High and Low Voltage Cutout with delay and Music
Voltage variations and power cuts adversely affect various equip- ment such
as TVs, VCRs, music systems and refrigerators. This simple circuit will protect
the costly equipment from high as well as low voltages and the voltage surges (when
power resumes). It also gives a melodious tune when mains power resumes. When
mains voltage is normal, the DC voltage at the cathode of zener diode D4 is less
then 5.6V. As a result transistor T1 is in ‘off’ state. The DC voltage at the
cathode of zener diode D5 is greater than 5.6V and as a result transistor T2 is
in ‘on’ state. Consequently, relay RL1 gets energised, which is indicated by
lighting up of green LED. Under high mains voltage condition, transistor T1
switches to ‘on’ state because the voltage at cathode of zener diode D4 becomes
greater than 5.6V. Consequently, transistor T2 switches to ‘off’ state, making
the relay to de-energise Under low mains voltage condition, transistor T1
switches to ‘off’ state and as a result transistor T2 also switches to ‘off’
state, making the relay to de-energise.
Timer IC 555 in the circuit is configured to operate in a monostable mode. The
pulse width is about 10 seconds with the timing component values used in the
circuit. When the power resumes after a break, pin 2 of IC 555 goes low briefly
and this triggers it. Its output makes music IC UM66 to operate through
transistor T3. Simultaneously, transistor T1 also gets forward biased as the
monostable IC1 output is connected to its base via diode D8 and resistor R7. As
a result, transistor T1 conducts and biases transistor T2 to cut off. Thus relay
RL1 remains de-energised for the duration of mono pulse and the load is
protected against the voltage surges.
To adjust presets VR1 and VR2, you may use a manually variable auto-transformer.
Set the output of auto-transformer to 270V AC and connect it to the primary of
transformer X1. Adjust preset VR1 such that relay RL1 just de-energises. Next
set the output of auto-transformer to 170V AC. Now adjust preset VR2 such that
relay RL1 again de-energises. Volume control VR3 may be adjusted for the desired
output volume of the tune generated by IC UM66
Title: High and Low Voltage Cutout with delay and Music
electronic circuit
Source: www.electronic-circuits-diagrams.com
Published on: 2005-02-01
Reads: 951
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