Author Topic: temperature coefficent of a audio balun transformer?  (Read 923 times)

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Offline CopperConeTopic starter

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temperature coefficent of a audio balun transformer?
« on: January 18, 2018, 01:45:44 pm »
Does anyone know what the typical temperature coefficient of a audio balun transformer might be?

That is, how much the output signal amplitude varies per degree Celsius?
 

Offline schmitt trigger

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Re: temperature coefficent of a audio balun transformer?
« Reply #1 on: January 18, 2018, 02:04:09 pm »
All I know is that copper's resistance increases 0.39% per each degree C.
I would not think that the steel core's properties would change very much.
 

Offline CopperConeTopic starter

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Re: temperature coefficent of a audio balun transformer?
« Reply #2 on: January 18, 2018, 05:09:24 pm »
I am interested in the comparison of capacitors and inductors.

I can very precisely make a push pull driver with opamps and thermally matched resistors. This can be coupled with two foil capacitors and the drift is the tempco of the capacitor. Its reactance will have a voltage drop proportionalto temp. Its approximately 160ppm/degree c.

The capacitor can be made large to lower the effect of its reactance drop, however i am also very concerned about dc leakage, and dc leakage over temperature. This forces me to use foil capacitors, which are rather large past 10uf or so.

I am interested in taking ppm measurements to make a choice.

Should i focus on measuring steel laminated ones to get some sort of idea?

My measurements on inductors lead me to believe they have a tempco of approximately 600ppm/degree c. This is worse then capacitors, so the reactance would need to be four times lower to match the performance of capacitors.

Anyone got any numbers? Otherwise i need to make a tempco box.

In that case, any suggestions on a good balun to test? Will the materials used in a common mains transformer be the same as an audio transformer? The type of steel?

Also it looks like i need to meausure both dc resistance drift and inductance drift and correlate them
« Last Edit: January 18, 2018, 05:17:37 pm by CopperCone »
 

Offline Conrad Hoffman

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Re: temperature coefficent of a audio balun transformer?
« Reply #3 on: January 18, 2018, 06:11:58 pm »
I'm sure there's some inductance and resistance change, but the output is determined by turns ratio. If you have low impedance drive, and don't load the output, it should be almost unaffected by temperature. You should read the manuals for precision ratio transformers like the old General Radio 1493. They don't talk about temperature at all, yet the things are good to less than a ppm and were recognized as primary standards by NIST.
 

Offline CopperConeTopic starter

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Re: temperature coefficent of a audio balun transformer?
« Reply #4 on: January 18, 2018, 08:50:36 pm »
the load is unfortunately not high impedance  >:D

I guess that I am in uncharted territory

Since there is mutual coupling between the primary and secondary, must its drift be evaluated too?

Easy enough to setup a LCR meter to measure a winding across a temperature shift, but could this value be used or do I need to use the test signal? I think that there are some losses that might effect it more. Fringing loss comes to mind but can it just be ignored for the sake of stability?
« Last Edit: January 18, 2018, 09:04:15 pm by CopperCone »
 


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