# Electrical Appliances Over / Under Volt Protection Circuit Diagram

It is very important to tell the limitation of voltage so that the electric device will work properly. Up and down fluctuation in Voltage it in very bad effect on the health of electric device, that up and down fluctuation of voltage is occurs when voltage-surges, lightning, over-load, short circuit etc. now let see how all fluctuation is occur, Over-voltages that mean the flow of voltage that are coming normally is changed. Now the voltage is coming higher so in this phase higher voltage can damage your electronic equipment and short circuit may be occur. In other way, down voltage is occur when we connect lot of electronic equipment are attached so voltage are divided into parts but that voltage is not efficient for running that equipment and they effect on performance and may flicker due to deficiency of voltage. We are try to give use basic understanding of over-voltage and under-voltage in above. Now we will discussing how prevent this problem.

In order to understand this concept & know it better, one needs to go through 3 different types of over-voltage protection circuits that use comparators & timers

For the better understanding of the topic below you have some basic understanding of under and over-voltage prevent circuits.

1. Protection of Under-Voltage & Over-Voltage Circuit Using Comparators

On in this article we study how to design a circuit that have tripping mechanism which prevent our load for any damage due to under and over –voltage. In many homes & industries, fluctuation in AC main supplies takes place rapidly.  The electronic devices & appliances get damaged due to these up and down voltage. To avoid this, we are making a tripping method of under/over voltage protection circuit to prevent the appliances from damage.

Working of circuit:

• As displayed in the block diagram given above, the mains AC power provides power to the entire circuit & for operating loads by means of relays, & mechanism that tripping the load (lamps) in the under the action voltage input which falls below or above a set value.
• 2 comparators being considered as a window comparator are made up of one quad comparator-IC. Due to this phenomena passing an error to the output if the input-voltage given to the comparator exceeds the limit over the voltage window.
• In this circuit an un-regulated power-supply is interfaced with the both op amps’ terminals, in which each none modify terminal is connected through the 2 resistors in series & a potential-meter arrangement. In the same way, modify terminal is also powered through Zener-diode & the resistance that we attached, as seen in given below in under-voltage or over-voltage protection circuit.
• The Potential-meter’s preset ‘VR1’ is adjusting of meter the voltage at non-modify terminal is smaller than (6.8volt) for ‘stable maintenance’ of devices. The supply that commonly use are (180-220volt) & the voltage of modify-terminal is (6.8Volt) and constant because of Zener diode.
• Hence the operational amplifier output is zero (0volt) under that limit & thus the relay coil is disconnect & the load isn’t break the continuity during this safe operation.
•  The voltage crossing 240Volt, the voltage and at the non-modify terminal is more than 6.8volt, so the operational-amplifier output goes to large then (0volt). So, on that output handle transistor & thus the relay coil gets connected & when relay get in connected to the circuit that mean voltage is over from the load voltage, and load will be disconnected from circuit.
• In the same way, under-voltage, lesser comparator connected the relay when the supply-voltage falls below the 180Volt by preserving 6Volt at the modify terminal. The under-voltage & over-voltage settings can be varied by changing the respective potential-meters.
1. Over-voltage and Under-voltage Preventing Circuit using Timers

In case for timer, under / over voltage preventing circuit created for low voltage & high     voltage preventing mechanism. This mechanism will help to protect and safe the appliances from damaged if occur. Such simple electronic circuits use timers in place of comparators as in the case mentioned above as a control mechanism. Combination of these 2 timers give the worry output to trig the relay method when the voltage crosses its specified limits. This is how it protects the loads from the really bad effect of supply-voltage.

Working of circuit:

• The whole circuit is provided power with a rectified direct-current-supply but DC power is joined to timers & AC power is joined with potential-meters to get the variable-voltage.
• Now this 2 timers’ set to work as comparators. For example as long as the input presents at pin 2 of timer, is small +ve than 1/3 voltage at common collector, then the output present at pin 3 goes large then pin 2. And reverse will happen once the input at pin 2 is more +ve than the 1/3 Voltage of common collector.
• The Potential-meter VR1 is joined with timer one for under-voltage cut-off, & the ‘VR2’ is to 2nd timer for over voltage cut-off. The 2 transistors are joined with 2 timers for making logic of switch.

• In normal operating situations, (between 160 & 250Volt) the result of first timer is become low that why first transistor is on cut-off condition at this output, they reset pin of the second timer, so timer generate is high output, that make the 3 number pin result is high, that why second transistor operates & conducts, then the relay coil is connected by doing this voltage become stable, so load is not effected by that fluctuation.
• In the over-voltage case (above 260Volt), the input-voltage at 2 number. Pin of second timer is high. This makes the output low at the pin number 3, in which turns operates the second transistor into a cut-off condition. Then the relay coil gets disconnected & the load is shifted from the Alternative current supply.
• In the same way, under-voltage case, the timer number one output is large then (0volt) & it operates the transistor number one into conduction condition. As a result of which, the reset pin of second timer becomes low & therefore, the transistor number 2 is in cut-off state. And eventually, the relay is operated to separate the loads/appliances from the mains supply.
• These over-voltage & under-voltage position are also displayed as LED indications which are connected to the respective timer.

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