Real View
TIP31CNPN power transistor
Drive the base. Switch a controlled load.
TIP31C is a 100 V, 3 A NPN bipolar power transistor for amplification and switching. Base current controls collector current, while the actual operating point is limited by voltage, heat and safe operating area. It is a single transistor, not a Darlington pair. The selected onsemi TIP31CG TO-220 uses base 1, collector 2 and emitter 3. MJD31CT4G is the documented electrically similar DPAK alternative, with the same functions and a surface-mount collector pad. Its power ratings and leakage limits are separate from the through-hole part. The example uses a 12 V resistor load and a buffered 0/5 V base driver through 330 Ω. A 10 kΩ base-emitter resistor defines the off state. Calculated readings use explicit voltage assumptions rather than treating the transistor as an ideal switch.
3Physical pins
TIP31CGTO-220AB
Manufacturer-referencedonsemi
Pin diagram
Select a pin to explore its connection
Highlight
TIP31CGTO-220ABFront view · B1, C2, E3 · tab = C
MJD31CT4GDPAKTop view · B1, collector pad 2, E3
Click a lead or use the arrow keys. Front view · B1, C2, E3 · tab = C
PIN 1 · Base / drive
BaseB
Function
Current-driven control junction.
How to connect
Use the example’s 330 Ω base resistor and 10 kΩ base-emitter return.
Electrical note
The buffered 5 V driver must source approximately 12.7 mA; do not assume every GPIO can do so.
PIN 2 · Collector / load
CollectorC
Function
Load terminal, also connected to the metal tab.
How to connect
Connect the 100 Ω resistor load to this terminal.
Electrical note
The exposed tab is electrically live; insulate it when required.
PIN 3 · Ground
EmitterE
Function
Current return and base-drive reference.
How to connect
Connect emitter to common driver and load ground.
Electrical note
Front view: B1, C2, E3; tab is collector.
Key specifications
The 3 A limit does not promise 3 A from any control output. The saturation test uses 375 mA base current, and allowable dissipation depends on case temperature or the specified PCB.
Collector limit100 V · absolute VCEO
DC collector limit3 A magnitude · thermal limits apply
DC gain minimum25 IC 1 A · VCE 4 V magnitudes
Junction limit150 °C · absolute
Package details
TIP31CG · TO-220AB
| Property | Details |
|---|---|
| Manufacturer | onsemi |
| Part number | TIP31CG |
| Package | TO-220AB |
| Connections | 3 pins |
| Mounting | Through-hole |
| Lead pitch | 2.54 mm |
| Package code | 221A style 1 |
| Thermal reference | 40 W at case 25°C; 2 W at ambient 25°C |
Device and package scope
Two separately documented selections
Manufacturer specifications 5 parameters
Scroll sideways to see all columns.
| Parameter | Value | Conditions / notes |
|---|---|---|
| Through-hole | TIP31CG · TO-220 | TIP31A/D Rev. 17, June 2024 |
| Surface-mount | MJD31CT4G · DPAK | MJD31/D Rev. 21, May 2026 |
| Polarity | NPN | Manufacturer tables use magnitudes; reverse voltage/current signs for PNP |
| Terminals | B1 · C2 · E3 | Tab/contact 4 is electrically collector |
| SMD relationship | Electrically similar manufacturer counterpart | Different power and leakage limits; check the selected package |
No specifications match. Try a parameter name or a unit.
Pin function is preserved when the package changes.
Absolute voltage and current limits
Magnitudes; individual stress limits
Manufacturer specifications 5 parameters
Scroll sideways to see all columns.
| Parameter | Value | Conditions / notes |
|---|---|---|
| Collector-emitter / collector-base | 100 / 100 V | Selected C-voltage grades only |
| Emitter-base reverse voltage | 5 V | Do not apply a reverse drive without limiting it |
| DC / peak collector current | 3 / 5 A | Thermal and pulse restrictions also apply |
| Base current | 1 A | Absolute maximum |
| Junction and storage | −65 to +150°C | Both selected references |
No specifications match. Try a parameter name or a unit.
These are not simultaneous operating targets.
Gain and on-state characteristics
TC 25°C; pulse ≤300 µs, duty ≤2%
Manufacturer specifications 6 parameters
Scroll sideways to see all columns.
| Parameter | Value | Conditions / notes |
|---|---|---|
| hFE at IC 1 A | 25 minimum | VCE 4 V |
| hFE at IC 3 A | 10–50 | VCE 4 V |
| Collector-emitter saturation | 1.2 V maximum | IC 3 A; IB 375 mA |
| Base-emitter on voltage | 1.8 V maximum | IC 3 A; VCE 4 V |
| Current gain-bandwidth | 3 MHz minimum | IC 500 mA; VCE 10 V; test 1 MHz |
| Small-signal gain | 20 minimum | IC 500 mA; VCE 10 V; 1 kHz |
No specifications match. Try a parameter name or a unit.
Active-region gain does not replace a saturation base-current budget.
Off-state characteristics
Maximum magnitudes at TC 25°C
Manufacturer specifications 5 parameters
Scroll sideways to see all columns.
| Parameter | Value | Conditions / notes |
|---|---|---|
| TO-220 ICEO | 0.3 mA | VCE 60 V; base open |
| DPAK ICEO | 50 µA | VCE 60 V; base open |
| TO-220 ICES | 200 µA | VCE 100 V; VEB 0 |
| DPAK ICES | 20 µA | VCE 100 V; VEB 0 |
| Emitter leakage | 1 mA | VBE reverse 5 V; collector open |
No specifications match. Try a parameter name or a unit.
Leakage can matter even when the load is meant to be off.
Package-specific thermal limits
The boundary condition changes the rating
Manufacturer specifications 7 parameters
Scroll sideways to see all columns.
| Parameter | Value | Conditions / notes |
|---|---|---|
| TO-220 power / derating | 40 W / 0.32 W per °C | Case 25°C / above 25°C |
| TO-220 ambient power | 2 W | Ambient 25°C; derate 0.016 W/°C |
| TO-220 RθJC / RθJA | 3.125 / 62.5°C/W | Maximum reference values |
| DPAK power / derating | 15 W / 0.12 W per °C | Case 25°C / above 25°C |
| DPAK ambient power | 1.56 W | FR-4, 165 mm², 1 oz copper; derate 0.012 W/°C |
| DPAK RθJC / RθJA | 8.3 / 80°C/W | Specified mounting and minimum-pad conditions |
| Safe operating area | Check manufacturer curves | Voltage, current, duration and starting temperature together |
No specifications match. Try a parameter name or a unit.
The package image is not a heatsink rating.
12 V resistor-load switch
Explicit illustrative assumptions
Manufacturer specifications 7 parameters
Scroll sideways to see all columns.
| Parameter | Value | Conditions / notes |
|---|---|---|
| Load | 100 Ω, at least 3 W | Supply to collector |
| Base resistor / return | 330 Ω / 10 kΩ | Return resistor goes from base to emitter |
| Buffered driver | 0 V off / 5 V on | Must source about 12.7 mA |
| Assumed junctions | |VBE| 0.8 V; |VCE| 0.2 V | Teaching assumptions, not guaranteed test points |
| Base current | 12.65 mA | (5−0.8)/330−0.8/10000 |
| Collector current / forced ratio | 118 mA / 9.33 | (12−0.2)/100; IC/IB |
| Transistor / load loss | 33.7 mW / 1.392 W | Include base contribution; allow resistor thermal margin |
No specifications match. Try a parameter name or a unit.
Inductive loads require a suitable clamp and a separate transient check.
Connections by function
Select a pin for its function, connection guidance and electrical notes.
Base / drive1 pin
Collector / load1 pin
Ground1 pin
Base / drive1 pin
Collector / load1 pin
Ground1 pin
TIP31C at a glance
Follow the labeled connections and functional stages
How it works
3 stages · Explore one step at a time
Establish base current
Raise base above emitter through the resistor.
Control the load path
Conventional current flows from collector to emitter.
Release the base charge
The base-emitter return defines off; switching speed depends on drive and stored charge.
Step 1 of 3
TIP31C in a circuit
The supply, driver, load and return are shown explicitly.
Connect it, step by step
Follow the component values and pin connections
Connect the load
100 Ω from +12 V to collector.
Drive base deliberately
330 Ω limits drive current; 10 kΩ returns base to emitter.
Check heat
Use at least a 3 W load resistor and check transistor safe operating area.
Inside TIP31C
Three semiconductor regions, two junctions and one controlled current path.
Explore the circuit
Select a stage to see its role and connections
Base junction
The thin base controls carrier transport.
Collector region
The collector supports off-state voltage and carries load current.
Emitter region
The emitter injects carriers when the base junction is forward biased.
Selected packageTO-220ABTIP31CG
Physical connections3 pinsPackage-specific numbering
Reference collection7 tables35 parameters & pin functions
Pin reference
Signal names, electrical functions and connection guidance
Physical pin numbers3 pins
Scroll within the table to see all columns and rows.
| Pin | Signal | Type | Function & connection |
|---|---|---|---|
| B | Base | Current-driven control junction.Connection guidanceUse the example’s 330 Ω base resistor and 10 kΩ base-emitter return. The buffered 5 V driver must source approximately 12.7 mA; do not assume every GPIO can do so. | |
| C | Collector | Load terminal, also connected to the metal tab.Connection guidanceConnect the 100 Ω resistor load to this terminal. The exposed tab is electrically live; insulate it when required. | |
| E | Emitter | Current return and base-drive reference.Connection guidanceConnect emitter to common driver and load ground. Front view: B1, C2, E3; tab is collector. |
No pins match these filters. Try another signal name or reset the filters.
Device and package scope
Two separately documented selections
Manufacturer-referenced values5 parameters
Scroll within the table to see all columns and rows.
| Parameter | Value | Conditions / notes |
|---|---|---|
| Through-hole | TIP31CG · TO-220 | TIP31A/D Rev. 17, June 2024 |
| Surface-mount | MJD31CT4G · DPAK | MJD31/D Rev. 21, May 2026 |
| Polarity | NPN | Manufacturer tables use magnitudes; reverse voltage/current signs for PNP |
| Terminals | B1 · C2 · E3 | Tab/contact 4 is electrically collector |
| SMD relationship | Electrically similar manufacturer counterpart | Different power and leakage limits; check the selected package |
No specifications match. Try a parameter name or a unit.
Pin function is preserved when the package changes.
Absolute voltage and current limits
Magnitudes; individual stress limits
Manufacturer-referenced values5 parameters
Scroll within the table to see all columns and rows.
| Parameter | Value | Conditions / notes |
|---|---|---|
| Collector-emitter / collector-base | 100 / 100 V | Selected C-voltage grades only |
| Emitter-base reverse voltage | 5 V | Do not apply a reverse drive without limiting it |
| DC / peak collector current | 3 / 5 A | Thermal and pulse restrictions also apply |
| Base current | 1 A | Absolute maximum |
| Junction and storage | −65 to +150°C | Both selected references |
No specifications match. Try a parameter name or a unit.
These are not simultaneous operating targets.
Gain and on-state characteristics
TC 25°C; pulse ≤300 µs, duty ≤2%
Manufacturer-referenced values6 parameters
Scroll within the table to see all columns and rows.
| Parameter | Value | Conditions / notes |
|---|---|---|
| hFE at IC 1 A | 25 minimum | VCE 4 V |
| hFE at IC 3 A | 10–50 | VCE 4 V |
| Collector-emitter saturation | 1.2 V maximum | IC 3 A; IB 375 mA |
| Base-emitter on voltage | 1.8 V maximum | IC 3 A; VCE 4 V |
| Current gain-bandwidth | 3 MHz minimum | IC 500 mA; VCE 10 V; test 1 MHz |
| Small-signal gain | 20 minimum | IC 500 mA; VCE 10 V; 1 kHz |
No specifications match. Try a parameter name or a unit.
Active-region gain does not replace a saturation base-current budget.
Off-state characteristics
Maximum magnitudes at TC 25°C
Manufacturer-referenced values5 parameters
Scroll within the table to see all columns and rows.
| Parameter | Value | Conditions / notes |
|---|---|---|
| TO-220 ICEO | 0.3 mA | VCE 60 V; base open |
| DPAK ICEO | 50 µA | VCE 60 V; base open |
| TO-220 ICES | 200 µA | VCE 100 V; VEB 0 |
| DPAK ICES | 20 µA | VCE 100 V; VEB 0 |
| Emitter leakage | 1 mA | VBE reverse 5 V; collector open |
No specifications match. Try a parameter name or a unit.
Leakage can matter even when the load is meant to be off.
Package-specific thermal limits
The boundary condition changes the rating
Manufacturer-referenced values7 parameters
Scroll within the table to see all columns and rows.
| Parameter | Value | Conditions / notes |
|---|---|---|
| TO-220 power / derating | 40 W / 0.32 W per °C | Case 25°C / above 25°C |
| TO-220 ambient power | 2 W | Ambient 25°C; derate 0.016 W/°C |
| TO-220 RθJC / RθJA | 3.125 / 62.5°C/W | Maximum reference values |
| DPAK power / derating | 15 W / 0.12 W per °C | Case 25°C / above 25°C |
| DPAK ambient power | 1.56 W | FR-4, 165 mm², 1 oz copper; derate 0.012 W/°C |
| DPAK RθJC / RθJA | 8.3 / 80°C/W | Specified mounting and minimum-pad conditions |
| Safe operating area | Check manufacturer curves | Voltage, current, duration and starting temperature together |
No specifications match. Try a parameter name or a unit.
The package image is not a heatsink rating.
12 V resistor-load switch
Explicit illustrative assumptions
Manufacturer-referenced values7 parameters
Scroll within the table to see all columns and rows.
| Parameter | Value | Conditions / notes |
|---|---|---|
| Load | 100 Ω, at least 3 W | Supply to collector |
| Base resistor / return | 330 Ω / 10 kΩ | Return resistor goes from base to emitter |
| Buffered driver | 0 V off / 5 V on | Must source about 12.7 mA |
| Assumed junctions | |VBE| 0.8 V; |VCE| 0.2 V | Teaching assumptions, not guaranteed test points |
| Base current | 12.65 mA | (5−0.8)/330−0.8/10000 |
| Collector current / forced ratio | 118 mA / 9.33 | (12−0.2)/100; IC/IB |
| Transistor / load loss | 33.7 mW / 1.392 W | Include base contribution; allow resistor thermal margin |
No specifications match. Try a parameter name or a unit.
Inductive loads require a suitable clamp and a separate transient check.
No matching rowsTry a pin name, parameter, unit or test condition, or reset the filters.
Load switching
Control modest DC loads with explicit base drive and thermal checks.
Manufacturer application guideAmplifier stages
Use the transistor in its active region within safe operating area.
Manufacturer application guideComplementary stages
Pair NPN and PNP devices with suitable bias and protection.
Manufacturer application guideTake it into ProTech
Find TIP31C in the Components Library to place its schematic symbol and connect its pins.
Reference page · circuit simulation model not yet availableOpen ProTech