Transistor

The transistor works like an electronic switch. A transistor is similar to a relay in the sense that you can use it to turn something ON and OFF. It can also be used for amplification, switching, voltage stabilization, signal modulation and many other functions.

It is made of semiconductor material. Transistors are found in most electronic devices. The transistor was a major advancement after the triode tube, with using much less electricity, and lasting many years longer, to switch or amplify another electronic current.

Types of transistor

There are two types of standard (bipolar junction) transistors, NPN and PNP, with different circuit symbols. The letters refer to the layers of semiconductor material used to make the transistor. Most transistors used today are NPN because this is the easiest type to make from silicon. The leads are labeled as base (B), collector (C) and emitter (E). These terms refer to the internal operation of a transistor.

How Transistors Work (NPN type)

When a little bit of current flows from the base of a transistor to the emitter, the transistor "closes the switch" so that current can also flow from the collector to the emitter.

Transistor currents and Gain:

Transistor application circuits

Simple touch switch:The LED in the circuit lights up, when someone touchesthe two endpoints in the circuit, and it turns off when the finger is removed.

Auto Off LED Night Lamp: You can use this circuit as a night lamp when going to sleep! When you touch the positive terminal of the 9V battery to the positive pole of the capacitor in the circuit, the LED lights up. It remains ON for some time delay and then fades away. The time taken for the LED to turn-off is determined by the value of this capacitor.

Light Alarm:You can use this circuit as a wakeup alarm.

Automatic Night Lamp:You can use this circuit as a study lamp. This lamp automatically turns ON, when sunlight fails.