BRIEF DESCRIPTION OF THE DRAWING
The invention is described in more detail below with reference to the exemplary embodiment shown in the FIGURE.
DETAILED DESCRIPTION OF INVENTION
FIG. 1 shows an inventive analog current output, which has by way of example eight current sources IS1-IS8, in a simplified diagram, which only shows the essential parts and the positive current sources IS1-IS8. Each of the current sources IS1-IS8 supplies a quarter of the output current Iout. As shown there are four current sources IS1-IS4 in circuit, supplying four times the current value of the individual source to Iout. The current source IS5 is also active but does not contribute to the total current Iout. The current sources IS1-IS5 form a first set of current sources, which are switched to active to generate an output current Iout, in other words the switches SW11-SW15 are closed. The current sources IS6-IS8 form a second set of current sources, which are kept ready in an inactive state, in other words the switches SW16-SW18 are open. According to the invention the five active current sources IS1-IS5 are switched cyclically by way of a corresponding logic as follows to the current output Iout by means of the changeover switches SW1-SW5: four current sources (IS1-IS4 in the diagram) respectively to Iout and one current source IS5 to the resistor Rv. For the current source IS5 switched to Rv a setpoint/actual comparison is carried out by means of Rv, the reference source IR and the error amplifier EA. In this way all the active current sources IS1-IS5 are checked once within a cycle and the result is made available by way of the error output Err for evaluation. If an error is identified, the defective, in other words unserviceable, current source (e.g. IS5) is disconnected immediately by way of the corresponding switch (e.g. SW15) and a hitherto inactive current source, for example IS6, is connected by means of SW16. The function of the newly connected current source IS6 is then advantageously first tested and the cycle for checking serviceability then continues excluding the defective and including the connected current source IS6. In the event that the function check on a current source IS5 only takes half the time provided for operation of the active current sources IS1-IS4, in other words one cycle step, the current source originating from the second set and now switched to active and assigned to the first set, e.g. IS6, can also be tested within the cycle step, in which failure of the current source IS5 was determined. Error identification and switching therefore take practically no time, resulting in a continuous current flow without interruptions. Availability and redundancy can be adjusted finely in any manner—depending on the number of inactive current sources IS6-IS8. The entire sequence can hereby be controlled both by a general controller and by a specific sequence controller, such as an ASIC (Application Specific Integrated Circuit) for example or an FPGA (Field Programmable Gate Array). If the analog current output is embodied as an integrated circuit, the sequence controller for example can be integrated therein.
To summarize, the invention relates to a method for increasing the availability and redundancy of an analog current output as well as an analog current output with increased availability and redundancy. To improve the availability and also the redundancy behavior of an analog current output, it is proposed that a first set of current sources be switched to active to generate an output current, one current source respectively of the first set being checked cyclically for serviceability and the other current sources respectively generating the output current in equal parts and where unserviceability is determined, the corresponding current source being disconnected and removed from the first set. If a malfunction occurs, such as a failure of a current source for example, the output current advantageously does not drop out completely due to the allocation of generation to a number of current sources. The cyclical checking of the current sources allows the unserviceable current source to be removed quickly from the first set, with the remaining current sources still being able to supply the fall output current, without being exposed to a greater load due to increased energy output. Error identification and switching therefore take practically no time, resulting in a continuous flow of current without interruptions.
Patent Application
20080073976
