Microelectromechanical isolating circuit

• US 20040189142A1
• Filed: 03/25/2003
• Published: 09/30/2004
• Est. Priority Date: 03/25/2003
• Status: Active Grant

• Current Assignee: Rockwell Automation Technologies Incorporated (Allen-Bradley Co., Inc.)
• Original Assignee: Rockwell Automation Technologies Incorporated (Allen-Bradley Co., Inc.)
• Inventors: Kretschmann, Robert J., Harris, Richard D., Discenzo, Frederick M., Pond, Robert J., Herbert, Patrick C., Szabo, Louis F., Lucak, Mark A., Knieser, Michael J.
• Granted Patent: US 6,975,193 B2
• Time in Patent Office: Days
• US Class Current: 310/309
• CPC Class Codes: H01H 59/0009 making use of micromechanics

Abstract

Microelectromechanical (MEMS) switches are used to implement a flying capacitor circuit transferring of electrical power while preserving electrical isolation for size critical applications where transformers or coupling capacitors would not be practical. In one embodiment, the invention may be used to provide input circuits that present a programmable input impedance. The circuit may be modified to provide for power regulation.

Claims

1. An electrical isolator comprising:

a MEMS switch array having an actuator receiving an actuator signal to alternately connect a capacitor between two input terminals and two output terminals, the MEMS switch array operating so that in a first switch state, the capacitor is connected to the input terminals and not the output terminals, and in a second switch state, the capacitor is connected to the output terminals and not the input terminals; and

an actuator signal generator providing the actuator signal to repeatedly switch the MEMS switch array between the first and second states.

2. The electrical isolator of claim 1 wherein the actuator signal generator is a connection to the capacitor so that a predetermined voltage on the capacitor causes a switching of the MEMS switch array from the first state to the second state.

3. The electrical isolator of claim 1 wherein the actuator signal generator is an electronic oscillator.

4. The electrical isolator of claim 1 wherein the electronic oscillator is adjustable to provide an oscillator output that adjustably controls electrical power at the output terminal.

5. The electrical isolator of claim 1 wherein the electronic oscillator communicates with the output terminals to provide an oscillator output that is a function of the electrical signal at the output terminal to provide regulation of electrical power at the output terminal.

6. The electrical isolator of claim 1 wherein the switch array is constructed from four single pole single throw switches.

7. The electrical isolator of claim 1 wherein the switch array includes at least one beam supported on flexible transverse arms to move longitudinally above a substrate, the beam carrying at least one transversely extending contact arm to connect and disconnect from a stationary contact pylon extending from the substrate.

8. The electrical isolator of claim 7 having at least two contact arms extending transversely from the beam in opposite directions to alternately connect and disconnect from respective corresponding stationary contact pylons extending from the substrate, wherein the contact arms are-sized and placed so that beam and contact arms are longitudinally and transversely symmetrical.

9. The electrical isolator of claim 7 wherein the actuator is selected from the group consisting of:

a Lorentz actuator, an electrostatic actuator, a piezoelectric actuator, or a thermal actuator.

10. The electrical isolator of claim 7 wherein the beam supported one or more pairs of flexible transverse arms extending in a bow to present force increasingly resisting longitudinal motion of the beam in a first direction up to a snap point after which the force abruptly decreases.

11. The electrical isolator of claim 10 wherein the snap point changes as a function of direction of motion on the beam.

12. A MEMS device comprising:

a MEMS switch array receiving at least one actuator signal to alternately connect a capacitor between two input terminals and two output terminals, the MEMS switch array operating so that in a first switch state, the capacitor is connected to the input terminals and not the output terminals and in a second switch state, the capacitor is connected to the output terminals and not the input terminals, wherein the switching of the MEMS switch array is according to at least one actuator signal;

a shunt for discharging the capacitor when it is connected to the output terminals, either transferring the charge to the supply return or to a supply capacitor for subsequent use in powering circuitry; and

a controller providing the actuator signal to the MEMS switch array to control the duty cycle of switching to present a predetermined effective impedance at the input terminal.

13. The MEMS circuit of claim 12 wherein the predetermined resistance may be selected from among a set of different predetermined resistances suitable for different input voltages.

14. The MEMS circuit of claim 12 including further a resistance in series with the input terminals

15. The MEMS circuit of claim 12 including further a voltage sensor connected to the output terminals and communicating with the controller to change the predetermined effective resistance as a function of sensed voltage.

19. The isolating input circuit of claim 12 wherein the bias means is electronically controllable so that the predetermined magnitude may be set electronically from a set of magnitudes.

20. The isolating input circuit of claim 12 wherein the predetermined resistance may be selected from among a set of different predetermined resistances.

21. The isolating input circuit of claim 12 including a setting control setting the predetermined resistance as a function of the predetermined magnitude.

22. The electrical isolator of claim 12 wherein the actuator is selected from the group consisting of:

a Lorentz actuator, an electrostatic actuator, a piezoelectric actuator, or a thermal actuator.

23. The electrical isolator of claim 12 wherein the bias means is selected from the group consisting of:

a Lorentz actuator, an electrostatic actuator, a piezoelectric actuator, or a thermal actuator.

16. An input circuit for an industrial controller comprising:

at least one MEMS switch array receiving at least one actuator signal to alternately connect a capacitor between two input terminals and two output terminals, the MEMS switch array operating so that in a first switch state, the capacitor is connected to the input terminals and not the output terminals and, in a second switch state, the capacitor is connected to the output terminals and not the input terminals, wherein the switching of the MEMS switch array is according to at least one actuator signal;

a shunt for discharging the capacitor when it is connected to the output terminals;

a controller providing the actuator signal to the MEMS switch array to control the duty cycle of switching to present a predetermined effective impedance at the input terminal; and

a detector attached to the output terminals to deduce a predetermined switching voltage at the input terminals

17. An isolating input circuit for an industrial control comprising:

a MEMS isolator having an actuator communicating with a set of input terminals and attached to one end of a movable element joined through an insulating section with a sensor element whereby electrical signals attached to the actuator are mechanically communicated in isolation from the sensor element;

a MEMS switch connected across the input terminals and activated by a switch signal to shunt the input terminals; and

a controller providing the switch signal to control the duty cycle of switching to present a predetermined effective impedance at the input terminal.

18. The isolating input circuit of claim 17 wherein the movable element of the MEMS isolator includes a bias means resisting the actuator whereby the electrical signals attached to the actuator must be of a predetermined magnitude to cause motion of the movable element.

24. A method for electrically isolated power transfer comprising the steps of:

(a) at a first time, connecting a first and second terminal of a capacitor to corresponding input terminals using a MEMS switch array;

(b) at a second time, connecting the first and second terminal of the capacitor to corresponding output terminals using the MEMS switch array; and

(c) repeating steps (a) and (b) repeatedly;

whereby electrical power may be transferred between the input terminals and the output terminals while maintaining electrical isolation between the input and output terminals.

25. The method of claim 24 wherein the repetition of step (c) occurs at a regular interval.

26. The method of claim 24 wherein the repetition of step (c) occurs at a variable interval related to a transfer of power from the output terminals to a connected circuit thereby providing electrical regulation of power.

27. The method of claim 24 wherein the switch array is constructed from four single-pole, single-throw switches.

28. The method of claim 24 wherein the switch array includes at least one beam supported on flexible transverse arms to move longitudinally above a substrate, the beam carrying at least one transversely extending contact arm to connect and disconnect from a stationary contact pylon extending from the substrate.