Part of the Day · MMBT3904 — SOT-23 NPN transistor (marking 1AM)

Part of the Day · 2026-10-23

The SMD small-signal NPN transistor you see most often on PCBs. It is marked 1AM instead of the part number, and is the SMD version of the leaded 2N3904 with the same ratings.

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 1AM

Key specifications

Values are from the onsemi datasheet.

Marking and pins

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

Typical uses

• Small-signal switching — LED and relay drivers, logic level shifting
• Small-signal amplification

Companion & similar parts

• MMBT3906 — PNP complement (marking code 2A) — opposite polarity, not a substitute
• 2N3904 — Leaded TO-92 version with the same ratings — pin order E-B-C
• MMBT2222A — Also a SOT-23 NPN, higher-current 600mA type (marking code 1P)

Marking code 1AM follows onsemi. For parts from other makers, check the logo and the Marking table in that maker's datasheet.