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Charging circuit for a lead-acid storage battery
| Details |
Inventors: Ramme, Friedrich;
Assignee: Robert Bosch GmbH (Stuttgart, DE)
Primary Examiner: Peckman; Kristine L.
Assistant Examiner:
Attorney, Agent or Firm: Frishauf, Holtz, Goodman & Woodward
A charging circuit for a lead-acid storage battery for a mobile radio transceiver which operates effectively with an input from a vehicular battery terminal that may vary over a range of 25 volts in output voltage has a control circuit for regulating the charging current connected between the charging current output and the same control input of the same pulse width modulator that is used for output voltage control. The pulse width modulator is part of an integrated circuit which includes also a d.c. to d.c. voltage converter and an output voltage regulator. A branch circuit includes a current sensing resistor (45) of less than 1 ohm. The voltage drop across said sensing resistor is too small to control a control transistor network (46, 52) and therefore a constant voltage is added thereto by a voltage adding resistor network (56, 57, 47, 48) coupled to said transistor network. |
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DETAILED DESCRIPTION .
The drawing is a diagram of a circuit for charging the lead-acid storage battery 50 of a mobile telephone 51 from an input from a d.
c.
voltage source, shown as an automobile storage battery 12.
10 designates the charging circuit as a whole, which has an input terminal 11 for connection to the d.
c.
voltage source 12.
Battery 12 has a fluctuating d.
c.
voltage U and, as already mentioned, is typically a lead-acid storage battery installed in a motor vehicle.
The input connection 11 of the charging circuit is connected to the input terminal A4 of a d.
c.
to d.
c.
voltage converter 14.
Converter 14 has five terminals A1 to A5, the terminal A2 being the unregulated output voltage terminal, the terminal A1 being a regulated voltage output terminal, the terminal A5 being a control voltage input terminal for the pulse width modulator 19 built into the d.
c.
to d.
c.
converter 14 and the terminal A3 being the terminal for a connection to ground or the chassis of the circuit.
A capacitor 15 is connected between ground and the input terminal A4 of the d.
c.
to d.
c.
converter and that terminal is also connected to a series branch circuit containing the Zener diode 16 and two resistors 17 and 18 leading to ground or chassis.
The d.
c.
to d.
c.
converter includes also a voltage regulator 20 for regulating the charging voltage made available at the terminal A1, which is connected through a network of resistors R3-R7 to the output terminal 53 of the charging circuit which also forms the input for the storage battery 50.
In accordance with a feature of the invention, a resistor 45, of a resistance less than 1 ohm, for example 0.
25 ohm, is connected in parallel the input to the storage battery 50.
Resistor 45 is connected to the emitter electrode of a transistor 46 and also to one electrode of a capacitor C6 of which the other electrode is connected to ground or chassis.
Resistors 56 and 57 are connected in parallel, to the base electrode of the transistor 46, and to the resistor 45 and its connection to the transistor 46
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Electrical and Wave 
