Knife deployment mechanisms for surgical forceps

A surgical instrument includes an end effector assembly having jaw members movable between spaced-apart, first approximated, and second approximated positions. A knife is selectively movable relative to the end effector assembly between a retracted position, a first extended position, and a second extended position. A trigger is selectively actuatable between a un-actuated position, a first actuated position, and a second actuated position for moving the knife between its respective positions. A control member prevents movement of the trigger when the jaw members are disposed in the spaced-apart position, permits movement of the trigger to the first actuated position but prevents movement beyond the first actuated position when the jaw members are disposed in the first approximated position, and permits movement of the trigger to the second actuated position but prevents movement beyond the second actuated position when the jaw members are disposed in the second approximated position.