# Patent

## Title
Power saving circuit

## Abstract

A power saving circuit (PSC) may include a first circuit and a second circuit electrically coupled in series in a power sharing configuration. The PSC may further include a regulator that is electrically coupled to a first node between the first and second circuits. The regulator can supply current to the first node when the first circuit requires less current or the second circuit requires more current, and the regulator can remove current from the first node when the first circuit requires more current or the second circuit requires less current.

## Background
INCORPORATION BY REFERENCE
This Application is a continuation of U.S. application Ser. No. 11/777,758, filed Jul. 13, 2007, which claims priority under 35 U.S.C. §119(e) to U.S. Provisional Application No. 60/831,804, filed Jul. 19, 2006. The disclosures of the applications referenced above are incorporated herein by reference.


BACKGROUND
The present disclosure relates to a power saving circuit, and more particularly to a power saving circuit capable of controlling an amount of current flowing through a load circuit by regulating a voltage of a node.
Power saving circuits are incorporated into a vast number of devices used in everyday life. For example, power saving circuits are used in automobile engines, cellular telephones, magnetic hard disk drives, fiber optic communication systems, and even children's toys.
Unfortunately, many power saving circuits suffer from such performance shortfalls as limited cross-talk control and interference decoupling. In a power sharing configuration, any variance in the power requirement of a first circuit may substantially vary the power available to a second circuit, thus having a detrimental effect on the operation of the second circuit. The variance in the power requirement of a circuit may be due to either a predetermined change in the operation of the circuit, manufacturing process variations, response to environmental circumstances, or the like.
Power saving circuits having limited cross-talk and interference control may not sufficiently lessen the effect of the variance of one circuit's power requirements on another circuit, and thus, result in improper operation of the circuits and inefficient use of power. Accordingly, it should be appreciated that, either due to the internal or external factors discussed above, a particular power saving circuit may cross-couple dynamic current or voltage fluctuations of one circuit to another to the detriment of the system incorporating the power saving circuit.
SUMMARY OF THE DISCLOSURE
A power saving circuit (PSC) is disclosed that includes a first circuit and a second circuit electrically coupled in series in a power sharing configuration. The PSC may further include a regulator that is electrically coupled to a first node between the first and second circuits. The regulator can supply current to the first node when the first circuit requires less current or the second circuit requires more current, and the regulator can remove current from the first node when the first circuit requires more current or the second circuit requires less current.
The regulator determines whether to supply or remove current by comparing a first reference voltage with a first node voltage, so that when the first node voltage is less than the first reference voltage, the regulator increases an amount of current supplied to the first node, and when the first node voltage is greater than the first reference voltage, the regulator decreases an amount of current supplied to the first node.
The PSC can further include a first voltage controlling circuit that is coupled between the first circuit and the first node, and a second voltage controlling circuit that is coupled between the first node and the second circuit. The first voltage controlling circuit can include a first transistor coupled in series between the first circuit and the first node, and a first amplifier having its non-inverting input coupled to a second reference voltage, its inverting input coupled to a second node between the first circuit and the first transistor, and its output coupled to the gate of the first transistor. Similarly, the second voltage controlling circuit can include a second transistor coupled in series between the second circuit and the first node, and a second amplifier having its non-inverting input coupled to a third reference voltage, its inverting input coupled to a third node between the second circuit and the first transistor, and its output coupled to the gate of the second transistor.
The first voltage controlling circuit compares the second reference voltage with a voltage of the second node, so that when the second node voltage is less than the second reference voltage, the first voltage controlling circuit increases a resistance between the source and drain of the first transistor, and when the second node voltage is greater than the second reference voltage, the first voltage controlling circuit decreases a resistance between the source and drain of the first transistor. Similarly, the second voltage controlling circuit compares the third reference voltage with a of the third node, so that when the third node voltage is less than the third reference voltage, the second voltage controlling circuit increases a resistance between the source and drain of the second transistor, and when the third node voltage is greater than the third reference voltage, the second voltage controlling circuit decreases a resistance between the source and drain of the second transistor.



BRIEF DESCRIPTION OF THE DRAWINGS
Embodiments of the power-saving circuit (PSC) will be described with reference to the following drawings, wherein like numerals designate like elements, and wherein:
FIG. 1 shows a block diagram of an exemplary circuit configuration of PSC;
FIG. 2 shows a first exemplary PSC scheme;
FIG. 3 shows a second exemplary PSC scheme;
FIG. 4 shows a flow-chart of an exemplary PSC process for regulating voltage at one node; and
FIG. 5 shows a flow-chart of an exemplary PSC process for regulating voltage at more than one node.



DETAILED DESCRIPTION OF EMBODIMENTS
In the following descriptions, many of the exemplary circuits are shown to include n-channel metal-oxide-semiconductor field-effect transistors (MOSFETs) in a variety of configurations. While MOSFET devices are used by example, the disclosed circuits may be implemented using any number of other transistor types, such as J-FETs, bipolar transistors, and the like. Additionally, while n-channel devices are used in the following examples, the same general approaches may also apply to circuits incorporating p-channel FETs or PNP bipolar transistors, for example.
Still further, while the terms “drain” and “source” are used for ease of explanation and to adhere to traditional engineering usage, it should be recognized that a drain and source of a FET transistor may be considered interchangeable, and for the following descriptions merely thought of as a first end and a second end of a semiconductor channel unless otherwise stated or apparent to one of ordinary skill in the art.
FIG. 1 shows a block diagram of an exemplary configuration of a power-saving circuit (PSC) 100 that may include a first circuit 110, a regulator 150, and a second circuit 120 coupled in series between a supply voltage VDD and a ground GND. Generally, the arrangement is a power sharing configuration between the first circuit 110 and second circuit 120. As can be seen, currents I1 and I2 are the electric currents flowing through first circuit 110 and second circuit 120, respectively.
In this configuration, regulator 150 can be any device that ensures that a voltage of at least one node (not shown) located between first circuit 110 and second circuit 120 is substantially constant during operation by regulating the amount of current flowing through that node. For example, a regulator 150 can include one or more voltage amplifiers, current amplifiers, operational amplifiers, transconductance amplifiers, transimpedance amplifiers, differential pairs, pulse width modulation devices, switching regulators, or the like. By regulating an amount of current at the node, the dynamic current usage of the first circuit 110 can be isolated from the second circuit 120, and vice versa. Thus, the operation of the first circuit 110 should not interfere with that of the second circuit 120, and vice versa.
It should be understood that first and second circuits 110 and 120 are not limited to any particular circuit and can be any digital, analog, or mixed signal load circuit including any combination of active and passive electronic devices or the like.
During operation, the PSC 100 operates to reduce or eliminate interference between first circuit 110 and second circuit 120, which can occur as a result of the power sharing configuration. For example, when first circuit 110 and second circuit 120 dynamically require more or less power, and therefore require more or less current, a change in the power requirements of the first circuit 110 can affect the current available to second circuit 120, and vice versa. By monitoring a voltage between first and second circuits 110 and 120, regulator 150 can adjust the current passing between the first and second circuits 110 and 120 so that dynamic current usage by first circuit 110 does not affect the current usage of second circuit 120, and vice versa.
While FIG. 1 only shows first and second circuits 110 and 120, and a single voltage regulator 150, it should be understood that any number of circuits may be provided with any number of voltage regulators. Furthermore, in order to facilitate ease of understanding, the operation of the exemplary embodiments of the PSC will be described with the assumption that first and second circuits 110 and 120 are treated as variable resistors.
As shown in FIG. 2, regulator 250, which corresponds to regulator 150, can include an amplifier AMPA and a capacitor C201. In this case, amplifier AMPA of PSC 200 has a non-inverting terminal coupled to a reference voltage supply circuit (not shown) that applies a reference voltage VREF—A to the non-inverting terminal. Further, both an inverting input terminal and an output terminal of amplifier AMPA, as well as first circuit 110 and second circuit 120 are coupled together at node A. As also shown, capacitor C201 can be coupled in series between node A and power supply GND in order to further stabilize the voltage at node A and also possibly to reduce or prevent any high frequency components of the current flowing through node A.
In the configuration shown in FIG. 2, amplifier AMPA maintains node A at a reference voltage VREF—A. As described above, during operation, first and second circuits 110 and 120 may dynamically require more or less power, and thus, more or less current. As the requirement for current of either one or both of first and second circuits 110 and 120 changes, these circuits adjust their respective equivalent resistance in order to change an amount of current they draw, and thus, change the voltage at node A. Amplifier AMPA senses this voltage change and adjusts the voltage at node A back to reference voltage VREF—A by feeding or sinking an amount of electric current I3 at node A.
For example, when first circuit 110 draws a first current I1 from VDD, second circuit 120 draws a second current I2 from node A, and when first currents I1 and I2 are equal, the voltage at node A is equal to reference voltage VREF—A. Under these circumstances, because amplifier AMPA detects no change in the voltage at node A, it does not pass an additional third current I3 through node A.
If, however, first circuit 110 requires more current, amplifier AMPA will sink third current I3 from node A, and allow first circuit 110 to draw more current from VDD, thus, satisfying first circuit's 110 need for more current while maintaining node A at reference voltage VREF—A. Specifically, when first circuit 110 requires more current, it will lower its equivalent resistance. Consequently, this will decrease the voltage drop across terminals 1 and 2 of first circuit 110, and thus, increase the voltage at node A to a voltage greater than VREF—A. Amplifier AMPA will sense that node A is at a voltage greater than VREF—A, and will begin to sink third current I3 from node A.
In this case, first current I1 will increase by an amount equivalent to third current I3. The increase of first current I1 will increase the voltage drop across terminals 1 and 2 of first circuit 110, and, as a result, lower the voltage at node A back to reference voltage VREF—A. Accordingly, second current I2 will remain substantially unchanged because the additional current that first circuit 110 will be drawing from VDD will be drawn out by amplifier AMPA at node A. This situation results in a relationship between I1, I2, and I3 illustrated by equation (1) shown below.

I1=I2+I3  (1)

On the other hand, if first circuit 110 requires less current, amplifier AMPA will feed third current I3 into node A, and allow first circuit 110 to draw less current from VDD, thus, satisfying first circuit's 110 need for less current while maintaining node A at reference voltage VREF—A. Specifically, when first circuit requires less current, it will increase its equivalent resistance. Consequently, this will increase the voltage drop across terminals 1 and 2 of first circuit 110, and thus, lower the voltage at node A to a voltage less than VREF—A. Amplifier AMPA will sense that node A is at a voltage less than VREF—A, and will begin to feed third current I3 into node A.
In this case, first current I1 will decrease by an amount equivalent to third current I3. The decrease of first current I1 will decrease the voltage drop across terminals 1 and 2 of first circuit 110, and, as a result, raise the voltage at node A back to reference voltage VREF—A. Accordingly, second current I2 will remain substantially unchanged because amplifier AMPA will supply second circuit 120 to compensate for the reduction in first current I1 passing through first circuit 110. This situation results in a relationship between I1, I2, and I3 illustrated by equation (2) shown below.

I1=I2−I3  (2)

When second circuit 120 requires more current, amplifier AMPA will feed third current I3 into node A, and allow second circuit 120 to draw more current from node A, thus, satisfying second circuit's 120 need for more current while maintaining node A at reference voltage VREF—A. Specifically, when second circuit requires more current, it will lower its equivalent resistance. Consequently, this will decrease the voltage drop across terminals 1 and 2 of second circuit 120, and thus, lower the voltage at node A to a voltage less than VREF—A. Amplifier AMPA will sense that node A is at a voltage less than VREF—A, and will begin to feed third current I3 into node A.
In this case, second current I2 will increase by an amount equivalent to third current I3. The increase of second current I2 will increase the voltage drop across terminals 1 and 2 of second circuit 120, and, as a result, increase the voltage at node A back to reference voltage VREF—A. Accordingly, first current I1 will remain substantially unchanged because the additional current required by second circuit 120 will be supplied by amplifier AMPA via node A. This situation results in a relationship between I1, I2, and I3 illustrated by equation (3) shown below.

I2=I1+I3  (3)

Conversely, when second circuit 120 requires less current, amplifier AMPA will sink third current I3 from node A, and allow second circuit 120 to draw less current from node A, thus, satisfying second circuit's 120 need for less current while maintaining node A at reference voltage VREF—A. Specifically, when second circuit requires less current, it will raise its equivalent resistance. Consequently, this will raise the voltage drop across terminals 1 and 2 of second circuit 120, and thus, raise the voltage at node A to a voltage greater than VREF—A. Amplifier AMPA will sense that node A is at a voltage greater than VREF—A, and will begin to sink third current I3 from node A.
In this case, second current I2 will decrease by an amount equivalent to third current I3. The decrease of second current I2 will decrease the voltage drop across terminals 1 and 2 of second circuit 120, and, as a result, lower the voltage at node A back to reference voltage VREF—A. Accordingly, first current I1 will remain substantially unchanged because the additional current not used by second circuit 120 will be drawn out of node A via amplifier AMPA. This situation results in a relationship between I1, I2, and I3 illustrated by equation (4) shown below.

I2=I1−I3  (4)

FIG. 3 shows an exemplary schematic diagram of PSC 300 that includes first circuit 110, second circuit 120, transistors TP and TN, capacitors C301 and C302, and amplifiers AMPA, AMPB, and AMPC. PSC 300 includes nodes A, B, C, P, and N. As shown, node A couples drain terminals of transistors TP and TN and an inverting input terminal and an output terminal of AMPA; node B couples second terminals of first circuit 110 and capacitor C301, a source terminal of transistor TP, and an inverting input terminal of amplifier AMPB; node C couples first terminals of second circuit 120 and capacitor C302, a source terminal of transistor TN, and an inverting input terminal of amplifier AMPC; node P couples an output terminal of amplifier AMPB and a gate terminal of transistor TP; and node N couples an output terminal of amplifier AMPC and a gate terminal of transistor TN. A reference voltage supply circuit (not shown) is coupled to and applies reference voltages VREF—A, VREF—B, and VREF—C to non-inverting terminals of amplifiers AMPA, AMPB, and AMPC, respectively. First terminals of first circuit 110 and capacitor C301 are coupled to VDD; and second terminals of second circuit 120 and capacitor C302 are coupled to GND.
Capacitors C301 and C302 can be added in order to reduce or prevent the high frequency noise components of first and second currents I1 and I2, respectively.
Reference voltages VREF—A, VREF—B, and VREF—C are the voltages at which amplifiers AMPA, AMPB, and AMPC maintain nodes A, B, and C, respectively. It should be understood that the reference voltages can be set to various voltages depending on circuit design parameters.
Transistors TP and TN and amplifiers AMPA, AMPB, and AMPC compose a regulator 350. Regulator 350 is similar to regulator 250 in that it includes amplifier AMPA for regulating the voltage at node A. Regulator 350, however, differs from regulator 250 in that it additionally includes transistors TP and TN coupled to amplifiers AMPB and AMPC, respectively, for isolating first circuit 110 from second circuit 120 and regulating the voltages at nodes B and C. Because the voltages at nodes B and C are regulated, voltage variations at node A have a very minimal effect on the voltages at nodes B and C. Thus, with minimal voltage variations at nodes B and C, the currents through transistors TP and TN, and hence the currents through first and second circuits 110 and 120, can remain substantially constant.
For example, during operation, when first circuit 110 requires more current, it will lower its equivalent resistance. As a result, this will decrease the voltage drop across terminals 1 and 2 of first circuit 110 and increase the voltage at node B to a voltage greater than VREF—B. Amplifier AMPB will sense that node B is at a voltage greater than VREF—B, and will decrease the voltage at node P so as to lower the channel resistance of transistor TP and pull down the voltage at node B to reference voltage VREF—B. Lowering the channel resistance of transistor TP, however, will decrease the voltage drop across the source and drain of transistor TP, and thus, raise the voltage at node A. This, in turn, will trigger AMPA to sink third current I3 from node A in order to pull the voltage at node A back down to VREF—A.
During the period when the voltage at node A is pulled up, the voltage at node C may begin to rise. However, AMPC will sense the change in the voltage at node C and, due to its high gain response, will immediately adjust the channel resistance of transistor TN so as to pull the voltage at node C back down to reference voltage VREF—C. In this manner, amplifier AMPC will maintain the voltage at node C at reference voltage VREF—C to reduce or prevent fluctuation of second current I2 flowing through second circuit 120.
First current I1, however, will increase by an amount equivalent to third current I3, satisfying first circuit's 110 requirement for more current, and resulting in a relationship between I1, I2, and I3 illustrated by equation (1) shown above.
On the other hand, when first circuit 110 requires less current, it will raise its equivalent resistance. As a result, this will increase the voltage drop across terminals 1 and 2 of first circuit 110 and decrease the voltage at node B to a voltage less than VREF—B. Amplifier AMPB will sense that node B is at a voltage less than VREF—B, and will increase the voltage at node P so as to raise the channel resistance of transistor TP and pull up the voltage at node B to reference voltage VREF—B. Raising the channel resistance of transistor TP, however, will increase the voltage drop across the source and drain of transistor TP, and thus, lower the voltage at node A. This, in turn, will trigger AMPA to feed third current I3 into node A in order to pull the voltage at node A back up to VREF—A.
During the period when the voltage at node A is pulled down, the voltage at node C may begin to fall. However, AMPC will sense the change in the voltage at node C and, due to its high gain response, will immediately adjust the channel resistance of transistor TN so as to pull the voltage at node C back up to reference voltage VREF—C. In this manner, amplifier AMPC will maintain the voltage at node C at reference voltage VREF—C to prevent or reduce fluctuation of second current I2 flowing through second circuit 120.
First current I1, however, will decrease by an amount equivalent to third current I3, satisfying first circuit's 110 requirement for less current, which results in a relationship between I1, I2, and I3 illustrated by equation (2) shown above.
When second circuit 120 requires more current, it will lower its equivalent resistance. As a result, this will decrease the voltage drop across terminals 1 and 2 of second circuit 120 and decrease the voltage at node C to a voltage less than VREF—C. Amplifier AMPC will sense that node C is at a voltage less than VREF—C, and will increase the voltage at node N so as to lower the channel resistance of transistor TN and pull up the voltage at node C to reference voltage VREF—C. Lowering the channel resistance of transistor TN, however, will decrease the voltage drop across the source and drain of transistor TN, and thus, lower the voltage at node A. This, in turn, will trigger AMPA to feed third current I3 into node A in order to pull the voltage at node A back down to VREF—A.
During the period when the voltage at node A is pulled down, the voltage at node B may begin to fall. However, AMPB will sense the change in the voltage at node B and, due to its high gain response, will immediately adjust the channel resistance of transistor TP so as to pull the voltage at node B back up to reference voltage VREF—B. In this manner, amplifier AMPB will maintain the voltage at node B at reference voltage VREF—B to prevent or reduce fluctuation of first current I1 flowing through first circuit 110.
Second current I2, however, will increase by an amount equivalent to third current I3, satisfying second circuit's 120 requirement for more current, which results in a relationship between I1, I2, and I3 illustrated by equation (3) shown above.
Conversely, when second circuit 120 requires less current, it will raise its equivalent resistance. As a result, this will increase the voltage drop across terminals 1 and 2 of second circuit 120 and increase the voltage at node C to a voltage greater than VREF—C. Amplifier AMPC will sense that node C is at a voltage greater than VREF—C, and will decrease the voltage at node N so as to increase the channel resistance of transistor TN and pull up the voltage at node C to reference voltage VREF—C. Increasing the channel resistance of transistor TN, however, will increase the voltage drop across the source and drain of transistor TN, and thus, increase the voltage at node A. This, in turn, will trigger AMPA to sink third current I3 from node A in order to pull the voltage at node A back down to VREF—A.
During the period when the voltage at node A is pulled up, the voltage at node B may begin to rise. However, AMPB will sense the change in the voltage at node B and, due to its high gain response, will immediately adjust the channel resistance of transistor TP so as to pull the voltage at node B back down to reference voltage VREF—B. In this manner, amplifier AMPB will maintain the voltage at node B at reference voltage VREF—B to prevent or reduce fluctuation of first current I1 flowing through first circuit 110.
Second current I2, however, will decrease by an amount equivalent to third current I3, satisfying second circuit's 120 requirement for less current, which results in a relationship between I1, I2, and I3 illustrated by equation (4) shown above.
FIG. 4 shows a flow-chart 1000 of an exemplary PSC process. The exemplary PSC process can be implemented in a circuit where dynamic current usage of one component needs to be isolated from another component, such as the PSC circuit shown in FIG. 2.
The process begins and proceeds to step S1002 where a determination is made as to whether a voltage VA is equal to reference voltage VREF—A. If voltage VA is determined to not be equal to reference voltage VREF—A, then the process proceeds to step S1004. Otherwise, the process proceeds to step S1010.
In step S1004, a determination is made as to whether voltage VA is greater than reference voltage VREF—A. If voltage VA is determined to be greater than reference voltage VREF—A, then the process proceeds to step S1006. Otherwise, the process proceeds to step S1008.
In step S1008, the process raises voltage VA and returns to step S1002. In step S1006, the process lowers voltage VA and returns to step S1002. For example, in PSC 200, regulator 250 increases the voltage at node A if the voltage at node A is less than reference voltage VREF—A, and decreases the voltage at node A if the voltage at node A is greater than reference voltage VREF—A.
In step S1010, the process determines whether the PSC is powered off. If the PSC is not powered off, then the process returns to step S1002. Otherwise, the process ends.
FIG. 5 shows a flow-chart 2000 of an exemplary PSC process for regulating voltage at more than one node. The exemplary PSC process can be implemented in a circuit where dynamic current usage of one or more components needs to be isolated from another component, such as the PSC circuit shown in FIG. 3.
The process begins and proceeds to steps S2002, S2010, and S2018. In step S2002 a determination is made as to whether voltage VA is equal to reference voltage VREF—A. If voltage VA is determined to not be equal to reference voltage VREF—A, then the process proceeds to step S2004. Otherwise, the process proceeds to step S2026.
In step S2004, a determination is made as to whether voltage VA is greater than reference voltage VREF—A. If voltage VA is determined to be greater than reference voltage VREF—A, then the process proceeds to step S2006. Otherwise, the process proceeds to step S2008.
In step S2008, the process raises voltage VA and returns to step S2002. In step S2006, the process lowers voltage VA and returns to step S2002. For example, in PSC 300, regulator 350 increases the voltage at node A if the voltage at node A is less than reference voltage VREF—A, and decreases the voltage at node A if the voltage at node A is greater than reference voltage VREF—A.
In step S2010 a determination is made as to whether voltage VB is equal to reference voltage VREF—B. If voltage VB is determined to not be equal to reference voltage VREF—B, then the process proceeds to step S2012. Otherwise, the process proceeds to step S2026.
In step S2012, a determination is made as to whether voltage VB is greater than reference voltage VREF—B. If voltage VB is determined to be greater than reference voltage VREF—B, then the process proceeds to step S2014. Otherwise, the process proceeds to step S2016.
In step S2016, the process raises voltage VB and returns to step S2010. In step S2014, the process lowers voltage VB and returns to step S2010. For example, in PSC 300, regulator 350 increases the voltage at node B if the voltage at node B is less than reference voltage VREF—B, and decreases the voltage at node B if the voltage at node B is greater than reference voltage VREF—B.
In step S2018 a determination is made as to whether voltage VC is equal to reference voltage VREF—C. If voltage VC is determined to not be equal to reference voltage VREF—C, then the process proceeds to step S2020. Otherwise, the process proceeds to step S2026.
In step S2020, a determination is made as to whether voltage VC is greater than reference voltage VREF—C. If voltage VC is determined to be greater than reference voltage VREF—C, then the process proceeds to step S2022. Otherwise, the process proceeds to step S2024.
In step S2024, the process raises voltage VC and returns to step S2018. In step S2022, the process lowers voltage VC and returns to step S2018. For example, in PSC 300, regulator 350 increases the voltage at node C if the voltage at node C is less than reference voltage VREF—C, and decreases the voltage at node C if the voltage at node C is greater than reference voltage VREF—C.
In step S2026, the process determines whether the PSC is powered off. If the PSC is not powered off, then the process returns to steps S2002, S2010, and S2018. Otherwise, the process ends.
It should be understood that additional steps can be added where a determination is made as to whether a voltage at one or more additional nodes is equal to its respective reference voltage and is adjusted in a manner similar to that described above in steps S2002 through S2026.
Voltages VA, VB, and VC can be regulated either independently, simultaneously, or sequentially in a temporally overlapping or non-overlapping manner. For example, in PSC 300, when first circuit 110 requires more current, the voltage at node B will be adjusted first. However, after amplifier AMPB begins adjusting the voltage at node B, amplifier AMPC may start adjust the voltage at node C prior to when amplifier AMPA begins to sink third current I3 from node A to adjust the voltage at node A.
For purposes of explanation, in the above description, numerous specific details are set forth in order to provide a thorough understanding of the PSC. It will be apparent, however, to one skilled in the art that the PSC can be practiced without these specific details. In other instances, well-known structures and devices are shown in block diagram form in order to avoid obscuring the PSC.
While the PSC has been described in conjunction with the specific embodiments thereof, it is evident that many alternatives, modifications, and variations will be apparent to those skilled in the art. Accordingly, embodiments of the PSC as set forth herein are intended to be illustrative, not limiting. There are changes that may be made without departing from the spirit and scope of the invention.

## Claims

1. An isolation device that isolates a plurality of load circuits connected in series between two power sources, comprising:
a first node between a first load circuit and a second load circuit; and
a power source circuit regulating a voltage of the first node, the power source circuit determines a first current requirement of the first load circuit and a second current requirement of the second load circuit that is different from the first current requirement, the difference is changing dynamically, the power source circuit further comprising:
a second node between the first node and the first load circuit;
a first voltage regulating circuit regulating a second voltage at the second node;
a third node between the first node and the second load circuit; and
a second voltage regulating circuit regulating a third voltage at the third node.

2. The isolation device according to claim 1, the first voltage regulating circuit further comprising:
a first transistor that is connected in series between the first node and the second node, the first transistor maintaining the second voltage at the second node; and
a first amplifier having a first input coupled to the second node and a first output coupled to a first control terminal of the first transistor.

3. The isolation device according to claim 2, the second voltage regulating circuit further comprising:
a second transistor that is connected in series between the first node and the third node, the second transistor maintaining the third voltage at the third node; and
a second amplifier having a second input coupled to the second node and a second output coupled to a second control terminal of the second transistor.

4. The isolation device according to claim 3, wherein the second voltage has a first predetermined relationship with the first voltage of the first node and the third voltage has a second predetermined relationship with the first voltage of the first node.

5. The isolation device according to claim 4, wherein the first input of the first amplifier receives a first reference voltage corresponding to the first predetermined relationship and the second input of the second amplifier receives a second reference voltage corresponding to the second predetermined relationship.

6. The isolation device according to claim 3, the first and second transistors are selected from one or more of:
MOSFET transistors having gates as control terminals and sources and drains as first and second power terminals, respectively; and
bipolar transistors having bases as control terminals and collectors and emitters as first and second power terminals, respectively.

7. An isolation means for isolating a plurality of load circuits connected in series between two power sources, comprising:
a first node between a first load circuit and a second load circuit; and
a power source means for regulating a voltage of the first node, the power source means determines a first current requirement of the first load circuit and a second current requirement of the second load circuit that is different from the first current requirement, the difference is changing dynamically, the power source means further comprising:
a second node between the first node and the first load circuit;
a first voltage regulating means for regulating a second voltage at the second node;
a third node between the first node and the second load circuit; and
a second voltage regulating means for regulating a third voltage at the third node.

8. The isolation means according to claim 7, the first voltage regulating means further comprising:
a first switching means connected in series between the first node and the second node for maintaining the second voltage at the second node; and
a first amplifying means having a first input coupled to the second node and a first output coupled to a first control terminal of the first switching means for controlling the first switching means.

9. The isolation means according to claim 8, the second voltage regulating means further comprising:
a second switching means that is connected in series between the first node and the third node for maintaining the third voltage at the third node; and
a second amplifying means having a second input coupled to the second node and a second output coupled to a second control terminal of the second switching means for controlling the second switching means.

10. The isolation means according to claim 9, wherein the second voltage has a first predetermined relationship with the first voltage of the first node and the third voltage has a second predetermined relationship with the first voltage of the first node.

11. The isolation means according to claim 10, wherein the first input of the first amplifying means receives a first reference voltage corresponding to the first predetermined relationship and the second input of the second amplifying means receives a second reference voltage corresponding to the second predetermined relationship.

12. An isolation device comprising:
a first node between a first load circuit and a second load circuit; and
a power source circuit regulating a voltage of the first node, the power source circuit determines a first current requirement of the first load circuit and a second current requirement of the second load circuit that is different from the first current requirement, the difference is changing dynamically, the power source circuit further comprising:
a second node between the first node and the first load circuit;
a first transistor that is connected in series between the first node and the second node, the first transistor regulating a second voltage at the second node;
a first amplifier having a first input coupled to the second node and a first output coupled to a first control terminal of the first transistor;
a third node between the first node and the second load circuit;
a second transistor that is connected in series between the first node and the third node, the second transistor regulating a third voltage at the third node; and
a second amplifier having a second input coupled to the second node and a second output coupled to a second control terminal of the second transistor.