How to use transistor as a switch

 How to use transistor as a switch :

How to use transistor as a switch in electronics circuits, how to use transistor as a switch in microcontrollers projects.In many application we need to interface transistor with micocontroller. Why we need to interface transistor with micocontroller? The reason is that microcontroller pin can’t provide output current more than 3mA and voltage more than 5V. If we connect load having current demand more than 3mA, it will burn microcontroller. Many output devices will require a transistor switching circuit to operate high current requirement load. So in this tutorial I will show you how to use transistor with microcontroller.

Transistor interfacing with microcontroller

Transistor interfacing with microcontroller




Video lecture on how to use transistor as a switch

In above circuit logic probe is used as input from micrcontroller and diode D1 is used as a free wheeling diode to allow the current to flow when transistor is in off state.Remember that I have used 3904 transistor just for demonstration.While selecting transistor, you should take care off maximum current that can flow through transistor in on state. Microcontroller input is just used to operate transistor in on state or off state as shown in figure below.
Transistor interfacing with microcontroller

Transistor interfacing with microcontroller

Note that it is usual to connect a back emf suppression diode across the output device.This is essential with devices such as relays, solenoids and motors which create a back emf when power is switched off.

Practically we used mostly relays for high current demanding loads .In that case transistor used to operate relay and load is connected with relay.I will post tutorial on relay interfacing soon.

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if you still have any question,feel free to comment on this post.




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