Switch protection

A method for controlling a first and a second switch of a bridge circuit, wherein the bridge circuit comprises a first and a second input terminal for connecting a power source, a first branch connected between the first and the second input terminal and including a first section between the first input terminal and a centre tap forming an output terminal of the bridge circuit and including a second section between the centre tap and the second input terminal, where the first section includes a first switch and the second section includes a second switch, wherein

• A. there are predetermined preliminary closing and opening times of the first and the second switches and
• B. wherein the threshold is a first threshold with a positive sign and wherein there is a second threshold with a negative sign and
• whereby the method is characterized by the steps of
• a) determining a measured value by measuring a current in the bridge circuit or by measuring a voltage in the bridge circuit,
• b) carrying out a comparison of the measured value with a threshold and
• c) controlling a switching of the first and the second switch of the first branch in dependency of a result of said comparison,
• C. wherein the step of carrying out the comparison of the measured value with the threshold comprises the step of
• i. determining at a preliminary closing time of the first switch if the measured value is equal or smaller than the first threshold
• and
• ii. determining at a preliminary closing time of the second switch if the measured value is equal or greater than the second threshold and
• D. wherein the step of controlling the switching of the first and the second switch of the first branch in dependency of the result of said comparison comprises the following steps:
• i. if the result of the comparison is positive, and
• a) and if the comparison was done at the preliminary closing time of the first switch, closing the first switch immediately
• or
• b) if the comparison was done at the preliminary closing time of the second switch, closing the second switch immediately
• or
• ii. if the result of the comparison is negative, and
• a) if the comparison was done at the preliminary closing time of the first switch
• closing the first switch at or after a time of a subsequent negative crossing of the first threshold by the measured value
• if such a crossing occurs after the preliminary closing time at which the comparison was done and
• if the expected time of closing the first switch falls in a time frame between the preliminary closing time at which the comparison was done and the following preliminary opening time of the first switch
• or
• b) and if the comparison was done at the preliminary closing time of the second switch
• closing the second switch at or after the time of a subsequent positive crossing of the second threshold by the measured value
• if such a crossing occurs after the preliminary closing time at which the comparison was done and
• if the expected time of closing the second switch falls in a time frame between the preliminary closing time at which the comparison was done and the following preliminary opening time of the second switch.