The transistor BC547 is a popular NPN bipolar junction 3-terminal device widely used in electronic circuits for switching and amplification. It belongs to the BC54x series and is designed for low-current, medium-voltage, and low-power applications. With a maximum collector current of 100 mA and collector-emitter voltage of 45 V, it is well-suited for driving small loads such as LEDs and relays or as a signal amplifier in audio and sensor circuits.
The BC557 is a widely used PNP bipolar junction transistor also designed for low-power, low-frequency applications. It is the complementary pair of the BC547 (NPN) transistor. With a maximum collector current of 100 mA and collector-emitter voltage of -45 V, it is suitable for general-purpose switching and small-signal amplification.
Pinout of BC557 and BC547 Transistor
Technical Features BC547 and BC557
Here’s a clear comparison between BC547 and BC557.
| Feature | BC547 | BC557 |
|---|---|---|
| Type | NPN Bipolar Junction Transistor (BJT) | PNP Bipolar Junction Transistor (BJT) |
| Polarity | NPN | PNP |
| Maximum Collector Current (Ic) | 100 mA | 100 mA |
| Maximum Collector-Emitter Voltage (Vceo) | 45 V | –45 V |
| Collector-Base Voltage (Vcb) | 50 V | –50 V |
| Emitter-Base Voltage (Veb) | 6 V | –5 V |
| DC Current Gain (hFE) | 110–800 | 110–800 |
| Power Dissipation (Ptot) | 500 mW | 500 mW |
| Junction Temperature (Tj max) | 150°C | 150°C |
| Applications | Signal amplification, switching (low-side) | Signal amplification, switching (high-side) |
| Pinout (from flat side, left to right) | Collector–Base–Emitter | Collector–Base–Emitter |
Applications of BC547 and BC557 Transistor
| Aspect | BC547 (NPN) | BC557 (PNP) |
|---|---|---|
| Switching Role | Used as low-side switch (between load and ground) | Used as high-side switch (between load and +Vcc) |
| Biasing Requirement | Turns ON when base is given a positive voltage relative to emitter | Turns ON when base is given a negative voltage relative to emitter |
| Common Applications | – LED driver circuits – Relay drivers – Logic level switching – Signal amplification |
– LED control from positive rail – Complementary push-pull stages – High-side switching – Signal amplification |
| Amplifier Usage | Works as common emitter amplifier for positive signals | Works as common emitter amplifier for negative signals |
| Pairing | Mostly used with BC557 for complementary pairs in amplifier stages | Mostly used with BC547 for complementary pair in amplifier stages |
| Best Suited For | Interfacing microcontrollers (like Arduino, PIC, etc.) to ground-based loads | Interfacing to Vcc-based loads where negative base drive is available |
Leave a Reply