AC Over voltage indication

[vamanan]

Hi,
I need to glow a LED if the mains voltage is above 300V AC.Otherwise LED should be off. How can I do it ?

 

[IanP]

Simple and safe method of indicating higher ac voltage is to step it down with a small off-the-shelf transformer (most of available transformers should withstand voltages of up to 300Vac), then: bridge rectifier – zener diode (selected to indicate ac voltage above, say, 280Vac) – resistor – LED ..
Here is an example of a little bit more advanced circuit with comparator(s):
**broken link removed**

Rgds,
IanP