Method and apparatus for operating LED array and charging battery for emergency LED operation including DC boost circuit allowing series connection of LED array and battery

• US 5,739,639 A
• Filed: 07/03/1996
• Issued: 04/14/1998
• Est. Priority Date: 07/03/1996
• Status: Expired due to Term

• Current Assignee: ABL IP Holding LLC (Acuity Brands, Inc.)
• Original Assignee: NSI Enterprises Incorporated (Alsco Incorporated)
• Inventors: Johnson, James C.
• Primary Examiner(s): Pascal, Robert
• Assistant Examiner(s): VU, DAVID HUNG
• Application Number:
  US08/675,109
• Time in Patent Office: 650 Days
• Field of Search: 362/20, 362/800, 362/812, 315/86, 315/87, 315/160, 315/161, 315/170, 315/171, 315/172, 315/173-176, 315/200 R, 315/209 R, 315/291, 307/64, 307/66, 340/815.45
• US Class Current: 315/86
• CPC Class Codes: H02J 9/061 for DC powered loads

Abstract

Circuitry for operating an array of light emitting diodes such as in an emergency exit sign in a non-emergency AC mode while concurrently charging and maintaining the charge of a low-voltage battery used to drive the array in an emergency mode, the circuitry also allows operation of the same LED array in the emergency mode from the low-voltage battery. The advantages of the invention are realized in part through provision within the circuitry of a boost converter wherein the LED array and the battery are connected across the output of the usual boost circuit output capacitor, thereby allowing connection of the array and the battery in series to simplify operation from line power and to allow the same current limited source to operate the array and simultaneously charge the battery through the same current path. The functions so provided can be embodied in a form which allows all circuitry components including the battery to be mounted on a single, compact substrate such as a printed circuit board.

Claims

1. In a circuit having an array of light emitting diodes operable on AC mains power and on DC power from a battery when mains power is unavailable, battery charging and charge maintenance circuitry, a current limited source, and a boost converter circuit having an output capacitor, the LED array and the battery being connected across the output of the output capacitor to connect the LED array and the battery in series, thereby allowing the current limited source to operate the LED array on AC mains power with simultaneous charging and maintenance of charge of the battery through the same current path without switching or repositioning circuit components during DC operation.

2. In the circuit of claim 1 wherein the current limited source comprises at least one capacitor.

3. In the circuit of claim 1 wherein the current limited source comprises a switching power supply.

4. In the circuit of claim 1 wherein the boost converter circuit further comprises an inductor and a diode, the boost converter circuit being driven by a transistor having a base, energy being stored in the inductor when the transistor is in the "on" condition, the inductor therefore being directly across the battery to cause current to ramp up, stored energy within the inductor adding to battery voltage when the transistor is turned off to charge the output capacitor through the diode.

5. The circuit of claim 4 wherein the transistor comprises a bipolar transistor.

6. The circuit of claim 5 wherein the transistor has a saturation level as low as 200 millivolts.

7. In the circuit of claim 4 wherein the battery comprises a single 1.2 volt cell.

8. In the circuit of claim 4 and further comprising means for identifying the presence of AC power on the circuit.

9. In the circuit of claim 8 wherein the identifying means comprise a diode and a smoothing capacitor located in the circuit between the source of mains power and the LED array, the diode and the smoothing capacitor holding the base of the transistor below emitter potential during AC current flow.

10. In the circuit of claim 9 and further comprising an oscillator circuit which is turned on by forward biasing of the base of the transistor on loss of AC power.

11. In the circuit of claim 10 wherein the oscillator circuit comprises two transistors.

12. In the circuit of claim 4 and further comprising a drive circuit for operation of the boost converter circuit.

13. In the circuit of claim 1 and further comprising means for limiting voltage across the circuit in the event of interruption of circuit current path such as occasioned by removal of the battery from the current path.

14. In the circuit of claim 13 wherein the voltage limiting means comprises a Zener diode.

15. In the circuit of claim 1 wherein the current limited source comprises at least one capacitor and a switching power supply.

16. In the circuit of claim 1 and further comprising means for identifying the presence of AC power on the circuit.

17. A method for operating a circuit including an LED array by means of AC mains power and by DC power from a battery when AC power is unavailable and charging and maintaining charge of the battery during operation by AC mains power, the circuit including a boost converter circuit having an output capacitor and a current limited source, comprising the steps of:

connecting the LED array and the battery across the output of the output capacitor to connect the array and the battery in series;

operating the LED array by means of the current limited source on AC power; and

,

simultaneously charging and maintaining the charge of the battery through the same current path used for operation of the LED array.

18. The method of claim 17 wherein the current limited source comprises at least one capacitor.

19. The method of claim 17 wherein the current limited source comprises a switching power supply.

20. The method of claim 17 wherein the current limited source comprises at least one capacitor and a switching power supply.

21. In a circuit having an array of light emitting diodes operable on AC mains power and on DC power from a battery when mains power is unavailable, battery charging and charge maintenance circuitry, a current limited source, and a boost converter circuit having an output capacitor and being driven by a transister having a base, the light emitting diode array and the battery being connected across the output of the output capacitor to connect the light emitting diode array and the battery in series, the circuit further comprising means for identifying the presence of AC power on the circuit, the identifying means comprising a diode and a smoothing capacitor located in the circuit between the source of mains power and the light emitting diode array, the diode and the smoothing capacitor holding the base of the transistor below emitter potential during AC current flow, thereby allowing the current limited source to operate the LED array on AC mains power with simultaneous charging and maintenance of charge of the battery through the same current path.

22. In the circuit of claim 21 and further comprising an oscillator circuit which is turned on by forward biasing of the base of the transistor on loss of AC power.

23. In the circuit of claim 22 wherein the oscillator circuit comprises two transistors.