The Ultimate High/Low Voltage Protector Circuit
This circuit is a modified version of the previous one and is able to switch of the load and itself in case the input voltage reaches dangerous levels. It can thus provide an ultimate protection to any gadget connected at its output.
The circuit may be understood in the following manner (Click Image to Enlarge):
After the required settings of the presets are done as explained above, pressing the push button will initiate the circuit by connecting the AC supply to the transformer.
On receiving the supply voltage the circuit will operate by energizing T2 and the relay.
The relay contacts will get latched so that the entire circuit now receives the supply voltage through its N/O contacts and the push button may be simply released.
As long as the supply voltage is within the normal range, the circuit remains latched and the output appliance is safely powered. Now, if the voltage increases to an undesirable extent, T1 will conduct, bringing the base voltage of T2 to ground and thus deactivating T2 and the relay.
Once the relay contacts are dislodged, the supply to the appliance as well as the whole system is broken. The circuit will remain unlatched until two conditions are met viz. the push button is pressed and the voltage is restored to its normal position.
The same will happen during the unsafe low voltages.
QUIZ: Can anybody tell us why R1 has been included in the circuit?