![]() VCE(max) must be at least grater than 2 times the Relay operating DC voltage.If we consider worst case we should give 1V extra to the Relay coil circuit so that sufficient amount of voltage is provided to the Relay coil. As my relay works on 5V DC so to find the coil current which is basically ic ( collector current ) we need to measure the resistance of Relay coil.īut if I say there will be one more voltage drop in the path of this current that is VCE (collector Emitter junction drop) which is 300mV-1V(datasheet). So we are now going to find the threshold current to drive a relay properly. Step-1: Finding the minimum current required for energizing the relay coil So let’s go through different step to design a better Relay driving circuit. You can also consider working temperature range for your circuit.The 2N2222A transistor can be replace by any other 2N2222 transistor and it should not affect the functioning of the circuit even if it’s ᵝ (current gain) is different. ![]() It must be suitable for use with TTL circuit (means circuit behave well if base voltage V1 is in range 3.4-5V i.e.So if a large enough positive current is now driven into the Base to saturate the NPN transistor, the current flowing from Base to Emitter (B to E) controls the larger relay coil current flowing through the transistor from the Collector to Emitter. In case of NPN transistor as shown in fig when V1 is 0v or turn off then base current ( ib ) will not flow due to which transistor remain in cut-off region and hence ic will not flow and relay coil remain de-energized but when base current ( ib ) is provided sufficiently the maximum amount of collector current starts flowing which energized the relay coil and hence NO and Com of relay will get attached. The design and types of relay switching circuits is huge, but many small electronic projects use transistors and MOSFETs as their main switching device as the transistor can provide fast DC switching (ON-OFF) control of the relay coil from a variety of input sources so here is a small collection of some of the more common ways of switching relays.Ī relay switch circuit can be designed using NPN transistor. They are useful when we need to control(ON and OFF) a high power device using a electronic circuits. Relay is an output device (actuator) which come in various shapes, sizes and designs, and is very useful in electronic circuits. The first circuit is called the control circuit the second is called the load circuit. ![]() ![]() The magnetic force is, in effect, relaying the action from one circuit to another. When a power is supplied to the coil, it generates a magnetic force that actuates the switch mechanism. When the applied current or voltage exceeds a threshold value, the coil activates the armature, which operates either to close the open contacts or to open the closed contacts. The advantage of relays is that it takes a relatively small amount of power to operate the relay coil, but the relay itself can be used to control AC circuits and devices like motors, heaters, lamps which themselves can draw a lot more electrical power.Īll relays contain a sensing unit, the electric coil, which is powered by AC or DC current. Relays are electromechanical devices that has an electromagnet to operate a pair of movable contacts from an open condition to a closed condition. ![]()
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