Electronic Gas Discharge Tube Igniter

Abstract

In an electronic gas discharge tube igniter comprising a semiconductor switch element, a separate control signal terminal of said element is connected through a semiconductor A.C. diode with the tap of a voltage divider. The circuit elements are so dimensioned as to avoid reignition. The device is preferably used in combination with a circuit arrangement including a suppressing capacitor.

Description

This invention relates to a device for electronically igniting gas discharge tubes, such as luminescent lamps.

It is generally known to include such a device in a circuit with the gas discharge tube 1 to be ignited or started, as shown diagrammatically in FIG. 1. In this arrangement, the igniter or starter 5 is connected between the connectors A and B, and hence across the gas discharge tube 1 to be ignited.

A much used embodiment of such a starter, the so-called neon starter, comprises a neon tube capable of operating a bimetallic switch contact. In addition to the fact that the service life of such a neon starter is relatively short, the ignition process takes some time, and is moreover accompanied with annoying flashing.

According to other proposals, such a starter operates fully electronically, which lengthens the starter's service life, since there are no mechanical switch contacts. This arrangement, however, has the drawback that it tends to shorten the service life of the gas discharge tube operated by the starter.

It is an object of the invention to remove the drawbacks outlined above and to provide an igniter which makes it possible to ignite a gas discharge tube in a relatively short time and without annoying flashes, thereby to ensure an extremely long service life of both the gas discharge tube and the igniter proper.

It is a further object of the invention to provide a simple and compact igniter which, if so desired, can be accommodated in a removable housing as commonly used for the above-mentioned neon starters, or in the fitting of the gas discharge tube itself.

FIG. 1 is a circuit diagram illustrating an arrangement according to the prior art;

FIG. 2 is a circuit diagram illustrating an embodiment of the present invention;

FIG. 3 is a circuit diagram similar to FIG. 2 but showing a modified form of the invention;

FIG. 4 is a circuit diagram similar to FIG. 3 but showing a further modification of the invention;

FIG. 5A is a waveform showing the voltage characteristics while the tube is ignited;

FIG. 5B is a voltage waveform showing the effect created when the igniter 5 conducts every other half cycle;

FIG. 5C is a voltage waveform associated with the embodiment of FIG. 2;

FIG. 5D is a voltage waveform associated with the embodiment of FIG. 4;

FIG. 6 is a diagram similar to FIG. 1 but illustrating the capacitor 8 on the supply line side of the tube 1;

FIG. 7 is a circuit diagram similar to FIG. 2 but showing a modification thereof; and

FIG. 8 is a voltage-current waveform associated with the circuit of FIG. 7.

A first embodiment of an igniter according to the invention is shown diagrammatically in FIG. 2. In it, connectors A and B correspond with connectors A and B as shown in FIG. 1. In other words, the circuit arrangement of FIG. 2 is substituted for the block 5 of FIG. 1.

The circuit arrangement shown in FIG. 2 comprises a triode semiconductor A.C. switch element 10, such as a triac, connected between the nodes A' and B'. The gate of the triode switch semiconductor A.C. element 10 is connected through a diode semiconductor A.C. switch element 11, such as a diac, with the node of capacitor 12 and a capacitor 14. These capacitors constitute together with a resistor 13 a series circuit which is connected in parallel with the switch element 10. The functions of the capacitor 8 and the choke coil 9 will be described in detail hereinafter; these elements need not influence the switching action proper. The ignition moment of the switch element can be fixed at choice in dependence upon the values selected for the circuit elements 12, 13 and 14. The moments at which the switch element reaches its non-conductive state correspond with the zero crossings of the current; in other words, these moments cannot be influenced by selection of the circuit element 12, 13 or 14. As will be explained in greater detail hereinafter, the provision of capacitor 14 is essential to ensure reliable ignition without introducing spurious side-effects. As a matter of fact, without the capacitor 14, the igniter tends to begin re-starting time and again even after the gas discharge tube has been ignited, which is a serious drawback. In fact, if the resistor 13 should be directly connected with the capacitor 12 and the switch element 11, i.e. without the capacitor 14 being interconnected, the capacitor 12 will be charged through resistor 13 until the voltage generated across it has reached the ignition voltage value of the switch element 11.

After the switch element 11 has thus become conductive, the switch element 10 will begin to conduct current, as a result of which the voltage across the igniter is decreased abruptly (step function). When, upon the next zero crossing of the current flowing through the switch element 10 the latter becomes non-conductive again, such a high voltage is generated across the gas discharge tube connected with terminals A and B that the tube may be ignited. Once ignited, the burning voltage is established across the tube. In this connection it should be noted that the moment at which the switch element 10 becomes conductive is of great importance, since the time required for heating the filaments 2 and 3 of the gas discharge tube to the extent that the wires can ignite the tube is determined by the period during which the switch element 10 is conductive. For reliably igniting the gas discharge tube as rapidly as possible, it is required for the resulting current flowing through the filaments to have a value in excess of a given minimum value. It is found that the dimensioning of the capacitor 12 and the resistor 13 selected in view of this requirement is such that even when the burning voltage has been established across the gas discharge tube the switch element 10 becomes conductive again, the result of which is that the gas discharge tube is extinguished. It appears from the above that in the situation as outlined the gas discharge tube can again be extinguished after being ignited, so that the igniter keeps repeating the starting procedure.

An extremely simple and reliable solution is obtained according to the present invention by connecting the capacitor 14 in series with the resistor 13 as shown in FIG. 2.

The capacitors 12 and 14 actually form a capacitive voltage divider, the magnitude of capacitor 12 being substantially determined by the energy pulse to be supplied to the gate of the switch element 10 to make the later conductive. Capacitor 14 is so dimensioned that when the burning voltage has been generated across the gas discharge tube the ignition voltage of the switch element 11 is just not reached. In other words, once the gas discharge tube has been ignited, the igniter will remain at rest, i.e. the ignition procedure is not repeated. The capacitor 8 connected between connectors A and B is a suppressing capacitor, which reduces the spurious effect of the lighted tube to a tolerable minimum. When the switch element 10 becomes conductive, the capacitor 8 will be short-circuited, so that a strong peak current can be generated. Such a peak current is limited by incorporating a choke coil 9 in the discharge circuit of the capacitor 8. If so desired, the choke coil can be replaced by the resistor, which, however, involves heat wastage.

For realizing an embodiment of an igniter suitable for incorporation within a limited volume, it is recommendable for the suppressing capacitor 8 to be disposed at the "mains side" as indicated in FIG. 6. In such an arrangement, the choke coil 9 in igniter 5 can be omitted.

The above-described embodiments of the igniter can be used with gas discharge tubes included in an inductive circuit and capacitively compensated.

Another embodiment of the igniter, for use in case the gas discharge tube is connected in a circuit which, as shown in dash lines in FIGS. 1 and 6, comprises a series capacitor 6, is shown diagrammatically in FIG. 3. In it, a parallel circuit, constituted by a capacitor 15 and a resistor 16, is connected in series with the series circuit constituted by resistor 13 and capacitor 14. It has been found to be possible for the circuit elements of such a circuit arrangement to be so dimensioned as to result in a starting procedure in which, after a relatively short waiting time, the filaments reach the required emission temperature, and the tube lights up gradually until eventually the lighting intensity is reached.

This circuit arrangement may be successfully used, for example, in those cases where it is even undesirable directly to switch on incandescent lamps by reason of the sudden variations in light intensity caused thereby.

It is sometimes desired for the tubes to be used under widely varying conditions, involving, for example, great differences in mains voltage and temperature. This makes great demands on the igniter. Of importance is a sufficiently high filament current and a properly timed application of the ignition voltage, which moreover must be sufficiently high. When switch element 10 is substantially permanently conductive, a voltage configuration will be formed across it as shown in FIG. 5A. The filament current is then determined by the choke coil 4 and the resistance of the filaments 2 and 3. The effective current will be about 0.5 A (40 W tube). When the switch element 10 is conductive for a half cycle (FIG. 5B) the effective filament current will be about 1.5 A, which is mainly due to the fact that the choke coil 4 is now unidirectionally driven to saturation, and consequently provides a lower impedance and so permits a higher current. A situation as may occur in the circuit arrangement of FIG. 2 is shown in FIG. 5C. The filament current will now be broken in each half cycle. It is clear that the resulting filament current in that case will be less than 0.5 A.

According to another aspect of the invention, however, it is possible to increase the filament current at choice. An embodiment suitable for this purpose is shown in FIG. 4. Leaving the resistor 18 out of consideration for the time being, the resistor 13 is partly bridged by a diode 17. This causes the ignition moments of the switch element 10 to be different in each half cycle, as shown, by way of example, in FIG. 5D. As a result, the choke coil 4 is loaded "asymmetrically", in the sense that it is unidirectionally driven to saturation, and consequently provides a lower impedance and allows a higher filament current. Moreover, due to the lower impedance, phase-shifting between current and voltage will begin to vary. Therefore, the moments when the switch element is non-conductive will begin to shift in each half cycle. This means that the ignition voltage across the tube will also be shifting as viewed in the cycles.

It is thus possible to realize an igniter which, at a substantial filament current causes an ignition voltage to be generated across the tube and to be varied in width and place. Important in the selection of the dimensions of the components is the difference in attenuation between positive and negative sine halves. For the attenuation is accomplished by the resistor-capacitor combinations which are parallel to the switch element 10 and hence parallel to the tube. This asymmetry is beneficial for the ignition of the tube.

By providing a resistor 18, parallel to the capacitor 14, it is achieved that the light intensity of the tube is periodically (e.g. each second) decreased for a short time. For this purpose the resistor must have high resistance values (in excess of 1 M .OMEGA. ). The embodiment is then excellently suitable for advertising objects. FIG. 7 illustrates a circuit arranged which in an alternative manner causes the choke coil 4 to be "assymmetrically" excited. The triode A.C. semiconductor element 10 is in this instance replaced by the series connection of two parallel-circuits, one of which comprises a triode semiconductor switch element 18, such as a thyristor with a diode connected in parallel therewith, the direction of conductivity of which is opposite to that of the switch element 18. The other parallel-circuit is constituted by a capacitor 20 and a diode 21, the direction of conductivity of which is opposite to diode 19. The igniter of the switch element 18 again includes components 22, 23 and 24. Resistor 22 is series-connected with capacitor 14, the other end of 22 being connected through resistor 23 with terminal B, on the one hand, and through resistor 24 with the node of the two parallel-circuits, on the other.

Supposing that there is no resistor 24, the following occurs when an inductive auxiliary device is included, i.e. just employing choke coil 4 or capacitive compensation by means of a parallel capacitor 7. Diode 19 will in the first instance charge capacitor 20 (see FIG. 8). Switch element 18 can now be triggered in the same manner as switch element 10 in FIG. 2.

When capacitor 20 has just been discharged, its current will have the maximum value. This current is then taken over by the diode 21 and is further only determined by choke coil 4 and the filament resistance.

It will be clear that this makes it possible to select filament currents ranging between about 0.5 and 1.5 amps. The ignition of the tube is effected in a similar manner to the arrangement of FIG. 2. Here again, the remarkable feature is the difference in attenuation between the two halves of the voltage. In order that the starter may also be used for tubes provided with series capacitor compensation, the resistor 24 is provided.

The formation present at the node of the two parallel-circuits is required to level out the differences in phase-shifting between the two fundamentally different auxiliary devices.

By suitably selecting resistors 22, 23 and 24, there is provided a starter which is suitable for inductive and capacitive auxiliary devices.

Claims

I claim

1. An igniter device for use with a gas discharge tube having filament means which must be brought up to operating temperature before the tube may conduct current, a source of alternating current driving said tube, and means for controlling current through said tube once same is ignited, the igniter device comprising, in combination:

gate-controlled semiconductor switching means for effecting heating of the filament means to initiate current conduction by the tube and thereafter to remain in non-conductive state, said switching means having a gate electrode and having a current-conducting path adapted to connect the filament means in series with the source whereby said switching means is self-extinguishing at every zero crossing of the source; and

control means connected to said gate electrode for causing the switching means to conduct during half cycles of the source until the tube is ignited and thereafter to be ineffective to cause conduction of said switching means during current conduction by the tube, said control means comprising a semiconductor switching diode, and a voltage divider circuit connected in parallel with said switching means, said voltage dividing circuit including first capacitor means for causing conduction of said switching diode when the tube is not conducting and second capacitor means in series with said first capacitor means for maintaining the juncture between said first and second capacitor means below that value of voltage effective to cause conduction of said switching diode when the tube is conducting, said switching diode being connected between said juncture and said gate electrode.

2. A device according to claim 1, wherein one branch of the voltage divider comprises a first impedance formed by a resistor (13) and a capacitor (14), series-connected therewith, and a second impedance, constituted by a resistor (16) and a capacitor (15), parallel-connected therewith, said second impedance being series-connected with said first impedance, and the other branch exclusively comprises a capacitor (12).

3. A device according to claim 1, wherein one branch of the voltage divider comprises a series-circuit constituted by a resistor (13) and a capacitor (14), and the other branch exclusively comprises a capacitor (12).

4. A device according to claim 1, wherein one branch of the voltage divider comprises a first impedance formed by a resistor (13) and a capacitor (14), series-connected therewith, and a second impedance, constituted by a resistor (16) and a capacitor (15), parallel-connected therewith, said second impedance being series-connected with said first impedance, and the other branch exclusively comprises a capacitor (12).

5. A device according to claim 1, wherein one branch of the voltage divider comprises a resistor (13), part of which is bridged by a diode (17), said resistor (13) being series-connected with a capacitor (14), the other branch exclusively comprising a capacitor (12).

6. A device according to claim 5, wherein a resistor (18) is parallel-connected with said capacitor (14).

7. A device according to claim 4, in which said semiconductor switching means is constituted by a thyristor and a diode parallel-connected therewith, said diode being so connected that its direction of conductivity is opposite to that of the thyristor, and an impedance, series-connected therewith and constituted by a diode, the direction of conductivity of which is the same as that of said thyristor, and a capacitor parallel-connected therewith.

8. A device according to claim 7, wherein a resistor (24) is connected between the node of said impedance and the parallel-connected diode and thyristor, on the one hand, and a tap of said resistor (13), on the other.

9. In a device according to claim 1, a gas discharge tube including one of a series coil per se, a series coil and a series capacitor. and a series coil and a parallel capacitor.