TIP122 Reference Tables, Pins & Specifications

Pin reference

Signal names, electrical functions and connection guidance

TO-220AB

Physical pin numbers3 pins

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TIP122 pin functions and connections
Signal	Type	Function & connection
B	Base	Input of the first transistor in the Darlington pair. Connection guidance Use a current-limiting base resistor and a defined off-state return. Two base-emitter junctions give a higher on voltage than a single transistor.
C	Collector	Shared collector of the two internal NPN transistors. Connection guidance Connect to the low side of the controlled load. The metal tab, shown as contact 4 in the drawing, is also collector. Insulate it from a grounded heatsink where necessary.
E	Emitter	Output emitter and circuit return. Connection guidance Connect to the common control and load ground. Front view with leads down: B1, C2, E3.

A reviewed manufacturer reference

Manufacturer-referenced values6 parameters

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Parameter	Value	Conditions / notes
Selected device	onsemi TIP122G	Pb-free TO-220AB; 50 units per rail
Electrical reference	TIP120/D Rev. 10	June 2024
Package drawing	CASE 221A, style 1	2.54 mm lead pitch
Front pinout	1 B · 2 C · 3 E	Tab/contact 4 is collector
Construction	Monolithic NPN Darlington	Built-in base-emitter shunt resistors
Complementary device	TIP127	PNP; separate polarity and reference checks apply

TIP120 and TIP121 have lower collector-voltage ratings. Do not substitute their limits for TIP122.

Individual stress limits

Manufacturer-referenced values7 parameters

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Parameter	Value	Conditions / notes
Collector-emitter / collector-base	100 V / 100 V	VCEO / VCB
Emitter-base voltage	5 V	Reverse stress limit
Continuous / peak collector current	5 A / 8 A	Thermal and pulse constraints apply
Base current	120 mA	Absolute maximum
Case-cooled dissipation	65 W at TC = 25°C	Derate 0.52 W/°C above 25°C
Ambient dissipation	2 W at TA = 25°C	Derate 0.016 W/°C above 25°C
Junction / storage range	−65 to +150°C	Absolute range

The 65 W rating requires a controlled case temperature; it is not a free-air rating.

Pulsed test points at case 25°C

Manufacturer-referenced values6 parameters

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Parameter	Value	Conditions / notes
hFE at IC = 0.5 A	1000 minimum	VCE = 3 V
hFE at IC = 3 A	1000 minimum	VCE = 3 V
Typical gain headline	2500 at IC = 4 A	Typical, not a guaranteed minimum
VCE(sat), IC 3 A / IB 12 mA	2 V maximum	Forced ratio 250
VCE(sat), IC 5 A / IB 20 mA	4 V maximum	Forced ratio 250
VBE(on)	2.5 V maximum	IC = 3 A; VCE = 3 V

Pulsed tests use pulse width ≤ 300 µs and duty cycle ≤ 2%; do not assume these are thermally steady conditions.

TIP122 conditions from the selected reference

Manufacturer-referenced values6 parameters

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Parameter	Value	Conditions / notes
ICEO	0.5 mA maximum	VCE = 50 V; IB = 0
ICBO	0.2 mA maximum	VCB = 100 V; IE = 0
IEBO	2 mA maximum	VBE = 5 V; IC = 0
Small-signal current gain	4 minimum	IC 3 A; VCE 4 V; f 1 MHz
Output capacitance	200 pF maximum	VCB 10 V; IE 0; f 0.1 MHz
Switching scope	General-purpose low-speed switching	Storage time depends on base drive and turn-off circuit

Leakage and stored charge matter when driving small loads or switching quickly.

Current and voltage must be checked together

Manufacturer-referenced values6 parameters

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Parameter	Value	Conditions / notes
Junction-to-case resistance	1.92°C/W maximum	RθJC
Junction-to-ambient resistance	62.5°C/W maximum	RθJA
Active-region SOA	Use the manufacturer’s curves	Second breakdown can limit operation before the power rating
Pulse operation	Use transient thermal impedance	Pulse width, duty cycle and starting temperature matter
Collector tab	Electrically live	Add insulation if the heatsink must be at another potential
Flyback clamp	Required for inductive switching	Do not rely on the internal Darlington resistors as a load clamp

The example uses a resistor so the circuit can be understood without an inductive switching transient.

Explicit control and load values

Manufacturer-referenced values6 parameters

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Parameter	Value	Conditions / notes
Load	100 Ω, at least 2 W	From +12 V to collector pin 2
Base resistor	1 kΩ from 5 V buffered control	Into base pin 1
Pull-down	10 kΩ from base to emitter	Defines the external off-state path
Emitter pin 3	Common ground	Control and load return
Illustrative junction assumptions	VBE = 1.4 V; VCE = 1.0 V	Not guaranteed manufacturer test points
Control-source requirement	Approximately 3.6 mA	Verify the selected controller or buffer

Check the actual operating point and thermal margins before choosing a real load.

Nominal illustrative arithmetic

Manufacturer-referenced values7 parameters

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Parameter	Value	Conditions / notes
Drive-resistor current	3.60 mA	(5 − 1.4) / 1 kΩ
External pull-down current	0.14 mA	1.4 / 10 kΩ
Device base-terminal current	3.46 mA	3.60 − 0.14 mA; internal paths are part of the device
Collector current	110 mA	(12 − 1.0) / 100 Ω
Forced current ratio	Approximately 31.8	110 / 3.46
Device power	Approximately 0.115 W	1.0 × 0.110 + 1.4 × 0.00346
Load-resistor loss	1.21 W	(0.110 A)² × 100 Ω

These calculations are teaching values, not measured readings or a timed simulation.