DRIVE CIRCUIT FOR AN ELECTRO-OPTIC REARVIEW MIRROR SYSTEM

• US 20140209790A1
• Filed: 01/24/2014
• Published: 07/31/2014
• Est. Priority Date: 01/25/2013
• Status: Active Grant

• Current Assignee: Gentex Corporation
• Original Assignee: Gentex Corporation
• Inventors: Turnbull, Robert R., Poe, G. Bruce
• Granted Patent: US 9,908,474 B2
• Time in Patent Office: Days
• US Class Current: 250/208.2
• CPC Class Codes: B60R 1/088 using a cell of electrically changeable optical characteristic, e.g. liquid-crystal or electrochromic mirrors
• CPC Class Codes: G02F 1/163 Operation of electrochromic cells, e.g. electrodeposition cells; Circuit arrangements therefor

Abstract

An electro-optic rearview mirror system is provided. The electro-optic rearview mirror system includes an inside electro-optic rearview mirror element and an outside electro-optic rearview mirror element in series with the inside electro-optic rearview mirror element. A drive circuit is in electrical communication with the inside electro-optic rearview mirror element and the outside electro-optic rearview mirror element and includes a first power operational amplifier and a second power operational amplifier, both of which are configured as voltage followers. The drive circuit is configured to apply overvoltage to the inside electro-optic rearview mirror element if the outside electro-optic rearview mirror element is shorted.

Claims

1. An electro-optic rearview mirror system comprising:

an inside electro-optic rearview mirror element;

an outside electro-optic rearview mirror element electrically connected in series with the inside electro-optic rearview mirror element; and

a drive circuit in electrical communication with the inside electro-optic rearview mirror element and the outside electro-optic rearview mirror element and comprising a first power operational amplifier and a second power operational amplifier, both of which are configured as voltage followers, wherein the drive circuit is configured to apply overvoltage to the inside electro-optic rearview mirror element if the outside electro-optic rearview mirror element is shorted.

2. The electro-optic rearview mirror system of claim 1, wherein the inside electro-optic rearview mirror element comprises an inside electrochromic mirror element and the outside electro-optic rearview mirror element comprises an outside electrochromic mirror element.

3. The electro-optic rearview mirror system of claim 1, wherein the drive circuit further comprises a second outside electro-optic rearview mirror element electrically connected in series with a ground side of the outside electro-optic rearview mirror element.

4. The electro-optic rearview mirror system of claim 3, wherein the drive circuit further comprises a third power operational amplifier configured as a voltage follower that stabilizes a voltage at a center point of the outside electro-optic rearview mirror element and the second electro-optic rearview mirror element.

5. The electro-optic rearview mirror system of claim 1, wherein the drive circuit is configured to receive one of an input pulse-width modulation duty cycle and a digital-to-analog converter voltage that is reduced to approximately zero volts to initiate clearing of the inside and outside electro-optic rearview mirror elements.

6. The electro-optic rearview mirror system of claim 1, wherein the drive circuit is configured to receive a first pulse-width modulation signal for independently controlling a transmittance state of the inside electro-optic rearview mirror element and a second pulse-width modulation signal for independently controlling a transmittance state of the outside electro-optic rearview mirror element.

7. The electro-optic rearview mirror system of claim 6, wherein the drive circuit is further configured to average the second pulse-width modulation signal.

8. An electro-optic rearview mirror system comprising:

an inside electro-optic rearview mirror element;

an outside electro-optic rearview mirror element in series with the inside electro-optic rearview mirror element; and

a drive circuit in electrical communication with the inside electro-optic rearview mirror element and the outside electro-optic rearview mirror element, wherein the drive circuit is configured to differentially sense a voltage associated with the inside electro-optic rearview mirror element such that if the outside electro-optic rearview mirror element is shorted, a voltage associated with the inside electro-optic rearview mirror element remains substantially unchanged.

9. The electro-optic rearview mirror system of claim 8, wherein the inside electro-optic rearview mirror element comprises an inside electrochromic mirror element and the outside electro-optic rearview mirror element comprises an outside electrochromic mirror element.

10. The electro-optic rearview mirror system of claim 8, wherein the drive circuit comprises a first power operational amplifier and a second power operational amplifier, both of which are configured as differential amplifiers.

11. The electro-optic rearview mirror system of claim 8, wherein the drive circuit is configured to receive one of an input pulse-width modulation duty cycle and a digital-to-analog converter voltage that is reduced to approximately zero volts to initiate clearing of the inside and outside electro-optic rearview mirror elements.

12. The electro-optic rearview mirror system of claim 8, wherein the drive circuit is configured to receive a first pulse-width modulation signal for independently controlling a transmittance state of the inside electro-optic rearview mirror element and a second pulse-width modulation signal for independently controlling a transmittance state of the outside electro-optic rearview mirror element.

13. The electro-optic rearview mirror system of claim 12, wherein the drive circuit further comprises a first power operational amplifier configured as a differential amplifier and a second power operation amplifier configured as a voltage follower, further wherein a voltage across the inside electro-optic rearview mirror element is a function of an average voltage of the first pulse-width modulation signal.

14. The electro-optic rearview mirror system of claim 13, wherein the drive circuit is further configured to average the second pulse-width modulation signal.

15. An electro-optic rearview mirror system comprising:

a drive circuit for driving an inside electro-optic rearview mirror element and at least one outside electro-optic rearview mirror element of a vehicle, the vehicle having an ambient light sensor and a glare light sensor, the drive circuit comprising;

a controller responsive to outputs of the ambient light sensor and the glare light sensor for generating voltage control signals, the controller further generating a selection signal for alternatingly selecting one of the inside and outside electro-optic rearview mirror elements;

a variable voltage source for generating a drive voltage; and

a selection circuit coupled to the variable voltage source for receiving the drive voltage, the selection circuit also coupled to the controller for receiving the selection signal, the selection circuit further coupled to the inside electro-optic rearview mirror element and the outside electro-optic rearview mirror element for selectively supplying the drive voltage thereto in response to the selection signal.

16. The electro-optic rearview mirror system of claim 15, wherein the variable voltage source includes a first power transistor and a second power transistor connected in series.

17. The electro-optic rearview mirror system of claim 15, wherein the at least one outside electro-optic rearview mirror element comprises a first outside electro-optic rearview mirror element in parallel with a second outside electro-optic rearview mirror element.

18. The electro-optic rearview mirror system of claim 15, wherein the selection signal comprises a periodic square wave with a fixed duty cycle.

19. The electro-optic rearview mirror system of claim 15, wherein the selection circuit comprises a first selection switch for selectively enabling the drive voltage to be applied across the inside electro-optic mirror element and a second selection switch for selectively enabling the drive voltage to be applied across the outside electro-optic mirror element, wherein if it the controller detects that the outside electro-optic rearview mirror element is shorted, the controller stops applying the drive voltage to the outside electro-optic rearview mirror element while continuing to apply the selection signal to the first selection switch to allow for continued operation of the inside electro-optic rearview mirror element.

20. The electro-optic rearview mirror system of claim 19, further comprising a protection circuit configured to prevent the second selection switch from applying the drive voltage to the outside electro-optic rearview mirror element when the outside electro-optic rearview mirror element is shorted.