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Circuit arrangement for charging rechargeable batteries

  • US 5,598,085 A
  • Filed: 07/13/1994
  • Issued: 01/28/1997
  • Est. Priority Date: 07/14/1993
  • Status: Expired due to Fees
First Claim
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1. A circuit arrangement for charging rechargeable batteries, comprising:

  • a first terminal and a second terminal to which at least one battery is connectable in order to be charged, a charging current source connected to both terminals and adapted to supply thereto charging current pulse trains, said current source having a control input to which a pulse-shaped control signal can be applied to enable and to inhibit the supply of a charging current pulse train, and wherein the current source, in accordance with the pulse-shaped control signal applied to its control input, supplies to the at least one battery the charging current pulse train of charging current pulses which occur during successive charging periods which are spaced from one another by charging pauses, whereinthe first terminal of the circuit arrangement is coupled to an input of a first detection device which receives a voltage which is proportional to a sum voltage at the first terminal and comprising the battery no-load voltage and a pulse-shaped charging voltage which is superposed on said battery no-load voltage and which is proportional to the charging current pulses via the internal resistance of the battery, and to derive an actual voltage proportional to an average sum voltage, which comprises the battery no-load voltage and the average-value voltage superposed on said battery no-load voltage and resulting from the pulse-shaped charging voltage, wherein the first detection device detects the actual voltage dependent upon a variable reference voltage available in the first detection device, and generates at its output a detection signal which corresponds to the detection result and depends on the actual voltage and on the reference voltage,means coupling the output of the first detection device to an input of a control pulse generator for generating the pulse-shaped control signal, the detection signal enabling said control pulse generator to control the duty cycle of the pulse-shaped control signal generated by said control pulse generator at an output thereof,second means coupling the output of the control pulse generator to the control input of the charging current source to enable or inhibit the supply of a charging current pulse train, andfor an increasing actual voltage or a decreasing reference voltage in the first detection device the control pulse generator, dependent on the detection signal applied to its input, varies the duty cycle the pulse-shaped control signal which it can generate such that the charging current source reduces the ratio between the charging period and the charging pause in the charging current pulse train, andmeans for varying the reference voltage available in the first detection device in the same sense as the duty cycle of the pulse-shaped control signal at the output of the control pulse generator dependent on said duty cycle.

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