Battery charge indicating circuit

• US 20040046673A1
• Filed: 09/05/2002
• Published: 03/11/2004
• Est. Priority Date: 09/05/2002
• Status: Active Grant

• Current Assignee: Credo Technology Corporation
• Original Assignee: S-B Power Tool Corporation
• Inventors: Kovarik, Illya, Gawell, George R.
• Granted Patent: US 6,950,030 B2
• Time in Patent Office: Days
• US Class Current: 340/636.1
• CPC Class Codes: G01R 31/3646 for indicating electrical conditions or variables, e.g. visual or audible indicators
• CPC Class Codes: G01R 31/388 involving voltage measurements

Abstract

A voltage indicator circuit for indicating a charge state of a power supply, such as a battery pack, is disclosed. The voltage indicator circuit includes a voltage divider circuit that connects to a plurality of series connected light sources, such as light emitting diodes. Upon activation of the voltage divider circuit, one or more of the light sources may illuminate to provide a visual indication of the current charge state of the power supply. More particularly, the number of light sources illuminated varies according to the charge state of the battery pack.

Claims

1. A voltage indicator circuit for a power source, comprising:

a voltage divider circuit;

a plurality of series connected light sources coupled to said voltage divider circuit; and

means for connecting said voltage divider circuit to the power source.

2. The circuit of claim 1 wherein said means for connecting said voltage divider circuit to the power source comprises a switch connected in series therebetween.

3. The circuit of claim 2 further comprising a zener diode connected in series between said voltage divider circuit and said switch.

4. The circuit of claim 1 formed as part of a battery pack, wherein the power source is a rechargeable battery.

5. The circuit of claim 4 wherein said rechargeable battery, upon being fully charged, has a voltage less than 30V.

6. The circuit of claim 4 wherein said plurality of series connected light sources are light emitting diodes.

7. The circuit of claim 6 comprising three light emitting diodes for indicating one of a low, medium, and high charge state of said rechargeable battery.

8. The circuit of claim 1 wherein said voltage divider circuit comprises a resistor ladder having four resistors in series.

9. The circuit of claim 7 wherein said voltage divider circuit comprises four resistors defining nodes therebetween, and wherein each of said nodes connects to separate anodes of said light emitting diodes.

10. A device for providing power to a load, comprising:

a battery pack; and

a battery charge indicator circuit connected to said battery pack to indicate a charge state of said battery pack;

said battery charge indicator circuit further comprising;

a voltage divider circuit having a plurality of nodes;

a plurality of series connected light emitting diodes each having an anode connected to separate nodes of said voltage divider circuit; and

means for controlling a flow of electric power from said battery pack to said battery charge indicator circuit.

11. The device of claim 10 wherein said battery pack is a rechargeable battery pack.

12. The device of claim 10 wherein said voltage divider circuit further comprises a resistor ladder having first, second, third, and fourth resistors connected to said plurality of series connected light emitting diodes.

13. The device of claim 12 wherein said plurality of series connected light sources comprises:

a first light emitting diode having an anode connected to the first resistor and a cathode connected to said second and third resistors;

a second light emitting diode having an anode connected to said second and third resistors and a cathode connected to the third and fourth resistors; and

a third light emitting diode having an anode connected to said third and fourth resistors and a cathode connected to said fourth resistor and a ground.

14. The device of claim 10 further comprising a zener diode connected in series between said voltage divider circuit and said means for controlling a flow of electric current.

15. The device of claim 10 wherein said means for controlling a flow of electric power comprises a switch.

16. A battery powered device for supplying power to a load, comprising:

a battery having first and second terminals;

a voltage detection circuit, connected to said battery, for detecting a charge state of said battery and having at least two series connected light emitting diodes for generating a visual signal upon a flow of electric current from said battery to said voltage detection circuit.

17. The device of claim 16 wherein said voltage detector circuit includes at least four resistors connected in series.

18. The device of claim 17 further comprising three light emitting diodes in series and connected to said at least four resistors for generating said visual signal.

19. The device of claim 18 wherein each of said light emitting diodes is connected in parallel to separate resistors of said at least four resistors.

20. The device of claim 16 further comprising a switch for controlling said flow of electric current between said battery and said voltage detection circuit.

21. The device of claim 20 further comprising a zener diode connected in series between said voltage divider circuit and said switch.

22. The device of claim 16 wherein said battery is a rechargeable battery.

23. The device of claim 18 wherein the load is a motor and said light emitting diodes are configured to determine a speed of the motor.

24. A power source comprising:

a battery pack; and

a battery charge indicator circuit connected to said battery pack to indicate a charge state of said battery pack, said battery charge indicator circuit further comprising;

a voltage divider circuit having a first, second, third, and fourth resistor connected in series;

a first light emitting diode connected in parallel to said second resistor;

a second light emitting diode connected in parallel to said third resistor;

a third light emitting diode connected in parallel to said third resistor; and

a switch for controlling a flow of electric power from said battery pack to said battery charge indicator circuit.

25. The power source of claim 24 wherein said first and second resistors connect to an anode of said first light emitting diode.

26. The power source of claim 25 wherein said second and third resistors connect to an anode of said second light emitting diode, and said third and fourth resistors connect to an anode of said third light emitting diode.

27. The power source of claim 26 wherein said second and third resistors connect to a cathode of said first light emitting diode, and said third and fourth resistors connect to a cathode of said second light emitting diode.

28. The power source of claim 27 wherein said fourth resistor connects to a cathode of said third light emitting diode and a ground.