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Current regulating circuit
| Details |
Inventors: Hoffman, Philip A.;
Assignee: Solid State Chargers Research and Development Limited Partnership (Lutherville, MD)
Primary Examiner:
Assistant Examiner:
Attorney, Agent or Firm:
A battery charger which includes terminals for connection to an electric power source, an electrical charging circuit and an operative arrangement for connecting at least one rechargeable battery cell in series with the charging circuit across the terminals. The battery charger has a charging circuit which includes a first resistor, a second resistor, a third resistor and a rectifier, constituted by at least one diode, in series. A first transistor, which has a collector-emitter path and a base-emitter path, is operatively connected so that the base-emitter path is connected in parallel with the first resistor. A fourth resistor is provided, the fourth resistor being connected in series with the collector-emitter path of the transistor and the third resistor. In one species, a plurality of additional transistors, connected in Darlington configuration, includes a second transistor and a final transistor, each of the additional transistors having its collector connected to a circuit point between the third resistor and an electrode of the diode. The first transistor and the last transistor in the one species have their emitters connected via a current-limiting PTC fifth resistor which may act as a fuse. The first transistor and the second transistor have their respective collector and base conductively connected. In another species, a field effect transistor, preferably a MOSFET, is used instead of the Darlington configuration. The connection of the third resistor provides internal feedback. The fifth resistor, when in series with the first resistor in the base-emitter circuit, provides external feedback. |
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DETAILED DESCRIPTION An object of the present invention is to provide an improved current regulating circuit for recharging small batteries, which is free of all transformers, smoothing capacitors and inductors.
Another object of the present invention is to provide a current regulating circuit which is simple, inexpensive and can readily be realized as an integrated circuit.
An additional object of the present invention is to provide a current regulating circuit which is simple, inexpensive, small and lightweight and which can be incorporated directly into a cordless, battery-operated device.
A further object of the present invention is to provide a simple, inexpensive battery charger which can be operated from a conventional 117 volt, 60 H.
sub.
z, or 234 volt A.
C.
, 60 H.
sub.
z, power sources and which can be operated as well from power sources having different voltages and frequencies.
Yet another object is to provide a battery charger which utilizes the instant current regulating circuit and achieves the respective objects set out above.
The foregoing objects, as well as others which are to become apparent from the text below, can be achieved in accordance with the present invention by providing an improvement in a battery charger including terminals for connection to an electric power source and further including an electrical charging circuit and operative arrangements for connecting at least one rechargeable battery cell in series with the charging circuit across the terminals.
In particular, the battery charger is constituted by a charging circuit which consists of a first resistance (defined substantially by two resistors considered to be in parallel), a second resistance (resistor) and a third resistance (resistor) in series in the denominated order and a rectifier, constituted by at least one diode for developing a D.
C.
voltage.
A first transistor, which has a collector-emitter path and a base-emitter path, is operatively connected so that the base-emitter path is connected in parallel with the first resistance
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Electrical and Wave 
