DC-DC Boost converter Enter in DCM mode

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Alberto Dan

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Hy I have a problem with a DC Boost converter.I want to use them on a alimentation module for constant current for optic bloc that used LED technologie,Headlights with LED technology.Input voltage will be between 12V and 24V and output between 30V and maxim 36V with 900mA current consumption.In atach i put a schematic and a pic from simulation issue on Ltspice tool.I don t know how to go out from DCM mode because enter in this mode.Can anybody help me please hot to mantain in CCM mode,or how to know where is the limit from CCM to DCM?Please!!

 

It may be impossible to enter CCM with a boost converter, due to its innate behavior, that is, by sending current through an inductor for a long time, you get stepped-up voltage during a short time.
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Otherwise as a general rule, you enter CCM by doing any of the following:

* increase inductor value
* increase switching frequency
* make hysteresis range narrower
* increase duty cycle

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The 4uH inductor can be in CCM if you increase frequency (theoretically) upwards of 1MHz.
 

Hy,I increased inductor value,frequency for 1Mhz but still nothink.
I put a series led of aoutput feedback and still work,and i make some ajusted value on inductor and capacitor but i don t think if with that led will work in real life...what you think?
 

Just as a comparison of waveforms, here is my simulation of a simple boost converter.
Inductor current is always flowing. It is in CCM.

 

Alberto please zoom in to your current so we can see it better.
Or if you want send me the sim and i will fix it for you and post it back in a few minutes....

in post#2 that is good advice for you
 

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