BC557 Pinout
BC557 PNP Transistor · General-purpose PNP transistor; the PNP complement of the BC547, for small-signal / low-side-of-supply switching.
TO-92 flat (printed) face toward you, pins down: left to right is C-B-E (Collector, Base, Emitter) — the same pin order as the BC547, but it is a PNP, so the emitter goes to the positive rail.
| Pin | Name | Type | Function |
|---|---|---|---|
| 1 | C · Collector | Output | Collector |
| 2 | B · Base | Input | Base (control) |
| 3 | E · Emitter | I/O | Emitter |
How to read the BC557 pinout
- 01
Find pin 1
One end of the chip has a half-circle notch or a dot; with the notch facing up, the top-left pin is pin 1.
- 02
Count counter-clockwise
Count counter-clockwise from pin 1: go down the left side first, then up the right side from the bottom.
- 03
Check the table below
Look up each pin's function by number in the table below; power/ground are color-coded, and alternate-function signals are in parentheses.
Frequently asked questions
What is the BC557 pin order?
In the TO-92 package, flat face toward you and pins down, left to right is C-B-E (Collector, Base, Emitter). This matches the BC547 layout; the difference is polarity — the BC557 is PNP.
How do I use the BC557 as a switch?
As a PNP, the emitter goes to the positive supply and the load hangs off the collector to ground; pull the base low (through a resistor, e.g. 1–10kΩ) to turn it on. It pairs with the NPN BC547 for push-pull / complementary stages.
Pinout data comes from onsemi BC557 datasheet (standard TO-92 numbering). Refer to the actual device datasheet as authoritative for the pinout.