Transformers for High Frequency: Size and Step-Up Ratio Considerations

[m718]

How small can I make a transformer and still get 1:30 or preferably higher step-up ratio ?
I have been reading a lot about transformers and I know using higher frequency will reduce the size, and I need to use ferrite core for high frequency. I don't want to use really high frequency, probably up to 2Mhz. The size limit is 0.5 cm2, input voltage is
6-10v from button cell batteries. What shape core should I use and what kind of winding scheme?

 

[berkeman]

How small can I make a transformer and still get 1:30 or preferably higher step-up ratio ?
I have been reading a lot about transformers and I know using higher frequency will reduce the size, and I need to use ferrite core for high frequency. I don't want to use really high frequency, probably up to 2Mhz. The size limit is 0.5 cm2, input voltage is
6-10v from button cell batteries. What shape core should I use and what kind of winding scheme?

How are you chopping the DC input? Is this like a little mini-flyback or mini-forward converter? How much power are you looking to convert?

 

[m718]

How are you chopping the DC input? Is this like a little mini-flyback or mini-forward converter? How much power are you looking to convert?

A sine wave generator circuit before the transformer For the dc and the power output about 10 microwatt. What is the difference between a flyback and a forward converter?. What ever type of transformer doesn't matter the only thing is it must be in .5 cm2 and 1:30 ratio or higher.

 

[berkeman]

A sine wave generator circuit before the transformer For the dc and the power output about 10 microwatt. What is the difference between a flyback and a forward converter?. What ever type of transformer doesn't matter the only thing is it must be in .5 cm2 and 1:30 ratio or higher.

The most efficient transformer would be a toroidal transformer, but as you can see from this thread, they are not easy to wind (especially with a 30:1 ratio):

https://www.physicsforums.com/showthread.php?t=130135&highlight=toroid

Next up would be something like a small pot core transformer. You would wind your two windings on the bobbin, and clamp the pot core around it.

What is the application? What do you need 300Vac at 10mW for?

 

[mheslep]

A sine wave generator circuit before the transformer For the dc and the power output about 10 microwatt. What is the difference between a flyback and a forward converter?. What ever type of transformer doesn't matter the only thing is it must be in .5 cm2 and 1:30 ratio or higher.

As I vaguely recall, it is preferable to avoid ratios that high and use multiple stages instead. Perhaps someone with more recent experience can confirm, but vaguely some of the problems with high ratios include:
-keeping the turns down in the primary to avoid high turns in the secondary makes the design very sensitive to winding technique and materials used.
-difficulties in meeting material safety voltage isolation between pri/sec windings.
-some xformer parasitics are directly proportional to turn count.

I know plenty of manufactured cores with high ratios exist, but I believe they directly address these issues, with potted cores, etc, i.e. things you'll want to avoid.

 

[Studiot]

Berkeman did ask what the application was for and I didn't follow the answer if there was one, except that the power was low.

You might find a ready made trigger or pulse transformer adequate for your needs for example

http://www.maplin.co.uk/Module.aspx?ModuleNo=2298

Or you might find that stripping out the ferrite transformer from a redundant computer power supply might also do.

 

[m718]

Berkeman did ask what the application was for and I didn't follow the answer if there was one, except that the power was low.

You might find a ready made trigger or pulse transformer adequate for your needs for example

http://www.maplin.co.uk/Module.aspx?ModuleNo=2298

Or you might find that stripping out the ferrite transformer from a redundant computer power supply might also do.

I will look into those they look exactly like what I need but since they are used for camera flash I wonder if they can operate continuously.

 

[berkeman]

I will look into those they look exactly like what I need but since they are used for camera flash I wonder if they can operate continuously.

Can you say what your application is?

 

[Studiot]

I was just looking quickly round, I don't even know what continent you are on so UK suppliers may be inappropriate.

There are plenty of US suppliers of ferrite cores and bobbins to roll your own and they are as cheap as muck.

http://uk.rs-online.com/web/search/...method=retrieveTfg&Ne=4294957561&N=4294957271

 

[m718]

I'm using it to generate electrostatic like when you touch a car and get a small shock.
Power needs to be very small like the natural electrostatic so that shouldn't be a problem.

 

[Studiot]

I'm using it to generate electrostatic like when you touch a car and get a small shock.
Power needs to be very small like the natural electrostatic so that shouldn't be a problem.

What on Earth do you mean? The above suggests you do not know enough about electricity to be playing with several hundred volts.

Whilst I can think of a few legitimate uses for generating several hundred volts at low power from a 6 volt battery I can also think of several less savoury ones.

Since you show a remarkable reluctance to define your application and neither PF nor I condone inappropriate uses I can only suggest you abandon your project.

 

[berkeman]

I agree. This thread is closed.