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

• US 6,054,861 A
• Filed: 08/25/1998
• Issued: 04/25/2000
• 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:
  US09/139,756
• Time in Patent Office: 609 Days
• Field of Search: 324/426, 324/427, 324/428, 324/433, 340/636, 320/134, 320/149
• 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 a power of a battery which supplies an electric power to a load, comprising:

a micro current detection resistor Rs2, disposed in a signal line connecting a minus terminal of said battery and a ground and provides, when current flows therethrough, a detection voltage V2 that is proportional to a charge current Ic which flows when the battery is charged;

a voltage buffer circuit which receives said detection voltage V2 generated across said current detection resistor and converts into an output voltage V0 that is derived by subtracting said detection voltage V2 from a voltage that is derived by doubling a predetermined threshold voltage Vth;

a current converting circuit including an operational amplifier in which an output of said voltage buffer circuit is connected to an inverting input terminal and a plus terminal side of said battery is connected to a non-inverting input terminal through an input resistor Rf, said current converting circuit also including an FET which is driven by an output of said operational amplifier and which outputs a micro charge detection current Is which is derived by multiplying said battery charge current Ic with a ratio Rs2/Rf between said current detection resistor Rs2 and said input resistor Rf;

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

a comparing circuit for discharge 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 to provide a count value and measuring a charged amount of the battery based upon said count value.

2. An apparatus according to claim 1, wherein said integrating circuit comprises a firs capacitor in which a capacitance change ratio has a positive temperature coefficient and a second capacitor in which a 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 charged amount of the battery by multiplying the count value derived by counting up the pulse signal from said comparing circuit with said unit charge amount.

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

a micro first current detection resistor Rs1 which is disposed in a signal line connecting a plus terminal of a battery and a load and provides, when current flows therethrough, a detection voltage V1 which is proportional to a discharge current Id flowing from said battery to said load;

a first current converting circuit including an operational amplifier to which said detection voltage is inputted through an input resistor Rf, said first current converting circuit also 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 between said current detection resistor Rs1 and said input resistor Rf from said FET;

a first integrating circuit for charging a capacitor by the discharge detection current Is of said first current amplifying circuit, said first integrating circuit forming an integration voltage;

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

a micro second current detection resistor which is disposed in a signal line connecting a minus terminal of said battery and a ground and provides, when current flows therethrough, a detection voltage V2 that is proportional to a charge current Ic flowing from a power source for charging to the battery;

a voltage buffer circuit which receives said detection voltage V2 and converts into an output voltage V0 that is derived by subtracting said detection voltage V2 from a voltage that is derived by doubling a predetermined threshold voltage Vth;

a second current converting circuit including an operational amplifier in which an output of said voltage buffer circuit is connected to an inverting input terminal and a plus terminal side of said battery is connected to a non-inverting input terminal through an input resistor Rf, said second current converting circuit also 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 Rs2/Rf between said current detection resistor Rs2 and an input resistor Rf;

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

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

a measuring unit for measuring the capacitance of the battery based upon the pulse signal outputted by said first comparing circuit and the pulse signal outputted by said second comparing circuit.

5. An apparatus according to claim 4, wherein in each of said first and second integration circuits, a first capacitor in which a capacitance change ratio has a positive temperature coefficient and a second capacitor in which a capacitance change ratio has a negative temperature coefficient are connected in parallel, thereby suppressing a capacitance change due to a temperature.

6. An apparatus according to claim 4, wherein said measuring unit obtains a charged amount of the battery by multiplying a value which is derived by counting the pulse signal of said second comparing circuit with said unit charge amount, a discharged amount by multiplying the count value obtained by counting the pulse signal of said first comparing circuit with said unit charge amount, and a present charge amount of the battery by subtracting said discharged amount from said charged amount.

7. An apparatus according to claim 4 wherein said measuring unit obtains a count value by counting up the pulse signal of said second comparing circuit and by counting down the pulse signal of said first comparing circuit, and obtains a value derived by multiplying said count value with said unit charge amount as a present capacitance of the battery.

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

a micro current detection resistor which is disposed in a signal line connecting a minus terminal of said battery and a ground and which provides a detection voltage V2 when a current flows therethrough that is proportional to a charge current Ic;

a voltage buffer circuit which receives said detection voltage V2 generated across said current detection resistor and converts into an output voltage V0 on the basis of a predetermined threshold voltage Vth;

a current converting circuit for generating a charge detection current Is obtained by reducing said battery charge current Ic at a predetermined ratio based upon an output of said voltage buffer circuit;

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

a comparing circuit for discharge 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 a number of pulse signals outputted from said comparing circuit to generate a count value and for measuring a charged amount of the battery based upon said count value.