Battery charging circuit

Claim 2

A battery charger comprising a pair of battery terminals for connection to a rechargeable battery, a pair of input terminals for connection to an electrical power source, and an electrical charging circuit coupling said input terminals to said battery terminals for supplying a charging current to said battery terminals, said charging circuit comprising a switching transister having a control electrode and a current amplifier coupled to said input terminals permitting charging current flow to said battery terminals when a conventional 60 Hz. household outlet electrical source is applied to said input terminals only during those portions of a source cycle when the source voltage is below a predetermined voltage level substantially less than its maximum, and negative feedback means coupling the output of said current amplifier to said control electrode of said transistor whereby greater charging current flows at lower source voltage levels.

Claim 3

A battery charger according to claim 1 wherein said charging circuit starts to reduce said charging current when said source potential exceeds approximately six times the battery potential.

Claim 4

A battery charger according to claim 2 wherein said charging circuit comprises means for reducing said charging current to zero when the source potential at said input terminals exceeds the potential of a battery connected to said battery terminals by a predetermined amount.

Claim 5

A battery charger according to claim 3 wherein said charging circuit reduces said charging current to zero when said source potential exceeds approximately nine times the battery potential.

Claim 6

A battery charger according to claim 1 wherein said charging circuit provides charging current only when the source potential has a magnitude between about one and ten times the battery potential.

Claim 7

A battery charger according to claim 1 including at least one rectifier diode coupling said input terminals to said current amplifier.

Claim 8

A battery charger according to claim 1 wherein said charging circuit includes an incandescent lamp for compensating for variations in supply voltage.

Claim 9

A battery charger according to claim 1 wherein said charging circuit comprises means for automatically varying the charging rate in accordance with the charge on a battery connected to said battery terminals.

Claim 10

A battery charger according to claim 8 wherein said automatic rate varying means comprises a resistor and a zener diode coupled across said battery terminals.

Claim 11

A battery charger according to claim 1 comprising a hand tool housing, said charging circuit being located in said housing, an electrical motor in said housing for operating said tool, and means in said housing for coupling said motor to said battery terminals.

Claim 12

A battery charger according to claim 10 wherein said housing includes an electrical AC power connector coupled to said charging circuit, and a cord for directly connecting said AC power connector to a conventional household power outlet.

Claim 13

A battery charger comprising a pair of battery terminals for connection to a rechargable battery, a pair of input terminals for connection to an electrical power source, and an electrical charging circuit coupling said input terminals to said battery terminals for supplying a charging current to said battery terminals, said charging circuit comprising a switch coupled to said input terminals permitting charging current flow to said battery terminals when a conventional 60 Hz. household outlet electrical source is applied to said input terminals only during those portions of a source cycle when the source voltage is below a predetermined voltage level substantially less than its maximum, said switch comprising a transistor and feedback means coupled to said transistor for varying the impedance of said switch in accordance with variations in source voltage whereby greater charging current flows at lower source voltage levels, said charging circuit including means for increasing said charging current with increasing source potential below said predetermined level.

Claim 14

A battery charger comprising a pair of battery terminals for connection to a rechargable battery, a pair of input terminals for connection to an electrical power source, and an electrical charging circuit coupling said input terminals to said battery terminals for supplying a charging current to said battery terminals, said charging circuit comprising a switch coupled to said input terminals permitting charging current flow to said battery terminals when a conventional 60 Hz. household outlet electrical source is applied to said input terminals only during those portions of a source cycle when the source voltage is below a predetermined voltage level substantially less than its maximum, said switch comprising a transistor and feedback means coupled to said transistor for varying the impedance of said switch in accordance with variations in source voltage whereby greater charging current flows at lower source voltage levels, said charging circuit including means for increasing said charging current with increasing source potential below said predetermined level.