Electrical transmission or interconnection systems – Switching systems – Condition responsive
Patent
1999-03-24
2000-11-21
Ballato, Josie
Electrical transmission or interconnection systems
Switching systems
Condition responsive
323222, 361 936, H01H 4700
Patent
active
061507393
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a circuit configuration for supplying power to electronic tripping devices, the circuit configuration having a current-transforming device, whose output voltage is rectified and can be fed to a charging capacitor, which provides the electronic tripping device with power.
BACKGROUND INFORMATION
Circuit configurations of this kind are described in German Patent No. 32 46 329. When an upper voltage limit is reached, the voltage is short-circuited in such a way that the current of the current-transforming device no longer flows into the charging capacitor. In this switching operation, electromagnetic interference fields arise which corrupt the measurement current, thereby causing erroneous tripping.
European Patent No. 0 130 254 describes relevant tripping device with two capacitors, which are to be charged by the current-transforming device for the operation of this device.
SUMMARY OF THE INVENTION
An object of the present invention is to define a circuit configuration for supplying power to electronic tripping devices, ensuring the lowest possible influence on the current of the current-transforming device, and, in addition, limiting the emission of electromagnetic interference fields to a minimum.
A further object of the present invention is to achieve the quickest possible charging of a capacitor at a voltage which is just sufficient.
According to the present invention, these objects are achieved by the following features: charging capacitor CL in the manner of a choke/step-up transforming device DR or a flyback converter SW (according to the transformer principle), charging an output capacitor CA, which is connected in parallel with and functioning as the power supply of electronic tripping device AE, to control the charging of output capacitor CA, the switching transistor TR being controlled by a pulse width modulation circuit PW, set point of an output voltage UA at output capacitor CA is reached, then switching transistor TR can be controlled with a very high pulse duty factor, i.e., is only blocking for a short moment in each case, and, as a refinement of the present invention, with pulse width modulation circuit PW for controlling purposes, controlling it from the beginning of charging output capacitance CA so as to adjust it to optimal power matching (11, 111, . . . ).
By controlling the switching transistor with the pulse width modulation circuit, a constant current is impressed, as opposed to the usual constant-current power supply. In fact, as soon as the output voltage at the output capacitor has reached the set point, the switching transistor is no longer controlled with a low but with a very high pulse duty factor. Accordingly, in the case of very high currents of the current-transforming device, these are led (via the choke/step-up transforming device) through conductively connected transistor TR in the switched-mode power supply unit, and only switched through to output capacitor CA via the diode during the very short opening times of the switching transistor. In the case of high currents, this operating mode maintains the voltage at the charging capacitor low, resulting in an approximately constant power input at a low voltage level. This favors an exact current measurement by the current transformer. The electronic control assembly of the switched-mode power supply unit is supplied with the output voltage of capacitor CA, since the input voltage at the switched-mode power supply unit is too low, particularly in the case of high currents of the current-transforming device. The current is measured in a conventional manner at a shunt resistor, which can also be arranged upstream of the rectifying device if required.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows a first embodiment of a circuit configuration according to the present invention.
FIG. 2 shows a characteristic of a current transformer, in particular voltage plotted over current between no load operation and short circuit and a power dissipation curve.
FIG. 3 shows a
REFERENCES:
patent: 4992723 (1991-02-01), Zyistra et al.
Markus Niebauer et al., "Solarenergie Optimal Nutzen Intelligentes MPP-Tracking Mit Einen ST62-Mikrocontroller", Elektronik, No. 16, Aug. 6, 1996*.
Baumgartl Ulrich
Rohl Wolfgang
Ballato Josie
DeBeradinis Robert L
Siemens AG
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