BC109 is a general purpose NPN transistor, Which is comes from the BC107 and BC108 transistor family. In this article sharing information’s about BC109 Transistor Pinout, Features, Equivalent transistors as substitute and it’s applications.
What is the BC109 Transistor?
The BC109 transistor is a low noise generating NPN transistor. This transistor is comes in a TO-18 metal packaging. This metal packaging is enough to maintain good heat transfer when transistor is working. This transistor is mainly using in switching and audio amplification and other audio circuits due to its low noise performance.
BC109 Transistor Pinout
Facing the transistor tag at bottom left side and count the pins from left to right. The pin near to the tag is emitter center pin is base and third pin is collector. The detailed diagram is given below,
Pin Configuration
| Pin | Name |
|---|---|
| 1 | Emitter |
| 2 | Base |
| 3 | Collector |
BC109 Symbol and Bottom view
Characteristics
| Parameter | Value |
|---|---|
| Collector-Base Voltage | Max 30 V |
| Collector-Emitter Voltage | Max 20 V |
| Emitter-Base Voltage | Max 5 V |
| Collector Current (DC) | Max 100 mA |
| Power Dissipation | Max 300 mW |
| DC Gain (hFE) | 200 – 800 (at IC = 2 mA) |
| Transition Frequency (fT) | Min 100 MHz |
| Noise Figure | ~4 dB (low noise) |
PNP Complement
- BC177 is the complementary PNP transistor.
Equivalent NPN Transistors to BC109
The equivalent transistor for BC109 is given in the table below. You must compare the hfe value, pinout configuration and other parameters before replacing with the substitutes.
| Transistor | Description |
|---|---|
| BC108 | Very similar specs, slightly lower noise handling |
| BC107 | Higher voltage rating, slightly lower gain |
| BC549 | Plastic TO-92 version, similar characteristics, good for audio |
| BC550 | Low-noise version, TO-92 package, ideal for audio applications |
| 2N2222 | Higher current (800 mA), TO-18 metal can, commonly available |
| 2N3904 | Popular general-purpose NPN, TO-92, lower gain |
| S8050 | General-purpose NPN transistor, TO-92, low cost |
| KT315 | Russian equivalent, used in older Soviet electronics |
Difference between BC109 and BC108
The BC109 and BC108 both are NPN transistors and comes from the same family and are very similar in construction and function. However, they have some important differences especially in noise performance and gain range.
The BC109 transistor is a low noise version of the BC108, so it is used for sensitive audio and RF applications. If you’re working on audio preamps, microphone circuits or signal stages recommended to choose BC109. For general switching circuit or amplification purpose the BC108 is sufficient.
Applications
- Audio preamplifiers and low-level audio stages
- Signal processing
- General-purpose low-noise amplification
- Switching circuits
