Devices and techniques for cutting and coagulating tissue

A generator for driving an ultrasonic end effector of an ultrasonic drive system, the generator comprising a control circuit, configured to:

• drive the ultrasonic end effector at a resonant frequency thereof;
• monitor the resonant frequency of the ultrasonic end effector;
• increment a timer when the resonant frequency is less than a threshold frequency;
• and
• compare the timer to a required trigger time.

A generator for driving an ultrasonic end effector of an ultrasonic drive system, the generator comprising a control circuit, configured to:

• drive the ultrasonic end effector at a resonant frequency thereof;
• monitor the resonant frequency of the ultrasonic end effector;
• compare the resonant frequency of the ultrasonic end effector to a threshold frequency;
• generate a first pulse amplitude for a first period over which the generator is driven;
• and
• generate a second pulse amplitude for a second period over which the generator is driven.