Emergency Instant-start Lighting System For Arc Discharge Devices

Abstract

An emergency lighting system for at least one arc discharge device, utilizing an impedance mismatch between the emergency lighting system and a ballast provided for normal 60 Hz. power operation. This emergency lighting system will be activated when a normal AC voltage source falls below a predetermined level, and operates the arc discharge devices in an instant-start lighting system mode without the requirement for active switching between the normal and emergency modes of operation.

Description

BACKGROUND OF THE INVENTION

The present invention relates to an instant-start stand-by power system which will provide emergency lighting when the normal source of power for an arc discharge lighting system fails. This emergency lighting system may be utilized with rapid-start lamps, instant-start lamps, trigger-start lamps, or high intensity discharge lamps. Typically, rapid-start lighting systems comprise one or a plurality of serially connected arc discharge devices. When more than one arc discharge device is used in a series connection, a starting capacitor is included in a well-known electrical configuration to aid starting of the discharge devices.

Emergency lighting systems are well known in the art. Rapid-start lighting systems utilizing serially connected arc discharge devices with an associated starting capacitor are well known, as evidenced by Pat. No. 2,796,554, issued to C. E. Strecker and assigned to the assignee of the present application.

Utilizing an emergency power source for a rapid-start lighting system provides numerous problems. One problem arises when a high frequency inverter powered from an independent source of power is utilized as the emergency power source. The circuitry associated with a high frequency inverter has had an effect on starting an arc discharge device when the normal 60 Hz. source of supply is operatively connected to the lighting system and the converse has likewise been true, in that the ballast utilized with the normal source of supply has had an effect on the powering of the arc discharge from an emergency supply, leading to the necessary inclusion of active switching devices.

The foregoing problems have been substantially eliminated, according to my invention, by providing an impedance mismatch between the ballast and the emergency power system. An illustrative embodiment of my invention as it is used in an emergency power system for providing means for instant starting of a rapid-start lighting system of the type utilizing a starting capacitance connected across all but one of a plurality of serially connected arc discharge devices is hereinafter described in detail.

Typical ballasts for rapid-start lighting systems have a characteristic impedance when measured across the lamps. This impedance conveniently may have a resonant frequency at approximately 6.5 KHz. At this resonant frequency, the ballast will present its highest impedance across the lamps a frequency range of 5.75 KHz to 7.5 KHz, which is approximately 6.5 KHz, is acceptable for most fluorescent ballasts. By utilizing an emergency lighting inverter to operate at this resonant frequency, the ballast will present a high impedance to the inverter. The operating frequency of the inverter is also sufficiently high, such that the impedance of the starting capacitor, shunting all but one of the lamps, will be a low impedance and prevent the shunted lamp from starting. This insures that only the lamp or lamps which are not shunted by starting capacitors will operate in the emergency mode. Likewise, the output terminals of the inverter, which are across the serially connected arc discharge devices, will provide a high impedance at the normal operating frequency of the ballast in the rapid-start lighting system. This impedance mismatch of ballast-to-inverter and inverter-to-ballast allows both devices to operate the arc discharge devices without active switching being required. Also with a starting capacitor shunting all but one fluorescent lamp, only one lamp is operated in the emergency mode.

SUMMARY OF THE INVENTION

It is therefore an object of my invention to provide a new and improved emergency power system for an arc discharge lighting system.

It is another object of my invention to provide a new and improved emergency power system which will have minimum effect on normal starting of an arc discharge lighting system when a 60 Hz. source of supply is utilized to power the arc discharge lighting system.

It is another object of my invention to provide a new and improved emergency power system for rapid-start arc discharge devices which will start and operate these rapid-start lamps in an instant-start mode regardless of whether or not the 60 Hz. ballast had recently been operating the lamps.

It is a further object of my invention to provide a new and improved emergency power system for rapid-start arc discharge devices without the utilization of active switching between the inverter and the 60 Hz. ballast usually associated with such arc discharge devices.

Briefly stated, and according to one aspect of the invention, the foregoing objects are achieved by utilizing an impedance mismatch between the emergency power system and the ballast of the arc discharge devices. The new and improved emergency instant-start lighting system, when utilized with a rapid-start lamp system, includes an inverter powered from a DC power source such as a battery. The inverter provides a high impedance to the normal 60 Hz. power source and is held off until the normal 60 Hz. power source falls below a predetermined level. When activated, the high frequency output of the inverter is applied across the serially connected arc discharge devices at a frequency at which a starting capacitor utilized in the lighting system presents a low impedance path to the emergency power current, and the AC ballast acts as a high impedance, thus powering the arc discharge devices, which are not shunted by a starting capacitor, from the high frequency inverter.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention, both as to its organization and principle of operation together with further objects and advantages thereof, may better be understood by reference to the following detailed description of an embodiment of the invention when taken in conjunction with the accompanying drawings in which:

FIG. 1 is a block diagram illustrating the basic components of an emergency lighting system.

FIG. 2 is a circuit diagram illustrating the basic concepts of an emergency instant-start lighting system for rapid-start arc discharge devices utilizing a starting capacitor in accordance with this invention.

DESCRIPTION OF A PREFERRED EMBODIMENT

In FIG. 1, a power source 10, usually at 60 Hz., is connected to ballast 12 which in turn activates and ballasts lamp unit 14. A second power source 15 is connected to charge emergency power source 20, normally a battery, through charger 22 and is also connected to inverter holdoff means 18. When the voltage of power source 15 falls below a predetermined level, the reduced voltage on holdoff means 18 causes release of its holdoff on inverter 16. Emergency power is then supplied to lamp 14 through inverter 16. Power sources 10 and 15 are supplied from a common source so that the reduced voltage appears at both power sources. However, power source 10 may be switched to permit the lighting system to be deliberately turned off, while power source 15 is unswitched so as to energize the holdoff means when the lighting system is switched off.

Referring now to FIG. 2, inverter 16, which will provide emergency power to a rapid-start lighting system 24, comprises transformer 30 with feedback windings 31 and 32, primary windings 33 and 34, and secondary winding 36. Feedback windings 31 and 32 are serially connected to each other at a common terminal and poled as shown in FIG. 2.

The free end of feedback winding 31 is connected through a parallel combination of resistor 37 and capacitor 38 to the base of a PNP transistor 26. Likewise, the free end of feedback winding 32 is connected through the parallel combination of resistor 39 and capacitor 40 to the base of transistor 25. The emitters of transistors 25 and 26 are connected together and are further connected to the positive terminal of battery 35 and the common terminal of feedback windings 31 and 32.

Primary windings 33 and 34, which are poled as shown in FIG. 2, are connected serially and, at their common terminal, are connected to the negative terminal of a battery 35. The free end of primary winding 33 is connected to the collector of PNP transistor 25. Likewise, the free end of the primary winding 34 is connected to the collector of transistor 26. The base of transistor 25 is connected through resistor 44 to the negative terminal of battery 35.

The ends of the secondary 36 of transformer 30 are connected to a capacitor 41, which tunes the inverter to a predetermined frequency and which transformer ends provide the power during emergency conditions to operate the arc discharge lamps illustratively used to describe the invention. Two separately packaged multiple capacitor units 46 and 47 are connected in series between one end of the secondary winding 36 and the lighting system 52. Multiple capacitor unit 46 comprises serially connected capacitors 48 and 49, and multiple capacitor unit 47 comprises serially connected capacitors 50 and 51. The multiple capacitor units 46 and 47 are provided to keep all voltage stress below the corona level. The capacitor units 46 and 47 also, and more importantly, provide a capacitive coupling between inverter 16 and rapid-start system 24 and further provide a high impedance mismatch respective the normal 60 Hz. power source.

In order to prevent the inverter 16 from turning on until a power failure is realized, holdoff means 18 is provided. When the rapid-start system is operating normally, holdoff means 18, which is described and claimed in patent by W. M. Niederjohn, U.S. Pat. No. 3,771,012 issued Nov. 6, 1973 filed May 24, 1972, and assigned to the present assignee, receives a 60 Hz. voltage across primary winding 42 of transformer A. This voltage is transformed to secondary winding 43 of transformer A and applied across a full wave rectifier 52 comprising diodes 52a, 52b, 52c, and 52d, with output terminals 53 and 54 to charge capacitor 55 connected between terminals 53 and 54. Terminal 53 is further connected to the base of transistor 25 through the serial connection of resistor 56 and diode 57 and to the base of transistor 26 through the serial connection of resistor 58 and diode 59 to provide current of a magnitude sufficient to reverse bias transistors 25 and 26 to hold the inverter 16 in the off state.

Transformer A is provided with a second secondary winding 60 connected at a first end to the positive terminal of battery 35. The other end or second end of secondary winding 60 is connected through a properly poled diode 61 to the negative terminal of battery 35 to provide a means for charging battery 35. One end of a pilot light 62 is connected to the second end of the secondary winding 60 through a diode 63, diode 63 being poled to operate on alternate half cycles respective diode 61. The second end of pilot light 62 is connected to the first end of secondary winding 60.

First and second means 64 and 65 for receiving an arc discharge device are provided to receive the free ends of series lamps 66 and 67. First and second means 64 and 65 provide the electrical connection between lighting system 24 and the output from inverter 16 as at points B and C. Lighting system 24, which comprises arc discharge devices 66 and 67, here in the form of fluorescent lamps, serially connected in a manner well known in the art, further comprises an AC ballast 12 connected across the serially connected devices 66 and 67. Ballast 12 includes terminals or leads 68 and 69 for receiving the normal 60 Hz. AC voltage and includes a starting capacitor 70 connected across fluorescent lamp 66 in a manner well known in the art to provide for rapid starting.

During normal operation, the 60 Hz. voltage is applied to the AC ballast 12 at terminals 68 and 69 to operate arc discharge devices 66 and 67 in a manner well known in the art and to the primary winding 42 of transformer A of holdoff circuit 18. The voltage at primary winding 42 is transformed to secondary winding 60 of transformer A and then is rectified by diodes 61 and 63 to allow the battery 35 to be charged on the first half cycles from the 60 Hz. voltage and to allow an associated pilot light 62 to be activated on the second half cycles from the AC signal. The pilot light 62 will therefore indicate that power is on and being applied to the charging circuit for the battery.

Inverter 16, which illustratively is a tuned secondary, two transistor, self-oscillating inverter, is held off by holdoff circuit 18 in the presence of the normal 60 Hz. power source. When the normal 60 Hz. voltage is present at the primary winding 42 of transformer A, capacitor 55 is charged through rectifier 52 to produce a positive potential which is applied through resistors 56 and 58 in conjunction with diodes 57 and 59 respectively to the bases of transistors 25 and 26 respectively to reverse bias transistors 25 and 26 and to hold the inverter 16 in the off state.

When the normal 60 Hz. voltage is significantly reduced, capacitor 55 will discharge removing the effect of holdoff circuit 18. The emergency source voltage from battery 35 is applied to inverter 16 to allow current to flow through the emitter base junction of transistor 25 and starting resistor 44. This current forward biases transistor 25 into conduction applying a voltage equal to the battery voltage less the voltage drop between the collector and emitter of transistor 25 to primary winding 33 of transformer 30. The voltage transformed to feedback winding 32 of transformer 30 in conjunction with resistor 39 and capacitor 40 biases transistor 25 into saturation. A tuned circuit, comprising the leakage reactance of transformer 30 and secondary winding 36 in parallel with capacitor 41 and the series combination of the capacitive value of multiple capacitor units 46 and 47, starting capacitor 70, and the resistance of arc discharge device 67 is set to resonate at an approximate frequency of 6.5 KHz, which is in the range of 5.75 KHz to 7.5 KHz. The voltage transformed from primary winding 33 to secondary winding 36 charges the equivalent capacitance of this tuned circuit. When the circuit resonates and the capacitance discharges into tuned winding 36, feedback winding 32 is forced to reverse its polarity as the voltage goes through zero. Transistor 25 is then reverse biased and comes out of saturation. At the same time, feedback winding 31 forward biases transistor 26 which applies a third voltage equal to battery voltage less the voltage drop between the collector and emitter of transistor 26, to primary winding 34 of transformer 30. The equivalent capacitance of the tuned circuit is charged in the opposite direction. When the voltage again goes through zero, transistor 26 is biased off, transistor 25 on, and the inverter 16 has completed one cycle. Starting capacitor 70 in AC ballast 12 effectively shorts out arc discharge device 66 at 6.5 KHz. and provides emergency power to arc discharge device 67. Capacitors 38 and 40 are used to speed up the reaction time of transistors 25 and 26 respectively. Inverter 16 will thus start and continue to run whenever appropriate voltage is applied to transistors 25 and 26.

The secondary 36 of transformer 30 provides sufficient voltage to start rapid-start lamps in the instant-start mode, that is, with no lamp filament heat provided. This mode of starting allows the emergency lighting system to start a lamp even when the lamp has not recently been operated.

The foregoing has shown that, when the normal 60 Hz. voltage is significantly reduced, capacitor 55 will discharge and allow the inverter 16 to take over powering lamp 67 at a reduced light output preferentially at about 20 percent of the normal power at 60 Hz.

It has further been shown that the capacitance of multiple capacitor units 46 and 47 provide a high impedance at 60 Hz. thus substantially reducing the electrical effect between the inverter 16 and the lighting system during the normal mode of 60 Hz. ballast operations. Likewise, at 6.5 KHz. (the approximate operating frequency of inverter 16) the AC ballast 12 forms a high impedance and thus substantially reduces the electrical effect of the ballast 12 and does not substantially hinder the operation of the emergency system. The emergency power system and the ballast of the arc discharge devices are impedance mismatched and each does not substantially affect the operation of the other.

It has been shown that, by providing an instant-start, standby emergency power system, which will be activated when the normal 60 Hz. source falls below a predetermined level and wherein the emergency power system is impedance mismatched to the ballast of an arc discharge device or devices, a reliable emergency system to provide instant starting of an arc discharge lighting system without the use of active switching can be obtained.

While an embodiment and application of this invention has been shown and described, it will be apparent to those skilled in the art that modifications are possible without departing from the inventive concepts herein described. The invention, therefore, is not to be restricted except as is necessary by the prior art and by the spirit of the appended claims.

Claims

What is claimed as new and desired to be secured by Letters Patent of the United States is:

1. An emergency lighting system for arc discharge devices and for use with a normal A.C. ballast having a starting capacitor comprising:

a first and second means for electrically connecting the emergency lighting system across at least a pair of serially connected arc discharge devices;

means for connecting said first means to the starting capacitor;

the starting capacitor being adapted to be connected across at least one of the pair of arc discharge devices for providing starting assistance during the normal and emergency modes;

circuit means for providing emergency power having an input means for connection to an emergency power source;

said circuit means having first and second output means;

capacitance means connected between said first means and said first output means of said circuit means for providing a high impedance when power for the arc discharge devices is provided through the normal A.C. ballast;

said circuit means operating at least one of the pair of arc discharge devices at a frequency at which the normal A.C. ballast will have a relatively high impedance; means for inhibiting operation of said circuit means until normal A.C. voltage drops below a predetermined level, wherein said predetermined level could be substantially above zero.

2. The system as in claim 1 wherein said emergency power source comprises a DC power source.

3. The system as in claim 1 wherein said DC power source is a rechargeable power source and further including:

means for recharging the power source.

4. The system as in claim 1 including a multiple of series connected capacitor units, each unit comprising at least one capacitive device, connected in series with said first output of said circuit means.

5. The system as in claim 1 wherein said circuit means is an inverter.

6. The system as in claim 5 wherein said inverter is a tuned secondary, two-transistor, self-oscillating inverter.

7. A system as in claim 1 wherein said emergency lighting system is adapted for operating fluorescent lamps of the rapid start type in an instant start mode.

8. A system as set forth in claim 1 wherein said circuit means operates in a frequency range of 5.75 to 7.5 KHz for maximizing ballast impedance.

9. A system as set forth in claim 1 wherein the frequency of said circuit means is such that the starting capacitor exhibits a relatively low impedance during the operation of said circuit means whereby at least one of the pair of arc discharge devices is inactivated during the emergency operation.

10. An emergency lighting system for arc discharge devices and for use with a normal A.C. ballast comprising:

a first and second means for connecting the emergency lighting system across at least one arc discharge device;

circuit means for providing emergency power having an input means for connection to an emergency power source;

said circuit means having first and second output means;

means for activating said circuit means when normal power drops below a predetermined level, wherein said predetermined level could be substantially above zero; said circuit means being operated in such frequency range so that the normal A.C. ballast will exhibit substantially its highest impedance across the at least one arc discharge device; capacitance means connected between said first means and said first output means for providing a high impedance when the power for the at least one arc discharge devices is provided through the normal A.C. ballast.

11. A system as set forth in claim 10 wherein said circuit means operates in a frequency range of 5.75 to 7.5 KHz.