What is the difference between them: 2N3904 vs. BC547?

It is good to compare two components, which is also a good technique to have a better understanding of a component and to see if it can be replaced with something else. Both the 2N3904 and the BC547 have commonly used transistors that are also well-known among electronic enthusiasts and tinkerers.

2N3904 Features:

• Bi-Polar NPN Transistor

• DC Current Gain (hFE) is 300 maximum

• Continuous Collector current (IC) is 200mA

• Base- Emitter Voltage (VBE) is 6V

• Collector-Emitter Voltage (VCE) is 40V

• Collector-Base Voltage (VCB) is 60V

• Available in To-92 Package

BC547 Features:

• Bi-Polar NPN Transistor

• DC Current Gain (hFE) is 800 maximum

• Continuous Collector current (IC) is 100mA

• Emitter Base Voltage (VBE) is 6V

• Base Current(IB) is 5mA maximum

• Available in To-92 Package

2N3904 vs. BC547 Pinout

Both transistors are packaged in the TO-92 package, which is a plastics packaging, as shown in the image above. However, when we compare pins, we find that both are distinct in this regard. The first pin on the 2N3904 is Emitter, the second is Base, and the third is Collector, whereas the first pin on the BC547 is Collector, the second is Base, and the third is Emitter.

The equivalent for 2N3904:

BC548, BC547, BC636, BC639, 2N2222A, 2N2222, 2N2369, 2N3055, 2N3906, 2SC5200 are equivalent to 2N3904.

The equivalent for BC547:

BC547 can be replaced by BC548, BC549, 2N2222, 2N3904, 2N4401, and BC337 are equivalent to BC547.

The highest Collector to Emitter Voltage (Vceo) of the 2N3904 is 40V, but the BC547 Vceo is 50V, as shown in the table above. When changing a transistor, the Collector to Emitter voltage is vital to look at, although a difference of 10V isn't a concern unless your load is under 40V. The maximum collector current of the 2N3904 is 200mA, while the collector current of the BC547 is 100mA. The total device dissipation of the 2N3904 is 625mW, while the BC547 is 500mW. This is a little change that will not affect performance. When utilizing a transistor in a high-frequency or RF circuit, its (fT) is taken into account. However, because the (fT) value of 300MHz is quite good, both of these transistors can be employed in RF circuits without difficulty. We can deduce from these details that the 2N3904 transistor can be used instead of the BC547.

The BC547 transistor can be used in place of the 2N3904 transistor, however, there are some conditions that must be met before utilizing it instead of the 2N3904. The collector current differential between the two transistors is the most important factor to consider. Because the collector current of the 2N3904 is 200mA and the collector current of the BC547 is 100mA, you can replace the 2N3904 with BC547 if the load you're driving is less than 100mA, but you can't use BC547 if the load is greater than 100mA.

2N3904 Datasheet

BC547 Datasheet

Because the transistors 2N3904 and BC547 are nearly identical and have few differences, they can be utilized interchangeably in most situations.

However, keep in mind that pin configuration must be maintained because the pinout and collector current of both transistors are different, therefore you must know how much load you are driving in your circuit to replace these transistors with each other.