US3320473A

US3320473A - Emergency lighting system

Info

Publication number: US3320473A
Application number: US398176A
Authority: US
Inventors: Denis R Grafham
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1964-09-22
Filing date: 1964-09-22
Publication date: 1967-05-16
Anticipated expiration: 1984-05-16

Description

May 16, 1967 D. RwGRAFHAM 3,320,473

EMERGENCY LIGHTING SYSTEM Filed Sept. 22, 1.)64

INVENTORI DENIS R. GRAFHAM,

BY %M 7 ,Q

HIS ATTORNEY.

United States Patent 3,320,473 EMERGENCY LIGHTING SYSTEM Denis R. Grafham, Auburn, N.Y., assiguor to General Electric Company, a corporation of New York Filed Sept. 22, 1964, Ser. No. 398,176 3 Claims. (Cl. 315-86) My invention relates to an emergency lighting system and, more particularly, to an emergency lighting system for producing light upon the failure of a conventional power supply.

There are many places which must be constantly supplied with light to prevent the possibility of danger to persons utilizing the particular facilities found in such a place. Places of this sort include restricted areas where failure of a light source could promote panic, such as in an elevator cab; regions lighted to prevent the possibility of personal attack, such as corridors and entrance ways; and those areas lighted to prevent the possibility of accident, such as in narrow, steep or winding stairways.

Failure of the light source in any of these locations could greatly increase the chances of danger for any individual in such a location. Therefore, when the conventional power supply for the lighting system in such a region fails, it is desirable to have some means for producing emergency light. This may be achieved by substitution of a stand-by power supply, or by providing a completely separate emergency lighting system which detects a failure of the conventional power supply and utilizes this detected information to cause energization of the emergency light. This latter approach has the advantage that the lighting circuit may be engineered for the particular emergency supply involved, rather than having the emergency supply shifted into a circuit designed for the conventional power supply. It is this separate type of lighting system that is the subject of my invention Most prior art systems have depended upon the use of relays to switch the emergency power supply into a circuit to energize and to provide emergency light. These prior art systems have the disadvantages that accompany the use of moving mechanical parts for switching control, such as sensitivity to vibrations, humidity, vapor and climatic conditions. By providing a static switching circuit for controlling energization of the emergency lamp upon failure of the conventional power supply, in ac cordance with my invention, the emergency lighting systern is unaffected by these factors.

Thus, it is an object of my invention to provide an improved static switching circuit for controlling the energization of an emergency lamp in case of power failure.

Other objects and advantages of my invention will become apparent as the following description proceeds and the features of novelty which characterize my invention will be pointed out with particularity in the claims annexed to and forming part of this specification.

For a better understanding of my invention, reference may be made to the accompanying drawing, the single figure of which is a circuit diagram of one embodiment of my invention.

Briefly stated, in one of form of my invention, a voltage-controlled switching device such as a silicon controlled rectifier (SCR) is placed in series with an electrically energizable lamp which provides emergency light in the event of failure of the main power supply. To achieve the desired energization of the emergency lamp in case of power failure, a capacitor circuit is utilized to control the firing of the SCR. During normal energization of the conventional light source by the main power supply, the capacitor is charged in such a direction as to prevent firing of the SCR and, thereby, prevent energization of the 3,320,473 Patented May 16, 1967 emergency lamp. A relatively slow discharge path for the capacitor is provided which does not affect normal operation. However, a failure of the power supply for a predetermined number of cycles will permit discharge of the capacitor to the point that a firing voltage will be applied to the gate electrode of the SCR. Application of the firing voltage to the SCR initiates conduction of the SCR and subsequent energization of the emergency lamp by a battery. The battery is charged on alternate half cycles of the main power supply through a series diode and resistor halfwave charging circuit.

Referring now to the embodiment illustrated in the single figure of the drawing, it is seen that the emergency lamp 1 is connected in series with the silicon controlled rectifier (SCR) 2. SCR 2 has an anode 3, a cathode 4, and a gate 5.

Alternating current from a main power supply is introduced into the circuit by means of transformer 6, which has a primary winding 7 and a secondary winding 8, having a first side 8a and a second side 8b. The secondary winding 8 and a battery 9 are connected in series with the emergency lamp 1 and the SCR 2.

In order to maintain SCR 2 in a non-conducting state during the time that the primary 7 of transformer 6 is supplied with an alternating current, a capacitor 19 is connected to the gate electrode 5 of SCR 2. Capacitor 10 is charged through diode 11 and resistor 12. Diode 11 and resistor 12 are connected in series between the battery 9 and capacitor 10. A discharge path for the capacitor 10 is provided by resistor 13 which is relatively large compared to the combined resistance of diode 11 and resistor 12.

To provide a path for trickle charging the battery 9 on alternate half cycles of the alternating current appearing across secondary winding d, diode 14 and resistor 15 are connected in series between winding 8 and battery 9. The series connection of diode 14 and resistor 15 is a conventional half-wave charging circuit, to maintain the battery at its rated capabilities.

A path for the firing voltage to SCR 2 is provided by the diode 16. To produce the voltage necessary to fire SCR 2, resistor 17 is connected from the gate 5 of SCR 2 to the other side of battery 9, so that a series firing circuit is formed by resistor 13, diode 16 and resistor 17.

The operation of the circuit will now be explained in detail. During normal operation of the alternating current supply, the primary winding 7 of transformer 6 is supplied with an alternating current signal. This signal is transformed and appears across the secondary winding 8 of the transformer 6. During the half cycle that the side 8a of secondary winding 8 is negative, there is a flow of current to the capacitor such that it is charged, through the diode 11 and resistor 12, with the polarity indicated in the single figure of the drawing.

With this charge on the capacitor the diode 16 is prevented from conducting and SCR 2 is maintained in a blocking state. Also during this half cycle of the alternating current, the battery 9 is provided with a trickle charge through diode 14 and resistor 15.

During the half cycle that side 8a of secondary winding 8 is positive, capacitor 10 tends to discharge through resistor 13. However, the resistance of resistor 13 is made sufiiciently large that the time constant for the capacitor 10 and resistor 13 is much greater than the time constant for the capacitor 10 and the combined resistances of diode 11 and resistance 12. Thus, during this half cycle of the applied alternating current the discharge of capacitor 10 is not sufiicient to permit firing of SCR 2 through the diode 16.

If there is a power failure so that there is no alternating current voltage across the secondary winding 8, then there will be a continuous discharge of capacitor 10 through resistor 13. After the charge on the capacitor 10 has decreased sufficiently SCR 2 will be fired by battery 9 through resistor 13 and diode 16. Firing of SCRZ places it in a conductive state, thereby energizing the emergency lamp 1 through the series circuit of battery 9, emergency lamp 1, SCR 2 and secondary winding 8. Thus, failure of the alternating current supply causes energization of the emergency lamp 1 to insure continued illumination of the affected area during the power failure.

After the power failure has creased and normal A.C. power is returned to the circuit, the emergency lamp 1 is automatically extinguished. Automatic extinction is obtained by commutation, or turn-off, of SCR 2, which occurs upon return of normal power, since the peak line voltage exceeds the battery voltage and biases SCR 2 to the off condition. Thus, another important feature of this invention is the automatic turn-off of the light upon renewal of normal energization.

I do not desire my invention to be limited to the particular construction shown and described, and I intend to cover all modifications and changes within the spirit and scope of my invention by the appended claims.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. An emergency lighting system comprising: a series circuit including a secondary winding, a battery, an electrically energizable lamp and a silicon controlled rectifier; a capacitor to control the firing of said silicon controlled rectifier; means for charging said capacitor from an A.C. power supply through said secondary winding to prevent firing of said silicon controlled rectifier; means for 4- discharging said capacitor upon the failure of said power supply to permit firing of said silicon controlled rectifier. by said battery, thereby energizing said lamp from said battery.

2. An emergency lighting system as recited in claim 1 wherein said charging means comprises the series combination of a diode and a first resistor; and said discharging means comprises a second resistor in parallel with the series combination of said diode and said first resistor, and second resitor having a reistance relatively large compared to the combined resistance of said diode and said first resistor, whereby the discharge through said second resistor is sufliciently low to prevent the capacitor from normally discharging below the value necessay to prevent firing of said silicon controlled rectifier.

3. An emergency lighting system as recited in claim 2 and further including: the series combination of a second diode and a third resistor connected across said battery and said secondary winding, whereby said battery is charged from said power supply.

References Cited by the Examiner UNITED STATES PATENTS 2,889,490 6/1959 Paradise 315-86 X 3,114,095 12/1963 Palmer 320-39 3,143,729 8/1964 Power 340253 3,159,755 12/1964 Duncan 307-88.5

JAMES W. LAWRENCE, Primary Examiner.

C. R. CAMPBELL, Assistant Examiner.

Claims

1. AN EMERGENCY LIGHTING SYSTEM COMPRISING: A SERIES CIRCUIT INCLUDING A SECONDARY WINDING, A BATTERY, AN ELECTRICALLY ENERGIZABLE LAMP AND A SILICON CONTROLLED RECTIFIER; A CAPACITOR TO CONTROL THE FIRING OF SAID SILICON CONTROLLED RECTIFIER; MEANS FOR CHARGING SAID CAPACITOR FROM AN A.C. POWER SUPPLY THROUGH SAID SECONDARY WINDING TO PREVENT FIRING OF SAID SILICON CONTROLLED RECTIFIER; MEANS FOR DISCHARGING SAID CAPACITOR UPON THE FAILURE OF SAID POWER SUPPLY TO PERMIT FIRING OF SAID SILICON CONTROLLED RECTIFIER BY SAID BATTERY, THEREBY ENERGIZING SAID LAMP FROM SAID BATTERY.