How does a latching circuit work

The data latch is an easy expansion to the gated SR-latch that eliminates the chance of unacceptable states of input. The D-latch outputs the input of the D when the Enable line is high, otherwise, the output is whatever the D input was whenever the Enable input was last high. This is the reason it is known as a transparent latch. A gated D latch is designed simply by changing a gated SR-latch, and the only change in the gated SR-latch is that the input R must be modified to inverted S.

The circuit of the latch will not at all experience a Race state due to the only D input is reversed to offer to both the inputs. Therefore, there is no possibility for similar input state. Thus the circuit of D-latch can be securely used in several circuits. The both JK latch , as well as RS latch, is similar. This latch comprises two inputs namely J and K which are shown in the following logic gate diagram.

In this type of latch, the unclear state has been removed here. Current Limiting resistors must be used at the bases of BJT transistors, otherwise they might burn. Before going into the explanation, we should note that Transistor Q1 BC is a NPN transistor , which conducts or Turns On, when a small positive voltage is applied to its base.

Initially, both the transistors are in OFF state, and Relay is deactivated. Capacitor C1 has been used precautionary, to prevent the accidental and false triggering of circuit.

Resistor R2 and R3 prevents the short circuit in this condition. Now when Base of Transistor BC gets grounded, it starts conducting and energises the Coil of relay, which activates the Relay and turns ON the device connected to Relay.

In our case LED will glow. And when the Transistor BC turns ON, current flow in two directions, first to the relay and second to the base of transistor Q1. So this Feedback voltage to the base of Transistor BC, keeps the transistor BC ON for indefinite period, even after the input trigger voltage is removed.

The relay remembers which button was pressed last see description below. The diagram above shows how such a relay can be used to make a latching relay circuit.

The circuit has two buttons — one is a push to make which closes when pressed but is otherwise open, and the other is a push to break which opens when pressed but is otherwise closed.

When the push to make button is pressed, 12V goes across the coil energising the relay. This closes the two internal relay switches connecting A to B, and C to D.

Latching is widely used with start-ups so that the initial switch on of an application becomes latched on. You can also follow us on Facebook and Twitter to receive daily updates. Recommended Articles. More Articles. PLC Tutorials. Send this to a friend. Send Cancel.