Measuring device for measuring an electrical current

1. A measuring device for measuring an electrical current having an alternating-current converter that possesses a primary inductance (L H ) and an ohmic secondary resistance (R S ) and whose output is connected across a measured-value signal conditioning device to a measurement output for a current measurement signal, wherein an active compensation circuit, at least partially compensates for the voltage drop caused by a current flow in the secondary resistance (R S ) at the primary inductance (L H ) by applying a voltage at the output of the alternating-current converter, is disposed between the output of the alternating-current converter and the measurement output.

2. The measuring device of claim 1 , wherein the compensation circuit is an INIC whose internal resistance preferably is quantitatively somewhat smaller or larger than the secondary resistance (R S ).

3. The measuring device of claim 1 , wherein said measuring device has at least one clocked semiconductor switch that is connected by means of a control connection to a control device, and the input of the alternating-current converter is connected in series to the semiconductor switch.

4. The measuring device of claim 3 , wherein the measured-value signal conditioning device has means for generating at least two measured-value signals, of which a first measured-value signal corresponds to the output current of the alternating-current converter when the semiconductor switch is closed and a second measured-value signal corresponds to the output current of the alternating-current converter when the semiconductor switch is open, and the connections carrying measured-value signals are connected to the measurement output across a subtraction element.

5. The measuring device of claim 4 , wherein the sample-and-hold element is connected by means of a control connection to the control device for the semiconductor switch in such a way that the sampling for the first measured-value signal occurs centered in a time interval while the semiconductor switch is closed, and/or the sampling for the second measured-value signal occurs centered in a time interval while the semiconductor switch is open.

6. The measuring device of claim 4 , wherein the output of the alternating-current converter is connected to a first input of a subtraction element, and the output of the subtraction element is connected to the measurement output and to an input of an additional sample-and-hold element, whose output is connected to a second input of the subtraction element, and a sampling input of the additional sample-and-hold element is connected to the control device by means of a control connection in such a way that the measurement output is regulated to a specified electrical potential when the first semiconductor switch is closed or open.

7. The measuring device of claim 3 , includes a second alternating-current converter, wherein the output of the first alternating-current converter and the output of the second alternating-current converter are connected to the inputs of a first addition element and its output to a buffer, the buffer has a control connection to the control device for closing the connection between the output of the first addition element and the buffer when the semiconductor switch is closed, following the buffer, a second addition element is connected to the buffer, and its one input is connected to the buffer and its other input is connected to the output of the second alternating-current converter, and the output of the second addition element forms the output current measuring output.

8. The measuring device of claim 3 , wherein said measuring device has a second semiconductor switch that is connected in series to the first semiconductor switch and whose connection node is connected to an output connection, and the semiconductor switches can be controlled in push-pull operation by means of the control device in order to form a clocked half-bridge circuit.

9. The measuring device of claim 7 , wherein the second alternating-current converter has a second primary inductance and a second ohmic secondary resistance; and a second active compensation circuit, which at least partially compensates for the voltage drop caused at the second primary inductance by a current flow in the second secondary resistance by applying a voltage at the output of the second alternating-current converter, is located between the output of the second alternating-current converter and the inputs of the first addition element.

10. The measuring device of claim 8 , wherein the output connection is connected to the winding of an electric motor, in particular a stepper motor.