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.

Read Datasheet of AN6780

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.

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
R6, R7, R14________820 ohms
R8, R12___________24K
R9________________910 ohms
R11_______________220 ohms
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.


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