Development of low frequency ultrasonic atomizing nozzle driving circuit with class E resonant inverter

Ultrasonic atomization atomizers are widely used in many fields with their excellent atomization properties.However, as a key part of ultrasonic atomization system, ultrasonic atomization nozzle driving powers are still costly,inefficient and unstable.In order to design an ultrasonic atomization driving circuit with high efficiency and low cost, aclass E resonant converter of high efficiency and low power dissipation was developed in this paper.The class E inverter isa well known resonant converter that can generate high frequency sinusoidal current and has high power conversionefficiency.Only one transistor with a control circuit was used in the main power circuit, which made the class E resonantconverter high efficiency and low cost solution for low frequency ultrasonic atomization atomizers.The nozzle adopted inthis paper was a novel micro index and low frequency ultrasonic nozzle whose parameters were as follows: input voltage36 V, resonant frequency 60 kHz and output power 15 W.A class E resonant inverter merged with the series resonanceequivalent circuit of nozzle at its resonance frequency was used to drive the low frequency ultrasonic atomizer at zerovoltage switching.It was analyzed that the basic circuit structure, working principles and circuit characteristics of class Eresonant inverter circuit under the optimal working condition.Additionally, a simplified model and merged model wererespectively used to calculate waveforms and ideal parameters of this ultrasonic nozzle.The ideal parameters werevalidated based on the theoretical calculations and simulations conducted in saber software.However, the voltagewaveform across the switch S was the key point to determine circuit performances.The shunt capacitor C,which was one of key parameters, was composed of the MOSFET output capacitance, the choke parasitic capacitance and the external shuntcapacitance.When the value of the shunt capacitor C was properly designed, the energy stored in the shunt capacitor C discharged entirely just before the switch S turned on and the switch turned on at zero voltage.In this case, with lessswitching lost, the maximum power could be achieved.When the value of shunt capacitance C was larger than optimal value, the voltage rate of rise and fall across the shunt capacitance C decreased during the switch off and the switch voltagewaveform did not reach zero prior to turn on switching.Therefore, the switching losses occurred instantly when the switchturned on and the MOSFET may be burned out.In contrast, when the value of capacitance C was smaller than ideal value, the energy stored in the shunt capacitor C was discharged completely in advance.Furthermore, the MOSFET body diodeturned on when the switch current was negative.Therefore, the turn on switching losses and the large conduction losses ofthe body diode occurred at the same time.In order to verify the design method, a driving circuit of a 15 W ultrasonicatomization nozzle was built.The experimental results showed that the class E resonant inverter could be succeeded inapplying to drive the low frequency nozzle and the circuit efficiency was 85% or more.The designed circuit wasinvestigated as a good solution to drive the low frequency ultrasonic atomization nozzle.Additionally, experimentalwaveforms were in a good agreement with simulation results.From the waveform charts, we can obtain methods of thequantitative parameter adjustment to reach optimum condition.