Overview

The 2N3906 is the industry-standard general-purpose PNP Bipolar Junction Transistor (BJT) manufactured by ON Semiconductor, STMicroelectronics, and Fairchild. It is the direct complementary PNP pair to the 2N3904 NPN transistor, widely used for high-side power switching, push-pull audio amplifiers, and inverted digital control logic.

Housed in a 3-pin TO-92 plastic package, the 2N3906 is rated for a collector-emitter breakdown voltage (VCEOV_{CEO}) of −40 Volts-40\text{ Volts} and continuous collector current (ICI_C) of −200 mA-200\text{ mA}.

Quick reference

Transistor TypeGeneral-Purpose PNP Bipolar Junction Transistor (BJT)
PackageTO-92 (Flat face front, leads pointing down) / SOT-23 (MMBT3906)
Pinout (TO-92)Pin 1: Emitter (E), Pin 2: Base (B), Pin 3: Collector (C) — E-B-C
Collector-Emitter Voltage (VCEOV_{CEO})−40 V-40\text{ V} max
Collector-Base Voltage (VCBOV_{CBO})−40 V-40\text{ V} max
Continuous Collector Current (ICI_C)−200 mA-200\text{ mA} continuous
DC Current Gain (hFEh_{FE})100…300100 \dots 300 at IC=−10mA,VCE=−1.0VI_C = -10\text{mA}, V_{CE} = -1.0\text{V}
Transition Frequency (fTf_T)250 MHz250\text{ MHz} min
Power Dissipation (PDP_D)625 mW625\text{ mW} at TA=25∘CT_A = 25^\circ\text{C}

Pinout (TO-92 Package)

Looking at the flat face of the TO-92 package with leads pointing down:

text
        ┌─────────────┐
        │   2N3906    │  (Flat Package Face)
        └─┬───┬───┬───┘
          1   2   3
          E   B   C
PinNameDescription
1EMITTER (E)Emitter terminal (Connect to +VCC+V_{CC} positive supply rail)
2BASE (B)Base input control terminal (Pull LOW to turn ON)
3COLLECTOR (C)Collector terminal (High-side load output)

Specifications

ParameterSymbolMinTypMaxUnitConditions
Collector Breakdown VoltageV(BR)CEOV_{(BR)CEO}-40——VIC=−1.0mA,IB=0I_C = -1.0\text{mA}, I_B = 0
Emitter Breakdown VoltageV(BR)EBOV_{(BR)EBO}-5.0——VIE=−10 μA,IC=0I_E = -10\ \mu\text{A}, I_C = 0
Collector Saturation VoltsVCE(sat)V_{CE(sat)}—-0.25-0.4VIC=−50mA,IB=−5.0mAI_C = -50\text{mA}, I_B = -5.0\text{mA}
Base Saturation VoltageVBE(sat)V_{BE(sat)}-0.65—-0.95VIC=−50mA,IB=−5.0mAI_C = -50\text{mA}, I_B = -5.0\text{mA}

High-Side PNP Switching Circuit

In high-side PNP switching, the load is connected between the Collector pin and Ground. Pulling the Base pin LOW (0V) turns the 2N3906 ON, supplying positive power to the load:

text
        +5V DC Power Rail
             │
        [Pin 1: EMITTER]
         2N3906
        [Pin 3: COLLECTOR] ─── [ LED / Load ] ─── GND
             │
  MCU ── [ R_B = 1kΩ ] ─── [Pin 2: BASE]

(Setting MCU pin to LOW (0V) turns PNP ON; setting MCU pin to HIGH (5V) turns PNP OFF).

Common mistakes

  • Attempting to switch high voltages (VCC>VMCUV_{CC} > V_{MCU}): Switching a 12V high-side load with a 2N3906 using a 5V MCU pin will keep the transistor permanently ON. The 5V5\text{V} output from the MCU pin is 7V7\text{V} lower than the 12V12\text{V} Emitter, maintaining base-emitter forward bias. Use an NPN driver transistor (2N3904) to pull the 2N3906 base down to GND.
  • Forgetting base current limiting resistor: Always place a series base resistor (470 Ω…1 kΩ470\ \Omega \dots 1\ \text{k}\Omega) between the GPIO pin and the Base to limit base current.

Notes

  • 2N3906 vs 2N3904: 2N3906 is PNP (Active LOW high-side switch); 2N3904 is NPN (Active HIGH low-side switch).

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