Study On The Monitoring Method Of Output Electrolytic Capacitor For The DCM Flyback Converter

As the upgrade of power electronic devices,power electronic technology has been widely applied to the traffic,Military,Aerospace,computer,LED and so on.And the power supply circuit is the foundation and guarantee for the power electronic equipments.Compared to other power supplies,switching mode power supplies(SMPS)have smaller volume,higher efficiency,higher power factor(PF)and the technology about them are more mature.Therefore,they are widely used.In the SMPS,the electrolytic capacitors have the shortest life and high failure rate which restricts the reliability and the lifetime of SMPS.On many occasions,these features may affect power electronic equipments.The value of capacitance C and the equivalent series resistance ESR of the electrolytic capacitors can reflect the fail of it.To avoid the negative effects caused by the aged electrolytic capacitors,they can be replaced before failure.For timely replacement,parameter value of electrolytic capacitors should be monitored,and then compared with the initial value.The short life of electrolytic capacitors caused by their own structure and in the LED systems,the lifetime of LED is about 10 times as much as the electrolytic capacitor.Thus the electrolytic capacitor is necessary to be removed.However,the peak value is too high compared to the average value(peak-average ratio)which can't meet the requirement of LED in the electrolytic capacitor-less driver.And the lifetime of LED will reduce because of the high peak-average ratio.So it is essential to reduce the peak-average ratio of the output current for the electrolytic capacitor-less driver.Aiming at the above problems,this paper presents an online parameter monitoring system of the output capacitor's C and ESR for the DC/DC DCM Flyback converter.For the AC/DC DCM Flyback LED driver,a method of trapezoidal output current driving control to reduce the peak-average ratio was presented so as to remove the output electrolytic capacitor.All of the theoretical derivations,the design of the monitoring/controlling circuit and the main circuit are completed.Finally,the experiment prototype has been built and the experimental results show the effectiveness of the theory.