TIP31C — NPN Power Bipolar Junction Transistor

Overview

The TIP31C is a general-purpose NPN power bipolar junction transistor (BJT) manufactured by STMicroelectronics and ON Semiconductor. Packaged in a robust TO-220AB enclosure, it is designed for medium-power linear voltage regulators, audio power amplifiers, motor speed controls, and high-voltage DC load switching.

Supporting collector-emitter voltages up to $100\text{ Volts}$ and continuous collector currents up to $3.0\text{ Amps}$ (with peak currents up to $5.0\text{ A}$ ), the TIP31C is frequently paired with its PNP complementary power transistor, the TIP32C.

Quick reference


Transistor Type	NPN Power Bipolar Junction Transistor
Package	TO-220AB (Metal tab connected to COLLECTOR)
Collector-Emitter Voltage ( $V_{CEO}$ )	$100\text{ V}$ max
Collector-Base Voltage ( $V_{CBO}$ )	$100\text{ V}$ max
Continuous Collector Current ( $I_C$ )	$3.0\text{ A}$ continuous ( $5.0\text{ A}$ peak)
Base Current ( $I_B$ )	$1.0\text{ A}$ max
DC Current Gain ( $h_{FE}$ )	25 to 50 at $I_C = 1.0\text{A}$ ( $10\dots50$ at $I_C = 3.0\text{A}$ )
Transition Frequency ( $f_T$ )	$3.0\text{ MHz}$ min
Power Dissipation ( $P_D$ )	$40\text{ W}$ ( $T_C = 25^\circ\text{C}$ ) / $2.0\text{ W}$ ( $T_A = 25^\circ\text{C}$ )

Pinout (TO-220AB Package)

Looking at the front labeled face of the TO-220 package with leads pointing down:

text

        ┌─────────────┐
        │   O   [TAB] │  (Metal Mounting Tab = COLLECTOR)
        ├─────────────┤
        │   TIP31C    │  (Front Package Face)
        └─┬───┬───┬───┘
          1   2   3
          B   C   E

Pin	Name	Description
1	`BASE` (`B`)	Base control input
2	`COLLECTOR` (`C`)	Collector terminal (Connected internally to tab)
3	`EMITTER` (`E`)	Emitter terminal (Ground reference 0 V)

Specifications

Parameter	Symbol	Min	Typ	Max	Unit	Conditions
Collector-Emitter Breakdown	$V_{(BR)CEO}$	100	—	—	V	$I_C = 30\text{mA}, I_B = 0$
DC Current Gain ( $I_C=1\text{A}$ )	$h_{FE}$	25	—	50	—	$V_{CE} = 4\text{V}, I_C = 1\text{A}$
DC Current Gain ( $I_C=3\text{A}$ )	$h_{FE}$	10	—	50	—	$V_{CE} = 4\text{V}, I_C = 3\text{A}$
Collector Saturation Volts	$V_{CE(sat)}$	—	—	1.2	V	$I_C = 3\text{A}, I_B = 375\text{mA}$
Base-Emitter Voltage	$V_{BE(on)}$	—	—	1.8	V	$V_{CE} = 4\text{V}, I_C = 3\text{A}$

Common mistakes

Expecting high gain from an MCU GPIO pin: Unlike Darlington transistors (such as TIP120 with $h_{FE} \ge 1000$ ), the TIP31C has a relatively low DC current gain ( $h_{FE} \approx 25$ ). To switch a $1.0\text{ A}$ load, the Base requires $I_B \approx 40\text{ mA}$ , which exceeds the safe pin current limit of most microcontrollers ( $20\text{ mA}$ ). Use a pre-driver transistor (e.g. 2N3904) or a Darlington/MOSFET.
Operating without a heatsink at high power levels: When conducting $2\text{A}$ , $V_{CE(sat)}$ power dissipation reaches $\sim 2.4\text{ Watts}$ . A heatsink is necessary to prevent thermal shutdown.

Notes

TIP31 vs TIP31A vs TIP31B vs TIP31C: TIP31 (40V), TIP31A (60V), TIP31B (80V), TIP31C (100V). The "C" suffix version is the most common because it covers all lower voltage requirements.