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The 2SC828 is a classic NPN transistor recognized for its reliability, low noise, and suitability for small-signal amplification. This article will discuss the characteristics, uses, and essential details of the 2SC828 transistor.
The 2SC828 is a low-noise NPN amplifier transistor widely used in vintage and modern audio circuits. Known for its stable performance and clean signal amplification, it became a popular choice in radios, cassette players, and small audio preamps. Its ability to handle weak input signals with minimal distortion makes it ideal for early amplification stages.
With a collector-emitter voltage rating of up to 50V (depending on suffix) and a current capability of around 100mA, the 2SC828 performs well in low-power applications. It is also available in several gain groups, allowing you to match the transistor’s characteristics with specific circuit needs. Because of its broad frequency response and dependable TO-92 package, it remains a practical option for both repair and new designs.
If you are interested in purchasing the 2SC828 transistor, feel free to contact us for pricing and availability.
| Model Name (with Gain Rank) | Gain Group | Typical hFE Range | Notes |
| 2SC828-O | O | 70 – 140 | Lowest gain group; general-purpose use |
| 2SC828-Y | Y | 120 – 240 | Moderate gain; common in amplifiers |
| 2SC828-GR | GR | 200 – 400 | Higher gain; good for low-noise stages |
| 2SC828-BL | BL | 350 – 700 | Highest gain; preferred for sensitive audio preamps |
| Pin Number | Pin Name | Description |
| 1 | Emitter | Current flows out; connected to ground or low-side of the circuit |
| 2 | Collector | Main current-carrying terminal; connects to load |
| 3 | Base | Controls transistor operation; receives input signal |
| Parameter | 2SC945 | 2SC1815 | 2SC829 | BC549 | BC550 |
| Polarity | NPN | NPN | NPN | NPN | NPN |
| Vceo (Max Voltage) | 50V | 50V | 25–50V | 30V | 45V |
| Ic (Max Current) | 150mA | 150mA | 100mA | 100mA | 100mA |
| Power (Pc) | 400mW | 400mW | 400mW | 500mW | 500mW |
| hFE Gain Range | 70–700 (similar groups) | 70–700 | 70–700 | 110–800 | 110–800 |
| Noise Level | Low noise | Very low noise | Low noise | Low noise | Very low noise |
| fT (MHz) | 80–150 | 80–200 | ~150 | 100 | 100 |
| Pinout | E–C–B | E–C–B | E–C–B | C–B–E | C–B–E |
| Parameter | Specification |
| Transistor Type | NPN |
| Mounting Type | Through-Hole (Not Surface Mount) |
| Configuration | Single BJT |
| Collector Current (Ic) Max | 0.05A (50mA) |
| Power Dissipation (Pc) | 0.25W (250mW) |
| DC Current Gain (hFE) Min | 65 (varies by gain group O/Y/GR/BL) |
| Operating Temperature (Max) | 125°C |
| Polarity / Channel Type | NPN Bipolar |
| Package Type | TO-92 (or similar small signal package) |
| Typical Vceo (Collector-Emitter Voltage) | 25–50V (depending on version) |
| Frequency (fT) | ~100–150 MHz (typical) |
In the first circuit, the 2SC828 is used as a small-signal audio amplifier. The audio input passes through capacitor C1, which blocks unwanted DC and allows only the AC audio waveform to enter the base of the transistor. Resistors R1 and R2 set the correct bias so the transistor stays in its active region and can amplify without distortion. As the audio signal changes, the transistor produces larger variations in collector current, and resistor RC converts these current changes into an amplified voltage. Capacitor C2 sends this amplified AC signal to the output while filtering out DC. In this configuration, the 2SC828 boosts weak audio inputs so they are strong enough for further processing or output stages.
In the second diagram, two 2SC828 transistors (Q1 and Q2) operate together to form an oscillator and driver circuit for a flyback transformer. The capacitors and resistors around the transistors create feedback that causes continuous oscillation. Q1 amplifies the small signal coming from the timing network, and Q2 takes this amplified signal and provides the power needed to drive the transformer. As Q2 switches rapidly, it generates alternating pulses that the transformer converts into high voltage. The meter monitors the current, while VR1 adjusts the sensitivity of the oscillation. Here the 2SC828 is used because of its good switching speed and suitable gain, making it effective for generating high-frequency pulses required to energize the transformer.
In the third circuit, the 2SC828 acts as a sensitive amplifier for a touch-switch system. Touching the pads produces a very tiny electrical signal that Q1 (2SC828) amplifies. This first gain stage is necessary because the touch input is far too weak to trigger a relay directly. The amplified signal is passed to Q2 and Q3, which add additional amplification and ensure a stable control signal. Once strong enough, the signal activates Q4, which energizes the relay and lights the indicator LED. The protection diode prevents voltage spikes from damaging the transistor when the relay switches. In this application, the 2SC828 is chosen for its high gain and sensitivity, enabling it to detect and amplify extremely small touch signals reliably.
-Audio preamplifiers
-Small-signal audio boosters
-General-purpose switching
-LED drivers
-Relay driver stages
-Oscillator circuits
-Multivibrators
-Pulse generators
-Flyback transformer drivers
-Sensor amplifiers
-Touch-switch circuits
-Vibration detector circuits
-Light-sensing circuits
-RF/IF amplifier stages (low-power)
-Battery-powered devices
-Alarm and trigger circuits
-Voltage level shifters
-Motor control pre-driver stages
-Analog signal conditioning circuits
-High gain (hFE)
-Low noise
-Low power consumption
-Suitable for small-signal amplification
-Widely available
-Easy to bias
-Good for audio and sensor circuits
-Stable operation in low-voltage designs
-Inexpensive
-Compatible with many general-purpose NPN transistors
-Low current handling
-Limited power dissipation
-Not suitable for high-power loads
-Not designed for high-frequency RF
-Temperature sensitivity
-Requires careful biasing for clean audio
-May vary in gain between batches
-Not ideal for fast switching applications
-Outdated compared to modern low-noise transistors
-Restricted voltage rating compared to power transistors
Overall, the 2SC828 remains a dependable choice for low-noise amplification, small-signal switching, and sensitive detector circuits. Its availability in multiple gain ranks allows designers to match the right amplification level to specific project needs, while its straightforward operation makes it easy to integrate into both new designs and restoration work. For those seeking a practical and well-understood NPN transistor, the 2SC828 remains a reliable and widely supported option.
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