MAINS MANAGER

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Very often we forget to switch off
the peripherals like monitor, scanner,
and printer while switching off
our PC. The problem is that there are separate
power switches to turn the peripherals
off. Normally, the peripherals are connected
to a single of those four-way trailing
sockets that are plugged into a single
wall socket. If that socket is accessible, all
the devices could be switched off from
there and none of the equipment used will
require any modification.
Here is a mains manager
circuit that allows you to turn
all the equipment on or off by
just operating the switch on
any one of the devices; for
example, when you switch off
your PC, the monitor as well
as other equipment will get
powered down automatically.
You may choose the main
equipment to control other
gadgets. The main equipment
is to be directly plugged into
the master socket, while all
other equipment are to be connected
via the slave socket.
The mains supply from the
wall socket is to be connected
to the input of the mains manager
circuit.
The unit operates by
sensing the current drawn by
the control equipment/load
from the master socket. On
sensing that the control
equipment is on, it powers up the other
(slave) sockets. The load on the master
socket can be anywhere between 20 VA
and 500 VA, while the load on the slave
sockets can be 60 VA to 1200 VA.
During the positive half cycle of the
mains AC supply, diodes D4, D5, and D6
have a voltage drop of about 1.8 volts
when current is drawn from the master
socket. Diode D7 carries the current during
negative half cycles. Capacitor C3, in
series with diode D3, is connected across
the diode combination of D4 through D6,
in addition to diode D7 as well as resistor
R10. Thus current pulses during positive
half-cycles, charge up the capacitor to 1.8
volts via diode D3. This voltage is sufficient
to hold transistor T2 in forward biased
condition for about 200 ms even after
the controlling load on the master
socket is switched off.
When transistor T2 is ‘on’, transistor
T1 gets forward biased and is switched
on. This, in turn, triggers Triac 1, which
then powers the slave loads. Capacitor C4
and resistor R9 form a snubber network to
ensure that the triac turns off cleanly with
an inductive load.