Hi guys, just signed up right now due to a seemingly simple issue I've been having problems with...

The last time I dealt with transformers, magnetic fields, etc was back when I was doing my A levels which seems like far longer than I'd like to admit

I've been planning on building a switch mode power supply operating on 50khz (square wave), and throughout this build I was wondering whether I could build my own transformer based off of an eBay toroid (made from ferrite...whether it's MnZn or NiZn, I have no clue...)

According to one source, magnetic saturation (B,max) of ferrite is 0.3 to 0.5T according to one source. Is this correct? Only using this as a general use of thumb, due to me using 2x or 3x factors of safety wherever I can

The EMF equation (for a square wave) dictates the following;
E,max = 4.f.N.B.A

where...
E,max is maximum voltage of square wave (in this case, for the primary side of transformer, which is fixed)
f is frequency at which transformer will be running at (another fixed constant)
N is the number of turns (again, in this case, for the primary side)
B is the magnetic flux density
A is the cross sectional area of the toroid (fixed constant)

Rearranging the equation above, does it mean the larger number of turns around the toroid, the lesser amount of magnetic flux density for a fixed primary voltage source? This seems counter intuitive, hence the reason why I'm asking my question here...
I am under the impression that the higher number of turns around a ferrite / iron core, the higher the amount of flux created...

Thank you in advance for anybody wishing to answer my question

 

Hi guys, just signed up right now due to a seemingly simple issue I've been having problems with...

The last time I dealt with transformers, magnetic fields, etc was back when I was doing my A levels which seems like far longer than I'd like to admit

I've been planning on building a switch mode power supply operating on 50khz (square wave), and throughout this build I was wondering whether I could build my own transformer based off of an eBay toroid (made from ferrite...whether it's MnZn or NiZn, I have no clue...)

According to one source, magnetic saturation (B,max) of ferrite is 0.3 to 0.5T according to one source. Is this correct? Only using this as a general use of thumb, due to me using 2x or 3x factors of safety wherever I can

The EMF equation (for a square wave) dictates the following;
E,max = 4.f.N.B.A

where...
E,max is maximum voltage of square wave (in this case, for the primary side of transformer, which is fixed)
f is frequency at which transformer will be running at (another fixed constant)
N is the number of turns (again, in this case, for the primary side)
B is the magnetic flux density
A is the cross sectional area of the toroid (fixed constant)

Rearranging the equation above, does it mean the larger number of turns around the toroid, the lesser amount of magnetic flux density for a fixed primary voltage source? This seems counter intuitive, hence the reason why I'm asking my question here...
I am under the impression that the higher number of turns around a ferrite / iron core, the higher the amount of flux created...

Thank you in advance for anybody wishing to answer my question

Hi,

Welcome to the forum.

It's only counter intuitive if you look at it from the prospective of current, a constant current, because more ampere turns means more flux, but if you look at it from the prospective of voltage (constant voltage which your input will look like) then it's very intuitive because more turns means higher inductance and at any give frequency (like 50 or 60 Hz) that means less current, which in turn means less flux.

So in short, we dont drive them with a constant current we drive them with a constant voltage. If we drove them with a constant current then you would be right.