Electricity: battery or capacitor charging or discharging – Battery or cell discharging – With charging
Reexamination Certificate
2000-11-13
2001-09-04
Wong, Peter S. (Department: 2838)
Electricity: battery or capacitor charging or discharging
Battery or cell discharging
With charging
C320S130000
Reexamination Certificate
active
06285164
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates in general to apparatus for detecting the integrated value of current flow, apparatus for detecting the value of current flow and a battery pack employing those apparatus each of which serves to display the data relating to the battery energy remainder of a primary battery or a secondary battery/rechargeable battery for use in portable information terminals and the like, and more particularly to the circuit technology of making each of apparatus for detecting the integrated value of current flow and apparatus for detecting the value of current flow insensitive to the undesired offset of a detection circuits.
2. Description of the Related Art
In a portable information terminal which is typified by a note type personal computer, a user is very anxious about how much battery energy remainder the battery in use has and how long the battery in use can be used. Then, when the battery energy remainder has become equal to or lower than a predetermined value, it is required to take measures to warn a user of this fact and also to back up the data. For this purpose, there is required a method wherein the battery energy remainder of the battery can be aware of as precisely as possible.
Then, heretofore, the method has been proposed in which the charging/discharging current of the battery is monitored at all times to be integrated in order to display the data relating to the battery energy remainder. As for an example thereof, the method disclosed in JP-A-6-258410 is known. In JP-A-6-258410, there is shown the method wherein a resistor for detecting the current flow is inserted in series with a current part of a battery; the voltage which is developed across the resistor is amplified at a predetermined amplification factor; the voltage thus amplified is supplied as a control voltage to a voltage controlled oscillator; and as a result, a pulse oscillation signal having a frequency corresponding to the charging/discharging current value is obtained. In addition, there is also shown the method wherein by counting the number of pluses of the pulse oscillation signal, the integrated value of current flow is obtained.
SUMMARY OF THE INVENTION
The resistance value of the resistor for detecting the value of current flow can not be made excessively large in order to suppress the power loss due to the voltage drop across the resistor as much as possible. In an example of the note type personal computer, the resistance value of that resistor is set to a very small value of about 20 &OHgr;m, and the voltage developed thereacross in the range of about 1 mV to about 100 mV is obtained in correspondence to the load current which changes from several tens mA to a few A. This voltage is supplied as the control voltage either directly or after having been amplified predetermined times to the above-mentioned voltage controlled oscillator. On the other hand, normally, for an operational amplifier for use in the amplification or an operational amplifier for use in configuration of a voltage controlled oscillator, it can not be avoided to involve the offset of about ±5 mV due to the dispersion in manufacture of semiconductor devices and other causes. Then, for the above-mentioned control voltage of about 1 mv to about 100 mV, the bad influence provided by the offset will become so large as not to be able to be disregarded. By the way, in the case where the resistance value of the resistor for detecting the value of current flow is 20 m&OHgr; as described above, the offset of 5 mV corresponds to 250 mA in current detection error.
The influence of the current detection error due to the offset is further increased when obtaining the integrated value of current flow. For example, actually, in the case as well where the load current is zero, the load current may be recognized by mistake as if the current of 250 mA is continuously consumed, and hence the load current may exhibit as the integrated value the large value in some cases.
In this connection, while the main cause of generating the offset is the unbalance in threshold voltage of a pair of differential transistors at the first stage constituting the operational amplifier, in addition thereto, the main cause may be various every circuit configuration method.
The theme of the present invention is therefore to provide apparatus for detecting the value of current flow and apparatus for detecting the integrated value of current flow each of which becomes insensitive to the offset of those operational amplifiers and the like.
In order to solve the above-mentioned problems associated with the prior art, each of apparatus for detecting the integrated value of current flow, apparatus for detecting the value of current flow and a battery pack employing those apparatus according to the present invention includes: a current sensor resistor which is inserted in series with a current path of a battery; an integrator; an input status selector through which a voltage developed across the current sensor resistor is introduced into an input of an integrator; an integration capacitor connected to the integrator; a connection-polarity inverter for the integration capacitor provided between the integrator and the integration capacitor for switching the connection-polarity of the integration capacitor; a first voltage comparator for outputting, when an output voltage of the integrator changing with the transition of time has reached a first predetermined threshold voltage for integration reset which is located on the plus side with respect to the output voltage, as the reference voltage, of the integrator which is obtained by clearing the electric charges of the integration capacitor, a voltage transition exhibiting that fact; a second voltage comparator for outputting, when the output voltage of the integrator has reached a second predetermined threshold voltage for integration reset which is located on the minus side with respect to the reference voltage, a voltage transition exhibiting that fact; integration resetting means for clearing the accumulated electric charges in the integration capacitor when the first or second voltage comparator outputs the voltage transition; a pulse counter for up-counting, of pulses generated at an output of the first or second voltage comparator at operation frequency of the integration resetting means, the output pulses of one voltage comparator and for down-counting the output pulses of the other voltage comparator; and a up/down inverter for inverting the up/down count input to the pulse counter.
The input status selector switches regularly, alternately two statuses of a status a and a status b, and in the status a, introduces a battery current sensor voltage developed across terminals of the current sensor resistor into the integrator. On the other hand, in the status b, the input status selector either inverts the polarity of the battery current sensor voltage developed across the terminals of the current sensor resistor to introduce the resultant voltage into the integrator, or introduces the voltage of zero into the input of the integrator. More specifically, the voltage at one of the terminals of the current sensor resistor is introduced into a pair of input terminals of the integrator.
The connection-polarity inverter of the integration capacitor switches alternately the connection polarity of the integration capacitor synchronously with the status a and the status b of the input status selector.
Then, the integrator time-integrates, during a time period of the status a, the current corresponding to the battery current together with the current due to the above-mentioned undesirable offset to accumulate the resultant electric charges as the integration electric charges in the integration capacitor, while in the status b, time-integrates the current which is obtained by inverting the current corresponding to the battery current together with the current due to the above-mentioned undesirable offset, or time-integrates only the current due to the
Noda Masaru
Takeuchi Takashi
Tanaka Shinji
Tsuchiya Mitsunori
Yamaguchi Takeshi
Antonelli Terry Stout & Kraus LLP
Hitachi , Ltd.
Luk Lawrence
Wong Peter S.
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