Push-Pull SMPS overshoot problem

[jamesrnz]

wel the main transistor get way warm. they are single to-247's. so i am going to change them out to three or four paralleled to-220's on each leg.

i was trying to save space, but i think that the parallelled transistors will distribute the current better.........................

 

[luka]

Hi

But why change anything if the thing is not even working? what can you post now, like scope waveforms, any other pictures anything, coz I just can't see how you would "lose" 27A if you even got this right, coz that is 351w, something should be red hot or in smoke if this was true.Can you check again?

 

[jamesrnz]

oh it gets hot

i had to go back to work so it will be a few weeks before i get back.

i was thinking that may be both sets are overlapping and on at the same time.

when i get back i will be able to post some waveforms and updated information..


thanks!!

 

[luka]

Hi

Cross conduction is one thing, but if you can't have limited input, your fets should be dead if you have overlapping. If you have current limited, your input voltage should be lower because of limit, and last one is by some freak coincidence you don't hae current limit but circuir doesn't draw more current then it does now...anyway check this for sure, you can't have this big power difference