1. What is a transistor and what are its types?

A transistor is a semiconductor device used to amplify or switch electronic signals and electrical power. It is composed of semiconductor material usually with at least three terminals for connection to an external circuit. Transistors are basically classified into two types; they are Bipolar Junction Transistors (BJT) and Field Effect Transistors (FET)

2. How do transistors work? What is its working principle?

Transistors are three terminal devices, namely collector, emitter and base. When the minimum voltage of 0.7 (for Si) is applied between the base and the emitter, the channel between the collector and emitter opens, thus opening the circuit. In this mode the transistor acts as a switch. Similarly, the transistor can also behave in amplifying mode as the base-emitted voltage can be anywhere between fully on and fully off, thereby limiting the collector emitter channel.

3. What is a PNP transistor?

A PNP transistor is a triode that has a P doped emitter, followed by an N doped base and again a P doped channel collector.

4. What is an NPN transistor?

A NPN transistor is a triode that has a N doped emitter, followed by an P doped base and again a N doped channel collector.

5. Can I use PNP instead of NPN?

Yes you can. If you have an exact PNP model that corresponds to NPN, you can directly replace it and just switch the current direction, for you to obtain similar output as previous.

6. What is the difference between PNP and NPN transistors?

The main difference between NPN and PNP is that in NPN, the circuit turns on when the current flows between base and emitter while in PNP the circuit turns on when there is no current flow between base and emitter.

7. How long do transistors last?

Transistors are components that usually lasts indefinitely unless there was a major change in circuitry that ends up damaging the component itself

8. Where can I buy transistors online?

Transistors are available from almost all online electronics shops such as Robocraze

9. Where can I buy transistors at a shop near me?

Transistors are found in many of the local electronics shops

10. How to choose transistors online?

You can choose the appropriate transistor for your project by cross checking the tolerances and conditions in the provided datasheet.

11. What are the prices of a transistor in India?

Transistors can be obtained for a few rupees to couple of hundred rupees from online stores or local shops

Transistors – SMD & Through-Hole Electronic Components

Transistor Selection Guide

Transistors are used as electronic switches, amplifiers, and signal control devices. Use this quick guide to pick the right one for your circuit:

Type: – NPN / PNP (BJT) for general switching & small-signal amplification. – N-MOSFET / P-MOSFET for efficient, high-current switching (motors, LEDs, loads).

Maximum Collector/Drain Current (Ic / Id): Choose a transistor that can handle at least 2× your expected load current.

Maximum Voltage (Vce / Vds): Must be higher than the supply voltage (with margin) to avoid breakdown.

Gain / Rds(on): – BJTs: look at hFE (gain) to size the base resistor. – MOSFETs: look for low Rds(on) at your gate voltage (e.g., 5V or 3.3V logic).

Package & Cooling: TO-92 for small loads, TO-220 or similar for higher power (can add heatsink).

Logic Level: For microcontroller projects, choose logic-level MOSFETs that fully turn on at 5V or 3.3V on the gate.

Usage Diagram – Transistor as a Switch (BJT)

Example: NPN transistor switching a DC load (e.g., motor, LED strip) with an Arduino pin.

Add a diode across inductive loads (motors, relays) for flyback protection.

Choose base resistor R_B so base current ≈ Ic / 10.

Usage Diagram – Transistor as an Amplifier (Common Emitter)

Small-signal NPN amplifier to boost audio or sensor signals.

+V (e.g., 9V) | R_C | Output ─●────────→ Vout | C ┌─────┐ Input ──C_in──┤B NPN (AC) ┤ └─────┘ | E R_E | GND

Coupling capacitor C_in blocks DC and passes AC signal.

Resistors R_C and R_E set gain and bias; add a bias divider on the base for stable operation.

Product	Price
2N2222 NPN Transistor (Pack of 5)	Rs. 40
TIP122 Darlington NPN Transistor - (Pack of 5)	Rs. 27
BC547 Transistor IC (Pack of 5)	Rs. 20
BC557 PNP Transistor - (Pack of 5)	Rs. 19
TIP127 Darlington PNP Transistor - (Pack of 5)	Rs. 62
TIP31C NPN Power Transistor - (Pack of 5)	Rs. 62
LM1117 IC Transistor - (Pack of 5)	Rs. 235
BC548 NPN Transistor (Pack of 5)	Rs. 7
BC558 Transistor (Pack of 5)	Rs. 9

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Transistor Selection Guide

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Transistors Prices in India

Frequently Asked Questions

1. What is a transistor and what are its types?

2. How do transistors work? What is its working principle?

3. What is a PNP transistor?

A PNP transistor is a triode that has a P doped emitter, followed by an N doped base and again a P doped channel collector.

4. What is an NPN transistor?

A NPN transistor is a triode that has a N doped emitter, followed by an P doped base and again a N doped channel collector.

5. Can I use PNP instead of NPN?

Yes you can. If you have an exact PNP model that corresponds to NPN, you can directly replace it and just switch the current direction, for you to obtain similar output as previous.

6. What is the difference between PNP and NPN transistors?

The main difference between NPN and PNP is that in NPN, the circuit turns on when the current flows between base and emitter while in PNP the circuit turns on when there is no current flow between base and emitter.

7. How long do transistors last?

Transistors are components that usually lasts indefinitely unless there was a major change in circuitry that ends up damaging the component itself

8. Where can I buy transistors online?

Transistors are available from almost all online electronics shops such as Robocraze

9. Where can I buy transistors at a shop near me?

Transistors are found in many of the local electronics shops

10. How to choose transistors online?

You can choose the appropriate transistor for your project by cross checking the tolerances and conditions in the provided datasheet.

11. What are the prices of a transistor in India?

Transistors can be obtained for a few rupees to couple of hundred rupees from online stores or local shops

Let customers speak for us

All Categories

Transistors – SMD & Through-Hole Electronic Components

Categories

Refined By Clear all

Featured Products

Sort by:

All About Transistors – SMD & Through-Hole Electronic Components

Buy Transistors Online in India

Transistor Selection Guide

Usage Diagram – Transistor as a Switch (BJT)

Usage Diagram – Transistor as an Amplifier (Common Emitter)

Transistors Prices in India

Frequently Asked Questions

1. What is a transistor and what are its types?

2. How do transistors work? What is its working principle?

3. What is a PNP transistor?

A PNP transistor is a triode that has a P doped emitter, followed by an N doped base and again a P doped channel collector.

4. What is an NPN transistor?

A NPN transistor is a triode that has a N doped emitter, followed by an P doped base and again a N doped channel collector.

5. Can I use PNP instead of NPN?

Yes you can. If you have an exact PNP model that corresponds to NPN, you can directly replace it and just switch the current direction, for you to obtain similar output as previous.

6. What is the difference between PNP and NPN transistors?

The main difference between NPN and PNP is that in NPN, the circuit turns on when the current flows between base and emitter while in PNP the circuit turns on when there is no current flow between base and emitter.

7. How long do transistors last?

Transistors are components that usually lasts indefinitely unless there was a major change in circuitry that ends up damaging the component itself

8. Where can I buy transistors online?

Transistors are available from almost all online electronics shops such as Robocraze

9. Where can I buy transistors at a shop near me?

Transistors are found in many of the local electronics shops

10. How to choose transistors online?

You can choose the appropriate transistor for your project by cross checking the tolerances and conditions in the provided datasheet.

11. What are the prices of a transistor in India?

Transistors can be obtained for a few rupees to couple of hundred rupees from online stores or local shops

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