Abstract: The invention in general relates to Medical Instruments for bone fracture healing, ultrasonic surgery, tissue ablation and cutting and drilling, dry powder inhalers and more particularly to a method to monitor load condition and overall efficiency, safety and reliability of ultrasonic energy delivery using a Class E power Amplifier. Three parameters: frequency (f), duty cycle (D) and Power Amplifier supply voltage (Vdd) are continuously adjusted in order to maintain optimal and suboptimal Class E operation. The load for the power driver can be a single element or a stack. For every frequency and duty cycle of operation the MOSFET drain voltage is compared to a known value which is proportional to Power Amplifier supply voltage Vdd. During the MOSFET OFF part of operation a timer is started when drain voltage falls below a known threshold value. The timer is stopped by the MOSFET leading edge gate clock.