1:1:1 Transformer is outputting 1/2 the Voltage

[swb1]

Hi,

I am using a 1:1:1 transformer and I have +/- 3.25V going in and +/- 1.6V coming out. Why is this?? Shouldn't the voltage going in be the same as the voltage going out?? I have a differential op amp driving the transformer and 0 Ohm series resistors on the + and - output pins of the op amp and I have a 75 Ohm resistor across the output of the transformer.

Thanks,

swb1

 

[geekEE]

What's the frequency of the waveform going in? What shape is the waveform? Is there any DC offset? Does the output get closer to the expected value if you increase the value of the resistor across the output?

 

[swb1]

Thanks for replying. I have a 10MHz square wave going in to the Transformer. No DC offset. The output does not change when changing the value of the resistor across the output.

swb1

 

[geekEE]

A square wave through a transformer? Are you looking at the input and output waveforms with a scope or are you measuring them with a meter? If you're measuring with a meter, you might be missing the fact that the output waveform is a much different shape than the input? Also, is that transformer made for such high frequencies?

 

[itsmoked]

Also since the difference is exactly 1/2 you may be misinterpreting your transformer ratios or miswiring something.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[swb1]

As a lab experiment, I slowed down the bit rate to 1 MHz and there was no difference in the output voltage.

swb1

 

[Skogsgurra]

Sorry. Can not help you any better than you should be able to yourself. You seem to expect the world to be perfect. It seldom is. A 1:1:1 transformer may be a device without internal impedance or saturation - but it seldom is. An opamp seldom has zero ohms impedance - at least not at 10 MHz. What you see is probably an interaction between real-world variables and you can find out what is happening by taking these real-world data into account when you test your circuit. And, make sure that you read those data (including foot-notes) and also that you interpret them correctly.

Gunnar Englund

http://www.gke.org

--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[jimkirk]

As a quick experiment, try reversing your primary and secondary. That should tell you if the winding ratio is really 1:1:1. If the voltage roughly doubled, itsmoked is probably correct. If not, welcome to the real world.

 

[waross]

After you have verified your transformer ratio with jimkirk's method, consider this.
An alternating voltage applied to a transformer causes an alternating magnetic field. This magnetic field induces EMFs in both windings. The induced voltage in the secondary winding is the open circuit terminal voltage. The induced voltage in the primary winding is the back EMF. The difference between the applied voltage and the back EMF is the voltage that drives the exciting current through the primary winding.
It will be interesting to view both applied voltage and primary current on a dual trace scope. I expect that you will see the higher frequency components of the square wave attenuated. There are too many variables that will affect the wave form of the current for me to guess at its shape, but I expect you will see a difference between the voltage trace and the current trace.
However if the two to one voltage ratio persists when you change the frequency or loading, I suspect that jimkirk is correct in suspecting a ratio error, and that your transformer has a good high frequency responce.
respectfully

 

[nbucska]

1.) scope it
2.) Try the trafo with sine wave.

Plesae read FAQ240-1032
My WEB: <

http://geocities.com/nbucska/>

 

[automatic2]

Increase the ohmage across the secondary (1k) and scope the wave form. You'll probably find that your far exceeding the current capacity of the output.