Patent ID: 9664742
Date: 2017-05-30
CPC Classifications: G01R

Claim:
1. A method for measuring a current through a semiconductor switch having an unknown internal resistance, the switch having two connections, the method comprising: providing an AC source as part of an AC circuit connected in parallel with the switch, wherein both an amplitude and a frequency of a current provided by the AC source are known; during an operation, superimposing the current provided by the AC source on a current through the switch to be measured; determining an AC voltage component of a voltage difference across the switch and an amplitude thereof as a maximum voltage value; connecting a gate signal generator for controlling the switch resistance to the switch; interrupting the current provided by the AC source, periodically modulating the switch resistance by the gate signal generator, and determining a further AC voltage component of the voltage difference, wherein the current between the connections is determined proportionally to a product of the amplitude of the current of the AC source and the further AC voltage component; a) selecting a first setting of the switch resistance; b) determining a first AC voltage component of the voltage difference; c) selecting a second setting of the switch resistance; d) determining a second AC voltage component of the voltage difference; e) deactivating the AC source; f) periodically switching over the switch resistance between the first and second settings, corresponding to a square wave signal, by the gate signal generator; g) determining a third AC voltage component of the voltage difference; h) determining and outputting the current between the connections from a maximum current of the AC source and a ratio of the third AC voltage component and a difference between the first and second AC voltage components.