How to design a control or sensor circuit for following

thanks

Can u plz elaborate on wat u mean by peak detect the AC voltage and how much value shall i convert to dc voltage i.e whats the valueof dc voltage . And abt op-amp i have no ideaso iam goin thru it now so will get back to u later with doubts.

Thanks Jayesh

ok so if its say 120-277V ac then dc will be (120-277 )* 1.4 DC But i cannot supply such large voltage to Op-amp so what do i do

Thanks jayesh

You would use what's called a 'voltage divider' - two resistors in series, such that the voltage drop is proportional to their resistance.

Maybe if you need to ask this question, you shouldn't be messing with 277 volts!

Can this voltage change unexpectedly? You could simply install a switch, or give the user three input jacks, so they could plug the unit in to either power at the site.

But automatic switching isn't that hard - you could use what's called a "signal transformer" or some such - a 277/12V ordinary transformer, and when the input is 120V, the output will be

Good Luck! Rich

thanks but can it be done without using a transformer what abt power loss at resistor .

Jayesh

The approach would be:

use a diode and capacitor to peak detect the AC voltage and convert it to a DC voltage

Use 3 OpAmps or comparitor IC's set to detect a voltage below 120, between

Apply logic (relay or solid state ) to determine which taps to connect.

Can't be any more specific with the minimum information you have supplied

Dan

Use a diode and capacitor to make a simple dc power supply from the ac in put voltage The dc voltage will be approximately 1.4 times the AC voltage