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some questions about DC to DC converter

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wei9321

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I have some questons:
(1)the output inductor (for forward),L=V*(1-D)/f*ΔI,where D is Dmin or Dmax,
which one is better ? why?
(2)current mode pwm ic ,connect a small value ceramic capacitor between CS pin
and RT/CT pin,someone said,it can improve steady the dc to dc converter,
why?
thanks!
 

Miguel Gaspar

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If Dmin = ton/T min that implies the charging time of the Inductor, capacitor and conduction of the device (transitor and diode) is minimum and the current is greater because it must provide energy to the load and carge the inductor and capacitor. So in the toff the energy stored in C and L flows to the Load.

about (2) I have no idea what are you talking about.
 

dick_freebird

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This (2) might be a poor man's slope compensation when
no such feature is built in.
 

wei9321

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If Dmin = ton/T min that implies the charging time of the Inductor, capacitor and conduction of the device (transitor and diode) is minimum and the current is greater because it must provide energy to the load and carge the inductor and capacitor. So in the toff the energy stored in C and L flows to the Load.

about (2) I have no idea what are you talking about.
about (1),you means,we must confirm L at Dmin,the L have enough energy to provide the C and Load ,right ?
about (2),I means,I have had the experience of a problem about mosfet wave shake problem,
when I connect a small value ceramic capacitor between CS pin and RT/CT pin,
the mosfet wave will be stable,but I don't understand it's principle
 

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