Research On Prognostic Cell For DC/DC Converters Based On VDMOSFET Radiation Damage

DC/DC converters are widely used as the second power sources in the space radiation environment. Its irradiation damage is an urgent reliability problem needed to be solved. Traditional radiation harden and screening methods have some disadvantages like long periods, high expenditure and low capability etc. The ePHM technique was exploringly adopted to solve the irradiation damage problem of DC/DC converters.Based on the radiation damage mechanism of DC/DC converter and VDMOSFET, which is one of the most vulnerable units in converter, ionization irradiation experiments were done. After analyzing the degradation of parameters, the most sensitive, faithful and measurable ones were selected. Then based on VDMOSFET, DC/DC converters radiation damage prediction model was established. Finally, according to this model,the prognostics cell of DC/DC converter radiation damage was designed.Theoretical study shows that: after irradiation, the failure modes of VDMOSFETs are: threshold voltage drift negatively, Tranconductance degrade, low frequency electronical noise increased etc; DC/DC converters appear efficiency reduced, output voltage drift, low frequency electronical noise increased failure modes.VDMOSFETs'threshold voltage negative drift caused DC/DC converters two failure modes, 1. VDMOSFETs can not be divorced from saturation state when the threshold voltage lower than the low potential of PWM output voltage. 2.conversion efficiency of DC/DC converters reduced caused by leakage current increases which origins form threshold voltage negatively drift .The irradiation experiments of VDMOSFET and DC/DC converters were accomplished . Theoretical research results were verified by the experimental results. through the analysis of electrical parameters and noise parameter ,the threshold voltage of VDMOSFET, DC/DC converters'output Voltage and conversional efficiency were selected for prognostics cell designing, noise amplitude B was selected as the sensitive characterization parameters for screening and reliability evaluation.The DC/DC converters radiation damage prediction model based on VDMOSFET was established by the in-depth studying of the radiation damage relation between VDMOSFETs and DC/DC converter. Theoretical calculations and experimental results show that the radiation damage prediction model is correct, and can accurately reflect the radiation damage of DC/DC converters.According to the failure mechanism, failure modes and the measures of ePHM , the monitor parameter alarm method was selected. The schematic and layout of prognostics cell were designed based on the radiation damage prediction model. Simulation and analysis show that the prognostics cell satisfies the design requirements. The prognostics cell was fabricated by Chartered Semiconductor , Sample testing and the irradiation experiments show that the prognostics cell can alarm successfully, and fully meet the design requirements.