Input regulated DC to DC converter for power scavenging

• US 20090015216A1
• Filed: 06/13/2008
• Published: 01/15/2009
• Est. Priority Date: 06/15/2007
• Status: Active Grant

• Current Assignee: Fisher Controls International LLC (Emerson Electric Company)
• Original Assignee: Fisher Controls International LLC (Emerson Electric Company)
• Inventors: Seberger, Stephen G., Wittkop, Adam J.
• Granted Patent: US 7,911,189 B2
• Time in Patent Office: Days
• US Class Current: 323/234
• CPC Class Codes: H02J 7/345 using capacitors as storage or buffering devices
• CPC Class Codes: H02M 1/0006 Arrangements for supplying an adequate voltage to the control circuit of converters
• CPC Class Codes: H02M 1/0022 the disturbance parameters being input voltage fluctuations
• CPC Class Codes: H02M 3/155 using semiconductor devices only

Abstract

A method of scavenging power in a circuit having a power source generating electric current includes connecting a power scavenging device having an input terminal pair and an output terminal pair to the circuit via the input terminal pair, dynamically regulating a voltage drop across the input terminal pair of the power scavenging device, harvesting electrical energy available at the regulated voltage drop from the electric current flowing through the first input terminal pair of the power scavenging device, and providing the harvested electrical energy at the output terminal pair of the power scavenging device.

Claims

1. A method of scavenging power in a circuit including a power source generating electric current, the method comprising:

connecting a power scavenging device having an input terminal pair and an output terminal pair to the circuit via the input terminal pair;

dynamically regulating a voltage drop across the input terminal pair of the power scavenging device;

harvesting electrical energy available at the regulated voltage drop from the electric current flowing through the first input terminal pair of the power scavenging device; and

providing the harvested electrical energy at the output terminal pair of the power scavenging device.

2. The method of claim 1, wherein dynamically regulating a voltage drop across the input terminal pair includes maintaining a constant voltage drop across the input terminal pair when the electric current in the circuit varies with time.

3. The method of claim 1, wherein further comprising connecting a scavenger powered load to the output terminal pair.

4. The method of claim 1, wherein providing the harvested electrical energy at the output terminal pair includes regulating a voltage drop across the output terminal pair of the power scavenging device using an adjustable shunt regulator.

5. The method of claim 1, wherein harvesting electrical energy includes storing the electrical energy in a power storage device.

6. The method of claim 5, wherein the power storage device is a supercapacitor.

7. The method of claim 1, wherein connecting the power scavenging device to the electrical circuit includes connecting the power scavenging device in series with the electrical power source.

8. The method of claim 7, wherein the electrical circuit further includes a power consuming device having a time-variable power requirement;

and wherein

connecting the scavenging device to the electrical circuit further includes connecting the power scavenging device in series with the power consuming device; and

wherein dynamically regulating a voltage drop across the input terminal pair includes regulating the voltage drop according to the power requirement of the power consuming device.

9. The method of claim 1, wherein dynamically regulating the voltage drop includes using an input voltage regulating circuit to generate a voltage control signal and an inductor to accumulate current.

10. The method of claim 9, wherein using the inductor includes adjusting a period of time during which the inductor accumulates current in one cycle of operation based on the voltage control signal.

11. The method of claim 1, wherein regulating the voltage drop across the input of the power scavenging device includes regulating the voltage drop according to an inverse relationship between input current entering through one of the pair of input terminals of the power scavenging device and the voltage drop across the input terminal pair of the power scavenging device.

12. The method of claim 11, wherein regulating the voltage drop across the input of the power scavenging device further includes maintaining the voltage drop in a range between a minimum tolerable value and a maximum tolerable value.

13. The method of claim 11, wherein regulating voltage drop across the input of the power scavenging device further includes regulating the voltage drop using a current sensor and an inverting amplifier, wherein the inverting amplifier generates a feedback signal controlling a period of time during which an inductor accumulates current in one cycle of operation and wherein the inductor supplies current to the output terminal pair of the power scavenging device.

14. The method of claim 1, wherein harvesting electrical energy available from an electric current includes limiting an amount of energy which can be transferred from the power scavenging device to the electrical circuit in a fault condition.

15. The method of claim 14, wherein limiting an amount of energy which can be transferred from the power scavenging device to the electrical circuit in a fault condition includes cyclically accumulating and discharging electrical current flowing through an isolation transformer;

wherein a first winding of the isolation transformer is connected to the positive terminal of the input of power scavenging device and a second winding of the isolation transformer is an output of the power scavenging device.

16. The method of claim 15, further including:

limiting the amount of power which can be transferred to the output of the power scavenging device across the isolation transformer.

18. The method of claim 15, wherein limiting the amount of energy which can be transferred from the power scavenging device to the electrical circuit in a fault condition includes meeting an intrinsic safety energy limitation of a scavenger powered load, wherein the scavenger powered load is connected to the output of the power scavenging device.

19. The method of claim 1, wherein regulating a voltage drop across the input of the power scavenging device further includes providing a line filter characteristic in the power scavenging device, wherein the line filter characteristic allows for voltage modulation across the electrical circuit,

20. The method of claim 19, wherein providing the line filter characteristic includes regulating the rate of change of current flowing through the power scavenging device.

17. The method of clam 15, further including:

providing at least a third winding to the isolation transformer, wherein the second and the third windings provide separate outputs of the power scavenging device.

21. A scavenging circuit for harvesting excess power from a source circuit, comprising:

a pair of input terminals to connect the scavenging circuit to a source circuit;

voltage regulating circuit to generate a voltage regulation signal based on a voltage drop across the pair of input terminals;

an accumulation element for temporary accumulation of electric energy harvested from the electric circuit;

a boost DC to DC controller that controls the accumulation element based on the signal from the voltage regulating circuit; and

a pair of output terminals to output electrical power accumulated by the accumulation element;

wherein the scavenging circuit maintains a controlled voltage across the pair of input terminals.

22. The scavenging circuit of claim 21, wherein the current accumulating circuit element is an inductor.

23. The scavenging circuit of claim 21, wherein the source circuit is associated with a DC current varying with time.

24. The scavenging circuit of claim 21, wherein the DC to DC controller is a boost DC to DC controller including:

a switching pin connected to one of the terminals of the accumulation element; and

a ground pin that connects connected to ground;

wherein

the scavenging circuit electrically connects the switching pin to the ground pin in a first mode of operation to cause the accumulation element to build up electrical current, and wherein the scavenging circuit disconnects the switching pin from the ground pin in a second mode of operation to cause the accumulation element to direct the built up electrical current to one of the pair of output terminals.

25. The scavenging circuit of claim 24, wherein the DC to DC controller further includes a feedback pin through which the DC to DC controller receives the signal generated by the voltage regulating circuit;

wherein the DC to DC controller determines the amount of time the DC to DC controller operates in the first mode of operation and the amount of time the DC to DC controller operates in the second mode of operation based on the signal received via the feedback pin.

26. The scavenging circuit of claim 21, further comprising a capacitor connected across the pair of output terminals that filters output voltage at the pair of output terminals.

27. The scavenging circuit of claim 21, wherein the voltage regulating circuit includes an inverting amplifier and a current sensor operatively coupled to the inverting amplifier.

28. The scavenging circuit of claim 21, wherein the voltage regulating circuit generates a voltage regulation signal further based on the current flowing through the pair of input terminals.

29. The scavenging circuit of claim 28, wherein the voltage regulating circuit includes a gain-limiting resistor to generate a stronger voltage regulation signal when the current is weaker.

30. The scavenging circuit of claim 21, wherein the accumulation element is an isolation transformer that provides a fault energy limitation.

31. The scavenging circuit of claim 30, wherein the isolation transformer includes a:

a first coil in electrical communication with the pair of input terminals; and

a second coil in electrical communication with the pair of output terminals and separated from the first coil by a core element;

wherein the first coil induces current in the second coil during operation of the scavenger circuit.

32. The scavenging circuit of claim 30, wherein the isolation transformer includes a plurality of windings to provide voltage to a corresponding plurality of outputs.

33. A circuit for communicating information in a process control environment, comprising:

a first device that generates a DC current signal and propagates the signal through the circuit;

a second device that receives the signal;

a power scavenging device connected in series with the first device and with the second device that harvests excess electrical power at a regulated voltage drop across the scavenger device, the power scavenging device including;

a pair of input terminals connected to the circuit; and

a pair of output terminals for connecting to a consumer circuit.

34. The circuit of claim 33, further including an adjustable shunt regulator adapted to regulate an output voltage across the pair of output terminals of the power scavenging device.

35. The circuit of claim 33, wherein the first device is a controller associated with a distributed control system, the second device is a field device that performs a function in a process control environment, and wherein the DC current signal is in the 4 to 20 mA range.

36. The circuit of claim 33, wherein the consumer circuit includes a supercapacitor coupled to the pair of output terminals of the power scavenging device.