[001] The present invention relates to a home inverter design with SMD MoSFET package. The present invention more particularly relates to a heatsink-less inverter with brass jumpers for heat dissipation.
BACKGROUND OF THE INVENTION
[002] Inverters, especially home inverter, are used as important electrical devices for conversion of electricity in the form of direct current (DC) to an alternating current (AC), which is being connected to an AC power grid through electrical cables. Generally, heat is generated in inverters during the process of converting DC to AC due to current flow in an inverter circuitry, i.e. printed circuit board (PCB). So, heat dissipation is very important to allow the inverter to operate in an efficient and reliable manner. At the same time, this heat dissipation has to be done using cost-effective materials and components without increasing the cost of the inverter.
[003] Over the decades, in the existing inverter systems, both the performance and reliability of electronic equipment are inversely related to the component temperature of the equipment. The relationship between the reliability and the operating temperature of typical silicon semi-conductor devices and components shows that a reduction in the temperature corresponds to an increase in the reliability and life expectancy of the inverter. Therefore, long life and reliable performance of components may be achieved by effectively controlling

the device operating temperature within the limits set by the inverter design engineers.
[004] In the conventional inverters, the device operating temperature are controlled with the help of heatsinks that are mounted on the inverter PCB to enhance heat dissipation from a hot surface of heat generating components in the inverter PCB to a cooler ambient (usually air assumed to be act as coolant). In most situations, the heatsink lowers this barrier mainly by increasing the surface area that is in direct contact with the coolant, which allows more heat to be dissipated and/or lowers the device operating temperature. The primary purpose of the heatsink is to maintain the device temperature below the maximum allowable temperature specified by the device manufacturers.
[005] The conventional inverter system is provided with the heatsink and a through hole based packaged metal-oxide-semiconductor-field-effect transistor (MoSFET). In the inverter PCB, one set of conductive fasteners is used to mount the MoSFET on the heatsink whereas another set of fasteners is used on the PCB to mount and connect the heatsink, which results in lots of fasteners being used in the mounting process of MoSFET and heatsink on the inverter PCB.
[006] In general, the heatsinks are long in length and aluminium based heat dissipating passive devices, which can have significant amount of resistance and add in series of current flow in the inverter circuitry. Further, the through-hole MoSFET has very tiny terminal leads for all three terminals (drain, source and gate), which can also have significant amount of resistance and add in series of current flow in the inverter circuitry. Thus, the below equation (1) can clearly represent the presence of mammoth total amount of path resistance in the existing inverter system, i.e. equivalent resistance of the heatsink based design is algebraic sum of all resistance.

Req = RHS + RFET + RFET Leg+ RCU Pad (1)
Where,
RHS - Heatsink Resistance RFET - MoSFETRDSon
RFETleg - Resistance of Drain Lead of FET which presence in all through hole package Mosfets 220
RCuPad - Copper Pad Resistance on PCB
Thus, the efficiency of the inverter is inversely proportional to path resistance of the system, which results in that net losses in this existing system are very high and significant amount of efficiency is reduced with rise in temperature simultaneously.
[007] With respect to these conventional home inverters, the through-hole MoSFET and the heatsink consumes more time for assembly and process time due to various steps required for fixing the heatsink using multiple fasteners, where the various process steps involve step 1 of applying the solder paste on both MoSFET and heatsink for thermal and electrical bonding; step 2 of conductive fastener used to mount the MoSFET to the heatsink; step 3 of placing the heatsink on the PCB; step 4 of conductive fastener used to mount the heat sink to the PCB; and finally step 5 of soldering the MoSFET terminals on the PCB. Thus, the possibility of reliability issues during manufacturing and transportation are high due to chances of loose fasteners and bulk the heatsink, where the looseness in heatsink affects normal operation and also improper transfer of heat from the MoSFET to the heatsink, which can burn MoSFET and other components in the inverter. Further, the heatsinks and the MoFETs terminal leads creates more resistivity added in series to current path, where such high resistivity has significant effect on efficiency of the inverter system. Also, the usage of heatsink increases cost

involved in material procurement process and manufacturing, and occupies more space in the PCB of the inverter.
[008] Hence, there is a need in that art to provide a solution to address all the above mentioned problems. The present invention relates to a cost effective heatsink-less inverter designed to moderately assessment better performance, reliability and heat dissipation through the semiconductor device without heatsink, which addresses and overcomes all the existing art problems in a unique and simple manner.
SUMMARY OF THE INVENTION
[009] The following summary is provided to facilitate an understanding of some of the innovative features unique to the disclosed embodiments and is not intended to be a full description. A full appreciation of the various aspects of the embodiments disclosed herein can be gained by taking the entire specification, claims, drawings, and abstract as a whole.
[0010] A primary objective of the present invention is to provide a heatsink-less inverter, which is capable of improving thermal conduction and decreasing thermal resistance on current conduction path, which results in efficient dissipation of heat in inverter circuitry without any need of heatsink construction.
[0011] Another objective of the present invention is to provide a heatsink-less inverter, which improves the efficiency of inverter system and minimizes temperature rise.
[0012] Another objective of the present invention is to provide a heatsink-less inverter, which achieves better performance, reliability, manufacturability and

productivity by eliminating the need for manual involvement to mount heatsinks and MoSFET using conductive fasteners.
[0013] Another objective of the present invention is to provide a heatsink-less inverter, which simplifies the inverter design, reduces time consumption and easy to implement in a more efficient and cost effective manner.
[0014] According to the embodiment of the present invention to achieve the objective of the invention, a heatsink-less inverter which comprises a printed circuit board enclosed with a housing and connected between a battery and an alternating current (AC) power grid through a plurality of electrical cables. A plurality of surface mount device (SMD) transistors are electrically connected and mounted on contact pads in the printed circuit board, where the SMD transistor is a SMD metal-oxide-semiconductor-field-effect transistor (MoSFET). A plurality of drain wire entries on which drain wires are electrically connected and mounted on drain contact pads in the printed circuit board. A plurality of brass jumper members are attached to the contact pads in the printed circuit board. Each of the brass jumper members is placed in close proximity to the SMD transistors and the drain wire entries at a same direction of drain current flow of the SMD transistors such that overall drain current equally and uniformly flows through both the contact pads and the brass jumper members in the printed circuit board. Thus, this heatsink-less inverter improves thermal conduction and decreases thermal resistance on current conduction path, which results in efficient dissipation of heat in inverter circuitry without any need of heatsink construction. It leads to improve the efficiency of inverter system and minimize temperature rise.
[0015] Furthermore, each brass jumper member is formed of an elongated plate-like member being mounted vertically upright on the printed circuit board at its both ends. The brass jumper members build a low impedance path for current
6

flow in parallel to the contact pads in the printed circuit board in order to share the same amount of drain current to flow on the contact pads and the brass jumper members, where each of the brass jumper members acts as a heat dissipation member in the inverter.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] These and other objects, features and advantages of the present invention will be further apparent from the following description taken in conjunction with the several figures of the accompanying drawings which show, by way of example only one form of this present invention. The invention will be discussed in greater detail with reference to the accompanying figures.
[0017] FIG. 1 illustrates a schematic view of heatsink-less inverter with brass jumper members, in accordance with an exemplary embodiment of the present invention;
[0018] FIG. 2 illustrates an example circuit diagram of MoSFET connections (a full bridge configuration) in an inverter design, in accordance with an exemplary embodiment of the present invention; and
[0019] FIG. 3 illustrates a schematic layout of PCB with connections of MoSFET and brass jumpers, in accordance with an exemplary embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0020] The following description is of exemplary embodiment of the invention only, and is not the limited scope, applicability or configuration of the
7

invention. Rather, the following description is intended to provide a convenient illustration for implementing various embodiments of the invention. As will become apparent, various changes may be made in the function and arrangement of the structural/operational features described in these embodiments without departing from the scope of the invention as set forth herein. It should be appreciated that the description herein may be adapted to be employed with alternatively configured devices having different shapes, components, material and the like and still fall within the scope of the present invention. Thus, the detailed description herein is presented for the purposes of illustration only and not of limitation.
[0021] The present invention will be described based on the illustrated examples as shown below. The present embodiment will be described, herein below, paragraphs by referring the accompanying drawings. A heatsink-less home inverter with surface mount device (SMD) transistor package and brass jumpers is described herein.
[0022] The present invention relates to a cost effective home (sine-wave) heatsink-less inverter design with surface mount device (SMD) transistor package, i.e. SMD metal-oxide-semiconductor-field-effect transistor (MoSFET) package, which is intended to simplify the inverter design for efficient dissipation of heat in inverter circuitry (100) even without heatsink construction. The present disclosure aims to provide embodiments to solve one or more of the above problems. The present disclosure, which describes improvements to the inverter design with SMD MoSFET packaging and brass jumper, describes embodiments that allow the inverter to be more efficient and cost effective. This allows benefits when producing inverters on an industrial scale. This heatsink-less inverter is easy to implement and resolve all issues arise on the heatsink based design approach.
8

[0023] The present inverter design is analysed with its performance and thermal test to optimise the thermal design on system without heatsink design, such that the brass jumper is designed to control junction temperatures of semiconductor devices (MoSFET and other components) inside the inverter current. The present invention is designed to moderately assessment the better performance, reliability and heat dissipation through the semiconductor devices (MoSFET and other components) without heatsink, where the present invention is implemented based on (a) superior PCB layout design, (b) selection and placement of critical components like semiconductor devices, and (c) adopt low impendence path for both current and heat dissipation with the help of brass jumpers.
[0024] Figure 1 illustrates a schematic view of heatsink-less inverter (100) with brass jumper members (4), in accordance with an exemplary embodiment of the present invention. The present heatsink-less inverter (100) is primarily composed and housed of a printed circuit board (PCB) (1), surface mount device (SMD) transistors (2), i.e. MoSFET (2), drain wire entries (3) and brass jumper members (4). The printed circuit board (1) is enclosed with a housing, where the PCB (1) is connected between a battery and an alternating current (AC) power grid (not shown) through several electrical cables. This PCB (1) plays an important role in the inverter for conversion of electricity in the form of direct current (DC) to the alternating current (AC), which is being connected to the AC power grid through electrical cables.
[0025] In this PCB (1), several SMD transistors (2), i.e. SMD MoSFET (2), are electrically connected and mounted on contact pads (i.e. copper pads) formed in the printed circuit board (1) at its appropriate places predesigned in the PCB layout. Hereafter, the contact pads are referred as copper pads or Cu pads throughout the description only for the purpose of explanation and understanding; but not by the way of any limitations. The PCB layout contains a provision for
9

several drain wire entries (3) on which drain wires are electrically connected and mounted on drain copper pads formed in the printed circuit board (1). In the exemplary inverter PCB circuit (1), inputs of the circuit are battery positive terminal (Batt +ve) and battery negative terminal (Batt –ve) whereas output of the circuit is fed to a low frequency (50Hz) transformer, as clearly shown in Figure 2, which illustrates an example circuit diagram of MoSFET connections (a full bridge configuration) in an inverter PCB design (1), in accordance with an exemplary embodiment of the present invention.
[0026] In this heatsink-less inverter, a plurality of brass jumper members (4) is attached to the copper pads in the printed circuit board (1), where each brass jumper member (4) is formed of an elongated plate-like member being mounted vertically upright on the printed circuit board (1) at its both ends. These brass jumper members (4) act as heat dissipation members in the inverter for dissipating overall heat generated due to current flow in copper pad and Mosfets (1) of the inverter during the process of converting DC to AC. Each of the brass jumper members (4) is placed in close proximity to the SMD MoSFET (2) and the drain wire entries (3) at a same direction of drain current flow of the SMD MoSFET (2) such that overall drain current equally and uniformly flows through both the copper pads and the brass jumper members (4) in the PCB (1). In particular, the brass jumper members (4) build a low impedance path for current flow in parallel to the copper pads in the printed circuit board (1) in order to share the same amount of drain current to flow on the copper pads and the brass jumper members (4).
[0027] Figure 3 illustrates a schematic layout of PCB with connections of MoSFET (2) and brass jumpers (4), in accordance with an exemplary embodiment of the present invention. In the present invention, it is essential that the brass jumper members (4) are being placed in same direction to drain current flow of the
10

SMD MoSFET (2), so that total drain current flows through both the copper pad of the PCB (1) and the brass jumper members (4), which shares same amount of current flow on the copper pad on the PCB (1) and the brass jumper members (4). These brass jumper members (4) replace the heat sinks being used in existing arts for heat dissipation, where these brass jumper members (4) can also be referred as brass jumpers. From above, it is important regarding the placement of brass jumper members (4) in the inverter PCB circuitry (1).
Placement of Brass Jumper:
[0028] For example, the placement of brass jumper members (4) has been carried out by placing it in three different locations in the PCB (1) and by analyzing their results.
[0029] Initially, in the first scenario, the brass jumper members (4) are placed at top side of both the drain wire entry (3) and the MoSFET (2), i.e. placed opposite to the drain current flow direction. It is noted that there is no much improvement in both thermal conductive and current conductive path of the drain copper pad in the PCB (1). It is concluded that in this placement, the brass jumper members (4) have no role to reduce the current burden on the PCB drain pad.
[0030] Further, in the second scenario, the brass jumper members (4) are placed at bottom side of both the drain wire entry (3) and the MoSFET (2), i.e. placed perpendicular to the drain current flow direction. In this case also, it is noted that there is no much improvement in both thermal conductive and current conductive path of the drain copper pad in the PCB (1). It is concluded that in this placement, the brass jumper members (4) reduce only thermal resistance and has no role to reduce the current burden on the PCB drain pad.
11

[0031] In these above two cases of the placement of the brass jumper members (4), power losses are as follows with their equivalent electrical circuit and equations depicted below:


Where, R is copper pad resistance to mosfet drain
RGJA is thermal resistance of the PCB Copper pad with Mosfet drain
[0032] In both the above cases, the power losses are same there is not much improvement while keeping the brass jumper members (4) in opposite direction or perpendicular direction of the drain current flow with the reduction of only thermal resistance.
[0033] Finally, in next scenario, the brass jumper members (4) are placed in same direction of the drain current flow and their results are analyzed. In the final scenario, the brass jumper members (4) are placed at same direction of the drain current flow direction. In this case, it is noted that thermal conduction is much improved now where the brass jumpers is solving two purpose, i.e. it decreases thermal resistance of track and also shares current of track in the PCB (1), especially current flow in the PCB drain pad is reduced into half of actual so that the amount of drain current is equally and uniformly shared to flow on both the copper pads and the brass jumper members (4). Their equivalent electrical circuit and equations depicted below:
12


When the current (I) the two equal resisters in of the total current equally power losses as follows:

is flow through
parallel, then half
share. Then,


Where /l = 12 = -
So the power losses can effectively 25% of actual losses in MoSFET drain copper pad
Whereas temp rise: T= R6JA * Ploss Without Brass Jumper: Trise = ROJA * Ploss With Brass Jumper: Trise = ROJA * Ploss/4
Hence, the placement of the brass Jumpers in proper direction of drain current flow can improve the thermal and reduce the current stress on the copper pad (Cu pad) of the PCB, which effectively reduces temperature rise by 4 considering equal resistance of the brass jumpers.
[0034] In the existing heatsink design, many and several resistances are being added in the circuitry, which results in degradation in the inverter performance and reliability, i.e. the requirement of heatsink based inverter design is algebraic sum of all resistances, which is clearly shown in the below equation (1).
13

Req = RHS + RFET + RFET Leg+ RCU Pad (1)
Where,
RHS - Heatsink Resistance
RFET - MoSFET (2)RDSon
RFETleg - Resistance of Drain Lead of FET which presence only TO 220
RCuPad - Copper Pad Resistance on PCB
[0035] But, in the present invention of the heatsink-less design, only few resistances are being added in the circuitry, which results in improving the inverter performance and reliability, i.e. the requirement of heatsink-less based inverter design is algebraic sum of few resistances, which is clearly shown in the below equation (2).
Req = (RBJ ǁ RCU Pad) + RFET (2)
Where,
RBJ - Brass Jumper Resistance
RCuPad - Copper Pad Resistance on PCB
RFET - MoSFET (2)RDSon
[0036] Let assume that the value of resistance of the brass jumpers (RBJ) (4) is select to equal valve of the copper pad (Cu Pad) resistance. So, the effective resistance of R Cu Pad can be half, the above equation (2) can be rewritten as the below equation (3).
Req = —-f+RFET ----------------------------------(3)
14

From the equations (1) and (3), it is conclude that there is mammoth total amount path resistance is presence in the existing heatsink and through-hole based inverter design, which create more loss and temperature rise than the brass jumpers in the heatsink-less based inverter design.
[0037] MoSFET Selection Criteria:

Parameters Existing System Proposed System Units
mΩ Volts Amps
Output of System Square Wave Sine Wave

Part number STP105 CSD17576

Rdson Max 3.5 2

VDS 30 30

MoSFET Current 44 58

For same amount of output power to deliver, by keeping output power constant in both system and their Rdson selection for MoSFET as follows:

Based on tabulated data:
15
Keeping the output power constant, then the required Rdson in Proposed system can be



[0038] Therefore, the present invention with heatsink-less and SMD based packaged MoSFET implemented with the brass jumpers, can eliminate all losses due to the heatsinks and the drain lead resistance of the MoSFET, and more importantly it makes half the drain copper pad (Cu pad) resistance (approx.) on the PCB with the aid of brass jumpers, which results in the efficiency in inverter system is high and temperature rise is low as compare with the existing heatsink based inverter system. In the present invention, the reduction of PCB Cu Pad thermal impedance (R&JA) improves thermal conductive area, whereas the current sharing of inherent quality of the brass jumper provides low impedance path for current in addition to the PCB Cu pad.
[0039] The present effective heatsink-less inverter with SMD MoSFET package improves performance, reliability, manufacturability, productivity and cost. In particular, the present invention is provided with SMD MoSFET and reduced Cu Pad resistance by implementing of the brass jumpers, which in turns achieves performance and reliability improvement by eliminating parasitic parameters losses and manual intervention involved in the through hole MoSFETs with heatsink based existing inverters. The advantages of the present heatsink-less inverter with SMD MoSFET package are provided below in detail:
1) Performance and Reliability Improvement: By adopting the heatsink-less and SMD based Package MoSFET with better PCB layout Design, it can eliminate use of heatsinks and leaded MoSFET, which reduces the series path resistance as well as increases the efficiency and reliability of the inverter system.
16

2) Process Improvement and better Productivity: There is no need of any manual involvement for mounting of MoSFET, all are mount along with other SMD components through automatic SMD Machines. It improves process during manufacturing and allow for more productivity because of less time consumption.
3) Current Sharing through the Brass Jumper: Since all brass jumpers are placed in the direction of current, the total drain current flows through both the PCB copper pad and the brass jumpers, so that same amount of current is equally shared on the PCB copper pad and the brass jumper.
[0040] In the present invention, the MoSFET is mounted on PCB without any conductive fastener. Particularly, the single-step implementation of brass jumpers in the present invention reduces time consumption process, which improves manufacturability and productivity and also reduces the cost by eliminating multiple steps for implementation of the heatsinks and through hole MoSFET package in the existing inverters, i.e. the process of bulk heatsinks with tighting fasteners in the heatsink based inverter design involve much less cost as compare to the heatsink-less inverter design.
[0041] It is to be understood that the above description is intended to be illustrative, and not restrictive. Many other embodiments will be apparent to those of skills in the art upon reading and understanding the above description. Although the present invention has been described referring to specific exemplary embodiments, it will be recognized that the invention is not limited to the embodiments described, but can be practiced with modification and alteration within the spirit and scope of the appended claims. Accordingly, the specifications and drawings are to be regarded in an illustrative sense rather than a restrictive
17

sense. The scope of the invention should, therefore, be determined with respect to the appended claims, along with the full scope of equivalents to which such claims are entitled.

We Claim:

1.A heatsink-less inverter, comprising:
a printed circuit board (1) enclosed with a housing and connected between a battery and an alternating current (AC) power grid through a plurality of electrical cables;
a plurality of surface mount device (SMD) transistors (2) electrically connected and mounted on contact pads in the printed circuit board (1);
a plurality of drain wire entries (3) on which drain wires are electrically connected and mounted on drain contact pads in the printed circuit board (1); and
a plurality of brass jumper members (4) attached to the contact pads in the printed circuit board (1),
wherein each of the brass jumper members (4) is placed in close proximity to the SMD transistors (2) and the drain wire entries (3) at a same direction of drain current flow of the SMD transistors (2) such that overall drain current equally and uniformly flows through both the contact pads and the brass jumper members (4) in the printed circuit board (1).
2. The inverter as claimed in claim 1, wherein the brass jumper members (4) build a low impedance path for current flow in parallel to the contact pads in the printed circuit board (1) in order to share the same amount of drain current to flow on the contact pads and the brass jumper members (4).
3. The inverter as claimed in claim 1, wherein each brass jumper member is formed of an elongated plate-like member being mounted vertically upright on the printed circuit board (1) at its both ends.
4. The inverter as claimed in claim 1, wherein each of the brass jumper members (4) acts as a heat dissipation member in the inverter.

5. The inverter as claimed in any of the preceding claims 1-4, wherein the SMD transistor (2) is a SMD metal-oxide-semiconductor-field-effect transistor (MoSFET).