The 2SC1815 transistor (commonly written C1815) is a general-purpose NPN bipolar junction transistor (BJT) widely used in small signal amplification and switching circuits.
1. Basic Description
Type: NPN Transistor
Package: TO-92
Application: Amplifier, switching circuits, audio circuits, sensor circuits
Polarity: NPN (current flows from collector to emitter when base is activated)
2. Pin Configuration
When the flat side faces you and the pins point downward:
| Pin | Name | Function |
|---|---|---|
| 1 | Emitter (E) | Connected to ground in many circuits |
| 2 | Collector (C) | Connects to load |
| 3 | Base (B) | Controls the transistor |
Order:
E – C – B
3. Electrical Characteristics
| Parameter | Value |
|---|---|
| Collector-Emitter Voltage (Vce) | 50V |
| Collector Current (Ic) | 150mA |
| Power Dissipation | 400mW |
| Gain (hFE) | 70 – 700 |
| Frequency | ~80 MHz |
4. Common Uses
Audio signal amplification
Relay driving circuits
Sensor signal switching
Microcontroller interface circuits
Small power control circuits
Example:
Arduino / NodeMCU → Base resistor → C1815 → Relay or LED control.
5. Multimeter Testing (Simple Check)
Set multimeter to diode mode.
Expected readings:
| Probe Connection | Reading |
|---|---|
| Base → Emitter | ~0.6 – 0.7 V |
| Base → Collector | ~0.6 – 0.7 V |
| Collector ↔ Emitter | OL / no conduction |
If different, the transistor may be damaged.
6. Equivalent / Replacement Transistors
You can replace C1815 with:
BC547 transistor
2N3904 transistor
S8050 transistor
