In this tutorial, we are going to make a project of a Push button ON-OFF switch using transistors. These switches are commonly used in prototypes, projects, demos, and more advanced products as they provide a familiar way to open/close a circuit. The circuit that we are making is ideal to use as a push-button switch. It will allow switching loads on and off through a push button.
Usually, these switches can be made by using a binary divider or 555 timer IC but they consume current even in the OFF state and it makes the process a bit complicated. Therefore we designed this circuit using two transistors that don’t consume current in off state and are suitable for battery power.
Hardware Components
The following components are required to make the ON-OFF Switch Circuit
| S.no | Components | Value | Qty |
|---|---|---|---|
| 1. | Battery | 9-12V | 1 |
| 2. | Push Buttons | – | 2 |
| 3. | Transistor | 2N3904, 2N3906 | 1, 1 |
| 4. | Resistor | 1K, 100K, 10K | 1, 2, 1 |
| 5. | Electrolytic Capacitor | 10µF | 1 |
| 6. | Relay | 12V | 1 |
| 7. | Diode | 1N4007 | 1 |
| 8. | Connecting Wires | – | 1 |
| 9. | Breadboard | – | 1 |
2N3906 Pinout
For a detailed description of pinout, dimension features, and specifications download the datasheet of 2N3906
2N3904 Pinout
For a detailed description of pinout, dimension features, and specifications download the datasheet of 2N3904
ON-OFF Switch Circuit
Working Explanation
This circuit operates on a battery of 9 to 12 volts DC. Initially, the circuit will remain in the off state because the push button has not been pressed and no current is flowing through the transistor.
When you push the button, the current will flow through the base of transistor 2N304 which will turn it on. Now the current flowing through this transistor will be the base current for the second transistor 2N3906. Both transistors will be activated now and as a result, the 12V Relay will activate as well. You can connect any AC/DC appliance according to the relay’s value and operate them through this circuit.
Because the second transistor is in parallel with the first push button it will make sure that the circuit remains on even when the push button bounces off. To turn the circuit off the second push button is pressed. It will ground the base of the second transistor and it will deactivate. As a result, it will break off the flow of the base current of the first transistor to the ground. This will turn the whole system off.
Applications and Uses
This circuit has a 12V relay at the output which can be connected with any AC or DC appliance having the same voltage value as the relay to turn it ON/OFF.
