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.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application benefits from U.S. provisional application 61/060,878 filed on Jun. 12, 2008 by the present inventors. 
     
    
     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. 1   a  and  1   b  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  104   a  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  104   a  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  104   a  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 transistor (IGBT). 
         [0008]      FIG. 2   a  shows a conventional full bridge converter  20 . Full bridge DC to DC converter  20  has four main switches S 1 , S 2 , S 3  and S 4  connected together in a full bridge configuration. Switches S 1 , S 2 , S 3  and S 4  are insulated gate bipolar transistors. The collectors of switch S 1  and switch S 3  are connected together at node Y 1  and the emitters of switch S 2  and switch S 4  are connected together at node Y 2 . The emitter of switch S 1  is connected to the collector of switch S 2  and the emitter of switch S 3  is connected to the collector of switch S 4 . Each of the four main switches (S 1 , S 2 , S 3  and S 4 ) has respective diode shunts (D 1 , D 2 , D 3  and D 4 ) connected in parallel thereto. The diode shunts may be inherent parasitic diodes of the IGBTs, or may be discrete components. The diodes placed across switches S 1  and S 2  are in both the same direction similarly the diodes of switch S 3  and switch S 4  are both in the same direction. In the case where full bridge converter  50  is operated as a DC-to-DC converter all diodes (D 1 , D 2 , D 3  and D 4 ) connected across switches S 1 , S 2 , S 3  and S 4  are reverse biased with respect to the input voltage V in . An input voltage (V in   − ) of full bridge converter  20  is connected across the node (Y 2 ) between switches S 2  and S 4  and an input voltage (V in   + ) is connected at the node (Y 1 ) between switches S 1  and S 3 . An output voltage (V out   − ) of full bridge converter  20  is connected across the node (X 1 ) between switches S 1  and S 2  and output voltage V out + is connected at the node (X 2 ) between switches S 3  and S 4 . Switching of full bridge converter  20  is typically done in a manner such that while switches S 1  and S 4  are ON, switches S 3  and S 2  are OFF and vice versa. 
         [0009]      FIG. 2   b  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 in  with an input capacitor C 1  connected in parallel across V in . Two switches are implemented as field effect transistors (FET) with integral diodes: a high side buck switch Q 1  and a low side buck switch Q 2  connected in series by connecting the source of Q 1  to the drain of Q 2 . The drain of Q 1  and the source of Q 2  are connected parallel across an input capacitor C 1 . A node is formed between switches Q 1  and Q 2  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 Q 4  and a low side boost switch Q 3  together in series where the source of Q 4  connects to the drain of Q 3  to form node B. The drain of Q 4  and the source of Q 3  connect across an output capacitor C 2  to produce the output voltage V 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 L =2πfL) 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 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 2 R (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 a 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 the endpoints of a right-angle cross. The layout is adapted for locating the switches substantially symmetrically with respect to the endpoints of the right-angle cross. The right-angle cross is formed from two line segments intersecting 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 a counterclockwise 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 a switching converter 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 a right-angle cross or substantially symmetrically with respect to the endpoints of the right-angle 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 right-angle cross is formed from two line segments intersecting 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 a counterclockwise 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 switching converter switches alternately the first pair of switches and the second pair of switches. The right-angle cross is formed from two line segments intersecting with substantially 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 counterclockwise direction. The switching converter 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 switching converter 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]      FIGS. 1   a  and  1   b  show a plan and side view of a circuit board with heat sink according to conventional art; 
           [0016]      FIG. 1   b  shows a plan and side view of the circuit board with heat sink  102  shown in  FIG. 1   a  according to conventional art; 
           [0017]      FIG. 2   a  shows a conventional full bridge converter according to conventional art; 
           [0018]      FIG. 2   b  shows a typical conventional buck-boost DC-to-DC converter circuit according to conventional art; 
           [0019]      FIG. 3   a  shows a right-angle cross topology according to an exemplary embodiment of the present invention; 
           [0020]      FIG. 3   b  shows a fylfot cross topology according to an exemplary embodiment of the present invention; 
           [0021]      FIG. 3   c  shows another fylfot cross topology according to an exemplary embodiment of the present invention; 
           [0022]      FIG. 4   a  shows a plan view of a circuit board and heat sink according to an exemplary embodiment of the present invention; 
           [0023]      FIG. 4   b  which shows the side view of the circuit board and heat sink shown in  FIG. 4   a  according to an exemplary embodiment of the present invention; 
           [0024]      FIG. 5   a  shows a plan view of a circuit board and heat sink according to another exemplary embodiment of the present invention; and 
           [0025]      FIG. 5   b  which shows the side view of the circuit board and heat sink shown in  FIG. 5   a  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-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. 3   a , the term “right-angle cross” as used herein is a cross of two line segments (arm  36  and arm  34 ) typically at or near their center points  30  at or close to right angles (e.g. about 80-100 degrees). The two line segments are optionally of equal length or unequal length. 
         [0034]    With reference to  FIGS. 3   b  and  3   c  the term “fylfot cross” as used herein has two arms; arm  36  and arm  34  which are crossed a right angles 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. 3   b . 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. 3   b . In  FIG. 3   c , 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. 3   c.    
         [0035]    Reference is now made to  FIGS. 4   a  and  4   b  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 S 1 , S 2 , S 3  and S 4  connected electrically to circuit board  400  via leads  406 . Switches S 1 , S 2 , S 3  and S 4  are preferably insulated gate bipolar junction transistors (IGBTs). Switches S 1 , S 2 , S 3  and S 4  are preferably connected electrically together according to full bridge converter  20  shown in  FIG. 2   a . Circuit board  400  is mechanically attached to heat sink  406  for instance via a screw and pillar arrangement  410 . Switches S 1 , S 2 , S 3  and S 4  are mechanically and thermally attached to heat sink  406 . Cutouts CO 1 , CO 2 , CO 3  and C 04  in circuit board  400  allow the mechanical and thermal attachment of switches S 1 , S 2 , S 3  and S 4  to heat sink  406 . 
         [0036]    The layout of switches S 1 , S 2 , S 3  and S 4  is based upon a right-angle cross topology with dotted lines  404  and  402  forming the two arms of the right-angle cross topology. Switches S 1  and S 4  lay on or symmetrically with respect to arm/axis  402  and switches S 2  and S 3  lay on an arm/axis  404 . The intersection between arm/axis  402  and arm/axis  404 , forms the cross portion of right-angle cross topology. In further embodiments of the present invention, perpendicular offsets of switches S 1 , S 4 , S 2  and S 3  (and cutouts C 01 , CO 2 , CO 3  and C 04  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 S 1 , S 2 , S 3  and S 4  such that while switches S 1  and S 4  are ON, switches S 3  and S 2  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 S 1 , S 2 , S 3  and S 4  flows vertically by convection. Using the plan view of  FIG. 4   a  as the vertical mounting of circuit board  400  and heat sink  406 , layout of switches S 1 , S 2 , S 3  and S 4  are such that for example; the heat in heat sink  406  from switches S 2  and S 3  does not flow near switches S 1  and S 4  and the distance between S 1  and S 4  is such that the vertical flow of heat in heat sink  406  of switches S 1  and S 4  does not affect each other. Alternatively just switches S 1  and S 4  can be offset in either a clockwise or anti-clockwise direction, so that the vertical flow of heat in heat sink  406  of switches S 1  and S 4  does not affect each other. 
         [0037]    In a typical computer aided design/simulation of circuit board  400 , perpendicular offsets of switches S 1 , S 4 , S 2  and S 3  relative to arms/axis  402  and arm/axis  404  respectively and the distance between switches S 1  and S 4  along arm/axis  402  and switches S 2  and S 3  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 S 1 , S 2 , S 3  and S 4  and heat sink  406 . 
         [0038]    Reference is now made to  FIGS. 5   a  and  5   b  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 S 1 , S 2 , S 3  and S 4  connected electrically to circuit board  500  via leads  506 . Switches S 1 , S 2 , S 3  and S 4  are preferably insulated gate bipolar junction transistors (IGBTs). Switches S 1 , S 2 , S 3  and S 4  are preferably connected electrically together according to full bridge converter  20  shown in  FIG. 2   a . Circuit board  500  is mechanically attached to heat sink  506  via a screw and pillar arrangement  510 . Switches S 1 , S 2 , S 3  and S 4  are mechanically and thermally attached to heat sink  506 . Cutouts CO 1 , CO 2 , C 03  and CO 4  in circuit board  500  allow the mechanical and thermal attachment of switches S 1 , S 2 , S 3  and S 4  to heat sink  506 . 
         [0039]    Referring again to  FIG. 5   a , the layout of switches S 1 , S 2 , S 3  and S 4  is based upon a fylfot cross topology. Switches S 1  and S 4  lay parallel to arm/axis  502  and switches S 2  and S 3  lay parallel to arm/axis  504 . The intersection between arm/axis  502  and arm/axis  504 , form the right-angle 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 S 1  and S 4  with respect to arm/axis  502 . Hand  516  and hand  518  represent respectively the offsets of switches S 2  and S 3  with respect to arm/axis  504 . In  FIG. 5   a  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 S 1 , S 2 , S 3  and S 4  flows vertically by convection. Using the plan view of  FIG. 5   a  as an example of vertically mounting circuit board  500  and heat sink  506 , the layout of switches S 1 , S 2 , S 3  and S 4  are such that for example; the vertical flow of heat from switch S 2  does not significantly run into the vertical heat flow of switch S 1 , the vertical flow of heat from switch S 1  does not significantly run into the vertical heat flow of switch S 4  and the vertical flow of heat from switch S 4  does not run significantly into the vertical heat flow of switch S 3 . 
         [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. 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.