2N4031 - 80V 1A PNP BJT Transistor TO-39 | Central Semiconductor
MPN: 2N4031 β Active| Qty | Unit Price | Extended |
|---|---|---|
| 1 | $0 | $0.00 |
| 10 | $0 | $0.00 |
| 100 | $0 | $0.00 |
| 500 | $0 | $0.00 |
| 1,000 | $0 | $0.00 |
2N4031 Overview
A bipolar junction transistor is a three-terminal current-controlled semiconductor device that amplifies or switches electronic signals. Within the component hierarchy, the 2N4031 belongs to the small-signal and medium-power PNP transistor family, which sits under discrete semiconductors, alongside MOSFETs and other transistor technologies. PNP transistors conduct when the base is pulled low relative to the emitter, making them complementary counterparts to NPN devices in push-pull output stages and level-shifting circuits.
Key features of the 2N4031 include its 80 V breakdown rating, which provides generous headroom for industrial supply rails; its 1 A continuous collector current capability for driving loads such as relays, lamps, and small motors; and its hermetically sealed TO-39 metal can, which offers superior moisture immunity and thermal stability compared to plastic packages. The 150 MHz transition frequency also supports low-noise large-signal amplifier designs.
The silicon planar epitaxial construction delivers stable hFE and low leakage across temperature, a key reason this JEDEC-registered 2N series part has remained in production for decades. Manufacturers including Central Semiconductor, Comset Semiconductor, and legacy Motorola/Philips semiconductor lines all documented the 2N4031 as intended for large-signal, low-noise industrial applications.
Typical applications include low-noise industrial amplifiers, relay and solenoid drivers on 24 V or 48 V rails, complementary push-pull audio output stages, and general-purpose switching in instrumentation. The metal TO-39 package makes it especially attractive for harsh environments where plastic-packaged parts would degrade.
When designing with the 2N4031, verify power dissipation against the 1.25 W rating and provide adequate heatsinking of the metal can, since the TO-39 case is electrically connected to the collector and can be mounted to a heat sink with proper isolation hardware.
This page synthesizes distributor pricing context, cross-referenced drop-in alternatives, pinout data, and practical design notes not consolidated in any single manufacturer datasheet.
Drop-in alternatives for 2N4031 β same package, pin-to-pin compatible. Different-package parts requiring PCB rework are excluded.
Quick Comparison Tool β Select alternative parts for side-by-side comparison:
2N4033
β Drop-In β οΈ εζ°εΎ ιͺθ―π Reference alternative (not in catalog)
2N4032
β Drop-In β οΈ εζ°εΎ ιͺθ―π Reference alternative (not in catalog)
2N4030
β Drop-In β οΈ εζ°εΎ ιͺθ―π Reference alternative (not in catalog)
2N5320
β Drop-Inπ Reference alternative (not in catalog)
2N4239
β Drop-Inπ Reference alternative (not in catalog)
2N3020
β Drop-Inπ Reference alternative (not in catalog)
2N5335
β Drop-Inπ Reference alternative (not in catalog)
2SC510
β Drop-Inπ Reference alternative (not in catalog)
2N4031 Maximum Ratings & Electrical Characteristics
| Transistor Type | PNP Bipolar Junction Transistor (BJT) |
| Collector-Emitter Voltage (VCEO) | 80 V |
| Maximum Collector Current (IC) | 1 A |
| Power Dissipation (PD) | 1.25 W |
| Transition Frequency (fT) | 150 MHz |
| Package | TO-39 metal can, hermetically sealed |
| Mounting Type | Through Hole |
| Technology | Silicon planar epitaxial |
| Configuration | Single transistor |
| Applications | Large signal, low noise industrial amplifiers and switches |
| RoHS Status | Compliant |
| Pin Count | 3 |
| Pinout (TO-39) | Emitter - Base - Collector |
2N4031 Pin Configuration
| Pin 1 | Emitter β Emitter terminal (current flows out for PNP conduction) |
| Pin 2 | Base β Base control terminal (pull low relative to emitter to turn on) |
| Pin 3 | Collector β Collector terminal; also electrically connected to the TO-39 metal case |
Typical Applications
2N4031 is suitable for 6 applications: Low-Noise Industrial Amplifiers, Relay and Solenoid Drivers, Complementary Push-Pull Output Stages, General-Purpose Switching in Instrumentation, Harsh Environment and Legacy Mil-Aero Hardware, Level Shifting on Higher-Voltage Analog Rails.
Low-Noise Industrial Amplifiers
The 2N4031 was expressly designed for large-signal, low-noise industrial amplifier applications, per the Comset and Central Semiconductor datasheets. Its silicon planar epitaxial PNP construction provides stable gain and low flicker noise, while the hermetically sealed TO-39 metal can shields the die from moisture ingress and electromagnetic coupling - a measurable benefit in electrically noisy factory environments. In a typical class-A driver stage, the transistor's 150 MHz transition frequency keeps phase shift negligible at audio and low-RF frequencies, and the 80 V VCEO permits operation from 48 V industrial rails with comfortable margin. Bias the base through a low-impedance divider and decouple the collector rail to preserve the low-noise figure the metal-can construction enables.
Recommended
Relay and Solenoid Drivers
With a 1 A continuous collector current rating and 80 V breakdown, the 2N4031 directly drives relay and solenoid coils on 24 V or 48 V industrial control rails. The generous VCEO margin absorbs the inductive flyback excursions that exceed the rail voltage, though a flyback diode across the coil remains mandatory to protect the junction from repetitive stress. The 1.25 W dissipation rating must be checked against coil current: for example, a 24 V, 30 mA relay coil dissipates only tens of milliwatts in the transistor at saturation, well within rating. The TO-39 through-hole package withstands vibration and thermal cycling in panel-mounted control gear better than small plastic SMD packages, improving long-term reliability in harsh cabinets.
Recommended
Complementary Push-Pull Output Stages
The 2N4031 serves as the PNP half of complementary push-pull audio and servo output stages, paired with an NPN TO-39 transistor of matched voltage and current rating. Its 1 A collector current supports loudspeaker or actuator loads, and the 150 MHz fT minimizes crossover-transition distortion at audio frequencies. The metal can's low thermal resistance allows the pair to share a heatsink (with collector isolation hardware, since the case is the collector), which improves quiescent-current thermal tracking and reduces drift-induced bias errors. Designers should match hFE groups between the PNP and NPN devices to minimize distortion, a practice recommended in classic complementary-pair application notes from the original 2N-series manufacturers.
Recommended
General-Purpose Switching in Instrumentation
As a general-purpose switch, the 2N4031 toggles lamps, LEDs, small motors, and logic-level loads in bench and rack instrumentation. Its hermetically sealed TO-39 can resists corrosive atmospheres and humidity that degrade plastic-encapsulated parts, a documented advantage for laboratory and field instruments. Switching performance is supported by the 150 MHz transition frequency, which yields fast edge rates when driven into saturation; note that storage time in saturated PNP BJTs requires a base discharge resistor or Baker clamp for sub-microsecond turn-off. The 80 V rating also allows the device to switch loads on 48 V telecom-style rails directly, eliminating an intermediate level-shift stage that a lower-voltage transistor would require.
Recommended
Harsh Environment and Legacy Mil-Aero Hardware
The hermetically sealed TO-39 metal package of the 2N4031 makes it a preferred choice for sustaining legacy industrial, marine, and avionics-adjacent hardware where plastic packages would absorb moisture and fail. Metal-can hermetic parts exhibit dramatically lower moisture-related leakage drift over decades of service, which is why many 2N-series JEDEC parts survive in long-life systems. For repair and sustaining engineering, the 2N4031's JEDEC registration guarantees cross-vendor equivalence - Central Semiconductor, Comset Semiconductor, and legacy Motorola production all conform to the same registered ratings (80 V, 1 A, 1.25 W, TO-39), so a replacement from any qualified source preserves form, fit, and function without redesign.
Recommended
Level Shifting on Higher-Voltage Analog Rails
The 2N4031's 80 V VCEO makes it effective for PNP level-shift and current-source circuits referenced to 24 V to 48 V analog rails, where common low-voltage PNPs (typically 40 V to 60 V) lack margin. Used as a high-side current source or a cascode element, it provides stable bias for diff pairs and ADC input stages in industrial data acquisition systems. The 150 MHz fT keeps current-source output impedance high across the signal band, and the low-noise character of the planar epitaxial process protects sensitive analog nodes. Designers should budget base-emitter headroom and verify power dissipation against the 1.25 W limit at the chosen bias current.
Recommended
Recommended Products Summary
Engineering reference data for 2N4031 β comparison, design guidance, and compliance information.
Selection Guide
Comparison with Alternatives
| Parameter | This Product | 2N4033 | 2N4032 | 2N4030 | 2N5320 | 2SC510 |
|---|---|---|---|---|---|---|
| Package | TO-39 metal can | TO-39 metal can - same | TO-39 metal can - same | TO-39 metal can - same | TO-39 metal can - same | TO-39 metal can - same |
| Brand | Central Semiconductor | Central Semiconductor | Central Semiconductor | Central Semiconductor | Central Semiconductor | Toshiba |
| Polarity | PNP | PNP | PNP | PNP | PNP | Verify per datasheet |
| Hermetic Package | Yes | Yes | Yes | Yes | Yes | Yes |
Key Differentiators
- Hermetically sealed metal can for harsh environments (vs 2N5320)
- Higher voltage headroom within the 2N403x family (vs 2N4030)
- High transition frequency for a medium-power PNP (vs 2SC510)
Design Notes
The 2N4031 is rated 1.25 W in free air. Estimate: at 500 mA collector current and 5 V VCE, dissipation is 2.5 W (500 mA x 5 V), double the free-air rating, so the metal can must couple to a heatsink or chassis mass. Because the TO-39 case is the collector terminal, use a mica washer or similar isolator plus insulating bushing when mounting to grounded heatsinks, and derate linearly toward the maximum junction temperature per the manufacturer datasheet derating curve.
The TO-39 pinout is Emitter-Base-Collector, but some 2N-series metal-can parts use different orders - always confirm pinning against the datasheet before drop-in substitution. When replacing with cross-referenced parts such as 2N5320 or 2SC510, verify hFE group: a substitute with different gain grading changes bias point in linear amplifier stages. Also remember inductive loads (relays, solenoids) require a flyback diode even though the 80 V rating provides margin.
For through-hole TO-39 layouts, keep base traces short and routed away from the collector to limit feedback capacitance effects at high fT (150 MHz). Add a small base stopper resistor (tens of ohms, estimated value; verify by test) if the stage shows RF oscillation, which high-fT transistors can exhibit in low-impedance circuits. The metal can can be bonded to a PCB-mounted shield clip for mechanical stability in vibration-prone industrial equipment.
Compliance Information
RoHS compliance stated in Comset Semiconductor datasheet summary. REACH, lead-free, halogen-free, and conflict-minerals status not stated in verified data; request certificates from supplier.
