BATTERY CHARGERS

• US 3,800,208 A
• Filed: 11/08/1972
• Issued: 03/26/1974
• Est. Priority Date: 11/16/1971
• Status: Expired due to Term

• Current Assignee: James Adrian Macharg
• Original Assignee: James Adrian Macharg
• Inventors: Macharg, James Adrian
• Primary Examiner(s): Miller, J. D.
• Assistant Examiner(s): Hickey, Robert J.
• Application Number:
  US05/304,590
• Time in Patent Office: 503 Days
• Field of Search: 320/14,39,40,43,24,22
• US Class Current: 320/139
• CPC Class Codes: H02J 7/007182 in response to battery voltage

Abstract

A controlled current battery charger in which the charging current is cycled between upper and lower limits at varying rates throughout the charging period dependent on firstly a comparison between a reference voltage which is itself varied between upper and lower limits and the battery terminal voltage, and secondly the integrated value of the ON/OFF ratio of the time that switch means, operable from the result of the comparison of the reference voltage with the battery terminal voltage, is actuated, said switch means having an ON time which is either a substantially constant value or is itself varied in accordance with its own integrated output, the reference voltage being varied also in accordance with the integrated output of the switch means. The integrated output from said switch means which is utilized firstly to vary the ON time of said switch means and secondly to vary the reference voltage may be inverted so as to provide one of four different types of charging cycles.

Claims

1. A battery charger for charging batteries by cyclically increasing and decreasing the magnitude of the charging current towards given upper and lower limits:

including means for deriving a reference voltage;

comparator means for comparing this reference voltage with the terminal voltage of the battery;

time controlled switching means operable from the comparator means for providing a constant output signal for a substantially predetermined period, every time the terminal voltage drops below a given value in comparison with the instantaneous value of the reference voltage after the termination of the predetermined period;

means for integrating the output of the switch means;

means for progressively varying the reference voltage between predetermined upper and lower limits in accordance with the integrated value of the ON/OFF ratio of the switch means; and

means for controlling the variation of said charging current between said upper and lower limits in accordance with the output of said switch means.

2. A battery charger according to claim 1, wherein the given lower limit to which the charging current is reduced in each cycle is zero.

3. A battery charger according to claim 1, wherein the charging current is controlled between upper and lower limits in accordance with a function of the integrated output from said switch means.

4. A battery charger according to claim 1, wherein means are provided for controlling the time controlled switching means from the output of the integrator means so as to vary the ON period of the switching means in accordance with the state of charge of the battery.

5. A battery charger according to claim 2, wherein the time controlled switching means includes an input stage;

a level controlled switch acting as an output stage; and

a capacitor, said capacitor being charged by the ON output signal from the comparator through a diode and said transistor, so as to switch the level controlled switch to provide the said output signal from said time controlled switching means, the capacitor maintaining the level controlled switch in the On state for a predetermined time after the output signal from the comparator has fallen to zero.

6. A battery charger according to claim 4, wherein the time controlled switching means includes an input stage;

a capacitor;

a level controlled switch acting as an output stage; and

means for allowing said capacitor to discharge at any predetermined rate, said capacitor being charged through a diode and said input stage from the ON output signal from the comparator means, so as to switch the level controlled switch to provide the said output signal from said time controlled switching means, the capacitor discharging at a rate determined by the integrated value of the output signal from said time controlled switch means once the ON signal from the comparator has fallen to zero, so as to provide an ON period of the switching means which is dependent on the state of charge of the battery.

7. A battery charger according to claim 6, wherein said capacitor discharging means includes a Darlington pair whose collector-emitter path is in parallel with said capacitor and whose control electrode is connected to the output of said integrator means.

8. A battery charger according to claim 5, wherein said level controlled switch is a Schmitt trigger.

9. A battery charger according to claim 1, wherein said integrating means includes a capacitor, a pair of resistors and a transistor in series across the D.C. supply to the control circuitry, said integrated output for controlling the reference voltage being derived directly across said capacitor and said integrated output for controlling the charging current being derived from the junction point between said pair of resistors.

10. A battery charger according to claim 9, wherein said integrating means additionally includes a zener diode which acts as a level shift from the output of the time controlled switching means.

11. A battery charger according to claim 9, wherein an additional capacitor is provided for smoothing the integrated output which controls the value of the reference voltage.

12. provided battery charger according to claim 1, wherein means are procided for controlling the pulse height in the charging current as an inverse function of the charging current.

13. A battery charger according to claim 9, wherein said means for controlling said pulse height include a voltage to current converter in the form of a Darlington pair.

14. A battery charger according to claim 1, wherein the charging current is controlled by means of at least one thyristor, circuit means being provided for counteracting the sine-function which appears between the thyristor control voltage and the charging current.

15. A battery charger according to claim 14, wherein said circuit means for counteracting the sine-function is in the form of a dynamic load and includes a first zener diode and resistor in parallel therewith between said output from the integrator means and a power stage controlling the thyristor or thyristors, a second zener diode in series with the emitter-collector path of a transistor, said second zener diode preventing the transistor conducting as long as the voltage across the dynamic load exceeds the break-down voltage of the second zener diode, thus providing a corrected linearized signal to said power stage, said first zener diode shifting the origin at which the thyristors will start to conduct so that it coincides with the zero level of the output signal from the integrator means.

16. A controlled current battery charger, including means for deriving a reference voltage;

comparator means for comparing this reference voltage with the terminal voltage of the battery;

variable time controlled switching means comprising an input stage, a capacitor charged from the input stage, a level controlled switch acting as an output stage for providing a constant output signal for a period of time depending on the rate of discharge of the capacitor, said output signal being produced every time the terminal voltage drops below a given value in comparison with the instantaneous value of the reference voltage after cessation of said constant signal;

means for integrating the output of the switch means;

means for progressively varying the reference voltage between predetermined upper and lower limits in accordance with the integrated value of the ON/OFF ratio of the switch means;

means for controlling the rate of discharge of the capacitor from the output of the integrator means so as to vary the ON period of the time controlled switching means in accordance with the state of charge of the battery; and

means for controlling the variation of said charging current between upper and lower limits in accordance with the output from said variable time controlled switching means.

17. A battery charger according to claim 16, wherein an inverter circuit is inserted between the output of the integrator means and the means which allows the capacitor to discharge at a rate determined by the integrated output from the integrator means.

18. A battery charger according to claim 17, wherein said inverter circuit additionally inverts the output from the integrator means which is applied to said means for varying the value of the reference voltage between predetermined upper and lower limits.

19. A battery charger according to claim 1, wherein the means for deriving the reference voltage include a first controlled current source supplying a resistor across which a reference voltage is developed, and wherein the means for varying the value of the reference voltage between upper and lower limits is a second controlled current source arranged in parallel with the first controlled current source to augment the current through the reference resistor, said second controlled current source being progressively switched '"'"''"'"''"'"''"'"'on'"'"''"'"''"'"''"'"' and '"'"''"'"''"'"''"'"'off'"'"''"'"''"'"''"'"' so as to raise and lower the reference voltage between said limits in accordance with the output of said integrator means.

20. A battery charger according to claim 19, wherEin the output from said integrator means is inverted before being applied to the progressive switching means which control the second current source.

21. A battery charger according to claim 19, wherein means are provided for controlling the time controlled switching means from the output of the integrator means so as to vary the ON period of the switching means in accordance with the state of charge of the battery.

22. A battery charger according to claim 21, wherein the output from said integrator means is inverted before being applied to both the progressive switching means which control the second current source and the time controlled switching means.

23. A battery charger according to claim 16, wherein a transistor stage is inserted in series between the output of the integrator means and a power stage for controlling the charging current, said transistor having its base electrode connected to the output circuit of said transistor in series with the integrating capacitor and a pair of resistors.