How to Transistor Test?

In this tutorial, we are going to learn about How to Transistor Test?

Transistor –                                                                                           

Transistor is the central component in all modern electronics. In special applications single transistors are still required. Power electronics or high frequency applications still require single transistors.Of course, the main applications of transistors are inside of integrated circuits [ICs] or electronics chips. Starting from simple integrated audio amplifiers up to highly complex chips like microprocessors a memory chips, no modern circuit can do without the transistors. Simple components only use a few internal transistors, but modern processors  use billions of internal  transistor functions. Therefore, if one would like to understand the operation principles of modern circuitry, a basic knowledge of the transistor mode of operation is absolutely essential.The following figure shows how a transistor actually looks like. It is usually contained in a black plastic housing with three electric connections.     

How does Transistor Work?

The following two illustrations show the basic principle how a transistor operates. As per showing image, the transistor blocks the current. Its means which no current is going through the collector emitter connection. One could imagine which a wedge is blocking this path. Only if a small basis current is introduced, the transistor will start to let the current pass through. Like a stream of water pushes the wedge in image. Aside, the base current opens the transistor’s collector emitter connection. The larger the base is, the larger the collector emitter will be. In this way, a very small basis current can control a much bigger collector emitter current. Similar to the fluid example the amplification also works for electrical currents. Of course things are a little more complicated in reality, but using this simple model, a lot of basic transistor circuits can be understood quite well. The current gain which can be obtained using a single transistor ranges between 10x(for power transistors) and up to 1000x for small signal types.

Blocking Transistor
Conducting Transistor

A Transistor Tester :                                                                                 

The following figures shows a simple transistor tester. If the circuit is built exactly as shown, then the LED will light up brightly is the transistor is ok.But this still does not guarantee that the transistor really works fine. A transistor can be damaged in several ways :

1) The transistor I permanently non conductive (“open”) 

2) The transistor is permanently conduction, no matter of its control current (“short circuit condition”) It is the transistor does not work due to second fault, the LED would also glow, is the transistor is defective. In order to check this out, the 100 k resistor must be removed from the circuit. If the LED stops to emit light now, then one can be sure, that the transistor is ok.       

Dangers for transistors : 

As mentioned already, transistor can easily be damaged.Only a very few short over current is sufficient and it  will be permanently damaged. Therefore, similarly to LEDs, transistors have to be protected by appropriate current limiting resistors. In the collector circuit, always a resistor of no less than 1K Ohm should be used, for the basis of even, If too much current goes through the transistors, it will heat up immediately. Temperatures of 100* c  and more are reached with in. If It feels warm, one should immediately disconnect the battery from the circuitry and look for a  possible error in the set-up. But keep in mind, that this method is not very reliable, since a transistor can be defective long before you will recognize its heat up.On the other hand, watch out in order not to burn you fingers.Besides, it is recommended to complete your circuit before connecting it to a battery. Then check it and recheck it again before you connect it to a battery or another power source. If the circuit is not working correctly, disconnect it immediately from the power source and look for errors. In doing so you might be able to save some of your components from permanent damage. 

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