Charge/discharge protection apparatus having a charge-state overcurrent detector, and battery pack including the same

• US 20020050806A1
• Filed: 09/19/2001
• Published: 05/02/2002
• Est. Priority Date: 09/28/2000
• Status: Active Grant

• Current Assignee: RICOH Electronic Devices Co., Ltd. (Nisshinbo Holdings Incorporated)
• Original Assignee: Ricoh Company Limited
• Inventors: Fujiwara, Akihiko
• Granted Patent: US 6,501,248 B2
• Time in Patent Office: Days
• US Class Current: 320/136
• CPC Class Codes: H02J 7/00302 Overcharge protection
• CPC Class Codes: H02J 7/00304 Overcurrent protection
• CPC Class Codes: H02J 7/00306 Overdischarge protection
• CPC Class Codes: H02J 7/0031 using battery or load disconnect circuits H02J9/002 takes precedence

Abstract

A charge/discharge protection apparatus of the present invention includes a switch provided on a charge/discharge current line, the charge/discharge current line being connected to a secondary battery of a battery pack. A charge-state overcurrent detector outputs a control signal when a charge-state overcurrent condition of the battery is detected in a charge state of the battery pack. A control unit sets the switch in OFF state to cut off connection between the charge/discharge current line and the battery in response to the control signal output by the charge-state overcurrent detector. The charge/discharge protection apparatus has a capability to detect the charge-state overcurrent condition of the battery, and protects the secondary battery from being damaged due to the charge-state overcurrent condition.

Claims

1. A charge/discharge protection apparatus for protecting a secondary battery of a battery pack from damage, comprising:

a switch provided on a charge/discharge current line, the charge/discharge current line being connected to the battery;

a charge-state overcurrent detector outputting a control signal when a charge-state overcurrent condition of the battery is detected in a charge state of the battery pack; and

a control unit setting the switch in OFF state to cut off connection between the charge/discharge current line and the battery in response to the control signal output by the charge-state overcurrent detector.

2. The charge/discharge protection apparatus according to claim 1, wherein the charge/discharge protection apparatus includes a first terminal connected to a positive electrode of the battery, a second terminal connected to a negative electrode of the battery, and a third terminal connected to a negative terminal of the battery pack,

the charge-state overcurrent detector comprising:

a first MOS transistor having a drain connected to the first terminal, and a source and a gate being connected together;

a second MOS transistor having a gate, a drain connected to the source of the first MOS transistor, and a source connected to the second terminal;

a third MOS transistor having a drain connected to the drain of the first MOS transistor, a source connected to the gate of the second MOS transistor, and a gate connected to the source of the first MOS transistor;

first and second resistors connected in series between the third terminal and the source of the third MOS transistor;

a third resistor connected between the second terminal and the source of the source of the third MOS transistor; and

a comparator having a first input connected to the second terminal and a second input connected to an intermediate point between the first resistor and the second resistor, the comparator outputting the control signal when the charge-state overcurrent condition of the battery is detected in the charge state of the battery pack.

3. The charge/discharge protection apparatus according to claim 2, wherein the charge-state overcurrent detector includes a second switch connected between the first resistor and the third resistor, said second switch being set in OFF state to cut off connection between the first resistor and the third resistor when an over-discharge condition of the battery is detected.

4. The charge/discharge protection apparatus according to claim 1, further comprising:

a delay circuit delaying supply of the control signal to the switch by a predetermined delay time after the detection of the charge-state overcurrent condition of the battery, the delay circuit having an internal oscillator and a counter;

a test-mode switch setting a potential of a test terminal to one of a low level and a high level when conducting an operation test of the charge/discharge protection apparatus; and

a delay time changing means for reducing the delay time of the delay circuit when the potential of the test terminal is set to one of the low level and the high level by the test-mode switch.

5. The charge/discharge protection circuit according to claim 4, wherein the internal oscillator is configured into a ring oscillator having a plurality of constant-current inverters and a plurality of constant-current sources, and the delay time changing means reduces, when the operation test is conducted, the delay time of the delay circuit by changing a current value of the constant-current sources in the ring oscillator.

6. The charge/discharge protection circuit according to claim 5, wherein, when reducing the delay time of the delay circuit, the delay time changing means activates at least one of the constant-current sources of the ring oscillator in order to increase the current value of the constant-current sources and increase an oscillation frequency of the ring oscillator.

7. The charge/discharge protection circuit according to claim 4, wherein the internal oscillator is configured into a ring oscillator having a plurality of constant-current inverters and a plurality of capacitors, and the delay time changing means reduces, when the operation test is conducted, the delay time of the delay circuit by changing a capacitance value of the capacitors in the ring oscillator.

8. The charge/discharge protection circuit according to claim 7, wherein, when reducing the delay time of the delay circuit, the delay time changing means inactivates at least one of the capacitors of the ring oscillator in order to reduce the capacitance value of the capacitors and increase an oscillation frequency of the ring oscillator.

9. The charge/discharge protection circuit according to claim 4, wherein the internal oscillator is configured into a ring oscillator having a plurality of constant-current inverters, and the delay time changing means reduces, when the operation test is conducted, the delay time of the delay circuit by changing a threshold voltage of the constant-current inverters in the ring oscillator.

10. The charge/discharge protection circuit according to claim 9, wherein each of the constant-current inverters includes a CMOS inverter, and, when reducing the delay time of the delay circuit, the delay time changing means connecting a MOS transistor in series to at least one of the constant-current inverters in order to increase the threshold voltage thereof.

11. The charge/discharge protection circuit according to claim 4, wherein the delay time changing means reduces, when the operation test is conducted, the delay time of the delay circuit by changing one of a plurality of signal output positions of the counter of the delay circuit to another.

12. The charge/discharge protection apparatus according to claim 4, wherein the oscillator of the delay circuit includes a low-frequency oscillator and a high-frequency oscillator, the charge/discharge protection apparatus selecting one of the low-frequency oscillator and the high-frequency oscillator in response to the potential of the test terminal.

13. A battery pack in which a secondary battery and a charge/discharge protection apparatus are provided, the charge/discharge protection apparatus comprising:

a switch provided on a charge/discharge current line, the charge/discharge current line being connected to the battery;

a charge-state overcurrent detector outputting a control signal when a charge-state overcurrent condition of the battery is detected in a charge state of the battery pack; and

a control unit setting the switch in OFF state to cut off connection between the charge/discharge current line and the battery in response to the control signal output by the charge-state overcurrent detector.