# Current and transformers

#### Rufinus

Joined Apr 29, 2020
243
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

#### crutschow

Joined Mar 14, 2008
34,689
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.

#### Rufinus

Joined Apr 29, 2020
243
Thank you.

#### MisterBill2

Joined Jan 23, 2018
18,986
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.

Joined Jul 18, 2013
28,768
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.

#### Rufinus

Joined Apr 29, 2020
243

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

#### DickCappels

Joined Aug 21, 2008
10,230
Caution! When one reduces the number of turns on the primary one usually see and increase in magnetizing current.

#### BobTPH

Joined Jun 5, 2013
9,154

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.

#### Rufinus

Joined Apr 29, 2020
243