|
Circuits designed by David Johnson, P.E.
Last Updated on:
Saturday, December 23, 2017 03:21 PM
List of Dave's Circuit Designs
The contents & graphics
of Discovercircuits.com are copyright protected.
LINKING to Dave's circuits is permitted but DO NOT COPY any files to your WEB
SITE server |
|
|
|
|
More
AC Power Line Circuits
Alarms
Voltage Sensors |
AC Line Under/Over Voltage Alarm
(March 29, 2009) |
Power lines, which deviate much beyond normal voltages can damage expensive electronic
equipment. The circuit below sounds an alarm whenever the line voltage is higher
or lower than normal. I set the alarm limits at about +-15% from standard
levels. The circuit rectifies and filters the power line signal. I set the
resistor values, so the DC voltage produced is close to 1% of the RMS value of the
line. Thus, a 120vac line would yield about 1.2v DC. That voltage is fed
to a pair of voltage comparators. |
|
|
The
outputs of the comparators decide if the sampled voltage is above, below or acceptable.
Three LEDs indicate the voltage range. A green LED is lit if the voltage is OK. If
the voltage is outside normal levels, the circuit sounds an alarm using a small magnet or
piezoelectric beeper. I have shown recommended resistor values for both 120vac and
240vac power lines. |
|
Click
on Drawing Below to view PDF version of Schematic |
|
|
|