The present invention concerns a control device for a converter- current valve for operating a gas discharge tube from a D.C- source, . which converter-current valve comprises a transformer across the secon¬ dary winding, of which the gas discharge tube is connected and across the primary winding of which an RC-circuit is connected in series with the base-collector circuit of a-power transistor. The emitter of the power transistor is connected to the ground pole of the D.C. source, while a tap on.-the .primary winding..is connected to the plus pole of the D.C. source, which tap divides the primary winding into an opera-

> ting winding and a feed-back winding for the RC-circuit.

A converter-current valve of this kind is made known from e.g. Swedish Patent Application No 8001853-4.

By this known converter-current valve, the only possibility to control the light flux from the gas discharge tube is to modify either the voltage of the D.C. source, or the length of the gas discharge tube, which, however, is disadvantageous, as you in many cases may wish to control the light flux from the gas discharge tube with a • retained high conversion efficiency. The light table may exemplify such _. applications. The object of the present invention is thus to produce a simple, inexpensive and practically lossless control device for controlling the light flux of a gas discharge tube.

This is achieved, according to the invention in the previously mentioned converter-Current valve, in that the control device com- prises a transistor, the collector of which is connected to the inter¬ connection point between the RC-circuit and the base of the power ^• transistor, and the emitter of which:,is.^connected to ^' -thε ground pole of the D.C. source, and the base of which is connected to a control pulse source for emitting rectangular pulses for controlling the light flux of the gas discharge tube in dependence of the pulse ratio of the pulses emitted from the control pulse source.

The invention is described below more in detail, with reference to attached drawing, on which Fig. 1 shows a circuit diagram of a known converter-current valve with a control device according to the present invention,.-.and Figs. 2a and 2b show curves appearing in dif¬ ferent points in the circuit as per Fig. 1.

The circuit marked 1 in Fig. 1 comprises the converter-current

converter-current valve comprises a transformer across the seconda winding D of which the gas .discharge tube LR is connected, and acr the primary winding B, C of which an RC-circuit A in series with t base-collector circuit of a power transistor T. is connected, the emitter of the power transistor T. is connected to the ground pole of the D.C. source, while a tap on the primary winding B, C of the ^• transformer is connected to the plus pole, the tap of which divide the primary winding into one operating winding B and one. feed-back winding C for the RC-circuit A. The RC-circuit A comprises a capac tor A-,, which is connected in parallel with a resistor A^.

The converter-current valve generates pulses of type as per Fig. 2a for operating the gas discharge tube LR with a constant li flux.

To control the light flux of the gas discharge tube LR, a co trol device 2, according to the present invention, is connected to the converter-current valve _. 1. The control device 2 comprises a tr sistor T„, the collector of which is connected to the interconnect point between the RC-circuit A and the base of the power transistor and the emitter of which is connected to the ground pole of the D. source and the base of which is connected to a control pulse sourc (not shown in detail) via a resistor R.. The ^" base of transistor T„ is also connected to the ground pole of the D.C. source via a. resis tor R~. The resistor R_. is intended to protect the transistor T_, resistor R-> ensures a complete cut-off of the transistor T-. The control pulse source S (not shown in detail) is adapted emit rectangular pulses of type shown in Fig. 2b.

When these pulses are applied to the base b of transistor T _? , this transistor will become conducting, and-fche interconnection poi between the RC-circuit A and the power transistor T. will be ground via the emitter-collector circuit of transistor T„. During the time these pulses appear on the base of transistor T„, no pulses will ap on the collector a of power transistor T. , apparent from Fig. 2a, a consequently the fluorescent tube LR will be turned off.

By varying the pulse width and the pulse distance, i.e. the pulse ratio of the pulses that are emitted by the control pulse sou S, the light flux of the ^" gas discharge tube LR may thus be varied i a simple and inexpensive way.

When the output signal level.of the control pulse source on t base of transistor T~ is constantly low, there will thus be a maxim

light flux from the gas discharge tube LR, while the gas discharge tube LR will be completely turned off when the output signal level of the control pulse source is constantly high.

The control device according to the invention may thus be used both to start and to turn off a gas discharge tube, as well as to control its light flux,,in dependence of the pulse ratio of the pulses emitted by the control pulse source. _

Apart from its application for light tables, as mentioned in the beginning of this description, the control device, according to the invention, may be applied in e.g. neon tubes formed as letters, nume¬ rals and/or figures;. ^*1 The neon tubes may, for example, be arranged to illuminate from below dance floors in e.g. discoteques. It is also possible to freeze such neon tubes in the ice on ice-hockey or bandy grounds for advertising purposes. If the control pulse source S con- sists of a microphone connected to an analog-to-digital converter, it is furthermore possible to transfer speech information via the gas discharge tube, which speech information may be converted into audible sound by means of e.g. a photo.transistor and a digital-to-analog con¬ verter connected to a loud speaker.