Part of the Day · MMBT3906 — SOT-23 PNP transistor (marking 2A)

Part of the Day · 2026-10-23

The SMD small-signal PNP transistor that pairs with the MMBT3904. It is marked 2A instead of the part number and is often found on PCBs as a high-side switch or small-signal amplifier.

Actual size

↓ Actual size, left edge aligned to 0 on the ruler

One ruler tick = 1mm. On PC this is actual size on a 24-inch FHD monitor at 100% zoom; on iPhone it adjusts automatically. For other screens, use “Calibrate ruler” below.

Enlarged (SOT-23 · top view · approx. 20×)

Pins 1 Base · 2 Emitter · 3 Collector

Package SOT-23 · Marking 2A

Key specifications

Values are from the onsemi datasheet.

Marking and pins

Marking code 2A · Pins 1 Base · 2 Emitter · 3 Collector

Typical uses

• Small-signal switching — switching on the supply side (high side)
• Small-signal amplification, push-pull circuits paired with an NPN

Companion & similar parts

• MMBT3904 — NPN complement (marking code 1AM) — opposite polarity, not a substitute
• 2N3906 — Leaded TO-92 version of the same family — pin order differs, check the datasheet

Marking code 2A follows onsemi. For parts from other makers, check the logo and the Marking table in that maker's datasheet.