DC DC converter stage problem

[--BawA--]

i have designed a DC DC converter stage using push-pull topology(12vdc to 311vdc, 400VA), now as i apply a load of approx 100 watt , the one side mosfet bank become more hot than the other side mosfet bank, i think this is due to staircase saturation . does any one have idea, how to overcome this problem?

 

[dick_freebird]

Is the core being fully "reset" every cycle, or is there any
attempt at balancing flux about zero? I've seen this called
out as a design issue in more complex converter architectures
(buck and boost are as fancy as I get).

You might look also at gate pulse width asymmetry, which
could produce an accumulation of current imbalance over
time (this is where you'd try to inject the flux-balance
feedback I expect). What you'd sense, to create that
feedback, I do not know - but if you find out, it's probably
your next debug method too.

 

[--BawA--]

i have used sg3525 @25khz to produce gate pulse , and i have used voltage divider feedback to get constant voltage at the output.

 

[mossses]

i experienced the same thing when i was building smps inverter.use totem pole from your sg3525

 

[--BawA--]

i have used dedicated mosfet driver TC427 in my design.. i am facing another problem too, when i connect a heavy load at the output ,the battery terminal voltage goes to 10v , now i have to give 12v constant to SG3525 and other ICs, so is there any method to overcome this problem? is auxilary winding in the transformer has some relation to solve this problem??

 

[mossses]

check ur sg3525(pin 11 &14) output voltage,it should be equal or with different of 1mv.check the duty cycle of both side.what the amp of your battery? since your smps capacity is 400va.you should put a fuse of 40amps at the center tap of your transformer.

 

[--BawA--]

the voltage is around 7.65v , the battery is 12v 7.2ah, my question is "i want to supply all the ICs from the auxilary winding of the transformer (which is 12vdc constant), how to do this?

 

[mossses]

why do you wanna use aux windin to supply power to your ics? 7.2ah battery is ok to supply power needed for your circuitary.Note:Your battery amps to too small to handle 400va.12*7.2=86.4va...upload your diagram

- - - Updated - - -

the voltage is around 7.65v

since you're using a 12v battery,your output at both pin 11& 14 should be around 6.64volt or lower that for a fully charged battery

 

[--BawA--]

but when i apply a load of approx 100 watt the voltage of battery goes to approx 10.5, ,now the VCC of sg3525 is also seeing the same voltage (10.5V) , which is certainly not desirable, i want some modifiaction ,such that even if the battery voltage goes to 10V , then also the sg3525 can get a vcc of 12V, ?

 

[picgak]

but when i apply a load of approx 100 watt the voltage of battery goes to approx 10.5, ,now the VCC of sg3525 is also seeing the same voltage (10.5V) , which is certainly not desirable, i want some modifiaction ,such that even if the battery voltage goes to 10V , then also the sg3525 can get a vcc of 12V, ?

1.Did you check the current drawn from battery at 100w , if normal your battery is weak
2.If current is more then I suspect the primary winding of the pushpull Tx

 

[schmitt trigger]

Staircase saturation is a tough problem for voltage mode push pull converters.
You need to use a more advanced chip, like the UC3846, which employs current mode control.

 

[--BawA--]

You need to use a more advanced chip, like the UC3846, which employs current mode control.

can u please explain in detail about what is current mode control?

 

[schmitt trigger]

can u please explain in detail about what is current mode control?

Go to the Texas Instruments website and go to the app notes section, and look for the following documents:
https://www.ti.com/lit/an/slua119/slua119.pdf
https://www.ti.com/lit/an/slua101/slua101.pdf
https://www.ti.com/lit/an/slua075/slua075.pdf

The last one, in particular, addresses the flux imbalance in push-pull converters.