Constant current battery charging circuit

• US 3,925,714 A
• Filed: 09/26/1974
• Issued: 12/09/1975
• Est. Priority Date: 09/26/1974
• Status: Expired due to Term

• Current Assignee: Telefonaktiebolaget LM Ericsson
• Original Assignee: Ralph r. Sherman, Jr.
• Inventors: Sherman, Ralph R. Jr.
• Primary Examiner(s): Miller, J. D.
• Assistant Examiner(s): Hickey, Robert J.
• Application Number:
  US05/509,359
• Time in Patent Office: 439 Days
• Field of Search: 320/39,40,32 323/4,22T,225CR
• US Class Current: 320/143
• CPC Class Codes: H02J 7/007182 in response to battery voltage

Abstract

A constant current battery charging circuit is provided by a current control device which supplies rectified charging current at a magnitude determined by the time occurrence of a control signal applied to the control device. The control signal is produced in response to a sawtooth voltage exceeding an error signal. The error signal is produced in response to the relative magnitudes of a voltage indicating charging current and a reference voltage.

Claims

1. An improved battery charging circuit comprising:

a. main input terminals adapted to be connected to a source of alternating current;

b. main output terminals adapted to be connected to a battery to be charged;

c. a rectifier circuit having input terminals connected to said main input terminals and having output terminals for producing rectified alternating current;

d. a reference voltage circuit connected to said rectifier output terminals for producing a direct current reference voltage;

e. a first operational amplifier having first input terminals connected to said rectifier output terminals, second input terminals connected to said reference voltage circuit, and output terminals for producing reset pulses;

f. a second operational amplifier having first input terminals connected to said first operational amplifier output terminals, second input terminals connected to said reference voltage circuit, output terminals, and a capacitor connected between one of said output terminals and one of said first input terminals for producing a sawtooth voltage at said output terminals;

g. a current control device having an anode-cathode path connected in series between said rectifier output terminals and said main output terminals, and having a control electrode;

h. a current sensing resistor connected in series with said anode-cathode path of said current control device;

i. a third operational amplifier having first input terminals, second input terminals connected to said second operational amplifier output terminals, and output terminals;

j. a fourth operational amplifier having first input terminals connected to said reference voltage circuit, second input terminals connected to said current sensing resistor, and output terminals for producing an error signal indicative of the relative magnitude of the current in said resistor and a selected reference current;

k. means connecting said fourth operational amplifier output terminals to said first input terminals of said third operational amplifier for permitting said third operational amplifier to produce a control signal in response to said sawtooth voltage exceeding said error signal;

1. and means connecting said output terminals of said third operational amplifier to said control electrode for causing said current control device to conduct in response to said control signal.

2. The improved battery charging circuit of claim 1 wherein said rectifier circuit provides full wave rectification.

3. The improved battery charging circuit of claim 1, and further comprising a switch connected between said second input terminals of said second operational amplifier and said reference voltage circuit for stopping the charging circuit when desired.