Ballast with random switch-on times

Abstract

 A load conditioner (1) for the protection of lamp units (2) in a light system in which each lamp unit (2) comprises a lamp and lamp control circuitry (3), including a ballast circuit (4), the lighting system having a main power input switch for connecting the lighting system to an AC power supply, the load conditioner (1) having randomising means to vary the time at which the connection of the lamp unit (2) to the power supply occurs. There is further described a method of controlling the operation of such a lighting system.

Description

Introduction

[0001] The present invention relates to a load conditioner or protection device for the protection of lamp units in a lighting system in which each lamp unit comprises a lamp and lamp control circuitry including a ballast circuit, the lighting system having a main power input switch for connecting the lighting system to an AC power supply, the load conditioner including means to protect the lamp unit from harmful variations in the inputted power supply.

[0002] Due to the increasing use of electronic lamp control devices such as electronic ballast devices, communications systems and timers, there is an increased need for protection of these devices as they are more susceptible to interference than the more conventional electromechanical controls that were used heretofore. Problems relate to, for example, timer resetting, the prevention of noise in communications or lightning damaging electronic devices. Such devices are also subject to regulations concerning emissions and EMC immunity. Additionally, in conventional lighting, difficulties can arise where inrush current puts an increasing burden on switching contactors, connectors and fusing.

[0003] There is a need to have electronic based lamp controls with a level of robustness normally associated with electromechanical applications. Further, there is a need to remove the inrush current burden from contactors, connectors and fusing of all types of lighting installations, whether they be electronic or more conventional electromechanical systems.

[0004] The invention is directed towards achieving at least some of these objects.

Statements of Invention

[0005] According to the invention there is provided a load conditioner for the protection of lamp units in a lighting system in which each lamp unit comprises a lamp and lamp control circuitry including a ballast circuit, the lighting system having a main power input switch for connecting the lighting system to an AC power supply, characterised in that the load conditioner comprises randomising means for varying the time at which the connection of the lamp unit to the power supply occurs whereby the lamp units in the lighting system are powered at different times during a start-up period. Such a load conditioner will limit the inrush current when power is first applied to the circuits. No two units will engage the load simultaneously to safeguard each unit against potential damage.

[0006] In another embodiment of the invention there is provided a load conditioner in which there is provided means to protect external wiring and external components from current surges caused by electronic circuitry in the lamp unit. Such a load conditioner will provide a more robust device that will require less maintenance and repair.

[0007] In a further embodiment of the invention there is provided a load conditioner in which there is provided a central processing unit (CPU), the CPU having means for setting the number of half cycles after the main input switch has closed and applied current to the load conditioner when the load conditioner will transmit onwards to the lamp unit. By having such a system the operator can determine when each lamp unit will light up and accordingly may ensure that each lamp lights in a predetermined sequence.

[0008] In another embodiment there is provided a load conditioner in which the randomising means comprises means for causing the connection to the load at mains zero cross current. When the connection to the load occurs at mains zero cross current, the load conditioner minimises the inrush currents to the circuitry as well as minimising any back EMF voltage.

[0009] In another embodiment still of the invention there is provided a load conditioner in which the randomising means comprises a circuit for onward transmission of power, the circuit comprising switches with random response times. This too will enable the load conditioner to limit the inrush currents when power is first applied as well as starting the lamps at different times.

[0010] In a preferred embodiment of the invention there is provided a load conditioner in which a current limit device is provided, the current limit device entering a linear region of operation as it approaches a preset limit current. This provides very fast detection of an over current situation and current is held at the limit value without any delay. The circuit can handle fast changes in current in an efficient manner. The current is limited to an acceptable value thereby circumventing delays that may occur in level detection circuitry.

[0011] In another embodiment of the invention there is provided a load conditioner in which the current limit device comprises two identical symmetrically inverted stages, each stage comprising a control transistor, a power supply transistor and a resistor, the control transistor removing the bias current from the power supply transistor once the voltage across the resistor exceeds a predetermined level. The above configuration provides a simple and effective configuration. There are of course very few components which also leads to a cost effective device.

[0012] In another embodiment of the invention a cut-out device is provided to operate when the current limit device enters the linear region. This becomes useful as the circuit does not have to operate in the linear region for extended periods of time, thereby preventing exposure to large currents for sustained periods.

[0013] In a further embodiment of the invention there is a provided a mains filter at the input to the load conditioner to attenuate conducted emissions above a preset frequency. There is also provided means to attenuate the higher frequency components of any conducted emissions generated by the lamp unit. Such means will enable the load conditioner to comply with emission standards and eliminate high frequency noise from the circuit.

[0014] In a still further embodiment of the invention there is provided a method of controlling the operation of a lighting system which comprises a plurality of lamp units, each in turn comprising a lamp and lamp control circuitry including a ballast circuit, the system being connected to a mains AC power supply through a power input switch, the method comprising varying the time at which the connection of the lamp units to the power supply takes place after the input switch is used to connect the power supply to the light system. Such a method will limit the inrush current to the lighting system when power is first applied to the system. No two units will have to engage loads simultaneously.

[0015] In a further embodiment still of the invention there is provided a method in which zero crossover time of the power supply is detected and the lamp unit is connected to the power supply at zero crossover. Such a method will further minimise inrush currents and back EMF voltage.

[0016] In another embodiment of the invention there is provided a computer program comprising program instructions for causing a computer to perform the method of operation of a lighting system which comprises a plurality of lamp units, each in turn comprising lamp control circuitry including a ballast circuit, the lighting system being connected to a mains AC power supply through a power input switch, the method comprising varying the time which the connection of the lamp units takes place after the input switch is used to connect the power supply to the light system, and in which the zero cross over time of the power supply may be detected and the lamp unit is connected to the power supply at zero cross over.

[0017] In another embodiment still of the invention the computer program may be embodied on a record medium, stored in a computer memory, embodied on a read-only memory or indeed carried on an electrical or radio carrier signal.

Detailed Description of the Invention

[0018] The invention will be more clearly understood from the following description of an embodiment thereof, given by way of example only, with reference to the accompanying drawings, in which:-

Fig. 1 is a diagrammatic view of a typical load conditioner application according to the invention,

Fig. 2 is a block diagram of the functions of the load conditioner,

Fig. 3 is a circuit of portion of the load conditioner, and

Fig. 4 is a circuit of the remainder of the load conditioner shown in block form in Fig. 3.

[0019] Referring to the drawings, there is illustrated a load conditioner according to the invention, identified by the reference numeral 1, connected to a lamp unit, identified by the reference numeral 2, comprising a lamp control circuitry 3 including an electronic ballast 4 and communications devices 6, all connected by system cabling 7 with the load conditioner 1 fed by a mains cable input 8.

[0020] Referring now to Fig. 2, the load conditioner 1 is illustrated showing its various functions, namely, a mains filter stage 10, a transient lighting protection stage 11, a soft start stage 12, a cut-out stage 13 and a current limit stage 14.

[0021] Essentially, in Fig. 3, there is only illustrated the circuit of the mains filter stage 10 and the transient lightning protection stage 11. Strictly speaking, the mains filter stage 10 comprises two functional blocks, namely a fuse stage and a filter stage, the former provided by a fuse 20. Since normally the load conditioner ensures that no excess of current ever flows to the load, the fuse 20 in most situations is redundant. It's function is to provide protection should the electronic systems fail for any reason. The mains filter stage 10 comprises filtering capacitors, indicated generally by the reference numeral 21. The mains filter stage is of conventional construction.

[0022] The mains filter stage 10 is required to attenuate conducted emissions in the frequency 1MHz and upwards so as to allow easier implementation of emissions standard compliant lighting systems. The higher frequency is also the range that is dependent on wiring methods within the lamp. Thus, this will have a considerable advantage.

[0023] The transient lightning protection stage 11 is also illustrated and is provided by voltage dependent resistors (more commonly known as VDRs or Varistors) 25 that will clamp the input voltage transient to a level below the breakdown value of the components provided that the current, in the particular transient, does not exceed the specified current limits.

[0024] Referring now to Fig. 4, there is illustrated the remainder of the circuit, namely, the starting stage 12, the cut-out stage 13 and the current limit stage 14. The starting stage 12 limits the inrush current present in the lighting system when power is first applied. This is accomplished by "randomising" the switch-on time of the load conditioner so that no two lamp units within the lighting system engage the mains power simultaneously. Each load conditioner waits a pre-programmed number of mains half cycles before engaging the load. This will result in delays between the power being applied to the load conditioner and the light switching on.

[0025] In one embodiment of the invention, the maximum time between power being applied to the load conditioner and the light being switched on is 2.56 seconds which means that 256 effectively random start-up times may be applied in a system containing up to or more than 256 lamp units. While the word "random" is used, strictly speaking, it is not "random", it is a pre-programmed start-up time.

[0026] The cut-out stage 13 and the current limit stage 14 operate in tandem, the purpose of which is to disconnect power from the lamp control circuitry faster than any conventional fuse and thus to minimise damage. This is useful when an electronic device such as the ballast 4 or communications device 6 is subject to a transient. If power is removed quickly, then there is a reasonable possibility of avoiding damage. The functionality of the circuit is such that when a short circuit or over current situation is detected, the constant limit of the circuit immediately activates, preventing a further rise in current. The advantage of this is that the delays that occur with a limit detection and cut-out circuit are circumvented. A short time after this constant current is achieved, the cut-out stage activates and the lamp is disconnected. Needless to say, in the case of slowly increasing the currents, the cut-out will activate as soon as the current limit is reached, without recourse to the current limit circuit.

[0027] It is envisaged that the load conditioner may be programmed to reconnect the load every ten mains half cycles or some other suitable time.

[0028] Referring again to Fig. 4 the circuit consists of two identical stages but symmetrically inverted. The first stage consists of a transistor Q1 and a transistor Q2 which in turn feeds through a resistor R1. The other stage also consists of a transistor Q3, transistor Q4 and resistor R2. It will be noted that there are diodes D1 and D2 respectively across the transistors Q2 and Q4. The transistors Q1 and Q2 are current limit devices which will remove bias current from the gates of the transistors Q2 and Q4 respectively, if the current through the transistors Q2 or Q4 is sufficient to raise the voltage on the resistors R1 and R2 above a preset voltage, in this embodiment, approximately 0.7 volts. For an AC supply, current of one polarity will flow through the diode D2, transistor Q2 and the resistor R1. For the other polarity, it will flow through the diode D1, the transistor Q4 and the resistor R2. A pair of opto-couplers OC1 and OC2, each formed from an open base transistor and light emitting diode (LED), regulate the current flowing to the transistors Q2 and Q4 respectively. By altering the current through the LEDs, the current flowing through the open base diodes is controlled and subsequently the current flowing through the transistors is controlled. This allows the control circuit to remain isolated from the output circuit.

[0029] There is further provided a central processing unit (CPU) which measures the voltage across the resistor R3. If again the current through the resistor R3 is too high, the voltage across it becomes too high, then the bias to the opto-coupler is removed and the transistors Q2 and Q4 are switched off.

[0030] Further, it will be noted that the CPU is connected directly to the AC supply to allow determination of zero cross over points in the current. The CPU is programmed to activate the opto-coupler at power activation only on the zero cross region. The CPU is also programmed to count the number of mains half cycles it detects before engaging the lamp unit.

[0031] It is envisaged that means other than a computer or central processing unit could be used to randomise the application of power to the loads to reduce inrush currents. Indeed, it is envisaged that many circuits could be provided. However, a programmed CPU is probably one of the easiest ways of doing it.

[0032] It will be appreciated that various aspects of the invention may be embodied on a computer that is running a program or program segments originating from a computer readable or usable medium, such medium including but not limited to magnetic storage media (e.g. ROMs, floppy disks, hard disks, etc.), optically readable media (e.g. CD-ROMs, DVDs, etc.) and carrier waves (e.g., transmissions over the internet). A functional program, code and code segments, used to implement the present invention can be derived by a skilled computer programmer from the description of the invention contained herein.

[0033] It will be appreciated therefore that a computerised program may be provided providing program instructions which, when loaded into a computer, will constitute the means in accordance with the invention and that this computer program may be embodied on a record medium, a computer memory, a read only memory or carried on an electrical carrier signal.

[0034] In the specification the terms "comprise, comprises, comprised and comprising" or any variation thereof and the terms "include, includes, included and including" or any variation thereof are considered to be totally interchangeable a nd they should all be afforded the widest possible interpretation.

[0035] The invention is not limited to the embodiments hereinbefore described but may be varied in both construction and detail.

Claims

1. A load conditioner (1) for the protection of lamp units (2) in a lighting system in which each lamp unit comprises a lamp and lamp control circuitry (3) including a ballast circuit (4), the lighting system having a main power input switch for connecting the lighting system to an AC power supply, characterised in that the load conditioner (1) comprises randomising means for varying the time at which the connection of the lamp unit to the power supply occurs whereby the lamp units (2) in the lighting system are powered at different times during a start-up period.

2. A load conditioner (1) as claimed in claim 1 in which there is provided means to protect external wiring and external components from current surges caused by electronic circuitry in the lamp unit.

3. A load conditioner (1) as claimed in claim 1, in which there is provided a central processing unit (CPU), the CPU having means for setting the number of half cycles after the main input switch has closed and applied current to the load conditioner (1) when the load conditioner (1) will transmit onwards to the lamp unit (2).

4. A load conditioner (1) as claimed in any preceding claim, in which the randomising means comprises means for causing the connection to the load at mains zero cross current.

5. A load conditioner (1) as claimed in claim 1, in which the randomising means comprises a circuit for onward transmission of power, the circuit comprising switches with random response times.

6. A load conditioner (1) as claimed in any preceding claim, in which a current limit device is provided, the current limit device entering a linear region of operation as it approaches a preset limit current.

7. A load conditioner (1) as claimed in claim 6 in which the current limit device comprises two identical symmetrically inverted stages, each stage comprising a control transistor (Q1, Q3), a power supply transistor (Q2, Q4) and a resistor (R1, R2), the control transistor (Q1, Q3) removing the bias current from the power supply transistor (Q2, Q4) once the voltage across the resistor (R1, R2) exceeds a predetermined level.

8. A load conditioner (1) as claimed in claim 6 or 7 in which a cut-out device is provided to operate when the current limit device (14) enters the linear region.

9. A load conditioner (1) as claimed in any preceding claim, in which there is provided a mains filter (10) at the input to the load conditioner (1) to attenuate conducted emissions above a preset frequency.

10. A load conditioner (1) as claimed in claim 8, in which there is a means of attenuating the higher frequency components of any conducted emissions generated by the lamp unit (2).

11. A method of controlling the operation of a lighting system which comprises a plurality of lamp units (2), each in turn comprising a lamp and lamp control circuitry (3) including a ballast circuit (4), the system being connected to a mains AC power supply through a power input switch, the method comprising varying the time at which the connection of the lamp units (2) to the power supply takes place after the input switch is used to connect the power supply to the light system.

12. A method as claimed in claim 11 in which zero crossover time of the power supply is detected and the lamp unit (2) is connected to the power supply at zero crossover.

13. A computer program comprising program instructions for causing a computer to perform the method of claims 11 or 12.

14. A computer program as claimed in claim 13, embodied on a record medium.

15. A computer program as claimed in claim 13, stored in a computer memory.

16. A computer program as claimed in claim 13, embodied on a read-only memory.

17. A computer program as claimed in claim 13, carried on an electrical signal carrier.

Drawing