U.S. patent application number 14/143699 was filed with the patent office on 2014-07-03 for switching circuit layout with heatsink.
This patent application is currently assigned to Solaredge Ltd.. The applicant listed for this patent is Solaredge Ltd.. Invention is credited to Tzachi Glovinski, Amir Grossberg, Lior Handelsman, Sonke Rogalia, Heribert Schmidt.
Application Number | 20140185245 14/143699 |
Document ID | / |
Family ID | 42171896 |
Filed Date | 2014-07-03 |
United States Patent
Application |
20140185245 |
Kind Code |
A1 |
Handelsman; Lior ; et
al. |
July 3, 2014 |
SWITCHING CIRCUIT LAYOUT WITH HEATSINK
Abstract
A circuit board adapted for use in an switching converter for
connecting a plurality of switches including a first switch, a
second switch, a third switch and a fourth switch. The circuit
board has a layout for connecting the switches. The layout is
adapted for locating the switches substantially at or symmetrically
with respect to the endpoints of a right-angle cross. The
right-angle cross is formed from two line segments intersecting
with a ninety degree angle. The circuit board may offsets the
switches perpendicularly to the line segments at the endpoints of
the line segments either in a clockwise or a counterclockwise
direction.
Inventors: |
Handelsman; Lior;
(Givatayim, IL) ; Glovinski; Tzachi; (Petach
Tikva, IL) ; Grossberg; Amir; (Tel Aviv, IL) ;
Rogalia; Sonke; (Freiburg, DE) ; Schmidt;
Heribert; (Freiburg, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Solaredge Ltd. |
Hod Hasharon |
|
IL |
|
|
Assignee: |
Solaredge Ltd.
Hod Hasharon
IL
|
Family ID: |
42171896 |
Appl. No.: |
14/143699 |
Filed: |
December 30, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
12483933 |
Jun 12, 2009 |
8630098 |
|
|
14143699 |
|
|
|
|
61060878 |
Jun 12, 2008 |
|
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|
Current U.S.
Class: |
361/720 ;
361/781 |
Current CPC
Class: |
H05K 2201/09418
20130101; H05K 1/182 20130101; H05K 1/0216 20130101; H05K 3/0061
20130101; H02M 7/003 20130101; H05K 2201/10522 20130101; H05K 1/021
20130101; H05K 1/0203 20130101; H05K 1/18 20130101; H05K 2201/10166
20130101 |
Class at
Publication: |
361/720 ;
361/781 |
International
Class: |
H05K 1/18 20060101
H05K001/18; H05K 1/02 20060101 H05K001/02 |
Claims
1. A circuit board adapted for use in a switching converter for
connecting a plurality of switches including a first switch, a
second switch, a third switch and a fourth switch, wherein the
circuit board comprises: a layout for connecting said switches,
wherein said layout is adapted for locating said switches
substantially at the endpoints of a right-angle cross.
2. The circuit board of claim 1, wherein said layout is adapted for
locating said switches substantially symmetrically with respect to
the endpoints of said right-angle cross.
3. The circuit board of claim 1, wherein said right-angle cross is
formed from two line segments intersecting with a ninety degree
angle, wherein the circuit board offsets all said switches
perpendicularly to said line segments at the endpoints of the line
segments either in a clockwise or a counterclockwise direction.
4. The circuit board of claim 1, wherein said layout includes a
respective cutout for said switches wherein said switches are
chassis mounted.
5. A switching converter comprising: a plurality of switches
including a first switch, a second switch, a third switch and a
fourth switch; a circuit board having a layout for connecting said
switches, wherein said layout locates said switches substantially
at the endpoints of a right-angle cross.
6. The switching converter of claim 5, wherein said layout is
adapted for locating said switches substantially symmetrically with
respect to the endpoints of said right-angle cross.
7. The switching converter of claim 5, wherein said switches are
interconnected in a full bridge switching topology.
8. The switching converter of claim 5, wherein said switches are
interconnected in a buck-boost switching topology.
9. The switching converter of claim 5, further comprising a
heat-sink operatively attached to said switches for conducting heat
from said switches.
10. The switching converter of claim 5, wherein said first switch,
said second switch, said third switch and said fourth switch are
selected from the group consisting of: a silicon controlled
rectifier (SCR), an insulated gate bipolar junction transistor
(IGBT), a bipolar junction transistor (BJT), a field effect
transistor (FET), a junction field effect transistor (JFET), a
switching diode, an electrical relay, a reed relay, a solid state
relay, an insulated gate field effect transistor (IGFET), a diode
for alternating current (DIAC), and a triode for alternating
current (TRIAC).
11. The switching converter of claim 5, wherein said switches are
insulated gate bipolar junction transistors (IGBT), wherein said
layout includes cutouts for said switches, the converter further
comprising: a chassis mounting said insulated gate bipolar junction
transistors; and a heat sink attached to said transistors and said
chassis.
12. The switching converter of claim 5, wherein said right-angle
cross is formed from two line segments intersecting with a ninety
degree angle, wherein the circuit board offsets all said switches
perpendicularly to said line segments at the endpoints of the line
segments either in a clockwise or a counterclockwise direction,
thereby forming said layout of said switches in the shape of a
fylfot cross.
13. The switching converter of claim 5, wherein said right-angle
cross is formed from two line segments, including a first line
segment and a second line segment intersecting with a ninety degree
angle, wherein said first switch and said third switch are at the
endpoints of said first line segment forming a first pair of said
switches and said second switch and said fourth switch are at the
endpoints of said second line segment forming a second pair of said
switches, and wherein the switching converter switches alternately
said first pair of switches and said second pair of switches.
14. The switching converter of claim 5, wherein said right-angle
cross is formed from two line segments intersecting with a ninety
degree angle, wherein the circuit board offsets two of said
switches perpendicularly to one of said line segments at the
endpoints of said one line segment either in a clockwise or a
counterclockwise direction.
15. The switching converter of claim 14, which when mounted
vertically said one line segment is substantially vertical and one
of said two switches is substantially below the second of said two
switches so that while the switching converter is operating the
heat from the lower of said two switches does not flow near the
upper of said two switches.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] The present application is a continuation of co-pending U.S.
application Ser. No. 12/483,933 filed Jun. 12, 2009, which claims
benefit from US provisional application 61/060878 filed on Jun. 12,
2008 by the present inventors, the entire contents of which are
incorporated by reference.
BACKGROUND
[0002] 1. Technical Field
[0003] The present invention relates to switching converters and to
specifically a circuit layout of four switches
[0004] 2. Description Of Related Art
[0005] The thermal resistance of materials used to package
electronic components is of great interest to electronic engineers,
because most electrical components generate heat and need to be
cooled. Electronic components need to be cooled to avoid premature
aging and consequent failure. Also, effective cooling of the
electronic component(s) susceptible to generating heat in a circuit
allows for a stable, efficient and predictable performance of the
circuit. In particular, heat generated from electronic components
in power supply/conversion circuits are mostly derived from the
main switching devices.
[0006] Heat sinks function by efficiently transferring thermal
energy or heat from a first object at a relatively high temperature
to a second object or the environment at a lower temperature with a
much greater heat capacity. This rapid transfer of thermal energy
quickly brings the first object into thermal equilibrium with the
second object or environment, lowering the temperature of the first
object thus fulfilling the role of a heat sink as a cooling
device.
[0007] FIGS. 1a and 1b show a plan and side view respectively of a
circuit board 100 with heat sink 102 according to conventional art.
Four switches 104 are shown. Switches 104 are electrically
connected to circuit board 100 via legs 106. Plate 104a is used to
mechanically attach switch 104 to heat sink 102 using threaded
screw 108. An application of a heat sink compound (typically made
from zinc oxide in a silicone base) is applied between plate 104a
and heat sink 102 prior to fastening with threaded screw 108. The
heat sink compound allows for better heat transfer from switch 104
and heat sink 102 to allow for the uneven surfaces of either plate
104a or heat sink 102. Typically switch 104 is a semiconductor
switch such as a metal oxide semi-conductor field effect transistor
(MOSFET) or insulated gate bipolar junction transistor (IGBJT).
[0008] FIG. 2a shows a conventional full bridge converter 20. Full
bridge DC to DC converter has four main switches S1, S2, S3 and S4
connected together in a full bridge configuration. Switches S1, S2,
S3 and S4 are insulated gate bipolar transistors. The collectors of
switch S1 and switch S3 are connected together at node Y1 and the
emitters of switch S2 and switch S4 are connected together at node
Y2. The emitter of switch S1 is connected to the collector of
switch S2 and the emitter of switch S3 is connected to the
collector of switch S4. Each of the four main switches (S1, S2, S3
and S4) has respective diode shunts (D1, D2, D3 and D4) connected
in parallel thereto. The diodes placed across switches S1 and S2
are in both the same direction similarly the diodes of switch S3
and switch S4 are both in the same direction. In the case where
full bridge converter 50 is operated as a DC-to-DC converter all
diodes (D1, D2, D3 and D4) connected across switches S1, S2, S3 and
S4 are reverse biased with respect to the input voltage V.sub.in.
An input voltage (V.sub.in) of full bridge converter 20 is
connected across the node (Y2) between switches S2 and S4 and an
input voltage (V.sub.in.sup.+) is connected at the node (Y1)
between switches S1 and S3. An output voltage (V.sub.out.sup.-) of
full bridge converter 20 is connected across the node (X1) between
switches S1 and S2 and output voltage V.sub.out+ is connected at
the node (X2) between switches S3 and S4. Switching of full bridge
converter 20 is typically a 50% duty cycle such that while switches
S1 and S4 are ON, switches S3 and S2 are OFF and vice versa.
[0009] FIG. 2b shows a typical conventional buck-boost DC-to-DC
converter circuit 22. The buck circuit of buck-boost DC-to-DC
converter 22 has an input voltage V.sub.in with an input capacitor
C.sub.1 connected in parallel across V.sub.in. Two switches are
implemented as field effect transistors (FET) with integral diodes:
a high side buck switch Q.sub.1 and a low side buck switch Q2
connected in series by connecting the source of Q.sub.1 to the
drain of Q2. The drain of Q.sub.1 and the source of Q2 are
connected parallel across an input capacitor C.sub.1. A node is
formed between switches Q.sub.1 and Q2 to which one end of an
inductor 206 is connected. The other end of inductor 206 is
connected to the boost circuit of buck-boost DC-to-DC converter 22
at a second connecting two switches: a high side boost switch Q4
and a low side boost switch Q.sub.3 together in series where the
source of Q.sub.4 connects to the drain of Q.sub.3 to form node B.
The drain of Q.sub.4 and the source of Q.sub.3 connect across an
output capacitor C.sub.2 to produce the output voltage V.sub.out of
buck-boost DC-to-DC converter 22.
[0010] At higher switching frequencies of switched
inverters/converters, lower values of reactive components can be
used in circuit to achieve the required output characteristics of
the inverters/converters. However, the increase in frequency can
have the undesirable effect of increasing electromagnetic
interference (EMI) if good circuit design and good circuit layout
practices are not followed. Remembering that currents flowing in a
closed path, i.e. a loop (formed by circuit board traces) acts as
an efficient radiator of electromagnetic energy, maximum radiation
efficiency occurs when the loop dimension is on the order of
one-half wavelength. To minimize the radiation efficiency, that is
to reduce radiated noise, the loop is made as physically small as
possible by being aware of parasitic inductances in the board
traces. High-frequency currents follow the path of least impedance
(and not the path of least resistance) and a way to reduce the
inductive impedance (X.sub.L=2.pi.fL) of parasitic inductances (L)
is to reduce the frequency (f) or to reduce the size of the loop,
since a longer loop gives more parasitic inductance (L). Power loss
(P) in the loop is the product of the inductive impedance (X.sub.L)
squared and the high frequency current in the loop.
[0011] Both static and dynamic power losses occur in any switching
inverter/converter. Static power losses include I.sup.2R
(conduction) losses in the wires or PCB traces, as well as in the
switches and inductor, as in any electrical circuit. Dynamic power
losses occur as a result of switching, such as the charging and
discharging of the switch gate, and are proportional to the
switching frequency.
BRIEF SUMMARY
[0012] According to an embodiment of the present invention there is
provided a circuit board adapted for use in an inverter for
connecting a plurality of switches including a first switch, a
second switch, a third switch and a fourth switch. The circuit
board has a layout for connecting the switches. The layout is
adapted for locating the switches substantially at the endpoints of
an equilateral cross. The layout is adapted for locating the
switches substantially symmetrically with respect to the endpoints
of the equilateral cross. The equilateral cross is formed from two
line segments of equal length intersecting at their centers with a
ninety degree angle. The circuit board offsets all the switches
perpendicularly to the line segments at the endpoints of the line
segments either in a clockwise or an anticlockwise direction. The
layout typically includes a respective cutout for the switches. The
switches are typically chassis mounted.
[0013] According to yet another embodiment of the present invention
there is provided an inverter having multiple switches including a
first switch, a second switch, a third switch and a fourth switch.
A circuit board has a layout for connecting the switches. The
layout locates the switches substantially at the endpoints of an
equilateral cross or substantially symmetrically with respect to
the endpoints of the equilateral cross. The switches are
interconnected in a full bridge switching topology. The switches
are interconnected in a buck-boost switching topology. A heat-sink
is operatively attached to the switches for conducting heat from
the switches. The switches are preferably insulated gate bipolar
junction transistors (IGBT). The layout includes cutouts for the
switches, having a chassis mounting for the insulated gate bipolar
junction transistors; and a heat sink attached to the transistors
and the chassis. The equilateral cross is formed from two line
segments of equal length intersecting at their centers with a
ninety degree angle. The circuit board may offset the switches
perpendicularly to the line segments at the endpoints of the line
segments either in a clockwise or an anticlockwise direction,
thereby forming the layout of the switches in the shape of a fylfot
cross. The first switch and the third switch are at the endpoints
of the first line segment forming a first pair of the switches and
the second switch and the fourth switch are at the endpoints of the
second line segment forming a second pair of the switches. The
inverter switches alternately the first pair of switches and the
second pair of switches. The equilateral cross is formed from two
line segments of equal length intersecting at their centers with a
ninety degree angle. The circuit board may offset only two of the
switches perpendicularly to one of the line segments at the
endpoints of the one line segment either in a clockwise or an
anticlockwise direction. The inverter is mounted vertically so that
the one line segment is substantially vertical and one of the two
switches is substantially below the second of the two switches so
that while the inverter is operating, the heat from the lower of
the two switches does not flow near the upper of the two switches.
The first switch, the second switch, the third switch and the
fourth switch may include: silicon controlled rectifier (SCR),
insulated gate bipolar junction transistor (IGBT), bipolar junction
transistor (BJT), field effect transistor (FET), junction field
effect transistor (JFET), switching diode, electrical relay, reed
relay, solid state relay, insulated gate field effect transistor
(IGFET), diode for alternating current (DIAC), and/or triode for
alternating current TRIAC.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] The invention is herein described, by way of example only,
with reference to the accompanying drawings, wherein:
[0015] FIG. 1a and 1b show a plan and side view of a circuit board
with heat sink according to conventional art.
[0016] FIG. 1b shows a plan and side view of the circuit board with
heat sink 102 shown in FIG. 1a according to conventional art.
[0017] FIG. 2a shows a conventional full bridge converter according
to conventional art.
[0018] FIG. 2b shows a typical conventional buck-boost DC-to-DC
converter circuit according to conventional art.
[0019] FIG. 3a shows an equilateral cross topology according to an
exemplary embodiment of the present invention.
[0020] FIG. 3b shows a fylfot cross topology according to an
exemplary embodiment of the present invention.
[0021] FIG. 3c shows another fylfot cross topology according to an
exemplary embodiment of the present invention.
[0022] FIGS. 4a shows a plan view of a circuit board and heat sink
according to an exemplary embodiment of the present invention.
[0023] FIG. 4b which shows the side view of the circuit board and
heat sink shown in FIG. 4a according to an exemplary embodiment of
the present invention.
[0024] FIGS. 5a shows a plan view of a circuit board and heat sink
according to another exemplary embodiment of the present
invention.
[0025] FIG. 5b which shows the side view of the circuit board and
heat sink shown in FIG. 5a according to an exemplary embodiment of
the present invention.
[0026] The foregoing and/or other aspects will become apparent from
the following detailed description when considered in conjunction
with the accompanying drawing figures.
DETAILED DESCRIPTION
[0027] Reference will now be made in detail to embodiments of the
present invention, examples of which are illustrated in the
accompanying drawings, wherein like reference numerals refer to the
like elements throughout. The embodiments are described below to
explain the present invention by referring to the figures.
[0028] By way of introduction, an intention of embodiments of the
present invention is to minimize the lengths of the conductors
between switches of a switching converter/inverter, minimizing
interference due to parasitic capacitance and inductance, reducing
electro-magnetic interference (EMI) emissions and thereby
maximizing the efficiency of the switching converter.
[0029] It should be noted, that although the discussion herein
relates to switching topology for a four insulated gate bipolar
junction transistors (IGBT) full bridge inverter, the present
invention may, by non-limiting example, alternatively be configured
as well using other types of DC-DC converters AC-DC inverters
including buck, boost, buck-boost full bridge topologies with 4
switch topologies for both power supply and regulation
applications.
[0030] Before explaining embodiments of the invention in detail, it
is to be understood that the invention is not limited in its
application to the details of design and the arrangement of the
components set forth in the following description or illustrated in
the drawings. The invention is capable of other embodiments or of
being practiced or carried out in various ways. Also, it is to be
understood that the phraseology and terminology employed herein is
for the purpose of description and should not be regarded as
limiting.
[0031] The term "switch" as used herein refers to any type of
switch known in the art of electronics switches such as silicon
controlled rectifier (SCR), insulated gate bipolar junction
transistor (IGBT), metal oxide semi-conductor field effect
transistor (MOSFET), bipolar junction transistor (BJT), field
effect transistor (FET), junction field effect transistor (JFET),
switching diode, electrical relay, reed relay, solid state relay,
insulated gate field effect transistor (IGFET), DIAC, and
TRIAC.
[0032] The term "switching converter" as used herein applies to
power converters, AC-to-DC converters, DC-to-AC inverters, buck
converters, boost converters, buck-boost converters, full-bridge
converters or any other type of electrical power
conversion/inversion known in the art.
[0033] With reference to FIG. 3a an "equilateral cross" as used
herein is a cross of two line segments (arm 36 and arm 34) of equal
length at their center points 30 at right angles.
[0034] With reference to FIGS. 3b and 3c the term "fylfot cross" as
used herein has two arms; arm 36 and arm 34 which are crossed
equilaterally at a point 32. Arm 36 at each end has a hand 300 and
a hand 304 which are offset perpendicular to arm 36 in an
anti-clockwise direction in FIG. 3b. Arm 34 at each end has a hand
302 and a hand 306 which are offset perpendicular to arm 34 in an
anti-clockwise direction in FIG. 3b. In FIG. 3c, arm 36 at each end
has a hand 312 and a hand 308 which are offset perpendicular to arm
36 in a clockwise direction. Arm 34 at each end has a hand 310 and
a hand 314 which are offset perpendicular to arm 34 in a clockwise
direction in FIG. 3c.
[0035] Reference is now made to FIGS. 4a and 4b which show a plan
and side view respectively of a circuit board 400 and heat sink 406
according to an exemplary embodiment of the present invention.
Circuit board 400 has four switches S1, S2, S3 and S4 connected
electrically to circuit board 400 via leads 406. Circuit board 400
has four diodes D1, D2, D3 and D4 connected electrically to circuit
board via leads 408. Switches 51, S2, S3 and S4 are preferably
insulated gate bipolar junction transistors (IGBTs). Switches 51,
S2, S3 and S4 and diodes D1, D2, D3 and D4 are preferably connected
electrically together according to full bridge converter 20 shown
in FIG. 2a. Circuit board 400 is mechanically attached to heat sink
406 for instance via a screw and pillar arrangement 410. Switches
S1, S2, S3 and S4 are mechanically and thermally attached to heat
sink 406. Cutouts CO1, CO2, CO3 and CO4 in circuit board 400 allow
the mechanical and thermal attachment of switches S1, S2, S3 and S4
to heat sink 406.
[0036] The layout of switches S1, S2, S3 and S4 is based upon an
equilateral cross topology with dotted lines 404 and 402 forming
the two arms of the equilateral cross topology. Switches S1 and S4
lay on or symmetrically with respect to arm/axis 402 and switches
S2 and S3 lay on an arm/axis 404. The intersection between arm/axis
402 and arm/axis 404, forms the cross portion of equilateral cross
topology. In further embodiments of the present invention,
perpendicular offsets of switches S1, S4, S2 and S3 (and cutouts
CO1, CO2, CO3 and CO4 in circuit board 400) relative to arms/axis
402 and arm/axis 404 respectively are made such that the offsets
are in either a clockwise or anti-clockwise direction. Typically a
50% switching duty cycle is applied to 1, S2, S3 and S4 such that
while switches S1 and S4 are ON, switches S3 and S2 are OFF and
vice versa. Typically circuit board 400 and heat sink 406 are
mounted vertically so that the flow of heat in heat sink 506
generated by switches S1, S2, S3 and S4 flows vertically by
convection. Using the plan view of FIG. 4a as the vertical mounting
of circuit board 400 and heat sink 406, layout of switches S1, S2,
S3 and S4 are such that for example; the heat in heat sink 406 from
switches S2 and S3 does not flow near switches S1 and S4 and the
distance between S1 and S4 is such that the vertical flow of heat
in heat sink 406 of switches S1 and S4 does not affect each other.
Alternatively just switches S1 and S4 can be offset in either a
clockwise or anti-clockwise direction, so that the vertical flow of
heat in heat sink 406 of switches S1 and S4 does not affect each
other.
[0037] In a typical computer aided design/simulation of circuit
board 400; perpendicular offsets of switches Si, S4, S2 and S3
relative to arms/axis 402 and arm/axis 404 respectively and the
distance between switches S1 and S4 along arm/axis 402 and switches
S2 and S3 along arm/axis 404 respectively, are preferably chosen in
order to achieve minimal electromagnetic interference (EMI),
minimal impedance of circuit board 400 traces and efficient heat
transfer between switches S1, S2, S3 and S4 and heat sink 406.
[0038] Reference is now made to FIGS. 5a and 5b which show a plan
and side view respectively of a circuit board 500 and heat sink 506
according to an exemplary embodiment of the present invention.
Circuit board 500 has four switches S1, S2, S3 and S4 connected
electrically to circuit board 500 via leads 506. Circuit board 500
has four diodes D1, D2, D3 and D4 connected electrically to circuit
board via leads 508. Switches S1, S2, S3 and S4 are preferably
insulated gate bipolar junction transistors (IGBTs). Switches S1,
S2, S3 and S4 and diodes D1, D2, D3 and D4 are preferably connected
electrically together according to full bridge converter 20 shown
in FIG. 2a. Circuit board 500 is mechanically attached to heat sink
506 via a screw and pillar arrangement 510. Switches S1, S2, S3 and
S4 are mechanically and thermally attached to heat sink 506.
Cutouts CO1, CO2, CO3 and CO4 in circuit board 500 allow the
mechanical and thermal attachment of switches S1, S2, S3 and S4 to
heat sink 506.
[0039] Referring again to FIG. 5a, the layout of switches S1, S2,
S3 and S4 is based upon a fylfot cross topology. Switches S1 and S4
lay parallel to arm/axis 502 and switches S2 and S3 lay parallel to
arm/axis 504. The intersection between arm/axis 502 and arm/axis
504, form the equilateral cross portion of the fylfot cross
topology. The hands of the fylfot cross topology are represented by
dotted lines as hand 512, hand 516, hand 514 and hand 518. Hand 512
and hand 514 represent respectively the offsets of switches S1 and
S4 with respect to arm/axis 502. Hand 516 and hand 518 represent
respectively the offsets of switches S2 and S3 with respect to
arm/axis 504. In FIG. 5a hand 512, hand 516, hand 514 and hand 518
are offset from axis/arms 502 and 504 in an anti-clockwise
direction, alternatively hand 512, hand 516, hand 514 and hand 518
may be offset from axis/arms 502 and 504 in a clockwise direction.
Typically circuit board 500 and heat sink 506 are mounted
vertically so that the flow of heat in heat sink 506 generated by
switches S1, S2, S3 and S4 flows vertically by convection. Using
the plan view of FIG. 5a as an example of vertically mounting
circuit board 500 and heat sink 506, the layout of switches S1, S2,
S3 and S4 are such that for example; the vertical flow of heat from
switch S2 does not significantly run into the vertical heat flow of
switch S1, the vertical flow of heat from switch S1 does not
significantly run into the vertical heat flow of switch S4 and the
vertical flow of heat from switch S4 does not run significantly
into the vertical heat flow of switch S3.
[0040] The definite articles "a", "an" is used herein, such as "a
switch converter", "a switch" have the meaning of "one or more"
that is "one or more switch converters" or "one or more
switches".
[0041] Although selected embodiments of the present invention have
been shown and described, it is to be understood the present
invention is not limited to the described embodiments.
[0042] Instead, it is to be appreciated that changes may be made to
these embodiments without departing from the principles and spirit
of the invention, the scope of which is defined by the claims and
the equivalents thereof.
* * * * *