GB2046538A

GB2046538A - Time delay circuits for controlling lights

Info

Publication number: GB2046538A
Application number: GB7849622A
Authority: GB
Original assignee: CP Electronics Ltd
Current assignee: CP Electronics Ltd
Priority date: 1978-12-21
Filing date: 1978-12-21
Publication date: 1980-11-12
Also published as: GB2046538B

Abstract

An electrical time delay circuit provides a conducting path across a pair of terminals T1, T2 for a predetermined time period. The period is controlled by an electrical circuit 15 powered by a rechargeable battery 14. The battery 14 is recharged from a circuit 31 powered from a potential applied across the terminals N T2, which circuit 31 is operative when the conducting path is broken. When a switch 11 is closed, a capacitor 16 is charged and a triac 13 is switched on to energise lamps 12. The capacitor then discharges through resistors 23, 24 and at the end of the predetermined period the triac 13 is switched off to de-energise the lamps. A charging current then flows to the battery via the lamps 12, a resistor 32 and diodes 33, 34, the current being insufficient to cause lighting of the lamps. In a modification the triac is replaced by an electromechanical relay. <IMAGE>

Description

SPECIFICATION Time delay electrical switch This invention relates to time delay electrical switches. Such switches can be used in controlling the lighting of communal areas. A common time delay electrical switch for such a purpose uses a pneumatic control of the time delay, a plunger being depressed to energise the lighting, the period of illumination being controlled by the passage of air releasing the plunger two its rest position in a predetermined period after which the lighting is extinguished. This pneumatic system is not entirely satisfactory, but the difficulty in providing an electrical control of the time delay is that the switch to the lighting is connected in the live line and there is no means to supply power to the electrical control circuit without providing a separate return wire.

This problem is overcome in the present invention by providing a rechargeable battery to supply the electrical time delay control circuit, and a charging device to re-charge the battery when the time delay control circuit is not in operation.

The invention provides a time delay electrical switch comprising a pair of terminals, an electrical circuit which provides a conducting path for a time delay period across said pair of terminals, a rechargeable battery for driving said circuit and means connected across said terminals for recharging said battery when said electrical circuit is inoperative.

Examples of the invention will now be described with reference to the accompanying drawings, in which: Figs. 1 and 2 are circuit diagrams of alternative time delay circuits for controlling the illumination of lamps. The same components which appear in both figures are given the same reference numbers.

In Fig. 1, a plurality of push button switches 11 are connected in parallel and located at different points to switch on a lamp or lamps 12. The lamps 12 are illuminated when a conducting path is created across terminals T1, T2. Power is applied at points N and T2 and the lamps are illuminated when the Triac 13 is triggered.

A pair of nickel cadmium cells 14 provide an electrical supply to the triggering circuit generally indi cated at 15. When any switch 11 is closed, a capacitor 16 in the triggering circuit 15 is charged through a low resistance 17 and the closed switch 11 thereby switching on the Darli ngton transistor pair 18 and triggering the SCR 19. Each transistor of the pair 18 has a gain of about 102, giving a combined gain of 104. The conducting state of the SCR 19 switches on the transistor 21 thereby triggering the Triac 13. The lamps 12 will continue to be energised while the transistors, SCR and Triac remain conduct ing.

The period of illumination is controlled by the dis charge of the capacitor 16through a limiting resistor 23 and an adjustable control resistor 24. When the potential of the base of the first transistor of the Darlington pair drops to a sufficient value, the transistors, SCR and Triac switch off, thereby extinguishing the lamps. The SCR 19 ensures that the lamps are sharply cut off at the end of the timing period, so as not to cause interference.

When the Triac 13 is conducting, it short circuits a charging circuit 31 for the nickel cadmium cells 14, but when it ceases to conduct a small current from the power supply passes through the lamps (without noticeably illuminating them) to operate the charging circuit 31. The circuit 31 includes a limiting resistor 32, and two diodes 33 and 34. The junction of the diodes 33 and 34 is connected to a capacitor 35 to the L line and the cathode of the second diode 34 is connected to the positive terminal of the nickel cadmium cell pair 14. Diode 33 acts as a half-wave rectifier: diode 34 prevents discharge of the cells 14 through capacitor 35.

In Fig. 2, the SCR 19, the transistor 21 and the Triac 13 are replaced by a NPN transistor 41 and an electro-mechanical relay 42 connected in series across the nickel cadmium cells 14. The relay 42 controls the closure of contacts 43 in series with the lamps 12 across the main supply terminals T1, T2.

When the time delay circuit is used for controlling the occasional illumination of communal areas, the proportion of time during which the time delay circuit is energised is usually very small. It has been found that the cells will not become discharged provided that the proportion of time during which the time delay circuit is energised does not rise above 10%, and this proportion is rarely exceeded in such applications.

The control resistor 24 is a preset resistor, adjustable only when the switch unit has been disassembled, and is not intended to be adjustable with disassembling the unit. This avoids tampering with the unit by unauthorised persons unless they go to the extent of dis-assembling the unit.

The leakage resistance of the triggering circuit 15 is sufficiently high that the cells can be left permanently connected in the switch, even during reasonable storage of the switch before installation.

The circuit components shown in each figure are conveniently mounted in a single housing, with the exception of the lamps and the switches 11. If the housing is located at a switch position, then one switch 11 can be mounted on the housing. At least the majority of the components in the housing are preferably encapsulated for protection.

1. A time delay electrical switch comprising a pair of terminals, an electrical circuit which provides a conducting path for a time delay period across said pair of terminals, a rechargeable battery for driving said circuit and means connected across said terminals for recharging said battery when said electrical circuit is inoperative.

2. A switch as claimed in claim 1, wherein said electrical circuit comprises a Triac connected across said terminals.

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

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Time delay electrical switch This invention relates to time delay electrical switches. Such switches can be used in controlling the lighting of communal areas. A common time delay electrical switch for such a purpose uses a pneumatic control of the time delay, a plunger being depressed to energise the lighting, the period of illumination being controlled by the passage of air releasing the plunger two its rest position in a predetermined period after which the lighting is extinguished. This pneumatic system is not entirely satisfactory, but the difficulty in providing an electrical control of the time delay is that the switch to the lighting is connected in the live line and there is no means to supply power to the electrical control circuit without providing a separate return wire. This problem is overcome in the present invention by providing a rechargeable battery to supply the electrical time delay control circuit, and a charging device to re-charge the battery when the time delay control circuit is not in operation. The invention provides a time delay electrical switch comprising a pair of terminals, an electrical circuit which provides a conducting path for a time delay period across said pair of terminals, a rechargeable battery for driving said circuit and means connected across said terminals for recharging said battery when said electrical circuit is inoperative. Examples of the invention will now be described with reference to the accompanying drawings, in which: Figs. 1 and 2 are circuit diagrams of alternative time delay circuits for controlling the illumination of lamps. The same components which appear in both figures are given the same reference numbers. In Fig. 1, a plurality of push button switches 11 are connected in parallel and located at different points to switch on a lamp or lamps 12. The lamps 12 are illuminated when a conducting path is created across terminals T1, T2. Power is applied at points N and T2 and the lamps are illuminated when the Triac 13 is triggered. A pair of nickel cadmium cells 14 provide an electrical supply to the triggering circuit generally indi cated at 15. When any switch 11 is closed, a capacitor 16 in the triggering circuit 15 is charged through a low resistance 17 and the closed switch 11 thereby switching on the Darli ngton transistor pair 18 and triggering the SCR 19. Each transistor of the pair 18 has a gain of about 102, giving a combined gain of 104. The conducting state of the SCR 19 switches on the transistor 21 thereby triggering the Triac 13. The lamps 12 will continue to be energised while the transistors, SCR and Triac remain conduct ing. The period of illumination is controlled by the dis charge of the capacitor 16through a limiting resistor 23 and an adjustable control resistor 24. When the potential of the base of the first transistor of the Darlington pair drops to a sufficient value, the transistors, SCR and Triac switch off, thereby extinguishing the lamps. The SCR 19 ensures that the lamps are sharply cut off at the end of the timing period, so as not to cause interference. When the Triac 13 is conducting, it short circuits a charging circuit 31 for the nickel cadmium cells 14, but when it ceases to conduct a small current from the power supply passes through the lamps (without noticeably illuminating them) to operate the charging circuit 31. The circuit 31 includes a limiting resistor 32, and two diodes 33 and 34. The junction of the diodes 33 and 34 is connected to a capacitor 35 to the L line and the cathode of the second diode 34 is connected to the positive terminal of the nickel cadmium cell pair 14. Diode 33 acts as a half-wave rectifier: diode 34 prevents discharge of the cells 14 through capacitor 35. In Fig. 2, the SCR 19, the transistor 21 and the Triac 13 are replaced by a NPN transistor 41 and an electro-mechanical relay 42 connected in series across the nickel cadmium cells 14. The relay 42 controls the closure of contacts 43 in series with the lamps 12 across the main supply terminals T1, T2. When the time delay circuit is used for controlling the occasional illumination of communal areas, the proportion of time during which the time delay circuit is energised is usually very small. It has been found that the cells will not become discharged provided that the proportion of time during which the time delay circuit is energised does not rise above 10%, and this proportion is rarely exceeded in such applications. The control resistor 24 is a preset resistor, adjustable only when the switch unit has been disassembled, and is not intended to be adjustable with disassembling the unit. This avoids tampering with the unit by unauthorised persons unless they go to the extent of dis-assembling the unit. The leakage resistance of the triggering circuit 15 is sufficiently high that the cells can be left permanently connected in the switch, even during reasonable storage of the switch before installation. The circuit components shown in each figure are conveniently mounted in a single housing, with the exception of the lamps and the switches 11. If the housing is located at a switch position, then one switch 11 can be mounted on the housing. At least the majority of the components in the housing are preferably encapsulated for protection. CLAIMS

3. A switch as claimed in claim 2, wherein said electrical circuit comprises an SCR for controlling said Triac.

4. A switch as claimed in claim 1, wherein said electrical circuit comprises an electromagnetic relay whose contacts are connected across said terminals.

5. A time delay electrical switch substantially as hereinbefore described with reference to and as illustrated in Fig. 1 or Fig. 2 of the accompanying drawings.