ir2153d/ir21531d transformer and mosfets

[paol]

Hi

Anyone with experience that can help matching mosfets and transformer primary (push-pull conf) inductance for best performance ?

My schematic attached.

Basically what I want is to carry input voltage of 24 to 63V (irs is powered from other power source 13V input) - then transformer is push pull (1:0.7 RATIO)
Currently it is working with setup as on schematic - but it draws about 4W at idle (for me it is a little too much)

Increasing working freq. for half bridge from 79kH to 98kH makes things worst (5W)

I can prepare any transformer for this - but for now it is like (rewinding history)
Also currently using 18mOhm (rdson) transistors - 200V .... so not cheap - I think all this stuff can be optimized to draw less power with cheaper transistors (safer higher voltage for DS and higher RDSon) but as I said ... currently rewinding history to optimize this

Thanks for any help.
 

[paol]

Also

increasing RDSon from 18mOhm to 140mOhm (mosfet) is lowering power usage - without load (from 4W to 3W) seems normal as there will be higher resistance when mosfet is on but also how power will be dissipated at mosfets...

[paol]

Or maybee eliminate snubbers... cause they are 1W

But eliminating snubbers can make things worst - have some voltage spikes when switching and for 200V mosfets and +48V DC input sometimes it is 180V+ without snubbers so no margin - with snubbers there is not much ringing and no overshooting more than 110V

Anyone have idea how to minimize ringing on that implementation ?
Increasing rdson to 300-400mOhm and using 500V mosfets can allow me to resign from snubbers i think - but need to check this currently waiting for other mosfets.
But then I will need to rethink also mosfet heatsinks that currently are on PCB (more heat will be dissipated on fets)

Or maybee someone have better idea how to controll push-pull transformer (cheap) - maybee self oscilating circuit with transistors ? but also I dont want to increase number of parts needed to solder...