BETACollector limit100 V · absolute VCEO
NPN Darlington power transistor
TIP122 Specifications
Review TIP122 electrical specifications, operating conditions and package details.
Key specifications
The Darlington connection multiplies current gain, but its two junctions and collector path need more voltage headroom. Check dissipation rather than treating it as an ideal closed switch.
DC collector limit5 A · absolute
DC gain minimum1000 At specified test points
Junction limit150 °C · maximum
Package details
TIP122G · TO-220AB
| Property | Details |
|---|---|
| Manufacturer | onsemi |
| Part number | TIP122G |
| Package | TO-220AB |
| Connections | 3 pins |
| Mounting | Through-hole |
| Lead pitch | 2.54 mm |
| Package code | 221A style 1 |
| Thermal reference | 65 W at case 25°C; 2 W at ambient 25°C |
Device and package
A reviewed manufacturer reference
Manufacturer specifications 6 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 |
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TIP120 and TIP121 have lower collector-voltage ratings. Do not substitute their limits for TIP122.
Absolute maximum ratings
Individual stress limits
Manufacturer specifications 7 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 |
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The 65 W rating requires a controlled case temperature; it is not a free-air rating.
Gain and on-state behavior
Pulsed test points at case 25°C
Manufacturer specifications 6 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 |
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Pulsed tests use pulse width ≤ 300 µs and duty cycle ≤ 2%; do not assume these are thermally steady conditions.
Off-state and dynamic data
TIP122 conditions from the selected reference
Manufacturer specifications 6 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 |
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Leakage and stored charge matter when driving small loads or switching quickly.
Thermal and safe operating area
Current and voltage must be checked together
Manufacturer specifications 6 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 |
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The example uses a resistor so the circuit can be understood without an inductive switching transient.
12 V resistor-load switch
Explicit control and load values
Manufacturer specifications 6 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 |
No specifications match. Try a parameter name or a unit.
Check the actual operating point and thermal margins before choosing a real load.
Example calculations
Nominal illustrative arithmetic
Manufacturer specifications 7 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 |
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These calculations are teaching values, not measured readings or a timed simulation.
Connections by function
Select a pin for its function, connection guidance and electrical notes.