Patent ID: 6420853
Filing Date: 2002-07-16
Classification: H02J

Abstract:
A battery charger comprising:supplying means for supplying a charge current to a battery; battery voltage detection means for periodically detecting a battery voltage across the battery; a memory storing data on at least one battery voltage that is detected by said battery voltage detection means; updating means for updating the data stored in said memory whenever the battery voltage is newly detected by said battery voltage detection means; calculating means for calculating a difference between the newly detected battery voltage and the battery voltage stored in said memory, said calculating means calculating the difference whenever the battery voltage is newly detected by said battery voltage detection means; first detection means for detecting that a value of the difference calculated by said calculating means has become equal to or exceeded a first critical value and a second critical value greater than the first critical value; second detection means for detecting that the value of the difference has become equal to or less than a third critical value after the difference had become equal to or exceeded the first critical value and that the value of the difference has become equal to or less than a fourth critical value greater than the third critical value after the difference had become equal to or exceeded the second critical value; and determining means for determining that the battery has reached a fully charged condition when said second detection means detects that the value of the difference has become equal to or less than the third critical value after said first detection means detects that the value of the difference has become equal to or exceeded the first critical value, or when said second detection means detects that the value of the difference has become equal to or less than the fourth critical value after said first detection means detects that the value of the difference has become equal to or exceeded the second critical value.