| 摘要 |
In a method of charging at least one lithium ion cell (21, Fig. 1) in a battery powered appliance (20), such as a mobile telephone, a charger (10) applies a constant charging current via a switch (14) in a first charging phase until the charger output voltage, monitored at the output side of the switch (14), reaches a predetermined maximum voltage (eg. 4.2 volts). A second charging phase is then started in which switch (14) is opened and closed to apply constant current charging pulses of fixed duration (eg. 10 seconds), the output voltage at the output side of the switch (14) is monitored, and the duration of the intervals between charging pulses is controlled to maintain the average output voltage at a predetermined average value. In the second phase, the output voltage is periodically sampled to provide a running average voltage since the start of the most recent charging pulse, and the switch (14) is closed again to start a new charging pulse when the average voltage has fallen to a desired average value. A count of the number of times the voltage is sampled is reset to zero each time a new pulse is started. If the count reaches a maximum value before the next current pulse is started (in response to the average voltage falling to the desired value), this indicates that the duty cycle of the charging pulses has fallen to such a low level that the cell (21) can be regarded as fully charged, at which point charging is terminated. |
