Transistor as a Switch
Category: Transistor Logic
Designer: RANA MUHAMMAD ADNAN KHALIL
Notes
This circuit is designed in simulated in Proteus 7.10. In this circuit you will learn a basic concept, that how to use a npn and pnp transistor as switch. The working of this circuit is given below. 1. The npn transistor used in this is 2N3904 and pnp transistor is 2N3906. 2. The npn and pnp both transistor works opposite to each other. 3. The npn transistor turns ON at 1 logic, and pnp transistor turns ON at zero logic. 4. In the simulation Q1 is npn transistor, when switch with Q1 closes the transistor recieves 1 logic signal and it turns ON. 5. When Q1 is ON the path of LED D1 completes and it glows (yellow color). 6. The Q2 pnp transistor is placed in opposite configuration as compare to npn. 7. When the switch of Q2 transistor closes, it recieves zero logic signal and turns ON. 8. When Q2 is ON, the LED D2 recieves positive voltage and its path completes, so it starts glowing (green color). Application: 1. This concept is used in almost all digital circuits where a soft switch is required. 2. Transistor life is greater than the Relay life. Download the files to perform more experiments.