Instrument for coagulation and targeted dissection of biological tissue, with a tool which has at least one first coagulation electrode and one second coagulation electrode that are movable relative to one another in order to hold tissue between them, and which has at least one cutting electrode for cutting through tissue held between the least one first coagulation electrode and the at least one second coagulation electrode, with an electrical circuit which is connected to the coagulation electrodes (22, 29) and to the cutting electrode and contains or can be connected to a cutting voltage source and a coagulation voltage source, wherein the cutting voltage source is formed by a transformer which is arranged in the instrument and is or can be connected on the input side to the HF output voltage source, and wherein the HF output voltage source serves to supply the coagulation voltage source, wherein the circuit has three output ports (M, K and S), of which the one output port is a ground port connected to the at least one second coagulation electrode, the one further output port is a coagulation port connected to the at least one first coagulation electrode, and the other further output port is a port connected to the at least one cutting electrode for a cutting voltage of the cutting voltage source, wherein the electrical circuit has a power switch which is arranged in a current path between the cutting voltage source and the cutting electrode and is configured for optional isolation of the cutting electrode from the cutting voltage source or for optional connection of the cutting electrode to the cutting voltage source, and an activation switch which is configured for optional activation of the coagulation voltage source, the cutting voltage source or the HF output voltage source, wherein the activation switch and the power switch are controlled in series by a common actuation element. with a tool which has at least one first coagulation electrode and one second coagulation electrode that are movable relative to one another in order to hold tissue between them, and which has at least one cutting electrode for cutting through tissue held between the least one first coagulation electrode and the at least one second coagulation electrode, with an electrical circuit which is connected to the coagulation electrodes (22, 29) and to the cutting electrode and contains or can be connected to a cutting voltage source and a coagulation voltage source, wherein the cutting voltage source is formed by a transformer which is arranged in the instrument and is or can be connected on the input side to the HF output voltage source, and wherein the HF output voltage source serves to supply the coagulation voltage source, wherein the circuit has three output ports (M, K and S), of which the one output port is a ground port connected to the at least one second coagulation electrode, the one further output port is a coagulation port connected to the at least one first coagulation electrode, and the other further output port is a port connected to the at least one cutting electrode for a cutting voltage of the cutting voltage source, wherein the electrical circuit has a power switch which is arranged in a current path between the cutting voltage source and the cutting electrode and is configured for optional isolation of the cutting electrode from the cutting voltage source or for optional connection of the cutting electrode to the cutting voltage source, and an activation switch which is configured for optional activation of the coagulation voltage source, the cutting voltage source or the HF output voltage source, wherein the activation switch and the power switch are controlled in series by a common actuation element.