the electrical components and PCB.
The horizontal or vertical mounted PCBs with overmolded heat sinks are mounted within power supply chassis 20. The heat generated is thermally conducted away from the PCB and the electrical components through the overmolded heat sink. A fan circulates air over the heat sink to further dissipate the heat into surrounding air space.
The overmolded heat sink 54 on PCB 50 provides a number of advantages. The overmolded polymer compound is in direct contact with substantially the entire surface of PCB 50 and electrical components 52 and operates as an effective thermal conductor to extract heat from the electrical components on the PCB and from the PCB itself in an efficient manner. The heat generated by PCB 50 during the power conversion process is dissipated through the heat sink, which is in direct and continuous contact with the printed circuit board and electric components. By having the heat sink disposed over substantially the entire surface of PCB 50 and electrical components 52, or at least over the electrical components generating the most heat, the heat sink is able to remove more heat from the power supply module. Accordingly, the power supply module can provide more output load current given the same physical size of electrical components and PCB, and same ambient operating temperature.
While one or more embodiments of the present invention have been illustrated in detail, the skilled artisan will appreciate that modifications and adaptations to those embodiments may be made without departing from the scope of the present invention as set forth in the following claims.
