TIP122 — 100V 5A NPN Power Darlington Transistor (TO-220)

Overview

The TIP122 is a 100V 5A complementary silicon NPN power Darlington transistor manufactured by STMicroelectronics, onsemi, and Texas Instruments. Housed in an industry-standard TO-220AB through-hole package, it is the highest-voltage member of the ubiquitous TIP120 series (TIP120: 60V, TIP121: 80V, TIP122: 100V).

Featuring a monolithic Darlington pair with built-in base-emitter bleed resistors and an integrated reverse collector-emitter flywheel protection diode, the TIP122 provides an immense DC current gain ( $h_{FE} \ge 1000$ ). With a $100\text{V}$ breakdown voltage rating, it provides substantial voltage safety margin against inductive kickback, making it the most popular Darlington transistor for driving $24\text{V} \dots 48\text{V}$ unipolar stepper motors (in 3D printers and CNC machines), pinball machine high-power solenoid coils, electromagnetic brakes, and automotive power actuators directly from 3.3V/5V microcontroller pins.

Quick reference


Transistor Type	Monolithic NPN Silicon Power Darlington BJT
Package	TO-220AB (3-pin through-hole)
Collector-Emitter Voltage ( $V_{CEO}$ )	$100\text{ V}$ max (Highest in TIP120 family)
Collector-Base Voltage ( $V_{CBO}$ )	$100\text{ V}$ max
Continuous Collector Current ( $I_C$ )	$5.0\text{ A}$ max ( $8.0\text{ A}$ pulsed)
Base Current ( $I_B$ )	$0.12\text{ A}$ ( $120\text{ mA}$ )
DC Current Gain ( $h_{FE}$ )	$1000$ min ( $1000 \dots 5000$ at $I_C = 3.0\text{A}, V_{CE} = 3.0\text{V}$ )
Collector Saturation ( $V_{CE(sat)}$ )	$2.0\text{ V}$ max at $I_C = 3.0\text{A}$ ( $4.0\text{ V}$ max at $5.0\text{A}$ )
Total Power Dissipation ( $P_D$ )	$65\text{ Watts}$ ( $T_C = 25^\circ\text{C}$ with heatsink) / $2.0\text{ W}$ free air
Integrated Components	Base-Emitter Bleed Resistors + Flywheel Protection Diode
Complementary PNP Pair	TIP127 (100V PNP Darlington)

Pinout (TO-220AB Package - B-C-E Standard)

Looking at the front labeled face with leads pointing downward:

text

        ┌──────────────┐
        │  O  [Metal]  │ ── Tab is internally connected to Pin 2 (Collector)
        ├──────────────┤
        │    TIP122    │
        └─┬────┬────┬──┘
          1    2    3
          B    C    E

Pin	Name	Type	Description
1	`BASE`	Base Input	Base control input (Driven with logic current from MCU via $1\text{ k}\Omega$ resistor)
2 (Tab)	`COLLECTOR`	Power Collector	Collector output (Internally connected to metal mounting tab)
3	`EMITTER`	Power Emitter	Emitter terminal (Connect to common system ground / $0\text{ V}$ )

Specifications

Parameter	Symbol	Min	Typ	Max	Unit	Conditions
Collector-Emitter Breakdown	$V_{(BR)CEO}$	100	—	—	V	$I_C = 30\text{mA}, I_B = 0$
Collector-Base Breakdown	$V_{(BR)CBO}$	100	—	—	V	$I_C = 1.0\text{mA}, I_E = 0$
Emitter-Base Breakdown	$V_{(BR)EBO}$	5.0	—	—	V	$I_E = 2.0\text{mA}, I_C = 0$
Collector Cutoff Current	$I_{CEO}$	—	—	500	µA	$V_{CE} = 50\text{V}, I_B = 0$
DC Current Gain ( $h_{FE}$ )	$h_{FE}$	1000	—	—	—	$I_C = 0.5\text{A}, V_{CE} = 3.0\text{V}$
DC Current Gain ( $h_{FE}$ )	$h_{FE}$	1000	—	—	—	$I_C = 3.0\text{A}, V_{CE} = 3.0\text{V}$
Collector Saturation Voltage	$V_{CE(sat)}$	—	—	2.0	V	$I_C = 3.0\text{A}, I_B = 12\text{mA}$
Base-Emitter On Voltage	$V_{BE(on)}$	—	—	2.5	V	$I_C = 3.0\text{A}, V_{CE} = 3.0\text{V}$

Typical Application Circuit: Arduino 4-Phase Unipolar Stepper Motor Driver

In unipolar stepper motor systems (such as 28BYJ-48 or 6-wire NEMA 17/23 motors), four TIP122 transistors drive the coil phases:

text

                            +24V to +36V Motor Supply Rail
                                          │
                               [ + Motor Coil Phase - ]
                                          │
                                          ├───[ External 1N4007 Diode ]────────┐
                                          │   (Anode to Collector, Cathode to +V)
                                    [Pin 2: COLLECTOR]                         │
                                         TIP122                                │
  Arduino Digital Pin (0 - 5V)      [Pin 1: BASE]                              │
          │                               │                                    │
          ├───[ 1kΩ Resistor ]────────────┤                                    │
          │                               ├───[ 10kΩ Base Pull-Down Resistor ]─┤
         GND                              │                                    │
                                    [Pin 3: EMITTER]                           │
                                          │                                    │
                                         GND ──────────────────────────────────┴─── Common GND

Comparison: TIP120 vs TIP121 vs TIP122

Parameter	TIP120	TIP121	TIP122
$V_{CEO}$ Voltage	$60\text{ V}$	$80\text{ V}$	$100\text{ V}$
Max Current ( $I_C$ )	$5.0\text{ A}$	$5.0\text{ A}$	$5.0\text{ A}$
DC Gain ( $h_{FE}$ )	$\ge 1000$	$\ge 1000$	$\ge 1000$
Saturation $V_{CE(sat)}$	$2.0\text{ V}$	$2.0\text{ V}$	$2.0\text{ V}$
Complementary PNP	TIP125	TIP126	TIP127

Common mistakes

Operating above 1.5A continuous without a heatsink: Darlington transistors have a higher saturation voltage ( $V_{CE(sat)} \approx 1.5\text{V} \dots 2.0\text{V}$ ) than single BJTs or low- $R_{DS(on)}$ MOSFETs. Dissipated power ( $P = V_{CE(sat)} \times I_C$ ) reaches $6\text{W}$ at $3\text{A}$ . Always attach a stamped aluminum heatsink for currents above $1.5\text{A}$ .
Driving fast PWM (> 20kHz) without considering storage time: Darlington pairs exhibit longer turn-off storage times ( $t_{off} \approx 2\ \mu\text{s} \dots 4\ \mu\text{s}$ ) than modern MOSFETs. For ultrasonic PWM motor speed control above $20\text{kHz}$ , a logic-level power MOSFET (such as IRLZ44N or IRLB8721) is recommended.

Notes

Pinball Machine Standard: The TIP122 and TIP102 are standard replacement transistors for Bally, Williams, and Stern pinball solenoid driver boards.

Interface	Direct MCU Logic Gate Drive Compatible (hFE >= 1000)
Package	TO-220AB (3-pin through-hole)