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Home > Products > Discrete Semiconductor Products > Transistors > Bipolar (BJT) > Single Bipolar Transistors

onsemi 2N4918

Name: 2N4918
Brand: onsemi
SKU: 2N4918
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

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Part No.:: 2N4918

Manufacturer:: onsemi

Category:: Single Bipolar Transistors

Package:: TO-225AA, TO-126-3

Datasheet:: 2N4918.pdf

Description:: TRANS PNP 40V 1A TO-126

Quantity:: RFQ Add To RFQ list

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Product details

Overview

2N4918 from onsemi is a medium-power plastic PNP silicon transistor designed for driver circuits, switching, and amplifier applications. It features V_CEO = 40 Vdc, I_C = 1.0 A (JEDEC), P_D = 30 W @ T_C = 25°C, V_CE(sat) ≤ 0.6 Vdc @ I_C = 1.0 A, and h_FE ≥ 40 @ I_C = 50 mA - used in industrial relay drivers and DC motor control stages.

For engineers reviewing the 2N4918 datasheet, pinout, applications, or equivalent options, this page delivers verified electrical parameters, TO-225 package mapping, safe operating area limits, saturation behavior at 1 A, and validated alternatives for PNP power switching designs.

Technical Context

The 2N4918 operates as a single-element PNP bipolar junction transistor with fixed emitter-base-collector terminal assignment in TO-225 (Case 077, Style 1). Its design emphasizes low-saturation switching and linear amplification up to 3 MHz f_T, supported by specified h_FE down to I_C = 1.0 A and thermal resistance θ_JC = 4.16°C/W.

It is explicitly rated for continuous collector current of 1.0 A per JEDEC requirements and 3.0 A based on physical current-handling capability, with second-breakdown-limited SOA curves defined up to 150°C junction temperature and pulse durations from 100 μs to DC.

Key Specifications

Parameter	Value and Actual Design Meaning
V_CEO	40 Vdc - maximum collector-emitter voltage before breakdown under open-base conditions; defines upper rail limit in switching topologies.
I_C (JEDEC)	1.0 Adc - guaranteed minimum DC current gain compliance point; used for gain binning and production test criteria.
P_D @ T_C = 25°C	30 W - total power dissipation limit with case held at 25°C; requires heatsinking above ambient derating threshold.
V_CE(sat)	≤ 0.6 Vdc @ I_C = 1.0 A, I_B = 0.1 A - ensures <0.6 W conduction loss at full rated current, critical for efficiency in saturated-switching stages.
h_FE	40–150 @ I_C = 50 mA - wide DC current gain range supports robust bias network design across temperature and unit-to-unit variation.
f_T	3.0 MHz - usable bandwidth for audio-frequency amplification and moderate-speed switching (e.g., PWM up to ~300 kHz).
θ_JC	4.16°C/W - junction-to-case thermal resistance; determines minimum heatsink requirement when mounted with thermal compound.

Pinout & Package

2N4918 is housed in a TO-225 plastic package (Case 077, Style 1), featuring three leads and a metal tab connected to the collector. The package is Pb-free compliant and rated for operation from −65°C to +150°C junction temperature.

Pin/Terminal	Circuit Role	Design Meaning
1	Emitter	Current sink node; connects to load return or ground reference in common-emitter configurations.
2 & 4	Collector	Shared collector terminal via internal connection to metal tab; must be electrically isolated from PCB ground unless intended as heatsink path.
3	Base	Control input; requires current-limited drive (I_B ≤ 1.0 A) to achieve full saturation at I_C = 1.0 A.

Key Features

Feature	Design Value
Low V_CE(sat)	0.6 V max at 1 A enables <0.6 W conduction loss - reduces thermal stress in high-duty-cycle switching.
High Safe Operating Area	SOA curves validated to 150°C junction temperature support reliable pulsed operation up to 50 A peak without second breakdown.
Gain Specified at High Current	h_FE guaranteed down to I_C = 1.0 A - simplifies bias design for linear amplifiers and high-current switches without extrapolation.
Complementary Pairing	Direct complement to NPN 2N4921 - enables matched push-pull output stages with symmetrical V_CEO, I_C, and thermal characteristics.
Pb-Free Packaging	TO-225 (Pb-Free) variant available - meets RoHS Directive 2011/65/EU and JEDEC J-STD-609A Class 3 moisture sensitivity.

Applications

Industrial Relay Driver	DC Motor Direction Control
Use Scenario: Driving 24 VDC industrial relays with coil currents up to 800 mA in PLC output modules. IC Role / Device Role / Timing Role: PNP switch providing active-low control interface between microcontroller GPIO and relay coil. Use Value: V_CE(sat) ≤ 0.6 V ensures <500 mW dissipation at full coil current, eliminating need for auxiliary heatsinking in compact DIN-rail enclosures.	Use Scenario: Half-bridge leg in bidirectional 12–24 V brushed DC motor controllers for HVAC actuators. IC Role / Device Role / Timing Role: High-side PNP switch enabling reverse polarity drive while maintaining logic-level base control. Use Value: 40 V V_CEO rating accommodates 24 V supply plus inductive kickback margin; SOA supports 100 ms stall current pulses.
Linear Audio Amplifier Stage	Power Supply Pass Transistor
Use Scenario: Output stage in low-fidelity 1–3 W audio amplifiers for intercom systems and annunciators. IC Role / Device Role / Timing Role: Class-A or Class-AB emitter-follower configured PNP transistor delivering speaker current. Use Value: f_T = 3 MHz and h_FE ≥ 40 at 100 mA ensure stable gain and minimal distortion up to 10 kHz with proper biasing.	Use Scenario: Series pass element in adjustable 0–30 V, 1 A bench power supplies. IC Role / Device Role / Timing Role: Voltage-controlled current source regulating output against load and line variations. Use Value: 30 W P_D rating allows 1 A × 10 V dropout = 10 W dissipation at full load - sufficient headroom for thermal management with modest heatsink.

Industrial Relay Driver

DC Motor Direction Control

Use Scenario: Driving 24 VDC industrial relays with coil currents up to 800 mA in PLC output modules.

IC Role / Device Role / Timing Role: PNP switch providing active-low control interface between microcontroller GPIO and relay coil.

Use Value: V_CE(sat) ≤ 0.6 V ensures <500 mW dissipation at full coil current, eliminating need for auxiliary heatsinking in compact DIN-rail enclosures.

Use Scenario: Half-bridge leg in bidirectional 12–24 V brushed DC motor controllers for HVAC actuators.

IC Role / Device Role / Timing Role: High-side PNP switch enabling reverse polarity drive while maintaining logic-level base control.

Use Value: 40 V V_CEO rating accommodates 24 V supply plus inductive kickback margin; SOA supports 100 ms stall current pulses.

Linear Audio Amplifier Stage

Power Supply Pass Transistor

Use Scenario: Output stage in low-fidelity 1–3 W audio amplifiers for intercom systems and annunciators.

IC Role / Device Role / Timing Role: Class-A or Class-AB emitter-follower configured PNP transistor delivering speaker current.

Use Value: f_T = 3 MHz and h_FE ≥ 40 at 100 mA ensure stable gain and minimal distortion up to 10 kHz with proper biasing.

Use Scenario: Series pass element in adjustable 0–30 V, 1 A bench power supplies.

IC Role / Device Role / Timing Role: Voltage-controlled current source regulating output against load and line variations.

Use Value: 30 W P_D rating allows 1 A × 10 V dropout = 10 W dissipation at full load - sufficient headroom for thermal management with modest heatsink.

Equivalent & Alternatives

The following parts are listed as comparable options for similar PNP power transistor applications.

Alternative Part	Technical Difference	Application Difference	Selection Advice
MJD2955G	V_CEO = 60 V, I_C = 12 A, P_D = 115 W, TO-263 package - higher voltage/current but surface-mount only.	Requires PCB redesign for SMT layout; unsuitable for through-hole legacy boards using 2N4918.	Select when upgrading to higher-power SMT designs with adequate thermal pad area and reflow capability.
BD140	V_CEO = 80 V, I_C = 1.5 A, P_D = 12.5 W, TO-126 package - lower power rating and different pinout (E-B-C vs E-C-B).	Not pin-compatible; base drive impedance mismatch may require circuit revision for stable biasing.	Choose only for cost-sensitive replacements where 12.5 W P_D suffices and board layout permits pinout adaptation.

Compared with MJD2955G and BD140, the 2N4918 offers through-hole TO-225 compatibility, precise 40 V/1.0 A/30 W specification alignment for legacy industrial controls, and documented SOA curves - making it uniquely suitable for drop-in replacement in existing relay driver and motor control PCBs.

Availability

2N4918 is available at Aetrix Electronics and suitable for industrial relay drivers, DC motor direction control, linear audio amplifier stages, and adjustable power supply pass transistor applications requiring stable component supply and long-term BOM continuity.

Supply support for 2N4918 includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.

Manufacturer

onsemi (formerly ON Semiconductor) is a global semiconductor supplier specializing in energy-efficient power, analog, sensor, and connectivity solutions for automotive, industrial, cloud, and consumer markets.

The 2N4918 belongs to onsemi's legacy general-purpose power transistor product line, engineered for ruggedness and reliability in industrial control, power conversion, and electromechanical interface applications.

FAQ

What is the maximum continuous collector current rating for the 2N4918?

The 2N4918 has two defined collector current ratings: 1.0 A is the JEDEC-compliant current gain test condition, while 3.0 A reflects its actual current-handling capability per Figure 5 SOA data. For sustained DC operation, 1.0 A is the recommended maximum to maintain guaranteed h_FE and thermal safety within the 30 W power limit at T_C = 25°C. Exceeding 1.0 A continuously requires careful thermal analysis and derating.

Is the 2N4918 pin-compatible with other transistors in the 2N4918–2N4920 series?

Yes, all devices in the 2N4918–2N4920 series share identical TO-225 (Case 077, Style 1) packaging and pinout: Pin 1 = Emitter, Pins 2 & 4 = Collector, Pin 3 = Base. However, their V_CEO, V_CBO, and SOA differ - 2N4918 is rated for 40 V, while 2N4919 and 2N4920 support 60 V and 80 V respectively. Substitution requires verifying voltage margin in the target circuit.

Does the 2N4918 have a Pb-free version, and how is it marked?

Yes, the Pb-free version of the 2N4918 is designated as 2N4918G and uses the same TO-225 package. Per onsemi documentation, the "G" suffix indicates Pb-free compliance, and the marking may include a microdot or "G" code on the device body. This variant meets RoHS Directive 2011/65/EU and is processed per J-STD-609A Class 3 moisture sensitivity standards.

What is the thermal resistance from junction to case (θ_JC) for the 2N4918, and how does it affect heatsink selection?

The 2N4918 has a maximum junction-to-case thermal resistance (θ_JC) of 4.16°C/W. When dissipating 15 W at T_C = 25°C, this results in a junction temperature rise of 62.4°C - well within the −65°C to +150°C operating range. To maintain T_J ≤ 125°C at full 30 W, the case must be held ≤ 62.6°C, requiring a heatsink with θ_CA ≤ 2.1°C/W when ambient is 25°C and thermal compound is applied.

Can the 2N4918 be used as a direct replacement for the 2N4921 NPN transistor?

No - the 2N4918 is a PNP transistor, while the 2N4921 is its complementary NPN counterpart. They are not functionally interchangeable without circuit topology changes. The 2N4918 sinks current from the load to ground (high-side switch), whereas the 2N4921 sources current from V_CC to the load (low-side switch). Using them interchangeably would invert logic states and likely damage the circuit unless biasing and signal paths are fully redesigned.

2N4918 Specifications

Product attributes: Attribute value

Manufacturer:: onsemi

Series:: -

Package/Case:: TO-225AA, TO-126-3

Packaging:: Bulk

Product Status:: Obsolete

Transistor Type:: PNP

Current - Collector (Ic) (Max):: 1 A

Voltage - Collector Emitter Breakdown (Max):: 40 V

Vce Saturation (Max) @ Ib, Ic:: 600mV @ 100mA, 1A

Current - Collector Cutoff (Max):: 500µA

DC Current Gain (hFE) (Min) @ Ic, Vce:: 30 @ 500mA, 1V

Power - Max:: 30 W

Frequency - Transition:: 3MHz

Operating Temperature:: -65°C ~ 150°C (TJ)

Grade:: -

Qualification:: -

Mounting Type:: Through Hole

Supplier Device Package:: TO-126

2N4918 FAQ

1.How can I place an order for 2N4918 through Aetrix?

Please submit a Request for Quotation (RFQ) for 2N4918 on Aetrix. Our sales agent will provide a competitive quotation and guide you through the order confirmation once you accept the terms.

2.Are the price and stock information for 2N4918 reliable?

The price and inventory of 2N4918 are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for 2N4918 is usually 5 days.

3.What payment methods are accepted for 2N4918?

We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for 2N4918 transactions.

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for 2N4918?

2N4918 orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.

Once your 2N4918 order is processed, you will receive an email with the shipment details and tracking number.

Note: Tracking information may take up to 24 hours to appear. Express delivery typically takes 3–5 business days.

5.How can I obtain technical support or documentation for 2N4918?

For technical support, including 2N4918 datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your 2N4918 requirements.

6.How does Aetrix verify that 2N4918 is sourced from the original manufacturer or authorized distributors?

All 2N4918 products on Aetrix are procured from qualified distributors and authorized channels. Our dedicated quality assurance team conducts strict verification, including traceability checks and, if necessary, third-party testing. This ensures that 2N4918 meets industry standards.

7.What is the process for return or replacement of 2N4918?

All 2N4918 units undergo pre-shipment inspection (PSI). If there is an issue with 2N4918, returns or replacements are accepted under the following conditions:

1.Quantity discrepancies, incorrect items, or visible external defects (such as breakage or corrosion), acknowledged by Aetrix.

2.The issue is reported within 90 days of delivery.

3.The 2N4918 part is unused and in its original packaging.

Return procedure for 2N4918:

1.Submit a request within 90 days.

2.Obtain a Return Material Authorization (RMA) from Aetrix.

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