论述PFM(Pulse Frequency Modulation)脉冲频率调制型X光机电源的原理及系统构成.其主要功率器件选用目前国际上最先进的IGBT绝缘栅双极型晶体管.整流可控硅移相融发脉冲是由单结晶体管产生.PFM脉冲信号是由压频(V/F)振荡器产生.控制电...论述PFM(Pulse Frequency Modulation)脉冲频率调制型X光机电源的原理及系统构成.其主要功率器件选用目前国际上最先进的IGBT绝缘栅双极型晶体管.整流可控硅移相融发脉冲是由单结晶体管产生.PFM脉冲信号是由压频(V/F)振荡器产生.控制电路采用预置X射线管电压,管电流以及设置X射线管阳极最高工作温度、连续工作时间等多环节调节.展开更多
Playbills, covers, and logo of an opera often reflect the meanings of the drama. This paper focuses on above mentioned issues with reference to Dracula, the rock opera of Italian band PFM （Premiata Forneria Marconi）...Playbills, covers, and logo of an opera often reflect the meanings of the drama. This paper focuses on above mentioned issues with reference to Dracula, the rock opera of Italian band PFM （Premiata Forneria Marconi）, explaining how every visual aspects （also considering scenography and costumes） are closely linked to libretto and music to show the consistency among the different facets of the opera production. In this procedure, graphic artists and designers confirm their knowledge, but apart from this awareness, there are some symptoms of an tmconscious creativity as much coherent. As a result, this study aims to show how the management of the biggest colossal in the history of rock opera tries--constantly torn between art and advertising--to attract a potential audience by means of the iconography both of the composers and of the most famous vampire in the world.展开更多
针对原边反馈反激变换器具有辅助绕组而成本偏高的问题,基于原边反馈与峰值电流控制方案,提出了一种基于开关管漏极反馈的反激变换器模型。与原边反馈反激变换器相比,漏极反馈反激变换器能够减少变压器辅助绕组,降低了成本,且具有较高...针对原边反馈反激变换器具有辅助绕组而成本偏高的问题,基于原边反馈与峰值电流控制方案,提出了一种基于开关管漏极反馈的反激变换器模型。与原边反馈反激变换器相比,漏极反馈反激变换器能够减少变压器辅助绕组,降低了成本,且具有较高的稳定性。首先,对此漏极反馈反激变换器模型进行了理论分析,并提出了一种高精度漏极采样方法。其次,基于开关网络模型法对工作在断续导通模式(Discontinuous conduction mode,DCM)下脉冲频率调制(Pulse frequency modulation,PFM)的漏极反馈反激变换器进行了小信号建模并进行补偿设计。通过Matlab/Simulink搭建模型验证其正确性;最后搭建试验平台来进行验证。结果表明,所提出的漏极反馈反激变换器模型是可行的。展开更多
提出一种可根据负载变化在脉冲宽度调制(pulse width modulation,PWM)和脉冲频率调制(pulse frequency modulation,PFM)两种工作模式间自动切换的降压DC-DC芯片的设计法,推导出临界切换状态下的负载电流值表达式,在此基础上设计了一种PW...提出一种可根据负载变化在脉冲宽度调制(pulse width modulation,PWM)和脉冲频率调制(pulse frequency modulation,PFM)两种工作模式间自动切换的降压DC-DC芯片的设计法,推导出临界切换状态下的负载电流值表达式,在此基础上设计了一种PWM/PFM自动切换的DC-DC芯片.该系统在较大的负载变化范围内均具有较高效率.展开更多
文摘论述PFM(Pulse Frequency Modulation)脉冲频率调制型X光机电源的原理及系统构成.其主要功率器件选用目前国际上最先进的IGBT绝缘栅双极型晶体管.整流可控硅移相融发脉冲是由单结晶体管产生.PFM脉冲信号是由压频(V/F)振荡器产生.控制电路采用预置X射线管电压,管电流以及设置X射线管阳极最高工作温度、连续工作时间等多环节调节.
文摘Playbills, covers, and logo of an opera often reflect the meanings of the drama. This paper focuses on above mentioned issues with reference to Dracula, the rock opera of Italian band PFM （Premiata Forneria Marconi）, explaining how every visual aspects （also considering scenography and costumes） are closely linked to libretto and music to show the consistency among the different facets of the opera production. In this procedure, graphic artists and designers confirm their knowledge, but apart from this awareness, there are some symptoms of an tmconscious creativity as much coherent. As a result, this study aims to show how the management of the biggest colossal in the history of rock opera tries--constantly torn between art and advertising--to attract a potential audience by means of the iconography both of the composers and of the most famous vampire in the world.
基金Supported by Natural Science Foundation of Tianjin （07JCY- BJC05400）, Opening Project of National Laboratory of Industrial Control Technology of Zhejiang University （0708001）, Program for New Century Excellent Talents in University （NCET-06-0210）
文摘针对原边反馈反激变换器具有辅助绕组而成本偏高的问题,基于原边反馈与峰值电流控制方案,提出了一种基于开关管漏极反馈的反激变换器模型。与原边反馈反激变换器相比,漏极反馈反激变换器能够减少变压器辅助绕组,降低了成本,且具有较高的稳定性。首先,对此漏极反馈反激变换器模型进行了理论分析,并提出了一种高精度漏极采样方法。其次,基于开关网络模型法对工作在断续导通模式(Discontinuous conduction mode,DCM)下脉冲频率调制(Pulse frequency modulation,PFM)的漏极反馈反激变换器进行了小信号建模并进行补偿设计。通过Matlab/Simulink搭建模型验证其正确性;最后搭建试验平台来进行验证。结果表明,所提出的漏极反馈反激变换器模型是可行的。
文摘提出一种可根据负载变化在脉冲宽度调制(pulse width modulation,PWM)和脉冲频率调制(pulse frequency modulation,PFM)两种工作模式间自动切换的降压DC-DC芯片的设计法,推导出临界切换状态下的负载电流值表达式,在此基础上设计了一种PWM/PFM自动切换的DC-DC芯片.该系统在较大的负载变化范围内均具有较高效率.
