Precaution

Before making use of the circuit in this design project, ensure that you first set the variable resistor and check the value at which the relay gets activated. Increase the value of the input voltage using a digital multimeter and make sure that you have achieved the correct preset value of the potentiometer.

The board can be used in overvoltage protection for both the AC and the DC currents because of the relay incorporation into the circuit. Our circuit above should be used for the DC power supply as per the output specification where our input AC is converted into DC.

How the Circuit Works

When the connected voltage is below the maximum limit, the maximum voltage is dropped through the 2.2k resistor R2 into the ground. This makes the base of the BC547 transistor Q1 not get enough switching power. Thus the transistor Q1 remains In the OFF state and the relay K1 does not get enough activation power supply.

On increasing the input voltage above the maximum limit, the input voltage across the resistor R1 and also across the potentiometer increases. Even though there is a voltage drop occurring at R3, there is still enough voltage at the transistor base to switch the transistor ON thus allowing the supply to pass through the emitter and the collector. This voltage activates the relay and the power supply is disconnected from the connected appliance hence protecting the appliance against the high input voltage supply.

Before using the system, ensure that it is adjusted to get the best-preset value through testing of the input voltage and have the best auto-cut voltage level according to your suitability.

Selected Components

1;"R2

R3";"R_0603_1608Metric";2;"2.2k";;;

1

2;"J2";"PinHeader_1x02_P2.00mm_Vertical";1;"LOAD";;;

1

3;"D3";"LED_0603_1608Metric";1;"LED";;;

1

4;"K1";"Relay_DPDT_AXICOM_IMSeries_JLeg";1;"DIPxx-1Axx-11x";;;

1

5;"D4

D1

D2";"D_0603_1608Metric";3;"1N4007";;;

1

6;"R1";"R_0603_1608Metric";1;"33k";;;

1

7;"C1";"C_0603_1608Metric";1;"1mF";;;

1

8;"RV1";"Potentiometer_Bourns_3266W_Vertical";1;"5k";;;

1

9;"J1";"PinHeader_1x02_P2.00mm_Vertical";1;"INPUT";;;

1

10;"Q1";"SOT-89-3_Handsoldering";1;"BC547";;;

1

11;"T1";"Autotransformer_ZS1052-AC";1;"Transformer_1P_SS";;;

1

 The Circuit Diagram

The circuit diagram is implemented using KiCAD EDA software as shown below.

The circuit diagram is converted into a PCB diagram using KiCAD. This is achieved through PCB layout, after adding relevant footprints, drawing of necessary standard traces that are needed to connect various components that make up the schematic, and finally checking that the design respects the electrical rules which can be checked using the DRC button on KiCAD. Attached is the PCB layout from the KiCAD EDA tool.

New Opportunity for PCB Lovers

As you keep ordering your printed circuit boards through various manufacturers, think about this great opportunity offered by PCBWay as they celebrate their 9th anniversary. The celebration is accompanied by so many healthy free coupons that could be beneficial to you and help you achieve your dream of building your PCBs. Visit them and enjoy the offer while it lasts. See the benefits in the image below.