The present patent application relates to a transforming device for cold cathode lighting tubes charged with neon or argon or mixed gases, that is capable of controlling and changing the intensity of the current that circulates in the tubes by means of a suitable electronic circuit, so that the current value remains always equal, or approximately equal, to the set reference value within the tolerance range.

To better understand and appreciate the advantages offered by the transforming device according to the present invention, it is necessary to describe the functional limits of the currently available models of transformers for cold cathode lighting tubes charged with gas, of the type universally used in luminous signs.

This type of lamps must be powered with high voltage, approximately from 1,000 to 15,000 Volt, and therefore need a transformer capable of generating the high voltage necessary to lit the tubes from the low voltage (220 Volt) of the electrical mains.

It must be noted, however, that the good operation of these lamps depends on the current used to power them, meaning that the intensity value must be exact and constant in time, within a very strict tolerance range.

On the other hand, the current generated on the secondary winding (the high voltage winding) of the transformer depends on the length and diameter of the lighting tubes, as well as on the gas contained inside the tubes.

This means that each time a suitable transformer must be designed according to the geometrical dimensions and type of the tubes used.

Currently, transformers usually feature a fixed magnetic shunt, capable of automatically setting off the voltage variations on the secondary winding of the transformer caused by small load or voltage variations in the electrical mains.

In any case, although the transformer is specifically designed for each lighting installation, during installation specialised technicians need to calibrate the current of the secondary winding, using sophisticated, expensive measurement and calibration instruments.

A second calibration would be necessary after some time, in order to complete the mercury migration on the electrodes, which determines the current that circulates on the secondary winding of the transformer, as mentioned above.

Most of the times, however, the second calibration is not carried out, thus causing the maifunctioning of the lighting installation.

In any case, the most frequent disadvantages of the current transformers are: -overpowering, with risk of burning, of the transformer because of the higher intensity of the current with respect to the rated value ; -flickering of the tubes due to the use of a transformer that it not suitable for the characteristics of the lighting installation or to the considerable variations in the line voltage that cannot be set off by the magnetic shunt.

Some of the models currently available on the market feature a sliding magnetic shunt-instead of a fixed one-capable of being manually inserted in the transformer core according to the specific requirements, in order to adjust the current value on the secondary winding and, consequently, the value of the current that circulates in the tubes.

This solution eliminates the need of designing a suitable transformer for each lighting installation, since the same model of transformer can be used in installations with different characteristics thanks to the wide adjustment and caiibration range allowed by the mobility of the magnetic shunt.

This type of transformers with mobile magnetic shunt, however, are not totally satisfactory, since they leave some problems unsolved, and at the same time feature some disadvantages.

More specifically, the use of transformers with mobile magnetic shunt: -requires to carry out the first calibration when the transformer is installed ; -requires to carry out the second caiibration ; -is often associated with the annoying noise caused by the vibrations of the

mobile magnetic shunt due to the frequency of the alternate current from the mains.

In view of the above, a transforming device has been devised, capable of controlling and changing the intensity of the current that circulates in the tubes by means of a suitable electronic circuit, so that the current value remains always equal, or approximately equal, to the set reference value within the tolerance range.

In other words, the electronic circuit is capable of automatically changing the intensity of the current that circulates in the tubes as necessary, according to the set reference value.

This means that the transforming device according to the present invention is capable of self-calibrating during installation according to the characteristics of the lighting tubes used. At the same time, it is also capable of setting off all the variations of the current that circulates in the tubes during operation, whatever their cause is, such as a load or voltage variation in the electrical mains.

Multiple alternative constructive solutions exist within the scope of the present invention, all of them capable of automatically changing the current that circulates in the tubes.

The first technical solution includes a device that is installed before the transformer and capable of changing the voltage on the primary winding of the transformer.

The second technical solution, instead, includes a device installed after the transformer and capable of changing the current that circulates in the tubes.

Both solutions include a device used to measure the current that circulates in the tubes and send the measurement value to a control circuit. In the first solution, if necessary, the control circuit enables the device capable of changing the voltage on the primary winding of the transformer; while in the second solution, it enables the device capable of changing the current that circulates in the tubes.

A third constructive solution exists, that is conceptually identical to the first one, with the only difference that the measurement device

measures the current that circulates in the primary winding.

For major clarity the description of the transforming device according to the present invention continues with reference to the enclosed drawing, which is intended for purposes of illustration and not in a limiting sense, whereby: -Figure 1 is a block diagram that shows the transforming device according to the present invention, in its preferred embodiment; -Figure 2 is a block diagram that shows the transforming device according to the present invention, in its second embodiment; -Figure 3 is a block diagram that shows the transforming device according to the present invention in its third embodiment.

With reference to Figure 1, it must be noted that the transforming device according to the present invention uses a traditional transformer (1) made up of the core (N), the primary winding (P) and the secondary winding (S).

The electronic circuit associated with the transformer (1) includes : -a unit (2) used to measure the current that circulates on the secondary winding (S), that preferably consists in a current transformer positioned between the tubes (T) and the secondary winding (S); -a power circuit (3) positioned between the electrical mains (R) and the primary winding (P), that is capable of changing the voltage on the primary winding (P) upon request; -a controi circuit (4) capable of comparing the current value measured by the device (2) with the memorised reference value and changing the voltage on the primary winding (P) by means of the power circuit (3), if necessary.

The operation of the electronic circuit is based on the fact that the control circuit (4) is capable of automatically enabling the power circuit (3) whenever the value of the current that circulates in the tubes (T) is not equal to the set value, so that the voltage of the primary winding (P) of the transformer (1) is capable of generating a current on the secondary winding (S), whose value is equal to the reference value that is set and memorised in the control circuit (4).

The technical solution illustrated in Figure 2 differs from the one shown in Figure 1 in the absence of the power circuit (3) positioned before the

transformer (1) and in the presence of a current adjustment device (5) positioned between the transformer (1) and the measurement unit (2); it being provided that the control circuit (4) is capable of enabling the device (5) whenever the current value measured by the device (2) is not equal to the memorised reference value.

The technical solution illustrated in Figure 3 differs from the one shown in Figure 1 only in the different location of the measurement unit (2), which is positioned before the transformer (1) in order to measure the current that circulates on the primary winding of the transformer.

The third solution is more economic than the first one, in that it uses a simple resistance as measurement unit (2). As a matter of fact, the resistance cannot be used in the first and second solution since in these cases the reading is carried out directly on the secondary winding, which must be earthed, as required by safety regulations.

Therefore, the first solution requires the use of a more expensive current transformer as measurement unit (2).

As regards the control circuit (4), it must be noted that it can be of either analogue or digital type.

Although more expensive, a digital control circuit (4) can provide additional functions by simply changing the software, without the need of modifying the circuit or the components.