Hi all.
I am looking to make a pfc cct using the uc3852 chip and have a few
questions.The info I have is the U-132 app note from Unitrode and the
uc3852 datasheet.
I am just going through some equations and have a question.
In the datasheet they have an application for a 100W power factor
preregulator(page 5)
I can't figure out how they get some of the values thay do.It's getting
late in the day and maybe I'm missing something :0(.
The cap and resistor (C4 and R4) that are used to determine the max on
time are 13.3K and 180pF.That give a t(on)Max of 4.2uS - That relates
to a min frequency of 237KHz ?? (formula from u-132:
T(on)Max = Rset*C(ramp)) / 0.568
The value of the inductor is 680uH.
I can't get this to tie up with the formula to calculate the inductance
(formula 16A)
L = (VP(min)^2 * [Vo - VP(min)] ) / (( 4*Po(max)* Vo * F(conv)min)
Po =100
Vo =400
Vp = 127 , I assume as they say 90 - 160V rms input.
I have a feeling that I am missing something obvious.
Any help appreciated.
Cheers
Rob
I am looking to make a pfc cct using the uc3852 chip and have a few
questions.The info I have is the U-132 app note from Unitrode and the
uc3852 datasheet.
I am just going through some equations and have a question.
In the datasheet they have an application for a 100W power factor
preregulator(page 5)
I can't figure out how they get some of the values thay do.It's getting
late in the day and maybe I'm missing something :0(.
The cap and resistor (C4 and R4) that are used to determine the max on
time are 13.3K and 180pF.That give a t(on)Max of 4.2uS - That relates
to a min frequency of 237KHz ?? (formula from u-132:
T(on)Max = Rset*C(ramp)) / 0.568
The value of the inductor is 680uH.
I can't get this to tie up with the formula to calculate the inductance
(formula 16A)
L = (VP(min)^2 * [Vo - VP(min)] ) / (( 4*Po(max)* Vo * F(conv)min)
Po =100
Vo =400
Vp = 127 , I assume as they say 90 - 160V rms input.
I have a feeling that I am missing something obvious.
Any help appreciated.
Cheers
Rob
