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

onsemi 2N4921G

Name: 2N4921G
Brand: onsemi
SKU: 2N4921G
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

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Part No.:: 2N4921G

Manufacturer:: onsemi

Category:: Single Bipolar Transistors

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

Datasheet:: 2N4921G.pdf

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

Quantity:: RFQ Add To RFQ list

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Product details

Overview

2N4921G from onsemi is a medium-power plastic NPN silicon transistor designed for driver circuits, switching, and amplifier applications. It features 40 V_CEO, 1.0 A continuous collector current, 30 W total power dissipation at T_C = 25°C, low 0.6 V_CE(sat) at I_C = 1.0 A/I_B = 0.1 A, and TO-225 package with emitter-base-collector pinout. It is used in industrial relay drivers and DC-DC converter switch stages.

For engineers reviewing the 2N4921G datasheet, pinout, applications, or equivalent options, key selection criteria include V_CEO rating, safe operating area (SOA) curves, thermal resistance (R_θJC = 4.16°C/W), saturation voltage under high-current drive, and Pb-free RoHS-compliant packaging.

Technical Context

The 2N4921G operates as a general-purpose bipolar junction transistor optimized for linear amplification and hard-switching duty. Its SOA is thermally limited at low pulse widths and second-breakdown limited at longer durations, with validated operation up to 150°C junction temperature.

It delivers h_FE = 40–150 (I_C = 50 mA to 1.0 A), f_T = 3.0 MHz, C_ob = 100 pF, and exhibits stable V_BE(sat) ≤ 1.3 V across temperature. The device is complemented by PNP 2N4920G for push-pull configurations.

Key Specifications

Parameter	Value and Actual Design Meaning
V_CEO	40 Vdc - Maximum collector-emitter voltage before breakdown in common-emitter configuration.
I_C (continuous)	1.0 Adc - Sustained collector current capability without exceeding thermal or SOA limits at T_C = 25°C.
P_D @ T_C = 25°C	30 W - Total power dissipation limit with case held at 25°C; derates 0.24 W/°C above that temperature.
V_CE(sat)	≤ 0.6 Vdc at I_C = 1.0 A, I_B = 0.1 A - Low saturation voltage enables efficient switching with minimal conduction loss.
R_θJC	4.16 °C/W - Junction-to-case thermal resistance; determines temperature rise per watt dissipated when mounted with thermal compound.
f_T	3.0 MHz - Current-gain bandwidth product; defines usable frequency range for small-signal amplification.
h_FE	40–150 - DC current gain range across I_C = 50 mA to 1.0 A, enabling predictable base drive sizing.

Pinout & Package

2N4921G is housed in a TO-225 package (Case 77-09, Style 1), featuring three leads plus an internal collector-connected tab (pins 2 and 4 both serve as collector terminals). The package is Pb-free and RoHS compliant, with mechanical dimensions including D = 10.6–11.1 mm, E = 7.4–7.8 mm, and L = 14.5–16.63 mm.

Pin/Terminal	Circuit Role	Design Meaning
Pin 1	Emitter	Main current exit path; connects to ground or low-side return in common-emitter configurations.
Pins 2 & 4	Collector	Shared collector terminals; pins 2 and 4 are internally bonded to the same die region and must be connected to the same potential (e.g., heatsink or high-side rail).
Pin 3	Base	Control input; requires ~0.1 A base current to saturate the transistor at 1.0 A collector load.

Key Features

Feature	Design Value
Low saturation voltage	V_CE(sat) ≤ 0.6 V at full 1.0 A load enables <1.0 W conduction loss in switching applications.
Excellent SOA	Validated safe operating area up to 150°C junction temperature supports robust pulsed operation beyond DC ratings.
Thermal performance	R_θJC = 4.16°C/W allows effective heat transfer to external heatsinks when using thermal compound.
Pb-free & RoHS	G-suffix confirms lead-free termination and compliance with EU RoHS Directive 2011/65/EU.
Complementary pairing	Designed as NPN counterpart to 2N4920G PNP, enabling matched push-pull output stages.

Applications

Industrial Relay Drivers	DC-DC Converter Switches
Use Scenario: Driving electromagnetic relays requiring 1 A peak coil current in programmable logic controller (PLC) output modules. IC Role / Device Role / Timing Role: High-current NPN switch controlling relay coil energization/de-energization with fast turn-on/turn-off times. Use Value: Low V_CE(sat) minimizes power loss and self-heating during sustained coil hold; SOA ensures reliability under inductive kickback stress.	Use Scenario: Main switching element in non-isolated buck converter stages delivering up to 30 W output in industrial power supplies. IC Role / Device Role / Timing Role: Hard-switched power transistor operating at ≤100 kHz with fixed duty cycle control. Use Value: 30 W power rating and 4.16°C/W R_θJC support thermal management without oversized heatsinks; 40 V_CEO accommodates 24 V input with margin.
Linear Audio Amplifiers	Motor Control H-Bridge Legs
Use Scenario: Output stage in Class AB audio amplifiers for low-frequency signal reproduction in instrumentation test equipment. IC Role / Device Role / Timing Role: Medium-power amplifying transistor biased in active region for analog signal gain. Use Value: h_FE stability across I_C = 50 mA–1.0 A simplifies bias network design; f_T = 3.0 MHz supports fidelity up to mid-audio frequencies.	Use Scenario: Low-side switch in half-bridge motor driver circuits for 24 V brushed DC motors in factory automation actuators. IC Role / Device Role / Timing Role: Saturated switch controlling motor winding current direction and magnitude via PWM. Use Value: Dual collector pins (2 & 4) allow direct mounting to heatsink while maintaining electrical connection; 1.0 A I_C rating matches typical motor stall currents.

Industrial Relay Drivers

DC-DC Converter Switches

Use Scenario: Driving electromagnetic relays requiring 1 A peak coil current in programmable logic controller (PLC) output modules.

IC Role / Device Role / Timing Role: High-current NPN switch controlling relay coil energization/de-energization with fast turn-on/turn-off times.

Use Value: Low V_CE(sat) minimizes power loss and self-heating during sustained coil hold; SOA ensures reliability under inductive kickback stress.

Use Scenario: Main switching element in non-isolated buck converter stages delivering up to 30 W output in industrial power supplies.

IC Role / Device Role / Timing Role: Hard-switched power transistor operating at ≤100 kHz with fixed duty cycle control.

Use Value: 30 W power rating and 4.16°C/W R_θJC support thermal management without oversized heatsinks; 40 V_CEO accommodates 24 V input with margin.

Linear Audio Amplifiers

Motor Control H-Bridge Legs

Use Scenario: Output stage in Class AB audio amplifiers for low-frequency signal reproduction in instrumentation test equipment.

IC Role / Device Role / Timing Role: Medium-power amplifying transistor biased in active region for analog signal gain.

Use Value: h_FE stability across I_C = 50 mA–1.0 A simplifies bias network design; f_T = 3.0 MHz supports fidelity up to mid-audio frequencies.

Use Scenario: Low-side switch in half-bridge motor driver circuits for 24 V brushed DC motors in factory automation actuators.

IC Role / Device Role / Timing Role: Saturated switch controlling motor winding current direction and magnitude via PWM.

Use Value: Dual collector pins (2 & 4) allow direct mounting to heatsink while maintaining electrical connection; 1.0 A I_C rating matches typical motor stall currents.

Equivalent & Alternatives

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

Alternative Part	Technical Difference	Application Difference	Selection Advice
MJD127	TO-252 (DPAK), V_CEO = 80 V, I_C = 2.0 A, R_θJC = 3.0°C/W, higher f_T (30 MHz)	Surface-mount alternative with higher voltage/current rating and superior thermal performance	Select for new designs requiring SMT assembly, higher SOA, or improved high-frequency response.
BD139	TO-126, V_CEO = 80 V, I_C = 1.5 A, R_θJC = 5.0°C/W, lower cost, legacy through-hole	Widely available general-purpose NPN with broader voltage margin but higher thermal resistance	Select where 80 V rating is required and TO-126 footprint is acceptable; verify SOA fit for pulsed loads.

Compared with MJD127 and BD139, the 2N4921G offers a balanced combination of 40 V rating, 1.0 A capacity, and proven TO-225 thermal interface-ideal for cost-sensitive through-hole driver stages where exact 40 V system margin is sufficient and legacy compatibility matters.

Availability

2N4921G is available at Aetrix Electronics and suitable for industrial relay drivers, DC-DC converter switches, and linear audio amplifiers requiring stable component supply and long-term obsolescence management.

Supply support for 2N4921G 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, medical, and IoT applications.

The 2N4921G belongs to onsemi's legacy general-purpose power transistor family, engineered for robustness in industrial driver and switching applications where reliability, thermal stability, and Pb-free compliance are essential.

FAQ

Is the 2N4921G still recommended for new designs?

No-the official onsemi datasheet explicitly states "DISCONTINUED" and notes "This device is not recommended for new design." While 2N4921G remains available for legacy repair and continuity, Aetrix Electronics advises evaluating alternatives like MJD127 or BD139 for new projects. The 2N4921G datasheet revision 16 (October 2024) confirms this status, and no new manufacturing commitments are planned for the 2N4921G.

What does the 'G' suffix mean in 2N4921G?

Per onsemi documentation, the 'G' suffix in 2N4921G indicates a Pb-free (lead-free) package compliant with the EU RoHS Directive 2011/65/EU. It replaces legacy tin-lead terminations and requires compatible reflow profiles. The marking diagram confirms 'G' appears on the device body, and the ordering information specifies "(Pb−Free)" for all 2N492xG variants.

Can 2N4921G be used in place of 2N4922G or 2N4923G?

No-2N4921G, 2N4922G, and 2N4923G are distinct variants with different maximum ratings: only 2N4921G is rated for 40 V_CEO/V_CB; 2N4922G is 60 V; 2N4923G is 80 V. Substituting 2N4921G into a circuit designed for 60 V or 80 V operation risks premature breakdown. Electrical characteristics (e.g., ICEO test conditions) are also variant-specific and not interchangeable.

What is the correct pinout orientation for 2N4921G in TO-225 package?

Per the official onsemi mechanical drawing (Case 77-09, Style 1), the 2N4921G TO-225 pinout is: Pin 1 = Emitter, Pins 2 & 4 = Collector (internally connected), Pin 3 = Base. When viewing the front (marked side) with leads down and flat side facing outward, the leftmost lead is Pin 1 (Emitter), center is Pin 3 (Base), and rightmost is Pin 2 (Collector); Pin 4 is the metal tab on the backside, also Collector.

Does 2N4921G require a heatsink in normal operation?

Yes-when dissipating >5 W continuously, a heatsink is required. With R_θJC = 4.16°C/W and max T_J = 150°C, even at T_C = 50°C ambient, 30 W operation would exceed junction limits. Derating begins above 25°C case temperature (0.24 W/°C), so for 10 W dissipation at 75°C case, a heatsink lowering R_θCA is mandatory. Thermal compound is recommended per onsemi Note 3.

2N4921G Specifications

Product attributes: Attribute value

Manufacturer:: onsemi

Series:: -

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

Packaging:: Bulk

Product Status:: Obsolete

Transistor Type:: NPN

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

2N4921G FAQ

1.How can I place an order for 2N4921G through Aetrix?

Please submit a Request for Quotation (RFQ) for 2N4921G 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 2N4921G reliable?

The price and inventory of 2N4921G are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for 2N4921G is usually 5 days.

3.What payment methods are accepted for 2N4921G?

We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for 2N4921G transactions.

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for 2N4921G?

2N4921G orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.

Once your 2N4921G 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 2N4921G?

For technical support, including 2N4921G datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your 2N4921G requirements.

6.How does Aetrix verify that 2N4921G is sourced from the original manufacturer or authorized distributors?

All 2N4921G 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 2N4921G meets industry standards.

7.What is the process for return or replacement of 2N4921G?

All 2N4921G units undergo pre-shipment inspection (PSI). If there is an issue with 2N4921G, 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 2N4921G part is unused and in its original packaging.

Return procedure for 2N4921G:

1.Submit a request within 90 days.

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

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