Transistor explained | How Transistors work

Welcome to Professor MAD Electronics for Everyone. Today we are going to talk about transistors. Transistors are one of the most  important inventions of the 20th century . because of the transistors, we are able to build much faster, much smaller and very energy efficient controller circuits at a very low cost. Your computer or mobile phone  consists of microprocessors   and ICS which contain billions of transistors. The transistor is a three-terminal  solid-state device   that can do two different jobs.  It can work either as an Amplifier or a Switch. There are two basic types of transistors out there. Bipolar Junction or BJT and Metal Oxide Field Effect or MOSFET. In this tutorial we'll focus on the  BJT because it's slightly easier to understand. The bipolar Junction transistors or BJTs are divided into two groups NPN and PNP   The circuit symbols for both the NPN and PNP BJTs are like this. The pins are labeled Collector C, Base B and Emitter E. The only difference between the symbols of NPN and PNP is the direction of the arrow and the emitter. The arrow on an NPN points out and on  the PNP it points in. In NPN transistors, one p-type  semiconductor layer is sandwiched between the two  n-type semiconductor layers. In PNP transistors, one n-type semiconductor layer is sandwiched  between the two p-type semiconductor layers. In NPN transistors the current flows from the collector terminal to the Emitter terminal. In PNP transistors the current flows from the Emitter to the Collector terminal. we use transistors for two purposes As a Switch and as an Amplifier. Let's talk about how to use a transistor as a switch. A switch is a device we use to power ON and OFF a load. We are all familiar with mechanical switches. We can change the states of the switch  and power ON and OFF the load as we need. we can use the transistor for the same  purpose Instead of moving mechanical parts the transistor turns ON using an electrical signal. The switching happens between the   Collector and Emitter terminal. Under normal conditions there is a high resistance between the collector and emitter terminals. So the transistor acts as an OFF switch. But when we apply a + 0.7 V to the Base Junction of an NPN transistor, the resistance between the emitter and collector terminal becomes zero. It acts as an ON switch. Likewise we can control the switching action using the electric signal applied to the Base terminal.   Unlike mechanical switches, transistors do not contain moving parts. So we call those solid-state switches. Hence transistors are more durable and can have very high switching frequencies. Can you turn ON and OFF a mechanical  switch 100 times per second?   Even if we manage to do that how long  will it last at such speed ? But we can switch transistors more  than one billion times per second. And more importantly we can contain billions  of these transistors in a small chip. This is a simple example of a transistor  switch circuit. A Rain Detector. We can use two separate conductor plates as the rain sensor. In dry conditions no current flows through it. since the voltage of the base  terminal is zero volts. so the transistor is at OFF State. The buzzer makes no sound. When water droplets hit the sensing pad it becomes wet and the water allows a little current from it to be. This tiny current will be enough to increase the potential of the base terminal to 0.7 V. Then the transistor will saturate and the buzzer will turn ON.   When an NPN transistor is  used as a switch, if we set the base to zero volts it acts as an OFF switch We call this cutoff mode. If we set the base to 0.7 V then it acts as an ON switch. We call this saturate mode We can use transistors as  Amplifiers. Some of the most powerful transistor applications involve Amplification. Turning a low power signal into one of a higher power. When it works as an amplifier, it takes in a tiny electric signal with almost no energy at one end and produces a much bigger copy at the other end. In other words it's a kind of power  booster. Amplifiers can increase the voltage or current of a signal Taking something from the micro Volt or micro ampere range and converting it to a more useful high power level Transistor Amplifiers are useful in things like hearing aids A hearing aid has a tiny microphone in it that picks up sounds from the world around you, and turns them into fluctuating electric currents. These are fed into a transistor that boosts them and Powers a tiny loudspeaker. So you hear a much louder version of the Sounds around you. That's all for today. Thank you for watching us. Like And subscribe professor mad for more educational videos. Don't hesitate to comment your thoughts.

Channel: Prof MAD

Views: 68,271

Keywords: how transistors work, prof mad, transistor, transistor animation, transistor explained, transistors explained, transistors introduction, what is a transistor

Id: Sod_5y7ZBlk

Length: 6min 34sec (394 seconds)

Published: Sat Oct 08 2022