How to make Transistor Latching Relay

Introduction

A Transistor latching relay is a device that is used to maintain a state when a momentary pulse is applied. This device is commonly used in electronic circuits that require switching between two states without the need for constant input. Making a transistor latching relay is a relatively simple process that can be achieved using BD139 and BD140 transistors. These transistors are widely available and can be easily purchased online or from electronics stores. In this article, we will discuss how to make a latching relay using BD139 and BD140 transistors which is one of the beginner circuit projects.

In this article I will discuss about how to make Transistor Latching Relay ON/OFF Circuit using 12V relay, NPN and PNP transistors, push buttons and some common components. You can use this circuit to turn on and off different circuits with two push buttons. One for turning on the circuit and the second for turning off.

Circuit Diagram of Transistor Latching Relay

This project can be designed using a few basic components. The circuit diagram of this project is shown below.

How to make Transistor Latching Relay Circuit Diagram — **Transistor Latching Relay Circuit Diagram**

How to make Transistor Latching Relay Schematic — **Transistor Latching Relay Schematic**

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Components List of Transistor Latching Relay

Following is the list of all components used in this project:

1X BD139 TRANSISTOR
1X BD140 TRANSISTOR
2X PUSH BUTTONS
1X 12V RELAY
1X LED
2X 1X 1K RESISTORS
1X 10K RESISTOR
1X 3 PIN TERMINAL BLOCK
1X 2 PIN TERMINAL BLOCK
VERO BOARD
JUMPER WIRES

Explanation of Transistor Latching Relay

The first step in making a latching relay is to get the required materials. List of all material is provided above.

After getting the materials, the next step is to assemble the circuit. The circuit diagram for making a transistor latching relay using BD139 and BD140 transistors is shown above. The next step is to follow the circuit diagram to assemble the circuit.

The first step to assemble the circuit is to insert the BD139 and BD140 transistors into the breadboard. The BD139 transistor should be placed on the left side of the breadboard, while the BD140 should be placed on the right side of the breadboard. The power supply should be connected to the breadboard according to the circuit diagram.

After connecting the power supply, the next step is to connect the capacitors, resistors and the output terminals. All the components should be connected to their respective terminals according to the diagram.

Once all the components are connected, the circuit is ready to be tested. The switching action of the latching relay can be tested by applying a momentary pulse to the input. The relay should switch between the two states and maintain the last state when the pulse is removed.

Conclusion

Making a transistor latching relay using BD139 and BD140 transistors is a relatively simple process that can be achieved using readily available components. The latching relay is a useful device in electronic circuits as it provides a stable switching state without the need for constant input. The circuit diagram provided in this article can be used as a guide to assemble the latching relay. Therefore, if you need a reliable latching relay for your electronic circuits, try making one using BD139 and BD140 transistors.

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For more project and circuit diagrams, you can go through the Schematics in the main menu where you can watch many interesting projects and circuit diagrams like audio amplifier circuits, voltage booster circuit, battery charger circuit and timer circuits etc., which are all beginner circuit projects. Feel free to check them out!

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