Patent ID: 8643990

Claim:
A protection circuit comprising: a controllable discharge transistor having a load path coupled between a first circuit node and a second circuit node and having an on state or an off state, wherein the discharge transistor provides a discharge path between the first and the second circuit nodes when the discharge transistor is in the on state; a trigger circuit having a first connection coupled to the first circuit node and a second connection coupled to the second circuit node, wherein: the trigger circuit comprises series connected elements coupled between the first and second connections, the trigger circuit has a third connection from an intermediate node of the series connected elements that is directly connected to a control terminal of the discharge transistor, the trigger circuit is configured to supply a drive signal to the control terminal of the discharge transistor, and the drive signal is operable to switch the discharge transistor to the on state when the voltage between the first and the second circuit nodes reaches a trigger value; and a setting circuit coupled to the trigger circuit, the setting circuit configured to change the trigger value from a first trigger value to a second trigger value depending on at least one of a voltage between the first and the second circuit nodes and the drive signal, wherein the second trigger value is less than the first trigger value.