Abstract:
A voltage conversion device is disclosed which is to be used particularly in motor vehicles. For voltage conversion, a plurality of small voltage converters are connected as partial converters parallel to one another. By sequentially turning on the individual partial converters and superposition of the output current, a uniform output current at low input load is attained.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a voltage conversion device, particularly for motor vehicles, and especially a voltage conversion device for a motor vehicle, which includes at least two parallel-connected voltage converters with a common input via which the voltage to be converted is supplied and with a common output at which the converted voltage is picked up. 
     2. Prior Art 
     In voltage supply systems, for instance in motor vehicles, the usual on-board electrical voltage is varied, with the aid of direct voltage converters, in such a way that voltages which are optimal to supply the consumers are obtained. One such voltage supply system for an on-board motor vehicle electrical system is known for instance from European Patent Disclosure EP-0 363 356 B1. In this voltage supply system, a plurality of direct voltage converters decoupled on the secondary side are present, whose input is supplied with the battery voltage. On the output side, the voltage converters lead via decoupling diodes to various electronic components, which they supply with a regulated direct voltage. The use of a plurality of direct voltage converters to generate a single output voltage is not contemplated in the known voltage supply system. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide an improved voltage conversion device, especially for a motor vehicle. 
     This object, and others which will be made more apparent hereinafter, is attained in a voltage conversion device comprising at least two voltage converters connected in parallel with each other, having a common input at which a voltage to be converted is supplied and a common output at which an output converted voltage is delivered. 
     The voltage conversion device of the invention has the advantage over known devices that a voltage conversion is attained which has little load variations on the supply current. This advantageously assures that the supply current causes only little electromagnetic emission, and in general only slight supply fluctuations occur. Also advantageously, output current fluctuations are reduced compared with conventional systems, so that again only slight electromagnetic emission is produced by the output current, and only slight output current fluctuations occur. Since the individual load on the components used is low, an advantageous embodiment with small available, economical components is possible. A technologically complex parallel circuit, for instance using additional resistors with parallel-connected diodes, can be dispensed with. 
     These advantages are attained by using, instead of a single voltage converter, a selectable number of parallel-connected partial converters, which are synchronously sequentially triggered with the aid of a synchronizing device. 
     Further advantages of the invention are attained by the characteristics recited in the dependent claims. It is especially advantageous that depending on the needs and/or expense, partial converters that each have one complete regulator part and power part can be used. It is also possible to design the partial converters such that one partial converter has a complete regulator part and power part, while the other partial converter has only its own power parts and is triggered by a common controller. 
     In another advantageous feature, only a single regulator component is required, whose high switching frequency is distributed to various parallel power parts via a multiplexer that then drives the individual power parts. This makes maximum correction possible with little regulation expense and complication. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     Exemplary embodiments of the invention are shown in the drawing and will be described in further detail in the ensuing description. Specifically, FIGS. 1, 2 and 3 are block diagrams three different exemplary embodiments. In FIG. 4, a timing graph is shown for the multiplexing operation of the third exemplary embodiment. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In FIG. 1, a first exemplary embodiment of the invention is shown. In this exemplary embodiment, the voltage converter is divided up into a plurality of separate regulators 10a, 10b, 10c, . . . , 10n and associated power parts 11a, 11b, 11c, . . . , 11n. Triggering of the regulator is done with the aid of a synchronizing device 12. The power parts 11a, 11b, 11c, . . . , 11n are connected to one another at their outputs and lead to the load 14 that is to be supplied. The voltage U to be regulated or converted is supplied to the various power parts. At the outputs of the various power parts, the currents I a , I b , I c , etc. occur, whose courses over time are also plotted in FIG. 1. 
     With the voltage converter shown in FIG. 1, which includes a plurality of complete regulators as well as a plurality of complete power parts each forming one partial converter, the supply current load and the alternating output current level can both be reduced, compared to a voltage converter which includes only one regulator one power part, each with at least one switching transistor. Since the power parts are connected parallel, when the individual partial converters, each comprising one regulator on one power part, are sequentially turned on, an output current can be attained that represents one brief current pulse for each individual system. The current pulses I a , I b , I c , . . . of the individual partial regulators are staggered chronologically relative to one another. Before delivery to the load 14 to be supplied, the currents are superimposed on one another, so that the supply current for the load 14 is a relatively uniform and at most only slightly undulating current. In the ideal case, which always pertains with a constant input current U and a uniform output load as well as with complementary-switching transistors, the load variations on the input current drops toward zero. The output current fluctuation is likewise reduced. In the normal case, both the load variations and the output current fluctuations can be reduced to the following extent: 
     δIE=IGE/T 
     δIA=IGA/T 
     If the sequential triggering prevents switching partial converters from overlapping. The various abbreviations have the following meanings: 
     δIE: difference in the input current 
     IGE: total current at the input 
     δIA: difference in the output current 
     IGA: total current at the output 
     T: number of partial converters 
     The exemplary embodiment of FIG. 1 is distinguished by maximum correction of input and output fluctuations. Since this requires both a number of separate regulators and one power part each, the exemplary embodiment of FIG. 1 is quite complex. 
     Conventional voltage regulators or control parts of conventional voltage regulators can be used as the regulators. The power parts may be conventional power parts with a corresponding switching transistor. A microprocessor can be used as the synchronizing device 14. It is also possible to use a suitable timing element, shift register, ASIC logic, or a suitable clock generator for the synchronization. 
     In FIG. 2, an exemplary embodiment of a voltage converter with a synchronized regulator and controller is shown. This voltage converter is again used to supply a load 14. By replacing the individual regulators 10b-10n of FIG. 1 with a controller with sequentially controlled outputs, the expense and complication for regulation can be reduced compared to the exemplary embodiment of FIG. 1. The controller 15 is connected to the regulator 10a and triggers the power parts 11b, 11c, . . . , 11n. The correction of input and output fluctuations of the current or voltage is done directly, at the power part 12a, and at the power parts 11b-11n is done by the regulator 10a via the controller 15. 
     With the exemplary embodiment shown in FIG. 2, a further option for voltage conversion is presented. This comprises correcting only a partial load range via the power part 12a. The remaining power part, that is, the power of the power parts 10b-10n, remains constant because of the controller. 
     In FIG. 3, a third exemplary embodiment of the invention is shown. In this variant, only one regulating component 17 is needed, whose high switching frequency to n parallel power parts 11a, 11b, 11c, . . . , 11n is divided up via a multiplexer 16 with a logic circuit 16a connected to it. This enables maximum correction at little expense for regulation. 
     The distribution of the output signal of the regulator can be explained with the aid of the timing graph shown in FIG. 4. At its output, the regulator outputs a switching frequency of 100 kHz, for example. The distribution of the regulator output signal to power parts, for instance five power parts 1-5, is done with the of the logic signal S1. The leading edge of this signal is fixedly synchronized, and the trailing edge is varied by the regulator depending on the input signal. The multiplexer 16 distributes the negative variable edges to the outputs a-n of the logic. During each of the times marked X, the output signals of the regulator reach the corresponding power parts. The signal courses are designated by the symbol S2. 
     Drawing captions by block number 
     
         ______________________________________FIG. 112                 Synchronization10a                Regulator a10b                Regulator b10c                Regulator c10n                Regulator n11a                Power part a11b                Power part b11c                Power part c11n                Power part n14                 LoadFIG. 212                 Synchronization10a                Regulator a15                 Controller b              c              n11a                Power part a11b                Power part b11c                Power part c11n                Power part n14                 LoadFIG. 3              Regulator16                 Multiplexer16a                Logic11a                Power part a11b                Power part b11d                Power part c11n                Power part n14                 Load______________________________________