Control circuit with energy regulation for voltage regulators and control method thereof

A control circuit for a voltage regulator has an energy regulation circuit and a switching control circuit. The energy regulation circuit provides a regulation signal based on an output voltage, an output current, and a maximum energy reference. The maximum energy reference decreases with increasing of an ambient temperature and increases with decreasing of the ambient temperature. The switching control circuit provides a switching control signal based on the regulation signal to turn ON and turn OFF at least one switch of a plurality of switches of the voltage regulator, such that the output voltage and the output current satisfy a first relationship when the ambient temperature equals a first temperature value, and the output voltage and the output current satisfy a second relationship when the ambient temperature equals a second temperature value.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of CN application 202210219329.1, filed on Mar. 8, 2022, and incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to electronic circuits, and more particularly, relates to control circuits for voltage regulators and control methods thereof.

2. Description of Related Art

In power supplies for microprocessors with high current and low voltage, the power performance, especially the transient response is vital. To reduce voltage deviations of an output voltage (i.e., a power supply for microprocessors) during load transient, and to reduce power dissipation of the microprocessors when a load current increases, adaptive voltage position (AVP) control is widely used to insure the system stability.

The basic principle of traditional AVP control is shown inFIG.1. An output voltage Vo decreases linearly from a voltage level V1to a voltage level V2, as an output current Io (i.e. load current) increases from a minimum value (e.g., from zero Amps) to a maximum load point Im, wherein the voltage level V1may be a reference voltage set according to a voltage identification code (VID) provided by a microprocessor.

Power dissipation increases rapidly with fast development of the microprocessors, which also brings problems of heat dissipation of the microprocessors. Thus, an improved voltage regulator with better power management is in high demand to help the microprocessors with thermal management.

SUMMARY OF THE INVENTION

Embodiments of the present invention are directed to a control circuit for a voltage regulator, comprising an energy regulation circuit, a voltage reference regulation circuit, and a switching control signal generating circuit. The voltage regulator is configured to provide an output voltage and an output current. The energy regulation circuit is configured to provide an output energy based on the output voltage and the output current, provide a maximum energy reference based on an ambient temperature, and provide a regulation signal based on the output energy and the maximum energy reference. The maximum energy reference is configured to decrease with increasing of the ambient temperature and increase with decreasing of the ambient temperature. The voltage reference regulation circuit is configured to receive the regulation signal, and provide an output voltage reference based on a target voltage and the regulation signal, wherein the output voltage reference varies with the regulation signal. The switching control signal generating circuit is configured to provide a switching control signal based on the output voltage reference and the output voltage to turn ON and turn OFF at least one switch of the voltage regulator.

Embodiments of the present invention are directed to a control circuit for a voltage regulator, comprising an energy regulation circuit and a switching control circuit. The voltage regulator is configured to provide an output voltage and an output current. The energy regulation circuit is configured to provide a regulation signal based on the output voltage, the output current, and a maximum energy reference. The maximum energy reference is configured to change reversely with an ambient temperature. The switching control circuit is configured to receive the regulation signal and provide a switching control signal based on the regulation signal to turn ON and turn OFF at least one switch of the voltage regulator, such that the output voltage and the output current satisfy a first relationship when the ambient temperature is equal to a first temperature value, and the output voltage and the output current satisfy a second relationship when the ambient temperature is equal to a second temperature value.

Embodiments of the present invention are directed to a control method for a voltage regulator. The voltage regulator is configured to provide an output voltage and an output current. The control method comprises providing an output energy based on the output voltage and the output current, providing a maximum energy reference based on an ambient temperature, wherein the maximum energy reference reversely changes with the ambient temperature, and providing a switching control signal based on the regulation signal to turn ON and turn OFF at least one switch of the voltage regulator. As a result, the output voltage and the output current satisfy a first relationship when the ambient temperature equals a first temperature value, and the output voltage and the output current satisfy a second relationship when the ambient temperature equals a second temperature value.

DETAILED DESCRIPTION OF THE INVENTION

A voltage regulator illustrated in the embodiments provides an output voltage and an output current for a load. A control circuit for the voltage regulator illustrated in the embodiments comprises an energy regulation circuit and a switching control circuit. The energy regulation circuit provides a regulation signal based on the output voltage, the output current and a maximum energy reference, wherein the maximum energy reference decreases with increasing of an ambient temperature and increases with decreasing of the ambient temperature. The switching control circuit generates a switching control signal based on the regulation signal to turn ON and turn OFF at least one switch of the voltage regulator, such that the output voltage and the output current satisfy a first relationship when the ambient temperature is equal to a first temperature value, and the output voltage and the output current satisfy a second relationship when the ambient temperature is equal to a second temperature value. In one embodiment, the first relationship comprises that the output voltage and the output current vary along a first curve, and the second relationship comprises that the output voltage and the output current vary along a second curve. The control circuit can easily realize reliable energy management from the voltage regulator side, and can further ensure safe operation of the load while continuously providing the load with high-power energy.

FIG.2schematically shows a voltage regulator20in accordance with an embodiment of the present invention. The voltage regulator20provides an output voltage Vo and an output current Io for the load. The load of the voltage regulator20may be but not be limited to a central processing unit (CPU), a graphics processing unit (GPU), etc. The load may adjust its operating frequency based on its junction temperature, and send out a command to change the output voltage Vo of the voltage regulator20, but the response is slow. To suppress power dissipation before an over temperature event of the load occurs, the voltage regulator20actively regulates the output voltage Vo, the output current Io, or an output power Pload before the load sends out the command to change the output voltage Vo of the voltage regulator20, and thus realizes energy management ahead of time.

In the embodiment ofFIG.2, the voltage regulator20comprises a switching circuit210and a control circuit220. The switching circuit210may be a buck circuit, a boost circuit, a buck-boost circuit, or any other suitable circuit topology. The control circuit220comprises an energy regulation circuit22and a switching control circuit23. As shown inFIG.2, the energy regulation circuit22receives a voltage sensing signal Vdiff representative of the output voltage Vo, a current sensing signal Isum representative of the output current Io, and a temperature sensing signal Tasen representative of an ambient temperature Ta, and provides a regulation signal Jloop based on the output voltage Vo, the output current Io and the ambient temperature Ta to adjust an output energy Jout of the voltage regulator20within a time period. In one embodiment, the energy regulation circuit22generates a maximum energy reference Jmax based on the ambient temperature Ta, and provides the regulation signal Jloop based on the output voltage Vo, the output current Io and the maximum energy reference Jmax, wherein the maximum energy reference Jmax reversely changes with the ambient temperature Ta. For example, the maximum energy reference Jmax decreases with increasing of the ambient temperature Ta, and increases with decreasing of the ambient temperature Ta. In one embodiment, the temperature sensing signal Tasen may be but not be limited to the ambient temperature sampled by the control circuit220, a junction temperature of an integrated circuit (IC) where the control circuit220is located, the ambient temperature sampled by the load (e.g., a case temperature, a heatsink temperature, etc.), or the ambient temperature sampled by another power management IC (e.g., a junction temperature, a case temperature, or a heatsink temperature of the power management IC, etc.). The temperature sampled by the load or by another power management IC may be sent to the control circuit220via a communication bus.

The switching control circuit23is coupled to the energy regulation circuit22to receive the regulation signal Jloop. The switching control circuit23generates a switching control signal PWM1based on the regulation signal Jloop to turn ON and turn OFF at least one switch of the switching circuit210, such that the output voltage Vo and the output current Io satisfy a first relationship when the ambient temperature Ta equals the first temperature value, and the output voltage Vo and the output current Io satisfy a second relationship when the ambient temperature Ta equals the second temperature value. In one embodiment, the voltage regulator20comprises a voltage control state to regulate the output voltage Vo and a power control state to regulate an output power, when the voltage regulator20operates in the power control state and when the second temperature value is larger than the first temperature value, a product of the output voltage Vo and the output current Io under the second relationship is smaller than the product of the output voltage Vo and the output current Io under the first relationship.

FIGS.3A-3Cshow curves31-33of the output voltage Vo versus the output current Io in accordance with an embodiment of the present invention, wherein the vertical axis represents the output voltage Vo, and the horizontal axis represents the output current Io. The curve31shows the output voltage Vo and the output current Io which satisfy the first relationship when the ambient temperature Ta equals the first temperature value (e.g., 25° C.), the curve32shows the output voltage Vo and the output current Io which satisfy the second relationship when the ambient temperature Ta equals the second temperature value (e.g., 50° C.), and the curve33shows the output voltage Vo and the output current Io which satisfy the third relationship when the ambient temperature Ta equals the third temperature value (e.g., 75° C.). One with ordinary skill in the art should understand that the curves of the output voltage Vo versus the output current Io are not limited by the curves31-33shown inFIGS.3A-3C. For example, more curves of the output voltage Vo versus the output current Io under different ambient temperatures may be included, and curves of the output voltage Vo versus the output current Io may comprise other shapes different from the curves31-33shown inFIGS.3A-3C.

In one embodiment, when the output current Io is smaller than a current threshold Ith, the voltage regulator20operates in the voltage control state, for example, controlling the output voltage Vo constant or equal to a programmable voltage reference. When the output current Io is larger than the current threshold Ith, the voltage regulator20operates in the power control state, for example, controlling the output power Pload constant or equal to a programmable power reference. During the power control state, the output voltage Vo decreases with increasing of the output current Io. Until the output voltage Vo decreases to a minimum voltage threshold Vmin, the voltage regulator20operates in the voltage control state again, for example, controlling the output voltage Vo equal to the minimum voltage threshold Vmin. The current threshold Ith decreases with increasing of the ambient temperature Ta, and increases with decreasing of the ambient temperature Ta. In the example ofFIG.3A, when the ambient temperature Ta is equal to the first temperature value (refer to the curve31), if the output current Io is smaller than a current threshold Ith_1, then the output voltage Vo is controlled constant (e.g., equal to a maximum target voltage Vmax), and if the output current Io is larger than the current threshold Ith_1, then the product of the output voltage Vo and the output current Io (Vo*Io, i.e., the output power Pload) is controlled equal to a first power P1(e.g., 750 W). When the ambient temperature Ta is equal to the second temperature value (refer to the curve32), if the output current Io is smaller than a current threshold Ith_2, then the output voltage Vo is controlled constant (e.g., equal to the maximum target voltage Vmax), and if the output current Io is larger than the current threshold Ith_2, then the product of the output voltage Vo and the output current Io (Vo*Io) is controlled equal to a second power P2(e.g., 500 W). When the ambient temperature Ta is equal to a third temperature value (refer to the curve33), if the output current Io is smaller than a current threshold Ith_3, then the output voltage Vo is controlled constant (e.g., equal to the maximum target voltage Vmax), and if the output current Io is larger than the current threshold Ith_3, then the product of the output voltage Vo and the output current Io (Vo*Io) is controlled equal to a third power P3(e.g., 250 W). In the examples ofFIGS.3B-3C, with different ambient temperatures Ta, if the output current Io is larger than the corresponding current threshold Ith, the output voltage Vo varies along the curves31-33fitted by multiple straight lines as the output current Io increases.

FIG.4schematically shows the energy regulation circuit22in accordance with an embodiment of the present invention. The energy regulation circuit22generates the output energy Jout based on the output voltage Vo and the output current Io, and generates the maximum energy reference Jmax based on the ambient temperature Ta. The maximum energy reference Jmax decreases with increasing of the ambient temperature Ta, and increases with decreasing of the ambient temperature Ta. The energy regulation circuit22further generates the regulation signal Jloop based on the output energy Jout and the maximum energy reference Jmax. In one embodiment, the energy regulation circuit22may generate the output energy Jout by integrating the product of the output voltage Vo and the output current Io within a certain time period.

As shown inFIG.4, the energy regulation circuit22comprises a calculation circuit221, an integral circuit222, and a control loop223. One with ordinary skill in the art should understand that the detailed circuit structure of the energy regulation circuit22is not limited by the example shown inFIG.4. The calculation circuit221receives the temperature sensing signal Tasen, and generates the maximum energy reference Jmax based on the temperature sensing signal Tasen and a preset maximum energy reference Jb. For example, the maximum energy reference Jmax may be generated based on but not limited to a following formula (1), wherein “a” is a coefficient, and Ta_base is a temperature reference. In one example, the preset maximum energy reference Jb may be written via the communication bus, or be preset. The preset maximum energy reference Jb is the maximum energy reference Jmax when the temperature sensing signal Tasen equals the temperature reference Ta_base.
Jmax=Jb−a*(Tasen−Ta_base)  (1)

The integral circuit222receives the voltage sensing signal Vdiff and the current sensing signal Isum, and generates the output energy Jout based on, for example, a following formula (2), i.e., generating the output energy Jout by integrating a product of the voltage sensing signal Vdiff and the current sensing signal Isum in a time period Δt. The integral circuit222may be realized using an analog circuit or a digital circuit.
Jout=∫tt+ΔtVdiff*Isum  (2)

The control loop223receives the output energy Jout and the maximum energy reference Jmax, and generates the regulation signal Jloop based on the output energy Jout and the maximum energy reference Jmax. As an example and not by way of limitation, a difference between the output energy Jout and the maximum energy reference Jmax (Jout-Jmax) is loop regulated, e.g., is proportional integral (PI) regulated.

In one embodiment, when the output energy Jout is smaller than a regulation threshold, the control loop223is reset, and the regulation signal Jloop is default (e.g., zero). In other words, the regulation signal stops regulating the switching control signal in response to the output energy Jout being smaller than the regulation threshold. The regulation threshold is smaller than or equal to the maximum energy reference Jmax. For example, the regulation threshold may be equal to the maximum energy reference Jmax minus a hysteresis Hys (Jmax−Hys). The hysteresis Hys provides an opposite regulation with the loop regulation (e.g., the PI regulation and so on), which makes it easier to find a stable quiescent point for the regulation signal Jloop and thus improves the stability of the system.

FIG.5schematically shows the integral circuit222in accordance with an embodiment of the present invention. In the example ofFIG.5, the integral circuit222is a digital circuit for illustration, and one with ordinary skill in the art should understand that the detailed circuit structure of the integral circuit222is not limited by the example shown inFIG.5. In the example ofFIG.5, an analog-digital converter51receives the voltage sensing signal Vdiff, and provides a digital signal DV via analog to digital conversion, and an analog-digital converter51receives the current sensing signal Isum, and provides a digital signal DI via analog to digital conversion. A multiplication circuit53receives the digital signal DV and the digital signal DI, and provides a signal Multi. In one embodiment, the multiplication circuit53may be realized using adders. An accumulation circuit54receives the signal Multi, and generates the output energy Jout by accumulating the signal Multi within a certain time period.

FIG.6schematically shows the switching control circuit23in accordance with an embodiment of the present invention. As shown inFIG.6, the switching control circuit23comprises a voltage reference regulation circuit71, a switching control signal generating circuit72, and an alert circuit73.

The voltage reference regulation circuit71receives the regulation signal Jloop, and provides an output voltage reference Vref based on a target voltage Vtgt and the regulation signal Jloop, wherein the output voltage reference Vref is used to set the output voltage Vo, and the output voltage reference Vref changes dynamically with the change of the regulation signal Jloop. In one embodiment, the target voltage Vtgt may be written via the communication bus, be set by passive devices, be set by a voltage identification code VID which is provided by the load, or be preset. In one embodiment, the regulation signal Jloop stops regulating the output voltage reference Vref in response to the output energy Jout being smaller than the regulation threshold. As shown inFIG.6, the voltage reference regulation circuit71comprises a subtracting circuit711, a clipper circuit712, and a digital-analog converting circuit713. The subtracting circuit711receives the target voltage Vtgt and the regulation signal Jloop, and provides a difference value VIDx between the target voltage Vtgt and the regulation signal Jloop, wherein the difference value VIDx is equal to the target voltage Vtgt minus the regulation signal Jloop (Vtgt-Jloop). The clipper circuit712receives the difference value VIDx, and provides a dynamic voltage reference signal DVID by clipping the difference value VIDx. In one embodiment, the clipper circuit712controls the output voltage reference Vref to not be larger than the target voltage Vtgt by limiting a maximum value of the dynamic voltage reference signal DVID based on the target voltage Vtgt, and controls the output voltage reference Vref to not be smaller than the minimum voltage threshold Vmin by limiting the minimum value of the dynamic voltage reference signal DVID based on the minimum voltage threshold Vmin. The digital-analog converting circuit713converts the dynamic voltage reference signal DVID to generate the output voltage reference Vref.

The switching control signal generating circuit72generates the switching control signal PWM1based on the output voltage reference Vref and the output voltage Vo to turn ON and turn OFF the at least one switch of the switching circuit210. The embodiment ofFIG.6employs constant ON time control as an example, and one with ordinary skill in the art should understand that other control methods, e.g., peak current mode control, may also be used in the present invention. As shown inFIG.6, when the voltage sensing signal Vdiff is smaller than the output voltage reference Vref, a comparison signal SET is active so that the at least one switch of the switching circuit210is turned ON by the switching control signal PWM1, and the at least one switch is turned OFF by the switching control signal PWM1when an ON time period of the at least one switch reaches a preset time period. In the example ofFIG.6, the switching control signal generating circuit72comprises a comparison circuit722, an ON time control circuit723and a logic circuit724. A non-inverting input terminal of the comparison circuit722receives the output voltage reference Vref, an inverting input terminal of the comparison circuit722receives the voltage sensing signal Vdiff, and the comparison signal SET is provided at an output terminal of the comparison circuit722by comparing the output voltage reference Vref with the voltage sensing signal Vdiff. The ON time control circuit723provides an ON time control signal COT based on the switching control signal PWM1and an ON time signal TON. The logic circuit724receives the comparison signal SET and the ON time control signal COT, and provides the switching control signal PWM1based on the comparison signal SET and the ON time control signal COT. For example, the logic circuit724may be an RS flip-flop.

The alert circuit73provides an alert signal Alt1and an alert signal Alt2. When the output voltage reference Vref is different with the target voltage Vtgt, the alert signal Alt1indicates that the output energy is being regulated. When the output voltage reference Vref is equal to the minimum voltage threshold Vmin, the alert signal Alt2indicates that a regulation of the voltage regulator20has reached an upper limit.

FIG.7schematically shows the switching control circuit23in accordance with another embodiment of the present invention. As shown inFIG.7, the switching control circuit23comprises a current reference regulation circuit81, a switching control signal generating circuit82, and an alert circuit83.

The current reference regulation circuit81receives a maximum target current Imax and the regulation signal Jloop, and provides a maximum output current reference Iref based on the maximum target current Imax and the regulation signal Jloop. The maximum output current reference Iref is employed to set a maximum value of the output current Io, and the maximum output current reference Iref changes dynamically with the regulation signal Jloop. In one embodiment, the maximum target current Imax may be written via the communication bus, or be preset. As shown inFIG.7, the current reference regulation circuit81comprises a subtracting circuit811, a clipper circuit812, and a digital-analog converting circuit813. The subtracting circuit811receives the maximum target current Imax and the regulation signal Jloop, and provides a difference value Ix between the maximum target current Imax and the regulation signal Jloop, wherein the difference value Ix is equal to the maximum target current Imax minus the regulation signal Jloop (Imax−Jloop). The clipper circuit812receives the difference value Ix, and provides a dynamic output current reference signal DImax by clipping the difference value Ix. In one embodiment, the clipper circuit812controls the maximum output current reference Iref to not be larger than the maximum target current Imax by limiting the maximum value of the dynamic output current reference signal DImax based on the maximum target current Imax. The digital-analog converting circuit813receives the dynamic output current reference signal DImax and provides the maximum output current reference Iref via digital to analog conversion.

The switching control signal generating circuit82generates the switching control signal PWM1based on the output voltage reference Vref, the maximum output current reference Iref, the current sensing signal Isum, and the voltage sensing signal Vdiff to turn ON and turn OFF the at least one switch of the switching circuit210. In one example, the output voltage reference Vref may be generated based on the target voltage Vtgt. The embodiment ofFIG.7employs constant ON time control as an example, and one with ordinary skill in the art should understand that other control methods, e.g., peak current mode control, may also be used in the present invention. As shown inFIG.7, when the voltage sensing signal Vdiff is smaller than the output voltage reference Vref and the current sensing signal Isum is smaller than the maximum output current reference Iref, a set signal S1is active so that the at least one switch of the switching circuit210is turned ON by the switching control signal PWM1, and the at least one switch is turned OFF by the switching control signal PWM1when the ON time period of the at least one switch reaches a preset time period. One with ordinary skill in the art should understand that the control scheme of the output current Io is not limited by the circuit structure shown inFIG.7, and may also comprise any other suitable circuit structures which are not departed from the spirit and the scope of the present invention. In the example ofFIG.7, the switching control signal generating circuit82comprises a comparison circuit821, a comparison circuit822, a logic circuit823, an ON time control circuit824and a logic circuit825. A non-inverting input terminal of the comparison circuit821receives the maximum output current reference Iref, an inverting input terminal of the comparison circuit821receives the current sensing signal Isum, and a comparison signal Ocl is provided at an output terminal of the comparison circuit821by comparing the maximum output current reference Iref and the current sensing signal Isum. A non-inverting input terminal of the comparison circuit822receives the output voltage reference Vref, an inverting input terminal of the comparison circuit822receives the voltage sensing signal Vdiff, and an output terminal of the comparison circuit822provides the comparison signal SET by comparing the output voltage reference Vref and the voltage sensing signal Vdiff. The logic circuit823provides the set signal S1based on the comparison signal SET and the comparison signal Ocl. In one embodiment, the logic circuit823comprises an AND gate, wherein a first input terminal of the AND gate receives the comparison signal Ocl, a second input terminal of the AND gate receives the comparison signal SET, and the set signal S1is provided at an output terminal of the AND gate. The ON time control circuit824provides an ON time control signal COT based on the switching control signal PWM1and an ON time signal TON. The logic circuit825receives the set signal S1and the ON time control signal COT, and provides the switching control signal PWM1based on the set signal S1and the ON time control signal COT. For example, the logic circuit825may comprise an RS flip-flop.

The alert circuit83provides the alert signal Alt1based on the maximum output current reference Iref. When the maximum output current reference Iref is different with the maximum target current Imax, the alert signal Alt1indicates that the output energy is being regulated.

FIG.8schematically shows the voltage regulator20in accordance with another embodiment of the present invention. In one embodiment, the switching circuit210comprises a plurality of phases, and the switching control circuit23generates a plurality of switching control signals PWM1, PWM2, . . . , and PWMn based on the regulation signal Jloop, the output voltage Vo and the output current Io, and thus successively turns ON and turns OFF the at least one switch of each phase of the switching circuit210.

FIG.9illustrates a control method900for a voltage regulator in accordance with an embodiment of the present invention, wherein the control method900comprises steps S11-S14. The voltage regulator provides an output voltage and an output current for a load.

In step S11, generating an output energy based on the output voltage and the output current.

In step S12, generating a maximum energy reference based on an ambient temperature, wherein the maximum energy reference reversely changes with the ambient temperature.

In step S13, generating a regulation signal based on the output energy and the maximum energy reference.

In step S14, generating a switching control signal based on the regulation signal to turn ON and turn OFF at least one switch of the voltage regulator, and thus controlling the output voltage and the output current to vary along a first curve when the ambient temperature equals a first temperature value, and to vary along a second curve when the ambient temperature equals a second temperature value. In other words, the output voltage and the output current satisfy the first relationship when the ambient temperature equals a first temperature value, and varies the second curve when the ambient temperature equals a second temperature value. Wherein the operation of the voltage regulator comprises a voltage control state to regulate the output voltage and a power control state to regulate an output power. When the second temperature value is larger than the first temperature value and the voltage regulator operates in the power control state, a product of the output voltage Vo and the output current Io which vary along the second curve is smaller than the product of the output voltage Vo and the output current Io which vary along the first curve.

In one embodiment, generating the switching control signal based on the regulation signal further comprises generating an output voltage reference based on a target voltage and the regulation signal, and generating the switching control signal based on the output voltage reference and the output voltage to turn ON and turn OFF the at least one switch of the switching circuit, wherein the output voltage reference changes dynamically with the regulation signal.

In another embodiment, generating the switching control signal based on the regulation signal further comprises generating a maximum output current reference based on a maximum target current and the regulation signal, and generating the switching control signal based on the target voltage, the maximum output current reference, the output voltage and the output current to turn ON and turn OFF the at least one switch of the switching circuit, wherein the maximum output current reference changes dynamically with the regulation signal.

Note that in the flowchart described above, the functions indicated in the boxes can also occur in a different order than those shown inFIG.9. Fox example, two boxes presented one after another can actually be executed essentially at the same time, or sometimes in reverse order, depending on the specific functionality involved.

Obviously many modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described. It should be understood, of course, the foregoing disclosure relates only to a preferred embodiment (or embodiments) of the invention and that numerous modifications may be made therein without departing from the spirit and the scope of the invention as set forth in the appended claims. Various modifications are contemplated and they obviously will be resorted to by those skilled in the art without departing from the spirit and the scope of the invention as hereinafter defined by the appended claims as only a preferred embodiment(s) thereof has been disclosed.