Iron core transformer as flyback?

[roltex_rohit123]

Hey friends. I have a 3-0-3 transformer iron core. i dont know abt turns in primary or secondary windings. I want to use it a flyback transformer. I want to power it at 9 volts through a 555 timer. i want to know what amount of current and voltage i would get from 9 volts and what should be the pulse frequency to get most of it.

 

[Hero999]

Assuming the primary voltage is 230V, you'll probably get a peak voltage of just over 300V if you go in the turns ratio.

In reality the secondary voltage will be higher than the turns ratio because of the flyback effect, my guess is you'll get between 1kV and 3kV depending on the quality of the transformer.

The second current will be very low because the current is reduced.

 

[roltex_rohit123]

yeah I forgot to mention. its 500 mA. and another question that why are the ferrite core preferred to iron core?? i see in many lighting circuits that ferrite cores are used. is there a matter of size only?

 

[Nigel Goodwin]

Ferrite is used for high frequencies, iron for low frequencies. High frequencies mean much smaller windings and much smaller cores.

 

[roltex_rohit123]

with this transformer i intend to build a hand held mosquito zapper with 555 timer. can you suggest me anything better?

 

[Nigel Goodwin]

As you're likely to run at a fairly high frequency ferrite is likely to be better than irom.

 

[crutschow]

The reason ferrites are better at high frequency operation is that the high resistance of the ferrite material minimizes eddy current loses, which are proportional to frequency.

 

[MRCecil]

with this transformer i intend to build a hand held mosquito zapper with 555 timer. can you suggest me anything better?

I would suggest you look up the term permeability, and note the differences and effects of iron core, powdered-iron core and ferrite core transformers across the frequency spectrum for the application. Frequency makes a difference re: core material. Even without knowing your design parameters, it would seem that iron core would be the worst case choice.

 

[Hero999]

A high frequency wouldn't be required in a bug zapper.

Low frequency iron transformers are actually quite good for flyback transformers, because the core stores lots of energy you get of high intensity pulses or sparks which is why they're used in ignition systems. A ferrite transformer might have a higher power to weight ratio but what you tend to get is higher frequency but less intense pulses.

 

[MRCecil]

A high frequency wouldn't be required in a bug zapper.

Low frequency iron transformers are actually quite good for flyback transformers, because the core stores lots of energy you get of high intensity pulses or sparks which is why they're used in ignition systems. A ferrite transformer might have a higher power to weight ratio but what you tend to get is higher frequency but less intense pulses.

Hero,

I take your point insofar as an optional approach, but, as a designer, one must contemplate other practical aspects such as portability. Weight, size, ergonomics and battery life for a hand-held device, being part of the equation, are major factors for consideration in my way of thinking. But that's just me, perhaps. Silicon steel is heavy and can be very bulky. Powdered-iron cores are much lighter and compact, hence my comments re: frequency and core selection.

Cheers,
Merv

 

[Hero999]

Fair point.

A better approach might be to put a capacitor and rectifier on the output stage, maybe even a voltage doubler, so you get lower frequency but larger pulses of energy?