×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

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

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

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

(OP)
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

 

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

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?

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

(OP)
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

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

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?

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

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

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

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

swb1

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

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

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

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.  smile

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

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

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

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.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources