Last Updated on December 9, 2024
An SR Latch (Set – Reset) is a basic sequential logic circuit, that is commonly used in digital electronics and applications. It can be used as simple form of memory that can store one bit of information. Here the SR latch operates using two input S (Set) and R (Reset) and then two outputs Q (Current state) and Q’ (Complement of the current state).
This SR latch can be constructed using NAND Gates, NOR Gates. As we know this logic gate can be replicate by using transistor. So here we are going to make an experiment to construct SR Latch circuit using Transistor.
SR Latch Logic Diagram
SR Latch Truth Table
An NOR Logic Gate and its equivalent Transistor circuit.
SR Latch Circuit using Transistor Equivalent
Components Required
| Item | Component | Specification | Quantity |
|---|---|---|---|
| 1 | Transistor (Q1–Q4) | BC547 (NPN) | 4 |
| 2 | Resistor (R1–R4) | 1 kΩ | 4 |
| 3 | Resistor (R5, R6) | 470 Ω | 2 |
| 4 | Resistor (R7, R8) | 330 Ω | 2 |
| 5 | LED (D1, D2) | 5 mm (Red/Green) | 2 |
| 6 | Push Button (Switch) | Momentary (NO) | 2 |
| 7 | Power Supply | +5V DC | 1 |
| 8 | Connecting Wires | – | As required |
| 9 | PCB/Protoboard | – | 1 |
Working Video
Construction & Working
This schematic represents how we can built an NOR gate using two transistors by the way Constructing whole SR Latch using four transistors.
Here Q1, Q2 transistor makes first NOR gate and then Q3, Q4 makes another NOR gate, by connecting output to input for both transistor (Collector to base) we can easily form SR Latch.
SR Latch using Two Transistors
Here is the simplified version of SR Latch using two transistors.
This circuit uses two transistors (BC547 NPN) that have interconnected between collector to base. Here two base inputs acts as R (Rest) and S (Set ) input, two collector terminals acts as Q and Q’ outputs. This circuit also works as normal SR Latch.