Protection structure for an enhancement-mode FET of a circuit and corresponding method

A method for a circuit comprising a self-conducting power transistor, a further transistor referred to as control transistor, a second further transistor referred to as first protection transistor, and a string referred to as Zener string comprising at least one Zener diode, wherein the power transistor is a gallium nitride transistor or a silicon carbide transistor, wherein the power transistor is coupled between a first terminal of the circuit and a first node of the circuit, wherein the control transistor is coupled between the first node and a second terminal of the circuit, wherein a gate terminal of the control transistor is coupled to a third terminal of the circuit, wherein the first protection transistor is coupled between the first node and the second terminal, and wherein the Zener string is coupled between the first terminal and a gate terminal of the first protection transistor, and wherein the method comprises the steps of:

• a) driving the gate terminal of the control transistor via the third terminal so that the control transistor becomes conducting and sets the circuit in a state referred to as on state,
• b) driving the gate terminal of the control transistor via the third terminal so that the control transistor becomes blocking and sets the circuit in a state referred to as off state, and
• c) driving the gate terminal of the protection transistor via the Zener string, if a voltage across the Zener string exceeds a reverse voltage predefined by the at least one Zener diode, so that the protection transistor becomes conducting and sets and/or maintains the circuit in a state referred to as a protection state.