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Simple Transistor Tester Circuit

Transistors are small switches.

But how to check if they work or what type they are?

This Simple Transistor Tester Circuit is like a transistor checker.

It is an easy DIY project which uses few parts.

It tells us if transistor is good or bad and also shows if its NPN or PNP like two types.

In this circuit there are no fancy tools needed.

Circuit Working:

Parts List for both the diagram:

CategoryItemQuantity
Resistors (All resistors are assumed to be 1/4 watt)1k2
SemiconductorsNPN Transistor1
PNP Transistor1
5mm 20mA LED any color2
Battery 9V2

How basic transistor tester works with NPN or PNP transistors:

Use 9V battery, 1k resistor and LED.

Connect transistor legs in different ways like in circuit diagram above.

When LED lights up it means connection is good.

Brighter LED are the better transistor.

Find transistor type:

Diagrams help us to see if transistor is NPN or PNP.

Also it shows which leg is base, collector and emitter.

Bend legs if needed to match the diagram.

This tester works good with normal PNP and Darlington transistors.

How to Build a NPN Transistor Tester:

Build NPN transistor circuit:

How to test NPN transistor:

Formulas:

Transistor Tester Circuit with Simple Design & Analysis

To build and understand the circuit we need some basic formulas and ideas.

1. Ohms Law:

V = I × R

2. Current Limiting Resistor for LED:

To protect LED from too much current we used this formula:

R = (VS − VLED) / ILED

3. Power Dissipation:

Be sure parts do not overheat:

P = V × I

For Resistor:

PR = I² × R

For Transistor collector-emitter:

PCE = VCE × IC

Use these formulas to build and test the transistor circuit safely and correctly.

How to Build PNP Transistor Tester

Build PNP Transistor Circuit:

How to Test PNP Transistor:

Conclusion:

This easy and Simple Transistor Tester Circuit check if a transistor is working or not if its NPN or PNP.

Just a few parts needed and watch how LED lights up to understand the transistors type and condition.

References:

Transistor tester

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