GB2544165A

GB2544165A - Electric lamp circuits

Info

Publication number: GB2544165A
Application number: GB1615397.5A
Authority: GB
Inventors: Staniforth Peter
Original assignee: TIMEGUARD Ltd
Current assignee: TIMEGUARD Ltd
Priority date: 2015-09-10
Filing date: 2016-09-09
Publication date: 2017-05-10
Also published as: GB201516044D0; GB201615397D0; CN106993360A

Abstract

An electric lamp circuit includes an automatic switch device 4 connected in a two-wire 2, 8 alternating-current supply connection to an LED or fluorescent lamp 12. A by-pass unit 11 is connected in series with the switch device and to the lamp to avoid emission of light or flashing when the switch device is un-activated. A capacitor 17 of the by-pass unit connected between the live output 7 of the switch device and a neutral connection provides a leakage path for the low-magnitude current required by the circuitry 6 of the un-activated switch device. A metal-oxide varistor 18 shunts the capacitor to limit voltage spikes. Alternate half-cycles of voltage across the varistor are applied to a zener diode 22 to exceed its breakdown voltage while the switch device is activated, and results in the lamp being energised via closed contacts 28 of a relay 26. There is insufficient current flow for breakdown of the zener diode or closure of the relay contacts while the switch device is un-activated so that the lamp becomes effectively isolated for light emission.

Description

Electric Lamp Circuits

This invention relates to electric lamp circuits.

In electric lamp circuits where the lamp is to be operated automatically by a two-wire switch device such as a timer or sensor (for example, a light-level switch (dimmer) or sensor, a passive infra-red sensor or other presence or movement sensor), it is common for the automatic switch device to require electrical powering even when it is in its un-activated state; the current drawn in this state is of low magnitude as compared with the significantly-increased current drawn when the switch device is activated.

Where the wiring of the electrical power-supply to the automatic switch device is, or is to be, limited to two wires in the form of live and switched-live lines of a standard-wiring lighting circuit, the lamp used is most simply a filament lamp with power supplied to it from the live line via the automatic switch device with a return connection via the lamp to the neutral line. Until the automatic switch device is activated, the magnitude of current drawn through the automatic switch device, and thence through the lamp in these circumstances, is insufficient to result in emission of light from the lamp; sufficient current for the lamp to emit light occurs only while the automatic switch device is activated.

However, where the lamp used in the lamp circuit is to be a light-emitting diode (LED) or a fluorescent (including compact fluorescent or 2D) lamp, instead of a filament lamp, there is commonly the problem (especially with an LED of a low-wattage variety) that the lamp emits light, possibly in flashes of light, during the low-magnitude current flow occurring while the automatic switch device remains un-activated.

It is one of the main objects of the present invention to provide a form of electric lamp circuit by which this problem can be avoided.

According to the present invention there is provided an electric lamp circuit in which an automatic switch device is connected in a two-wire electrical power-supply connection to energise an electric lamp to emit light when the automatic switch device is activated, wherein a by-pass unit is responsive to the current drawn by the activated automatic switch device for switching a connection to the lamp through the by-pass unit from an open-circuit condition that exists while the automatic switch device is in an un-activated state, to a closed-circuit condition for energising the lamp while the automatic switch device is activated.

The lamp used in the electric lamp circuit of the present invention may be a light-emitting diode (LED) or a fluorescent (including compact fluorescent or 2D) lamp, and the two-wire electrical power-supply may be an alternating-current mains power-supply.

The by-pass unit of the lamp circuit may have first and second input terminals to which a switched connection from the automatic switch device and a neutral connection from the power supply are respectively to be connected. Also, the by-pass unit may have first and second output terminals from which switched-line and neutral-out connections to the lamp are respectively to be connected. In these circumstances, the by-pass unit may comprise capacitance connected between the input terminals to provide a low-impedance path for current passed by the automatic switch device when the automatic switch device is un-activated, and circuitry that includes a zener diode and a relay wherein voltage in excess of the breakdown voltage of the zener diode results from the increased current flow through the automatic switch device when the automatic switch device is activated, and the relay is operated in response to the breakdown of the zener diode so as to interconnect the second input terminal with the second output terminal.

An electric lamp circuit including a by-pass unit in accordance with the present invention will now be described, by way of example, with reference to the accompanying drawing which shows a schematic representation of the lamp circuit.

Referring to the accompanying drawing, a mains alternating-current power-supply source 1 has its live line 2 connected to an input terminal 3 of an automatic switch device 4. The automatic switch device 4, which may for example be a light-level switch (dimmer) or sensor, a passive infra-red sensor or other presence or movement sensor, includes switch contacts 5 that are connected in parallel with operational circuitry 6 between the terminal 3 and an output terminal 7 of the automatic switch device 4.

In circumstances in which a filament lamp (not shown) were to be used with the automatic switch device 4, the filament lamp would, according to standard practice, be connected in series with the device 4 between the terminal 7 and the neutral line 8 of the power-supply source 1. With this, the filament lamp would be energised to emit light whenever the operational circuitry 6 responds to the sensed condition, to close the switch contacts 5. The current drawn by the switch device 4 when activated in this way increases substantially as compared with the low-magnitude current required by the operational circuitry 6 in the unactivated state while the contacts 5 remain open.

The low-magnitude current drawn in these latter circumstance is insufficient to result in emission of light or flashes of light when a filament lamp is used. But there is the problem that there is the likelihood of light, or at least flashes of light, being emitted in the event that an LED or fluorescent lamp is used instead of a filament lamp. According to the present invention the problem is avoided by connecting a by-pass unit 11 in series with the automatic switch device 4 and to the LED or fluorescent lamp 12, as shown in the accompanying drawing.

The by-pass unit 11 has a first input terminal 13 to which the terminal 7 of the switch device 4 is connected, and a second input terminal 14 to which the neutral line 8 is connected from the power-supply source 1. The lamp 12 is connected externally of the unit 11 between a first output terminal 15 and a second output terminal 16.

Within the unit 11, the input terminal 13 and the output terminal 15 are connected in common and via a capacitor 17 to the input terminal 14 to provide a leakage path for the low-magnitude current required by the circuitry 6 of the switch device 4 in the un-activated state. A metal-oxide varistor 18 is connected in shunt with the capacitor 17 to limit the voltage spikes and swings in the switching of the alternating current to the unit 11 by the opening and closing of the contacts 5, and the energisation of the lamp 12 via the output terminals 15 and 16.

The resulting voltage across the varistor 18 is applied via a resistor 19 and a shunt-connected resistor 20 and capacitor 21 to a zener diode 22. When the switch device 4 is activated, the voltage across the zener diode 22 during alternate half-cycles of the alternating current exceeds the breakdown voltage of the zener diode 22, with the result that direct current is supplied via a diode 23 to charge an electrolytic capacitor 24 and, via a resistor 25, energise a relay 26 that is shunted by a diode 27. The contacts 28 of the relay 26, which are normally open, are closed by the energised relay 26 to close the circuit connection of the terminal 14 within the unit 11 to the terminal 16. This provides a return connection to the neutral line 8 for the connection from the terminal 15 to the lamp 12.

Accordingly, the LED or fluorescent lamp 12 is energised to emit light in the circumstances in which the automatic switch device 4 is activated. The current that flows following closure of the contacts 5 of the device 4 is effective to bring about closure of the normally-open relay contacts 28 and emission of light from the LED lamp 12. However, while the contacts 5 remain open the current supplied to terminal 13 of the by-pass unit 11 is of insufficient magnitude to bring about breakdown of the zener diode 22 to energise the relay 26. The contacts 28 accordingly remain open leaving the neutral-return circuit connection from the lamp 12 via the terminals 14 and 16 open, so that there is effective isolation of the LED lamp 12 from the possibility of emitting light in flashes or otherwise.

Claims

Claims :

1. An electric lamp circuit in which an automatic switch device is connected in a two-wire electrical power-supply connection to energise an electric lamp to emit light in response to current drawn by the automatic switch device from the power supply when the automatic switch device is activated, wherein a by-pass unit is responsive to the current drawn by the activated automatic switch device for switching a connection to the lamp through the by-pass unit from an open-circuit condition while the automatic switch device is in an unactivated state, to a closed-circuit condition for energising the lamp while the automatic switch device is activated.

2. An electric lamp circuit according to claim 1, wherein the lamp is a light-emitting diode (LED), or a fluorescent lamp.

3. An electric lamp circuit according to claim 1 or claim 2 wherein the two-wire electrical power-supply is an alternating-current mains power-supply.

4. An electric lamp circuit according to any one of claims 1 to 3 wherein the by-pass unit has first and second input terminals to which a switched connection from the automatic switch device and a neutral connection from the power supply are respectively connected.

5. An electric lamp circuit according to claim 4 wherein the by-pass unit has first and second output terminals from which switched-line and neutral-out connections to the lamp are respectively connected.

6. An electric lamp circuit according to claim 5 wherein the by-pass unit includes capacitance connected between the first and second input terminals to provide a low-impedance path for current passed by the automatic switch device when the automatic switch device is unactivated.

7. An electric lamp circuit according to claim 6 wherein the by-pass unit further includes circuitry that includes a zener diode and wherein voltage in excess of the breakdown voltage of the zener diode results from the increased current flow through the automatic switch device when the automatic switch device is activated.

8. An electric lamp circuit according to claim 7 wherein the circuitry that includes the zener diode also includes a relay that operates in response to the breakdown of the zener diode so as to interconnect the second input terminal with the second output terminal.