Xuerong Ye

A Tolerance Design Method for Electronic Circuits Based on Performance Degradation

Due to the effects of manufacturing tolerances and environmental conditions, component parameters vary and degrade with time. This may cause performance measures of electronic circuits to deviate from design specifications. Therefore, a tolerance design method based on performance degradation is proposed for electronic circuits, so as to improve the robustness of output characteristics. First, sensitive components causing output fluctuation are determined via orthogonal experiment and PSpice simulation. Then, degradation path models are established to describe the degradation process of sensitive components. The predicted values worked out by the degradation path models are substituted into the simulation model for Monte Carlo analysis. Besides, output characteristics and performance reliability are evaluated according to Monte Carlo simulation. Finally, optimum allocation is carried out for component tolerances as per minimum life cycle cost. The proposed method is illustrated by a case study of light-emitting diode (LED) driver. Copyright

Online Condition Monitoring of Power MOSFET Gate Oxide Degradation Based on Miller Platform Voltage

The condition monitoring problem of power devices is significant for diagnostics and prognostics of a switched-mode power supply (SMPS) system. For power mosfet, the gate oxide degradation often occurs in various applications. However, there is no online condition monitoring method for gate oxide degradation so far. In this paper, a new precursor that can be used for online condition monitoring of power mosfet gate oxide degradation is proposed. Gate oxide degradation mechanisms and effect are summarized, and the mosfet turn-on process is analyzed. Then, a theoretical model is established to describe the relationship between miller platform voltage and two types of gate oxide defects, and miller platform voltage is identified as a new precursor. The precursor can be extracted without impacting system operation, thus online condition monitoring can be accomplished. The accelerated degradation test is carried out for power mosfets with both high electric field and gamma irradiation methods, and the degraded devices injection and in situ monitoring of miller platform voltage are conducted on a BOOST circuit to verify the feasibility of the new precursor. Experimental results demonstrate that the new precursor can be applied to online condition monitoring of power mosfet gate oxide degradation in the SMPS system.

A new tolerance design method for LED Lamp driver with performance degradation model

This paper proposes a new tolerance design method for electronic system with performance degradation model to improve the robustness of output characteristic. The sensitive parameters that lead to output fluctuation are determined by sensitivity analysis based on experiment design. Statistical testing is used to characterize the trend patterns for the mean and the variance of critical components, from which different types of degradation paths will be extrapolated. The degraded distribution models are established for the output according to the sensitive component characteristic. Through the limit specification, the optimal tolerances are allocated to the sensitive parameters to minimize quality loss. A practical implementation of the method is manifested through evaluating probabilities by Monte Carlo simulation.

VDMOSFET HEF degradation modelling considering turn-around phenomenon

Abstract Gate oxide failure of power VDMOSFET has been researched for a long time. For BTI parameter degradation, some models are proposed. However, the degradation modelling of HEF still have challenges, one of which is the turn-around phenomenon. Due to the existence of the turn-around point, the threshold voltage degradation model under HEF cannot be described using classical models. Aiming at this problem, the experimental study and the argument are proposed in this paper. First, the theoretical model assumption is discussed based on the degradation mechanism. Second, the HEF stress experiments are carried out to acquire experimental data. Then the model fitting is processed. A three-phase model is proposed to describe threshold voltage degradation under HEF stress.

Converter-level FEM simulation for lifetime prediction of an LED driver with improved thermal modelling

Abstract Light-emitting diode (LED) drivers are widely regarded as the weakest link in the solid-state lighting systems. This paper proposes an improved thermal modelling process for the mission profile based lifetime prediction of reliability critical components in a LED driver for the outdoor lighting application. A converter-level finite element simulation (FEM) simulation is carried out to obtain the ambient temperature of electrolytic capacitors and power MOSFETs used in the LED driver, which takes into account the impact of the driver enclosure and the thermal coupling among different components. Therefore, the proposed method bridges the link between the global ambient temperature profile outside of the enclosure and the local ambient temperature profiles of the components of interest inside the driver. A quantitative comparison of the estimated annual lifetime consumptions of MOSFETs and capacitors are given based on the proposed thermal modelling process, and the datasheet thermal impedance models and the global ambient temperature.

Lifetime prediction of aluminum electrolytic capacitors in LED drivers considering parameter shifts

Abstract The electrolytic capacitor (Al-Cap) is widely considered as one of the reliability-critical components in LED driver applications. A realistic lifetime prediction of Al-Caps would be beneficial to the sizing of capacitors to fulfill a specified design lifetime. This paper investigates the impact of electrolytic capacitor parameter shifts on the LED driver performance and the capacitor reliability. The operation condition, degradation, and tolerance are considered as the main reasons that deviate the parameters from nominal values. A method to model the degradation of Al-Cap parameter is introduced as well. In the case study of a flyback LED driver for street lighting, the contribution of parameter shifts to the electrical performance of LED drivers and Al-Cap core temperature is evaluated based on both theoretical analysis and simulation. A quantitative comparison of the estimated lifetime of Al-Cap in the LED driver is given with and without the consideration of capacitor parameter shifts within the service life. The proposed method enables a more realistic way for electrolytic capacitor lifetime prediction in LED drivers, which would otherwise have the risk of overestimation.

Fault localization of a switched mode power supply based on extended integer-coded dictionary method

Abstract Switched mode power supply (SMPS) is widely used in various industrial fields. Due to the complex operational condition, various faults may occur in the SMPS. Localizing the faults efficiently is necessary for the SMPS. Based on the classical integer-coded dictionary (ICD) method, which has been widely used in board-level analog circuits fault localization, this paper presents an extended ICD method to solve the fault localization problem in SMPS. An optimal boundary determination method is adopted in the extended ICD, which can improve the separating ability of each feature. In the paper, faults in SMPS, the available test points as well as the experimental setup are introduced first. Then, the extended ICD method is presented. Finally, the developed method is applied in the SMPS, and the test result shows eight fault states can be isolated only using six features with an accuracy of 92.5%.

Manufacturing process-based storage degradation modelling and reliability assessment

Abstract Quality variations in manufacturing are significant factors for products reliability. In this paper, a manufacturing process-based storage degradation modelling and reliability assessment approach is proposed to describe the uncertainty of products storage degradation path caused by manufacturing process. Firstly, a storage degradation model of the output characteristic is constructed, by combining the functional relationship between output characteristic and bottom level performance (BLP for short, such as dimension, mechanical properties, material properties, etc.) with the storage degradation mechanism of products. This model is able to reflect the unit-to-unit variability of batch products. Secondly, based on finite element simulation and approximate modelling method, the unit-to-unit variability caused by manufacturing process is analysed, and the distribution characteristics of the random effect parameters (REPs) of the model are calculated accordingly. Finally, the storage reliability of the batch products is estimated based on the model and the calculated distribution characteristics of REPs. A case study of the aerospace relay is carried out to illustrate the effectiveness of the proposed approach.

In-situ prognostic method of power MOSFET based on miller effect

Power MOSFET plays an important role in power electronic systems, the failure of which will lead to system losing functions. Thus the degradation failure process and mechanism of MOSFET attract wide attention of scholars. However current research works cannot solve the real time degradation monitoring problem of MOSFET. Normally, MOSFET should be removed from the system for testing or monitoring. This paper presents a new in-situ prognosis method for MOSFET based on miller effect. According to the theory analysis, simulation and experiment results, the miller platform voltage is identified as a new degradation precursor. Then, particle filter algorithm is used for MOSFET remaining useful life (RUL) prediction based on the degradation data of miller platform voltage. Meanwhile, MOSFET samples with different degradation levels are formed by “overstress of gate bias” accelerating life test. The samples are placed into application circuit for the monitoring and extraction of miller platform voltage, so as to verify the method proposed in this paper.

Simulation and diagnosis of degradation failure on electromagnetic relay

Electromagnetic relay has a high failure rate, which is the severely afflicted area where components and parts easily lose efficacy in the electronic system. Monitoring and evaluation of relay status in key positions are a crucial method to improve operational reliability. Degradation is the significant cause for failure of electromagnetic relay. However, owing to few researches concerning degradation failure of relay at present, lacking of degradation data and ambiguity of degradation characteristics have already become the main factors restricting PHM application of relay. Aiming at this problem, this paper conducted a degradation failure of electromagnetic relay simulation based on the Virtual Prototyping Technology, obtained valuable failure data, and built state space of failure data, in order to extract the fault feature data and realize the diagnosis of failure type. This paper owns a certain practical significance for studying characterization of degradation state of relay, as well as its PHM application.