Hello, I'm taking apart an old tv and I found some strange transformer at the mains input I dont know what is doing there. This is the circuit


The output goes both to a regular transformer and directly into the main board of the tv.
I think is doing some kind of current comparison? There is no sensing element like a reel switch or a sensing loop.

Do you know whats the name of this configuration so I can do some further research?
Thanks!

 

Hello,

The shown schematic is not a transformer, but a common mode choke:
https://www.coilws.com/index.php?main_page=page&id=128

Bertus

 

Hello,

The shown schematic is not a transformer, but a common mode choke:
https://www.coilws.com/index.php?main_page=page&id=128

Bertus

Thanks! Now I can read all about it!

 

It is a common mode filter which attenuates electrical noise from the switch mode power supply. It helps reduce radiated interference from the mains cable. It also attenuates noise that is on the mains supply when it enters the TV. I would also expect to see a capacitor between the two wires exiting the right hand side of the schematic.

Les.

 

It is a common mode filter which attenuates electrical noise from the switch mode power supply. It helps reduce radiated interference from the mains cable. It also attenuates noise that is on the mains supply when it enters the TV. I would also expect to see a capacitor between the two wires exiting the right hand side of the schematic.

Les.

The TS said "old TV". What makes you think there is an SMPS inside, Les?

 

Hi Papabravo,
It was just an assumption. It is a very long time since I have seen a TV with a normal mains transformer.

Les.

 

Many 'old' TV's used a common mode choke or two on the input, some did not use any transformer or SMPS, just straight into a bridge or rectifier tube, the tube htrs were in series.
There were many variations over the years.
Max.

 

Old is a relative term. To some, products made in the 1980's and beyond are old.

 

Old is a relative term. To some, products made in the 1980's and beyond are old.

To be fair, I'd say 35-year old technology could be called old without too much trouble. It just doesn't seem like it should be old.

 

the tube htrs were in series

That's why there were a bunch of tubes with odd filament voltages.
And it was always fun determining which tube failed when all the filaments wouldn't light.

 

Hello,

The Vacuum tubes that where connected in series where from the P (300 mA) or U (100 mA) series:
https://www.electronics-notes.com/articles/electronic_components/valves-tubes/numbering-systems.php

Bertus