over and under voltage protection circuit

This is an over and under voltage protection circuit device sound disappeared. when too much voltage 220V, and protection when pressure is too low with Using the relay cut off power when voltage problems. In particular, If the voltage of the motor is lower, the coils of it can be a burn.

Simple over and under voltage protection circuit

Over voltage and low voltage protection circuit

From the circuit when the voltage is 220 volts AC through a transformer T1. It serves to reduce the pressure remaining 12 volts, through a D1-D4 connected to Direct rectifier bridge circuit. To convert the voltage, alternating current to direct current.

Then, through the C1 and C2 to the power filter smoothing. And entering a pin. Or input pin of IC1, a loan IC Rex bit computing to 12-volt power supply is fixed to the IC2. That it is IC Op Amp. Pressure acts edge IC2/1 High Voltage Detector, High Voltage ICs, if this current work to the Q1 and relay function, it works with.

Thus cutting off power from the load instantly. The IC2/2 serves to detect the lower voltage. The two components can be specified by VR1, VR2. LED1 display when power or low power over a specified.

The parts list
IC1___________LM324_ Quad/ 1MHz/ Operational Amplifiers for Commercial/ Industrial/ and Military Applications
IC2___________LM7812_______12V 1A DC voltage regulator IC
Q1____________2N3904__45V 100mA NPN Transistor
D1-D4_________1N4007___1A 1000V Diode
ZD1___________6V 0.5W Zener diode
ZD2___________6.8V 0.5W Zener Diode
C1_________470µF 25V Electrolytic Capacitors
C2,C3_________0.1µF 63V Polyester Capacitor
LED___________as you like

How to builds
This circuit is very useful. If you are interested in creating. It’s not too difficult. Because there is less equipment. And it certainly easy to buy. All equipment will be soldered onto the PCB purpose. Should be careful polarity of the diodes, Zener diodes, electrolytic capacitors types

Over and Under voltage protection of electrical appliances

This is an over and under voltage protection to all electrical appliances are safe. We use electronics circuits, high accurate work is fast LM393, AN6780 and more. Which cut off currents with power relay.

I’ve presented this way, it is Over & Under Voltage protection circuit. But today, I’d recommend this because there is a very good following.

1. The relay will work all time in under or over voltage range.
2. This circuit will time delay all time when under or over voltage or power outage awhile.
3. Can use full performance, though under voltage to 12 volts or over voltage to 380 volts
4. Can be adapted to the circuit breaker when the power falls to 180 volts (or much – less).
5. Can be adapted to the circuit breaker when the power is too high from 240 volts or more (or much-less).

Over and under voltage protection circuit working

As Figure 1 is circuit diagram of this project. The voltage input is entered to a transformer that designed with primary of 380 volts and secondary of 20 volts. From transformer feature as above will cause can get voltage at secondary of 12 volts. When the input voltage is 220 volts as normally.

0ver-under voltage protector using LM393
Figure 1 the over and under voltage protection circuit diagram

And will be output voltage of 9.5 volts. When voltage drop down to 180 volts, this voltage as above will entered to diode rectifiers D1-D4. Notice: we use primary coil transformer is 380 volts to protect them Not damaged by too over voltage.

The voltage that through a rectifier circuit will be separated to two way. First will be entered to IC3- LM7809 to The ability to maintain fixed voltage all time. Although the input voltage is lower as 110 volts or higher 380 volts to them.

The circuit has excellent performance at all times.

The other way voltage will be entered to R1, R2 and IC1 to compared with standard voltage from R5 and maintain fixed voltage to 5 volts stable by a zener diode-D5.

VR1 will adjusted voltage lower than pin 6 just slightly,and will higher, when input voltage higher this setting voltage. The output voltage at pin 7 will be positive to enter through D6, D8 and R8 to base of Q1 cause Q1 working.

While LED-D9 will grow to indicate we know that the circuit worked from the over voltage.

The working of Q1 will makes pin 3 of IC2- AN6780 has electrical potential as the ground, cause output at pin 6 is positive, Q2 will work and reduce voltage at base of Q3 to lower until Q3 stop. The relay will break the circuit to protect the circuit that we use.

When input voltage is normally high. The Q1’s base voltage will reduced until Q1 stop working. But IC2 will still continually works with time about for 3 minutes. Then relay so connects power to the normally electrical appliances.

The VR2 will adjust the voltage at pin 2 higher slightly than pin 3.

When input voltage lower than setting, when voltage at pin 2 lower than pin 3 will get positive voltage output pin 1 of IC1b fill through D7, D9 cause Q1 also work at over voltage.

LED-D11 will indicate the under voltage.
LED-D10 will indicate the over voltage.

AN6780-General Purpose Timer datasheet

The AN6780 and AN6780S are ICs designed for general purpose timer for long time. They consists of an oscillator, frequency divider (flip-flop 15steps), output circuit, and power circuit. A cycle can be freely set with the external resistor (R T ) and capacity (C T ) of the oscillator.

• High inflow and outflow current : I O =±15mA max
• Small variation of oscillations
• Long interval timer setting : max 1 week

7-pin SIL Plastic Package

Figur 2 : Block Diagram

Timers, integrating timers, superlow frequency oscillators

Build over and under voltage protection circuit

As Figure 2 is the actual size of single-sided copper PCB layout. And assemble on PCB as Figure 3 completely. Then test the working of the circuit with applies a normal voltage to the circuit. The three LEDs will go out, next 3-5 minutes long LED D12 lights to show that the circuit functions normally.

the PCB layout
Figure 2 the PCB layout

the component layout
Figure 3 the component layout.

For LED D9, D11 if growing in this time, to adjust VR1, VR2 until both LEDs go out.
Then test to reduce the voltage to 180 volts while adjusting VR2 until LED-D11 grow and within LED-D12 will go out. That show relay stops working and cut voltage of out the protected circuit show that it normally working.

Next test add voltage rises up to 240 volts, then adjust VR1 until LED-D9 will grow while LED-D12 will go out, it indicated the relay stop and cut off voltage to also protect the circuit.

If you do not have the AC variable voltage supply. You may use DC power supply adjustable voltage between 6-20 volts to connects at TP point. By the voltage of 13.5 volts will same input voltage of 180 volts and 17.8 volts for 240 volts

Components List of over voltage protection

IC1: LM393 Low Offset Voltage Dual Comparators
IC2: AN6780 General Purpose Long Interval Timers
IC3: LM7809, 9V Fixed Regulator IC.
Q1, Q2: BC547, 0.4A 40V NPN Transistor
Q3: BC337, 0.8A 40V NPN Transistors
D1-D4: 1N4007, 1A 1000V Diode
D5: Zener 5V 0.5W
D6, D7: Zener 3.9V 0.5W
D8, D9, D13: 1N4148
D10, D11, D12: LED, as you want.

The resistors 0.25W
R1, R2: 27K
R3, R5: 15K
R4: 12K
R6, R7, R14: 820 ohms
R8, R12: 24K
R9: 910 ohms
R10: 180K
R11: 220 ohms
R13: 68K
R15, R16: 1K

The Capacitors
C1: 470uF 35V Electrolytic capacitors
C2, C4: 0.1uF 63V Polyester Capacitor
C3: 10uF 16V Electrolytic capacitors
C5: 470uF 16V Electrolytic capacitors
RY: 9V Relay 1 contact.

Sharing is caring!

How to learn electronics with simple ways

Related Posts


I always try to make Electronics Learning Easy.

Leave a Reply

This site uses Akismet to reduce spam. Learn how your comment data is processed.

newest oldest most voted
Notify of
lord coulombs

some thing is wrong.the positive side of one of the z-diode should be in the non-inverting input. the other positive side of the z-diode to the inverting input of the other opamp, so to set the low and high cutoff.


kit pot seting.

Cruz Rdriguez

What is wrong in the circuit schematic is the pin designation on IC2/2. Pin 6 is negative and pin 5 positive.


thnxs if you are

Sakhilal Manjhi

Sir I want to know the working of each component saperatly on the circuit. so please provide me the information as soon as possible.


why not consinder using lm 358 instead of lm 324?since 324 has four op amps and 358 has two


you use a lot of components. Why not use a window comparator with 1 reference zener diode and 2 pots.

Florian Ion

Cracker is right. Helicoms is right.

Circuit is wrong.

Please be carefully.


sir i want explanation of the whole circuit please


sir can you please tell how to sets pot1 and pot 2? thank you.


how can you calculate variable resistor value ?


how we can analysis the above circuit


Thanks for every thing it is a perfect circuit


Circuit is gud. but I am confused that who will protect this circuit itself?! As transformer will burn due to over voltage.


I want to know about the designing of various components in the circuit..


sir ic1 pin 8 to 14 and ic2 pin 4,8,9,10,12,13,14. what is the fuction because they are not connected.


Dear sir, the above circuit you posted is very interesting to me. Really I’am very thankful to you for that. But,can you please clarify me before i test the circuit. In the given schematic diagram and in PCB layout D6,D7,D8,D9 are mentioned as 1n4148 zeners. and given in the parts list are D6,D7 = 3.9v 0.5w and D8,D9 = 1n4148 which one is correct…? i got all the components from the market except AN6780 long interval timer. so, can u please tell me shall i connect Q1 547 collector directly to R12 24K resistance by removing five components IC2 ,… Read more »

Arend van der Weide

I have build the circuit with lm358.
It works the first time.


This are tested ???????
Is it work???


please i saw a similar post in this link: freecircuitworks.blogspot.com/2016/03/low-battery-protection-and-alarm31.html which uses p mosfet or relay. i want members to check if i can also use that

lachhman Singh

please clrify regarding D6,D7 whether thes are Zenor or ordinary diod


where can i get the under and over voltage relays
input supply 550v output 550v


I read it and evaluate the circuit very carefully. I found this is really very interesting and attractive not only in term of home appliances protection but also the industry with little amendments. Only would interested to know how we can provide additional back emf’s protection. Because in case of low or high with relay tripping it might have produced the back EMF that may harm for the attached appliances.

Hope my comments would be useful for further evaluation, awaiting comments.

Mob: 00966 500193412


Please, Can you assist us with the following: To design a safety circuit that should provide for household appliances for over-and undervoltage protection. The protective circuit must immediately switch off upon detection of low-and high-voltage household appliance and upon detection of normal voltage switch on again after 3 minutes. The protective circuit must comply with the following: If the line voltage is within the normal range (100 to 130V ac), it will wait for the protective circuit 3 minutes before the output will be energized. During these 3 minutes there is an amber LED light. If the line voltage is… Read more »


how can analysis the above circuit brife calculation each value


Hi,How to add time delay to this circuit with 324 C & D?Thank u.

James Pogs

Hai sir, may i ask if the D6 D7 are Zener diode or just a 4148 diode? the list of component says that it is a zener diode but in the circuit diagram it is a 4148 diode. Which is correct?

Abhijit Maity

very nice . thanks

Daniel Nguyen

A hydraulic pump with a motor 15 HP, 480V, 3PH is powered by a combination starter with a 40A, 3P, 480V Allen-Bradley circuit breaker. Pump runs normally for a pressure at 300psi, and current 12A. When the pressure in a hydraulic tank reduced to very low level about 50 psi then the circuit breaker is tripped at a current 9A and the display screen showed “underload”. Could you please explain why the circuit breaker tripped at low current below overload circuit trip ? It happens again many times if the pressure would drop to very low levels.

Thank you

Gari Dizon

Dear Sir,
Please design a circuit board that should provide for AC220V power fluctuation protection. The protective circuit must immediately switch ON a 3 phase circuit breaker shunt coil (coil voltage is 220VAC) in the event of power fluctuation. Thank You

Close Menu