Can I use an audio transformer as AC voltage sensor

[Piet de Pad]

Dear reader,
I have a question about using audio transformers as 120Vac 60Hz line voltage sensors.

I know how to measure AC line voltages with dedicated AC voltage transformers like the ZMBT101B or the ZMBT107. To me, these transformers are nice but bulky for the small PCB's that I make. So I thought can I use the 600:600 Audio transformer transformers for this which exist in various sizes. They also exist in SMD formats.
My knowledge of transformer tells me that this should be possible as long the core is not saturated, I'm not so worried about the phase difference between input and output signal. It might be that the pri-sec isolation voltage is an issue.

Below you see some examples of these transformers, The two left are SMD audio transformers. The third from the left is a traditional 600:600 transformer, and the right is an AC voltage sensor. The schematic shows how I want to use it and that is including a series resistor. The transformer seer only 1mA of current.

My question is: does anyone have a good reason why it is better not to do this or better why it is possible but with some points to consider. Let me know in the comments.

Thanks

 

[Piet de Pad]

Hopefully it is very unlikely that a remote lightning strike will break down the insulation on the CM choke and render it a safety hazard from then on.

Hopefully the 120Vac ( to earth ) will not then travel across the carbon path thus created and provide a shock hazard for the unknowing end user.

Hopefully this never happens and the authorities never investigate and find negligence on the designer who was warned in this column that safety standards are indeed a real thing.

Fingers crossed then and no sleepless nights.


[ Espérons qu'il est très peu probable qu'un coup de foudre à distance brise l'isolation de la self CM et la rende désormais dangereuse pour la sécurité.

Espérons que le 120 V CA (vers la terre) ne traversera pas ensuite le chemin du carbone ainsi créé et ne présentera pas un risque de choc pour l'utilisateur final inconscient.

Espérons que cela n'arrive jamais et que l'État n'enquête jamais et ne constate aucune négligence de la part du concepteur qui a été averti dans cette chronique que les normes de sécurité sont effectivement une chose réelle.

On croise les doigts et pas de nuits blanches ].

I agree that the breakdown voltage is considered the key risk here but Isn't the beak down voltage between an AC to DC power supply always the risk. And if that is, why should that be different in this circuit. No one ask in a shop what the breakdown voltage of the fly back transformer in their USB charger is. And by my knowledge none has died neither from charging a mobile phone. So yes breakdown voltage is important but i have the feeling that people exaggerate also.