Title of Invention	STEP-DOWN VOLTAGE CONVERTER
Abstract	A step-down voltage converter (100) for generating an output voltage (VOUT) from an input voltage (VIN) is provided. The converter (100) includes a switch (111) having a first terminal (112) and a second terminal (114), wherein the second terminal (114) is electrically coupled with the output voltage (VOUT). Also included is a rectifier (117) having a first terminal (118) and a second terminal (120), wherein the second terminal (120) is electrically coupled with the output voltage (VOUT). A first inductor (124) electrically couples the first terminal (112) of the switch (111) with the input voltage (VIN). A second inductor (126) magnetically coupled with the first inductor (124) electrically couples the first terminal (118) of the rectifier (117) with a voltage reference (128). A switch controller (110) coupled with the output voltage (VOUT) is configured to control the switch (111).

Title of Invention

STEP-DOWN VOLTAGE CONVERTER

Abstract

A step-down voltage converter (100) for generating an output voltage (VOUT) from an input voltage (VIN) is provided. The converter (100) includes a switch (111) having a first terminal (112) and a second terminal (114), wherein the second terminal (114) is electrically coupled with the output voltage (VOUT). Also included is a rectifier (117) having a first terminal (118) and a second terminal (120), wherein the second terminal (120) is electrically coupled with the output voltage (VOUT). A first inductor (124) electrically couples the first terminal (112) of the switch (111) with the input voltage (VIN). A second inductor (126) magnetically coupled with the first inductor (124) electrically couples the first terminal (118) of the rectifier (117) with a voltage reference (128). A switch controller (110) coupled with the output voltage (VOUT) is configured to control the switch (111).

Full Text	STEP-DOWN VOLTAGE CONVERTER FIELD OF THE INVENTION Aspects of the invention relate generally to electrical voltage converters, and more particularly to electrical step-down voltage converters producing a direct-current (DC) voltage from an alternating-current (AC) voltage or a DC voltage. BACKGROUND OF THE INVENTION Various electrically-powered equipment within an industrial environment often depend upon any of a variety of AC and/or DC voltages for power. More specifically, DC-oriented systems tend to utilize relatively low DC voltages, typically ranging from 12 to 50 volts DC (VDC). AC-oriented systems, however, often employ higher AC voltages, sometimes ranging between 100 and 250 volts root-mean-square (VRMS), Other AC or DC voltages outside of these ranges may be employed as well. However, industrial instrumentation, such as a Coriolis flowmeter for measuring mass flow and other information concerning a material flowing through a conduit, often employ electrical components that require a low DC voltage, such as 1.2-24 VDC, as an electrical power source, and thus are not capable of withstanding such a large range of AC or DC input voltages. Thus, a step-down converter capable of producing a substantially fixed low DC output voltage from either an AC or DC mput voltage is often used to great advantage in such an environment. A simplified schematic diagram of one particular type of step-down, or "buck," converter or regulator 1 currently in use for converting a positive DC input voltage VIK to a DC output voltage VOUT is provided in Fig. 1. The input voltage VIM is asserted across an input capacitor CA coupled with a ground reference, and is coupled with the dram terminal of an n-channel power field-effect transistor (PET) switch Q. The input capacitor CA acts as a filter to help maintain the voltage level seen by the drain of the switch Q in the presence of changes in the input voltage VIN by providing additional current on a temporary basis to the drain of the switch Q. Similar functionality for the output voltage VOUT is provided by an output capacitor CB- The gate of the switch Q is driven by a switch controller 2, which turns the switch Q ON and OFF depending on the voltage level of the output voltage VOUT compared to the desired or target output voltage VQUT level Some other measurable quantity at the output, such as current, may be employed by the switch controller 2 alternatively or additionally. voltage VIN during the ON state. To turn the switch Q OFF3 the gate voltage must be near ground, since the source is driven to slightly below ground due to the diode D becoming forward-biased at that time due to the flyback of the inductor L. When the input voltage VIN is a relatively low DC voltage, generation of the proper gate voltage for the switch Q to be turned ON may be accomplished by way of a readily-available voltage "boost" circuit. However, when the input voltage VIN is a large AC voltage on the order of 265 VRMS, which translates to a maximum DC voltage level of about 375 VDC. timely and accurate control of the gate voltage while providing extremely large Voltage swings at the gate of hundreds of volts typically requires a reiatively complex circuit design for the switch controller 2 involving specialized electrical components. SUMMARY OF THE INVENTION Generally, embodiments of the present invention provide a step-down voltage converter for generating an output voltage from an input voltage. The converter includes a switch having first and second terminals, wherein the second terminal is electrically coupled with the output voltage. A rectifier has first and second terminalSj wherein the second terminal is electrically coupled with the output voltage. A first inductor electrically couples the first terminal of the switch with the input voltage. A second inductor magnetically coupled with the first inductor electrically couples the first terminal of the rectifier with a voltage reference. Also, a switching controller coupled with the output voltage is configured to control the switch. Additional embodiments and advantages of the present invention will be realized by those skilled in the art upon perusal of the following detailed description, taken in conjunction with the accompanymg drawings. ASPECTS One aspect of the invention includes a step-down voltage converter for generating an output voltage from an input voltage, comprising: a switch comprising a first terminal and a second terminal, wherein the second terminal of the switch is electrically coupled with the output voltage; a rectifier comprising a first terminal and a second terminal, wherein the second terminal of the rectifier is electrically coupled with the output voltage; a first inductor electrically coupling the first terminal of .the switch vvith the input voltage; a second inductor magnetically coupled with the first inductor, the second inductor electrically coupling the first terminal of the rectifier with a voltage reference; and a switching controller coupled with the output voltage and configured to control the switch. Preferably, the frrst inductor and the second inductor each comprise an inductance of 1.7 millihenries. Preferably, the step-down voltage converter further comprises: a first capacitor electrically coupling the mput voltage with the voltage reference; and a second capacitor electrically coupling the output voltage with the voltage reference. Preferably, the first capacitor comprises a capacitance of 22 microfarads. Preferably, the second capacitor comprises a capacitance of 120 microfarads. Preferably, voltage reference is ground. Preferably, a number of turns of the first inductor and a number of turns of the second inductor comprise a ratio of 1:1. Preferably, the first inductor comprises a first winding of a transformer, wherein the second inductor comprises a second winding of the transformer, and wherein the first inductor and the second mductor are wound about a core. Preferably, the core is a ferrite core. Preferably, the input voltage and the output voltage are positive direct-current voltages; the switch comprises an n-channel field-effect transistor, the first terminal of the switch comprises a drain terminal of the FET, the second terminal of the switch comprises a source terminal of the FET, and the switch controller controls the FET by way of a gate terminal of the FET; and the rectifier comprises a diode, the first terminal of the rectifier comprises an anode of the diode, and the second terminal of the rectifier comprises a cathode of the diode. Preferably, the input voltage and the output voltage are negative DC voltages; the switch comprises a p-channei field-effect transistor, the first terminal of the switch comprises a drain temiinal of the FET, the second terminal of the switch comprises a source terminal of the FET, and the switch controller controls the FET by way of a gate terminal of the FET; and the rectifier comprises a diode, the first terminal of the rectifier comprises a cathode of the diode, and the second terminal of the rectifier comprises an anode of the diode. Preferably, the switch controller is configured to control the switch by turning the switch on and off substantially periodically. Preferably, the switch controller is configured to control the switch based on the output voltage. Preferably, the switch controller is configured to control the switch based on a current at the output voltage. Preferably, the input voltage is an alternating current input voltage; and the step-down voltage converter further comprises an AC rectification circuit coupling the AC input voltage with the first mductor. Preferably, the AC rectification circuit is configured to convert the AC input voltage to a first positive DC voltage; and the output voltage is a positive DC output voltage having a lower magnitude that the first positive DC voltage. Preferably, the AC rectification circuit is configured to convert the AC input voltage to a first negative DC.voltage; and the output voltage is a negative DC output voltage having a lower magnitude that the first negative DC voltage. Preferably, an item of industrial instrumentation comprises the step-down voltage converter. Preferably, a Coriolis flowmeter comprises the step-down voltage converter. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a block diagram of a step-down voltage converter according to the prior ait. Fig. 2 is a block diagram of a step-down converter according to an embodiment of the invention. Fig. 3 is a schematic diagram of a step-down converter according to an embodiment of the mvention for generating a positive DC output voltage from a positive DC input voltage. Fig. 4 is timing diagram of the current through a first inductor and a second inductor, the voltage at the drain of a switch, and the voltage at the anode of a diode, as implemented in a particular embodiment of the step-down voltage converter of Fig. 3. Fig. 5 is a schematic diagram of a step-down converter according to an embodiment of the invention for generating a negative DC output voltage from a negative DC input voltage. Fig. 6 is block diagram of the step-down converter of Fig. 2 further employing an AC rectification circuit for an AC input voltage. DETAILED DESCRIPTION OF THE INVENTION Fig. 2 is a simplified block diagram of a step-down voltage converter 100 for generating an output voltage VOUT from an input voltage VIN according to an embodiment of the invention. Generally, the converter 100 includes a switch 111 having a first terminal 112 and a second tenninal 114, wherein the second terminal 114 is coupled with the output voltage VouT- The first terminal 112 of the switch 111 is electrically coupled with the input voltage VIN by way of a first inductor 124. The switch 111 is controlled by way of a switch controller 110 coupled with the output voltage Vour- In addition, a second inductor 126 magnetically coupled with the first inductor 124 electrically couples a first tenninal 118 of a rectifier 117 with a voltage reference 128, while a second terminal 120 of the rectifier 117 is electrically coupled with the output voltage VOUT- Fig. 3 is a simplified schematic diagram of a specific example of the step-down voltage converter 100: a voltage converter 200 for generating a positive DC output voltage VouT from a positive DC input voltage VIN according to an embodiment of the invention. The converter 200 includes a switch Q1 having a first terminal 212 and a second terminal 214, wherein the second terminal 214 is. coupled with the output voltage VQUT. The fust terminal 212 of the switch Qi is electrically coupled with the input voltage VIN by way of a first inductor L1. The switch Qj is controlled by way of a switch controller 210 coupled with the output voltage VQUT- In addition, a second inductor L3 magnetically coupled with the first inductor L1 electrically couples an anode 218 of a rectifier or diode D1 with a voltage reference, while a cathode 220 of the diode D1 is electrically coupled with the output voltage VQUT- More specifically regarding the particular example of the converter 200 of Fig. 3, the switch Q] may be a FET, such as an n-channel power FET, having a drain terminal 212, a source terminal 214, and a gate terminal 216. As is described in greater detail below, the switch controller 210 controls the FET Q1 by turning the FET Qi ON and OFF by way of the gate 216. In one embodiment, the switch controller 10 turns the FET Qi ON and OFF substantially periodically, based at least in part on the voltage level of the output voltage flows through the second inductor L2. Also, the voltage YD at the dram 212 of the switch Q1 remains at about VOUT due to the switch Q1 being ON, and the voltage VA at the anode 218 of the diode D1 is -(V1 - VOUT), as described earlier. In other words, the voltages VL1, VL2 across the mductors L1, L2 are equal at (YIN - VQUT). with the drain voltage VD offset higher than the anode voltage VA by the value of the input voltage VIn. A distinct advantage of various embodiments of the converter 200 described above is the limited voltage swing of the gate 216 of the switch Q1 required to turn ON and OFF the switch Q1. Since the source 214 of the switch Q1 is coupled directly to the output voltage VQUT, the voltage of the gate 216 is required to move only between the output voltage VouT and a few volts higher to operate the switch Q1. Thus, the gate 216 of Q1 may be driven by standard, readily-available electronic components, thereby simplifying the design of the switch controller 210. One or more of these advantages, or others, may also be realized in other applications employing one or more embodiments of the present invention. Similar advantages may also be realized by another voltage converter 300 according to another embodiment of the invention. Shown in Fig. 5, the converter 300, wliich operates in a manner analogous to that of the converter 200 described above, is configured to convert a negative DC input voltage VIH into a lower-magnitude negative DC output voltage VQUT. While most of the components of the converter 200 and the converter 300, such as the inductors L1. L2, the core 222, and the capacitors C1, C2, are the same, a few modifications are utilized to process the negative DC input voltage VIN. In place of the switch Q1 of the converter 200 is a switch Q2, which is a p-channel power FET in the particular example of Fig. 5. The switch Qn includes a drain terminal 312 coupled with the first inductor L1, a source terminal 314 coupled with the output voltage VOUT and a gate terminal 316. A switch controller 310, operating in a similar fashion to that of the switch controller 210 of the converter 200, controls the operation of the switch Q2 via the gate 316. The switch controller 310 need only move the voltage of the gate 316 between the output voltage VQUT and a few volts lower to operate the switch Q2, thus simplifying the design of the switch controller 310 compared to some prior ait converters. The converter 300 of Fig. 5 also includes a diode D2 having a first terminal 318 and a second terminal 320. Due to the negative polarity of the input and output voltages VIN, VQUT. the first terminal 318 is the cathode, while the second terminal 320 is the anode, opposite the orientation of the diode D1 of the converter 200. Operation of the converter 300 is analogous to that described above in conjunction with the converter 200 of Fig. 3, with the polarity of all voltages and currents essentially inverted. A further embodiment of a voltage converter 400 according to an embodiment of the invention for converting an AC input voltage VIK to a DC output voltage VQUT is presented in Fig. 6. In addition to the components described above in conjunction with the converter 100 of Fig. 2, an AC rectification circuit 430 for converting the AC input voltage VIN to a DC voltage usable by the remainder of the voltage converter 400 is utilized to generate the desired DC output voltage VOUT- In one embodiment in which a positive DC output voltage VouT is required, the AC rectification circuit 430 may be configured to convert the AC input voltage VIN to a first positive DC voltage, which may then be converted to a lower-magnitude DC output voltage VOUT by way of the converter 200 of Fig, 3. In another embodiment, if a negative DC output voltage VQUT is needed, the AC rectification circuit 430 may be configured to convert the AC input voltage VIN to a first negative DC voltage, which in one implementation is subsequently converted to a lower-magnitude negative DC output voltage VQUT via the converter 300 of Fig. 5. While several embodiments of the invention have been discussed herein, other embodiments encompassed within the scope of the invention are possible. For example, different AC and DC voltage levels may be involved m alternative embodiments, thus possibly indicating the use of component values other than those specifically disclosed herein. Further, references to positive and negative voltage polarities are provided for reference only, and other embodiments of the invention may utilize a different voltage referencing scheme. In addition, components that are electrically coupled may not necessarily be directly interconnected in alternative embodiments. Also, aspects of one embodiment may be combined with those of alternative embodiments to create further implementations of the present invention. Thus, while the present invention has been described in the context of specific embodiments, such descriptions are provided for illustration and not limitation. Accordingly, the proper scope of the present invention is delimited only by the following claims. CLAIMS What is claimed is: 1. A step-down voltage converter (100) for generating an output voltage (VOUT) from an input voltage (VIN), comprising: a switch (111) comprising a first terminal (112) and a second terminal (114), wherein the second terminal (114) of the switch (111) is electrically coupled with the output voltage (VOUT); a rectifier (117) comprising a first terminal (118) and a second terminal (120), wherein the second terminal (120) of the rectifier (117) is electrically coupled with the output voltage (VOUT); a first inductor (124) electrically coupling the first terminal (112) of the switch (111) with the input voltage (VIN); a second inductor (126) magnetically coupled with the first inductor (124), the second inductor (126) electrically coupling the first terminal (118) of the rectifier (117) with a voltage reference (128); and a switching controller (110) coupled with the output voltage (VOUT) and configured to control the switch (111). 2. The step-down voltage converter (100) of claim 1, wherein the first inductor (124) and the second inductor (126) each comprise an inductance of 1.7 millineries, 3. The step-down voltage converter (100) of claim 1, farther comprising: a first capacitor (C1) electrically coupling the input voltage (VIN) with the voltage reference (128); and a second capacitor (C2) electrically coupling the output voltage with the voltage reference (128). 4. The step-down voltage converter (100) of claim 3, wherein the first capacitor (C1) comprises a capacitance of 22 microfarads. 5. The step-down voltage converter (100) of claim 3, wherein the second capacitor (C2) comprises a capacitance of 120 microfarads. . 6. The step-down voltage converter (100) of claim 1, wherein the voltage reference (128) is ground, 7. The step-down voltage converter (100) of claim 1, wherein a number of turns of the first inductor (124) and a number of turns of the second inductor (126) comprise a ratio of 1:1. 8. The step-down voltage converter (100) of claim 1, wherein the first inductor (124) comprises a first winding of a transformer, wherein the second inductor (126) comprises a second winding of the transformer, and wherein the first mductor (124) and the second inductor (126) are wound about a core (222). 9. The step-down voltage converter (100) of clam 8, wherein the core (222) is a ferrite core. 10. The step-down voltage converter (100) of claim 1, wherein; the input voltage (VIN) and the output voltage (VOUT) are positive direct-current (DC) voltages; the switch (111) comprises an n-channel field-effect transistor (FET) (Q1), the first terminal (112) of the switch (111) comprises a drain terminal (212) of the FET (Q1), the second terminal (114) of the switch (111) comprises a source terminal (214) of the FET (Q1), and the switch controller (110) controls the FET (Q1) by way of a gate terminal (216) of the FET(Q1);and wherein the rectifier (117) comprises a diode (D1). the first terminal (118) of the rectifier (117) comprises an anode (218) of the diode (D1), and the second terminal (120) of the rectifier (117) comprises a cathode (220) of the diode (D1). 11. The step-down voltage converter (100) of claim 1, wherein: the input voltage (VIN) and the output voltage (VOUT) are negative DC voltages; the switch (111) comprises a p-charmel field-effect transistor (FET) (Q2), the first terminal (112) of the switch (111) comprises a drain tenninal (312) of the FET (Q2); the second terminal (114) of the switch (111) comprises a source terminal (314) of the FET (Q2), and the switch controller (110) controls the FET (Q2) by way of a gate terminal (316) of the FET(Q2);and wherein the rectifier (117) comprises a diode (D2), the first terminal (118) of the rectifier (117) comprises a cathode (318) of the diode (D2), and the second tenninal (120) of the rectifier (117) comprises an anode (320) of the diode (D2). 12. The step-down voltage converter (100) of claim 1, wherein the switch controller (110) is configured to control the switch (111) by turning the switch (HI) on and off substantially periodically. 13 The step-down voltage converter (100) of claim 1, wherein the switch controller (110) is configured to control the switch (111) based on the output voltage (VOUT). 14. The step-down voltage converter (100) of claim 1, wherein the switch controller (110) is configured to control the switch (111) based on a current at the output voltage (VQUT)- 15. The step-down voltage converter (100) of claim 1, wherein: the input voltage (VIN) is an alternating current (AC) input voltage; and the step-down voltage converter (100) further comprises an AC rectification circuit (430) coupling the AC mput voltage with the first inductor (124). 16. The step-down voltage converter (100) of claim 15, wherein: the AC rectification circuit (430) is configured to convert the AC input voltage to a first positive DC voltage; and the output voltage (VOUT) is a positive DC output voltage having a lower magnitude that the first positive DC voltage, 17. The step-down voltage converter (100) of claim 15, wherein: the AC rectification circuit (430) is configured to convert the AC input voltage to a first negative DC voltage; and the output voltage (VOUT) is a negative DC output voltage having a lower magnitude that the first negative DC voltage. 18. An item of industrial instrumentation comprising the step-down voltage converter (100) of claim 1. 19. A Coriolis flowmeter comprising the step-down voltage converter (100) of claim 1.

Full Text

STEP-DOWN VOLTAGE CONVERTER
FIELD OF THE INVENTION
Aspects of the invention relate generally to electrical voltage converters, and more particularly to electrical step-down voltage converters producing a direct-current (DC) voltage from an alternating-current (AC) voltage or a DC voltage.
BACKGROUND OF THE INVENTION
Various electrically-powered equipment within an industrial environment often depend upon any of a variety of AC and/or DC voltages for power. More specifically, DC-oriented systems tend to utilize relatively low DC voltages, typically ranging from 12 to 50 volts DC (VDC). AC-oriented systems, however, often employ higher AC voltages, sometimes ranging between 100 and 250 volts root-mean-square (VRMS), Other AC or DC voltages outside of these ranges may be employed as well. However, industrial instrumentation, such as a Coriolis flowmeter for measuring mass flow and other information concerning a material flowing through a conduit, often employ electrical components that require a low DC voltage, such as 1.2-24 VDC, as an electrical power source, and thus are not capable of withstanding such a large range of AC or DC input voltages. Thus, a step-down converter capable of producing a substantially fixed low DC output voltage from either an AC or DC mput voltage is often used to great advantage in such an environment.
A simplified schematic diagram of one particular type of step-down, or "buck," converter or regulator 1 currently in use for converting a positive DC input voltage VIK to a DC output voltage VOUT is provided in Fig. 1. The input voltage VIM is asserted across an input capacitor CA coupled with a ground reference, and is coupled with the dram terminal of an n-channel power field-effect transistor (PET) switch Q. The input capacitor CA acts as a filter to help maintain the voltage level seen by the drain of the switch Q in the presence of changes in the input voltage VIN by providing additional current on a temporary basis to the drain of the switch Q. Similar functionality for the output voltage VOUT is provided by an output capacitor CB-
The gate of the switch Q is driven by a switch controller 2, which turns the switch Q ON and OFF depending on the voltage level of the output voltage VOUT compared to the desired or target output voltage VQUT level Some other measurable quantity at the output, such as current, may be employed by the switch controller 2 alternatively or additionally.

voltage VIN during the ON state. To turn the switch Q OFF3 the gate voltage must be near ground, since the source is driven to slightly below ground due to the diode D becoming forward-biased at that time due to the flyback of the inductor L. When the input voltage VIN is a relatively low DC voltage, generation of the proper gate voltage for the switch Q to be turned ON may be accomplished by way of a readily-available voltage "boost" circuit. However, when the input voltage VIN is a large AC voltage on the order of 265 VRMS, which translates to a maximum DC voltage level of about 375 VDC. timely and accurate control of the gate voltage while providing extremely large Voltage swings at the gate of hundreds of volts typically requires a reiatively complex circuit design for the switch controller 2 involving specialized electrical components.
SUMMARY OF THE INVENTION
Generally, embodiments of the present invention provide a step-down voltage converter for generating an output voltage from an input voltage. The converter includes a switch having first and second terminals, wherein the second terminal is electrically coupled with the output voltage. A rectifier has first and second terminalSj wherein the second terminal is electrically coupled with the output voltage. A first inductor electrically couples the first terminal of the switch with the input voltage. A second inductor magnetically coupled with the first inductor electrically couples the first terminal of the rectifier with a voltage reference. Also, a switching controller coupled with the output voltage is configured to control the switch.
Additional embodiments and advantages of the present invention will be realized by those skilled in the art upon perusal of the following detailed description, taken in conjunction with the accompanymg drawings.
ASPECTS
One aspect of the invention includes a step-down voltage converter for generating an output voltage from an input voltage, comprising:
a switch comprising a first terminal and a second terminal, wherein the second
terminal of the switch is electrically coupled with the output voltage;
a rectifier comprising a first terminal and a second terminal, wherein the second terminal of the rectifier is electrically coupled with the output voltage;
a first inductor electrically coupling the first terminal of .the switch vvith the input voltage;

a second inductor magnetically coupled with the first inductor, the second inductor electrically coupling the first terminal of the rectifier with a voltage reference; and
a switching controller coupled with the output voltage and configured to control the switch.
Preferably, the frrst inductor and the second inductor each comprise an inductance of 1.7 millihenries.
Preferably, the step-down voltage converter further comprises:
a first capacitor electrically coupling the mput voltage with the voltage reference; and
a second capacitor electrically coupling the output voltage with the voltage reference.
Preferably, the first capacitor comprises a capacitance of 22 microfarads.
Preferably, the second capacitor comprises a capacitance of 120 microfarads.
Preferably, voltage reference is ground.
Preferably, a number of turns of the first inductor and a number of turns of the second inductor comprise a ratio of 1:1.
Preferably, the first inductor comprises a first winding of a transformer, wherein the second inductor comprises a second winding of the transformer, and wherein the first inductor and the second mductor are wound about a core.
Preferably, the core is a ferrite core.
Preferably, the input voltage and the output voltage are positive direct-current voltages;
the switch comprises an n-channel field-effect transistor, the first terminal of the switch comprises a drain terminal of the FET, the second terminal of the switch comprises a source terminal of the FET, and the switch controller controls the FET by way of a gate terminal of the FET; and
the rectifier comprises a diode, the first terminal of the rectifier comprises an anode of the diode, and the second terminal of the rectifier comprises a cathode of the diode.
Preferably, the input voltage and the output voltage are negative DC voltages;
the switch comprises a p-channei field-effect transistor, the first terminal of the switch comprises a drain temiinal of the FET, the second terminal of the switch comprises a source terminal of the FET, and the switch controller controls the FET by way of a gate terminal of the FET; and

the rectifier comprises a diode, the first terminal of the rectifier comprises a cathode of the diode, and the second terminal of the rectifier comprises an anode of the diode.
Preferably, the switch controller is configured to control the switch by turning the switch on and off substantially periodically.
Preferably, the switch controller is configured to control the switch based on the output voltage.
Preferably, the switch controller is configured to control the switch based on a current at the output voltage.
Preferably, the input voltage is an alternating current input voltage; and
the step-down voltage converter further comprises an AC rectification circuit coupling the AC input voltage with the first mductor.
Preferably, the AC rectification circuit is configured to convert the AC input voltage to a first positive DC voltage; and
the output voltage is a positive DC output voltage having a lower magnitude that the first positive DC voltage.
Preferably, the AC rectification circuit is configured to convert the AC input voltage to a first negative DC.voltage; and
the output voltage is a negative DC output voltage having a lower magnitude that the first negative DC voltage.
Preferably, an item of industrial instrumentation comprises the step-down voltage converter.
Preferably, a Coriolis flowmeter comprises the step-down voltage converter.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a block diagram of a step-down voltage converter according to the prior ait.
Fig. 2 is a block diagram of a step-down converter according to an embodiment of the invention.
Fig. 3 is a schematic diagram of a step-down converter according to an embodiment of the mvention for generating a positive DC output voltage from a positive DC input voltage.
Fig. 4 is timing diagram of the current through a first inductor and a second inductor, the voltage at the drain of a switch, and the voltage at the anode of a diode, as implemented in a particular embodiment of the step-down voltage converter of Fig. 3.

Fig. 5 is a schematic diagram of a step-down converter according to an embodiment of the invention for generating a negative DC output voltage from a negative DC input voltage.
Fig. 6 is block diagram of the step-down converter of Fig. 2 further employing an AC rectification circuit for an AC input voltage.
DETAILED DESCRIPTION OF THE INVENTION
Fig. 2 is a simplified block diagram of a step-down voltage converter 100 for generating an output voltage VOUT from an input voltage VIN according to an embodiment of the invention. Generally, the converter 100 includes a switch 111 having a first terminal 112 and a second tenninal 114, wherein the second terminal 114 is coupled with the output voltage VouT- The first terminal 112 of the switch 111 is electrically coupled with the input voltage VIN by way of a first inductor 124. The switch 111 is controlled by way of a switch controller 110 coupled with the output voltage Vour- In addition, a second inductor 126 magnetically coupled with the first inductor 124 electrically couples a first tenninal 118 of a rectifier 117 with a voltage reference 128, while a second terminal 120 of the rectifier 117 is electrically coupled with the output voltage VOUT-
Fig. 3 is a simplified schematic diagram of a specific example of the step-down voltage converter 100: a voltage converter 200 for generating a positive DC output voltage VouT from a positive DC input voltage VIN according to an embodiment of the invention. The converter 200 includes a switch Q1 having a first terminal 212 and a second terminal 214, wherein the second terminal 214 is. coupled with the output voltage VQUT. The fust terminal 212 of the switch Qi is electrically coupled with the input voltage VIN by way of a first inductor L1. The switch Qj is controlled by way of a switch controller 210 coupled with the output voltage VQUT- In addition, a second inductor L3 magnetically coupled with the first inductor L1 electrically couples an anode 218 of a rectifier or diode D1 with a voltage reference, while a cathode 220 of the diode D1 is electrically coupled with the output voltage VQUT-
More specifically regarding the particular example of the converter 200 of Fig. 3, the switch Q] may be a FET, such as an n-channel power FET, having a drain terminal 212, a source terminal 214, and a gate terminal 216. As is described in greater detail below, the switch controller 210 controls the FET Q1 by turning the FET Qi ON and OFF by way of the gate 216. In one embodiment, the switch controller 10 turns the FET Qi ON and OFF substantially periodically, based at least in part on the voltage level of the output voltage

flows through the second inductor L2. Also, the voltage YD at the dram 212 of the switch Q1 remains at about VOUT due to the switch Q1 being ON, and the voltage VA at the anode 218 of the diode D1 is -(V1 - VOUT), as described earlier. In other words, the voltages VL1, VL2 across the mductors L1, L2 are equal at (YIN - VQUT). with the drain voltage VD offset higher than the anode voltage VA by the value of the input voltage VIn.

A distinct advantage of various embodiments of the converter 200 described above is the limited voltage swing of the gate 216 of the switch Q1 required to turn ON and OFF the switch Q1. Since the source 214 of the switch Q1 is coupled directly to the output voltage VQUT, the voltage of the gate 216 is required to move only between the output voltage VouT and a few volts higher to operate the switch Q1. Thus, the gate 216 of Q1 may be driven by standard, readily-available electronic components, thereby simplifying the design of the switch controller 210. One or more of these advantages, or others, may also be realized in other applications employing one or more embodiments of the present invention.
Similar advantages may also be realized by another voltage converter 300 according to another embodiment of the invention. Shown in Fig. 5, the converter 300, wliich operates in a manner analogous to that of the converter 200 described above, is configured to convert a negative DC input voltage VIH into a lower-magnitude negative DC output voltage VQUT. While most of the components of the converter 200 and the converter 300, such as the inductors L1. L2, the core 222, and the capacitors C1, C2, are the same, a few modifications are utilized to process the negative DC input voltage VIN. In place of the switch Q1 of the converter 200 is a switch Q2, which is a p-channel power FET in the particular example of Fig. 5. The switch Qn includes a drain terminal 312 coupled with the first inductor L1, a source terminal 314 coupled with the output voltage VOUT and a gate terminal 316. A switch controller 310, operating in a similar fashion to that of the switch controller 210 of the converter 200, controls the operation of the switch Q2 via the gate 316. The switch controller 310 need only move the voltage of the gate 316 between the output voltage VQUT and a few volts lower to operate the switch Q2, thus simplifying the design of the switch controller 310 compared to some prior ait converters.
The converter 300 of Fig. 5 also includes a diode D2 having a first terminal 318 and a second terminal 320. Due to the negative polarity of the input and output voltages VIN, VQUT. the first terminal 318 is the cathode, while the second terminal 320 is the anode, opposite the orientation of the diode D1 of the converter 200. Operation of the converter 300 is analogous to that described above in conjunction with the converter 200 of Fig. 3, with the polarity of all voltages and currents essentially inverted.
A further embodiment of a voltage converter 400 according to an embodiment of the invention for converting an AC input voltage VIK to a DC output voltage VQUT is presented in Fig. 6. In addition to the components described above in conjunction with the converter 100 of Fig. 2, an AC rectification circuit 430 for converting the AC input voltage VIN to a

DC voltage usable by the remainder of the voltage converter 400 is utilized to generate the desired DC output voltage VOUT- In one embodiment in which a positive DC output voltage VouT is required, the AC rectification circuit 430 may be configured to convert the AC input voltage VIN to a first positive DC voltage, which may then be converted to a lower-magnitude DC output voltage VOUT by way of the converter 200 of Fig, 3. In another embodiment, if a negative DC output voltage VQUT is needed, the AC rectification circuit 430 may be configured to convert the AC input voltage VIN to a first negative DC voltage, which in one implementation is subsequently converted to a lower-magnitude negative DC output voltage VQUT via the converter 300 of Fig. 5.
While several embodiments of the invention have been discussed herein, other embodiments encompassed within the scope of the invention are possible. For example, different AC and DC voltage levels may be involved m alternative embodiments, thus possibly indicating the use of component values other than those specifically disclosed herein. Further, references to positive and negative voltage polarities are provided for reference only, and other embodiments of the invention may utilize a different voltage referencing scheme. In addition, components that are electrically coupled may not necessarily be directly interconnected in alternative embodiments. Also, aspects of one embodiment may be combined with those of alternative embodiments to create further implementations of the present invention. Thus, while the present invention has been described in the context of specific embodiments, such descriptions are provided for illustration and not limitation. Accordingly, the proper scope of the present invention is delimited only by the following claims.

CLAIMS
What is claimed is:
1. A step-down voltage converter (100) for generating an output voltage (VOUT) from
an input voltage (VIN), comprising:
a switch (111) comprising a first terminal (112) and a second terminal (114), wherein the second terminal (114) of the switch (111) is electrically coupled with the output voltage (VOUT);
a rectifier (117) comprising a first terminal (118) and a second terminal (120), wherein the second terminal (120) of the rectifier (117) is electrically coupled with the output voltage (VOUT);
a first inductor (124) electrically coupling the first terminal (112) of the switch (111) with the input voltage (VIN);
a second inductor (126) magnetically coupled with the first inductor (124), the second inductor (126) electrically coupling the first terminal (118) of the rectifier (117) with a voltage reference (128); and
a switching controller (110) coupled with the output voltage (VOUT) and configured to control the switch (111).
2. The step-down voltage converter (100) of claim 1, wherein the first inductor (124) and the second inductor (126) each comprise an inductance of 1.7 millineries,
3. The step-down voltage converter (100) of claim 1, farther comprising:
a first capacitor (C1) electrically coupling the input voltage (VIN) with the voltage reference (128); and
a second capacitor (C2) electrically coupling the output voltage with the voltage reference (128).
4. The step-down voltage converter (100) of claim 3, wherein the first capacitor (C1) comprises a capacitance of 22 microfarads.
5. The step-down voltage converter (100) of claim 3, wherein the second capacitor (C2) comprises a capacitance of 120 microfarads. .

6. The step-down voltage converter (100) of claim 1, wherein the voltage reference (128) is ground,
7. The step-down voltage converter (100) of claim 1, wherein a number of turns of the first inductor (124) and a number of turns of the second inductor (126) comprise a ratio of 1:1.
8. The step-down voltage converter (100) of claim 1, wherein the first inductor (124) comprises a first winding of a transformer, wherein the second inductor (126) comprises a second winding of the transformer, and wherein the first mductor (124) and the second inductor (126) are wound about a core (222).
9. The step-down voltage converter (100) of clam 8, wherein the core (222) is a ferrite core.
10. The step-down voltage converter (100) of claim 1, wherein;
the input voltage (VIN) and the output voltage (VOUT) are positive direct-current (DC) voltages;
the switch (111) comprises an n-channel field-effect transistor (FET) (Q1), the first terminal (112) of the switch (111) comprises a drain terminal (212) of the FET (Q1), the second terminal (114) of the switch (111) comprises a source terminal (214) of the FET (Q1), and the switch controller (110) controls the FET (Q1) by way of a gate terminal (216) of the FET(Q1);and
wherein the rectifier (117) comprises a diode (D1). the first terminal (118) of the rectifier (117) comprises an anode (218) of the diode (D1), and the second terminal (120) of the rectifier (117) comprises a cathode (220) of the diode (D1).
11. The step-down voltage converter (100) of claim 1, wherein:
the input voltage (VIN) and the output voltage (VOUT) are negative DC voltages;
the switch (111) comprises a p-charmel field-effect transistor (FET) (Q2), the first terminal (112) of the switch (111) comprises a drain tenninal (312) of the FET (Q2); the second terminal (114) of the switch (111) comprises a source terminal (314) of the FET (Q2), and the switch controller (110) controls the FET (Q2) by way of a gate terminal (316) of the FET(Q2);and

wherein the rectifier (117) comprises a diode (D2), the first terminal (118) of the rectifier (117) comprises a cathode (318) of the diode (D2), and the second tenninal (120) of the rectifier (117) comprises an anode (320) of the diode (D2).
12. The step-down voltage converter (100) of claim 1, wherein the switch controller (110) is configured to control the switch (111) by turning the switch (HI) on and off substantially periodically.
13 The step-down voltage converter (100) of claim 1, wherein the switch controller (110) is configured to control the switch (111) based on the output voltage (VOUT).
14. The step-down voltage converter (100) of claim 1, wherein the switch controller
(110) is configured to control the switch (111) based on a current at the output voltage
(VQUT)-
15. The step-down voltage converter (100) of claim 1, wherein:
the input voltage (VIN) is an alternating current (AC) input voltage; and the step-down voltage converter (100) further comprises an AC rectification circuit (430) coupling the AC mput voltage with the first inductor (124).
16. The step-down voltage converter (100) of claim 15, wherein:
the AC rectification circuit (430) is configured to convert the AC input voltage to a first positive DC voltage; and
the output voltage (VOUT) is a positive DC output voltage having a lower magnitude that the first positive DC voltage,
17. The step-down voltage converter (100) of claim 15, wherein:
the AC rectification circuit (430) is configured to convert the AC input voltage to a first negative DC voltage; and
the output voltage (VOUT) is a negative DC output voltage having a lower magnitude that the first negative DC voltage.
18. An item of industrial instrumentation comprising the step-down voltage converter
(100) of claim 1.

19. A Coriolis flowmeter comprising the step-down voltage converter (100) of claim 1.

Documents:

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Patent Number

271449

Indian Patent Application Number

916/CHENP/2008

PG Journal Number

09/2016

Publication Date

26-Feb-2016

Grant Date

22-Feb-2016

Date of Filing

25-Feb-2008

Name of Patentee

MICRO MOTION, INC

Applicant Address

7070 WINCHESTER CIRCLE BOULDER, COLORADO 80301

Inventors:

#	Inventor's Name	Inventor's Address
1	MANSFIELD, WILLIAM, M	475 DEERTRAIL ROAD BOULDER, COLORADO 80302
2	LINDEMANN, STIG	IVAR HUITFELDTS GADE 75, 4, SAL DK-8200 AARHUS N

PCT International Classification Number

H02M3/155

PCT International Application Number

PCT/US05/26456

PCT International Filing date

2005-07-26

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA