Charging circuit of secondary battery

A charging circuit of a secondary battery having a terminal comprising:

• an AC power source;
• a rectifier circuit having an input terminal connected to said AC power source, and an output terminal;
• a charging current limiting resistor connected between the output terminal of said rectifier circuit and said secondary battery;
• differential voltage detecting means for detecting difference between one of a voltage output from said output terminal of said rectifier circuit and a voltage proportional thereto on one hand, and one of a voltage at the terminal of said secondary battery and a voltage proportional thereto on the other;
• minute voltage change extracting means for extracting minute changes having components of a frequency higher than a predetermined level of a voltage output from said secondary battery during a process of charging said secondary battery, and generating output signals;
• shaping means for shaping the output signals from said minute voltage change extracting means into pulse signals;
• counting means for counting the pulse signals output from said shaping means;
• and
• charge control means for controlling the process of charging said secondary battery when the count of the pulse signals obtained by said counting means reaches a predetermined value.

A charging circuit of a secondary battery having a terminal comprising:

• a first rectifier circuit having an input terminal connected to an AC power source;
• a second rectifier circuit having an input terminal connected to the AC power source and an output terminal connected to said secondary battery;
• differential voltage detecting means for detecting the difference between one of a voltage output from said first rectifier circuit and a voltage proportional thereto on one hand, and one of a voltage at the terminal of said secondary battery and a voltage proportional thereto on the other;
• minute voltage change extracting means for extracting, in accordance with a detection result of said differential voltage detecting means, minute changes having components of a frequency higher than a predetermined level of a voltage output from said secondary battery during a process of charging said secondary battery, and generating output signals;
• shaping means for shaping the output signals from said minute voltage change extracting means into pulse signals;
• counting means for counting said pulse signals output from said shaping means;
• and
• charge control means for controlling the process of charging said secondary battery when the count of said pulse signals obtained by said counting means reaches a predetermined value.

A charging circuit of a secondary battery comprising:

• a first charging power source;
• a second charging power source for outputting a current smaller than said first charging power source;
• switching means for connecting said first charging power source to said secondary battery in a first charging period, and connecting said second charging power source to said secondary battery in a second charging period;
• first charge-completion detecting means including minute voltage change extracting means for extracting minute changes having components of a frequency a predetermined level higher than a voltage output from said secondary battery during a process of charging said secondary battery, and detecting completion of charging on the basis of a state of the minute voltage changes;
• second charge-completion detecting means for detecting completion of charging when said charging circuit is brought into a predetermined state after the start of the second charging period;
• and
• control means for terminating the first charging period and bringing said charging circuit into the second charging period when the first charge-completion detecting means detects completion of charging, and terminating the second charging period when the second charge-completion detecting means detects completion of charging during the second charging period.

A charging circuit for charging a battery having a first and a second terminal, comprising:

• a power source having a first output terminal and a second output terminal;
• a reference voltage generator, connected to the first and second output terminals of the power source, having an output terminal with a reference voltage which is a constant voltage amount different than a voltage of the first output terminal of the power source, an absolute value of the constant voltage amount being greater than zero;
• a minute voltage change extracting means, connected to the output terminal of the reference voltage generator and to the second terminal of the battery, for extracting minute changes having components of a frequency higher than a predetermined level of a voltage output from the charging of the secondary battery, the minute voltage change extracting means including two power supply terminals which are respectively connected to the two output terminals of the power source, and an output terminal for outputting the extracted minute changes;
• shaping means, connected to the output terminal of the minute voltage change extracting means, for shaping the extracted minute changes into output pulses, the output pulses being outputted by an output terminal of the shaping means;
• control means, connected to the output terminal of the shaping means and to the power source, for selectively connecting the power source to the first and second terminals of the battery so that the power source charges the battery, depending on a signal of the output terminal of the shaping means.