Apparatus for monitoring power of battery to supply electric power to load

• US 5,841,284 A
• Filed: 06/23/1995
• Issued: 11/24/1998
• Est. Priority Date: 11/11/1994
• Status: Expired due to Term

• Current Assignee: Fujitsu Limited
• Original Assignee: Fujitsu Limited
• Inventors: Takahashi, Susumu
• Primary Examiner(s): BROWN, GLENN WARNER
• Application Number:
  US08/494,059
• Time in Patent Office: 1,250 Days
• Field of Search: 324/426, 324/427, 324/428, 320/48, 340/636
• US Class Current: 324/428
• CPC Class Codes: G01R 31/3648 comprising digital calculation means, e.g. for performing an algorithm
• CPC Class Codes: G01R 31/3828 using current integration
• CPC Class Codes: G06F 1/26 Power supply means, e.g. regulation thereof for memories G11C
• CPC Class Codes: G06F 1/28 Supervision thereof, e.g. detecting power-supply failure by out of limits supervision

Abstract

A micro discharge detection current which is obtained by reducing a discharge current of a battery at a predetermined ratio is detected by a current amplifying circuit and an integration voltage showing a discharge charge amount is formed by charging a capacitor of an integrating circuit. The integration voltage of the integrating circuit is compared with a reference voltage showing a predetermined unit charge amount by a comparing circuit. When the integration voltage reaches the reference voltage, a comparison output is inverted and the capacitor of the integrating circuit is discharge reset and one pulse signal showing the unit charge amount is generated by the inversion of the comparison output. The pulse signal from the comparing circuit is counted by a counter and the count value is multiplied with the unit charge amount, thereby obtaining the present discharge charge amount of the battery.

Claims

1. An apparatus for monitoring power of a battery which supplies an electric power to a load, said apparatus comprising:

a micro current detection resistor Rs1 which is inserted in a signal line connecting a plus terminal of said battery and said load such that current flow through said resistor generates a detection voltage V1 across said resistor that is proportional to a battery discharge current Id flowing from said battery to said load;

a current converting circuit having an operational amplifier to which said detection voltage generated across said current detection resistor is inputted through an input high resistor Rf, said current converting circuit including an FET which is driven by an output of said operational amplifier and which outputs a micro discharge detection current Is which is derived by multiplying said battery discharge current Id with a ratio Rs1/Rf;

an integrating circuit for charging a capacitor by the discharge detection current Is of said current converting circuit and forming an integration voltage;

a comparing circuit for resetting said integrating circuit and outputting one pulse signal when the integration voltage of said integrating circuit reaches a reference voltage indicative of a unit charge amount; and

a measuring unit for counting the number of pulse signals outputted from said comparing circuit and generating a count value, and measuring the discharge charge amount of the battery on the basis of said count value.

2. An apparatus according to claim 1, wherein in said integrating circuit, a capacitor in which an electrostatic capacitance change ratio has a positive temperature coefficient and a capacitor in which an electrostatic capacitance change ratio has a negative temperature coefficient are connected in parallel, thereby suppressing a capacitance change due to a temperature.

3. An apparatus according to claim 1, wherein said measuring unit obtains the discharge charge amount of the battery by multiplying the count value which is derived by counting up the pulse signals from said comparing circuit with said unit charge amount.

4. An apparatus according to claim 1, wherein when a charged charge amount when said battery is fully charged has been determined, said measuring unit further obtains the value which is derived by subtracting said discharge charge amount from said charged charge amount as a present battery capacitance.