Secondary battery cell protection circuit

• US 6,297,619 B1
• Filed: 09/10/1999
• Issued: 10/02/2001
• Est. Priority Date: 10/01/1998
• Status: Expired due to Term

• Current Assignee: Mitsumi Electric Co., Ltd. (MinebeaMitsumi Inc.)
• Original Assignee: Mitsumi Electric Co., Ltd. (MinebeaMitsumi Inc.)
• Inventors: Terada, Yukihiro
• Primary Examiner(s): Wong, Peter S.
• Assistant Examiner(s): TIBBITS, PIA FLORENCE
• Application Number:
  US09/393,895
• Time in Patent Office: 753 Days
• Field of Search: 320/134, 320/136, 361/90, 361/92, 361/115, 307/10.1, 307/10.7
• US Class Current: 320/134
• CPC Class Codes: H02J 7/00302 Overcharge 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 secondary battery cell protection circuit protects a charge control FET, a discharge control FET, and a secondary battery cell from destruction due to use of a charger of greater than rated voltage to charge the secondary battery cell. The secondary battery cell protection circuit has a charger voltage detection circuit, a first charge circuit control circuit for cutting off a charge circuit when the charger voltage detection circuit detects a charger voltage in excess of a predetermined value, and a second charge control circuit for cutting off a charge circuit when the over-charge detection circuit detects a secondary battery cell charge voltage in excess of a predetermined value. When the charge control FET is OFF, a load voltage proportionate to the charge voltage of the charger appears at a −B terminal and is applied to the emitter of a transistor, activating the transistor. A current proportionate to the charge voltage of the charger then flows to the transistor. If at this time the charger voltage is above the rated voltage, then a resistor is set so that a voltage drop of the resistor exceeds a base voltage. As a result, when the charger voltage is above the rated voltage the charge voltage of the secondary battery cell declines thereafter and a charge control FET drive transistor remains in an OFF state even after the charge voltage is at or below a release charge voltage.

Claims

1. A secondary battery cell protection circuit for protecting a secondary battery cell according to the voltage of the secondary battery cell, comprising:

a charger voltage detection circuit detecting a charger voltage;

a first charge circuit control circuit cutting off a charge circuit when the charger voltage detection circuit detects a charger voltage in excess of a predetermined value; and

an over-discharge detection circuit and an over-charge detection circuit and a charge control field-effect transistor wherein the charge control field-effect transistor is turned off when the over-charge detection circuit detects an overcharge of the secondary battery cell.

2. The secondary battery protection circuit as claimed in claim 1, wherein the first the first charge circuit control circuit controls the charge control field-effect transistor (FET) Q2 inserted in series into the charge circuit and shuts off the charge control FET when the charger voltage detection circuit detects a chargers voltage in excess of the predetermined value.

3. The secondary battery protection circuit as claimed in claim 2, further comprising the over-charge detection circuit and a second charge circuit control circuit, the second charge circuit control circuit cutting off the charge circuit when the over-charge detection circuit detects a secondary battery cell charge voltage in excess of a predetermined value.

4. The secondary battery cell protection circuit as claimed in claim 3, wherein the first charge circuit control circuit and the second charge circuit control circuit, respectively, include a switching element which cuts off the charge circuit, the switching element being used for both the first and second charge circuit control circuits.

5. The secondary battery protection circuit as claimed in claim 1, further comprising the over-charge detection circuit and a second charge circuit control circuit, the second charge circuit control circuit cutting off the charge circuit when the over-charge detection circuit detects a secondary battery cell charge voltage in excess of a predetermined value.

6. The secondary battery cell protection circuit as claimed in claim 5, wherein the first charge circuit control circuit and the second charge circuit control circuit, respectively, include a switching element which cuts off the charge circuit, the switching element being used for both the first and second charge circuit control circuits.

7. The secondary battery cell protection circuit as claimed in claim 1, wherein the charger voltage detection circuit functions when the charge circuit is cut off.