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flyback vs push-pull vs forward converter

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uoficowboy

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Hi - can somebody tell me what advantages/disadvantages flybacks, push-pull, and forward converter DC/DCs have with respect to each other?

Here's my attempt:

Flyback:
+lowest part count (1 primary switch, 1 diode)
-inductor is typically larger, I think (since you're storing energy)
-Susceptible to ringing on primary

Push-pull:
-Highest part count (4 switches, 4 diodes)
-Most losses in signal path (current in primary flows through two switches, current in secondary flows through two diodes)
+transformer is smaller than flyback, I think
+least ringing on primary (this is a educated guess!)
-Output voltage is dependent on your transformer turns ratio

Forward converter
~less parts than push pull, more than flyback (1 switch, 2 diodes)
~transformer is a bit larger than push pull (I think)
-More ringing on primary than push pull, not sure about flyback
-Output voltage is dependent on your transformer turns ratio

How am I doing so far?

I should mention my eventual interest is in making a high Vout/Vin ratio DC/DC. Something like 5V to 1KV. But I'm also interested in comparing these topologies in the general sense.

Thanks!!
 

goldsmith

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Dear uoficowboy
Hi
I think you're a bit confused . push pull , just has two switch , not 4 switch , i think you're referring to the H bridge ( it has 4 switch) .
And about fly back , usually , we don't have an inductor in it's out put ! just a capacitor ! however you can see an inductor at some of designs ( to be in continuous mode ) .
And about disadvantages of fly back : 1- large value of ripple ( to increase the ripple we have to use larger capacitors ( naturally larger capacitors have larger ESR , so we have to use some capacitors in parallel ) .
2- bad spikes at out put .
3- limited power up to 400 w at best designs !


and about forward , it has two mode ! first one is single ended and the other is double ended . both of them have advantages and disadvantages . limited power but it is more than fly back . better load regulation . better safety . lower spikes and ... etc
And about push pull : we can consider that it is two forward converter . it has advantages of forward ( and it hasn't disadvantages of fly back ) and it's out put power can be very higher than a forward converter .
So i hope i understood what you want to know . if you need more informations , tell me , i'll explain all of them in detail .
Best Wishes
Goldsmith
 

atripathi

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I am not sure why would you want to compare these. For your application I would suggest you should go for flyback, assuming you need to deliver little power at 1KW.
 

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