同步整流模式控制的Buck变换器虽然提高了系统的工作效率,但是也带来了电流反灌现象,这种情况严重影响航天器二次电源系统的效率、寿命、安全性和可靠性。针对这一问题,该文设计并实现基于Buck电路的防电流反灌电路,该电路通过逐周期检...同步整流模式控制的Buck变换器虽然提高了系统的工作效率,但是也带来了电流反灌现象,这种情况严重影响航天器二次电源系统的效率、寿命、安全性和可靠性。针对这一问题,该文设计并实现基于Buck电路的防电流反灌电路,该电路通过逐周期检测低端Mos管关断后,高端Mos管开通前这一死区时间内低端Mos管Vds电压的高低电平状态,来判断电路处于何种工作模式,进而控制低端Mos管的驱动电压,实现当电路处于强制电流连续模式(FCCM,Forced Current Continuous Mode)时,关断低端Mos管驱动的控制逻辑功能。仿真和实验结果表明,加入该防电流反灌电路后,可有效防止电流反灌现象,提高电路的可靠性和稳定性。展开更多
Objective. To study the mechanism and effects of blood perfusion to the acute ischemic region of myocardium through Ho-YAG laser channels with myocardial contrast echocardiography. Methods. To produce the model of acu...Objective. To study the mechanism and effects of blood perfusion to the acute ischemic region of myocardium through Ho-YAG laser channels with myocardial contrast echocardiography. Methods. To produce the model of acute myocardial ischemia,we partially ligated the left anterior decending(LAD)coronary artery of canine hearts between lst.and 2nd.diagonal branches and then performed transmyocardial revascularization in this region with Ho-YAG laser.Myocardial contrast echocardiography was made with a new generation of ultrasound contrast agent and second harmonic imaging of this region before,after ischemia and after laser revascularization.Pictures were taken with “R” wave trigger skill. Results.Acoustic density derterming in the ischemia region (anterior wall)with MCE(myocardial contrast echocardiography)was obviously decreased(540±181) after the LAD was ligated,as compared with before(1169±161, P<001).It was increased remarkably after transmyocardial laser revascularizatuon(TMLR)(112±201, P<001)as compared with that when ischemia and approximated to that before ischemia(P>005).There were no differences in acoustic density in the lateral wall(as control)among these comprehensive three periods(P>005).Contrast in the laser region developed one cardiac cycle ahead of that in the non-ischemic normal region. Conclusion.Acute ischemic myocardium can be perfused by oxygenated blood from the left ventricle through Ho-YAG laser channels.Evidence of blood perfusion through laser channels during systolic phase was detected,and myocardial contrast ultrasonography using intravenous perfluorocarbon-exposed sonicated dextrose albumin rnay be regarded as a reliable method in the study of transmyocardial revascularization.展开更多
文摘同步整流模式控制的Buck变换器虽然提高了系统的工作效率,但是也带来了电流反灌现象,这种情况严重影响航天器二次电源系统的效率、寿命、安全性和可靠性。针对这一问题,该文设计并实现基于Buck电路的防电流反灌电路,该电路通过逐周期检测低端Mos管关断后,高端Mos管开通前这一死区时间内低端Mos管Vds电压的高低电平状态,来判断电路处于何种工作模式,进而控制低端Mos管的驱动电压,实现当电路处于强制电流连续模式(FCCM,Forced Current Continuous Mode)时,关断低端Mos管驱动的控制逻辑功能。仿真和实验结果表明,加入该防电流反灌电路后,可有效防止电流反灌现象,提高电路的可靠性和稳定性。
文摘Objective. To study the mechanism and effects of blood perfusion to the acute ischemic region of myocardium through Ho-YAG laser channels with myocardial contrast echocardiography. Methods. To produce the model of acute myocardial ischemia,we partially ligated the left anterior decending(LAD)coronary artery of canine hearts between lst.and 2nd.diagonal branches and then performed transmyocardial revascularization in this region with Ho-YAG laser.Myocardial contrast echocardiography was made with a new generation of ultrasound contrast agent and second harmonic imaging of this region before,after ischemia and after laser revascularization.Pictures were taken with “R” wave trigger skill. Results.Acoustic density derterming in the ischemia region (anterior wall)with MCE(myocardial contrast echocardiography)was obviously decreased(540±181) after the LAD was ligated,as compared with before(1169±161, P<001).It was increased remarkably after transmyocardial laser revascularizatuon(TMLR)(112±201, P<001)as compared with that when ischemia and approximated to that before ischemia(P>005).There were no differences in acoustic density in the lateral wall(as control)among these comprehensive three periods(P>005).Contrast in the laser region developed one cardiac cycle ahead of that in the non-ischemic normal region. Conclusion.Acute ischemic myocardium can be perfused by oxygenated blood from the left ventricle through Ho-YAG laser channels.Evidence of blood perfusion through laser channels during systolic phase was detected,and myocardial contrast ultrasonography using intravenous perfluorocarbon-exposed sonicated dextrose albumin rnay be regarded as a reliable method in the study of transmyocardial revascularization.
