hi, i am new to the design pfc, please suggest how to design a boost and buck converter pfc using LT1248 and LT1249 chip. I am presently using LT spice.
basically, slow voltage loop, and quicker current loop.
hERE IS SOME LTSPICE PFC circuits for you
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http://cds.linear.com/docs/en/datasheet/1248fd.pdf
you should see a precession of upside down half sine on pin 3, the current error amplifier output.....remember PFC is a bit different to normal vout reg'd smps, instead of the voltage error amplifier directly feeding a pwm comparator, ..with a pfc stage, (ccm), the voltage erorr amplifier feeds a current eror amplifier which itself feeds the pwm comparator......and to make things more interesting for us, the voltage error signal first gets multiplied by a voltage which is representative of the instantaneous primary bus voltage...and then the conglomeration of those signals gets stuffed into the current error amplifier......the result is that you get your vout, but you get it with current being delivered in phase with the primary bus voltage.