Overdischarge detection device and overdischarge prevention device for a chargeable electric cell, operable with a variable threshold voltage to prohibit discharge in accordance with relative weight of a load

Claim 2

An overdischarge detection device for use in a cell unit including a chargeable electric cell having a cell voltage which is supplied to a load through positive and negative load current lines to pass a load current through the load, said overdischarge detection device comprising: an overdischarge detection circuit connected between the positive and the negative load current lines, said overdischarge detection circuit including a voltage comparing section having an input terminal for the cell voltage of the chargeable electric cell and a threshold terminal for a controllable threshold voltage for prohibiting discharging operation, said voltage comparing section comparing the cell voltage with the controllable threshold voltage to produce a detection signal when the cell voltage falls below the controllable threshold voltage; and an adjusting device, connected to said overdischarge detection circuit, for detecting a particular voltage of a specified part in the cell unit that corresponds to the load current varying in response to relative weight of the load, and for adjusting the controllable threshold voltage based on the particular voltage; wherein said adjusting device comprises an overdischarge detection hysteresis circuit for changing the controllable threshold voltage by supplying a control current to said overdischarge detection circuit based on the particular voltage, and for clamping the controllable threshold voltage when the particular voltage is higher than a predetermined voltage.

Claim 3

An overdischarge detection device as claimed in claim 1, further comprising a semiconductor switch which is supplied with the detection signal produced by the voltage comparing section of said overdischarge detection circuit when the cell voltage of the chargeable electric cell falls below the controllable threshold voltage, said semiconductor switch having a source electrode and a drain electrode which are connected to the negative load current line, wherein the particular voltage is a voltage between the source electrode and the drain electrode in the semiconductor switch.

Claim 4

An overdischarge detection device as claimed in claim 2, wherein said adjusting device further comprises a voltage/current conversion circuit for converting the particular voltage into the control current, and said control current is supplied to the input terminal of the voltage comparing section.

Claim 5

An overdischarge detection device as claimed in claim 2, wherein said overdischarge detection hysteresis circuit comprises: a constant current source, connected to the positive load current line, for pouring a constant current; a first current mirror circuit, connected to the constant current source, for separating the constant current into first and second separated currents; a second current mirror circuit, connected to the first current mirror circuit, for current-amplifying the first separated current into the control current, said second current mirror circuit supplying the control current to said overdischarge detection circuit; first and second resistors connected between said second current mirror circuit and the negative load current line; and a transistor, connected between said first current mirror circuit and the specified part, for passing the second separated current to the specified part.

Claim 6

An overdischarge detection device as claimed in claim 2, wherein said overdischarge detection hysteresis circuit comprises: a constant current source, connected to the positive load current line, for pouring a constant current; a first current mirror circuit, connected to the constant current source, for separating the constant current into first and second separated currents; a second current mirror circuit, connected to the first current mirror circuit, for current-amplifying the first separated current into the control current, said second current mirror circuit supplying the control current to said overdischarge detection circuit; first and second resistors connected between said second current mirror circuit and the negative load current line; and a third resistor, connected between said first current mirror circuit and the specified part, for passing the second separated current to the specified part.

Claim 7

An overdischarge prevention device for use in a cell unit including a chargeable electric cell having a cell voltage which is supplied to a load through positive and negative load current lines to pass a load current through the load, said overdischarge prevention device comprising: an overdischarge detection circuit connected between the positive and the negative load current lines, said overdischarge detection circuit including a voltage comparing section having an input terminal for the cell voltage of the chargeable electric cell and a threshold terminal for a controllable threshold voltage for prohibiting discharging operation, said voltage comparing section comparing the cell voltage with the controllable threshold voltage to produce a detection signal when the cell voltage falls below the controllable threshold voltage; a switch circuit, connected to said overdischarge detection circuit, for stopping, in response to the detection signal, supply of the cell voltage from the electric cell to the load; and an adjusting device, connected to said overdischarge detection circuit, for detecting a particular voltage of a specified part in the cell unit that corresponds to the load current varying in response to relative weight of the load, and for adjusting the controllable threshold voltage based on the particular voltage; wherein said adjusting device comprises an overdischarge detection hysteresis circuit for changing the controllable threshold voltage by supplying a control current to said overdischarge detection circuit based on the particular voltage, and for clamping the controllable threshold voltage when the particular voltage is higher than a predetermined voltage.

Claim 8

An overdischarge prevention device for use in a cell unit including a chargeable electric cell having a cell voltage which is supplied to a load through positive and negative load current lines to pass a load current through the load, said overdischarge prevention device comprising: an overdischarge detection circuit connected between the positive and the negative load current lines, said overdischarge detection circuit including a voltage comparing section having an input terminal for the cell voltage of the chargeable electric cell and a threshold terminal for a controllable threshold voltage for prohibiting discharging operation, said voltage comparing section comparing the cell voltage with the controllable threshold voltage to produce a detection signal when the cell voltage falls below the controllable threshold voltage; a switch circuit, connected to said overdischarge detection circuit, for stopping, in response to the detection signal, supply of the cell voltage from the electric cell to the load; and an adjusting device, connected to said overdischarge detection circuit, for detecting a particular voltage of a specified part in the cell unit that corresponds to the load current varying in response to relative weight of the load, and for adjusting the controllable threshold voltage based on the particular voltage; wherein said adjusting device comprises an overdischarge detection hysteresis circuit for changing the controllable threshold voltage by supplying a control current to said overdischarge detection circuit based on the particular voltage, and for clamping the controllable threshold voltage when the particular voltage is higher than a predetermined voltage.

Claim 9

An overdischarge prevention device as claimed in claim 6, wherein said switch circuit comprises a semiconductor switch which is supplied with the detection signal, and said semiconductor switch has a source electrode and a drain electrode which are connected to the negative load current line, and wherein the particular voltage is equal to a voltage between the source electrode and the drain electrode in the semiconductor switch.

Claim 10

An overdischarge prevention device as claimed in claim 7, wherein said adjusting device further comprises a voltage/current conversion circuit for converting the particular voltage into the control current, and said control current is supplied to the input terminal of the voltage comparing section.

Claim 11

An overdischarge prevention device as claimed in claim 7, wherein said overdischarge detection hysteresis circuit comprises: a constant current source, connected to the positive load current line, for pouring a constant current; a first current mirror circuit, connected to the constant current source, for separating the constant current into first and second separated currents; a second current mirror circuit, connected to the first current mirror circuit, for current-amplifying the first separated current into the control current, said second current mirror circuit supplying the control current to said overdischarge detection circuit; first and second resistors connected between said second current mirror circuit and the negative load current line; and a transistor, connected between said first current mirror circuit and the predetermined part, for passing the second separated current to the predetermined part.

Claim 12

An overdischarge prevention device as claimed in claim 7, wherein said overdischarge detection hysteresis circuit comprises: a constant current source, connected to the positive load current line, for pouring a constant current; a first current mirror circuit, connected to the constant current source, for separating the constant current into first and second separated currents; a second current mirror circuit, connected to the first current mirror circuit, for current-amplifying the first separated current into the control current, said second current mirror circuit supplying the control current to said overdischarge detection circuit; first and second resistors connected between said second current mirror circuit and the negative load current line; and a third resistor, connected between said first current mirror circuit and the predetermined part, for passing the second separated current to the predetermined part.