GB2159009A

GB2159009A - Load supply circuit and lamp module

Info

Publication number: GB2159009A
Application number: GB08512337A
Authority: GB
Inventors: Karam Hussain Malik; Sydney Alfred Richard Rigden
Original assignee: General Electric Co PLC
Current assignee: General Electric Co PLC
Priority date: 1984-05-18
Filing date: 1985-05-15
Publication date: 1985-11-20
Also published as: EP0165701A1; GB2159009B; EP0165701B1; GB8512337D0; DE3579953D1; GB8412699D0

Description

1 GB 2 159 009 A 1

SPECIFICATION

Load Supply Circuit and Lamp Module This invention relates to -load supply circuits, and particularly to such a circuit enabling low voltage lamps to be used from a high voltage source such as 70 a domestic mains supply, and to lamp modules incorporating such a circuit.

It is known that ordinary general lighting service (G.L.S.) domestic tungsten lamps are a rather inefficient source of light considering their power consumption, and that tungsten-halogen lamps are more efficient because they are smaller and operate at higher pressures and temperatures. Tungstenhalogen lamps are, however, more efficient at lower voltages, for the same filament length, than the usual 240 volts mains supply: the peak of efficiency for a given filament length being at about 18--20 volts.

Clearly, therefore, it would be desirable to use a low voltage tungsten-halogen lamp for domestic purposes so as to increase efficiency and decrease power consumption. One way of reducing the mains voltage to that required for the lamp is by using a transformer, but this is rather large and heavy. An alternative method is to use an electronic circuit to step down the voltage. Electronic circuits for reducing voltages are known as in, for example, domestic dimming circuits, but such circuits only operate down to about 50-60 volts.

It is thus an object of the present invention to 95 provide a load supply circuit which reduces the mains voltage to a voltage suitable for a low voltage tungsten-halogen lamp.

Accordingly, the invention provides a load supply circuit which supplies a low voltage load from a high 100 voltage a.c. supply, comprising an a.c./d.c. switch means for switching said load into and out of the supply circuit and control means fortriggering the said switch means at a desired phase angle of the high voltage a.c. supply..

Preferably the circuit is integrally assembled in a complete unit to facilitate its use as a direct plug in replacementfor a G.L.S. filament lamp.

However, it may possibly be used separately say by inclusion in a wall switch.

The load is preferably a low voltage tungstenhalogen lamp and the a.c. supply is the domestic mains supply.

The switch means is preferably a solid state switch and may conveniently be a Gate Turn Off Thyristor (G.T.O.) or may possibly be a triac.

The control means for triggering the said switch means is preferably an integrated circuit which may also have incorporated therein, means for limiting the surge current when the circuit is first switched on, and/or means for feedback controlling the output of the integrated circuit to withstand varying temperature conditions.

Preferably, the supply circuit includes filter means for reducing radio frequency interference from the mains which can falsely triggerthe a.c. switch, and may also include an overcurrent trip means to safeguard the circuit in the event of a short-circuit in the load.

If the switch means is a G.T.O., the supply circuit may further include means for rectifying the supply voltage.

Conveniently, the load supply circuit is positioned, with a low voltage tungsten-halogen lamp as the load, within a lamp replacement unit shaped like an ordinary tungsten lamp and which is a direct replacement for such a lamp. The tungstenhalogen lamp is preferably, however, removeable from said unit and is itself replaceable within the unit.

The invention further comprises an overcurrent trip circuit including sensing means to sense the level of current through the part of the circuit to be protected and to produce a first signal consequent to a level of build-up of said current above a predetermined level, and signalling means for producing a second signal upon receiving said first signal, and means responsive to said second signal for effecting the tripping function. 85 Preferably, said sensing means is a capacitor connected to the base of a transistor and said signalling means is a timer or thyristor also connected to the base of a transistor. One embodiment of the invention will now be more fully described, byway of example, with reference to the drawings, in which:

Figure 1 is a schematic cross-sectional view through a lamp replacement unit according to the invention; Figure 2 is a schematic diagram of a load supply circuit in accordance with the invention; and Figure 3 is a schematic diagram of an overcurrent trip circuit according to the invention.

The lamp replacement unit shown in Figure 1 comprises a thermoplastic resin base 1 injection moulded to produce a cap 2 positioned at one end, shown lowermost. The cap 2 is of standard size and fitting so that it can be inserted into ordinary domestic lamp sockets, and has two contacts 3 to form the electrical connections with the socket. A component board 4 is contained within the body and thermally insulated from the lamp 6 by being wrapped in a suitable heat resisting and thermally insulating wool 9. The lamp 6 is a low voltage tungsten-halogen lamp and is positioned within socket 7 positioned on a support member 8 fastened to a heat shield 5 between the shield and the board 4. A transparent glass cover 10 surrounds the lamp 6 and is fastened to the base 1.

The component board 4 has electronic components mounted thereon, the components 11 forming part of a load supply circuit as shown diagrammatically in Figure 2. The board also has mounted thereon, connections to a Gate Turn-Off Thyristor 12 (G.T.O.) mounted on a heat sink 13 and connections 14 to a mains supply via the contacts 3 on the cap 2 when in place in a socket. As will be further explained below, the G.T.O. 12, and other components 11 form part of a circuit to power the lamp 6 from the mains supply.

Thus, as shown in Figure 2, the load supply circuit for supplying the low voltage tungsten-halogen lamp 6 from an a.c. mains supply 20, comprises a bridge rectifier part 21, a mains radio frequency 2 GB 2 159 009 A 2 interference filter circuit (A), a mains isolated low power d.c. supply circuit (B), a pulse supply part 22, a pulse conversion part 23, an overcurrent trip circuit (C) and a G.T.O. 12.

The circuit is designed such that a negative going pulse is provided by the pulse supply part 22 including integrated circuit 25 at a desired phase angle regulated by the variable resistance 24. This pulse is converted from negative going to positive going by the pulse conversion part 23 of the circuit and the positive going pulse is used to trigger the G.T.O. 12 to conduct and switch the lamp 6 on. The G.T.O. automatically turns "off" when the phase angle of the supply reaches zero, so by producing 70 the pulse at an appropriate phase angle, only the controlled part of the cycle will be passed via the G.T.O. to suit the low voltage lamp. The integrated circuit 25 provides this initial pulse and also provides, if necessary, a slow start feature to overcome the problem of initial switch on inrush surge current of the cold filament. Since the G.T.O. is a d.c. switch, the bridge rectifier part 21 of the circuit provides the G.T.O. with a full wave rectified d.c. from the mains a.c. supply. The mains isolated low power d.c. supply circuit (B) is used merely to provide the input supply for the integrated circuit 25 and other components at an appropriate level, whilst the mains radio frequency interference filter circuit (A) is used to remove the mains interference which could otherwise trigger the G.T.O. falsely. Both of circuits (A) and (B) are conventional and will not be further described.

The overcurrent trip circuit (C) is shown in more detail in Figure 3 and is basically composed of a sensing part 30 and a signal producing part 31. The sensing part 30 is connected to point X in Figure 2 and comprises a capacitor 32 which passes a voltage if a sharply rising current is passing through point X, for example, in the event of a filament end of life flashover producing a short circuit current. This voltage is passed to the base of a transistor 33 which produces a pulse. The signal producing part 31 receives this pulse at a timer 34 which, with the rest of the components of the signal producing part 31, produces a signal at X'for long enough to turn off the G.T.O. and thus protect the electronic components from a damaging high current. The G.T.O. is only switched off forthe particular halfcycle in which the short-circuit occurred and then the normal pulses switch it on again provided the lamp has not gone short circuit or into an arc condition. The timer could be replaced by a small thyristor if desired.

It will be appreciated that although the invention has been described with the load supply circuit within the lamp replacement unit, it could be positioned in the wall switch or anywhere else as required. Further, the transparent glass cover 10 may be replaced by suitable coloured covers made of similar material and may even if desired be made in novel shapes for decorative purposes.

D1 cl C2 C3 C4 C5 C6 R1 R2 R3 R4 R5 R6 R7 R8 80 R9 R10 TR1 I.C.i.

D5 85 C7 C8 C9 R11 R12 90 R13 R14 R15 TR2 TR3 95 I.C.2 List of components in Figures 2 and 3 Gate turnoff GTO thyristor to D4 diodes capacitor 11 Resistor 11 11 11 - (Variable) 11 11 11 Transistor ZENER diode capacitor resistor 11 Transistor 11 Timer LC.

BT1 57 IN4004 711F. 16 7nF 1 liF I1F 0liF 7nF 200KQ 330KQ 100K0 330KQ 1 KQ 5M 1OKC2 10M 470 50mf2 BCy70 TDA 2085 BZX87-ClO 4711F 1.nF LriF 1 K0 1 0M 1 KO 1 0M 470Q BD675 BC 107 555 3 GB 2 159 009 A 3

Claims

1. A load supply circuit which supplies a low voltage load from a high voltage a.c. supply, comprising an a.c./d.c. switch means for switching said load into and out of the supply circuit and control means for triggering the said switch means at a desired phase angle of the high voltage a.c. supply.

2. A load supply circuit according to Claim 1 wherein said load is a low voltage tungsten-halogen lamp and the a.c. supply is the domestic mains supply.

3. A load supply circuit according to either Claim 1 50 or Claim 2 wherein said switch means is a solid state switch.

4. A load supply circuit according to Claim 3 wherein said switch means is a Gate Turn Off Thyristor.

5. A load supply circuit according to Claim 4 wherein the supply circuit includes means for rectifying the supply voltage.

6. A load supply circuit according to Claim 3 wherein said switch means is a triac.

7. A load supply circuit according to any preceding claim wherein said control means for triggering said switch means is an integrated circuit.

8. A load supply circuit according to Claim 7 wherein said integrated circuit further incorporates means for limiting the surge current when the circuit is first switched on.

9. A load supply circuit according to either Claim 7 or Claim 8 wherein said integrated circuit further incorporates means for feedback controlling the output of the integrated circuit to withstand varying temperature conditions.

10. A load supply circuit according to any preceding claim further including filter means for reducing radio frequency interference from the mains supply.

11. A load supply circuit according to any preceding claim further including an overcurrent trip means to safeguard the circuit in the event of a short-circuit in the load.

12. A load supply circuit according to any one of Claims 2 to 11 which is integrally assembled into a complete lamp-replacement unit as a replacement for a G.L.S. tungsten filament lamp.

13. A load supply circuit according to Claim 12 wherein said low voltage tungsten-halogen lamp is positioned in said unit but is replaceable within the unit.

14. A load supply circuit according to any one of Claims 1 to 11 which is assembled to form part of a wall switch unit. 55

15. An overcurrent trip circuit including sensing means to sense the level of current through the part of the circuit to be protected and to produce a first signal consequent to a level of build-up of said current above a predetermined level, and signalling means for producing a second signal upon receiving said first signal, and means responsive to said second signal for effecting the tripping function.

16. An overcurrent trip circuit according to Claim 15 wherein said sensing means is a capacitor connected to the base of a transistor and said signalling means is a timer orthyristor also connected to the base of a transistor.

17. A load supply circuit substantially as hereinbefore described with reference to Figures 1 and 2 of the drawings.

18. An overcurrent trip circuit substantially as hereinbefore described with reference to Figure 3 of the drawings.

Printed for Her Majesty's Stationery Office by Courier Press, Leamington Spa. 1111985. Demand No. 8817443. Published by the Patent Office, 25 Southampton Buildings, London, WC2A lAY, from which copies may be obtained.