Test transformer with signal generator and oscilliscope - Page 1
Forum section: electronics / beginners

author: mikeinfodoc
author_rank: Regular Contributor
timestamp: February 25, 2020, 01:06:33 am
content: I would like to see how well a sine wave would pass thru a transformer. (from primary side to secondary)Is it possible/practical to test small transformers which you might find in small low powered consumer devices with a signal generator and an oscilliscope?sample transformer:https://www.hawkusa.com/manufacturers/hammond-mfg/power-products/pc-mount-transformers/161d120if so, is it really just connecting the signal generator (sine wave) to the primary, and the oscilloscope to the secondary?(assuming the windings ratio would not blow up anything)

author: bob91343
author_rank: Super Contributor
timestamp: February 25, 2020, 01:17:15 am
content: Yes that will work.

author: james_s
author_rank: Super Contributor
timestamp: February 25, 2020, 01:39:19 am
content: I've done that many times to characterize unknown transformers. You only have to be careful that the winding ratio is so high that the output could exceed the voltage rating of your scope or probe. Start at low amplitude and dial it up.

author: gbaddeley
author_rank: Regular Contributor
timestamp: February 25, 2020, 10:30:43 am
content: Signal transformers are usually designed to work into a particular impedance load. To properly measure its useful frequency range, you should add a load, eg resistor 100R - 10K ymmv.

author: Circlotron
author_rank: Super Contributor
timestamp: February 25, 2020, 12:19:00 pm
content: Best if you can drive the transformer from a small audio amplifier connected to the output of your signal generator. It will likely have a lower output impedance than the signal generator, so, within limits, the output level will stay constant regardless of load.Also, the particular style of transformer you linked to will have a relatively poor frequency response because the primary and secondary are side by side rather than one over the top of the other. Really good audio transformers have the primary and secondary divided into a number of layers and interleaved, part primary, part secondary, part primary etc.And yeah, the output side of the tranny needs to be loaded with a resistor for frequency response tests to make sense. See link regarding impedance ratio vs turns ratio.https://www.electronics-tutorials.ws/transformer/audio-transformer.html

author: mikeinfodoc
author_rank: Regular Contributor
timestamp: February 26, 2020, 08:21:09 pm
content: thank you for the tips. As far as using an audio amp for the input, I would like to try that.I would like to create a very simply audio amp which I could plug into my mp3/phone.I have a variety of opamp's in my toolbox. Do you recommend that I use a low level to line level op-amp?or a line-level to loud-level?(aka do you recommend a particular opamp chip ...and particular Vout range?)or should I just attempt to find the specs on these small transformers (which I desolder from various small devices)?

author: Circlotron
author_rank: Super Contributor
timestamp: February 26, 2020, 09:03:38 pm
content: Something that is capable of driving a loudspeaker. For example LM3876. They are pretty easy to use and have a degree of built-in protection. Doesn’t even need to be that powerful. Something capable of several watts would be enough. Plenty of prebuilt modules on eBay.

author: Electro Detective
author_rank: Super Contributor
timestamp: February 26, 2020, 10:10:04 pm
content: Get some fast blow fuses inline on the action in case something goes POP or fume..