Charge and discharge control circuit

• US 6,111,388 A
• Filed: 02/13/1998
• Issued: 08/29/2000
• Est. Priority Date: 02/14/1997
• Status: Expired due to Term

• Current Assignee: SII Semiconductor Corporation
• Original Assignee: Seiko Instruments Incorporated (Seiko Group)
• Inventors: Mukainakano, Hiroshi
• Primary Examiner(s): Tso, Edward H.
• Application Number:
  US09/023,963
• Time in Patent Office: 928 Days
• Field of Search: 320/110, 320/118, 320/123, 320/128, 320/132, 320/134, 320/136, 320/FOR 114, 320/FOR 120, 320/FOR 129, 320/FOR 138, 320/FOR 148
• US Class Current: 320/134
• CPC Class Codes: H02J 7/00302 Overcharge protection
• CPC Class Codes: H02J 7/00308 Overvoltage protection
• CPC Class Codes: H02J 7/0031 using battery or load disconnect circuits H02J9/002 takes precedence

Abstract

A charge/discharge control circuit is provided which prevents an abnormally high charging voltage from damaging a secondary cell. The charge/discharge control circuit has an overcharge detecting circuit for detecting whether the secondary cell is in an overcharged state by comparing a divided output voltage of the secondary cell with a reference voltage, a delay circuit for outputting a delayed version of an output of the overcharge detecting circuit delayed by a predetermined delay time, and a high voltage detecting circuit for detecting whether the secondary cell is in a high voltage supplying state by detecting whether a voltage of the secondary cell is more than a predetermined level higher than the overcharge detecting voltage detected by the overcharge detecting circuit. The switch circuit is turned OFF to stop charging of the secondary cell when either the overcharge state or the high voltage supplying state is detected in response to outputs of the delay circuit and the high voltage detecting circuit.

Claims

1. A charge and discharge control circuit for controlling the charging and discharging of a secondary cell connected to an external power source terminal through a switch circuit by ON/OFF controlling the switch circuit, comprising:

an overcharge detecting circuit for detecting whether the secondary cell is in an overcharged state by comparing a divided output voltage of the secondary cell with a reference voltage;

a delay circuit for outputting a delayed version of an output of the overcharge detecting circuit delayed by a predetermined delay time; and

a high voltage detecting circuit for detecting whether the secondary cell is in a high voltage supplying state by detecting whether a voltage of the secondary cell is more than a predetermined level higher than the overcharge detecting voltage detected by the overcharge detecting circuit;

wherein the switch circuit is turned OFF to stop charging of the secondary cell when either the overcharge state or the high voltage supplying state is detected in response to outputs of the delay circuit and the high voltage detecting circuit.