# DC proportional to AC voltage

Discussion in 'General Electronics Chat' started by vks_foe, Mar 8, 2009.

1. ### vks_foe Thread Starter Active Member

Jan 11, 2009
55
5
Hi,
i have to measure an AC voltage of peak 325 volts(230V rms) and get a DC equivalent of smaller magnitude.

i.e. for AC 230V rms...... DC o/p = 2 volts.
Also the DC output should vary linearly either with AC peak or AC rms.

RRITESH KAKKAR likes this.
2. ### DedeHai Active Member

Jan 22, 2009
39
0
very simple solution:
use a diode to cut off the negative half-waves, connect it to a capacitor to charge it to the peak voltage and use two resistors as a voltage divider. you may even use a trimmer as one of the resistors to adjust the desired output voltage (if needed)

3. ### vks_foe Thread Starter Active Member

Jan 11, 2009
55
5
Will the sensitivity be good???
i want 2 volts DC for 230 V AC.... that has to be fed to an error amplifier.. so the Dc voltage should be fairly stable and flat ... using capacitor can removes ripples but i fear that sensitivity will be poorer.
Even a 1 volt change in i/p(230 rms) should be detectable...

RRITESH KAKKAR likes this.
4. ### beenthere Retired Moderator

Apr 20, 2004
15,815
283
Use a step down transformer to reduce the AC voltage and for safety. Make the output on the order of 6 VAC. Use two op amps to make a precision rectifier and absolute value circuit. Gain in the absolute value stage can be adjusted for your 2 VDC output equivalent to 230 VAC in.

RRITESH KAKKAR likes this.

Jan 11, 2009
55
5