The invention relates to a converter system and a power pack for converting a D. C. input voltage into a D. C. output voltage, in particular for switched-mode power packs of devices in entertainment electronics, e. g. TV and audio devices, or chargers for mobile communications units of the GSM Global System for Mobile communications network.

Fig. 3 shows a converter module known from the state of the art. It has two input connections 1 and 2 for application of an individual input voltage V 1 and two output connections 3 and 4 for output of an individual D. C. output voltage V2. In addition it has a control input 6 to receive a control signal which influences the energy transfer behavior of the converter module, e. g. by modifying the pulse-duty factor of a power transistor in the converter module. The converter module also has a control output 5 which emits a control signal e. g. to control further converters. Such converter modules are available for wide ranges of D. C. input voltages and D. C. output voltages and also for a broad spectrum of power levels.

Modern converter systems or switched-mode power packs usually have only one such converter module to supply a particular consumer e. g. a TV. The converter module must supply the entire power for the consumer. The voltages to be processed by the converter module then correspond essentially to the D. C. input voltage of the converter system and the voltages which the consumer requires. This procedure allows the converter system to be produced with as few components as possible, which according to the present state of the art is usually the cheapest and most compact solution.

If necessary the power of a converter system is increased in that several similar converter modules (10-1.... 10-6) are connected in parallel on the input and output sides, as shown simplified in Fig. 4. Such converter systems are used in installations of telecommunications technology where complex control procedures guarantee an even division of the power to the individual converter modules.

However it must be accepted that the suitable switching frequencies cannot be very high, usually these are no higher than a few hundred kilohertz, in particular if either higher voltages or higher power levels occur. Higher switching frequencies, however, would allow further size and cost reduction of the individual converter modules and hence the entire

converter system. However, according to the current state of the art this is possible only in converter modules for low voltages and power levels, as power semiconductors which allow high voltages and currents and simultaneously high switching frequencies are not available economically. A further obstacle is the line-borne interference to be expected, in particular the common-mode interference, which increases further with the frequency and voltage to be switched.

Starting from this state of the art, the object of the invention is to refine a known converter system and known power pack, so that they can be used even at higher voltages and power levels for very high switching frequencies.

The object is achieved according to the subject matter of claim 1 in that at least two of the converter modules (10-1.... 10-6), of which at least one has a positive input impedance, are connected together in series on the input side.

This object is achieved according to the subject matter of claim 9 in that at least two of the converter modules (10-1..... 10-6), of which at least one has a positive output impedance, are connected together in series on the output side.

Such connection of the individual converter modules has the advantage that the individual converter modules no longer need to process high power levels but in particular also no high voltage levels. With a series connection of converter modules on the input side, the input voltage of the converter system is divided evenly over the individual converter modules. With a series connection on the output side, the output voltage of the converter system is divided evenly over the individual converter modules.

This structure of the converter system according to the invention is based on the fundamental principle of keeping away from the individual converter modules the high voltages and power levels damaging to the use of the high switching frequency. This is achieved in particular in that at the input or output from the converter system i. e. where high voltages would occur, the individual converter modules are connected in series leading to a voltage division. For power packs supplying a consumer from the mains supply, the higher voltages usually occur at the input to the converter system. The high voltages occur at the output of the converter system if a high output voltage is required there. This also means that an individual converter module need only transfer a fraction of the total power.

Because of the low power and high switching frequency, such converter modules can be produced particularly small and compact, and it is even possible to integrate the necessary inductive elements whereby a particularly simple and hence cheap production process is possible. Due to the large number of individual modules used in such a system,

mass production can be achieved particularly advantageously if the system consists only of the same type of converter modules. Production with integrated components also achieves a very high packing density.

The multiplicity of converter modules used would be preferably arranged spatially in one plane, whereby the height of the total system is extremely low and the loss power of the system can easily be dissipated over the large area. Depending on the connections used, various configurations can be achieved: parallel connection of outputs gives low voltages with high currents, series connection gives high voltages with low currents. There is therefore a type of module with which different requirements can be fulfilled with corresponding connection of the suitable number of converter modules, without the individual converter modules needing to have other properties. Thus a wide range of requirements can be covered with just a single module type.

To increase the overall power, the arrangements described previously can also be connected as a whole as multiple parallel. Such partly parallel and series connected arrangements allow the requirements of quite different applications to be fulfilled without the need to develop a special converter module.

The essential feature however is that by the selected connection, the voltages at both the input and output of each individual converter module can be kept low, i. e. in relation to the former state of the art at least on one side of the converter system a series connection is used. As a direct result, however, the problem arises of voltage distribution to the individual converter modules. The voltage distribution over the individual converters must be prevented from becoming uneven or even unstable due to unavoidable parameter spread. This behavior occurs, for example, with the use of commercial voltage-regulated converter modules with series connection on the input side and parallel connection on the output side. Even if all converter modules are structured so that in independent operation they set precisely the same D. C. output voltage, for example a transitory interference leading to a short-term increase in current on the input side can cause the D. C. input voltage of the converter module concerned to fall. This is unavoidable in a series connection.

A control system implemented in the converter module, however, leads to a retention of power consumption of the converter module causing a further increase in input current. Consequently, the input voltage falls further until a value is set at which the converter module fails. For the reliability of such systems with series connection it is therefore necessary for the converter module to have suitable energy transfer characteristics such that on deviations from an even distribution, the corresponding currents will change in a

stabilizing manner. This requires the converter modules connected in series on the input side to have a positive input impedance and those connected in series on the output side to have a positive output impedance. Converter modules with conventional control systems, however, have a negative impedance at least on the input side, which makes them unsuitable for use in converter systems according to the invention. Suitable switched-mode power packs for this converter system are, for example, flow converters with a preset pulse duty factor; unsuitable elements, are for example self-heterodyning blocking oscillators with preset nominal current.

To allow simple series connection, the inputs and outputs must be potential- free to each other i. e. the converter must contain a potential separation. Therefore, simple up- converters or down-converters are not suitable.

According to a first preferred embodiment of the invention the input side link between at least two converter modules is arranged as a series circuit. This linking allows the processing of a high D. C. system input voltage where the D. C. input voltage then active for one converter module only amounts to a fraction of this voltage. This allows the use of power semiconductors at high switching frequency and a simultaneous reduction in high frequency interference.

If instead, for a low preset D. C. system input voltage, a high D. C. output voltage is required, the system can be reversed i. e. on the input side a parallel connection is provided and on the output side a series connection of converter modules.

Further advantageous embodiments of the converter system are the dependent claims of the sub-claims. The embodiments of the converter system given in dependent claims 4-8 with at least partly a series connection of the converter modules on the input side apply accordingly also to the converter system with at least partly a series connection of the converter modules on the output side as claimed in claims 9 and 10.

This object is further achieved by a power pack as claimed in claim 12. The advantages of this power pack correspond to the advantages described above of the converter system in its various embodiments.

The invention will be further described with reference to examples of embodiments shown in the drawings to which however the invention is not restricted.

Fig. 1 shows a converter system according to the invention.

Fig. 2 shows a power pack according to the invention.

Fig. 3 shows an individual converter according to the state of the art ; and

Fig. 4 shows a converter system according to the state of the art.

A description is given below of preferred embodiments of the converter system according to the invention with reference to Figs. 1 and 2.

Fig. 1 shows a converter system 10 for converting a D. C. input voltage V1 into a D. C. output voltage V2. The D. C. input voltage V 1 can even be destabilized. The converter system comprises six converter modules 10-1... 10-6 all connected on the input side in series via connecting lines 12-1... 12-5. The D. C. input voltage V1 of the converter system is applied via the series connection of these six converter modules 10-1... 10-6, so that each converter module receives as its effective input voltage V1.... V6 one sixth of the D. C. input voltage V 1 of the converter system 10. On the output side the converter modules 10-1,10-2 and 10-3 are connected in parallel via connecting lines 14-1 and 14-2 and form a first module group. Because of the parallel connection, the individual output voltages V2-1,... V2-3 of converter modules 10-1... 10-3 are equally large. Similarly, the converter modules 10-4...

10-6 are connected in parallel via connecting lines 14-3 and 14-4 and form a second group; this group too has equal individual D. C. output voltages. The parallel connection into a group of three converter modules allows the achievement of a system output current which is three times as great as the maximum current of an individual converter module.

The output side series connection of the two groups via a connecting line 16 allows to double the system D. C. output voltage in comparison with the D. C. output voltage of an individual converter module.

The converter system 10 also has a differential amplifier 18 which emits a control signal in the form of an impressed current to the first converter module 10-6 connected in series. The control signal in the form of an impressed current is particularly advantageous as it is not sensitive to potential differences between transmitter and receiver of the signal and hence guarantees correct transfer of control information even if these potential differences change. This control signal is formed according to the conventional control technology process from the difference between the actual output voltage V2 of the converter and a preset nominal value Vref.

The control signal is used to adapt the energy transfer behavior of the individual converter modules. It is first supplied to converter module 10-6. This regenerates the control signal and passes it via connecting line 19-5 to the next converter module 10-5.

The procedure for regenerating the control signal and transferring it via connecting lines

19-4... 19-1 is then repeated in converter modules 10-4,10-3 and 10-2. Finally the signal reaches converter module 10-1 and has thus overcome the entire input potential difference.

Thus the transfer behavior of all converter modules is controlled in the same way. This achieves an even division of power to all converter modules.

Because of the compact structure of the individual converter modules, the low switching voltages and low capacitative coupling of the transformers, common mode interference in the converter system is considerably less than in individual converter modules with the same switching frequency.

As the switching frequencies of the individual converter modules in the converter system are not synchronized, in practice differences arise between the switching frequencies of the individual converters. This has the effect that consequently the interference levels of the individual converter modules accumulate no longer linearly but geometrically.

Thus the increase in interference power of the converter system is only linear with the power, in contrast to an individual converter module in which the interference power increase is quadratic in relation to the useful power.

Consequently the necessary filters for observation of the interference suppression regulations may be smaller and in certain cases even omitted completely.

According to an example of embodiment not shown, the power to be transferred by the converter system is 30-50 W. Thus the individual input voltages Vl-n for n=10 converter modules in each case are approx. 10 V, so that with a series connection of the ten converter modules on the input side a D. C. input voltage of approx. 100 V can be processed. The D. C. output voltage of the individual converter modules in this example is between 5 and 12 V.

Fig. 2 shows a switched-mode power pack according to the invention for converting an A. C. input voltage VO into a D. C. output voltage V2. It comprises a rectifier circuit 20 for converting the A. C. voltage VO into a smoothed but possibly unstable D. C. voltage V 1. This D. C. voltage supplies the converter system 10 according to the invention, which converts the D. C. voltage V1 into a D. C. output voltage V2.