How To Use a Transistor as a Switch

In my last article I discussed on how to construct basic electronics circuit using principles of diode forward biasing and other components such s capacitor and wire wound resistor base on your desire. Today I want to teach you another pattern that has to do with not just knowing what you want but also constructing basic circuits base on their uses and knowing how to join various component to form what you want.

First, I must apologies for my inability to post article for some few days as I was down health wise. So, back to the discussion of today.

If you know how a transistor operates, you could easily decide on what you could use it for. So, we shall be discussing basic operations of a Transistor, Diode, Capacitor and Resistor.

Transistor:

In my previous article I told you that a transistor is a semiconductor device made of 2 p-n junctions. It could either be a PNP type or an NPN type. The NPN type is mostly use in areas where the supply as in the power source is a positive +VCC while PNP is mostly used in power sources of negative rail –VEE.

A transistor can be use as a switch, as an amplifier, as a gate etc. first, lets start with it been used as a switch.

When you pass little current through the base of a transistor, it causes large amount of current to flow from the collector to the emitter. In order words, we can operate or energize a device or load connected in series between the collector of a transistor and the power source rail (line). Once the base senses a current capable of driving its junction or biasing its base emitter junction, the load connected across its collector will be energize instantly. Below is a simple way of illustrating this in energizing a Bulb of 12v.

As a switch in Logic circuit

, a transistor can be use in applications where you need a 1 (High) and a 0 (Low) signal. High signifies presence of a voltage or signal and Low signifies the absence of a voltage or signal. Below shows a basic arrangement of how it is use as a switch in logic circuit. Note, mostly used transistor types are C1815, BC108, C9018, C9014, BC547, BC548 and so on. The transistor type matters when it comes to power dissipation, current rating, frequency response range, Gain, Temperature range and lots more. Easy! I won’t rush all of them on you ok!

As a Signal Amplifier

, a transistor can be use in amplifying analogue signal such as audio signal from a microphone or an analogue signal generator. Due to the migration of electrons from the emitter to the collector, the higher voltage at the collector will flow down the emitter. That is to say, if we connect a load (which could be a speaker) in series with the collector of the transistor and the supply rail, when a little audio signal fed to the base of the transistor, a large signal will be replicated at the collector which is a capable of even driving an L.E.D or other forms of transducer such as a speaker.

Hmmmmm, i need have a drink and rest a little ok! lets make it a date tomorrow please, i will give you more tips you wont resist. Thanks so much my friends for your time with me. see ya!

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