flyback transformer design problem

[A'khz]

hello
im trying to design flyback transformer with marty brown book formulas .
it has two formulas in CGS and MKS system as it says .
ive just put same values in these two and getting different results .
what im doing wrong?

 

[goldsmith]

hello
im trying to design flyback transformer with marty brown book formulas .
it has two formulas in CGS and MKS system as it says .
ive just put same values in these two and getting different results .
what im doing wrong?
img_20140709_193201.jpg

Hi A'khz

I'm not using that way for design , if you want i can share you the way which i'm using ?


Best Wishes
Goldsmith

 

[A'khz]

sure i will appreciate that
kheyli mamnoon

 

[goldsmith]

sure i will appreciate that
kheyli mamnoon

OMG ! you're a compatriot too isn't it ?

Well , i suppose you know what , how a fly back converter does work , isn't it ? it will restore the energy while the switch is conducting , i give you a clue ,
WL=0.5LI^2 you know about this ? can you guess more or perhaps i must guide you more ?


Best Luck + موفق باشی
Goldsmith

 

[A'khz]

yes i am :wink:
are you sure that formula works fir this ?
i think thats for DC current and doesn't have dt effected.
it should be V=L.di/dt i think
but my problem is not actually about the inductance calculation .
its mostly about the Lgap and number of turns of an inductor .
can i find toroid gapped core online ?
i found at some stores but their gap size were not defined .

 

[goldsmith]

yes i am

Then good to know that ;-)

are you sure that formula works fir this ?
i think thats for DC current and doesn't have dt effected.

Question yourself ! would the flyback converter work if it was DC signal ? we break the switch before the inductor be saturated so now we can look into that , in another manner .

but my problem is not actually about the inductance calculation .
its mostly about the Lgap and number of turns of an inductor .
can i find toroid gapped core online ?
i found at some stores but their gap size were not defined .

I understood your problem as well and it is why i tried to lead you through the simpler way and you accepted , isn't it ?
Before try to design a converter you must know how it works , up to know , i understood you didn't realize that how a fly back converter works as well .
If you understand everything as well , then you can find another way to design everything .

A flyback converter will restore energy while the switch is on and will deliver the energy into the out put while the switch is off . So , it means as for primary you deal with a storage ! So you can use the formula of power storage at inductor . ( what i've suggested before )
If you realize this you'll be able to calculate everything as fast as most of the people think that that's impossible .

Good Luck
Goldsmith

 

[A'khz]

oh!
i was confused with joules and watts at first .
i think this is right :
Po=10w
Vo=10V @1A
Vin=100V
F=100k , T=10us , Ton=5us
so
Iinave=P/Vin=0.1A
Iinductor = Iinave/D=0.1/0.5 =0.2A
El=0.5LI^2=10*5*10^-6=0.5*L*0.2^2
L=2500uH
yes ?

 

[goldsmith]

oh!
i was confused with joules and watts at first .

Hi again
Why ? W/t= power in watt ! simply joul being converted by this simple thing !

Iinave=P/Vin=0.1A

theoretically if you consider the magnetic efficiency and overall efficiency around 100 percent it is right but for now it is absolutely wrong ! you looking for a clue ? i give you a rule of thumb ! add 15 or 20 percent to this ratio ! 0.1(1+20/100) Okay ?
W=0.5LI^2===> divide by time will consequence the power in watt hence :
P=(0.5LI^2)/T
then find L ( about t you must know what while switch is on it is restoring energy )
hence the Formula is :
L=Pton/0.5I^2
So yeah ! :wink:

Good Luck
Goldsmith