230V AC to 12v AC

[Lee Newsum]

this is going in the bin at work so i had a look.

2 transformers ? y need 2 of them?

[jmelson]

this is going in the bin at work so i had a look.

2 transformers ? y need 2 of them?

This is a lighting power supply, NOT a simple 230 to 12 V AC transformer.  It converts input AC to intermittant DC, then uses switching components to
convert to a high frequency (probably square wave) AC output.  I've worked with another version of the same thing that produces a 70 KHz output for
halogen lights.

Jon

[Zero999]

Yes, it's a high frequency electronic transformer which produces a 50kHz to 100kHz, modulated with the mains frequency.

The small transformer is to drive the switching transistors and the larger one handle the power. ST have made an application node detailing how to make one. They all use a similar schematic.
https://www.st.com/content/ccc/resource/technical/document/application_note/e5/88/46/11/35/8c/4a/bf/CD00003902.pdf/files/CD00003902.pdf/jcr:content/translations/en.CD00003902.pdf

They're not easy to use for powering electronic circuits. A high speed bridge rectifier will be required with an inductive, as well as capacitor filter, as they don't like current spikes. Attention also needs to be paid to high frequency interference.

[tooki]

Out of curiosity, what’s the advantage of such “electronic transformers” over an actual transformer, assuming it’s just for halogen lamps anyway?

[Zero999]

Out of curiosity, what’s the advantage of such “electronic transformers” over an actual transformer, assuming it’s just for halogen lamps anyway?

Electronic transformers are higher efficiency, smaller, lighter and cheaper, than traditional iron transformers. They work better with dimmers and can easily protected against short circuit, without a circuit breaker, bimetallic strip or PTC resistor.

[tooki]

OK, thank you! That's kinda what I figured, but wanted to be sure!