Research Of High-frequency Induction Brazing Power Source

High frequency induction brazing power is a heating tool which transfers the electricalenergy into the thermal power by using the electromagnetism induction phenomenon，belongs to the non-contact heating, with the advantage of fast heating, high heatingefficiency, good working environment, local heating, etc., which is widely used in thewelding of various cutting tools and drilling tools.The essay researches into the high frequency induction brazing power circuit topology,compares with two common load connection including series resonant and parallel resonanttype, and obtains the advantages and disadvantages of the two load connections; gets theresult that series resonant circuit generally supplied by the voltage source，you can regulatethe size of the power by controlling switch tube, and its anti-interference ability is strong.Therefore, the circuit load involved here adopts the series resonant connection.The main circuit of high frequency induction brazing power designed by the essaytakes MOSFET as a switching device, taking use of pulse density modulation (PDM), canflexibly adjust the output power, with the same pulse duty cycle, which can easily realizethe digital control. The essay makes a study of main circuit and the load working, and getsthe result that when the load circuit works in the resonant state, it has the highest efficiencyand output energy, and the greater the quality factor Q value is, the greater the heatproduced.The essay studies that the maximum output power appears when load works in theresonant state, but when the external conditions change, the frequency of the inverter outputpower is not equal to the natural frequency of the load, resonant circuit will deviate from theoptimal operating point resulting in the decrease of output power, therefore, the necessity ofthe PLL circuit is obtained. The essay studies the basic principle of phase-locked loop,designs phase-locked circuit based on the CD4046chip, the input of the PLL treated samplecurrent waveform which passes the phase-locked loop to make the output waveform to trackthe changes in sampling the current waveform to make the circuit work in the optimumoperating point, so that the entire power system maintains in the maximum output powerstate. The essay also designs the over voltage protection circuit to avoid excessive voltagedamaging the components.Finally, experiments are carried out. After measuring the main circuit and control circuit waveform of high frequency induction brazing power designed, and analyzing thetest waveform, results show that: the drive circuit designed works in the PDM poweradjustment mode, which can be adjusted conveniently; PLL design based on the CD4046chip can realize the lock-in function, its input and output has a fixed phase shift, and thefrequency remains the same; main circuit designed works in partial inductive state at theresonance point, and the switch stress is small.