# BC547 NPN transistor: specs and pinout

> A small general-purpose NPN bipolar transistor in a TO-92 package, used as a low-side switch or small-signal amplifier. The source sheet is the…

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A small general-purpose NPN bipolar transistor in a TO-92 package, used as a low-side switch or small-signal amplifier. The source sheet is the Fairchild BC546/547/548/549/550 data sheet (BC547 rows used); the stocked part's own maker markings were not verified.

Every value cites its sourceOfficial pinout

[Buy on Compoden](https://compoden.com/products/bc547-npn-transistor-45v-100ma-to-92-for-switching-amplification)

## Specs

| Spec | Value | Source |
|---|---|---|
| Collector-emitter voltage VCEO | 45 V (BC547) | source Absolute Maximum Ratings, p.1 |
| Collector-base voltage VCBO | 50 V (BC547) | source Absolute Maximum Ratings, p.1 |
| Emitter-base voltage VEBO | 6 V (BC546/547) | source Absolute Maximum Ratings, p.1 |
| Collector current IC | 100 mA DC | source Absolute Maximum Ratings, p.1 |
| Power dissipation PC | 500 mW | source Absolute Maximum Ratings, p.1 |
| DC current gain hFE | 110 min to 800 max at VCE 5 V, IC 2 mA; group A 110-220, B 200-450, C 420-800 | source Electrical Characteristics and hFE Classification, p.1 |
| Collector-emitter saturation VCE(sat) | 90 mV typ (250 mV max) at IC 10 mA, IB 0.5 mA; 200 mV typ (600 mV max) at IC 100 mA, IB 5 mA | source Electrical Characteristics, p.1 |
| Base-emitter on voltage VBE(on) | 660 mV typ (580-700 mV) at VCE 5 V, IC 2 mA | source Electrical Characteristics, p.1 |
| Transition frequency fT | 300 MHz typ at VCE 5 V, IC 10 mA | source Electrical Characteristics, p.1 |
| Junction and storage temperature | TJ 150 C max; storage -65 C to 150 C | source Absolute Maximum Ratings, p.1 |

## Power

| | Value | Source |
|---|---|---|
| Current | Collector current up to 100 mA DC; base drive 5 mA gives VCE(sat) at 100 mA | source Absolute Maximum Ratings and Electrical Characteristics, p.1 |

## Pinout

This is a bare transistor, not a module. Some makers' BC547 variants reorder the pins (check the marking on the stocked part's own sheet).

| Pin | Function | Voltage | Notes | Source |
|---|---|---|---|---|
| 1 | Collector | | TO-92; numbering as in the Fairchild package drawing | source Absolute Maximum Ratings / package drawing, p.1 |
| 2 | Base | | | source p.1 |
| 3 | Emitter | | | source p.1 |

## Build with it
Project ideas for the BC547 NPN transistor. Each link opens Soldr with the prompt filled in; Soldr assigns the pins, checks power and shows how to wire every part.

- [Dusk-to-dawn night light](https://app.soldr.ai/?prompt=I%20want%20to%20build%20an%20automatic%20night%20light%20that%20turns%20on%20in%20the%20dark%20using%20an%20ESP32%2C%20a%20light-dependent%20resistor%20and%20a%20BC547): The ESP32 reads the LDR on an analog input and switches an LED through the BC547; one LED is a few mA, far under 100 mA. The base resistor is sized from 3.3 V minus about 0.66 V.
- [Push-button LED driver](https://app.soldr.ai/?prompt=I%20want%20to%20build%20an%20LED%20blinker%20that%20a%20button%20controls%20with%20an%20Uno%20and%20a%20BC547): The Uno pin drives the base through a resistor and the transistor switches a few LEDs kept under the 100 mA limit.
- [Transistor switch learning board](https://app.soldr.ai/?prompt=I%20want%20to%20build%20a%20transistor%20switching%20demo%20that%20compares%20LED%20brightness%20at%20different%20base%20currents%20using%20an%20Uno%20and%20a%20BC547): Learning project: the datasheet's hFE range (110-800) shows why gain varies from part to part, which a potentiometer in the base circuit makes visible.

## Common mistakes

- Switching a load above 100 mA or 500 mW: those are the absolute maximums, so motors, buzzers with large coils or LED strips can exceed them ([source](https://www.sparkfun.com/datasheets/Components/BC546.pdf))
- Connecting the base straight to a pin with no resistor: the saturation rows assume a base current of about one twentieth of collector current (5 mA for 100 mA), so size a base resistor from the pin voltage minus VBE of about 0.66 V ([source](https://www.sparkfun.com/datasheets/Components/BC546.pdf))
- Reverse-biasing the emitter-base junction beyond 6 V ([source](https://www.sparkfun.com/datasheets/Components/BC546.pdf))

## Not covered by the official source

- Values are from the Fairchild BC546/BC547 sheet (now onsemi); the current onsemi edition and the stocked maker's part may differ slightly.
- Stocked part's maker not verified.

## Sources

- [link](https://www.sparkfun.com/datasheets/Components/BC546.pdf) (Fairchild BC546/547/548/549/550, Rev A2, Aug 2002; verbatim copy hosted on a mirror)