Overview

The PN2222A (and its metal-can variant 2N2222A) is a ubiquitous NPN silicon Bipolar Junction Transistor (BJT) housed in a 3-pin TO-92 plastic package. Found in virtually every electronics starter kit (Elegoo, SparkFun, Adafruit), it is used for low-power signal amplification and low-side digital switching of small DC loads (relays, piezo buzzers, small DC motors, LEDs).

Capable of handling a 40V40\text{V} collector-emitter breakdown voltage (VCEOV_{CEO}) and up to 600 mA600\text{ mA} continuous collector current (ICI_C), the PN2222A provides high DC current gain (hFE=100…300h_{FE} = 100 \dots 300) and fast switching speeds up to 300 MHz300\text{ MHz}.

Quick reference

Transistor typeNPN Bipolar Junction Transistor (BJT)
PackageTO-92 (TO-226AA) Plastic Package
Pinout (PN2222 TO-92)Pin 1: Emitter (E), Pin 2: Base (B), Pin 3: Collector (C)
Collector-Emitter Voltage (VCEOV_{CEO})40 V40\text{ V} max
Collector-Base Voltage (VCBOV_{CBO})75 V75\text{ V} max
Continuous Collector Current (ICI_C)600 mA600\text{ mA} max
DC Current Gain (hFEh_{FE})100 to 300100\text{ to }300 (at IC=150 mA,VCE=10VI_C = 150\text{ mA}, V_{CE} = 10\text{V})
Collector Saturation Volts (VCE(sat)V_{CE(sat)})0.3 V0.3\text{ V} max (at IC=150 mA,IB=15 mAI_C = 150\text{ mA}, I_B = 15\text{ mA})
Transition Frequency (fTf_T)300 MHz300\text{ MHz} min

Pinout (TO-92 Package)

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

text
        ┌─────────┐
        │  PN2222 │  (Flat Face Front)
        └─┬───┬───┬─┘
          1   2   3
          E   B   C
PinNameDescription
1Emitter (E)Connected to ground (or negative side of load circuit)
2Base (B)Control input (connected to MCU GPIO via base resistor)
3Collector (C)Connected to negative terminal of load (switched low-side)
Important

Pinout Pin Order Note:

  • Standard plastic PN2222 / PN2222A (TO-92) pinout order is E-B-C (Emitter, Base, Collector).
  • Metal-can 2N2222 / 2N2222A (TO-18) pinout order is E-B-C with the tab next to Emitter. Always verify pin configuration with a multimeter or component tester before powering up.

Specifications

ParameterSymbolMinTypMaxUnitConditions
Collector-Emitter VoltageVCEOV_{CEO}40——VIC=10 mA,IB=0I_C = 10\text{ mA}, I_B = 0
Collector-Base VoltageVCBOV_{CBO}75——VIC=10 μA,IE=0I_C = 10\ \mu\text{A}, I_E = 0
Emitter-Base VoltageVEBOV_{EBO}6.0——VIE=10 μA,IC=0I_E = 10\ \mu\text{A}, I_C = 0
Continuous Collector CurrentICI_C——600mAContinuous DC
Saturation VoltageVCE(sat)V_{CE(sat)}—0.20.3VIC=150 mA,IB=15 mAI_C = 150\text{ mA}, I_B = 15\text{ mA}
Base Saturation VoltageVBE(sat)V_{BE(sat)}0.60.851.2VIC=150 mA,IB=15 mAI_C = 150\text{ mA}, I_B = 15\text{ mA}
Total Power DissipationPDP_D——625mWAmbient TA=25∘CT_A = 25^\circ\text{C}

Low-Side Switch Circuit & Base Resistor Math

To switch a 200mA load (such as a 5V relay coil) from an Arduino 5V digital pin:

text
       +5V DC Power Rail
          │
        [RELAY COIL] (5V, 200mA Load)
          │
          ├──────────────┐
          │              │
       [Collector]  [1N4007 Flyback Diode]
       PN2222 BJT        │
       [Emitter] ────────┴─────── GND (0V Common Ground)
          │
        [Base]
          │
       [1kΩ] (Base Resistor)
          │
     Arduino Digital Output Pin (5V)

Base Resistor Calculation (RBR_B)

To drive the BJT into saturation (VCE(sat)≤0.3VV_{CE(sat)} \le 0.3\text{V}), enforce a forced saturation gain βsat≈10\beta_{sat} \approx 10:

IB=ICβsat=200 mA10=20 mAI_B = \frac{I_C}{\beta_{sat}} = \frac{200\text{ mA}}{10} = 20\text{ mA}

RB=VGPIO−VBE(sat)IB=5.0V−0.7V0.020A=4.3V0.020A=215 ΩR_B = \frac{V_{GPIO} - V_{BE(sat)}}{I_B} = \frac{5.0\text{V} - 0.7\text{V}}{0.020\text{A}} = \frac{4.3\text{V}}{0.020\text{A}} = 215\ \Omega

(A standard 220 Ω220\ \Omega or 330 Ω330\ \Omega base resistor ensures reliable saturation mode switching).

Common mistakes

  • Omitting the Base Resistor: Connecting a 5V MCU GPIO pin directly to the BJT Base pin creates a short circuit through the forward-biased internal Base-Emitter PN junction (VBE≈0.7VV_{BE} \approx 0.7\text{V}), destroying the MCU pin. Always include a 220 Ω…1 kΩ220\ \Omega \dots 1\ \text{k}\Omega base resistor.
  • Exceeding 600mA Collector Current: Attempting to drive high-current motors (>600 mA>600\text{ mA}) causes overheating and thermal runaway. Use a MOSFET (such as the IRLZ44N) for loads requiring >500 mA>500\text{ mA}.

Notes

  • PN2222 vs 2N3904 vs BC547: PN2222 handles up to 600 mA600\text{ mA}; 2N3904 and BC547 handle up to 200 mA200\text{ mA}.

Assets & downloads