GB2254970A

GB2254970A - Starter for a fluorescent lamp

Info

Publication number: GB2254970A
Application number: GB9206975A
Authority: GB
Inventors: Sigbert Mueller; Ulrich Biebel; Dieter Wahl
Original assignee: Patent Treuhand Gesellschaft fuer Elektrische Gluehlampen mbH
Current assignee: Osram GmbH
Priority date: 1991-04-05
Filing date: 1992-03-31
Publication date: 1992-10-21
Anticipated expiration: 2012-03-31
Also published as: IT1254751B; GB2254970B; GB9206975D0; FR2675004A3; DE9104136U1; ITMI920764A1; FR2675004B3; ITMI920764A0

Abstract

The starter contains a glow igniter 6, a resettable bimetallic switch 7 and an NTG resister 8 which are connected to one another in series. Parallel to the NTC resister 8 lies an ohmic resister 9 which is of considerably lower resistance than resister 8 in the temperature range of minus 20 DEG C to +80 DEG C and which ensures a fast preheating of the electrode coils of the lamp. In the event of the lamp failing to ignite, the bimetallic switch 7 latches open due to heat transmission thereto from resister 8, 9. The elements 6, 7, 8, 9 and a RFI suppressing capacitor 5 are all located in a housing with two external conductor pins (15), (16), (Fig 2), and a reset button for switch 7. <IMAGE>

Description

STARTER FOR AN ALTERNATING CURRENT LOW-PRESSURE DISCHARGE LAMP The present invention relates to starters for lowpressure discharge lamps supplied with alternating current. More specifically the present invention relates to starters which operate fluorescent tubes.

A known starter is described in DE-PS 23 21 212 which comprises a glow igniter, a rectifier and a disconnecting device which disconnects the starter after the fluorescent lamp has failed to light after several failed ignition attempts. The disconnecting device consists of a hot-conducting resistor and semiconductor diode connected in parallel which are in turn connected in series with a resettable bimetallic switch. At the beginning of the ignition phase of a fluorescent lamp, the diode rectifies the alternating current so that the current-limiting action of a series reactance or choke, connected in series with the tube, reduces so that the electrodes of the fluorescent lamp are heated by an increased current. After several failed ignition attempts the hot-conducting resistor heats up and reduces its resistance.The hot-conducting resistor then effectively short circuits the action of the diode so that the choke may operate as a current limiter and to reduce the electrode heater current. The resettable bimetallic switch is in thermal contact with the diode and the hot-conducting resistor to allow the starter to be switched off when either the glow igniter or the lamp is defective.

The starters according to DE-PS 23 21 212 may only be used for conventional series devices with 18 to 65 watt lamps. These starters cannot also be used in "lowloss" series devices which operate with excessive peak currents, since the diode substantially reduces the current-limiting action of the choke which may cause the electrode coils and choke reactor to be damaged by excessive peak currents. Furthermore, using a semiconductor diode limits the temperature range for reliable operation of the disconnecting mechanism from 50C to 800C for lamps of 18 W to 30W.Even with the use of suitable glow igniters and adjustment of the disconnecting devices, diode starters are not suitable for lights having two fluorescent lamps connected in series since depending upon the position of each starter in its holder the diodes of the appertaining starters may be arranged either in opposite directions (non-conducting direction) or in the same direction (conducting direction). In the first case, no ignition of the fluorescent lamps can take place and it may not be immediately apparent to the user that the starters have been positioned with their diodes acting in opposite directions.

According to the present invention there is provided a starter for an alternating current, low-pressure discharge lamp, operated with a choke, and having in series; a glow igniter, a hot-conducting resistor and a resettable bimetallic switch which is in thermal contact with the hot-conducting resistor whereby the bimetallic switch, in the event of the low pressure discharge lamp failing to ignite, interrupts the electrode heating circuit until the bimetallic switch is reset externally, wherein an ohmic resistor is connected in parallel to the hot-conducting resistor and in thermal contact to the bimetallic switch, the resistance of the ohmic resistor being considerably smaller than the resistance of the hot-conducting resistor in the temperature range -20 C to +800C.

The ohmic and the hot conducting resistor may have resistances of between 10 to 50 Q and 150 to 500 Q, respectively, at 250C.

The ratio of the resistances of the hot conducting resistor at 250C and 1000C may be between 2.5 and 5.

For a better understanding of the present invention, reference will now be made, by way of example to the accompanying drawings in which:- FIGURE 1 shows a circuit diagram of a low pressure discharge lamp using the starter of the present invention; and FIGURE 2 shows the spatial arrangement of the components of the starter according to the present invention.

In Figure 1, a fluorescent lamp 1 with electrode coils 2 and 3 is connected to be supplied with an alternating voltage UB through a choke which serves to limit the current in the electrodes after ignition of the lamp. The starter contains a capacitor 5 connected in parallel to the fluorescent lamp to suppress radio frequency interference, a glow igniter 6 and a disconnecting device 7, 8 and 9. The disconnecting device comprises a bimetallic switch 7, a hot-conducting resistor 8 with a resistance of approximately 300Q at 250C and a metal-wire resistor with a resistance of about 25 n. The parallel arrangement of the hot-conducting resistor 8 and the ohmic resistor 9 are connected in series with the bimetallic switch 7 and the glow igniter 6.

Figure 2 shows the preferred spatial arrangement of the starter components. The bimetallic switch 7 comprises a bimetallic electrode 10 with an offset end 10a and a spring-wire electrode 11 latched tight against the offset end 10a. The bimetallic electrode 10 is spotwelded at its other end lOb to a metallic mounting plate 12, supported by a plastic frame 13. Close to the bimetallic electrode 10 is the metal-wire resistor 9, the body of which, is welded to a punched-out and bent shackle to make one electrical contact (not illustrated) to the mounting plate 12. The other connection of the metal-wire resistor 9 leads to a contact element 14 which leads to a first electrode of the glow igniter 6, which in Figure 2 is for the most part covered by the mounting plate 12 and the plastic frame 13.The hot-conducting resistor 8 is soldered to the mounting plate 12 to make an electrical contact and is likewise connected to the contact element 14 so that it lies adjacent to the metalwire resistor 9. The spring electrode 11, supported by the plastic frame 13, closes the electrical contact between the offset end l0a of the bimetallic electrode 10 and the contact pin 15. The other contact pin 16 is connected by way of a further contact element 17 to the second electrode of the glow igniter 6. A 5 x 1 mm hole (not shown in Figure 2) in the mounting plate 12, between the metal-wire resistor 9 by the bimetallic electrode 10 is provided to regulate the transmission of heat to the bimetallic strip 10.

Not shown in Figure 2 are the capacitor 5, connected across the contact pin 16 and the mounting plate 12, a button which rests loosely on the horizontal part of the spring-wire electrode 11 and which helps the wire 11 to be latched tight against the offset end l0a of the bimetallic strip and a cylindrical housing which normally surrounds the components of the starter.

In operation, the ohmic resistor 9 short-circuits the hot-conducting resistor 8, having a high resistance when cool, so that the electrode coils 2 and 3 of the lamp 1 are quickly heated to approximately 9000C. If the lamp 1 does not ignite due to a fault, then both the ohmic resistor 9 and the hot-conducting resistor 8 heat up causing the resistance of the hot conductor to fall considerably between 2000C and 5200C, at a rate dependent upon the power of the lamp and the heater current. Heat from the resistors is transmitted by way of the mounting plate 12 by direct transmission to the bimetallic electrode 10. Under the influence of the heat, the electrode 10 bends and releases the electrical contact between the offset end 10a and the spring wire 11. After removal of the fault, the spring-wire electrode 11, actuated by the button resting loosely on it, may be relatched against the offset end l0a of the bimetallic electrode 10.

The disconnecting mechanism may still function even if the ohmic resistor 9 or the hot-conducting resistor 8 is defective. The remaining functioning component is then heated more intensely and alone triggers the bimetallic switch 7. The ohmic resistor 9 in some instances may heat up uncontrollably and would otherwise cause the starter housing to melt and is therefore provided with a heat-insulating casing comprising silicon cement. This casing can reduce a possible resistor temperature from 7550C to 5200C at a power of 65W in order to reduce the risk of the starter housing from melting.

In the event of a fault, the starter can disconnect a 65 W, 220 V lamp at +250C in 17 to 18 seconds. For a 20 W lamp, with similar conditions, the disconnecting time extends to about 75 s. This compares with the typical ignition times of this starter in interferencefree operation which amount to approximately 2 to 3 s.

In comparison with the known starter, the present starter contains in place of the semiconductor diode an ohmic resistor which is connected parallel to the hotconducting resistor and whose resistance is smaller by a factor of ten. Effectively, the hot-conducting resistor is short-circuited at the beginning of the ignition phase to cause the electrodes of the fluorescent lamp to be heated by an increased current. The present invention is therefore suitable for use in both conventional and "lowloss" series devices which operate with excessive peak currents. The risk of damage to the electrode coils or to the series reactance through excessive peak currents no longer exists with the starter according to the present invention.The starter can also be used advantageously in a damping or capacitive mode, wherein the addition of the capacitance to the series reactance allows peak currents to be controlled and to allow for relatively high current pulses.

Moreover, the temperature range in which the starter can be used widens to -200C to +800C, so that this starter is also suitable for outdoor uses. The disconnecting mechanism of the starter is suitable for all types of lamp with initial heater currents of 3501100 mA. Furthermore, with a suitable glow igniter the disconnecting mechanism can be used for two fluorescent lamps connected in series as well as for single connection at 110/130 V. Through variation of the components (i.e. adaptation of their electrical characteristics) the disconnecting mechanism according to the invention may be used not only for the power range of 18 W to 65 W, but also 80 W to 140 W or on 240 V systems for 75 W to 125 W. The disconnecting mechanism may still function if either the hot conductor or the ohmic resistor is defective, the other component then undertakes solely to heat the bimetallic strip to trigger the latched switch.

Claims

Claims:

1. A starter for an alternating current, lowpressure discharge lamp, operated with a choke, and having in series; a glow igniter, a hot-conducting resistor and a resettable bimetallic switch which is in thermal contact with the hot-conducting resistor whereby the bimetallic switch, in the event of the low pressure discharge lamp failing to ignite, interrupts the electrode heating circuit until the bimetallic switch is reset externally, wherein an ohmic resistor is connected in parallel to the hot-conducting resistor and in thermal contact to the bimetallic switch, the resistance of the ohmic resistor being considerably smaller than the resistance of the hot-conducting resistor in the temperature range -200C to +800C.

2. A starter as claimed in claim 1, wherein the ohmic resistor and the hot-conducting resistor have resistances of 10n to 50Q and 150Q to 500Q, respectively, at 250C.

3. A starter as claimed in claim 1 or 2, wherein the ratio of the resistance of the hot-conducting resistor at 250C and 1000C lies between 2.5 and 5.

4. A starter as claimed in any preceding claim, wherein the first electrode of the bimetallic switch comprises an offset bimetallic strip and the second electrode is a resilient conductor releasably latched to the offset bimetallic strip.

5. A starter as claimed in claim 4, wherein a button which rests loosely on the resilient conductor provides external means to reset the bimetallic switch.

6. A starter as claimed in claim 4, wherein the ohmic resistor is placed near the first electrode of the bimetallic switch.

7. A starter as claimed in any preceding claim, wherein the ohmic resistor is electrically and thermally connected to a shackle, punched out from a metallic mounting plate.

8. A starter as claimed in claim 7, wherein the bimetallic strip and the hot-conducting resistor are electrically and thermally connected to the mounting plate.

9. A starter as claimed in claim 8, wherein the mounting plate has one or more recesses to regulate the conduction of heat.

10. A starter as claimed in any preceding claim, wherein the ohmic resistor is a wire-resistor.

11. A starter as claimed in claim 10, wherein the ohmic resistor is provided with a heat-insulating casing.

12. A starter as claimed in any preceding claim, wherein the hot-conducting resistor comprises a semiconductor material.

13. A starter as claimed in any preceding claim, wherein the average disconnection time of the starter is between 10 and 150 seconds.

14. A starter substantially as hereinbefore described with reference to Figures 1 and 2 of the accompanying drawings.