Low battery power state determination apparatus and method for secondary battery

• US 5,675,236 A
• Filed: 05/24/1995
• Issued: 10/07/1997
• Est. Priority Date: 05/25/1994
• Status: Expired due to Fees

• Current Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Original Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Inventors: Nakanishi, Hideki
• Primary Examiner(s): Wong, Peter S.
• Assistant Examiner(s): Law, Patrick B.
• Application Number:
  US08/448,793
• Time in Patent Office: 867 Days
• Field of Search: 320/13, 320/21, 320/30, 320/32, 320/33, 320/48, 324/433
• US Class Current: 320/136
• CPC Class Codes: G01R 19/16542 for batteries charge condition monitoring in G01R31/36
• CPC Class Codes: G01R 31/3648 comprising digital calculation means, e.g. for performing an algorithm
• CPC Class Codes: G01R 31/3842 combining voltage and current measurements
• CPC Class Codes: H02J 7/0048 Detection of remaining charge capacity or state of charge [SOC]
• CPC Class Codes: Y10S 320/21 State of charge of battery

Abstract

Current of electricity provided from a secondary battery 1 to a load 2, such as a personal computer and a printer, is determined by a current determination circuit 8. The detected result is compared with a predetermined threshold by a comparing circuit 7, the comparison result is used to deciding a voltage threshold for judging whether or not the secondary battery is in a low battery power state. After the voltage threshold is decided, a terminal voltage of the secondary battery is measured by a voltage determination circuit 6, then the measured result is compared with the voltage threshold. Thereby whether or not the secondary battery 1 is in a low battery power state is judged.

Claims

1. A low battery power state detection apparatus for a secondary battery supplying power to an electrical apparatus whose load changes at a predetermined period, comprising:

voltage detection means for detecting a discharged voltage from the secondary battery when the load of said electrical apparatus is a predetermined load during discharge of the secondary battery;

current detection means for detecting a discharged current from the secondary battery when the load of said electrical apparatus is the predetermined load during discharge of the secondary battery;

determination means for determining a threshold voltage value on the basis of the current detected by said current detection means, said threshold voltage value being used for judging whether or not the secondary battery is in the low battery power state; and

judging means for judging whether or not the secondary battery is in the low battery power state by comparing the threshold voltage value determined by said determination means with the voltage detected by said voltage detection means.

2. A low battery power state detection method for a secondary battery supplying power to an electrical apparatus whose load changes at a predetermined period, comprising the steps of:

detecting a discharged current of the secondary battery when the load of said electrical apparatus is a predetermined load during discharge of the secondary battery;

determining a threshold voltage value on the basis of the discharged current detected by said current detection step, said threshold voltage value being used for judging whether or not the secondary battery is in the low battery state;

detecting a discharged voltage of the secondary battery when the load of said electrical apparatus is the predetermined load during discharge of the secondary battery; and

judging whether or not the secondary battery is in the low battery power state by comparing the threshold voltage value determined in said determining step with the discharged voltage detected in said voltage detecting step.

3. A low battery power state determination apparatus for a secondary battery supplying an electric apparatus with power, comprising:

voltage detection means for detecting a discharged voltage from the secondary battery at a first predetermined period during discharge of the secondary battery;

determination means for determining change of discharged voltage on the basis of the discharged voltage detected by said voltage detection means;

judging means for judging whether or not the secondary battery is in the low battery state on the basis of change of the discharged voltage from the secondary battery determined by said determination means and a predetermined value; and

inhibiting means for inhibiting said judging means from judging until a second predetermined period has elapsed after the secondary battery starts discharging, said second predetermined period being longer than the first predetermined period.

4. The low battery power state determination apparatus for a secondary battery according to claim 3, wherein said determination means comprises memory means for storing the discharged voltage detected in the previous routine of the low battery state determination process by said voltage detection means and subtraction means for calculating a difference between the discharged voltage stored in said memory means and the currently detected discharged voltage.

5. The low battery power state determination apparatus for a secondary battery according to claim 3, further comprising:

first control means for controlling said voltage detection means and said determination means to repeatedly operate after the secondary battery is judged by said judging means that it is not in the low battery power state;

second judging means for judging that the secondary battery is in the low battery power state when the change of voltage obtained by said determination means is larger than a predetermined value after a predetermined time period has elapsed under control of said first control means;

second control means for controlling said voltage detection means and said determination means to repeatedly operate when the change of voltage obtained by said determination means is larger than a predetermined value before the predetermined time period has elapsed under control of said first control means; and

stopping means for stopping discharging from the secondary battery, when the change of voltage obtained by said determination means is larger than the predetermined value, by determining that a load is too heavy for the secondary battery under control of said second control means.

6. A low battery power state determination method for a secondary battery supplying an electric apparatus with power, comprising:

a voltage detection step of detecting a discharged voltage of the secondary battery at a first predetermined period;

a determination step of determining change of discharged voltage on the basis of the discharged voltage detected in said voltage detection step;

a judging step of judging whether or not the secondary battery is in the low battery state on the basis of the change of the discharged voltage from the secondary battery determined in said determination step and a predetermined value; and

an inhibition step of inhibiting said judging step from judging until a second predetermined period has elapsed after the secondary battery starts discharging, said second predetermined period being longer than said first predetermined period.

7. The low battery power state determination method for a secondary battery according to claim 6, wherein said determination step comprises a memory step of storing the discharged voltage detected in the previous routine of the low battery state determination process in said voltage detection step and a subtraction step of calculating a difference between the discharged voltage stored in said memory step and the currently detected discharged voltage.

8. The low battery power state determination method for a secondary battery according to claim 6, further comprising:

a first control step of repeatedly operating said voltage detection step and said determination step after the secondary battery is judged in said judging step that it is not in the low battery power state;

a second judging step of judging that the secondary battery is in the low battery power state when the change of voltage obtained in said determination step is larger than a predetermined value after a predetermined time period has elapsed during said first control step;

a second control step of repeatedly operating said voltage detection step and said determination step when the change of voltage obtained in said determination step is larger than a predetermined value before the predetermined time period has elapsed during said first control step; and

a stopping step of stopping discharging from the secondary battery, when the change of voltage obtained in said determination step is larger than the predetermined value, by determining that a load is too heavy for the secondary battery during said second control step.