Hello.

If I'm right the power of a transformer is defined by the size of the core and the voltage output by the relation between primary and secondary turns. But there is a question I can't find.

A) if I reduce the turns in the primary and maintaining the secondary, I'll get more voltage, but less current? I mean, is the power is the same, the current has to decrease right?

Thank you

 

if I reduce the turns in the primary and maintaining the secondary, I'll get more voltage, but less current? I mean, is the power is the same, the current has to decrease right?

Yes, power in equals power out (reduced some by the transformer efficiency).

But note that if you reduce the input turns, the maximum input voltage is also reduced, to avoid core saturation.

 

Thank you.

 

In short, a transformer must not only have the correct turns ratio, but also an adequate number of turns so that it can operate in the most efficient level of magnetization. And THAT depends on the application. Audio signal transformers need to run in the very linear magnetization segment, power transformers can use the additional magnetization thatis a bit less linear, and some power oscillator circuit transformers can operate at the level where they go into saturation, as part of the oscillation sequence. That covers the three common schemes.
Reducing the primary turns to boost the output voltage is usually a poor choice, except for when it becomes a VERY POOR CHOICE.

 

Why not rewire the secondary to get the voltage required, In any case, It is wound on top of the primary, so you would have to remove it to change the primary anyway.
Place a simple 10 turn winding on and measure to obtain the turns/volt.
The V/A rating of the Transformer stays the same.

 

Thank for your answer.

Is a HF transformer with ferrite core. I'm using a ZVS to drive its primary witch is made of 5+5 turns and the output is very low, so instead incrementing the input voltage I was thinking in reducing the primary turns

 

Caution! When one reduces the number of turns on the primary one usually see and increase in magnetizing current.

 

Thank for your answer.

Is a HF transformer with ferrite core. I'm using a ZVS to drive its primary witch is made of 5+5 turns and the output is very low, so instead incrementing the input voltage I was thinking in reducing the primary turns

Reducing he primary turns by half would reduce the inductance by a factor of four. The circuit will likely not operate correctly with that change.

 

Thank for your answers. It is not by half, 4 instead 5.

But if it is better I will just increase the voltage in the primary instead changing the number of turns

 

If it is a Switching Mode PS transformer, the voltage translation is also dependent on the Pulse Width.

 

OK, for any who might be interested, "using a ZVS" implies to me that the TS is trying to make the transformer operate at the mains frequency, instead of the much higher frequency used by switchers. That will not work, because the core is constantly going far into saturation. A transformer spending most of it's time in saturation is terribly inefficient, and no amount of adjusting the turns ratio can fix that.

 

OK, for any who might be interested, "using a ZVS" implies to me that the TS is trying to make the transformer operate at the mains frequency, instead of the much higher frequency used by switchers. That will not work, because the core is constantly going far into saturation. A transformer spending most of it's time in saturation is terribly inefficient, and no amount of adjusting the turns ratio can fix that.

Zero Voltage Switching is a technique in switched-mode design where the drive voltage the winding is switched off, the inductance takes the winding to the opposite supply, and the power is not reapplied until the voltage has reached the opposite supply.
Why does a reference to ZVS imply to you that it is being operated at line frequency? Is there some other interpretation of ZVS that I don't know about?

 

Zero Voltage Switching is a technique in switched-mode design where the drive voltage the winding is switched off, the inductance takes the winding to the opposite supply, and the power is not reapplied until the voltage has reached the opposite supply.
Why does a reference to ZVS imply to you that it is being operated at line frequency? Is there some other interpretation of ZVS that I don't know about?

Reading all of the posts tells me that the TS is not very used to dealing with transformers and the magnetic saturation issues. Hence my guess.

 

Reading all of the posts tells me that the TS is not very used to dealing with transformers and the magnetic saturation issues. Hence my guess.

…and that is why we are here (to help),

 

And one more thing, related to that first post: The maximum power capability of a transformer IS LIMITED by the size of it's core.
In addition, given the cost of copper wire, usually the input winding of a power transformer number of turns, is already at a minimum determined by some variable. So removing primary turns will reduce some desirable aspect of the transformer operation.