Transistor Equivalent Finder Tool

How to Choose a Transistor Equivalent

Finding a replacement for a bipolar junction transistor (BJT) involves more than just matching a part number. To ensure your circuit works reliably, you must compare several key electrical parameters. Below is a guide to the most critical specifications to check.

1. Match Polarity (NPN vs. PNP)

This is the most fundamental rule. You must replace an NPN transistor with another NPN, and a PNP with a PNP. They control current in opposite ways and are not interchangeable.

2. Voltage Rating (VCEO) Must Be Equal or Higher

The Collector-Emitter Voltage (VCEO) is the maximum voltage the transistor can withstand when it is in the 'off' state. Your replacement part must have a VCEO equal to or greater than the original transistor. Using a part with a lower rating will cause it to break down.

3. Current Rating (Ic) Must Be Equal or Higher

The Collector Current (Ic) is the maximum amount of current the transistor can handle continuously. The replacement must have an Ic rating equal to or greater than the original part to avoid overheating and failure.

4. Physical Package and Pinout

The replacement must physically fit on your circuit board. Check if the original is a through-hole (like TO-92) or surface-mount (like SOT-23) component. You must also verify the pinout (the order of the Emitter, Base, and Collector pins) is the same, or you will have to adjust your layout.