Circuit For Operation Of Gas Discharge Lamps

Abstract

Circuit arrangement for operating gas discharge lamps having a feed voltage and firing current, both combined into a voltage multiplier circuit consisting of a number of series connected doubler steps.

Parent Case Text

This is a continuation of application Ser. No. 870,592, filed Aug. 13, 1970 and now abandoned.

Description

Gas discharge lamps, generally speaking, require a relatively high voltage for firing, while the conducting voltage is comparatively low. Normally a constant current transformer is used for feeding current; the transformer secondary winding supplying the high-firing voltage. The secondary winding, on the other hand, must provide excitation over the complete light performance range of the gas discharge lamp which also includes the requirement of a low conducting voltage. Such a transformer is therefore constructed to be overrated and is thus expensive and has large physical dimensions.

In order to lower the firing voltage requirements, hot electrodes have been used in many cases. With the use of special measures, for example, by interruption of the current heating the hot electrodes with the aid of glow starter switches, it is possible to produce a voltage surge of sufficient strength which will induce the firing of the lamp, even where the gas discharge lamp is energized from a grid by means of series reactors. The hot electrodes, however, are sensitive and considerably reduce the operating life of the gas discharge lamp. The glow starter switches are also especially sensitive and therefore subject to faults and have to be exchanged several times within the life of the gas discharge lamp. The flickering of the light, which occurs during the switching on of the lamp, is also objectionable.

A circuit arrangement for the operation of gas discharge lamps has been known using a supply circuit dimensioned for the conducting voltage and the conducting current and at least one firing voltage supplying a high voltage and having a weaker performance, whereby the supply circuit and firing circuit are voltage multiplier circuits built up of rectifier diodes and capacitors. This circuit avoids the disadvantages of the previously mentioned circuit arrangement and it is suitable particularly for gas discharge lamps, especially for gas discharge lamps with cold electrodes.

An important feature of the present invention is that the supply circuit and the firing circuit are combined into a voltage multiplier circuit comprising several series of connected voltage doubler steps. The capacitors of the individual firing voltage circuit stages are preferably selected to have a lower capacity in relation to the capacitors of the supply circuit stage or stages while the diodes of all stages are primarily selected to have a high constant current rating. It is also possible to add one or several voltage doubler stages to the basic firing circuit stage or stages.

The circuit arrangement according to the invention can be produced relatively inexpensively and by varying the capacitance values of the capacitors of the individual stages different voltage-current output characteristics are obtainable.

The invention will be more fully understood with the following description of an exemplary embodiment with the aid of the drawings by way of a design given as an example, and in which:

FIG. 1 is a circuit arrangement according to the invention, composed of five voltage doubler stages, and

FIGS. 2 to 4 are graphs each representing different voltage-current output characteristic of the circuit of FIG. 1 for different capacitance values of the voltage doubler stages.

In FIG. 1 a circuit arrangement according to the invention is illustrated which comprises five voltage doubler stages each individually being known to the art kind. Input terminals 10, 11 are connected to an alternating current power source (not shown) D.C. current output terminals 12, 13 are connected to a gas discharge lamp load which may include if necessary a stabilizing impedance.

The circuit arrangement shown supplies an output D.C. current of 2 n .times. 220 .times. .sqroot. 2 (volts) whereby n is the number of voltage doubler stages and the A.C. voltage input is assumed to be 220 volts. In the present case, for the purposes of describing the invention there are five stages that the circuit shown will supply a voltage of

10 .times. 220 .times. .sqroot. 2 = 3,120 V

At the same time, the slope of the output voltage-current characteristic curve depends on the capacitance of the capacitors used.

In the circuit shown in FIG. 1, the supply circuit stage consists, for example, of the two rectifier diodes 14a and 14b and the capacitors 15a and 15b. This stage supplies a voltage of 2 .times. 220 .times. .sqroot. 2 = 624 V.

The series-connected fining circuit stages contain the rectifier diodes and capacitors 16a to 23a and 16b to 23b. The capacitors 17a, 19a, 21a, 23a and 17b, 19b, 21b, and 23b have a lower capacity than the capacitors 15a and 15b of the supply circuit stage. The diodes of all stages, however, are selected for the highest permissible operating current since this current passes through all of them.

A circuit arrangement of the kind described can have, for example, the characteristic curve shown in FIG. 2. As long as the gas discharge lamp has not been fired, the circuit at the current "O" supplies a very high voltage which causes the firing of the gas discharge lamp. After the firing, the internal resistance of the gas discharge lamp decreases considerably so that the current will rise substantially. The voltage on the capacitors 17a, b, 19a, b, 21a, b and 23a, b collapses considerably so that the output voltage will essentially be determined by the voltage at the capacitors 15a and 15b, which have greater capacitance.

It is also possible to make the capacity of the series-connected firing voltage stages 31 to 34, which follow the feed circuit stages 30, so that the starting characteristic of the entire circuit will have sections of varying slopes. For example, the capacitors of the stages 31 and 32 may be provided with a decreased capacity, as compared to the capacitors 15a and 15b of the stage 30, while the stages 33 and 34 may be equipped with capacitors of a still further decreased capacity as a result of which the starting characteristic curve shown in FIG. 3 will result.

In the case of gas discharge lamps which, for a short time require a higher firing energy at a high firing voltage, the last step 34, for example, can be equipped with capacitors 23a and 23b of a relatively large capacity, as a result of which a relatively high current at high voltage can flow for a short time until the charge of the capacitor has been reduced. FIG. 4 shows the corresponding starting characteristic curve.

The stabilization of the discharge current necessary for the gas discharge is achieved in the case of the circuits of the foregoing mentioned type essentially by the fact that the voltage at the capacitors collapses with the discharge of current into the gas discharge lamp load. In case this stabilization alone is not sufficient, an additional ohmic dropping resistor, or an inductor may be provided in a manner known per se for the additional necessary stabilization and for the filtering of the load current. It is also possible to combine the resistor and the inductor.

The circuit arrangement according to the invention is usable not only exclusively for gas discharge lamps since it is usable, in principle, for all D. C. current load consumption which requires a more or less high limitation of current and an open-circuit voltage, which is high in comparison to the operating voltage as is the case especially with gas discharge lamps.

Claims

We claim:

1. An AC to DC converter for driving a gas discharge lamp type load from an AC source, comprising:

at least one first circuit connected to said AC source for generating a first voltage output which is a multiple of the peak voltage of said AC source,

at least one second circuit connected to said AC source and to the output of said at least one first circuit for generating a second voltage output which is a multiple of said first voltage output,

at least one third circuit connected to said AC source and to said second voltage output for generating a third voltage output which is a multiple of said second voltage output, said at least third circuit including output terminals for driving said load,

said at least one first circuit comprises first and second rectifying elements connected to one terminal of said AC source for respectively rectifying alternate half cycles of said AC source, and first and second capacitor elements respectively connected from the output of said first and second rectifying elements to the other terminal of said AC source,

said at least one second circuit comprises third and fourth rectifying elements respectively connected to the output of said first and second rectifying elements for respectively rectifying the same alternate half cycles of said AC source as said first and second rectifying elements, and third and fourth capacitor elements respectively connected from the output of said third and fourth rectifying elements to said one AC source terminal,

said at least one third circuit comprises fifth and sixth rectifying elements respectively connected to the output of said third and fourth rectifying elements for respectively rectifying the same alternate half cycles of said AC source as said third and fourth rectifying elements, and fifth and sixth capacitor elements respectively connected from the output of said fifth and sixth rectifying elements to said other AC source terminal,

the capacitance of said first and second capacitor elements is equal, the capacitance of said third and fourth capacitor elements is equal, and the capacitance of said fifth and sixth capacitor elements is equal, and

the capacitance of said fifth and sixth capacitor elements is less than the capacitance of said third and fourth capacitor elements, and the capacitance of said third and fourth capacitor elements is less than the capacitance of said first and second capacitor elements.

2. An AC to DC converter as in claim 1 wherein said at least said first, second and third circuits total n in number and wherein the DC output voltage is 2n E.sub.eff .sqroot. 2, wherein n is equal to or greater than 2 and E.sub.eff is the effective voltage of said AC source.