WO2008065383A1

WO2008065383A1 - Inverters

Info

Publication number: WO2008065383A1
Application number: PCT/GB2007/004533
Authority: WO
Inventors: Charles Daniel
Original assignee: Charles Daniel
Priority date: 2006-11-27
Filing date: 2007-11-27
Publication date: 2008-06-05
Also published as: EP2092801A1; GB0623625D0; CN101627664A

Abstract

Drive circuitry for a fluorescent lamp comprising inverter circuitry having outputs for connection to respective terminals of a fluorescent lamp and an extra low voltage transformer connected to the inputs of the inverter circuitry. The drive circuitry can be connected to one or more fluorescent lamps.

Description

Inverters

Field of the Invention

The present invention relates to inverters. In particular it relates to a low (more preferably extra low) voltage AC high frequency inverter that can be used in the drive circuitry for a gas discharge lamp, for example a fluorescent lamp.

Background

Gas discharge lamps generate light by passing an electrical discharge through an ionized gas. The principles of operation of such lamps are well known and need not be explained here. Some gas discharge lamps emit ultraviolet radiation that is converted to visible light by a fluorescent coating on the inside of the lamp's glass casing. These types of lamp are commonly referred to as "fluorescent lamps".

Gas discharge lamps, and fluorescent lamps in particular, offer significant advantages over incandescent lamps. In particular they tend to be more efficient than incandescent lamps of an equivalent brightness and last between 10 and 20 times as long. Their long life in particular makes them very attractive for commercial installations where the cost of replacing lamps (including labour costs) can be particularly significant.

Typically, fluorescent lamps are powered from a mains supply (e.g. 240V AC), a ballast being used between the power supply and the lamp to regulate the current flow through the lamp.

Summary of Invention

A general aim of the present invention is to enable fluorescent lighting installations that can be powered by conventional extra-low voltage transformers (i.e. power supplies). For example, such lighting installations could be beneficially used in commercial shelving installations (to light shelves), for example in supermarkets or other shops.

"Low voltage" in the context of this application means voltages up to 1000V AC but preferably below 240V (i.e. below mains voltage). "Extra low voltage" in the context of this application means voltages less than 50 volts RMS (AC), such as 24V, 18V and 12V or less. To achieve this aim, it has been necessary to develop a new low- / extra low voltage AC high frequency inverter as known extra low voltage inverters are not suitable.

In particular, there are two main known types of extra low voltage inverters:

1. A DC type is powered through a DC power supply. A problem with this type of inverter is that the positive and negative polarities must be strictly insulated and kept clear from contact with the polarities of the adjacent units.

2. An AC Low frequency unit, which is powered by Low frequency AC traditional heavy wire-wound transformers (non-electronic). A problem with this type of inverter is that the electrical contacts from the output of the transformer to the fitting(s) must be solid, (hard wired) otherwise they could generate excessive heat with consequent Arcs and Sparks and a high noise level. Additionally, from a safety point of view these transformers only have a thermal safety cut out.

In contrast, embodiments of the present invention can use a standard electronic transformer to power a fluorescent light fitting. This has never been done before, because these electronic transformers are designed to be directly connected to halogen lamps, rather than connected to a lamp via an inverter as is required for (i.e fluorescent lamps need an inverter between themselves and the transformer). Such an inverter has never been made. This has only been made possible by the use of a combination of tuning capacitors, resistors and copper coils, which are not present in standard inverters.

Thus, the present invention consists of a Low voltage AC high frequency inverter. This inverter could be powered by a standard Extra low voltage AC high frequency electronic transformer (e.g. the same type of electronic transformer as used to power low voltage Halogen incandescent lamps.) These transformer also incorporate an extra safety overload, short-circuit and thermal protection features, offering additional benefits.

One difference between low frequency and high frequency transformers that are preferred for use with embodiments of the present invention is that whereas the output of conventional wire wound transformers is at the same frequency as the input (i.e. 50Hz) with a sinusoidal waveform, the output of (high frequency) electronic transformers is an envelope which is basically sinusoidal at twice the frequency of the input, e.g. modulated with a 35KHz (nominal) square wave.

With lighting installations employing preferred embodiments of this new invention, fittings would not be affected if they made contact with polarities of adjacent fittings. Furthermore it only requires touch contacts to function, and the noise problems are alleviated. There would also be the advantage of instantaneous cut-outs if things went wrong.

In preferred embodiments, the light fitting also features side springs which make instant contact with conductors mounted on shelving brackets, without using input wires. The brackets make contact with two conductors, which link the inputs of the inverters to the two outputs of the electronic transformer.

Brief Description of the Drawings An example of the invention will now be described by referring to the accompanying drawings:

Fig. 1 shows part of an inverter circuit for an embodiment of the present invention;

Fig. 2 shows another part of the inverter circuit of fig. 1 ;

Fig. 3 shows a light-fitting assembly with inverter and side springs in accordance with an embodiment of the present invention;

Fig. 4 shows a PCB, which attaches to side bracket of shelves and can be used with embodiments of the present invention;

Fig. 5 shows a side mounting spring that can be used on the side of the fitting in the assembly of fig. 3 (could also be other cushioning material);

Fig. 6 shows a diagram of electronic transformers in combination with inverters. (Could also be one inverter);

Fig. 7 shows a shelving system with which the present invention can be used to power fluorescent tubes mounted on the shelving system; and Fig. 8 shows circuit diagrams for an embodiment of the invention.

Description of Embodiment An exemplary inverter circuit in accordance with an embodiment of the invention will be described with reference to figures 1 and 2.

Looking first at fig. 1 , from left to right, we have two low voltage AC currents outputs from the electronic transformer (A1 & A2) - the electronic transformer itself is not shown. The flow goes through the inverter circuitry as follows:

- A1 goes through a safety fuse

- A1 & A2 go through a Choke (LO207). The choke acts as a suppressor to smooth AC supply.

- A1 & A2 go through an AC capacitor. The capacitor stores currents. Both the choke and capacitors act as a filter for AC current.,

- A1 & A2 go through a bridge of 4 Diodes, which changes the current from AC to

DC, this also results in a voltage increase.

DC+ and DC- go through three capacitors.

The flow continues in figure 2 (fig1 & fιg2 show one circuit)

DC+ goes through 4 resistors (R1, R2, R3.R4) then through a tuning coil, then to input 1 of the transformer.

- DC- Goes through one of 3 terminals of two thermal switches (TIP1 & TIP2) which act as tube starters

R1 & R2 are linked with 3^rd terminal of Tip1 , then to input 3 of the transformer.

- R3 & R4 are linked with 3^rd terminal of Tip2, the to input 2 of the transformer - Centre terminal of TIP1 goes through capacitor C4 then to input 5 of the transformer

- Centre terminal of TIP2 goes through capacitor C4 then to input 4 of the transformer

- Transformer outputi (TO1) goes through three series linked capacitors ( C5, C6 and C7) to one end of the tube.

- The second transformer output (TO2) goes directly to the second end of the tube.

Conveniently, the inverter circuitry can be incorporated in a fluorescent lamp fitting, as shown for example (in exploded form) in Fig. 3. The inverter circuitry can be housed within the body of the fitting, outputs from the circuit being connected to respective terminals of the fluorescent lamp (a fluorescent tube in the present case).

The fitting illustrated in this example also has spring connectors at each end to make contact with power supply tracks in the shelf brackets on which the fitting is to be mounted (as described, for example, in our earlier patent application GB2428141). A detailed view of the spring mounting clip is shown in fig. 5.

Also as described in GB2428141 , the power supply track on the shelf bracket may be provided by a PCB strip, as illustrated in Fig. 4. This PCB strip attaches to a side bracket of the shelf.

As illustrated schematically in Fig. 6, multiple inverter circuits can be connected to respective fluorescent lamps in a shelving installation, all powered by a single transformer (e.g. an extra low voltage transformer). In alternative embodiments, a single inverter circuit could be used to drive multiple lamps.

Fig. 7 shows a shelving system with which the present invention can be used to power fluorescent tubes mounted on the shelving system. Fig. 8 shows circuit diagrams for an embodiment of the invention.

Various modifications can be made to the specifically described and illustrated embodiments without departing from the spirit and scope of the present invention.

6a

|=lp. 3 parts list

Pl oa

D283-031 D2Θ3-056

FLUORESCENT RIVERTER POP RIVET

X1 3.2 X 8MM

X2

P2

D2B3-033 02

M3 X 8L COUNTERSUNK SCREW D283-036

X4 RIVET ASSEMBLY

X2 oa

D283-016 piO

LUMINAIRE END CAP RH D283-032

X1 BJ8

26.642.8601.05

UMP HOLDER

D283-025 X2

LUMINAIRE SPRING

X2 Edi

D283-032 βfi BJΘ 26.242.106

D283-035 CLIP

4 MM CRIMP CONNECTOR X2

X2

012

Qg D2B3-030

D2Θ3-034 UMP 21 W HEI 5-1

M3 SELF TAPPING SCREW X1

X2

BlS

QZ D283-020.

0283-01 θ LUMINAIRE

LUMINAIRE BODY DIFFUSER

X1 Xi

PH

D283-017

LUMINAIRE END CAP LH

X1

Claims

1. Drive circuitry for a fluorescent lamp comprising inverter circuitry having inputs for an extra low voltage alternating current supply from an extra low voltage transformer and outputs for connection to respective terminals of a fluorescent lamp.

2. Drive circuitry according to claim 1 , further comprising an extra low voltage transformer connected to the inputs of the inverter circuitry.

3. Drive circuitry according to claim 2, wherein the transformer is an electronic transformer.

4. Drive circuitry according to any one of the preceding claims in combination with one or more fluorescent lamps connected to the outputs from the inverter circuitry.

5. Drive circuitry according to any one of the preceding claims, wherein the inverter circuitry comprises a filter for the AC input current.

6. Drive circuitry according to claim 5, wherein the filter comprises a choke and an AC capacitor.

7. Drive circuitry according to any one of the preceding claims, wherein the inverter circuitry comprises an AC to DC converter.

8. Drive circuitry according to claim 7, where there is a voltage increase across the AC to DC converter.

9. Drive circuitry according to claim 7 or claim 8, wherein the AC to DC converter comprises a diode bridge.

10. Drive circuitry according to any one of the preceding claims comprising one or more thermal switches that serve as starters for the fluorescent lamp(s). 8

11. Drive circuitry according to any one of the preceding claims, wherein the inverter circuitry comprises a transformer on the output side, respective outputs from the transformer providing the outputs for connection to the fluorescent lamp(s).

12. A shelving installation comprising one or more fluorescent lamps for lighting the shelving installation, the fluorescent lamps being powered by an extra low voltage power source via drive circuitry according to any one of the preceding claims.

13. A shelving installation according to claim 12, wherein the fluorescent lamps are mounted in fixtures that house at least the inverter circuitry of the drive circuitry.

14. A shelving installation according to claim 13, wherein the fixtures comprise means for releasable mounting to a support structure of the shelving installation.

15. A shelving installation according to claim 14, wherein the fixture includes external electrical contacts that make contact with conductors in the support structure when the fixture is mounted on the support structure.

16. A shelving installation according to claim 15, wherein the contacts are resilient spring elements.

17. A fluorescent lamp fixture for a shelving installation according to any one of claims 12 to 16.

18. An extra low voltage alternating current high frequency inverter.