NPN transistor · TO-92
BC547 Pinout
Flat face toward you, legs pointing down, left to right: 1 collector, 2 base, 3 emitter (C-B-E).
The small NPN transistor in most beginner kits: switches LEDs, buzzers and small relays up to 100 mA.
- Pin 1: Collector (C)Goes to the load (LED, relay, buzzer). Current flows in here and out of the emitter.
- Pin 2: Base (B)The control pin. A small current into it, always through a resistor, switches the transistor on.
- Pin 3: Emitter (E)Goes to 0 V (ground) when the transistor is used as a switch.
Check your part before wiring. Read the maker and the full part number printed on it, open that maker's datasheet, or test the legs with a multimeter's diode setting.
PNG 1440 × 1280 pixels, SVG to any size. Both keep the wirecora.com mark along the bottom.
Pinout table
Which leg of the BC547 is which?
| Pin | Name | What it does |
|---|---|---|
| 1 | Collector C | Goes to the load (LED, relay, buzzer). Current flows in here and out of the emitter. |
| 2 | Base B | The control pin. A small current into it, always through a resistor, switches the transistor on. |
| 3 | Emitter E | Goes to 0 V (ground) when the transistor is used as a switch. |
Key ratings
How much can the BC547 take?
From the onsemi datasheet: BC546B, BC547A, B, C, BC548B, C Amplifier Transistors, NPN Silicon (BC546/D, Rev. 8). Stay well inside these limits: they are the most the part takes, not what it should run at.
Open the onsemi datasheet (PDF)Pin order by maker
Is every BC547 wired C-B-E?
The onsemi datasheet numbers the legs 1 collector, 2 base, 3 emitter: C-B-E with the flat face toward you.
BC547s are made by many companies, so do not take the order for granted on a part from an unknown maker. The 2N3904, which does the same job and often sits in the same drawer, is the other way round: E-B-C. The surface-mount version, BC847 in SOT-23, has a different pinout again.
A first circuit
Switch an LED from a button or an Arduino pin
- Supply: 5 V. LED and a 220 Ω resistor in a row from +5 V to the collector (the LED's long leg toward +5 V).
- Emitter straight to 0 V.
- A 10 kΩ resistor from the control (an Arduino pin, or a button to +5 V) to the base.
- Control high: about 0.43 mA flows into the base, the transistor turns on and about 13 mA lights the LED. Control low: the LED goes out.
The 10 kΩ base resistor matters: a base wired straight to 5 V takes far too much current and the transistor dies.
The wiring board has the BC547. Its night light uses one with a light sensor on the base: try covering the sensor.
Open the night light on the wiring boardBC547 questions
What is the BC547 pinout?
With the flat face toward you and the legs pointing down, from left to right: collector, base, emitter (C-B-E). That is pin 1, 2 and 3 in the onsemi datasheet.
Is the BC547 NPN or PNP?
NPN. Its PNP partner is the BC557, which has the same C-B-E leg order.
How much current can a BC547 switch?
100 mA continuous at most, and up to 45 V. In practice keep it under about 50 mA so it stays cool: enough for LEDs, small buzzers and small 5 V relays.
What is the difference between BC547A, BC547B and BC547C?
Only the current gain. A is 110 to 220, B is 200 to 450 and C is 420 to 800. For switching, any of them works.
Can I use a 2N3904 instead of a BC547?
Yes, for most small switching circuits, but turn it round: the 2N3904 is E-B-C, the BC547 is C-B-E.
Can I use this pinout picture?
Yes. Download it as PNG or SVG and use it in notes, lessons or posts. The wirecora.com mark along the bottom stays in the picture.
Pin order and ratings from the onsemi datasheet named above. Last reviewed .