News Column

Patent Issued for Voltage Regulating Circuit and a Method for Producing a Regulated DC Output Voltage from an Unregulated DC Input Voltage

August 13, 2014



By a News Reporter-Staff News Editor at Biotech Week -- A patent by the inventor Moane, Brian (Reheen, IE), filed on July 16, 2010, was published online on July 29, 2014, according to news reporting originating from Alexandria, Virginia, by NewsRx correspondents (see also Medical Device Companies).

Patent number 8791674 is assigned to Analog Devices, Inc. (Norwood, MA).

The following quote was obtained by the news editors from the background information supplied by the inventors: "The disclosed technology relates to voltage regulation, and in particular, to direct current (DC) voltage regulation.

"Voltage regulators for producing a regulated DC output voltage from an unregulated DC input voltage supply are known in the prior art. One such prior art voltage regulator which produces a regulated DC output voltage from an unregulated DC voltage supply is referred to as a linear voltage regulator. Such a prior art linear voltage regulator is illustrated in FIG. 1. The linear voltage regulator of FIG. 1 comprises a pair of input terminals 1 and 2 across which the unregulated DC voltage supply is applied, and a pair of output terminals 3 and 4 across which the regulated DC output voltage is produced and applied to a load 5. The input terminal 2 and the output terminal 4 are tied to a common voltage, typically ground voltage. The load current I.sub.l is drawn from the unregulated DC voltage supply and flows from the input terminal 1 to the output terminal 3 through a pass element 7 of variable impedance, which typically is provided by a field effect transistor M1.

"A resistor-divider circuit 9 connected across the output terminals 3 and 4 produces a voltage on an intermediate tap 10 which is indicative of the output voltage produced across the output terminals 3 and 4. The voltage on the intermediate tap 10 is applied to one of an inverting input and a non-inverting input of an error amplifier 12, and a voltage reference V.sub.ref is applied to the other of the inverting input and the non-inverting input of the error amplifier 12 in order to produce a negative feedback loop with the pass element 7. In the voltage regulating circuit of FIG. 1 the voltage on the intermediate tap 10 is applied to the non-inverting input, and the voltage reference V.sub.ref is applied to the inverting input. The voltage reference V.sub.ref is of value substantially similar to the value of the voltage which should appear on the intermediate tap 10 when the output voltage produced across the output terminals 3 and 4 is at the correct regulated voltage value. The error amplifier 12 produces a control signal which is indicative of the difference between the voltage on the intermediate tap 10 and the voltage reference V.sub.ref. The control signal is applied to the gate of the field effect transistor M1. The impedance of the field effect transistor M1 is responsive to the control signal from the error amplifier 12 for maintaining the output voltage produced across the output terminals 3 and 4 at the correct regulated voltage value.

"Such linear voltage regulators as the prior art linear voltage regulator of FIG. 1 have many advantages, one of which is that they tolerate a relatively wide variation in the voltage of the unregulated DC voltage supply between the minimum voltage to which the unregulated voltage supply may drop and the maximum voltage to which the unregulated voltage supply may rise. Additionally, such linear voltage regulators operate with a relatively small voltage difference between the unregulated voltage supply and the regulated output voltage. In other words, the dropout voltage which is the voltage of the unregulated voltage supply at which the voltage regulator ceases to produce the regulated voltage is relatively low, and in general is of value just above the regulated voltage value.

"However, a disadvantage of such linear voltage regulators is that since the load current I.sub.l is drawn through the pass element 7, the power dissipated by the pass element 7 is equal to the product of the load current I.sub.l by the voltage drop across the pass element. The voltage drop across the pass element is equal to the value of the voltage of the unregulated voltage supply less the value of the regulated output voltage. Thus, as the voltage of the unregulated voltage supply increases, the power dissipated by the pass element 7 also increases. Since the power dissipated by the pass element 7 is dissipated as heat, the heat produced by the pass element can be relatively high, and in particular, can be relatively high at the higher values of the voltage of the unregulated voltage supply. This is undesirable, and is particularly undesirable when the linear voltage regulator is implemented as an integrated circuit on a die due to the difficulty in dissipating heat from dies. The problem of heat dissipation is further aggravated when the load to which the regulated output voltage is being supplied is implemented as an integrated circuit on the same die or package as that on which the linear voltage regulator is formed.

"Efforts have been made to address the problem of heat dissipation in prior art linear voltage regulators of the type illustrated in FIG. 1. A typical prior art linear voltage regulator which reduces heat dissipation on a die is illustrated in FIG. 2. In the linear voltage regulator of FIG. 2 a voltage dropping resistor R.sub.ext is provided in series with the pass element 7, but is located externally of the die. Thus, the external voltage dropping resistor R.sub.ext drops some of the voltage between the unregulated voltage supply and the regulated output voltage while the remainder of the voltage between the unregulated voltage supply and the regulated output voltage is dropped across the pass element. This in turn splits the power dissipated by the voltage regulator between the power dissipated by the pass element 7 in the die and the power dissipated by the external resistor R.sub.ext externally of the die. However, a problem with this voltage regulator is that the dropout voltage, in other words, the value of the unregulated voltage supply at which the voltage regulator ceases to produce the regulated output voltage is increased by the voltage drop across the external resistor R.sub.ext.

"Accordingly, the external resistor R.sub.ext should be selected to have a maximum resistance value sufficiently low that, at the minimum value of the unregulated voltage supply and when the current drawn by the load is a maximum, the voltage dropped across the external resistor R.sub.ext is such that the voltage regulator continues to produce the regulated output voltage. This, however, imposes a limitation on the size of the external resistor R.sub.ext, and in turn the amount of heat which can be dissipated by the external resistor R.sub.ext.

"A computer simulation of the voltage regulator of FIG. 2 was carried out. The results of the computer simulation are illustrated by the graphs of FIG. 3 which are described below. In the computer simulation the voltage regulator was configured to operate with an unregulated voltage supply which varies between a minimum voltage value of 11 volts and a maximum voltage value of 25 volts, and to produce a regulated output voltage of 5 volts with a maximum load current of 50 mA. The resistance value of the external resistor R.sub.ext was selected to be sufficiently low that the voltage drop across the external resistor R.sub.ext was less than 6 volts. Otherwise, during periods when the unregulated voltage supply remained at its minimum voltage value, the voltage available to the pass element 7 would be insufficient for the voltage regulator to produce the regulated output voltage. In this case the resistance value of the external resistance was selected to be 120 ohms. Therefore, in this particular case when the unregulated supply voltage reached its maximum value of 25 volts, the voltage dropped across the external resistor R.sub.ext was still less than 6 volts, thus leaving a voltage of 14 volts to be dropped across the pass element 7. This resulted in a relatively high power dissipation by the pass element 7 in the form of heat, particularly at the relatively higher values of the unregulated input voltage.

"Referring now in particular to FIG. 3, FIG. 3 illustrates three graphs which represent power dissipated by the voltage regulator of FIG. 2 plotted against the unregulated input voltage obtained from the computer simulation. In FIG. 3 power is plotted in watts on the vertical Y-axis, and the voltage of the unregulated input voltage is plotted in volts on the horizontal X-axis. Graph X represents a plot of the total power dissipated by the external resistor R.sub.ext and the pass element 7 of the voltage regulator of FIG. 2 as the unregulated input voltage varies between the minimum value of 11 volts and the maximum value of 25 volts. Graph Y represents the power dissipated internally in the voltage regulating circuit of FIG. 2 by the pass element 7 as the unregulated input voltage varies from the minimum value of 11 volts to the maximum value of 25 volts. Graph Z represents the power dissipated by the external resistor R.sub.ext as the unregulated input voltage varies from the minimum value of 11 volts to the maximum value of 25 volts. As can be seen from graph Y, the power dissipated by the pass element 7 increases from zero watts to approximately 0.7 watts as the unregulated input voltage varies from 11 volts to 25 volts. However, from graph Z it can be seen that the power dissipated by the external resistor R.sub.ext remains constant at approximately 0.3 watts as the unregulated input voltage varies between 11 volts and 25 volts. Thus, the total power dissipated by the external resistor R.sub.ext and the pass element 7, as can be seen from graph X of FIG. 3, varies from approximately 0.3 watts to 1 watt. Accordingly, at the maximum value of the unregulated input voltage of 25 volts, the pass element dissipates approximately 0.7 watts, and since all the power dissipated by the pass element 7 is dissipated in the form of heat, the heat dissipated internally in the voltage regulating circuit of FIG. 2 by the pass element 7 is approximately 0.7 watts. However, at the maximum value of 25 volts of the unregulated input voltage, the external resistor R.sub.ext is still only dissipating the same amount of power, namely, approximately 0.3 watts, as it dissipates when the unregulated input voltage is at its minimum value of 11 volts when virtually no heat is being dissipated by the pass element 7. This is clearly undesirable.

"Thus, while the provision of the external resistor R.sub.ext assists to some extent in externally dissipating power and in turn heat produced by the linear voltage regulator of FIG. 2, its benefit is limited, particularly in cases where the unregulated voltage supply varies widely between an upper maximum voltage value and a lower minimum voltage value.

"There is therefore a need for a voltage regulating circuit which produces a regulated DC output voltage from an unregulated DC voltage supply, which addresses the problem of power dissipation by prior art voltage regulators.

"The present disclosure provides such a DC voltage regulating circuit, and the disclosure is also directed towards providing a method for producing a regulated DC output voltage from an unregulated DC voltage supply which addresses the problem of power dissipation of known voltage regulators."

In addition to the background information obtained for this patent, NewsRx journalists also obtained the inventor's summary information for this patent: "The disclosure provides a DC voltage regulating circuit having a pair of input terminals for receiving an unregulated DC input voltage, and a pair of output terminals across which a regulated DC output voltage is produced for applying to a load. The voltage regulating circuit includes a primary current path for accommodating current from a first one of the input terminals to a first one of the output terminals. The voltage regulating circuit also includes a primary pass element of variable impedance in the primary current path. A voltage dropping heat dissipating impedance element in the primary current path in series with the primary pass element and defining with the primary pass element a primary node therebetween in the primary current path is also included. The voltage regulating circuit additionally includes a bypass current path parallel with the primary current path bypassing the voltage dropping heat dissipating impedance element and a secondary pass element of variable impedance in the bypass current path. A primary control circuit is responsive to one of the voltage produced across the output terminals and the voltage on the primary node. If the primary circuit is responsive to the voltage produced across the output terminals, then the primary control circuit controls the impedance of the primary pass element to maintain the output voltage across the output terminals at the regulated voltage value. If the primary circuit is responsive to the voltage on the primary node, then the primary circuit controls the impedance of the primary pass element to control the voltage on the primary node. A secondary control circuit is responsive to the other one of the voltage produced across the output terminals and the voltage on the primary node. If the secondary circuit is responsive to the voltage produced across the output terminals, then the secondary control circuit controls the impedance of the secondary pass element to maintain the output voltage across the output terminals at the regulated voltage value. If the secondary circuit is responsive to the voltage on the primary node, then the secondary circuit controls the impedance of the secondary pass element to control the voltage on the primary node.

"In one embodiment of the invention, the primary control circuit is responsive to the voltage produced across the output terminals for controlling the impedance of the primary pass element to maintain the output voltage across the output terminal at the regulated voltage value, and the secondary control circuit is responsive to the voltage on the primary node for controlling the impedance of the secondary pass element to control the voltage on the primary node.

"In one aspect of the invention, the primary control circuit comprises a first comparing means for comparing a first voltage indicative of the output voltage produced across the output terminals with a second voltage, and for producing a first control signal indicative of the difference between the first voltage and the second voltage.

"In another aspect of the invention, the second voltage is derived from a first voltage reference.

"Preferably, the first control signal is applied to the primary pass element, and the impedance of the primary pass element is responsive to the first control signal.

"In another aspect of the invention, the first voltage indicative of the output voltage is derived from a first intermediate tap defined by a first impedance-divider circuit connected across the output terminals through a first current path. Preferably, the first impedance-divider circuit comprises at least two first electrically resistive elements between which the first intermediate tap is defined.

"Advantageously, the first comparing means comprises a first error amplifier for producing the first control signal, the first voltage indicative of the output voltage being applied to one of an inverting input and a non-inverting input of the first error amplifier, and the second voltage being applied to the other of the inverting input and the non-inverting input of the first error amplifier to produce a negative feedback loop with the primary pass element.

"Preferably, the primary pass element comprises a first transistor accommodating the primary current path therethrough, the first transistor being responsive to the first control signal for varying the impedance in the primary current path through the first transistor. Desirably, the first transistor comprises a first field effect transistor having a source, a drain and a gate, the primary current path extending through the first field effect transistor between the source and the drain, and the first control signal being applied to the gate thereof.

"In another aspect of the invention the secondary control circuit comprises a second comparing means for comparing a third voltage indicative of the voltage on the primary node with a fourth voltage, and for producing a second control signal indicative of the difference between the third voltage and the fourth voltage.

"In one aspect of the invention, the fourth voltage is derived from a voltage reference, and preferably, the voltage reference from which the fourth voltage is derived may be one of the first voltage reference and a second voltage reference.

"In one embodiment of the invention, the voltage reference from which the fourth voltage is derived is the second voltage reference.

"In an alternative embodiment of the invention, the fourth voltage is derived from a variable voltage, and preferably, the fourth voltage is derived from a variable voltage reference.

"In another alternative embodiment of the invention, the fourth voltage is programmable.

"In a further alternative embodiment of the invention, the fourth voltage is derived from the unregulated input voltage.

"In another embodiment of the invention, the fourth voltage is selectable.

"Advantageously, the second control signal is applied to the secondary pass element, and the impedance of the secondary pass element is responsive to the second control signal.

"In one embodiment of the invention, the third voltage is derived from a second intermediate tap defined by a second impedance-divider circuit connected through a second current path between the primary node and a common voltage at which the second ones of the input and output terminals are held. Preferably, the second impedance-divider circuit comprises at least two second electrically resistive elements defining the second intermediate tap therebetween.

"In one embodiment of the invention, the second comparing means comprises a second error amplifier for producing the second control signal, the third voltage being applied to one of an inverting input and a non-inverting input of the second error amplifier, and the fourth voltage being applied to the other of the inverting input and the non-inverting input of the error amplifier to produce a negative feedback loop with the secondary pass element.

"In another embodiment of the invention, the secondary pass element comprises a second transistor accommodating the bypass current path therethrough, the second transistor being responsive to the second control signal for varying the impedance in the bypass current path through the second transistor. Preferably, the second transistor comprises a second field effect transistor having a source, a drain and a gate, the bypass current path extending through the second field effect transistor between the source and the drain, and the second control signal being applied to the gate thereof.

"Preferably, the voltage dropping heat dissipating impedance element is located in the primary current path between the first input terminal and the primary pass element.

"Alternatively, the primary control circuit is responsive to the voltage on the primary node for controlling the impedance of the primary pass element to control the voltage on the primary node, and the secondary control circuit is responsive to the voltage produced across the output terminals for controlling the impedance of the secondary pass element to maintain the output voltage across the output terminals at the regulated voltage value.

"In one aspect of the invention, the primary control circuit comprises a first comparing means for comparing a third voltage indicative of the voltage on the primary node with a fourth voltage, and for producing a first control signal indicative of the difference between the third voltage and the fourth voltage.

"Preferably, the fourth voltage is derived from one of a voltage reference and the unregulated input voltage.

"Advantageously, the first comparing means compares the third voltage indicative of the voltage on the primary node with the unregulated input voltage.

"Desirably, the first control signal is applied to the primary pass element, and the impedance of the primary pass element is responsive to the first control signal.

"In one aspect of the invention, the secondary control circuit comprises a second comparing means for comparing a first voltage indicative of the voltage produced across the output terminals with a second voltage, and for producing a second control signal indicative of the difference between the first voltage and the second voltage.

"In another aspect of the invention, the second voltage is derived from one of a voltage reference and the unregulated input voltage.

"Preferably, the second voltage is derived from a first voltage reference.

"Advantageously, the second control signal is applied to the secondary pass element, and the impedance of the secondary pass element is responsive to the second control signal.

"In another embodiment of the invention, the voltage dropping heat dissipating impedance element is located in the primary current path between the primary node and the first output terminal.

"In one aspect of the invention, the voltage on the primary node is controlled so that the relationship between heat dissipated by the voltage dropping heat dissipating impedance element and the unregulated input voltage is a quadratic relationship.

"In another aspect of the invention, the voltage on the primary node is controlled so that the relationship between heat dissipated by the primary and secondary pass elements and the unregulated input voltage is a quadratic relationship.

"Desirably, with the exception of the voltage dropping heat dissipating impedance element the voltage regulating circuit is implemented as an integrated circuit on one or more dies, the voltage dropping heat dissipating impedance element being located externally of the one or more dies.

"In another embodiment of the invention, the one or more dies on which the integrated circuit is implemented is located in a package, and the voltage dropping heat dissipating impedance element is located externally of the package.

"The disclosure also provides an integrated circuit formed on one or more dies comprising the voltage regulating circuit according to the invention formed on the one or more dies with the exception of the voltage dropping heat dissipating impedance element, and a load formed on the one or more dies supplied with the regulated output voltage from the voltage regulating circuit, the voltage dropping heat dissipating impedance element being located externally of the one or more dies.

"Further the disclosure provides an integrated circuit formed on one or more dies comprising the voltage regulating circuit according to the invention with the exception of the voltage dropping heat dissipating impedance element, and a load formed on one of the one or more dies and another die in a package comprising the one or more dies on which the voltage regulating circuit is formed, the load being supplied with the regulated output voltage from the voltage regulating circuit, the voltage dropping heat dissipating impedance element being located externally of the package.

"Additionally the disclosure provides a method for producing a regulated DC output voltage from an unregulated DC input voltage, the method comprising: providing a primary current path in a voltage regulating circuit for accommodating current from a first one of a pair of input terminals to a first one of a pair of output terminals, providing a primary pass element of variable impedance in the primary current path, providing a voltage dropping heat dissipating impedance element in the primary current path in series with the primary pass element to define with the primary pass element a primary node therebetween in the primary current path, providing a bypass current path parallel with the primary current path bypassing the voltage dropping heat dissipating impedance element, providing a secondary pass element of variable impedance in the bypass current path, controlling the impedance of the primary pass element in response to one of the voltage produced across the output terminals, for maintaining the output voltage across the output terminals at the regulated voltage value, and the voltage on the primary node, for controlling the voltage on the primary node; and controlling the impedance of the secondary pass element in response to the other of the voltage produced across the output terminals, for maintaining the output voltage across the output terminals at the regulated voltage value, and the voltage on the primary node, for controlling the voltage on the primary node."

URL and more information on this patent, see: Moane, Brian. Voltage Regulating Circuit and a Method for Producing a Regulated DC Output Voltage from an Unregulated DC Input Voltage. U.S. Patent Number 8791674, filed July 16, 2010, and published online on July 29, 2014. Patent URL: http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum.htm&r=1&f=G&l=50&s1=8791674.PN.&OS=PN/8791674RS=PN/8791674

Keywords for this news article include: Analog Devices Inc., Medical Device Companies.

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Source: Biotech Week


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