Question of Flyback Transformer in DC Step-up Converter Design

Have a look at this, it will save some time and effort

www.farnellinone.com

look for dc - dc convertors, plenty of modules to choose from.

Rather curious why you want to step up from 3.3v rather than access the available 12v rail that is there or even the 5 volt rail as most pc power supplies have this in abundance.

Sorry for trouble, I've re attached the pic here:

Hi All,

Sorry, I am intereste to find out if the above circuit in Fig 2 can meet my electrical requirement.

How do I calculate the inductances (pri and sec), turns ratio, and switching frequency etc?

I think it would be efficient if I chose pri inductance to be same as sec inductance and the number of turns in sec winding to be less than pri winding so the sec coil can source more current. Is this correct?

Your reply is greatly appreciated

What is the point? Such supplies are straight catalog items. The price is something you cannot touch yourself, nor the efficiency.

Hope to bend the cost curve, or simply homework?

Possible - yes. We did this many times to get added voltages in Flyback converter TV sets to get added voltages just do some turns around the flyback transformer. Or to create the tuning voltage from a low voltage

Designwise it is much more trouble than to use a single choke step up transformer. Refer to LT catalog. A critical key item is the capacitor 191 and he overall ripple of he circuit.

2 Windings are always more expensive than a simple choke off the shelf....

Look for off-the-shelf converter as suggested by one friend.

For your information I add that Flyback circuits don't follow the Turns Ratio rule but frequency. If you have an old CRT TV look its HV transformer.

It is the field of Hi-Frequency which need ferrite core transformers and knowledge of SMPS like used in PCs.

I suggest to use (+) or (-) 12V which has much higher capacity of current than the 3.3V which only to switch on or off.

Circuit one will do if you can design the Regulator control properly.

The kick back of L1 will add its pulse to input voltage.

Find the detailed description for it.

Thanks! I think I'll stick to circuit in Fig 1.

One more question,I am curious to know does circuit of Fig 2 improves power conversion efficiency, since it "traps" more magnetic flux with its secondary inductance coil, as compared with Fig 1 circuit which has one coil? Or does this translates to the Vin source havs to supply more current to achieve the same amount of magnetic flux since it has to drive additional (secondary coil) compared with traditional circuit?

Cheers!