[Amps] transformer distortion question

[Manfred Mornhinweg]

Hi Drax,

 > I made a center tapped,  bifiliar wound, toroid transformer out of 26
 > turns of 22 ga. magnet wire on a 1" diameter core. This is so that I can
 > split the phases to drive the second stage as a push-pull.

Probably you will want to use fewer turns in the secondary, since the next stage 
will likely have a lower input impedance.

 > When I look at the output of the right side of the output of the
 > transformer it looks like a perfect sine wave.When I look at the left
 > side's output the negative dip looks distorted.

You are driving your IRF510 into saturation. Note that saturation of a MOSFET at 
RF isn't usually "hard" and defined by its RdsON, but rather is a kind of soft 
saturation caused by the drastically increasing drain-gate capacitance at low 
voltage.

 > Why is it only on one side of my transformer, only on the negative dip?

That's due to the transformer's leakage inductance, which reduces the coupling 
factor. Because of this, the two sides of the transformer aren't hard-coupled, 
and so they can have somewhat different waveforms and voltages.

The stray capacitance, along with this leakage inductance, act as a low pass 
filter, tending to remove harmonics, and thus smoothing out any distorted 
waveform into something closer to a pure sine.

To get a behaviour closer to that of a perfect transformer, eliminate those long 
leads, mount everything closer together, and improve the coupling of the two 
wires by twisting them tightly before you wind them on the core. A further 
improvement can be obtained by using a core shape that better surrounds the wire 
with ferrite, such as a two-hole core, or a pot core.  Toroids are the simplest 
closed core shape possible, but not the best.

Manfred


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