AC - DC ground.

[lord loh.]

A friend of mine recently purchased a project kit that had a strange circuit connection (strange to me ).

The circuit had a triac and the triac's gate was operated by a DC output from a 555 and the other two terminals of the triac was given 230v AC. I do not remember the triac number(BT something).

The strange thing was that one of the triac terminals that was given the AC was connected to the DC ground (output of the rectifier and filter).... Is this allowed???

These circuit kits are know for their notoriously poor designs....

Wont the 230v AC blow up everything?

I have never used a triac or studied it....

Also I wanted to know if one can short one terminal of primary and secondary coils of a transformer? (in phase and out of phase) ?

Thank you.

 

[Nigel Goodwin]

A friend of mine recently purchased a project kit that had a strange circuit connection (strange to me ).

The circuit had a triac and the triac's gate was operated by a DC output from a 555 and the other two terminals of the triac was given 230v AC. I do not remember the triac number(BT something).

The strange thing was that one of the triac terminals that was given the AC was connected to the DC ground (output of the rectifier and filter).... Is this allowed???

These circuit kits are know for their notoriously poor designs....

It sounds like perfectly normal design?, where EVERYTHING is live, it's commonplace in light dimmers and power controllers.

Wont the 230v AC blow up everything?

I have never used a triac or studied it....

Also I wanted to know if one can short one terminal of primary and secondary coils of a transformer? (in phase and out of phase) ?

Yes you can, it's no problem, and quite a common thing to do - you can use it to make an auto-transformer. If your mains is a liitle low, you can put the secondary in series with the primary and increase the mains voltage by the secondary voltage. Obviously bearing in mind the rating of the transformer!.