what effect will be if i change air gap in my this design

[anan1975]

hi
i design a smps supply in forward push pull topology with following specification
Np-primary turns 17-0-17
Ns -secondary turns 14-0-14
ip volt 75-85
op volt 5-48 volt adjustable
op amp 2.5 amp
swg 24 for eitherr side
core 424210
Lp pri inductance 300 uh(17-0 in 17-0-17 side)
frequency-45 khz
oscillating device sg3524,mosfet irf840.

i got the result as i required

and if i change the gap of core and got Lp-100uh, And if i reduce the gap Lp 400uh
what will be change?

Regards
anand

 

[rajudp]

in push pull no need of an gap in ferrite core

 

[eem2am]

sometimes you need air-gap to avoid saturation.............due to magnetising current building during fet on time.

in fact you usually end up need an air gap as ferrite has such low sat flux density

 

[pauloynski]

Re: what effect will be if i change air gap in my this desig

By increasing the gap the inductance wil go down. The inductor current will increase but, as previously mentioned, this is a technique used to avoid saturation. Your mosfet will heat more, leakage will increase (bad regulation) and the EMC will increase.