GB1578431A

GB1578431A - Lighting circuits

Info

Publication number: GB1578431A
Application number: GB2455476A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1977-09-14
Filing date: 1977-09-14
Publication date: 1980-11-05

Description

(54) IMPROVEMENTS IN LIGHTING CIRCUITS (71) I, NORMAN FENNO TURNER, a British subject, of 39 Mount Echo Drive, North Chingford, London E4 7LA, do hereby declare the invention, for which I pray that a patent may be granted to me, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to circuit arrangements for bringing into operation an auxiliary or secondary light source in the event of failure of a primary light source.

According to the invention, there is provided a circuit arrangement comprising a primary light source, a secondary light source, relay means connected in series with the primary light source and arranged to isolate the secondary light source from a power source when the primary light source is operative and to connect the secondary light source to the power source in the event of failure of said primary light source, and monitoring means for indicating when either of the light sources is defective and for continuously monitoring the operational state of the secondary light source.

Preferably, the circuit arrangement includes a further auxiliary lamp arranged to operate in the event of failure of both primary and secondary light sources.

According to a preferred embodiment of the invention, the circuit arrangement further includes an auxiliary voltage supply which is arranged to operate the auxiliary lamp in the event of failure of mains supply. This feature forms the subject of my Patent Application No. 7925141 (Serial No. 1,578,432).

The present invention will now be further described, by way of example, with reference to the accompanying drawings in which: Figure 1 is a circuit diagram of a first embodiment of a circuit arrangement according to the invention: and Figure 2 is a circuit diagram of a second embodiment of a circuit arrangement according to the invention.

In the drawings, like parts are denoted by like reference numerals.

Reference will first by made to Figure 1 of the drawings which shows a circuit arrangement comprising a primary light source in the form of a lamp L1, a secondary light source in the form of a lamp L2, and two magnetically operated relays RLA1 and RLA2. A low voltage auxiliary light source L3 and a resistor R1 are also provided.

As shown in Figure 1, the light source L1 is connected in series with the relay RLA1 which is arranged, when the circuit is switched on to illuminate the light source L1, to open the contacts 1 and 2 which break the supply to the rest of the circuit.

If the light source L1 fails, the relay RLA1 becomes de-energised and both the contacts 1 and 2 close. The contacts 1 are connected in series with the relay RLA2 and the light source L2 while the contacts 2 are connected in series with contacts 3 of the relay RLA2 and a transformer T1 supplying current to the auxiliary light source L3. If the light source L2 is functionable then, on closing the contacts 1, the relay RLA2 is energised and opens the contacts 3 which breaks the circuit to the transformer T1.

If the light source L2 should now fail, the relay RLA2 becomes de-energised and closes the contacts 3 thereby restoring the circuit to the transformer T1 which thus provides a low voltage supply to the auxiliary standby light source L3. The low level of illumination provided by the auxiliary light source L3 will indicate that the primary and secondary light sources L1 and L2 have both failed.

The light sources will normally take the form of lamps which are mounted in a housing and normally shielded from view by a diffuser or the like. In this case, since the lamps L1 and L2 have the same wattage, it is- not possible to see if the lamp L1 has failed and needs replacement or whether the lamp L2 is in working order - even though it is not actually functioning. In order to overcome these problems, an indicator N1 is mounted externally of the housing and is arranged to operate when either of the lamps L1 or L2 has failed by connecting it in parallel with the series connection of the lamp L2 and the relay RLA2.

The resistor R1 is connected between the relay RLA2 and the neutral side of the mains supply whereby there is a P.D. across the resistor provided by the filament of the lamp L2. This lamp has a non-linear current characteristic and the resistance of the resistor R1 is arranged to have such a value that the P.D. across the lamp L2 is insufficient to illuminate the indicator N1. The absence of illumination from the indicator N1 means that everything is in order.

If the filament of the lamp L2 fails for some reason, such as vibration, while it is inoperative due to the lamp L1 being on, the P.D. across the lamp L2 will increase to almost supply potential thereby lighting the indicator N1. If the lamp L1 fails and the contacts of the relay RLA1 close, the resistor R1 is shorted out and the P.D.

across the lamp L2 is the supply potential so that the indicator N1 again lights. Thus, the indicator N1 indicates not only when the lamp L1 has failed but also gives continuous monitoring as to the condition of the lamp L2.

Figure 2 shows a circuit in which a battery B1 is provided to illuminate an auxiliary low-voltage lamp P1 in the event of failure of the primary and secondary lamps L1 and L2. It will be seen that the circuit is similar to the circuit shown in Figure 1 except that in this case the secondary of the transformer T1 is connected across a full wave bridge rectifier MR1 which forms part of a constant voltage charging circuit indicated by the dbtted line in Figure 3.The coil of a relay RLA3 and a series-connected zener diode Z2 are connected across the output of the bridge rectifier MR1. A smoothing condenser C2 is also connected across the bridge rectifier MR1. The relay RLA3 has two sets of contacts 5, 6, 7 and 8, 9, 10 the action of which will be explained in the following description of the operation of the circuit shown in Figure 2.

When the circuit is connected in a normal mains supply, the lamp L1 is on and the coil of the relay RLA1, which is connected in series with the lamp L1, is activated. Two pairs of normally closed contacts 4,1 and 5,8 of the relay RLA1 are opened, the contacts 4,1 breaking the circuit to the lamp L2 via the coil of relay RLA2 so that the lamp L2 remains off. If the lamp L1 fails, it passes no current to the relay RLA1 which is thus de-activated and its contacts revert to the normally closed state. Contacts 4,1-of the relay RLA1, which are connected in series with the coil of relay RLA2 and the lamp L2, have now made a circuit for the relay coil and lamp so that the lamp L2 is now illuminated. The activated relay RLA2 opens its normally closed contacts 4,1.

If the lamp L2 now fails it breaks the feed to the coil of relay RLA2 which is thus de-activated so that its contacts 4,1 revert to the normally closed state, The contacts 4,1 of the relay RLA2 are connected in series with contacts 5,8 of relay RLA1, the contact 5 of relay RLA1 being connected to the contact 10 of relay RLA3 and the contact 1 of relay RLA2 being connected to the secondary of transformer T1.

The transformer T1 is a stepdown transformer whose secondary is of a suitable rating. The primary of the transformer is connected directly across the mains input and its secondary therefore supplies power as long as the mains supply is maintained via the full wave bridge rectifier MR1 to the constant voltage charging circuit and the coil of relay RLA3 is activated to close its normally open contacts 6,7 and 9,10.

The low voltage lamp P1 is connected between the contacts 6 and 9 of the relay RLA3 while the battery is connected across the contacts 5 and 8 of relay RLA3. The remaining contact 7 of the relay RLA 3 is connected to the opposite end of the secondary of the transformer T1 from the end to which the contact 1 of the relay RLA2 is connected. Therefore, if the relays RLA 1 and RLA2 are de-activated, owing to failure of the lamps L1 and L2, and relay RLA3 is activated, the lamp P1 will light being fed from the secondary of the transformer T1 through the respective contacts 5,8; 4,1 and 6,7-9,10 of the three relays RLA1, RLA2 and RLA3.

In the event of mains supply failure, the relay RLA3 will be de-activated so that its normally open contacts 6,7 and 9,10 will open and its normally closed contacts 5,6 and 8,9 will close to connect the lamp P1 to the battery B1. This state of affairs is shown in Figure 2.

The battery is a re-chargeable battery of suitable voltage and capacity which is normally maintained in a fully charged condition by being connected to a constant voltage supply regulator transistor TR1 via a diode1. The base of the transistor TR1 is held at a constant potential by the combination of the series connection of a base feed resistor R2, a zenor diode Z1 and a potentiometer or variable resistor VR1. The base is decoupled by a capacitor C1. The output from the emitter of transistor TR1 is thus held at a suitable voltage for charging and maintaining the battery B1 in a fully charged state. The maximum current delivered by the transistor TR1 when the battery Bl is in a discharged, state is governed by suitable components. The values are such that R the circuit is self-regulating. As the battery voltage rises towards the output voltaee of the transistor -TRi, the current diminishes, thus ensuring that the minimum of float current is used to keep the battery B1 in a fully charged condition. The variable resistor VR1 is adjusted to suit the charging characteristics of the battery B1 and thus enables batteries having different charging characteristics to be employed in the circuit. This is an advantage if it is not possible to replace the battery B1 by a battery having the same charging characteristics.

As in the circuit shown in Figure 1, an indicator N1, which may take the form of a neon lamp, is provided to indicate failure of either the primary lamp L1 or secondary lamp L2. The indicator also continuously monitors the condition of the lamp L2 when the lamp L1 is on. The operation of the indicator N1 is the same as in the embodiment shown in Figure 1 and reference should be made to the description of that figure for a full description of the operation of said indicator.

Owing to the voltage drop across the coils of the relays RLA1 and RLA2, the two main lamps L1 and L2 are under-run by a factor designed to give a useful extension of the calculated life of the lamps. Moreover, since the coils of the relays RLA1 and RLA2 are inductive, they will reduce the initial surge that occurs in all filament lamps when first switched on and which is a major cause of lamp failure. The zener diode Z2 in series with the coil of relay RLA3 provides for the operation of the emergency battery supply to the lamp P1 in the event of the mains voltage falling below a specified level. A light emitting diode LED1 and limiting resistor R3 connected between the emitter of transistor TR1 and the diode D1 form a charging indicator for the battery B1.

It will be seen that the circuits according to the invention provide a secondary lamp which is brought into service in the event of failure of a primary lamp and that one embodiment provides an auxiliary voltage supply in the event of failure of mains supply. Other embodiments and modifications are envisaged without departing from the scope of the invention.

WHAT I CLAIM IS: 1. A circuit arrangement comprising a primary light source, a secondary light source, relay means connected in series with the primary light source and arranged to isolate the secondary light source from a power source when the primary light source is operative and to connect the secondary light source to the power source in the event of failure of said primary light source, and monitoring means for indicating when either of the light sources is defective and for continuously monitoring the operational state of the secondary light source.

2. A circuit arrangement according to claim 1, and including a further auxiliary lamp arranged to operate in the event of failure of both primary and secondary light sources.

3. A circuit arrangement according to claim 2, wherein the relay means comprise a first relay having a coil connected in series with the primary light source and wherein said relay has a first set of normally closed contacts connected in series with the coil of a second relay connected in series with the secondary light source, the first relay having a second set of normally closed contacts connected in series with a set of normally closed contacts of the second relay in turn are connected to the auxiliary lamp and the arrangement being such that the contacts of each relay are held open when the associated relays are energised.

4. A circuit arrangement according to claim 3, wherein the relays are based on magnetic operation.

5. A circuit arrangement according to claim 3 or claim 4, wherein the monitoring means is connected in parallel with the secondary light source and the coil of the second relay and in series with a resistor which ensures that the monitoring means is activated only when one or both light sources is/are defective.

6. A circuit arrangement according to any one of claims 2 to 5, wherein an auxiliary voltage supply is provided for operating the auxiliary lamp in the event of failure of mains supply.

7. A circuit arrangement according to claim 6, wherein the auxiliary voltage supply comprises a rechargeable battery.

8. A circuit arrangement according to claim 7, and including a charging circuit comprising a step-down transformer for connection to a mains supply, a bridge rectifier connected to the secondary of the transformer, a transistor and a diode connected between one side of the bridge rectifier and one pole of the battery, the other pole of which is connected to the other side of the bridge rectifier, and further means for connecting the battery to the auxiliary lamp in the event of failure of mains supply.

9. A circuit arrangement according to claim 8, wherein said further means comprise a third relay having its coil connected -across the bridge rectifier and two sets of change-over contacts connected one on each side of the auxiliary lamp and arranged when the relay coil is de-energised through failure of the mains supply to connect the battery to the auxiliary lamp.

10. A circuit arrangement according to claim 9, wherein one of the second set of contacts of the first relay is connected to one of the first set of contacts of the third relay, one of the second set of contacts of the third relay is connected to one end of the secondary of the transformer and one of the contacts of the second relay is connected to the other end of the secondary of the transformer, whereby when the primary

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. charging characteristics of the battery B1 and thus enables batteries having different charging characteristics to be employed in the circuit. This is an advantage if it is not possible to replace the battery B1 by a battery having the same charging characteristics. As in the circuit shown in Figure 1, an indicator N1, which may take the form of a neon lamp, is provided to indicate failure of either the primary lamp L1 or secondary lamp L2. The indicator also continuously monitors the condition of the lamp L2 when the lamp L1 is on. The operation of the indicator N1 is the same as in the embodiment shown in Figure 1 and reference should be made to the description of that figure for a full description of the operation of said indicator. Owing to the voltage drop across the coils of the relays RLA1 and RLA2, the two main lamps L1 and L2 are under-run by a factor designed to give a useful extension of the calculated life of the lamps. Moreover, since the coils of the relays RLA1 and RLA2 are inductive, they will reduce the initial surge that occurs in all filament lamps when first switched on and which is a major cause of lamp failure. The zener diode Z2 in series with the coil of relay RLA3 provides for the operation of the emergency battery supply to the lamp P1 in the event of the mains voltage falling below a specified level. A light emitting diode LED1 and limiting resistor R3 connected between the emitter of transistor TR1 and the diode D1 form a charging indicator for the battery B1. It will be seen that the circuits according to the invention provide a secondary lamp which is brought into service in the event of failure of a primary lamp and that one embodiment provides an auxiliary voltage supply in the event of failure of mains supply. Other embodiments and modifications are envisaged without departing from the scope of the invention. WHAT I CLAIM IS:

1. A circuit arrangement comprising a primary light source, a secondary light source, relay means connected in series with the primary light source and arranged to isolate the secondary light source from a power source when the primary light source is operative and to connect the secondary light source to the power source in the event of failure of said primary light source, and monitoring means for indicating when either of the light sources is defective and for continuously monitoring the operational state of the secondary light source.

and secondary light sources have failed, the contacts of the first and second relays are closed and the contacts of the third relay are effective to connect the auxiliary lamp to the auxiliary voltage generated from mains supply by the transformer.

11. A circuit arrangement according to any one of claims 8 to 10, wherein the charging circuit further includes a variable resistor or potentiometer by means of which charging of the battery may be adjusted to suit the charging characteristics of the battery.

12. A circuit arrangement according to claim 11, wherein the variable resistor or potentiometer is connected in series with a resistor and a zener diode.

13. A circuit arrangement according to any preceding claim, wherein the monitoring means comprise an indicator lamp.

14. A circuit arrangement substantially as described herein with reference to Figure 1 of the drawings.

15. A circuit arrangement substantially as described herein with reference to Figure 2 of the drawings.