AC Band Pass Circuit

 

AC voltage fluctuation is a common cause for the failure of AC electronic appliance. The appliance fail to work in low voltage and even at high voltage. So why not to design a circuit which passes only the working band of AC voltage to the appliance. This brings our circuit to action. This circuit prevents the electronic appliance from failure by passing just the band of AC voltage. When the input voltage is in that band then only it get passed to the appliance and if the voltage is out of that band then this circuit will stop the voltage to go to the appliance.

Circuit

The circuit diagram for the AC band pass circuit is shown below.

Working

The working of this circuit can be understood very easily. The circuit majorly contains a relay which is operated on the working AC range only. The relay is driven by Q1 and its supporting components. This circuit doesn’t need any other power supply for the operation. Box capacitor C1, Resistor R1, R2 Electrolytic capacitor C2, 15V Zener diode D4 and rectifier diodes D1, D2, D5, D6 forms a miniature 15V transformer less power supply for the system. Another group of diodes forms the DC supply for the sensing circuit. The sensing circuit contains R4, R7 and C3. The sense voltage is trimmed using two setting pre-sets R5 and R8. R5 sets the lower value of AC voltage band and R8 sets the higher value of the AC voltage band.

Construction

The circuit is so small that it can be fit in any adaptor body. The circuit relay can drive up to 5A of AC load safely. And if the AC load is greater than 5A then either we need to use higher rating relay or the contractor.

Make sure that all the components are of same rating and value as shown in the diagram. The transformer less power supply section is quite dangerous and contains high voltages. Take necessary precaution while working with that part. Also make sure that no live part touches the metal part of the encloser.

Bill of Material

Item Quantity Reference Part

______________________________________________

1 1 C1 X2 105

2 1 C2 220uF

3 1 C3 10uF

4 9 D1,D2,D3,D5,D6,D7,D8,D10, 1N4007

D12

5 1 D4 Z 15V 1W

6 1 D9 Z 2V7

7 1 D11 Z 5V1

8 1 J1 Load

9 1 J2 AC

10 1 Q1 BD139

11 1 Q2 BC547

12 1 RL1 12V/10A

13 1 R1 680K / 1W

14 1 R2 680K

15 1 R3 220R / 1W

16 1 R4 47K

17 2 R8,R5 10K

18 2 R9,R6 1K

19 1 R7 27K

Author-

Aniruddh Kumar Sharma

Ani-Lab