IC card

• US 5,568,441 A
• Filed: 08/23/1995
• Issued: 10/22/1996
• Est. Priority Date: 09/27/1994
• Status: Expired due to Fees

• Current Assignee: Mitsubishi Denki Kabushiki Kaisha (Mitsubishi Electric Corporation)
• Original Assignee: Mitsubishi Denki Kabushiki Kaisha (Mitsubishi Electric Corporation)
• Inventors: Sanemitsu, Yoshikado
• Primary Examiner(s): NGUYEN, TAN
• Application Number:
  US08/518,458
• Time in Patent Office: 426 Days
• Field of Search: 365/228, 365/229, 365/226, 235/380, 235/441, 235/451, 235/492
• US Class Current: 365/229
• CPC Class Codes: G11C 5/141 Battery and back-up supplies

Abstract

An IC card according to the present invention includes a lithium cell that, when the IC card is disconnected from a system, supplies power required for retention of data in a volatile static random access memory (SRAM); a first capacitor connected in parallel with the lithium cell in order to accumulate charge, a second capacitor connected in parallel with the lithium cell in order to accumulate charge, and a switch for connecting the first capacitor and the second capacitor in series with each other during replacement of the lithium cell. The series circuit of the first and second capacitors serves as a backup power source during replacement of the lithium cell. As a result, the time available for cell replacement without loss of stored data is increased.

Claims

1. An IC card comprising:

a connector;

a volatile memory connected to said connector for storing data;

a primary cell for supplying power to said memory for data retention;

a first current limiting element for preventing overflow of current from said primary cell via said connector;

a second current limiting element for protecting said primary cell from being charged via said connector

a plurality of charge accumulation devices for accumulating charge supplied from said primary cell; and

a switch for connecting said plurality of charge accumulation devices in parallel with said primary normal operation and for connecting said plurality of charge accumulation devices in series during replacement of said primary cell.

2. The IC card according to claim 1, wherein said plurality of charge accumulation devices are two capacitors.

3. The IC card according to claim 2, wherein said memory is a static random access memory.

4. The IC card according to claim 2, wherein said plurality of charge accumaltion devices are a secondary cell and a capacitor.

5. The IC card according to claim 4, wherein said memory is a static random access memory.

6. The IC card according to claim 2, wherein said primary cell and said switch are interlocked so that, in order to remove said primary cell for replacement, said switch must be actuated to connect said charge accumulation devices in series.

7. The IC card according to claim 6, wherein said plurality of charge accumulation devices are two capacitors and said memory is a static random access memory.

8. The IC card according to claim 6, wherein said plurality of charge accumulation devices are a secondary cell and a capacitor and said memory a static random access memory.

9. The IC card according to claim 1, wherein said second current limiting element is interposed between said primary cell and said plurality of charge accumulation devices for charging said plurality of charge accumulations devices via said connector.

10. The IC card according to claim 9, including two charge accumulation devices and wherein said memory is a static random access memory.

11. The IC card according to claim 9, wherein said primary cell and said switch are interlocked so that, in order to remove said primary cell for replacement, said switch must be actuated to connect said charge accumulation devices in series.

12. The IC card according to claim 11, wherein said plurality of charge accumulation devices are two capacitors and said memory is a static random access memory.

13. The IC card according to claim 1, wherein said second current limiting element is connected to said plurality of charge accumulation devices so that any of said plurality Of charge accumulation devices can be charged via said connector.

14. The IC card according to claim 13, wherein said plurality of charge accumulation devices are two capacitors and said memory is a static random access memory.

15. The IC card according to claim 13, wherein said primary cell and said switch are interlocked so that, in order to remove said primary cell for replacement, said switch must be actuated to connect said charge accumulation devices in series.

16. The IC card according to claim 15, wherein said plurality of charge accumulation devices are two capacitors and said memory is a static random access memory.