Charge/discharge protection circuit and battery pack having the charge/discharge protection circuit

• US 6,316,915 B1
• Filed: 11/01/2000
• Issued: 11/13/2001
• Est. Priority Date: 11/02/1999
• Status: Expired due to Term

• Current Assignee: RICOH Electronic Devices Co., Ltd. (Nisshinbo Holdings Incorporated)
• Original Assignee: Ricoh Company Limited
• Inventors: Aota, Hideyuki, Fujiwara, Akihiko
• Primary Examiner(s): Wong, Peter S.
• Assistant Examiner(s): TIBBITS, PIA FLORENCE
• Application Number:
  US09/702,651
• Time in Patent Office: 377 Days
• Field of Search: 320/134, 320/136
• US Class Current: 320/134
• CPC Class Codes: H02J 7/00302 Overcharge protection
• CPC Class Codes: H02J 7/0031 using battery or load disconnect circuits H02J9/002 takes precedence

Abstract

A charge/discharge protection circuit of the present invention includes a first terminal to which a negative electrode of a charger is connected and an internal detector unit which has an input connected to the first terminal, and prevents the variation of the threshold voltage of the input transistors in a short-circuit detector unit and in an overcurrent detector unit when the improper charger is connected to the battery for a long time. An improper charger detector unit outputs a detection signal when an improper charger is connected to the battery pack, in response to a voltage supplied to the first terminal by the improper charger. A connection cutoff unit cuts off, when the detection signal is output by the improper charger detector unit, the connection between the internal detector unit input and the first terminal, so that, when the improper charger is connected to the battery pack, a voltage of the input of the internal detector unit is avoided from being lower than a voltage of a second terminal to which a negative electrode of the battery is connected.

Claims

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

a first terminal to which a negative electrode of a charger is connected;

an internal detector unit having an input connected to the first terminal;

an improper charger detector unit outputting a detection signal when an improper charger is connected to the battery pack and supplies a voltage exceeding a required charging voltage to the first terminal; and

connection cutoff means for cutting off, when the detection signal is output by the improper charger detector unit, the connection between the internal detector unit input and the first terminal, so that, when the improper charger is connected to the battery pack, a voltage of the input of the internal detector unit is avoided from being lower than a voltage of a second terminal to which a negative electrode of the battery is connected to substantially prevent variation of a threshold voltage of an input transistor in the internal detector unit when the improper charger is connected to the battery pack over an extended period of time.

2. The charge/discharge protection circuit according to claim 1, wherein the internal detector unit includes:

an overcurrent detector unit detecting whether an overcurrent condition of the battery occurs, the overcurrent detector unit having an input connected to the first terminal; and

a short-circuit detector unit detecting whether a short-circuit condition in the charge/discharge protection circuit occurs, the short-circuit detector unit having an input connected to the first terminal.

3. The charge/discharge protection circuit according to claim 1, wherein the connection cutoff means includes:

a first switch which is set in OFF state in response to the detection signal output by the improper charger detector unit so that the connection is cut off, and set in ON state when no detection signal is output by the improper charger detector unit so that the connection is established; and

a second switch which is set in ON state in response to the detection signal output by the improper charger detector unit so that the voltage of the input of the internal detector unit is set at the voltage of the second terminal, and set in OFF state when no detection signal is output by the improper charger detector unit so that the input of the internal detector unit is disconnected from the second terminal.

4. The charge/discharge protection circuit according to claim 1, wherein the charge/discharge protection circuit includes circuit elements which are connected directly to the first terminal and constructed in a high-voltage resistant structure, and circuit elements which are not connected directly to the first terminal and constructed in a high-voltage resistant structure.

5. The charge/discharge protection circuit according to claim 4, wherein the high-voltage resistant structure is a bi-directional local oxidation of silicon offset structure of a metal-oxide semiconductor transistor in which an element-isolating oxide layer, a first offset oxide layer for increasing a source voltage resistance, a second offset oxide layer for increasing a drain voltage resistance are formed on a substrate, and a gate of polysilicon, which is overlapped over the first offset oxide layer and the second offset oxide layer, are provided.

6. A battery pack including a rechargeable battery and a charge/discharge protection circuit for protecting the battery from damage, the charge/discharge protection circuit comprising:

a first terminal to which a negative electrode of a charger is connected;

an internal detector unit having an input connected to the first terminal;

an improper charger detector unit outputting a detection signal when an improper charger is connected to the battery pack and supplies a voltage exceeding a required charging voltage to the first terminal; and

connection cutoff means for cutting off, when the detection signal is output by the improper charger detector unit, the connection between the internal detector unit input and the first terminal, so that, when the improper charger is connected to the battery pack, a voltage of the input of the internal detector unit is avoided from being lower than a voltage of a second terminal to which a negative electrode of the battery is connected to substantially prevent variation of a threshold voltage of an input transistor in the internal detector unit when the improper charger is connected to the battery pack over an extended period of time.

7. The battery pack according to claim 6, wherein the internal detector unit of the charge/discharge protection circuit includes:

an overcurrent detector unit detecting whether an overcurrent condition of the battery occurs, the overcurrent detector unit having an input connected to the first terminal; and

a short-circuit detector unit detecting whether a short-circuit condition in the charge/discharge protection circuit occurs, the short-circuit detector unit having an input connected to the first terminal.

8. The battery pack according to claim 6, wherein the connection cutoff means of the charge/discharge protection circuit includes:

a first switch which is set in OFF state in response to the detection signal output by the improper charger detector unit so that the connection is cut off, and set in ON state when no detection signal is output by the improper charger detector unit so that the connection is established; and

a second switch which is set in ON state in response to the detection signal output by the improper charger detector unit so that the voltage of the input of the internal detector unit is set at the voltage of the second terminal, and set in OFF state when no detection signal is output by the improper charger detector unit so that the input of the internal detector unit is disconnected from the second terminal.

9. The battery pack according to claim 6, wherein the charge/discharge protection circuit includes circuit elements which are connected directly to the first terminal and constructed in a high-voltage resistant structure, and circuit elements which are not connected directly to the first terminal and constructed in a low-voltage resistant structure.

10. The battery pack according to claim 9, wherein the high-voltage resistant structure is a bi-directional local oxidation of silicon offset structure of a metal-oxide semiconductor transistor in which an element-isolating oxide layer, a first offset oxide layer for increasing a source voltage resistance, a second offset oxide layer for increasing a drain voltage resistance are formed on a substrate, and a gate of polysilicon, which is overlapped over the first offset oxide layer and the second offset oxide layer, are provided.