Desaturation detection circuit for use between the desaturation detection input of an optocoupler and the output of a power switching device

A method of operating a desaturation detection circuit for use between a desaturation detection input of an optocoupler and an output of a power switching device, the desaturation detection circuit including a threshold setting element having an input for connection to the output of the power switching device and an output, and a detector having an input connected to the output of the threshold setting element and an output connectable to the desaturation detection input of the optocoupler, the method comprising:

• monitoring the voltage input to the desaturation detection circuit,
• determining whether a voltage input to the desaturation detection circuit is greater than or equal to a threshold voltage set by the threshold setting element, the threshold voltage above a desaturation voltage, and
• when the voltage input to the desaturation detection circuit is greater than or equal to the threshold voltage above a desaturation voltage, outputting from the detector a control signal to trigger a desaturation routine in the optocoupler,
• wherein the threshold setting element includes a first switching element arranged to be in an on state during desaturation operation of the power switching device until the output of the power switching device reaches the threshold voltage and wherein the detector includes a second switching element arranged to be in an off state when the threshold setting element provides an output and arranged to provide the control signal when an output from the threshold setting element is provided.